,, 修立群, 吴迪, 孙媛媛, 顾闻琦, 张鈜贵, 孟军, 陈温福,*沈阳农业大学农学院/辽宁省生物炭工程技术研究中心, 辽宁沈阳 110866Review of biochar structure and physicochemical properties
ZHANG Wei-Ming,, XIU Li-Qun, WU Di, SUN Yuan-Yuan, GU Wen-Qi, ZHANG Hong-Gui, MENG Jun, CHEN Wen-Fu,*College of Agriculture, Shenyang Agricultural University / Biochar Engineering Technology Research Center of Liaoning Province, Shenyang 110866, Liaoning, China通讯作者:
收稿日期:2020-03-17接受日期:2020-08-19网络出版日期:2021-01-12
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Received:2020-03-17Accepted:2020-08-19Online:2021-01-12
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张伟明, 修立群, 吴迪, 孙媛媛, 顾闻琦, 张鈜贵, 孟军, 陈温福. 生物炭的结构及其理化特性研究回顾与展望[J]. 作物学报, 2021, 47(1): 1-18. doi:10.3724/SP.J.1006.2021.02021
ZHANG Wei-Ming, XIU Li-Qun, WU Di, SUN Yuan-Yuan, GU Wen-Qi, ZHANG Hong-Gui, MENG Jun, CHEN Wen-Fu.
生物炭(Biochar)是近年新兴的研究热点, 国内外相关研究发展迅速。我国的生物炭研究, 自2005年开始迅速升温, 特别是陈温福院士于2011年在《中国工程科学》上发表的“生物炭应用技术研究”一文, 系统阐述了生物炭的性质及应用, 极大推动了我国生物炭基础研究与应用技术的发展。时至今日, 国内外科学家在农业、环境、能源等诸多领域开展了卓有成效的科学探索与应用研究工作, 取得了一系列重要研究进展和成果, 可谓“百花齐放、百家争鸣”。
然而, 在众多科学研究结果中, 我们也发现了一些基本事实, 即不同研究结果之间差异较大且很难进行有效的共性比对, 甚至截然相反或相悖, 对基础研究和实践应用的指导意义和价值十分有限。分析发现, 造成研究结果的差异性主要与原料来源、材质, 炭化工艺条件以及应用对象、剂量、方法等有关。此外, 由于研究、使用者的研究背景、出发点、目标不同, 对生物炭的概念、来源、形成及特性等缺乏系统、准确认知, 也导致其主观上对不同生物炭研究及应用结果产生混淆或误解。因此, 十分有必要对生物炭的概念、来源、形成、结构、特性、功能及其调控技术等进行系统梳理和总结分析, 为生物炭研究与应用提供科学参考。
生物炭理化特性是开展生物炭研究与应用的重要基础, 也是最为关键的一环, 决定了生物炭功效及其应用“出口”, 是生物炭发挥作用的“源泉”。目前由于原材料来源、材质、炭化工艺及制备技术、使用方法等方面的差异, 使得生物炭基础科学与应用技术研究呈现“多元化、复杂化、碎片化”特征, 在不同领域、学科均有涉及, 其研究结果或结论也有着巨大差异性。特别是, 目前有关生物炭结构及理化特性研究多处于“散、杂、乱”状态, 缺少系统、有效的共性分析和比较研究。迄今, 亦鲜见针对生物炭结构及其理化特性的系统研究和总结分析。本文在系统梳理有关生物炭的结构及理化特性研究基础上, 分别从生物炭概念、来源、形成、结构、主要理化特性及其调控技术等方面, 对相关主要研究进展进行了归纳、总结和比较分析, 厘清了有关共性认知、研究结果及结论, 并结合生物炭研究与应用实际, 从资源与环境“和谐共生、循环利用、永续发展”视角, 对未来有关生物炭理化特性研究的基本原则、方向及主要问题等进行了展望, 以期为生物炭基础研究与应用发展提供基础和参考。
1 生物炭的概念
生物炭/生物质炭, 作为“旧物新识”的一种“新”事物, 追溯其产生历史, 其实早在我国两千多年前的唐代, 就有《卖炭翁》诗云“伐薪烧炭南山中……”, 生动再现了当时的制炭场景。随着人们对制炭技术、用途等方面的不断探索与实践, 不同材质、形态的“炭”层出不穷而又性质各异, 推动了炭化技术及其应用研究发展, 同时也使一些研究、使用者对生物炭概念、使用等产生了一些分歧、混淆或误解。生物炭/生物质炭, 其译文源于英文词——“Biochar”, 最早用于区分生物质与化石燃料所形成的活性炭材料[1]。在2006年, 美国康奈尔大学Lehman教授丰富了“Biochar”一词的含义, 将“Biochar”定义为生物质衍生黑炭, 即一种和木炭概念相近的材料, 可用于土壤碳库封存、改善土壤物理与生物学特性, 以及促进植物生长的土壤改良剂[2]。在早期的生物炭相关研究中, 由于其制炭工艺与木炭相近, 因而在国外研究中出现了“Charcoal”和“Biochar”混用的情况, Charcoal其含义多指现在的“Biochar” [3,4]。随着生物炭研究的深入, 生物炭概念也逐渐清晰, 在2013年生物炭国际倡导组织(International Biochar Initiative, IBI)将生物炭定义(简述)为, 生物质在限氧环境条件下通过热化学转化获得的固体材料[5]。
由于不同原料、炭化温度及工艺等条件下制备的生物炭材料, 在结构及性质上差异很大, 使其在应用对象、目标、范围、功效等方面存在显著差异, 导致一些分歧产生。目前, 在生物炭原料来源、炭化条件、理化特性等方面的定性、定量界定条件还存在不同观点, 争议来源主要为: 1)关于制炭原材料来源, 动物体及污泥等非植物源生物质是否列入其中;2)在炭化工艺条件方面, 高温(>700℃以上)快速裂解, 是否属于常规炭化工艺方式;3)制备技术方面, 采用非传统或多途径复合、多技术融合生产的改性生物炭或其他衍生性炭材料, 是否列为常规生物炭的一种。上述定义、内涵、界定条件等目前尚无统一定论, 随着炭化工艺、制备技术的不断改进与创新, 不同原理、技术及方法获得的生物炭千差万别, 也使得生物炭概念、定义等呈现“多元化、复杂化”趋势[6,7,8]。从目前多数研究来看, 基于生物炭来源及应用实际, 从废弃生物质资源循环利用角度, 一般认为生物炭来源于农、林等废弃生物质, 在一定炭化温度条件下(<700℃), 在限氧或缺氧条件下热解形成的富碳固体产物[9]。
目前, 尽管对生物炭概念、定义等方面的理解、认知等还存在一些不同观点, 但随着生物炭技术的创新与发展, 特别是多学科交叉、先进技术的不断涌现, 生物炭结构及其理化特性研究将不断推向深入, 届时生物炭概念、定义等将得到逐步统一、完善和发展。
2 生物炭的形成过程
生物炭, 是由生物质经热裂解反应过程后而形成的一种产物[10,11,12]。在热裂解过程中, 生物质会通过分子内、分子间的重排作用反应而形成由芳香多环等结构形成生物炭, 以及生物油、混合气等物质[13,14]。不同材质生物质的炭化形成过程存在差异。一般情况下, 制炭原料可分为木质和非木质纤维素类生物质[15,16]。其中, 木质纤维素类生物质主要来源于植物类废弃物[17,18], 其主要成分为纤维素、半纤维素、木质素等[19,20,21]。而非木质纤维素类生物质则主要包括动物粪便、一部分植物及其衍生物等[16], 其主要成分为蛋白质、脂类、糖类、无机物以及部分木质素、纤维素[22]。一般情况下, 木质纤维素类生物质在200~260℃时开始发生热裂解反应, 半纤维素的分支聚合物和短侧链先分解为低聚糖, 其后重新排列形成1,4-醚-D-木糖[23], 1,4-醚-D-木糖在经过脱水、脱羧、芳构化及分子内缩合等过程后形成炭, 或分解形成低分子量的生物油及混合气[24]。在300℃左右纤维素开始分解, 先解聚成低聚糖, 随后糖苷键断裂生成D-吡喃葡萄糖, 在分子内重排形成左旋葡萄糖聚糖[25], 其中一部分左旋葡聚糖经过脱羧、芳构化、分子内缩合等过程后形成炭, 另一部分在经重排、脱水过程后形成羟甲基糠醛, 进一步形成生物油及混合气[24]。在400℃时木质素开始大量分解为自由基, 并通过自由基取代、加成、碳碳偶合等过程后形成生物炭、生物油和混合气[26,27]。在超过500℃时, 生物炭孔隙内的聚合物、挥发性化合物会发生再聚合反应, 形成次生炭或经过重组产生分子量较高的焦油[28,29,30]。而非木质纤维素类生物质, 在200℃左右开始发生热解反应, 蛋白质、脂类、碳水化合物等有机物的低键能键(如氢键、氢氧化钙键)发生断裂[16], 键断裂随温度升高而增强, 主要热解过程发生在300~600℃, 最终热解形成生物炭、生物油及混合气[16,31]。一般情况下, 由于非木质纤维素类生物质中的蛋白质、脂类以及核酸中含有大量氮、磷和氧, 使其热解行为更为复杂而多变[32]。
在生物质热解炭化过程中, 完成了由“生物质—炭”的物质形态转变, 形成了极其丰富的多微孔碳架结构, 以及不同种类的表面官能团、有机小分子及矿物盐等[33], 为其作为吸附、载体等功能材料奠定了重要基础, 使其可在农业、环境、能源等领域广泛应用[34]。
3 生物炭的结构
3.1 表面及内部结构表征
生物炭的结构, 主要由生物质原有结构在经过失水、活性物质挥发、断裂、崩塌等一系列热解炭化过程后重构形成[35], 其“骨架”结构由稳定的芳香族化合物和矿物组成[4,36], 孔隙结构则由芳香族化合物和其他功能基团组成[37,38]。生物炭的孔隙表征, 参照国际纯粹与应用化学联合会(International Union of Pure and Applied Chemistry, IUPAC)的活性炭孔隙分类可分为微孔(< 2 nm)、中孔(2~50 nm)、大孔(> 50 nm), 生物炭中的孔隙多以微孔为主[39]。生物炭的结构表征与其炭化温度条件有关, 随着炭化温度升高, 生物炭的非晶态碳结构逐步转化为石墨微晶态结构, 晶体尺寸扩大、结构更加有序[40] (图1)。图1
新窗口打开|下载原图ZIP|生成PPT图1不同炭化温度下的生物炭结构表征示意图[4]
A: 生物炭结构中芳香族碳增加, 主要以无定型碳为主。B: 生物炭结构中涡轮层状芳香碳增加。C: 生物炭结构趋于石墨化。
Fig. 1Biochar structure representation under different carbonization temperature[4]
A: the aromatic carbon in biochar structure is increased, mainly part is amorphous carbon. B: the sheets of turbostratic aromatic carbon in biochar structure is increased. C: the biochar structure becomes graphitic.
3.2 生物炭结构形成的主要影响因素
制炭原料与炭化温度, 是生物炭结构形成的主要影响因素[41]。不同生物质原料在结构、内含物等方面存在本质差异, 导致其在炭化后的结晶度、交联和分支等结构特征上差异显著[42,43]。木质素含量高的生物质(如竹子、椰子壳等)在炭化后的大孔结构增多, 而纤维素含量高的生物质(如植物外壳)在炭化后形成的结构多以微孔为主[44], 这也使纤维素类生物炭的表面积(112~642 m2 g-1), 一般高于非纤维素类生物炭(3.32~94.2 m2 g-1)[45,46,47]。炭化温度条件, 也是影响生物炭结构的重要因素。在热解炭化过程中, 随着炭化温度升高, 生物炭中的挥发性物质逐渐热解分离、挥发, 形成更多新孔隙和不规则、粗糙的炭粒蚀刻表面[48,49]。当炭化温度高于700℃时, 生物炭表面微孔结构开始出现破坏, 超过800℃时生物炭的多孔碳架结构表现不稳定, 坍塌现象发生[50,51]。炭化停留时间, 也可在一定程度上影响生物炭的结构。当炭化温度为500~700℃、停留时间在2 h以内时, 生物炭的孔隙度随停留时间延长而增大, 但当超过2 h后则表现为负效应[52]。一般情况下, 慢速热解炭化更有利于生物炭的多微孔形成[23], 而在快速热解炭化过程中, 由于未完全热解的类焦油等物质可能会滞留、堵塞生物炭孔隙, 不利于生物炭的多微孔结构形成[53]。
生物炭的多微孔结构是其发挥作用的重要基础, 不同原料、炭化工艺条件下制备的生物炭结构表征、特性差异明显, 实际应用中可根据不同场景、目的及应用目标的需求, 通过材质定向筛选、炭化工艺定向调控等措施获得具有一定预期结构特征的生物炭, 从而充分发挥生物炭“构—效”优势及其作用潜力。
4 生物炭的主要理化特性
4.1 酸碱性
生物炭一般呈碱性, 但也有酸性表现, 其pH变幅范围在3~13[54,55]。一般情况下, 原料中的灰分含量越多, 其制备的生物炭pH越高[56]。在材质上, 由于非纤维素类生物质制备的生物炭具有较高灰分含量, 因此, 一般非纤维素类生物炭pH高于纤维素类生物炭[57,58]。而在相同炭化工艺条件下, 不同材质生物炭的pH表现为禽畜粪便>草本植物>木本植物[56,59]。一般认为, 生物炭pH随炭化温度升高而提高[55]。在较高炭化温度条件下, 会加速酸性官能团的分解如-COOH、-OH等, 使生物炭pH提高[46,60]。研究发现, 当温度由200℃升高到800℃时, 生物炭的酸性官能团由4.17 mm μg-1下降至0.22 mm μg-1、碱性官能团由0.15 mm μg-1升高到3.55 mm μg-1, 而pH则由7.37提高至12.40 [61]。较高炭化温度也有利于促进灰分中碱金属(Na、K)或碱土金属(Ca、Mg)等离子化合物的形成, 如KOH、NaOH、MgCO3、CaCO3等, 从而提高生物炭pH [60]。此外, 炭化停留时间亦可在一定程度上影响生物炭pH, 表现为炭化停留时间越长而pH越高[62,63], 但加热升温速率对生物炭pH的影响不大[64]。
生物炭的酸碱性, 是影响其特性及功能的重要指标之一。从目前研究来看, 由于原料、炭化工艺及制备技术等不同, 生物炭pH变化范围较广, 基本覆盖了“酸性、中性、碱性”不同状态。在实际生产和应用过程中, 可通过炭化工艺调控、改性等技术方法获得一定酸碱范围的生物炭材料, 根据使用目的、目标科学施用。
4.2 比表面积
生物炭丰富的多微孔结构, 使其具有较大的比表面积[65,66,67]。生物炭的比表面积, 与其制炭原料、炭化温度等有关。一般情况下, 纤维素类生物质因其具有丰富的内部孔隙, 炭化后形成的生物炭会保留原有生物质细微孔隙结构, 比表面积大幅提高, 而非纤维素类生物质的孔隙结构相对较少, 因此炭化后的生物炭比表面积小于纤维素类生物炭[68]。炭化温度, 是影响生物炭比表面积的重要因素之一。当炭化温度在400℃以下时, 生物质在炭化过程中形成的孔隙率降低, 可能与生物质中挥发性物质的热解分离和挥发不完全等有关[69,70]。随着炭化温度升高, 生物质分离、释放出更多挥发性物质, 孔隙更多、比表面积增大[24,71-73]。但是, 在高于800℃时, 生物炭中的多孔结构会发生部分坍塌, 从而堵塞孔隙, 使孔径变小[74,75]。灰分含量也会影响生物炭的比表面积, 一般情况下随着炭化温度升高, 生物炭的灰分含量增加, 会堵塞部分生物炭孔隙, 从而使其比表面积降低[76]。
比表面积大, 是生物炭作为载体和吸附功能材料的重要基础特性之一。在生物炭制备过程中, 比表面积大小可通过改性、调控工艺流程等进行一定程度的定向调控。
4.3 元素组成
生物炭主要由C、O、H、N、K、Ca、Na、Mg等元素组成[66,77]。其中, C元素主要为芳香环形式的固定碳, 而碱金属(K、Na等)、碱土金属(Ca、Mg)等则以碳酸盐、磷酸盐或氧化物形式存在于灰分中[60,78]。生物炭中的元素种类、含量, 主要与原材料有关[79,80]。研究认为, 纤维素类生物炭中的C含量高于非纤维素类生物炭, 木材、竹类生物炭的C含量较高[60,81]。而在其他元素中, 纤维素类生物炭中的K含量相对较高[77,82-84], 非纤维素类生物炭中的Ca、Mg、N、P等元素高于纤维素类生物炭[85]。炭化温度, 也是影响生物炭元素含量及组成的重要因素。一般情况下, 生物炭中的C、碱金属及其矿化物含量随炭化温度升高而提高, 而N、H、O等元素含量则随炭化温度升高而降低[77,86-88]。4.3.1 元素形态及有效性 生物炭中的C, 主要为芳香族碳, 以芳香环、不规则叠层堆积存在, 使生物炭具有稳定性高、抗分解能力强特性[4,89-90]。生物炭还含有一定有机碳, 主要为未完全碳化的生物质和脂肪酸、醇类、酚类、酯类化合物, 以及类黄腐酸、胡敏酸等物质组分, 一般在新制备生物炭、低温热解炭化形成的生物炭以及非纤维素类生物炭中的含量相对较高[54,62-91]。生物炭中的N、P、K及其他无机盐离子等元素, 可作为植物、微生物等生命体养分的来源之一[92], 但不同生物炭的养分元素含量、有效性等存在差异, 一般富含养分原料制备的生物炭, 其含有的营养元素相对较高, 反之亦然[93]。
生物炭中的元素有效性, 与生物炭的新鲜程度、pH、炭化温度等条件有关[94]。一般情况下, 新制备的生物炭可释放更多N、P、K等养分元素, 而陈化的生物炭在养分释放量、速度等方面相对弱一些[95,96,97]。生物炭pH也会影响其元素有效性, 当pH在2~7之间时, 生物炭释放PO43-和NH4+随pH提高而降低, 而K+含量则保持相对稳定[53], 而当pH从8.9降至4.5时, 生物炭中的Ca、Mg元素释放量会增加[98]。此外, 炭化温度亦会影响生物炭中的元素状态, 随着炭化温度提高, 生物炭中的碱金属等矿物组分趋于结晶态, 使其水溶性降低[78,99-100]。当热解温度由300℃升至600℃时, 生物炭中的可溶性PO43-由430 mg kg-1下降到70 mg kg-1 [101]。
