This study describes the treatment of composting leachate by the combination of coagulation and nanofiltration process. Poly ferric sulfate （PSF） was used as coagulant, and the effect of pH value and PSF dosage on t...This study describes the treatment of composting leachate by the combination of coagulation and nanofiltration process. Poly ferric sulfate （PSF） was used as coagulant, and the effect of pH value and PSF dosage on the coagulation performance was investigated. The results indicated that the chemical oxidation demand （COD） and turbidity removal efficiency could reach to 62.8% and 75.3%, respectively at an optimum dosage of 1200 mg·L-1 at pH 6,0. During the nanofiltration process, the operation conditions such as temperature and pressure were optimized, 89.7% of COD, 78.2% of TOC, 72,5% of TN, 83,2% of TP, and 78,6% of NH3-N were retained when tested at 0.6 MPa at 25 ℃. The final leachate effluent concentration of COD, BODs, NH3-N, TOC, SS was 92 mg.L 1, 31 mg,L 1 21 mg.L 1, 73 mg·L-1 and 23 mg·L -1, respectively, which reached the local discharge standard. The combination of coagulation-filtration is useful for composting leachate treatment.展开更多
Elevated arsenic（As） in groundwater poses a great threat to human health. Coagulation using mono- and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitat...Elevated arsenic（As） in groundwater poses a great threat to human health. Coagulation using mono- and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitation comes from insufficient understanding of the As removal mechanism from groundwater matrices in the coagulation process, which is critical for groundwater treatment and residual solid disposal. Here, we overcame this hurdle by utilizing microscopic techniques to explore molecular As surface complexes on the freshly formed Fe flocs and compared ferric（III） sulfate（FS） and polyferric sulfate（PFS）performance, and finally provided a practical solution in As-geogenic areas. FS and PFS exhibited a similar As removal efficiency in coagulation and coagulation/filtration in a two-bucket system using 5 mg/L Ca（ClO）_2. By using the two-bucket system combining coagulation and sand filtration, 500 L of As-safe water（〈 10 μg/L） was achieved during five treatment cycles by washing the sand layer after each cycle. Fe k-edge X-ray absorption near-edge structure（XANES） and As k-edge extended X-ray absorption fine structure（EXAFS） analysis of the solid residue indicated that As formed a bidentate binuclear complex on ferrihydrite, with no observation of scorodite or poorly-crystalline ferric arsenate. Such a stable surface complex is beneficial for As immobilization in the solid residue, as confirmed by the achievement of much lower leachate As（0.9 μg/L-0.487 mg/L）than the US EPA regulatory limit（5 mg/L）. Finally, PFS is superior to FS because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water.展开更多
基金Supported by the Natural Science Foundation of Zhejiang Province(LQ14B060001,Y14F030005)Foundation of Science and Technology Department of Zhejiang Province of China(2013C33019,2015C33232)Science and Technology Project of Lishui City(2015RC23)
文摘This study describes the treatment of composting leachate by the combination of coagulation and nanofiltration process. Poly ferric sulfate （PSF） was used as coagulant, and the effect of pH value and PSF dosage on the coagulation performance was investigated. The results indicated that the chemical oxidation demand （COD） and turbidity removal efficiency could reach to 62.8% and 75.3%, respectively at an optimum dosage of 1200 mg·L-1 at pH 6,0. During the nanofiltration process, the operation conditions such as temperature and pressure were optimized, 89.7% of COD, 78.2% of TOC, 72,5% of TN, 83,2% of TP, and 78,6% of NH3-N were retained when tested at 0.6 MPa at 25 ℃. The final leachate effluent concentration of COD, BODs, NH3-N, TOC, SS was 92 mg.L 1, 31 mg,L 1 21 mg.L 1, 73 mg·L-1 and 23 mg·L -1, respectively, which reached the local discharge standard. The combination of coagulation-filtration is useful for composting leachate treatment.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB14020201)the National Natural Science Foundation of China (Nos. 41373123, 21337004)the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences (No. YSW2013A01)
文摘Elevated arsenic（As） in groundwater poses a great threat to human health. Coagulation using mono- and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitation comes from insufficient understanding of the As removal mechanism from groundwater matrices in the coagulation process, which is critical for groundwater treatment and residual solid disposal. Here, we overcame this hurdle by utilizing microscopic techniques to explore molecular As surface complexes on the freshly formed Fe flocs and compared ferric（III） sulfate（FS） and polyferric sulfate（PFS）performance, and finally provided a practical solution in As-geogenic areas. FS and PFS exhibited a similar As removal efficiency in coagulation and coagulation/filtration in a two-bucket system using 5 mg/L Ca（ClO）_2. By using the two-bucket system combining coagulation and sand filtration, 500 L of As-safe water（〈 10 μg/L） was achieved during five treatment cycles by washing the sand layer after each cycle. Fe k-edge X-ray absorption near-edge structure（XANES） and As k-edge extended X-ray absorption fine structure（EXAFS） analysis of the solid residue indicated that As formed a bidentate binuclear complex on ferrihydrite, with no observation of scorodite or poorly-crystalline ferric arsenate. Such a stable surface complex is beneficial for As immobilization in the solid residue, as confirmed by the achievement of much lower leachate As（0.9 μg/L-0.487 mg/L）than the US EPA regulatory limit（5 mg/L）. Finally, PFS is superior to FS because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water.
