Effects of pH on the coagulation performance of algae-laden water with different alkalinity
ZHENG Lijuan1,2,, ZHANG Chongmiao1, XU Hui2,,, LI Mingshuang2, WANG Bin2,3, TONG Qing2,4, XIANG Yu2,4 1.Key Laboratory of Northwest Water Resource, Environment and Ecology, Ministry of Education, Shaanxi Key Laboratory of Environmental Engineering, Xi′an University of Architecture and Technology, Xi′an 710055, China 2.State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China 3.Key Laboratory of Environmental and Geological Disasters, Ministry of Nature Resources, Guizhou University, Guiyang 550004, China 4.School of Resources Environment and Chemical Engineering, Nanchang University, Nanchang 330031, China
Abstract:In order to investigate the influence of alkalinity on the removal of algal cells and the organic substances secreted by algal cells by coagulation and ensure the drinking water quality, aluminum chloride (AlCl3·6H2O) was used as a coagulant to conduct coagulation test for Microcystis aeruginosa removal. The coagulation performance, floc properties and residual aluminum in effluent were investigated during the treatment of algae-laden water with different basicity. The results showed that when the pHs of water samples were adjusted to 6.0, in comparison with water samples with low alkalinity (95, 175 and 245 mg·L?1 ), the Zeta potentials of water samples with high alkalinity (330 mg·L?1 and 415 mg·L?1 ) approached 0 mV, and the repulsive force between particles decreased effectively. The removal rates for algae cells could reach over 74.45%(below 31.64% for water samples with low alkalinity), the lowest residual aluminum in effluent was 0.003 6 mg·L?1(0.088 9 mg·L?1 for water samples with low alkalinity). When the pH of water sample was above 6.5, the removal rate for algae cells was up to 94.31% during the treatment of water sample with lower alkalinity due to the synergistic effects of bridging effects and sweep coagulation, and the residual aluminum in effluent decreased to 0.035 3 mg·L?1. With increasing the alkalinity, the colloidal precipitation of Al(OH)3 generated in the solution gradually changed to ${\rm{Al}}\left( {{\rm{OH}}} \right)_4^ - $, the effects of sweep coagulation decreased and the removal rate for algae cells decreased accordingly. When the pH of water sample was 7.5, the stable floc size decreased from 811.02 μm to 540.62 μm with the increase of alkalinity, its strength factor for decreased from 35.97% to 24.79%, its recovery factor increased from 35.31% to 47.88%, and its fractal dimension decreased from 1.586 to 1.372. The results indicated that pH regulation could alleviate the effect of alkalinity on the coagulation process of algae-laden water and increase the removal rate of algal cells. Key words:alkalinity/ pH of water sample/ coagulation property/ floc property/ Zeta potential/ residual aluminum in effluent.
图1AlCl3投加量对混凝性能的影响 Figure1.Effects of AlCl3 dosage on coagulation performances
表1各碱度含藻水样在不同pH条件下形成絮体的强度因子和恢复因子 Table1.Strength factors and recovery factors of flocs formed in algae-laden water sample with different alkalinity at different pHs
pH
碱度为175 mg·L?1
碱度为245 mg·L?1
碱度为330 mg·L?1
强度因子/%
恢复因子/%
强度因子/%
恢复因子/%
强度因子/%
恢复因子/%
6.5
37.41
30.12
32.98
38.97
25.95
39.20
7.5
35.97
35.31
32.29
44.42
24.79
47.88
8.5
34.19
47.68
27.39
45.86
21.17
73.99
pH
碱度为175 mg·L?1
碱度为245 mg·L?1
碱度为330 mg·L?1
强度因子/%
恢复因子/%
强度因子/%
恢复因子/%
强度因子/%
恢复因子/%
6.5
37.41
30.12
32.98
38.97
25.95
39.20
7.5
35.97
35.31
32.29
44.42
24.79
47.88
8.5
34.19
47.68
27.39
45.86
21.17
73.99
下载: 导出CSV 表2各碱度含藻水样在不同pH条件下形成絮体的分形维数 Table2.Fractal dimension of flocs formed in algae-laden water sample with different alkalinity at different pHs
STEFFEN M M, DAVIS T W, MCKAY R M L, et al. Ecophysiological examination of the Lake Erie Microcystis bloom in 2014: Linkages between biology and the water supply shutdown of Toledo, OH[J]. Environmental Science & Technology, 2017, 51(12): 6745-6755.
[2]
DONG F, LIU J, LI C, et al. Ferrate (VI) pre-treatment and subsequent chlorination of blue-green algae: Quantification of disinfection byproducts[J]. Environment International, 2019, 133: 105195. doi: 10.1016/j.envint.2019.105195
[3]
JIA P, ZHOU Y, ZHANG X, et al. Cyanobacterium removal and control of algal organic matter (AOM) release by UV/H2O2 pre-oxidation enhanced Fe (II) coagulation[J]. Water Research, 2018, 131: 122-130. doi: 10.1016/j.watres.2017.12.020
[4]
ZHOU Y, LI X, XIA Q, et al. Transcriptomic survey on the microcystins production and growth of Microcystis aeruginosa under nitrogen starvation[J]. Science of the Total Environment, 2020, 700: 134501. doi: 10.1016/j.scitotenv.2019.134501
[5]
HENDERSON R, PARSONS S A, JEFFERSON B. The impact of algal properties and pre-oxidation on solid-liquid separation of algae[J]. Water Research, 2008, 42(8/9): 1827-1845.