4.3.2 潜在有害元素 生物炭中的元素, 绝大部分对土壤、植物及环境等有益或无害, 但受制炭原料的材质、内含物及其炭化过程等因素影响, 某些情况下还可能含有一定潜在有害元素或物质。研究表明, 生物炭中的潜在有害物质主要包括有机污染物和重金属两大类[102]。
第一类: 有机污染物。生物炭中的有机污染物主要包括多环芳烃(polycyclic aromatic hydrocarbons, PAHs)、多氯二苯并二噁英(polychlorinated dibenzo dioxins, PCDDs)、多氯二苯并呋喃(polychlorinated dibenzo furans, PCDFs), 以及一些挥发性有机化合物、二甲苯酚、甲酚、丙烯醛、甲醛等[102], 这些物质主要在热解炭化过程中产生, 过量可能对土壤、微生物、植物等健康构成风险[103,104]。研究发现, 生物炭中的多环芳烃主要与原料中的木质素、纤维素和半纤维素含量有关[105], 一般情况下木质素含量高的原材料在炭化后的多环芳烃含量较低, 如木质生物炭的多环芳烃低于秸秆类生物炭[106]。不同种类生物炭的有机污染物含量差异显著, 多环芳烃(PAHs)含量从< 0.1 mg kg-1到>10,000 mg kg-1表现不等[107], 生物炭国际倡导组织(IBI)建议生物炭的多环芳烃含量应控制在6~20 mg kg-1 [5]。不同炭化温度, 也会影响生物炭的潜在污染物含量及形态。一般情况下, 低温制备的生物炭含有较高浓度的低分子量多环芳烃, 而在高温下制备的生物炭, 其高分子量多环芳烃的浓度相对较高[108]。炭化过程中, 可通过输入O2和CO2作为载气来降低PAH含量[107], 而在炭化后可通过在厌氧环境中冷却生物炭亦有助于降低其多环芳烃含量[107]。
第二类: 重金属。生物炭中的重金属元素, 主要包括Cd、Cu、Cr、Ni、Pb、Zn、Hg等[102], 其含量与原材料密切相关, 一般认为非纤维素类材质制备的生物炭, 其重金属含量高于纤维类生物炭[16]。在炭化过程中, 生物炭中残留的重金属形态相对稳定, 但其直接毒性、生物有效性比炭化前降低[16], 炭化温度越高, 生物炭中的重金属含量越高[109]、生物活性越低[109,110]。生物炭国际倡导组织(IBI)经过风险评估后, 对生物炭中的有害元素含量上限提出了明确建议(表1) [111]。
Table 1
表1
表1生物炭中有害元素含量上限阈值[111]
Table 1
| 有害元素 Toxic element | 含量 Content (mg kg-1) |
|---|---|
| 砷Arsenic | 13-100 |
| 镉Cadmium | 1.4-39.0 |
| 铜Copper | 143-6000 |
| 铬Chromium | 93-1200 |
| 镍Nickel | 47-420 |
| 铅Lead | 121-300 |
| 锌Zinc | 416-7400 |
| 汞Mercury | 1-17 |
| 钼Molybdenum | 5-75 |
| 钴Cobalt | 34-100 |
新窗口打开|下载CSV
生物炭中的潜在有害元素含量及其有效性, 若在安全范围内对土壤、作物及环境的影响很小, 但在超限投入条件下可能对生态环境安全造成一定风险。因此, 在规模化、工程化实施过程中, 要严格筛选、控制原料来源, 或采用如在炭化前添加磷酸二氢钙或沸石来降低原材料中重金属的生物利用度[112]等一些预处理措施来降低其重金属含量, 最大限度降低生物炭中的潜在有害元素风险, 使其在安全、可控范围内。同时, 通过调控炭化工艺条件及参数, 尽可能减少生物炭中的污染物及有害元素残留, 降低其生态环境安全风险。
生物炭的元素组成、含量及形态, 是生物炭的重要特性及其功效发挥的“源泉”。主要体现在: 1)释放N、P、K、Ca、Mg等大量及中微量元素, 为土壤提供一定外源养分, 促进植物生长[113];2)生物炭的重要组分——灰分, 除含有一定碱金属物质外, 可在吸附金属元素等过程中发挥关键作用[114]。
4.4 表面化学性质
4.4.1 表面官能团 生物质中的纤维素、半纤维素、蛋白质、脂肪等, 经热解炭化后在生物炭表面及内部形成大量羧基、羰基、内脂基及羟基、酮基等多种类型官能团, 其中大多为含氧官能团或碱性官能团, 使生物炭具有良好的吸附、亲水/疏水, 以及缓冲酸碱、促进离子交换等特性[38,115-116]。生物炭的表面官能团与制炭原料、炭化温度条件密切相关[46]。不同原材料中, 非纤维素类生物炭比纤维素类生物炭含有更多的N、S官能团[117]。在不同炭化温度条件下, 生物炭官能团的数量、密度随炭化温度升高而下降[92]。在185~200℃时, 生物炭表面官能团种类不会发生明显变化[46,118], 而当温度达到300℃时, 羧基、羰基含量则快速上升至最高点, 此后随炭化温度升高而降低[72]。至400~550℃时, 生物炭的脂肪族官能团随温度升高而逐渐消失[70,118], 当温度达到600℃时, 烷基碳官能团消失[46]。
4.4.2 阳离子交换量 阳离子交换量(cation exchange capacity, CEC), 是决定生物炭表面化学特性的基础指标, 也是衡量其离子交换、吸附性能的重要指标之一[119]。生物炭的阳离子交换量与制炭原料、炭化温度等有关[120]。研究发现, 非纤维素类生物炭的CEC比纤维素类生物炭高, 而原料发酵后制备的生物炭CEC要高于未发酵原料制备的生物炭[121,122], 不同原料炭化后形成的官能团数量不同, 导致其阳离子交换量存在差异[66]。在不同炭化温度条件下, 较低温度制备的生物炭表面含有更多含氧官能团, CEC较高, 而在较高温度下制备的生物炭, 其含氧官能团被破坏, 表面负电荷减少, CEC降低[121,122,123,124]。此外, 生物炭中的K、Ca、Mg等碱金属增加, 生物炭“激发”的土壤微生物活动增强, 也可能使生物炭CEC提高[78,125]。
4.5 吸附性
生物炭极其丰富的多微孔结构、大比表面积, 使生物炭具有强吸附力。生物炭的吸附性能与其多微孔结构、比表面积、表面官能团等有关, 亦受到生产工艺、热解炭化温度、酸碱环境条件等诸多因素影响[126], 不同介质中决定生物炭吸附性的因子多、吸附过程较为复杂[127]。生物炭所具有的吸附性, 使其可广泛用于重金属、有机污染物、有害气体等不同介质中的污染物防控, 并可作为吸附剂、载体或基质等功能材料广泛应用于农业、环境、化工等领域, 应用潜力、空间巨大[97,40]。目前, 关于生物炭吸附性的研究较多, 涉及领域多、范围广, 有关介质、吸附条件、作用因子、吸附过程等较为繁杂, 在此不再赘述。以下仅就生物炭在农业、环境等领域应用的基本吸附原理、过程等作以简述。环境领域。作为吸附功能材料, 利用生物炭进行重金属污染修复的研究较为常见, 其基本吸附过程如图2-a所示, 主要包括静电吸引、离子交换、物理吸附、表面络合和/或沉淀等过程[87]。生物炭对重金属的吸附作用, 主要源于生物炭表面所含有的丰富含氧基团对重金属的强吸附作用[87], 而生物炭的矿物成分在吸附过程中也具有至关重要的作用, 不仅可为重金属吸附提供结合位点[114], 而且可通过提高生物炭pH, 降低有效态重金属离子活性、促进重金属沉淀, 从而减少土壤中重金属浸出、降低重金属生物有效性[128]。与此同时, 生物炭极其丰富的多微孔结构也会增强其对重金属离子的吸附、拦截, 从而降低重金属离子活性及其移动性, 并可能使重金属形态发生改变[129]。
图2
新窗口打开|下载原图ZIP|生成PPT图2生物炭对重金属(a)和有机污染物(b)吸附模型[87]
Fig. 2Summary of mechanisms for heavy metals (a) and organic contaminants (b) adsorption on biochars[87]
农业领域。现实农业生产中, 过量化肥、农药施用等造成的面源污染日益突出, 已成为制约农业“低碳、绿色、可持续”发展的“瓶颈”。研究表明, 生物炭对降低农药等有机污染物残留, 减少土壤中过量化肥养分流失等农业面源污染问题具有重要作用[130]。生物炭对有机污染物的吸附作用如图2-b所示, 主要包括静电作用、疏水作用、氢键、π-π作用、孔隙填充等作用过程。生物炭对有机污染物的吸附, 主要源于生物炭中未炭化部分生物质的分配作用和炭化部分的吸附作用[87], 其中非炭化部分的分配作用是一个线性、非竞争性的吸附过程[127], 而炭化部分的吸附作用具有非线性等温线、共存吸附质间竞争的特性。生物炭对有机污染物的吸附作用过程不同, 主要与在相对较低炭化温度条件下(<700℃), 部分生物质未完全碳化[100,131], 使生物炭含有炭化/未炭化部分有关。在实际应用过程中, 生物炭对有机污染物的吸附一般为多种吸附作用过程的耦联、结合, 较为复杂[87]。在农业生产中, 生物炭可作为基质、载体或吸附剂材料, 用于吸附或固持N、P、K等养分离子, 减少土壤养分流失, 水体“富营养化”污染净化, 以及提高作物养分利用效率等[97], 其吸附作用与生物炭多微孔构造、表面官能团、比表面积及离子交换性能等有关[97,132]。
4.6 疏水/持水性
生物炭特殊的结构和理化特性使其具有一定疏水/持水性(图3)[133]。生物炭具有疏水性, 与其在炭化过程中的表面含氧官能团减少有关[8]。而生物炭具有持水性, 主要源于其丰富的多微孔结构增加了对水的吸附力[134]。生物炭持水性能主要取决于其疏水/持水性在水分吸附上的抵消、平衡或叠加作用[119]。图3
新窗口打开|下载原图ZIP|生成PPT图3生物炭的疏水性(a)和持水性(b)[133]
Fig. 3Hydrophobicity (a) and water holding capacity (b) of biochar[133]
生物炭的疏水性是其作为非溶性吸附质的重要基础, 其性能大小可通过测定其含O、N官能团数量来表征, 含O、N官能团数量越低、疏水性越强[8]。生物炭的疏水性与炭化温度密切相关, 炭化温度越高、疏水性越强, 与生物炭表面极性官能团减少、芳香性增加有关[45,50,135]。生物炭的持水性则与其多孔构造及不同炭化温度下的孔隙连通性有关[119], 在低温炭化条件下, 生物炭的孔径较小、互连性较低, 产生的焦油成分易堵塞孔隙, 导致其持水性能下降[136], 而在高温炭化条件下, 生物炭的多微孔结构及数量增加、孔隙连通性增强, 对水分的物理容纳和吸附力增强, 使其持水性能提高[119,137]。
4.7 稳定性
生物炭含有较高的C, 具有稳定的芳香族碳结构, 使其具有较高稳定性[138]。生物炭结构中的芳环凝聚程度, 影响生物炭功能的稳定性和持久性, 而非芳香族结构/官能团则有利于形成簇状结构, 也对生物炭稳定性产生一定影响[37]。生物炭的稳定性, 通常采用H/C、O/C表征[139]。低H/C和O/C比, 表明生物炭具有较高熔融芳香环结构、稳定性较强, 反之亦然[140]。一般认为, 生物炭的O/C摩尔比小于0.2被认为是最稳定的, 具有超千年的半衰期, O/C比在0.2~0.6之间的生物炭半衰期在100~1000年之间, 而O/C比大于0.6的生物炭半衰期小于100年[141]。原料类型、炭化温度是影响生物炭稳定性的主要因素[37]。在制备原料中, 木质素是最稳定的成分, 其次是纤维素和半纤维素[142], 原料中的木质素含量越高, 炭化形成的芳香族C含量越高, 生物炭的稳定性越强[90]。因此, 木质纤维素类生物炭比非木质纤维素类生物炭更稳定, 抗生物降解的能力更强[40]。原料中的金属、金属化合物或矿物等组分会在一定程度上降低生物炭的稳定性[143], 但一些碱金属、碱土金属及硅等元素会增强生物炭的稳定性, 如生物炭中的非晶硅与C相互作用形成稳定的Si-C, 从而防止C被氧化, 使生物炭稳定性增强[144]。此外, 原料尺寸也会在一定程度上影响生物炭的稳定性, 一般大颗粒/尺寸原料制备的生物炭稳定性高于小颗粒/尺寸原料制备的生物炭[145,146], 其主要原因在于大颗粒/尺寸原料在热解炭化时, 气相与固相物质之间的接触时间更长, 聚合形成更多的碳, 从而使生物炭固定碳含量提高、稳定性增强[139]。热解炭化温度, 则决定生物炭的芳香性及芳香凝聚度, 生物炭中的大部分不稳定组分会随着炭化温度升高而逐渐消失, 熔融芳香环结构增加, 不稳定的非芳香环结构、大小及数量呈下降趋势[37]。此外, 加热速率也会对生物炭稳定性产生一定影响, 加热速率慢利于增强生物炭稳定性[147]。
综上, 生物炭的原料来源丰富, 不以消耗不可再生资源和损害生态环境为代价, 具有“低成本、可再生、可持续”的突出优势, 且制备过程“低碳、环保”, 利于促进资源与环境的“循环、永续”发展;生物炭的“富碳”多微孔结构使其可作为载体、基质等“构架性”功能材料, 从而发挥稳定的“结构重建”或“构相改良”作用, 而生物炭呈碱性、含碳量高、比表面积大、吸附力强, 富含多种养分、表面官能团等多种特性, 则使其可在固碳减排、改土培肥、防控污染、节肥增效、促长增产等方面发挥综合性“叠加”效应, 其“多向、多效”增益及“累积、持续”性功效作用突出;生物炭独特的来源、结构、特性及功效优势, 使其有别于其他同类材料, 具有显著经济、生态和社会效益, 发展潜力和应用空间巨大。
5 生物炭理化特性调控技术进展
生物炭的理化特性, 是其功效发挥的“根源”, 重要性不言而喻。国内外研究者从不同学科、领域和研究背景出发, 采用不同技术与方法, 针对生物炭理化特性调控技术开展了积极、有益的科学探索, 取得了一定研究进展[148]。目前, 主要的调控技术途径: 1)在“前、中、后”炭化过程中添加外源物质, 使其与原料或炭化产物发生理化反应, 进而改变生物炭表面或内部结构及特性, 从而获得某些具有特定性质或功能的生物炭材料;2)通过调控、优化炭化工艺及制备方法, 对生物炭结构及理化性质进行调控, 使生物炭构相、特性发生某些定向或优化改变, 从而达到预期应用目的和目标。在实际运用过程中, 一般多采用上述两种或二者相结合的技术途径。5.1 外源介质添加改性技术
生物炭具有良好的多微孔、吸附性及稳定性, 但在某些特定用途、目标条件下还不能满足现实需求。因此, 一些研究者尝试在炭化过程中, 通过添加氧化剂、磁化物等外源介质, 使其与生物炭发生一些物理-化学反应, 重塑炭表面、内部某些结构及特性, 使之达到目标特性最优化[149,150]。目前, 主要有磁化改性、氧化剂改性、涂层/浸渍改性等调控技术。5.1.1 磁化改性 在污水净化、重金属污染修复等环保领域, 生物炭的使用需求和应用空间巨大。但是, 由于生物炭质轻、密度低, 不易与水等介质分离[154], 使生物炭的应用空间和量级受限。因此, 一些研究者通过将生物炭与磁性介质结合, 在外磁场控制下实现污水固、液分离[151,152,153], 取得了一定效果和进展。一般情况下, 磁性介质多采用铁或铁氧化物, 如铁(0)、γ-Fe2O3、Fe3O4、CoFe2O4等[148]。改性后的磁化生物炭, 阳离子交换量、孔隙数量等大幅提高, 对污染物的吸附、去除能力明显增强[155,156]。研究发现, 磁化改性生物炭对水体中的重金属离子、有机污染物等具有较强吸附作用, 其整体吸附性能高于非磁化生物炭[148,155]。磁化改性技术的应用, 进一步扩展了生物炭的应用空间, 实用性、易用性提高。
5.1.2 氧化剂改性 氧化剂改性, 一般采用化学氧化剂为介质, 使其与生物炭发生氧化反应, 改变生物炭的结构、酸碱性、官能团、比表面积等特性, 增强其吸附等性能, 从而提高生物炭对土壤、水体中污染物的吸附、去除效率[157]。一般情况下, 氧化剂改性多采用过氧化氢、强酸或强碱类化学剂。
过氧化氢改性, 其优点是成本低, 可避免与其他元素产生干扰, 适于土壤改良、水体净化等应用场景[148]。研究发现, 采用过氧化氢处理的改性生物炭, 其表面含氧官能团数量大幅增加、吸附能力明显提高[158,159]。强酸类氧化剂改性, 一般采用硫酸、硝酸等化学试剂为介质。研究表明, 当炭化温度达到700℃时, 以硫酸为介质氧化处理后的改性生物炭, 其比表面积显著提高, 是未活化改性前的250倍以上[160]。采用硝酸改性, 会造成生物炭的结构性坍塌和pH降低、比表面积减小, 但会增加生物炭的表面酸性基团数量, 提高其表面亲水性[148,161]。强碱类氧化剂改性, 一般采用氢氧化钠、氢氧化钾等化学剂。研究发现, 采用氢氧化钠改性, 会显著提高生物炭的表面积和微孔体积, 提高其对重金属离子的吸附能力[162,163,164]。而采用氢氧化钾改性, 生物炭的微孔数量、吸附性能也有一定程度提高[165,166]。
5.1.3 涂层/浸渍改性 一般指在炭化前或炭化后, 采用涂层或浸渍方法, 将外源金属氧化物、有机试剂、纳米材料等介质与生物炭进行物理或化学反应耦合, 从而使生物炭比表面积、多孔性、表面官能团、阳离子交换量等特性改变的方法[148,167]。
采用金属氧化物涂层改性, 可在不同程度上提高改性生物炭的吸附能力[168,169], 当浸有金属离子的生物质在炭化后, 其所含有的金属离子形成金属氧化物或氢氧化物, 成为负载金属的炭基复合材料[148]。研究发现, 与未改性生物炭相比, 钴涂层改性生物炭具有更高的表面积、孔体积, 对铬离子的吸附量显著增加[169], 而采用MgCl2-6H2O和AlCl3- 6H2O与生物炭复合制备的炭基复合材料, 对磷的最大吸附量提高了5~50倍[170]。此外, 有研究采用聚乙烯亚胺和戊二醛与生物炭复合, 发现改性后的生物炭含氧官能团数量明显增加, 对Cd6+的吸附性能明显提高, 最大吸附量是未改性生物炭的18.87倍[171]。而采用乙二胺、三甲胺等有机试剂作为介质, 改性后的生物炭孔隙结构更为发达、表面基团数量明显增加, 对硝酸盐的吸附、去除效能提高[172]。
