Effects of H2O2 addition on the physicochemical properties of the hydrothermal products from municipal sludge
ZHANG Peizheng1,2,, ZHANG Shouyu1,,, ZHANG Yifan3, HU Nan4, WU Yuxin5 1.School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China 2.Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering, Shanghai 200093, China 3.School of Mechanical Engineering Tongji University, Shanghai 200092, China 4.School of Energy and Power Engineering, Changchun Institute of Technology, Changchun 130012, China 5.Department of Thermal Engineering, Tsinghua University, Beijing 100084, China
Abstract:Aiming at the disadvantage of high energy consumption of municipal sludge treated by hydrothermal treatment, H2O2 addition was conducted to strengthen the hydrothermal treatment process of municipal sludge at low temperature in order to decrease the energy consumption. The experiments of hydrothermal treatment without and with H2O2 addition of municipal sludge were carried out in a high-pressure reactor to study the effects of H2O2 mass fraction (5%, 10% and 15%) on the distribution of the resulted products, the properties of the solid product including water content, the mass concentration and chemical speciation of the heavy metals (Pb and Cd), and the properties of the liquid product including pH value and Volatile Fatty Acids (VFAs), ammonia nitrogen (NH3-N). The results showed that the hydrothermal treatment with H2O2 mass fraction of 15% addition at 200 ℃ resulted in the optimum physicochemical properties of the resulted products from the municipal sludge. Compared with the hydrothermal treatment of the sludge, after the hydrothermal treatment with H2O2 mass fraction of 15% at 200 ℃, the moisture content of the solid product was reduced by 10.40% and Pb and Cd mass concentration increased by 79.96 and 1.57 mg·kg?1, respectively, meanwhile, the concentration of VFAs and NH3-N in the liquid product increased by 773.68 and 370.00 mg·L?1, respectively. The proportion of the non-toxic heavy metals contained in the solid product from the sludge hydrothermal treated with H2O2 mass fraction of 5% addition was the highest and its ecotoxicity was the smallest. When H2O2 mass fraction increased above 5%, the conversion of the heavy metals contained in the solid product to potentially toxic forms was enhanced, but the potential toxicity of the heavy metals contained in the resulted solid product was still lower than that the raw sludge. The research can provide reference for the application of adding oxidant to promote the hydrothermal treatment of municipal sludge to some extent. Key words:municipal sludge/ hydrothermal treatment/ H2O2 mass fraction/ mass concentration of heavy metals/ ecotoxicity.
图1FCF-1L型高压反应釜示意图 Figure1.Schematic diagram of FCF-1L high-pressure reactor
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1.School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China 2.Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering, Shanghai 200093, China 3.School of Mechanical Engineering Tongji University, Shanghai 200092, China 4.School of Energy and Power Engineering, Changchun Institute of Technology, Changchun 130012, China 5.Department of Thermal Engineering, Tsinghua University, Beijing 100084, China Received Date: 2021-07-14 Accepted Date: 2021-09-03 Available Online: 2021-09-23 Keywords:municipal sludge/ hydrothermal treatment/ H2O2 mass fraction/ mass concentration of heavy metals/ ecotoxicity Abstract:Aiming at the disadvantage of high energy consumption of municipal sludge treated by hydrothermal treatment, H2O2 addition was conducted to strengthen the hydrothermal treatment process of municipal sludge at low temperature in order to decrease the energy consumption. The experiments of hydrothermal treatment without and with H2O2 addition of municipal sludge were carried out in a high-pressure reactor to study the effects of H2O2 mass fraction (5%, 10% and 15%) on the distribution of the resulted products, the properties of the solid product including water content, the mass concentration and chemical speciation of the heavy metals (Pb and Cd), and the properties of the liquid product including pH value and Volatile Fatty Acids (VFAs), ammonia nitrogen (NH3-N). The results showed that the hydrothermal treatment with H2O2 mass fraction of 15% addition at 200 ℃ resulted in the optimum physicochemical properties of the resulted products from the municipal sludge. Compared with the hydrothermal treatment of the sludge, after the hydrothermal treatment with H2O2 mass fraction of 15% at 200 ℃, the moisture content of the solid product was reduced by 10.40% and Pb and Cd mass concentration increased by 79.96 and 1.57 mg·kg?1, respectively, meanwhile, the concentration of VFAs and NH3-N in the liquid product increased by 773.68 and 370.00 mg·L?1, respectively. The proportion of the non-toxic heavy metals contained in the solid product from the sludge hydrothermal treated with H2O2 mass fraction of 5% addition was the highest and its ecotoxicity was the smallest. When H2O2 mass fraction increased above 5%, the conversion of the heavy metals contained in the solid product to potentially toxic forms was enhanced, but the potential toxicity of the heavy metals contained in the resulted solid product was still lower than that the raw sludge. The research can provide reference for the application of adding oxidant to promote the hydrothermal treatment of municipal sludge to some extent.
根据质量守恒定律，污泥经水热处理后气、液、固三相产物的质量等于反应前混合溶液的总质量。因此，固相产率MS和液相产率ML的计算参考式(1)、式(2)，气相产率MG的计算根据差减法参考式(3)。固相产物含水率M的计算参考式(4)。 式中：Wms为污泥样品质量；WH2O为去离子水质量；WH2O2为H2O2溶液质量；W1和W11分别为盛装固相产物前后的烧杯质量；W2和W22分别为盛装液相产物前后的烧杯质量；W11′为装有固相产物烧杯干燥后的质量。以上变量单位均为g。 采用电感耦合等离子体质谱仪(7700，美国安捷伦科技有限公司)测定固相产物中重金属的质量浓度；重金属的赋存形态采用欧共体标准物质局(Community Bureau of Reference, BCR)提出的三步连续分级提取法进行分析(简称BCR法)[14]，根据BCR法可将重金属的赋存形态按照生态毒性分级为直接毒性形态(F1+F2)、潜在毒性形态(F3)和无毒性形态(F4)，具体步骤参考文献[15]。采用气相色谱-质谱联用仪(7890A-5975C，美国安捷伦科技有限公司)测定液相产物中挥发性脂肪酸质量浓度；基于纳氏试剂比色法，采用双光束紫外可见光分光光度计(UV-6300，上海美谱达仪器有限公司)测定液相产物中氨氮质量浓度；采用酸度计(PHS-3，上海佑科仪表有限公司)测定原污泥和液相产物的pH。
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