[6]
HU C, LIU H, QU J, et al. Coagulation behavior of aluminum salts in eutrophic water: Significance of Al13 species and pH control[J]. Environmental Science & Technology, 2006, 40(1): 325-331.
RATNAWEERA H, GJESSING E, OUG E. Influence of physical-chemical characteristics of natural organic matter (NOM) on coagulation properties: An analysis of eight Norwegian water sources[J]. Water Science & Technology, 1999, 40(9): 89-95.
QI J, LAN H, LIU R, et al. Fe(II)-regulated moderate pre-oxidation of Microcystis aeruginosa and formation of size-controlled algae flocs for efficient flotation of algae cell and organic matter[J]. Water Research, 2018, 137: 57-63. doi: 10.1016/j.watres.2018.03.005
ZHANG L, MAO J, ZHAO Q, et al. Effect of AlCl3 concentration on nanoparticle removal by coagulation[J]. Journal of Environmental Sciences, 2015, 38: 103-109. doi: 10.1016/j.jes.2015.04.014
[19]
XU H, JIANG W, XIAO F, et al. The characteristics of flocs and Zeta potential in nano-TiO2 system under different coagulation conditions[J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2014, 452: 181-188.
[20]
XU H, JIAO R, XIAO F, et al. Relative importance of hydrolyzed Al species (Ala, Alb, Alc) on residual Al and effects of nano-particles (Fe-surface modified TiO2 and Al2O3) on coagulation process[J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2014, 446: 139-150.
[21]
ZHANG H, YANG L, ZANG X, et al. Effect of shear rate on floc characteristics and concentration factors for the harvesting of Chlorella vulgaris using coagulation-flocculation-sedimentation[J]. Science of the Total Environment, 2019, 688: 811-817. doi: 10.1016/j.scitotenv.2019.06.321
[22]
WU R M, LEE D J, WAITE T D, et al. Multilevel structure of sludge flocs[J]. Journal of Colloid and Interface Science, 2002, 252(2): 383-392. doi: 10.1006/jcis.2002.8494
YU W, LIG, XU Y, et al. Breakage and re-growth of flocs formed by alum and PACl[J]. Powder Technology, 2009, 189(3): 439-443. doi: 10.1016/j.powtec.2008.07.008
[25]
WANG J, GUAN J, SANTIWONG S R, et al. Effect of aggregate characteristics under different coagulation mechanisms on microfiltration membrane fouling[J]. Desalination, 2010, 258(1/2/3): 19-27.
[26]
KIM S H, MOON B H, LEE H I. Effects of pH and dosage on pollutant removal and floc structure during coagulation[J]. Microchemical Journal, 2001, 68(2/3): 197-203.
1.Key Laboratory of Northwest Water Resource, Environment and Ecology, Ministry of Education, Shaanxi Key Laboratory of Environmental Engineering, Xi′an University of Architecture and Technology, Xi′an 710055, China 2.State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China 3.Key Laboratory of Environmental and Geological Disasters, Ministry of Nature Resources, Guizhou University, Guiyang 550004, China 4.School of Resources Environment and Chemical Engineering, Nanchang University, Nanchang 330031, China Received Date: 2020-02-07 Accepted Date: 2020-04-04 Available Online: 2021-01-13 Keywords:alkalinity/ pH of water sample/ coagulation property/ floc property/ Zeta potential/ residual aluminum in effluent Abstract:In order to investigate the influence of alkalinity on the removal of algal cells and the organic substances secreted by algal cells by coagulation and ensure the drinking water quality, aluminum chloride (AlCl3·6H2O) was used as a coagulant to conduct coagulation test for Microcystis aeruginosa removal. The coagulation performance, floc properties and residual aluminum in effluent were investigated during the treatment of algae-laden water with different basicity. The results showed that when the pHs of water samples were adjusted to 6.0, in comparison with water samples with low alkalinity (95, 175 and 245 mg·L?1 ), the Zeta potentials of water samples with high alkalinity (330 mg·L?1 and 415 mg·L?1 ) approached 0 mV, and the repulsive force between particles decreased effectively. The removal rates for algae cells could reach over 74.45%(below 31.64% for water samples with low alkalinity), the lowest residual aluminum in effluent was 0.003 6 mg·L?1(0.088 9 mg·L?1 for water samples with low alkalinity). When the pH of water sample was above 6.5, the removal rate for algae cells was up to 94.31% during the treatment of water sample with lower alkalinity due to the synergistic effects of bridging effects and sweep coagulation, and the residual aluminum in effluent decreased to 0.035 3 mg·L?1. With increasing the alkalinity, the colloidal precipitation of Al(OH)3 generated in the solution gradually changed to ${\rm{Al}}\left( {{\rm{OH}}} \right)_4^ - $, the effects of sweep coagulation decreased and the removal rate for algae cells decreased accordingly. When the pH of water sample was 7.5, the stable floc size decreased from 811.02 μm to 540.62 μm with the increase of alkalinity, its strength factor for decreased from 35.97% to 24.79%, its recovery factor increased from 35.31% to 47.88%, and its fractal dimension decreased from 1.586 to 1.372. The results indicated that pH regulation could alleviate the effect of alkalinity on the coagulation process of algae-laden water and increase the removal rate of algal cells.
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