近年来, 纳米材料的技术开发与应用得到了专家、****的广泛关注。但由于纳米材料颗粒小, 易团聚、氧化, 在一定程度上限制了其应用[173,174]。但如果将纳米材料通过预涂(炭化前)和浸渍(炭化后)等过程负载于生物炭表面, 制备成功能性炭基纳米复合材料, 可提供更多高亲和力吸附位点, 从而有效发挥纳米材料的优势, 改善生物炭的多孔结构及比表面积、官能团、热稳定性等特性(图4)[175]。研究认为, 采用预涂、浸渍等处理方法, 将纳米材料与生物炭结合, 可弥补高温热解后生物炭表面官能团减少等“缺陷”, 实现“纳米-生物炭”功能复合, 充分发挥纳米材料与生物炭材料的双重功效优势, 提高其对污染物的吸附、去除效能[176]。目前, 采用涂层/浸渍改性的纳米/高分子复合材料主要为石墨烯、碳纳米管、壳聚糖等, 具有良好的应用潜力和发展空间。
图4
新窗口打开|下载原图ZIP|生成PPT图4生物炭基纳米复合材料的合成制备过程[175]
Fig. 4Schematic diagram of synthesizing biochar-based nano-composites[175]
5.2 炭化工艺调控技术
炭化工艺及制备方法, 决定了生物炭的结构及主要理化特性。通过改进、优化和创新生物质炭化工艺及其制备方法, 实现对生物炭结构及特性的总体性、批量化调控, 是工程化、规模化开发生物炭功能材料及产品的必由之路。目前, 炭化工艺调控技术主要有气体活化、微波炭化、球磨、紫外辐照等。5.2.1 气体活化 气体活化, 一般指在一定炭化温度条件下, 采用水蒸气、二氧化碳等进行活化改性的方法[148]。通过气体活化技术, 可将常规生物炭改性为结构更为丰富、比表面积更大的活性生物炭材料[177]。研究发现, 在700℃条件下采用蒸汽活化的生物炭比未活化生物炭的表面积提高了一倍[178], 吸附性能显著提升。
气体活化改性生物炭, 多用于水体净化、污染物处理等领域[179,180,181]。研究发现, 经特定蒸汽流量活化后的生物炭, 对铜离子的吸附率可达93% [181], 对汞离子也表现良好吸附性[182]。另有研究表明, 与未活化生物炭相比, 蒸汽活化生物炭可提高其对土壤氮、磷等养分离子的固持能力, 减少养分流失[183]。气体活化改性是一种简单、有效的改性技术方法, 但由于生物炭非均质性强, 反应温度、活化程度等条件难以精确控制, 因而可能造成对生物炭活化不均、局部过热等问题, 影响生物炭的活化质量及其功能作用, 在工业化生产中尚需进行深入的工艺与技术创新[184]。
5.2.2 微波炭化 微波, 是一种频率在300兆赫至300千兆赫之间的高频电磁波, 可迅速穿透生物质并将能量传递给反应物官能团[185]。采用微波改性方法制备的生物炭, 在官能团数量、比表面积及稳定性等方面优于传统热解方法制备的生物炭[186,187]。研究表明, 微波改性生物炭可提高其对重金属污染物的吸附、去除效率[188,189,190]。另有研究通过在微波制炭过程中添加特定化学物质, 使生物炭与特定反应物在微波条件下发生物理-化学反应, 也取得了良好试验效果[191]。未来, 在精细化、多元化应用目标趋动下, 在微波裂解过程中添加化学改性剂或其他特性材料, 已成为一种发展趋势[148]。
5.2.3 球磨制炭 球磨制炭, 一般指采用球磨仪对生物炭材料进行机械球磨, 降低其固体颗粒粒度, 从而改变生物炭结构, 提高生物炭整体性能的方法[192]。球磨后的生物炭颗粒大小可达纳米级, 比表面积、吸附性能显著提高, 去除有机、无机污染物性能表现与碳纳米管相当[193]。由于球磨生物炭的颗粒更小, 使其比表面积更大, 利于增加对有机、无机离子的潜在吸附位, 使球磨生物炭具有优异的整体吸附性能[194,195]。经球磨优化条件下制备的生物炭, 其表面积增加60~194 m2 g-1, 吸附性能显著提高[196]。
但是, 由于球磨生物炭在水中的分散性强、不易控制, 在一定程度上限制了其在环保等领域的应用。此外, 由于球磨生物炭的颗粒较轻, 易发生地表径流侵蚀和场外输送, 因而可能造成潜在的生态安全风险。研究表明, 随着生物炭粒径减小, 生物炭迁移量明显增加[197]。生物炭胶体粒子的移动, 可能导致农药及其他污染物沿土壤剖面发生非现场迁移, 从而增加地下水的潜在环境安全风险[198]。目前, 在球磨生物炭的结构及特性研究方面, 已取得一定研究进展, 但受机械水平、产能及应用条件、范围、生态安全性等因素影响, 距“工程化、规模化”开发与应用还有一定距离。
5.2.4 紫外辐照 紫外辐照, 一般指采用一定波段的紫外光进行辐照改性的方法。紫外光辐照改性生物炭, 其比表面积、含氧官能团数量明显提高, 对Pb2+、Cd2+金属离子的吸附能力明显增强, 最大吸附量显著提升[199,200]。紫外辐照改性方法, 操作简单、环保、安全, 为生物炭改性技术发展提供了新途径。但是, 由于实施紫外辐照的条件、容量和规模等因素制约, 使其在“规模化、工程化”及“精准性、稳定性”等方面, 还存在一定局限性。
生物炭结构及理化特性, 决定了其作为载体、基质或吸附剂等功能材料的“适用、实用和经济性”, 采用新材料、新工艺、新方法对生物炭构相及其理化特性进行“定性、定量化”调控, 是一种必然趋势。目前, 生物炭改性技术已成为生物炭领域的研究热点之一, 正由单一技术转向“1+N”复合技术, 由原始、传统工艺转向“精准化、智能化、自动化”现代新工艺, 是目前改性技术的发展趋势, 生物炭改性技术的创新发展与应用有望为生物炭基础研究与应用提供新方向、新途径、新突破。
6 研究展望
时至今日, 生物炭在农业、环境、能源等领域所展现的重要功能、潜在价值与贡献, 已得到全球专家、****的广泛关注和研究认可。我国在陈温福院士等一批科学家的倡导和努力下, 在生物炭制备工艺、基础研究、应用技术、产品开发及产业化等方面所取得的研究进展与成果, 已处于国际前列。生物炭研究“方兴未艾”, 已步入“快车道”, 多领域、多学科先进技术的创新与发展, 必将推动生物炭研究与应用向“大范围、宽领域”、“综合性、交叉性”和“定制化、多元化”方向快速发展。开展生物炭特性及其应用研究, 在以下几个方面值得关注:6.1 研究方向
(1) 面向我国农业发展国情, 结合区域农业发展特征, 突破“低成本、高效、环保”炭化工艺瓶颈, 发展“小、中、大”兼具、“炭、油、气”联产, 适合不同农林废弃物来源的炭化生产系统, 建立“分散-集中”式、多向覆盖的炭化生产网络, 依靠科技创新扩大产能、降低生产与流通成本, 使炭化工艺技术、装备与产品真正“落地、触底”, 真正“可用、能用、适用”。(2) 基于农、林废弃物“循环、高效”利用, 聚焦农业、环境等领域“老、大、难”生产现实问题, 采用原创或交叉、集成创新技术, 深入挖掘生物炭“构-效”与“质-效”作用潜力及优势, 重点开发利于自然生态系统“平衡、稳定、永续”发展, 真正“低碳、生态、高效”的普适、多元、高值化系列炭基功能材料及产品。
(3) 建立“科学、系统、规范”的生物炭生产、测定与应用指标评价体系, 使生物炭研究与应用结果科学、准确, 有依据、可比较;创建基于不同来源、材质、工艺等条件下的生物炭理化特性与应用数据库, 使生物炭研究与应用“可查、可溯、可依”, 为相关研究、使用者提供有效参考;制定生物炭材料、产品及其应用等相关技术标准, 规范生物炭来源、生产、制备及应用等各环节, 破解生物炭制备、应用及市场乱象, 促进生物炭产业“健康、稳定、有序”发展。
(4) 生物炭研究与应用的“多领域融合、多学科交叉、多功能复合”, 生物炭材料及其产品的“特色化、功能化、定制化”, 是其未来发展的趋势和方向;未来, 生物炭基材料及产品很可能以“低碳、绿色、环保”等综合功效优势, 替代部分传统农业与环保投入品, 以“零资源损耗、低成本投入”, 获得“多效、稳定、可持续”收益, 实现经济、生态和社会效益最大化, 为农业、资源与环境的“循环、可持续”发展提供“趋动力”。
6.2 展望
目前, 生物炭理化特性及应用研究已取得一定进展, 但目前全球大多数研究仍处于实验室或模拟、小规模试验条件下, 距“批量化、规模化、工程化”应用和实施还存在较大差距。在基础研究方面, 不同来源、材质、炭化工艺条件下生物炭的“构-效”与“质-效”的定性、定量化关系, 炭基复合、载体功能材料制备及其应用的物理-化学反应过程、调控途径及作用原理、机制, 炭基功能材料的“可定制化”载体构建, 生物炭基材料及其产品应用的“长期性、安全性、可持续性”评估与预测等等, 还有诸多科学、技术问题亟待研究探索;在炭化工艺、装备及产品研制方面, 不同原料来源的“低成本、广适、环保”型炭化新工艺, 生物质炭化及其产品制备、生物炭改性条件的“精准、定量”化控制, 炭化副产物的“低成本、零污染、高效”回收与再利用, 改性生物炭的“稳定性、可控性、安全性”等方面, 尚需开展系统、深入的研究探索与实践;纳米等创新技术发展, 为炭基多功能、复合材料开发提供了新方向, 在炭基复合、介质材料的筛选、开发与应用, 复合技术的“精准、定量化”控制, 以及炭基多功能、复合材料与产品的“批量化、规模化”生产与应用等方面还有较大提升空间;打破传统技术的“单一性”桎梏, 融合多领域、多学科交叉技术, 探索“生物炭+”技术模式, 是未来突破未来生物炭特性与功能局限, 研发新一代“复合性、功能化、高效型”炭基材料及产品的发展重要方向;“多元化、功能化、定制化”是未来生物炭改性技术及其产品开发的发展趋势, 有望在解决农业、环境等领域突出问题中发挥重要支撑性作用。科学需要理性, 更应该理性对待科学。作为新生事物, 有关于生物炭的定义、结构、功效及其应用等方面还存在不同观点。但不可否认的是, 生物炭在农业、环境等领域应用确有着良好的综合效益及重要作用潜力、价值与贡献, 其独特的来源、结构、特性及功效是其他材料所不具备的, 也得到了全世界科学家的普遍关注和一致研究认可。当前, 我国正处于农业与经济、社会发展的战略转型期, 生物炭无疑为解决农林废弃物综合利用难题, 促进资源与环境“循环、永续”发展, 提供了重要、可行性新途径, 为保障国家粮食安全、提升耕地质量, 促进“三农”发展提供有效技术支撑。相信, 未来在国内外专家、****的共同努力下, 生物炭的研究与应用发展及其产业化实施, 必将为人类面对气候变化, 破解“沃土、碧水、蓝天”可持续发展问题与矛盾, 打造“绿水、青山”, 作出应有的重要贡献。
参考文献 原文顺序
文献年度倒序
文中引用次数倒序
被引期刊影响因子
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AbstractEnergy from biomass, bioenergy, is a perspective source to replace fossil fuels in the future, as it is abundant, clean, and carbon dioxide neutral. Biomass can be combusted directly to generate heat and electricity, and by means of thermo-chemical and bio-chemical processes it can be converted into bio-fuels in the forms of solid (e.g., charcoal), liquid (e.g., bio-oils, methanol and ethanol), and gas (e.g., methane and hydrogen), which can be used further for heat and power generation. This paper provides an overview of the principles, reactions, and applications of four fundamental thermo-chemical processes (combustion, pyrolysis, gasification, and liquefaction) for bioenergy production, as well as recent developments in these technologies. Some advanced thermo-chemical processes, including co-firing/co-combustion of biomass with coal or natural gas, fast pyrolysis, plasma gasification and supercritical water gasification, are introduced. The advantages and disadvantages, potential for future applications and challenges of these processes are discussed. The co-firing of biomass and coal is the easiest and most economical approach for the generation of bioenergy on a large-sale. Fast pyrolysis has attracted attention as it is to date the only industrially available technology for the production of bio-oils. Plasma techniques, due to their high destruction and reduction efficiencies for any form of waste, have great application potential for hazardous waste treatment. Supercritical water gasification is a promising approach for hydrogen generation from biomass feedstocks, especially those with high moisture contents.]]>
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This critical review provides a survey illustrated by recent references of different strategies to achieve a sustainable conversion of biomass to bioproducts. Because of the huge number of chemical products that can be potentially manufactured, a selection of starting materials and targeted chemicals has been done. Also, thermochemical conversion processes such as biomass pyrolysis or gasification as well as the synthesis of biofuels were not considered. The synthesis of chemicals by conversion of platform molecules obtained by depolymerisation and fermentation of biopolymers is presently the most widely envisioned approach. Successful catalytic conversion of these building blocks into intermediates, specialties and fine chemicals will be examined. However, the platform molecule value chain is in competition with well-optimised, cost-effective synthesis routes from fossil resources to produce chemicals that have already a market. The literature covering alternative value chains whereby biopolymers are converted in one or few steps to functional materials will be analysed. This approach which does not require the use of isolated, pure chemicals is well adapted to produce high tonnage products, such as paper additives, paints, resins, foams, surfactants, lubricants, and plasticisers. Another objective of the review was to examine critically the green character of conversion processes because using renewables as raw materials does not exempt from abiding by green chemistry principles (368 references).
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This article reviews the hydrothermal liquefaction of biomass with the aim of describing the current status of the technology. Hydrothermal liquefaction is a medium-temperature, high-pressure thermo-chemical process, which produces a liquid product, often called bio-oil or bi-crude. During the hydrothermal liquefaction process, the macromolecules of the biomass are first hydrolyzed and/or degraded into smaller molecules. Many of the produced molecules are unstable and reactive and can recombine into larger ones. During this process, a substantial part of the oxygen in the biomass is removed by dehydration or decarboxylation. The chemical properties of bio-oil are highly dependent of the biomass substrate composition. Biomass constitutes of various components such as protein; carbohydrates, lignin and fat, and each of them produce distinct spectra of compounds during hydrothermal liquefaction. In spite of the potential for hydrothermal production of renewable fuels, only a few hydrothermal technologies have so far gone beyond lab- or bench-scale. (C) 2011 Elsevier Ltd.
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AbstractThe change of mass and composition of biomass tar due to homogeneous secondary reactions was experimentally studied by means of a lab reactor system that allows the spatially separated production and conversion of biomass tar. A tarry pyrolysis gas was continuously produced by pyrolysis of wood chips (fir and spruce, 10–40 mm diameter) under fixed-bed biomass gasification conditions. Homogeneous secondary tar reactions without the external supply of oxidising agents were studied in a tubular flow reactor operated at temperatures from 500 to 1000 °C and with space times below 0.2 s. Extensive chemical analysis of wet chemical tar samples provided quantitative data about the mass and composition of biomass tar during homogeneous conversion. These data were used to study the kinetics of the conversion of gravimetric tar and the formation of PAH compounds, like naphthalene.It is shown that, under the reaction conditions chosen for the experiments, homogeneous secondary tar reactions become important at temperatures higher than 650 °C, which is indicated by the increasing concentrations of the gases CO, CH4, and H2 in the pyrolysis gas. The gravimetric tar yield decreases with increasing reactor temperatures during homogeneous tar conversion. The highest conversion reached in the experiments was 88% at a reference temperature of 990 °C and isothermal space time of 0.12 s. Hydrogen is a good indicator for reactions that convert the primary tar into aromatics, especially PAH. Soot appears to be a major product from homogeneous secondary tar reactions.]]>
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In this study, gas chromatography-mass spectrometry (GC-MS) was used to analyze the pyrolytic bio-oils and gas fractions derived from the pyrolysis of industrial sewage sludges using induction-heating technique. The liquid products were obtained from the cryogenic condensation of the devolatilization fraction in a nitrogen atmosphere using a heating rate of 300 degrees C/min ranging from 25 to 500 degrees C. The analytical results showed that the pyrolysis bio-oils were very complex mixtures of organic compounds and contained a lot of nitrogenated and/or oxygenated compounds such as aliphatic hydrocarbons, phenols, pyridines, pyrroles, amines, ketones, and so on. These organic hydrocarbons containing nitrogen and/or oxygen should originate from the protein and nucleic acid textures of the microbial organisms present in the sewage sludge. The non-condensable devolatilization fractions were also composed of nitrogenated and oxygenated compounds, but contained small fractions of phenols, 1H-indoles, and fatty carboxylic acids. On the other hand, the compositions in the non-condensable gas products were principally carbon dioxide, carbon monoxide and methane analyzed by gas chromatography-thermal conductivity detector (GC-TCD).
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AbstractThe aim of this study was to evaluate the production of pyrolysis oil from three types of sewage sludges. The flash pyrolysis was performed at 500 °C, the maximum oil yield was 43.1%, and the water content in bio-oils obtained from secondary sludges was relatively low – 10.3% and 17.0%. GC–MS results showed that pyrolytic bio-oils of studied sludges dominantly contained fatty acids and nitrogenous compounds with potential added value.Obtained solids had high ash content and low calorific value which make them unattractive for use in incineration. FT–IR results showed that solids gave similar IR features as notified alumino silicates; utilization of these solids as adsorbents could be a potential valorization.]]>
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Extensive and inefficient use of pesticides over the last several decades resulted in serious soil and water contamination by imposing severe toxic effects on living organisms. Soil remediation using environment-friendly amendments to counteract the presence of pesticides in soil seems to be one suitable approach to solve this problem. Biochar has emerged as a promising material for adsorbing and thus decreasing the bioavailability of pesticides in polluted soils, due to its high porosity, surface area, pH, abundant functional groups, and highly aromatic structure, mainly depending on the feedstock and pyrolysis temperature. However, biochar effects and mechanisms on the sorption and desorption of pesticides in the soil are poorly understood. Either high or low pyrolysis temperature has both positive and negative effects on sorption of pesticides in soil, one by larger surface area and the other by a large number of functional groups. Therefore, a clear understanding of these effects and mechanisms are necessary to engineer biochar production with desirable properties. This review critically evaluates the role of biochar in sorption, desorption, and degradation of pesticides in the soil, along with dominant properties of biochar including porosity and surface area, pH, surface functional groups, carbon content and aromatic structure, and mineralogical composition. Moreover, an insight into future research directions has been provided by evaluating the bioavailability of pesticide residues in the soil, effect of other contaminants on pesticide removal by biochar in soils, effect of pesticide properties on its behavior in biochar-amended soils, combined effect of biochar and soil microorganisms on pesticide degradation, and large-scale application of biochar in agricultural soils for multifunction.
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Experiments suggest that biomass-derived black carbon (biochar) affects microbial populations and soil biogeochemistry. Both biochar and mycorrhizal associations, ubiquitous symbioses in terrestrial ecosystems, are potentially important in various ecosystem services provided by soils, contributing to sustainable plant production, ecosystem restoration, and soil carbon sequestration and hence mitigation of global climate change. As both biochar and mycorrhizal associations are subject to management, understanding and exploiting interactions between them could be advantageous. Here we focus on biochar effects on mycorrhizal associations. After reviewing the experimental evidence for such effects, we critically examine hypotheses pertaining to four mechanisms by which biochar could influence mycorrhizal abundance and/or functioning. These mechanisms are (in decreasing order of currently available evidence supporting them): (a) alteration of soil physico-chemical properties; (b) indirect effects on mycorrhizae through effects on other soil microbes; (c) plant–fungus signaling interference and detoxification of allelochemicals on biochar; and (d) provision of refugia from fungal grazers. We provide a roadmap for research aimed at testing these mechanistic hypotheses.]]>
DOI:10.1016/j.biortech.2018.09.030URLPMID:30220436 [本文引用: 4]
Biochar produced from biomass pyrolysis is becoming a powerful tool for carbon sequestration and greenhouse gas (GHG) emission reduction. Biochar C recalcitrance or biochar stability is the decisive property determining its carbon sequestration potential. The effect of pyrolysis process parameters on biochar stability is becoming a frontier of biochar study. This review discussed comprehensively how and why biomass compositions and physicochemical properties and biomass processing conditions such as pyrolysis temperature and reaction residence time affect the stability of biochar. The review found that relative high temperature (400-700 degrees C), long reaction residence time, slow heating rate, high pressure, the presence of some minerals and biomass feedstock of high-lignin content with large particle size are preferable to biochar stability. However, challenges exist to mediate the trade-offs between biochar stability and other potential wins. Strategies were then proposed to promote the utilization of biochar as a climate change mitigation tool.
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Char black carbon (BC), the solid residue of incomplete combustion, is continuously being added to soils and sediments due to natural vegetation fires, anthropogenic pollution, and new strategies for carbon sequestration (
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Conversion of rice straw (RS) and pig manure (PM) into chars is a promising disposal/recycling option. Herein, pyrolysis and hydrothermal carbonization were used to produce bio- and hydrochars from RS and PM, affording lower biochar (300-700 degrees C) and hydrochar (180-300 degrees C) yields at higher temperatures within the specified range. The C contents and C/N ratios of RS chars were higher than those of PM ones, with the opposite trend observed for yield and ash content. C and ash contents increased with increasing temperature, whereas H/C, O/C, and (O+N)/C ratios decreased. The lower H/C ratio of biochars compared to that of hydrochars indicated greater stability of the former. KCl was the main inorganic fraction in RS biochars, whereas quartz was dominant in PM biochars, and albite in PM hydrochars. Thus, RS is more suitable for carbon sequestration, while PM is more suitable for use as a soil amendment substrate.
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The char's structure was set out by the mercury porosimetry and Brunauer-Emmett-Teller method. The phase composition of the solid residue after pyrolysis and carbon/silica ratio therein has been determined by thermal analysis (TG/DTA/MS) and XRD. The morphology of the materials has been studied using scanning electron microscopy.It was established that the slow pyrolysis in the investigated temperature range results in a solid residue with predominantly macro-porous structure and pore size distribution between 50 and 200 mu m. The sample obtained at 480 degrees C is characterized by the largest total pore volume and the largest average pore diameter. With increasing the pyrolysis temperature C:SiO2 ratio in the solid pyrolysis residue decreased from 1.38 to 0.85 and specific surface area increased from 7.0 up to 440.0 m(2) g(-1).]]>
DOI:10.1021/es035034wURLPMID:15461175 [本文引用: 2]
300 m2/g), little organic matter (20% oxygen). The char samples exhibited a significant range of surface acidity/basicity because of their different surface polar-group contents, as characterized by the Boehm titration data and the NMR and FTIR spectra. The NOC sorption by high-temperature chars occurred almost exclusively by surface adsorption on carbonized surfaces, whereas the sorption by low-temperature chars resulted from the surface adsorption and the concurrent smaller partition into the residual organic-matter phase. The chars appeared to have a higher surface affinity for a polar solute (nitrobenzene) than for a nonpolar solute (benzene), the difference being related to the surface acidity/basicity of the char samples.]]>
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In this study, the effects of pyrolysis temperature and heating time on the yield and physicochemical and morphological properties of biochar obtained from straw and lignosulfonate were investigated. As pyrolysis temperature increased, pH, ash content, carbon stability, and total content of carbon increased while biochar yield, volatile matter, total content of hydrogen, oxygen, nitrogen and sulfur decreased. The data from scanning electron microscope image and nuclear magnetic resonance spectra indicated an increase in porosity and aromaticity of biochar produced at a high temperature. The results showed that feedstock types could also influence characteristics of the biochar with absence of significant effect on properties of biochar for heating time.
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为明确生物炭对水稻根系与产量的效应，探明生物炭在水稻生产上应用的潜力与价值。采用盆栽试验研究了生物炭对超级粳稻不同生育期根系生长、形态特征及生理特性的影响。结果表明，土壤中施入生物炭能增加水稻生育前期根系的主根长、根体积和根鲜重，提高水稻根系总吸收面积和活跃吸收面积。在水稻生育后期，生物炭在一定程度上延缓根系衰老。根系伤流速率、根系活力和可溶性蛋白在整个生育期内均高于对照，同时维持了较为适宜的根冠比，根系生理功能增强；生物炭处理的水稻产量增加，表现为每穴穗数、每穗粒数、结实率提高，比对照平均增产25.28%。以每千克干土加20 g生物炭处理的产量最高，比对照提高了33.21%。生物炭处理对水稻根系形态特征的优化与生理功能的增强具有一定的促进作用。]]>
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350 degrees C) typically were dominated by sorbed aromatic compounds and longer carbon chain hydrocarbons. The presence of oxygen during pyrolysis also reduced sorbed VOCs. These compositional results suggest that sorbed VOCs are highly variable and that their chemical dissimilarity could play a role in the wide variety of plant and soil microbial responses to biochar soil amendment noted in the literature. This variability in VOC composition may argue for VOC characterization before land application to predict possible agroecosystem effects. Published by Elsevier Ltd.]]>
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Biochar was prepared using a low temperature pyrolysis method from nine plant materials including non-leguminous straw from canola, wheat, corn, rice and rice hull and leguminous straw from soybean, peanut, faba bean and mung bean. Soil pH increased during incubation of the soil with all nine biochar samples added at 10 g/kg. The biochar from legume materials resulted in greater increases in soil pH than from non-legume materials. The addition of biochar also increased exchangeable base cations, effective cation exchange capacity, and base saturation, whereas soil exchangeable Al and exchangeable acidity decreased as expected. The liming effects of the biochar samples on soil acidity correlated with alkalinity with a close linear correlation between soil pH and biochar alkalinity (R2 = 0.95). Therefore, biochar alkalinity is a key factor in controlling the liming effect on acid soils. The incorporation of biochar from crop residues, especially from leguminous plants, can both correct soil acidity and improve soil fertility.
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Conocarpus wastes were pyrolyzed at different temperatures (200-800 degrees C) to investigate their impact on characteristics and chemical composition of biochars. As pyrolysis temperature increased, ash content, pH, electrical conductivity, basic functional groups, carbon stability, and total content of C, N, P, K, Ca, and Mg increased while biochar yield, total content of O, H and S, unstable form of organic C and acidic functional groups decreased. The ratios of O/C, H/C, (O + N)/C, and (O + N + S)/C tended to decrease with temperature. The data of Fourier transformation infrared indicate an increase in aromaticity and a decrease in polarity of biochar produced at a high temperature. With pyrolysis temperature, cellulose loss and crystalline mineral components increased, as indicated by X-ray diffraction analysis and scanning electron microscope images. Results suggest that biochar pyrolized at high temperature may possess a higher carbon sequestration potential when applied to the soil compared to that obtained at low temperature.
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Biochar is carbon-rich product generated from biomass through pyrolysis. In this study, the effects of pyrolysis temperature and heating rate on the yield and physicochemical and morphological properties of biochars obtained from safflower seed press cake were investigated. The results showed that the biochar yield and quality depend principally on the applied temperature where pyrolysis at 600 degrees C leaves a biochar with higher fixed carbon content (80.70%) and percentage carbon (73.75%), and higher heating value (30.27 MJ kg(-1)) in comparison with the original feedstock (SPC) and low volatile matter content (9.80%). The biochars had low surface areas (1.89-4.23 m(2)/g) and contained predominantly aromatic compounds. The biochar could be used for the production of activated carbon, in fuel applications, and water purification processes.
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Soil fertility and leaching losses of nutrients were compared between a Fimic Anthrosol and a Xanthic Ferralsol from Central Amazônia. The Anthrosol was a relict soil from pre-Columbian settlements with high organic C containing large proportions of black carbon. It was further tested whether charcoal additions among other organic and inorganic applications could produce similarly fertile soils as these archaeological Anthrosols. In the first experiment, cowpea (Vigna unguiculata (L.) Walp.) was planted in pots, while in the second experiment lysimeters were used to quantify water and nutrient leaching from soil cropped to rice (Oryza sativa L.). The Anthrosol showed significantly higher P, Ca, Mn, and Zn availability than the Ferralsol increasing biomass production of both cowpea and rice by 38–45% without fertilization (P]]>
DOI:10.3724/SP.J.1006.2017.00072URL [本文引用: 1]
在黑龙江省早春水稻旱育苗背景下,研究稻田土壤育苗基质中添加生物炭对秧苗根系形态建成与解剖结构的影响,以明确生物炭在东北冷凉地区水稻生产上的应用潜力和价值。以东北稻田土壤为育苗基质,添加0、5.0%、10.0%、15.0%、20.0% (w/w)的生物炭,进行保护地旱育水稻秧苗。出苗后30 d,测定秧苗根系形态建成和解剖结构等性状,分析生物炭对水稻秧苗根系发育的影响。结果表明,在稻田土壤育苗基质中添加5.0%生物炭时,水稻秧苗根系长度、根系表面积和根系体积等明显增加；生物炭添加量为10.0%时,各项根系形态指标达到最高值；生物炭添加量超过10.0%时,根系形态指标下降。根长、根表面积和根体积增加的原因主要来自于细根增加。同时,添加5.0%生物炭时,根半径、根截面积、根表皮厚度、根皮层厚度、皮层腔面积、根导管数量及导管面积等性状指标也相应增加。生物炭添加量为5.0%~10.0%时,根解剖结构各项性状指标达到最大值。当生物炭添加量超过10.0%时,根系解剖结构性状指标也有下降趋势。根系增粗主要源于根表皮及皮层发育良好。在东北冷凉地区进行保护地水稻旱育苗,基质中添加适量生物炭(5.0%~10.0%)有利于秧苗根系的伸长及增粗,形成发达根系,提高秧苗素质。
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DOI:10.1007/s11356-015-5114-2URL [本文引用: 1]
DOI:10.1016/j.biortech.2017.08.122URLPMID:28863990 [本文引用: 1]
In recent years, there has been a significant interest on biochar for various environmental applications, e.g., pollutants removal, carbon sequestration, and soil amelioration. Biochar has several unique properties, which makes it an efficient, cost-effective and environmentally-friendly material for diverse contaminants removal. The variability in physicochemical properties (e.g., surface area, microporosity, and pH) provides an avenue for biochar to maximize its efficacy to targeted applications. This review aims to highlight the vital role of surface architecture of biochar in different environmental applications. Particularly, it provides a critical review of current research updates related to the pollutants interaction with surface functional groups of biochars and the effect of the parameters variability on biochar attributes pertinent to specific pollutants removal, involved mechanisms, and competence for these removals. Moreover, future research directions of biochar research are also discussed.
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The aim of this study was to investigate the influence of pyrolysis temperature on the physicochemical properties and structure of biochar. Biochar was produced by fast pyrolysis of pitch pine (Pinus rigida) using a fluidized bed reactor at different pyrolysis temperatures (300, 400 and 500 degrees C). The produced biochars were characterized by elemental analysis, Brunauer-Emmett-Teller (BET) surface area, particle size distributions, field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FTIR) spectroscopy, solid-state (13)C nuclear magnetic resonance (NMR) and X-ray diffraction (XRD). The yield of biochar decreased sharply from 60.7% to 14.4%, based on the oven-dried biomass weight, when the pyrolysis temperature rose from 300 degrees C to 500 degrees C. In addition, biochars were further carbonized with an increase in pyrolysis temperature and the char's remaining carbons were rearranged in stable form. The experimental results suggested that the biochar obtained at 400 and 500 degrees C was composed of a highly ordered aromatic carbon structure.
DOI:10.1016/j.jhazmat.2012.01.046URLPMID:22321858 [本文引用: 1]
Reclaimed water irrigation can satisfy increasing water demand, but it may also introduce pharmaceutical contaminants into the soil and groundwater environment. In this work, a range of laboratory experiments were conducted to test whether biochar can be amended in soils to enhance removal of sulfamethoxazole (SMX) from reclaimed water. Eight types of biochar were tested in laboratory sorption experiments yielding solid-water distribution coefficients (K(d)) of 2-104 L/kg. Two types of biochar with relatively high K(d) were used in column leaching experiments to assess their effect on reclaimed water SMX transport through soils. Only about 2-14% of the SMX was transported through biochar-amended soils, while 60% was found in the leachate of the unamended soils. Toxicity characteristic leaching experiments confirmed that the mobility and bioavailability of SMX in biochar-amended soils were lower than that of unamended soils. However, biochar with high accumulations of SMX was still found to inhibit the growth of the bacteria compared to biochar with less SMX which showed no effects. Thus, biochar with very high pharmaceutical sorption abilities may find use as a low-cost alternative sorbent for treating wastewater plant effluent, but should be used with caution as an amendment to soils irrigated with reclaimed water or waste water.
DOI:10.1016/j.fuel.2013.01.033URL [本文引用: 1]
It could be seen that higher water content led to a higher yield of condensable products and a lower amount of char. At a pyrolysis temperature of 500 degrees C the CO-content of the product gas did increase significantly with increasing water content. Moreover, initial water content had no significant effect on the microscopic structure of wood chars.The specific char surface area did increase with increasing initial water content up to the fiber saturation point. It was also observed that the specific char surface area was strongly influenced by the pyrolysis temperature. When the pyrolysis temperature increased from 500 to 800 degrees C, the BET surface area became at least 200 times smaller and the average size of micropores became about 10 times smaller. Most likely, pyrolysis at 800 degrees C induced more secondary reactions that were responsible for the occlusion of the micropores within the char [1].Finally, it was found that reactivity in CO2 significantly decreased with increasing pyrolysis temperature. However, initial wood water content did not have a significant effect on char reactivity in CO2. (c) 2013 Elsevier Ltd.]]>
DOI:10.1021/ef900268yURL [本文引用: 1]
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DOI:10.1016/j.jenvman.2010.09.008URL [本文引用: 1]
The important challenge for effective management of wastewater sludge materials in an environmentally and economically acceptable way can be addressed through pyrolytic conversion of the sludge to biochar and agricultural applications of the biochar The aim of this work is to investigate the influence of pyrolysis temperature on production of wastewater sludge biochar and evaluate the properties required for agronomic applications Wastewater sludge collected from an urban wastewater treatment plant was pyrolysed in a laboratory scale reactor It was found that by increasing the pyrolysis temperature (over the range from 300 C to 700 C) the yield of biochar decreased Biochar produced at low temperature was acidic whereas at high temperature it was alkaline in nature The concentration of nitrogen was found to decrease while micronutrients increased with increasing temperature Concentrations of trace metals present in wastewater sludge varied with temperature and were found to primarily enriched in the biochar (C) 2010 Elsevier Ltd All nghts reserved
DOI:10.1016/j.biortech.2014.04.048URLPMID:24835918
To investigate systematically the influence of pyrolysis temperature on properties and heavy metal adsorption potential of municipal sludge biochar, biophysical dried sludge was pyrolyzed under temperature varying from 500 degrees C to 900 degrees C. The biochar yield decreased with the increase in pyrolysis temperature, while the ash content retained mostly, thus transforming the biochars into alkaline. The structure became porous as the temperature increased, and the concentrations of surface functional group elements remained low. Despite the comparatively high content of heavy metal in the biochar, the leaching toxicity of biochars was no more than 20% of the Chinese standard. In the batch experiments of cadmium(II) adsorption, the removal capacity of biochars improved under higher temperature, especially at 800 degrees C and 900 degrees C even one order of magnitude higher than that of the commercial activated carbon. For both energy recovery and heavy metal removal, the optimal pyrolysis temperature is 900 degrees C.
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DOI:10.1016/j.biortech.2012.05.042URLPMID:22721877 [本文引用: 1]
Conversion of crop residues into biochars (BCs) via pyrolysis is beneficial to environment compared to their direct combustion in agricultural field. Biochars developed from soybean stover at 300 and 700 degrees C (S-BC300 and S-BC700, respectively) and peanut shells at 300 and 700 degrees C (P-BC300 and P-BC700, respectively) were used for the removal of trichloroethylene (TCE) from water. Batch adsorption experiments showed that the TCE adsorption was strongly dependent on the BCs properties. Linear relationships were obtained between sorption parameters (K(M) and S(M)) and molar elemental ratios as well as surface area of the BCs. The high adsorption capacity of BCs produced at 700 degrees C was attributed to their high aromaticity and low polarity. The efficacy of S-BC700 and P-BC700 for removing TCE from water was comparable to that of activated carbon (AC). Pyrolysis temperature influencing the BC properties was a critical factor to assess the removal efficiency of TCE from water.
DOI:10.1016/j.chemosphere.2014.12.058URLPMID:25618190 [本文引用: 6]
In recent years, many studies have been devoted to investigate the application of biochar for pollutants removal from aqueous solutions. Biochar exhibits a great potential to efficiently tackle water contaminants considering the wide availability of feedstock, low-cost and favorable physical/chemical surface characteristics. This review provides an overview of biochar production technologies, biochar properties, and recent advances in the removal of heavy metals, organic pollutants and other inorganic pollutants using biochar. Experimental studies related to the adsorption behaviors of biochar toward various contaminants, key affecting factors and the underlying mechanisms proposed to explain the adsorption behaviors, have been comprehensively reviewed. Furthermore, research gaps and uncertainties that exist in the use of biochar as an adsorbent are identified. Further research needs for biochar and potential areas for future application of biochars are also proposed.
DOI:10.1016/j.jclepro.2015.07.096URL [本文引用: 1]
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DOI:10.1111/ejss.12064URL [本文引用: 2]
The stability of biochar in soils is the cornerstone of the burgeoning worldwide interest in the potential of the pyrolysis/biochar platform for carbon (C) sequestration. While biochar is more recalcitrant in soil than the original organic feedstock, an increasing number of studies report greater C-mineralization in soils amended with biochar than in unamended soils. Soil organisms are believed to play a central role in this process. In this review, the variety of interactions that occur between soil micro-, meso- and macroorganisms and biochar stability are assessed. In addition, different factors reported to influence biochar stability, such as biochar physico-chemical characteristics, soil type, soil organic carbon (SOC) content and agricultural management practices are evaluated. A meta-analysis of data in the literature revealed that biochar-C mineralization rates decreased with increasing pyrolysis temperature, biochar-C content and time. Enhanced release of CO2 after biochar addition to soil may result from (i) priming of native SOC pools, (ii) biodegradation of biochar components from direct or indirect stimulation of soil organisms by biochar or (iii) abiotic release of biochar-C (from carbonates or chemi-sorbed CO2). Observed biphasic mineralization rates suggest rapid mineralization of labile biochar compounds by microorganisms, with stable aromatic components decomposed at a slower rate. Comparatively little information is available on the impact of soil fauna on biochar stability in soil, although they may decrease biochar particle size and enhance its dispersion in the soil. Elucidating the impacts of soil fauna directly and indirectly on biochar stability is a top research priority.
DOI:10.1016/j.jenvman.2014.07.016URLPMID:25190598 [本文引用: 1]
Biochars were produced from pinewood, peanut shell, and bamboo biomass through hydrothermal conversion (HTC) at 300 degrees C and comparatively by slow pyrolysis over a temperature range of 300, 400, and 500 degrees C. These biochars were characterized by FT-IR, cation exchange capacity (CEC) assay, methylene blue adsorption, as well as proximate and elemental analysis. The experimental results demonstrated higher retained oxygen content in biochars produced at lower pyrolysis temperatures and through HTC, which also correlated to the higher CEC of respective biochars. Furthermore, all types of biochar studied herein were capable of adsorption of methylene blue from solution and the adsorption did not appear to strongly correlate with CEC, indicating that the methylene blue adsorption appears to be dependent more upon the non-electrostatic molecular interactions such as the likely dispersive pi-pi interactions between the graphene-like sheets of the biochar with the aromatic ring structure of the dye, than the electrostatic CEC. A direct comparison of hydrothermal and pyrolysis converted biochars reveals that biochars produced through HTC have much higher CEC than the biochars produced by slow pyrolysis. Analysis by FT-IR reveals a higher retention of oxygen functional groups in HTC biochars; additionally, there is an apparent trend of increasing aromaticity of the pyrolysis biochars when produced at higher temperatures. The CEC value of the HTC biochar appears correlated with its oxygen functional group content as indicated by the FT-IR measurements and its O:C ratio.
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DOI:10.1016/j.geoderma.2012.10.002URL [本文引用: 1]
Biochar has shown promise as a soil amendment that increases carbon sequestration and fertility, but its effects on dissolved organic carbon (DOC), nitrogen (N) and phosphorus (P) cycling and loss is not well understood. Here, nutrient release from a variety of new and aged biochars, pure and mixed with soils, is examined using batch extraction and column leaching. In successive batch extractions of biochar, cumulative losses were about 0.1-2, 0.5-8 and 5-100% of the total C, N and P initially present, respectively, with greater releases from biochars made at lower temperature and from grass. Ammonium was usually the most abundant N form in leachates but nitrate was also abundant in some biochars, while organic N and P represented as much as 61% and 93% of the total N and P lost, respectively. Release of DOC, N and P into water was correlated with biochar volatile matter content and acid functional group density. However, P release via Mehlich-1 extraction was more strongly related to ash content, suggesting a mineral-associated P fraction. Columns with soil/biochar mixtures showed evidence of both soil nutrient sorption by biochar and biochar nutrient sorption by soil, depending upon biochar and soil type. This study demonstrates that biochars contain a range of nutrient forms with different release rates, explaining biochar's variable effect on soil fertility with soil and crop type and over time. (c) 2012 Elsevier B.V.
DOI:10.1016/j.biortech.2012.12.044URLPMID:23313694 [本文引用: 1]
To investigate the effect of pyrolysis temperature on properties and nutrient values, biochars were produced from giant reed (Arundo donax L.) at 300-600 degrees C and their properties such as elemental and mineral compositions, release of N, P and K, and adsorption of N and P were determined. With increasing temperatures, more N was lost and residual N was transformed into heterocyclic-N, whereas no P and K losses were observed. P was transformed to less soluble minerals, resulting in a reduction in available-P in high-temperature biochars. A pH of5 favored release of NH(4)(+), PO(4)(3-) and K(+) into water. Low-temperature biochars ( 400 degrees C) showed appreciable NH(4)(+) adsorption (2102mgkg(-1)). These results indicate that low-temperatures may be optimal for producing biochar from giant reed to improve the nutrient availability.
DOI:10.1007/s13593-016-0372-zURL [本文引用: 4]
DOI:10.1021/es101283dURLPMID:21090742 [本文引用: 1]
Surface charge and pH-dependent nutrient release properties of cornstraw biochar were examined to elucidate its potential agronomic benefits. Kinetics of element release was characterized by rapid H(+) consumption and rapid, pH-dependent P, Ca, and Mg release, followed by zero-order H(+) consumption and mineral dissolution reactions. Initial K release was not pH-dependent, nor was it followed by a zero-order reaction at any pH. Rapid and constant rate P releases were significant, having the potential to substitute substantial proportions of P fertilizer. K releases were also significant and may replace conventional K fertilizers, however, not long-term plant demand. The cation exchange capacity (CEC) of the biochar leached with a mild acidic solution increased linearly from 179 to 888 mmol(c) (kg C)(-1) over a pH range of 4-8, while the anion exchange capacity of 154 mmol(c) (kg C)(-1) was constant over the same pH range. Since native soil organic constituents have much higher CEC values (average 2800 mmol(c) (kg C)(-1) at pH 7), improved soil fertility as a result of enhanced cation retention by the biochar probably will be favorable only in sandy and low organic matter soils, unless surface oxidation during aging significantly increases its CEC.
DOI:10.1021/es803092kURLPMID:19534148 [本文引用: 1]
Biochar (BC) produced from agricultural crop residues has proven effective in sorbing organic contaminants. This study evaluated the ability of dairy-manure derived biochar to sorb heavy metal Pb and organic contaminant atrazine. Two biochar samples were prepared by heating dairy manure at low temperature of 200 degrees C (BC200) and 350 degrees C (BC350). The untreated manure (BC25) and a commercial activated C (AC) were included as controls. Sorption of Pb by biochar followed a dual Langmuir-Langmuir model, attributing to Pb precipitation (84-87%) and surface sorption (13-16%). Chemical speciation, X-ray diffraction, and infrared spectroscopy indicated that Pb was precipitated as beta-Pb9(PO4)6 in BC25 and BC200 treatment, and as Pb3(CO3)2(OH)2 in BC350. Lead sorption by AC obeyed a single Langmuir model, attributing mainly to surface sorption probably via coordination of Pb d-electron to C==C (pi-electron) and --0--Pb bonds. The biochar was 6 times more effective in Pb sorption than AC, with BC200 being the most effective (up to 680 mmol Pb kg(-1)). The biochar also effectively sorbed atrazine where atrazine was partitioned into its organic phase, whereas atrazine uptake by AC occurred via surface sorption. When Pb and atrazine coexisted, little competition occurred between the two for sorption on biochar, while strong competition was observed on AC. Results from this study indicated that dairy manure can be converted into value-added biochar as effective sorbent for metal and/or organic contaminants.
DOI:10.1016/j.biortech.2010.11.018URLPMID:21112777 [本文引用: 2]
The forms of alkalis of the biochars produced from the straws of canola, corn, soybean and peanut at different temperatures (300, 500 and 700 degrees C) were studied by means of oxygen-limited pyrolysis. The alkalinity and pH of the biochars increased with increased pyrolysis temperature. The X-ray diffraction spectra and the content of carbonates of the biochars suggested that carbonates were the major alkaline components in the biochars generated at the high temperature; they were also responsible for the strong buffer plateau-regions on the acid-base titration curves at 500 and 700 degrees C. The data of FTIR-PAS and zeta potentials indicated that the functional groups such as -COO(-) (-COOH) and -O(-) (-OH) contained by the biochars contributed greatly to the alkalinity of the biochar samples tested, especially for those generated at the lower temperature. These functional groups were also responsible for the negative charges of the biochars.
DOI:10.1016/j.biortech.2014.11.077URLPMID:25496953 [本文引用: 1]
The objective of this study was to investigate the relationship between Pb(2+) adsorption and physicochemical properties of biochars produced at different pyrolytic temperatures. Ten biochars were prepared from peanut shell (PS) and Chinese medicine material residue (MR) at 300-600 degrees C. Adsorption kinetics and isotherms were determined, and the untreated and Pb(2+)-loaded biochars were analyzed by FTIR, SEM-EDX and XRD. Functional groups complexation, Pb(2+)-pi interaction and precipitation with minerals jointly contributed to Pb(2+) adsorption on these biochars. New mineral precipitates (e.g., Pb2(SO4)O and Pb4(CO3)2(SO4)(OH)2) formed during Pb(2+) sorption. For high-temperature biochars (500 degrees C), Pb(2+) sorption via complexation reduced, but the contribution of Pb(2+)-pi interaction was enhanced. Dramatic reduction of Pb(2+) sorption on demineralized biochars indicated the dominant role of minerals. These results are useful for screening effective biochars as engineered sorbents to remove or immobilize Pb(2+) in polluted water and soil.
DOI:10.1007/s11368-016-1360-2URL [本文引用: 3]
DOI:10.1016/j.envpol.2016.08.014URLPMID:27537986 [本文引用: 1]
Biochars have increasingly been used as adsorbents for organic and inorganic contaminants in soils. However, during the carbonization process of pyrolysis, contaminants, including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dioxins and furans (PCDD/DF) can be generated. In this study, biochars made from sawdust, were prepared at various temperatures ranging from 250 to 700 degrees C. The Microtox((R)) and rat hepatoma cell line H4IIE-luc assays were used to characterize the general toxic and effects, mediated through the aryl hydrocarbon receptor (AhR), or dioxin-like potencies of organic extracts of biochars. The greatest total concentrations of PAHs (8.6 x 10(2) mug kg(-1)) and PCDD/DF (6.1 x 10(2) pg g(-1)) were found in biochar generated at 400 degrees C and 300 degrees C, respectively. Results of the H4IIE-luc assay, which gives total concentrations of 2,3,7,8-TCDD equivalents (TEQH4IIE-luc), indicated that total potencies of aryl hydrocarbon receptor (AhR) agonists were in decreasing order: 300 degrees C > 250 degrees C > 400 degrees C > 500 degrees C > 700 degrees C. The 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQchem) calculated as the sum of products of 16 PAHs and 17 PCDD/DF congers multiplied by their respective relative potencies (RePs) was less than that of TEQH4IIE-luc determined by use of the bioanalytical method, with the H4IIE-luc assay, which measures the total dioxin-like potency of a mixtures. The ratio of TEQchem/TEQH4IIE-luc was in the range of 0.7%-3.8%. Thus, a rather small proportion of the AhR-mediated potencies extracted from biochars were identified by instrumental analyses. Results of the Microtox test showed similar tendencies as those of the H4IIE-luc test, and a linear correlation between EC50 of Microtox test and EC20 of H4IIE-luc test was found. The results demonstrated that biochars produced at higher pyrolysis temperatures (>400 degrees C) were less toxic and had lower potencies of AhR-mediated effects, which may be more suitable for soil application.
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Biochar is increasingly being recognized by scientists and policy makers for its potential role in carbon sequestration, reducing greenhouse gas emissions, renewable energy, waste mitigation, and as a soil amendment. The published reviews on biochar application to soil have so far focused mainly on the agronomic benefits, and have paid little attention to the potential unintended effects. The purpose of this chapter is to provide a balanced perspective on the agronomic and environmental impacts of biochar amendment to soil. The chapter highlights the physical and chemical characteristics of biochar, which can impact on the sorption, hence efficacy and biodegradation, of pesticides. As a consequence, weed control in biochar-amended soils may prove more difficult as preemergent herbicides may be less effective. Since biochars are often prepared from a variety of feedstocks (including waste materials), the potential introduction of contaminants needs to be considered before land application. Metal contaminants, in particular, have been shown to impact on plant growth, and soil microbial and faunal communities. Biochar has also been shown to influence a range of soil chemical properties, and rapid changes to nutrient availability, pH, and electrical conductivity need to be carefully considered to avoid unintended consequences for productivity. This chapter highlights some key areas of research which need to be completed to ensure a safe and sustainable use of biochar. In particular, understanding characteristics of biochars to avoid ecotoxicological impacts, understanding the effects of biochar on nutrient and contaminant behavior and transport, the effects of aging and the influence of feedstock and pyrolysis conditions on key properties are some of the areas that require attention.
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The formation of condensed ring polycyclic aromatic hydrocarbons (PAHs) from the pyrolysis of ground tobacco in helium over the temperature range of 350-600 degrees C was investigated. PAH yields in the ng/g range were detected and the maximum yields of all PAHs studied including benzo[a]pyrene (B[a]P) and benzo[a]anthracene (B[a]A) occurred between 500 and 550 degrees C. The pathway to PAH formation in the 350-600 degrees C temperature range is believed to proceed via a carbonization process where the residual solid (char) undergoes a chemical transformation and rearrangement to give a more condensed polycyclic aromatic structure that upon further heating evolves PAH moieties. Extraction of tobacco with water led to a two fold increase in the yields of most PAHs studied. The extraction process removed low temperature non-PAH-forming components, such as alkaloids, organic acids and inorganic salts, and concentrated instead (on a per unit weight basis) tobacco components such as cell wall bio-polymers and lipids. Hexane extraction of the tobacco removed lipophilic components, previously identified as the main source of PAH precursors, but no change in PAH yields was observed from the hexane-extracted tobacco. Tobacco cell wall components such as cellulose, hemicellulose, and lignin are identified as major low temperature PAH precursors. A link between the formation of a low temperature char that evolves PAHs upon heating is established and the observed ng/g yields of PAHs from tobacco highlights a low temperature solid phase formation mechanism that may be operable in a burning cigarette.
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This study aimed to evaluate the chemical forms, behavior and environmental risk of heavy metal (HMs) Zn, Pb and Cd in phytoremediation residue (PMR) pyrolyzed at 350 degrees C, 550 degrees C and 750 degrees C, respectively. The behavior of HMs variation during the PMR pyrolysis process was analyzed and the potential HMs environmental risk of phytoremediation residue biochars (PMB) was assessed which was seldom investigated before. The results showed that the pyrolysis temperature increase decreased the soluble/exchangeable HMs fraction and alleviated the HMs bioavailability. When the temperature was over 550 degrees C, the adsorbed Zn(II), Pb(II) and Cd(II) were turned into oxides forms and concentrated in PMB with more stable forms exhibiting lower risk assessment code and potential ecological risk index. The ecotoxicity test showed higher pyrolysis temperature favored the reduction of PMB ecotoxicity. It is suggested that pyrolysis temperature above 550 degrees C may be suitable for thermal treatment of PMR with acceptable environmental risk.
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生物炭以其良好的解剖结构和理化性质，广泛的材料来源和广阔的产业化发展前景，成为当今农业、能源与环境等领域的研究热点。本文综合分析、评述了生物炭在土壤、作物、农田生态系统等领域应用的主要研究进展及其未来保障中国粮食安全的重要意义，从低碳、循环、可持续视角，客观、辩证地探讨了生物炭在农业上的应用价值及其产业化发展前景。生物炭在修复土壤障碍，提升耕地生产性能和作物生产能力，促进农业可持续发展和保障国家粮食安全等方面具有重要现实意义和应用价值，本文结合中国国情，提出了进一步深入研究与开发生物炭产业的方向与建议，旨在为中国生物炭产业的健康发展提供参考。
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DOI:10.1007/s11356-012-0873-5URL [本文引用: 2]
Biochar was produced from dairy manure (DM) at two temperatures: 200A degrees C and 350A degrees C, referred to as DM200 and DM350, respectively. The obtained biochars were then equilibrated with 0-5 mM Cu, Zn or Cd in 0.01 M NaNO3 solution for 10 h. The changes in solution metal concentrations after sorption were evaluated for sorption capacity using isotherm modeling and chemical speciation Visual MINTEQ modeling, while the solid was collected for species characterization using infrared spectroscopy and X-ray elemental dot mapping techniques.The isotherms of Cu, Zn, and Cd sorption by DM200 were better fitted to Langmuir model, whereas Freundlich model well described the sorption of the three metals by DM350. The DM350 were more effective in sorbing all three metals than DM200 with both biochars had the highest affinity for Cu, followed by Zn and Cd. The maximum sorption capacities of Cu, Zn, and Cd by DM200 were 48.4, 31.6, and 31.9 mg g(-1), respectively, and those of Cu, Zn, and Cd by DM350 were 54.4, 32.8, and 51.4 mg g(-1), respectively. Sorption of the metals by the biochar was mainly attributed to their precipitation with PO (4) (3-) or CO (3) (2-) originating in biochar, with less to the surface complexation through -OH groups or delocalized pi electrons. At the initial metal concentration of 5 mM, 80-100 % of Cu, Zn, and Cd retention by DM200 resulted from the precipitation, with less than 20 % from surface adsorption through phenonic -OH complexation. Among the precipitation, 20-30 % of the precipitation occurred as metal phosphate and 70-80 % as metal carbonate. For DM350, 75-100 % of Cu, Zn, and Cd retention were due to the precipitation, with less than 25 % to surface adsorption through complexation of heavy metal by phenonic -OH site or delocalized pi electrons. Among the precipitation, only less than 10 % of the precipitation was present as metal phosphate and more than 90 % as metal carbonate.Results indicated that dairy manure waste can be converted into value-added biochar as a sorbent for sorption of heavy metals, and the mineral components originated in the biochar play an important role in the biochar's high sorption capacity.]]>
DOI:10.1016/j.jaap.2015.07.012URL [本文引用: 1]
DOI:10.1016/j.clay.2017.12.023URL [本文引用: 1]
DOI:10.1016/j.biortech.2006.09.038URLPMID:17098423 [本文引用: 1]
Physico-chemical properties of a bioorganic char were modified by pyrolysis in the presence of NaOH, and with subsequent physical activation of carbonaceous species with CO2 a value-added activated carbon was fabricated. Bioorganic char is produced as a co-product during the production of bio-fuel from the pyrolysis of chicken litter. Untreated char contains approximately 37 wt% of C and approximately 43-45 wt% of inorganic minerals containing K, Ca, Fe, P, Cu, Mg, and Si. Carbonization and chemical activation of the char at 600 degrees C in the presence of NaOH in forming gas (4% H2 balanced with Ar) produced mainly demineralized activated carbon having BET (Brunauer, Emmett, and Teller) surface area of 486 m2/g and average pore size of 2.8 nm. Further physical activation with CO2 at 800 degrees C for 30 min resulted in activated carbon with BET surface area of 788 m2/g and average pore size of 2.2 nm. The mineral content was 10 wt%. X-ray photoelectron spectroscopy (XPS) indicated that the latter activation process reduced the pyrrolic- and/or pyridonic-N, increased pyridinic-N and formed quaternary-N at the expense of pyrrolic- and/or pyridonic-N found in the untreated char.
DOI:10.1016/j.jaap.2012.05.012URL [本文引用: 2]
DOI:10.1016/j.fuel.2017.12.054URL [本文引用: 4]
DOI:10.2136/sssaj2005.0383URL [本文引用: 1]
DOI:10.1021/es101337xURLPMID:20836548 [本文引用: 2]
Through cation exchange capacity assay, nitrogen adsorption-desorption surface area measurements, scanning electron microscopic imaging, infrared spectra and elemental analyses, we characterized biochar materials produced from cornstover under two different pyrolysis conditions, fast pyrolysis at 450 degrees C and gasification at 700 degrees C. Our experimental results showed that the cation exchange capacity (CEC) of the fast-pyrolytic char is about twice as high as that of the gasification char as well as that of a standard soil sample. The CEC values correlate well with the increase in the ratios of the oxygen atoms to the carbon atoms (O:C ratios) in the biochar materials. The higher O:C ratio was consistent with the presence of more hydroxyl, carboxylate, and carbonyl groups in the fast pyrolysis char. These results show how control of biomass pyrolysis conditions can improve biochar properties for soil amendment and carbon sequestration. Since the CEC of the fast-pyrolytic cornstover char can be about double that of a standard soil sample, this type of biochar products would be suitable for improvement of soil properties such as CEC, and at the same time, can serve as a carbon sequestration agent.
DOI:10.1016/j.biortech.2010.06.088URLPMID:20634061 [本文引用: 2]
This study was designed to investigate the effect of anaerobic digestion on biochar produced from sugarcane bagasse. Sugarcane bagasse was anaerobically digested to produce methane. The digested residue and fresh bagasse was pyrolyzed separately into biochar at 600 degrees C in nitrogen environment. The digested bagasse biochar (DBC) and undigested bagasse biochar (BC) were characterized to determine their physicochemical properties. Although biochar was produced from the digested residue (18% by weight) and the raw bagasse (23%) at a similar rate, there were many physiochemical differences between them. Compared to BC, DBC had higher pH, surface area, cation exchange capacity (CEC), anion exchange capacity (AEC), hydrophobicity and more negative surface charge, all properties that are generally desirable for soil amelioration, contaminant remediation or wastewater treatment. Thus, these results suggest that the pyrolysis of anaerobic digestion residues to produce biochar may be an economically and environmentally beneficial use of agricultural wastes.
URLPMID:28358986 [本文引用: 1]
DOI:10.1016/j.geoderma.2011.04.021URL [本文引用: 1]
While the idea that adding pyrogenic carbon (referred to as 'biochar' when used as a soil amendment) will enhance soil fertility and carbon sequestration has gained widespread attention, understanding of its chemical and physical characteristics and the methods most appropriate to determine them have lagged behind. This type of information is needed to optimize the properties of biochar for specific purposes such as nutrient retention, pH amelioration or contaminant remediation. A number of surface properties of a range of biochar types were examined to better understand how these properties were related to biochar production conditions, as well as to each other. Among biochars made from oak (Quercus lobata), pine (Pious taeda) and grass (Tripsacum floridanum) at 250 degrees C in air and 400 and 650 degrees C under N(2), micropore surface area (measured by CO(2) sorptometry) increased with production temperature as volatile matter (VM) decreased, indicating that VM was released from pore-infillings. The CEC, determined using K(+) exchange, was about 10 cmol(c) kg(-1) for 400 and 650 degrees C chars and did not show any pH dependency, whereas 250 degrees C biochar CECs were pH-dependant and rose to as much as 70 cmol(c) kg(-1) at pH 7. Measurements of surface charge on biochar particles indicated a zeta potential of -9 to -4 mV at neutral pH and an iso-electric point of pH 2-3. However, a colloidal or dissolved biochar component was 4-5 times more electronegative. Total acid functional group concentration ranged 4.4-8.1 mmol g(-1) (measured by Boehm titration), decreased with production temperature, and was directly related to VM content. Together, these findings suggest that the VM component of biochar carries its acidity, negative charge, and thus, complexation ability. However, not all acid functional groups exchanged cations as the number of cation exchanging sites (CEC) was about 10 times less than the number of acid functional groups present on biochar surfaces and varied with biomass type. These findings suggest that lower temperature biochars will be better used to increase soil CEC while high temperature biochars will raise soil pH. Although no anion exchange capacity was measured in the biochars, they may sorb phosphate and nitrate by divalent cation bridging. (C) 2011 Elsevier B.V.
DOI:10.1016/j.biortech.2017.08.009URLPMID:28844690 [本文引用: 1]
Algal biomass is known as a promising sustainable feedstock for the production of biofuels and other valuable products. However, since last decade, massive amount of interests have turned to converting algal biomass into biochar. Due to their high nutrient content and ion-exchange capacity, algal biochars can be used as soil amendment for agriculture purposes or adsorbents in wastewater treatment for the removal of organic or inorganic pollutants. This review describes the conventional (e.g., slow and microwave-assisted pyrolysis) and newly developed (e.g., hydrothermal carbonization and torrefaction) methods used for the synthesis of algae-based biochars. The characterization of algal biochar and a comparison between algal biochar with biochar produced from other feedstocks are also presented. This review aims to provide updated information on the development of algal biochar in terms of the production methods and the characterization of its physical and chemical properties to justify and to expand their potential applications.
DOI:10.1016/j.jclepro.2018.11.087URL [本文引用: 1]
DOI:10.1021/acs.est.7b02528URLPMID:29116778 [本文引用: 2]
Black carbon (BC) is ubiquitous in the environments and participates in various biogeochemical processes. Both positive and negative effects of BC (especially biochar) on the ecosystem have been identified, which are mainly derived from its diverse physicochemical properties. Nevertheless, few studies systematically examined the linkage between the evolution of BC molecular structure with the resulted BC properties, environmental functions as well as potential risk, which is critical for understanding the BC environmental behavior and utilization as a multifunctional product. Thus, this review highlights the molecular structure evolution of BC during pyrolysis and the impact of BC physicochemical properties on its sorption behavior, stability, and potential risk in terrestrial and aqueous ecosystems. Given the wide application of BC and its important role in biogeochemical processes, future research should focus on the following: (1) establishing methodology to more precisely predict and design BC properties on the basis of pyrolysis and phase transformation of biomass; (2) developing an assessment system to evaluate the long-term effect of BC on stabilization and bioavailability of contaminants, agrochemicals, and nutrient elements in soils; and (3) elucidating the interaction mechanisms of BC with plant roots, microorganisms, and soil components.
DOI:10.1016/j.ecoleng.2017.06.029URL [本文引用: 1]
DOI:10.1016/j.arabjc.2013.11.047URL [本文引用: 1]
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DOI:10.1021/es8002684URLPMID:18754360 [本文引用: 1]
The combined adsorption and partition effects of biochars with varying fractions of noncarbonized organic matter have not been clearly defined. Biochars, produced by pyrolysis of pine needles at different temperatures (100-700 degrees C, referred as P100-P700), were characterized by elemental analysis, BET-N2 surface areas and FTIR. Sorption isotherms of naphthalene, nitrobenzene, and m-dinitrobenzene from water to the biochars were compared. Sorption parameters (N and logKf) are linearly related to sorbent aromaticities, which increase with the pyrolytic temperature. Sorption mechanisms of biochars are evolved from partitioning-dominant at low pyrolytic temperatures to adsorption-dominant at higher pyrolytic temperatures. The quantitative contributions of adsorption and partition are determined by the relative carbonized and noncarbonized fractions and their surface and bulk properties. The partition of P100-P300 biochars originates from an amorphous aliphatic fraction, which is enhanced with a reduction of the substrate polarity; for P400-P600, the partition occurs with a condensed aromatic core that diminishes with a further reduction of the polarity. Simultaneously, the adsorption component exhibits a transition from a polarity-selective (P200-P400) to a porosity-selective (P500-P600) process, and displays no selectivity with P700 and AC in which the adsorptive saturation capacities are comparable to predicted values based on the monolayer surface coverage of molecule.
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[本文引用: 3]
DOI:10.1016/j.biombioe.2013.12.010URL [本文引用: 1]
We assessed the effects of porosity and hydrophobicity on water uptake by biochars. Biochars were produced from two feedstocks (hazelnut shells and Douglas fir chips) at three production temperatures (370 degrees C, 500 degrees C, and 620 degrees C). To distinguish the effects of porosity from the effects of hydrophobicity, we compared uptake of water to uptake of ethanol (which is completely wetting and not affected by hydrophobic materials). For both feedstocks, low temperature biochars took up less water than high temperature biochars but the same amount of ethanol, suggesting that differences in water uptake based on production temperature reflect differences in surface hydrophobicity, not porosity. Conversely, Douglas fir biochars took up more water than hazelnut shell biochars due to greater porosity. Thus, designing biochars for water holding applications requires two considerations: (a) creating sufficient porosity through feedstock selection, and (b) determining a production temperature that reduces hydrophobicity to an acceptable level. (C) 2013 Elsevier Ltd.
DOI:10.1021/es403711yURLPMID:24289306 [本文引用: 1]
The pH-dependent adsorption of perchlorate (ClO4(-)) by wood-derived biochars produced at 200-700 degrees C (referred as FB200-FB700) was investigated to probe the anion retention mechanisms of biochars and to identify the interactions of water and biochar. ClO4(-) adsorption was controlled by the surface polarities and structural compositions of the organic components of biochars, rather than their inorganic mineral components. FB500-FB700 biochars with low polarity and high aromaticity displayed a superior ClO4(-) adsorption capacity, but which was affected by solution pH. Besides electrostatic interaction, hydrogen bonding to oxygen-containing groups on biochars was proposed the dominant force for perchlorate adsorption, which led to the maximum adsorption occurring near pHIEP, where surface charge equals zero. The dissociation of these surface oxygen-containing groups was monitored by zeta potential curves, which indicated that the H-bonds donors on biochar surface for ClO4(-) binding were changed from -COOH (ClO4(-)...HOOC-) and -OH (ClO4(-)...HO-) to -OH alone with an increase in pH. The H-bond force was strengthened by the condensed aromatic surfaces, since high temperature biochars provided a hydrophobic microenvironment to accommodate weakly hydrated perchlorate and facilitated the H-bonds for ClO4(-) binding to functional groups by the large pi subunit of their aromatic substrate. Lastly, the batch and column tests of ClO4(-) adsorption showed that biochars like FB700 are effective adsorbents for anion pollutant removal via H-bonding interaction.
DOI:10.1016/j.scitotenv.2015.01.061URL [本文引用: 1]
DOI:10.1021/ef4000769URL [本文引用: 1]
The application of biomass char as a kind of soil amendment has an important role in soil water holding capacity (WHC), which has a close relationship with its own surface area, total pore volume, and porosity structure. In this research, the WHC and absorption properties of the chars were investigated. Two kinds of wood (poplar and pine) were pyrolyzed at both 450 and 550 degrees C to produce the chars for the experiments. The Boehm titration was used to measure the concentration of the functional groups. The surface area was determined through the Brunauer-Emmett-Teller (BET) method, while the morphological characteristic of the chars was studied by scanning electron microscopy (SEM). Furthermore, the total pore volume, average pore diameter, and porosity structure of the chars were measured by a mercury porosimeter. On the basis of the pore size distribution of the chars, the definition of the Soil Science Society of America was used as the classification standard. The results showed that there was a significant positive correlation between the WHC of the chars and the total pore volume. However, there was no obvious relationship between the surface area and the WHC of the wood chars. The water absorption rate (WAR) of chars was affected by both the total pore volume and the average pore diameter. The classification of the pore size was needed to further explain the differences of the WAR of the chars. The large pores can not only hold the water in it but also act as the passages to the small pores. The relatively small pore volume of mesopores seriously affected the WAR of the chars.
DOI:10.1016/j.orggeochem.2014.10.002URL [本文引用: 1]
DOI:10.1016/j.fuel.2014.05.019URL [本文引用: 2]
This study examines the effect of three key operating factors ( peak temperature, particle size and pressure) on the potential stability of the biochar produced by slow pyrolysis of vine shoots. The following response variables were considered as key indicators of the potential stability of biochar in soils: the fixed-carbon yield, the fraction of aromatic carbon, and the molar H: C and O:C ratios. Slow pyrolysis tests were conducted in a laboratory-scale fixed-bed unit and planned according to a 2-level factorial design. The behavior of the product gas yield and composition at the outlet of the secondary cracking reactor ( a fixed-bed of activated alumina particles at 700 degrees C) was also evaluated as a function of the three factors. The results from the statistical tests revealed that the particle size is the most significant factor in determining the potential stability of biochars. Using larger particles of biomass and, in a lesser extent, operating at higher peak temperatures leads to the production of more stable materials. Unexpectedly, the absolute pressure only plays a significantly positive role in decreasing the tar content in the producer gas at the outlet of a secondary cracking reactor. (C) 2014 Elsevier Ltd.
DOI:10.1021/es00010a034URLPMID:22191973 [本文引用: 1]
DOI:10.4155/cmt.10.32URL [本文引用: 1]
DOI:10.1016/j.biortech.2017.06.049URLPMID:28637163 [本文引用: 1]
This study evaluated the impact of biomass properties on the pyrolysis product yields, economic and environmental performance for the pyrolysis-biochar-bioenergy platform. We developed and applied a fast pyrolysis, feedstock-sensitive, regression-based chemical process model to 346 different feedstocks, which were grouped into five types: woody, stalk/cob/ear, grass/plant, organic residue/product and husk/shell/pit. The results show that biomass ash content of 0.3-7.7wt% increases biochar yield from 0.13 to 0.16kg/kg of biomass, and decreases biofuel yields from 87.3 to 40.7 gallons per tonne. Higher O/C ratio (0.88-1.12) in biomass decreases biochar yield and increases biofuel yields within the same ash content level. Higher ash content of biomass increases minimum fuel selling price (MFSP), while higher O/C ratio of biomass decreases MFSP within the same ash content level. The impact of ash and O/C ratio of biomass on GHG emissions are not consistent for all feedstocks.
DOI:10.1021/es302545bURLPMID:23013285 [本文引用: 1]
The stability of biochar carbon (C) is the major determinant of its value for long-term C sequestration in soil. A long-term (5 year) laboratory experiment was conducted under controlled conditions using 11 biochars made from five C3 biomass feedstocks (Eucalyptus saligna wood and leaves, papermill sludge, poultry litter, cow manure) at 400 and/or 550 degrees C. The biochars were incubated in a vertisol containing organic C from a predominantly C4-vegetation source, and total CO(2)-C and associated delta(13)C were periodically measured. Between 0.5% and 8.9% of the biochar C was mineralized over 5 years. The C in manure-based biochars mineralized faster than that in plant-based biochars, and C in 400 degrees C biochars mineralized faster than that in corresponding 550 degrees C biochars. The estimated mean residence time (MRT) of C in biochars varied between 90 and 1600 years. These are conservative estimates because they represent MRT of relatively labile and intermediate-stability biochar C components. Furthermore, biochar C MRT is likely to be higher under field conditions of lower moisture, lower temperatures or nutrient availability constraints. Strong relationships of biochar C stability with the initial proportion of nonaromatic C and degree of aromatic C condensation in biochar support the use of these properties to predict biochar C stability in soil.
DOI:10.1016/j.scitotenv.2017.11.014URL [本文引用: 1]
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DOI:10.1016/j.chemosphere.2013.12.024URLPMID:24397887 [本文引用: 1]
2 mm). The amount of CO2 evolved varied significantly between soils (pSS>SG>/=PC; Coxville: PC>SG>SS>PL). The average net CO2-C evolved from the Coxville soils (385 mg kg(-1)) was about threefold more than the CO2-C evolved from the Norfolk soils (123 mg kg(-1)). Our results suggest different particle sizes and sources of biochar as well as soil type influence biochar stability.]]>
DOI:10.1111/gcbb.2015.7.issue-2URL [本文引用: 1]
DOI:10.1080/10643389.2017.1418580URL [本文引用: 9]
DOI:10.1016/S1872-2067(19)63330-9URL [本文引用: 1]
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DOI:10.1016/j.watres.2014.10.009URLPMID:25462729 [本文引用: 1]
Iron (Fe)-impregnated biochar, prepared through a novel method that directly hydrolyzes iron salt onto hickory biochar, was investigated for its performance as a low-cost arsenic (As) sorbent. Although iron impregnation decreased the specific surface areas of the biochar, the impregnated biochar showed much better sorption of aqueous As (maximum sorption capacity of 2.16 mg g(-)(1)) than the pristine biochar (no/little As sorption capacity). Scanning electron microscope equipped with an energy dispersive spectrometer and X-ray diffraction analysis indicated the presence of crystalline Fe hydroxide in the impregnated biochar but no crystal forms of arsenic were found in the post-sorption biochar samples. However, large shifts in the binding energy of Fe(2)p, As(3)d, O(1)s and C(1)s region on the following As sorption indicated a change in chemical speciation from As(V) to As(III) and Fe(II) to Fe(III) and strong As interaction with oxygen-containing function groups of the Fe-impregnated biochar. These findings suggest that the As sorption on the Fe-impregnated biochar is mainly controlled by the chemisorption mechanism. Columns packed with Fe-impregnated biochar showed good As retention, and was regenerated with 0.05 mol L(-)(1) NaHCO(3) solution. These findings indicate that Fe-impregnated biochar can be used as a low-cost filter material to remove arsenic from aqueous solutions.
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DOI:10.1016/j.biortech.2012.11.132URLPMID:23313693 [本文引用: 1]
A magnetic biochar based adsorbent with colloidal or nanosized gamma-Fe(2)O(3) particles embedded in porous biochar matrix was fabricated via thermal pyrolysis of FeCl(3) treated biomass. The synthesized samples were studied systematically by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, selected-area electron diffraction pattern, scanning electron microscopy, energy-dispersive X-ray analysis, superconducting quantum interference device, and batch sorption measurements. The characterization analyses showed that large quantity of gamma-Fe(2)O(3) particles with size between hundreds of nanometers and several micrometers tightly grow within the porous biochar matrix. Biochar/gamma-Fe(2)O(3) composite exhibited excellent ferromagnetic property with a saturation magnetization of 69.2emu/g. Batch sorption experimental results showed that the composite has strong sorption ability to aqueous arsenic. Because of its excellent ferromagnetic properties, the arsenic-laden biochar/gamma-Fe(2)O(3) composite could be easily separated from the solution by a magnet at the end of the sorption experiment.
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DOI:10.1016/j.biortech.2010.08.067URLPMID:20863698 [本文引用: 2]
Biochar derived from agricultural biomass waste is increasingly recognized as a multifunctional material for agricultural and environmental applications. Three novel magnetic biochars (MOP250, MOP400, MOP700) were prepared by chemical co-precipitation of Fe3+/Fe2+ on orange peel powder and subsequently pyrolyzing under different temperatures (250, 400 and 700 degrees C), which resulted in iron oxide magnetite formation and biochar preparation in one-step. The MOP400 was comprised of nano-size magnetite particles and amorphous biochar, and thus exhibited hybrid sorption capability to efficiently remove organic pollutants and phosphate from water. For organic pollutants, MOP400 demonstrated the highest sorption capability, and even much larger than the companion non-magnetic biochar (OP400). For phosphate, magnetic biochars, especially MOP250, demonstrated much higher sorption capability than the companion non-magnetic biochars. No significantly competitive effect between organic pollutant and phosphate was observed. These suggest that the magnetic biochar is a potential sorbent to remove organic contaminants and phosphate simultaneously from wastewater.
DOI:10.1016/j.biortech.2015.12.056URLPMID:26748045 [本文引用: 1]
This paper discusses Cd(II) and Pb(II) sorption efficiency of biochars modified by impregnation with magnetic particles. All selected biochar characteristics were significantly affected after the modification. More specifically, the cation exchange capacity increased after the modification, except for grape stalk biochar. However, the changes in the pH value, PZC, and BET surface after modification process were less pronounced. The metal loading rate was also significantly improved, especially for Cd(II) sorption on/in nut shield and plum stone biochars (10- and 16-times increase, respectively). The results indicated that cation exchange (as a metal sorption mechanism) was strengthened after Fe oxide impregnation, which limited the desorbed amount of tested metals. In contrast, the magnetization of grape stalk biochar reduced Pb(II) sorption in comparison with that of pristine biochar. Magnetic modification is, therefore, more efficient for biochars with well-developed structure and for more mobile metals, such as Cd(II).
DOI:10.1021/jf2047898URLPMID:22280497 [本文引用: 1]
DOI:10.1016/j.jenvman.2015.08.046URLPMID:26402867 [本文引用: 1]
Biochar was produced from pinewood biomass by pyrolysis at a highest treatment temperature (HTT) of 400 degrees C. This biochar was then treated with varying concentrations of H2O2 solution (1, 3, 10, 20, 30% w/w) for a partial oxygenation study. The biochar samples, both treated and untreated, were then tested with a cation exchange capacity (CEC) assay, Fourier Transformed Infrared Resonance (FT-IR), elemental analysis, field water-retention capacity assay, pH assay, and analyzed for their capacity to remove methylene blue from solution. The results demonstrated that higher H2O2 concentration treatments led to higher CEC due to the addition of acidic oxygen functional groups on the surface of the biochar, which also corresponds to the resultant lowering of the pH of the biochar with respect to the H2O2 treatment. Furthermore, it was shown that the biochar methylene blue adsorption decreased with higher H2O2 concentration treatments. This is believed to be due to the addition of oxygen groups onto the aromatic ring structure of the biochar which in turn weakens the overall dispersive forces of pi-pi interactions that are mainly responsible for the adsorption of the dye onto the surface of the biochar. Elemental analysis revealed that there was no general augmentation of the elemental composition of the biochar samples through the treatment with H2O2, which suggests that the bulk property of biochar remains unchanged through the treatment.
DOI:10.1016/j.cej.2012.06.116URL [本文引用: 1]
DOI:10.1007/s11356-014-3434-2URL [本文引用: 1]
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DOI:10.1016/j.biortech.2010.04.046URLPMID:20457515 [本文引用: 1]
This study described the adsorption of chloramphenicol (CAP) in wastewater on the renewable bioresource of bamboo charcoal (BC). Results showed that CAP adsorption on BC (Ln q(e)=1.272 Ln C(e)+1.971) and H(2)SO(4) modified BC (Ln q(e)=1.851 Ln C(e)+0.659) were very slight, and on NaOH modified BC was significantly increased (Ln q(e)=0.344 Ln C(e)+6.490). The adsorbents were characterized by N(2) adsorption-desorption, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). It is revealed that BC and modified BC had very small surface areas of less than 1 m(2) g(-1), H(2)SO(4) treatment led to minimal variation in surface functional groups, and NaOH treatment increased the percentage of surface graphitic carbon and other oxygen-containing groups. The increased adsorption of CAP on NaOH modified BC was mainly ascribed to the enhancement of the pi-pi interaction between the adsorbent and adsorbate.
DOI:10.1016/j.chemosphere.2017.02.061URLPMID:28235742 [本文引用: 1]
In order to deal with cadmium (Cd(II)) pollution, three modified biochar materials: alkaline treatment of biochar (BC-NaOH), KMnO4 impregnation of biochar (BC-MnOx) and FeCl3 magnetic treatment of biochar (BC-FeOx), were investigated. Nitrogen adsorption-desorption isotherms, Fourier transform infrared spectroscopy (FTIR), Boehm titration, and scanning electron microscopy (SEM) were used to determine the characteristics of adsorbents and explore the main adsorption mechanism. The results show that manganese oxide particles are carried successfully within the biochar, contributing to micropore creation, boosting specific surface area and forming innersphere complexes with oxygen-containing groups, while also increasing the number of oxygen-containing groups. The adsorption sites created by the loaded manganese oxide, rather than specific surface areas, play the most important roles in cadmium adsorption. Batch adsorption experiments demonstrate a Langmuir model fit for Cd(II), and BC-MnOx provided the highest sorption capacity (81.10 mg g(-1)). The sorption kinetics of Cd(II) on adsorbents follows pseudo-second-order kinetics and the adsorption rate of the BC-MnOx material was the highest (14.46 g (mg.h)(-1)). Therefore, biochar modification methods involving KMnO4 impregnation may provide effective ways of enhancing Cd(II) removal from aqueous solutions.
DOI:10.1016/j.micromeso.2015.11.041URL [本文引用: 1]
DOI:10.1016/j.jenvman.2012.04.047URLPMID:22687632 [本文引用: 1]
Biochar produced from switchgrass via hydrothermal carbonization (HTC) was used as a sorbent for the removal of copper and cadmium from aqueous solution. The cold activation process using KOH at room temperature was developed to enhance the porous structure and sorption properties of the HTC biochar. The sorption efficiency of HTC biochar and alkali activated HTC biochar (HTCB) for removing copper and cadmium from aqueous solution were compared with commercially available powdered activated carbon (PAC). The present batch adsorption study describes the effects of solution pH, biochar dose, and contact time on copper and cadmium removal efficiency from single metal ion aqueous solutions. The activated HTCB exhibited a higher adsorption potential for copper and cadmium than HTC biochar and PAC. Experiments conducted with an initial metal concentration of 40 mg/L at pH 5.0 and contact time of 24 h resulted in close to 100% copper and cadmium removal by activated HTCB at 2 g/L, far greater than what was observed for HTC biochar (16% and 5.6%) and PAC (4% and 7.7%). The adsorption capacities of activated HTCB for cadmium removal were 34 mg/g (0.313 mmol/g) and copper removal was 31 mg/g (0.503 mmol/g).
DOI:10.1016/j.biortech.2016.05.057URLPMID:27241534 [本文引用: 1]
Modified biochar (BC) is reviewed in its preparation, functionality, applications and regeneration. The nature of precursor materials, preparatory conditions and modification methods are key factors influencing BC properties. Steam activation is unsuitable for improving BC surface functionality compared with chemical modifications. Alkali-treated BC possesses the highest surface functionality. Both alkali modified BC and nanomaterial impregnated BC composites are highly favorable for enhancing the adsorption of different contaminants from wastewater. Acidic treatment provides more oxygenated functional groups on BC surfaces. The Langmuir isotherm model provides the best fit for sorption equilibria of heavy metals and anionic contaminants, while the Freundlich isotherm model is the best fit for emerging contaminants. The pseudo 2(nd) order is the most appropriate model of sorption kinetics for all contaminants. Future research should focus on industry-scale applications and hybrid systems for contaminant removal due to scarcity of data.
DOI:10.1016/j.jece.2013.08.009URL [本文引用: 1]
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DOI:10.1016/j.biortech.2016.04.093URLPMID:27131871 [本文引用: 3]
Synthesizing biochar-based nano-composites can obtain new composites and combine the advantages of biochar with nano-materials. The resulting composites usually exhibit great improvement in functional groups, pore properties, surface active sites, catalytic degradation ability and easy to separation. These composites have excellent abilities to adsorb a range of contaminants from aqueous solutions. Particularly, catalytic material-coated biochar can exert simultaneous adsorption and catalytic degradation function for organic contaminants removal. Synthesizing biochar-based nano-composites has become an important practice for expanding the environmental applications of biochar and nanotechnology. This paper aims to review and summarize the various synthesis techniques for biochar-based nano-composites and their effects on the decontamination of wastewater. The characteristic and advantages of existing synthesis methods are summarized and discussed. Application of biochar-based nano-composites for different contaminants removal and the underlying mechanisms are reviewed. Furthermore, knowledge gaps that exist in the fabrication and application of biochar-based nano-composites are also identified.
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DOI:10.1016/j.chemosphere.2016.01.043URLPMID:26820777 [本文引用: 1]
The use of biochar has been suggested as a means of remediating contaminated soil and water. The practical applications of conventional biochar for contaminant immobilization and removal however need further improvements. Hence, recent attention has focused on modification of biochar with novel structures and surface properties in order to improve its remediation efficacy and environmental benefits. Engineered/designer biochars are commonly used terms to indicate application-oriented, outcome-based biochar modification or synthesis. In recent years, biochar modifications involving various methods such as, acid treatment, base treatment, amination, surfactant modification, impregnation of mineral sorbents, steam activation and magnetic modification have been widely studied. This review summarizes and evaluates biochar modification methods, corresponding mechanisms, and their benefits for contaminant management in soil and water. Applicability and performance of modification methods depend on the type of contaminants (i.e., inorganic/organic, anionic/cationic, hydrophilic/hydrophobic, polar/non-polar), environmental conditions, remediation goals, and land use purpose. In general, modification to produce engineered/designer biochar is likely to enhance the sorption capacity of biochar and its potential applications for environmental remediation.
DOI:10.1016/j.jhazmat.2015.02.046URLPMID:25734533 [本文引用: 1]
Recent investigations have shown frequent detection of pharmaceuticals in soils and waters posing potential risks to human and ecological health. Here, we report the enhanced removal of sulfamethazine (SMT) from water by physically activated biochar. Specifically, we investigated the effects of steam-activated biochars synthesized from an invasive plant (Sicyos angulatus L.) on the sorption of SMT in water. The properties and sorption capacities of steam-activated biochars were compared with those of conventional non-activated slow pyrolyzed biochars. Sorption exhibited pronounced pH dependence, which was consistent with SMT speciation and biochar charge properties. A linear relationship was observed between sorption parameters and biochar properties such as molar elemental ratios, surface area, and pore volumes. The isotherms data were well described by the Freundlich and Temkin models suggesting favorable chemisorption processes and electrostatic interactions between SMT and biochar. The steam-activated biochar produced at 700 degrees C showed the highest sorption capacity (37.7 mg g(-1)) at pH 3, with a 55% increase in sorption capacity compared to that of non-activated biochar produced at the same temperature. Therefore, steam activation could potentially enhance the sorption capacities of biochars compared to conventional pyrolysis.
DOI:10.1007/s11356-018-2521-1URL [本文引用: 1]
DOI:10.1002/jpln.201300495URL [本文引用: 1]
Steam-activation increased CH4 emission of stover biochar but decreased it for wood biochar by 14%(-)70%. Biochar generally increased CH4 emission but reduced N2O emission by 10%-41%. Emission of N2O was 17% lower for maize-stover biochar compared to Eucalyptus-wood biochar, and 3% lower for 350 degrees C compared to 550 degrees C pyrolysis temperature. Emission of CH4 was 21% higher for activated stover biochar compared to Eucalyptus-wood biochar and 10% lower for 350 degrees C compared to 550 degrees C pyrolysis temperature. No difference in net CO2 equivalent was observed among biochar grades.
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A low-cost and recyclable biosorbent derived from jute fiber was developed for high efficient adsorption of Pb(II), Cd(II) and Cu(II) from water. The jute fiber was rapidly pretreated and grafted with metal binding groups (COOH) under microwave heating (MH). The adsorption behavior of carboxyl-modified jute fiber under MH treatment (CMJFMH) toward heavy metal ions followed Langmuir isotherm model (R(2)>0.99) with remarkably high adsorption capacity (157.21, 88.98 and 43.98mg/g for Pb(II), Cd(II) and Cu(II), respectively). Also, CMJFMH showed fast removal ability for heavy metals in a highly significant correlation with pseudo second-order kinetics model. Besides, CMJFMH can be easily regenerated with EDTA-2Na solution and reused up to at least four times with equivalent high adsorption capacity. Overall, cheap and abundant production, rapid and facile preparation, fast and efficient adsorption of heavy metals and high regeneration ability can make the CMJFMH a preferred biosorbent for heavy metal removal from water.
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This paper describes a new method for pyrolyzing sewage sludge using a microwave furnace. It was found that if just the raw wet sludge is treated in the microwave, only drying of the sample takes place. However, if the sludge is mixed with a small amount of a suitable microwave absorber (such as the char produced in the pyrolysis itself) temperatures of up to 900 degrees C can be achieved, so that pyrolysis takes place rather than drying. Microwave treatments were also compared with those carried out in a conventional electric furnace, as well as the characteristics of their respective carbonaceous solid residues.
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Land application of biochar has been increasingly recommended as a powerful strategy for carbon sequestration and soil remediation. However, the biochar particles, especially those in the nanoscale range, may migrate or carry the inherent contaminants along the soil profile, posing a potential risk to the groundwater. This study investigated the transport and retention of wood chip-derived biochar nanoparticles (NPs) in water-saturated columns packed with a paddy soil. The environmentally-relevant soil solution chemistry including ionic strength (0.10-50 mM), electrolyte type (NaCl and CaCl2), and natural organic matter (0-10 mg L(-1) humic acid) were tested to elucidate their effects on the biochar NPs transport. Higher mobility of biochar NPs was observed in the soil at lower ionic strengths, with CaCl2 electrolyte being more effective than NaCl in decreasing biochar NPs transport. The retained biochar NPs in NaCl was re-entrained ( approximately 57.7%) upon lowering transient pore-water ionic strength, indicating that biochar NPs were reversibly retained in the secondary minimum. In contrast, negligible re-entrainment of biochar NPs occurred in CaCl2 due to the primary minimum and/or particle aggregation. Humic acid increased the mobility of biochar NPs, likely due to enhanced electrosteric repulsive interactions. The transport behaviors of biochar NPs can be well interpreted by a two-site kinetic retention model that assumes reversible retention for one site, and irreversible retention for the other site. Our findings indicated that the transport of wood chip biochar NPs is significant in the paddy soil, highlighting the importance of understanding the mobility of biochar NPs in natural soils for accurately assessing their environmental impacts.
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