Study Of Biodegradability Improvement Of Animal Carcass Wastewater Bio-treated Effluent By Heterogeneous Fenton Based On Zero-valent Iron

Ministry of agriculture issued “Dead animal disposal technical specification” to satisfy the increasing standard of public health.Wet digestion method is a method to dispose the carcass and a high concentration with color and odor wastewater,termed as animal carcass wastewater（ACW）,is generated during this process.ACW is treated by anaerobic-aerobic biological technology,but the bio-treated effluent is complicated,high color and poor biodegradability.The deep treatment of effluent will be more necessary with the increasing of discharge standard.Heterogeneous Fenton technology based on zero-valent iron is a novel advanced oxidation processes（AOPs）,it overcomes the restrictions of homogeneous Fenton,such as low Fe2+ utilization efficiency,high ferrous salt dosage and a large amount of iron-containing sludge.However,no research about biodegradability of ACW bio-treated effluent by this novel AOP has been reported.This study built Fe⁰/H₂O₂ and Fe⁰/S₂O₈^2-heterogeneous Fenton systems and investigated the biodegradability improvement of bio-treated effluent.In present study,the effluent of anaerobic-aerobic biological reactor treating ACW was collected as the research subject and Fe⁰/H₂O₂ heterogeneous Fenton system was established.The effects of initial p H value,H₂O₂ and Fe⁰ dosage on the degradation,the transformation of recalcitrant pollutants and the biodegradability improvement were investigated.When the initial p H value is 6.2,Fe⁰ dosage is 4 g/L and H₂O₂ dosage is 50 mmol/L,after 8 h reaction time the COD removal and decolorization were 52% and 36%,respectively.The Fe³⁺ concentration of solution after the reaction was only 1.42 mg/L and the system reduced the iron-containing sludge compared to homogeneous Fenton system.In this condition,Fe⁰/H₂O₂ system improved the biodegradability,with enhancing BOD5/COD from 0.086 to 0.63 and increasing biodegradation 16% to 57%.The UV-vis spectral indicated that the recalcitrant aromatic pollutants relative amounts were decreased.The analysis of GC/MS and GC showed that the aromatic pollutants were transformed into biodegradable fatty acid.The acetic,propionic and butyrate were generated during the process and the concentrations were 9,1 and 2 mg/L,respectively.H₂O₂ was replaced with S₂O₈^2-and Fe⁰/S₂O₈^2-heterogeneous Fenton system was established.The effects of initial p H value,S₂O₈^2-and Fe⁰ dosage on the degradation were investigated.UV-vis spectrum,GC/MS and GC analysis of the bio-treated effluent were tested for the transformation of recalcitrant pollutants and the biodegradability improvement.When the initial p H value is 6.2,Fe⁰ dosage is 4 g/L and S₂O₈^2-dosage is 25 mmol/L,after 6 h reaction time the COD removal and decolorization were 60% and 60%,respectively.The Fe³⁺ concentration of solution after the reaction was only 9.6 mg/L which is much less than the concentration of homogeneous Fenton system.In this condition,Fe⁰/S₂O₈^2-system improved the biodegradability,with enhancing BOD5/COD from 0.086 to 0.57 and increasing biodegradation 16% to 54%.The UV-vis spectral indicated that the recalcitrant aromatic pollutants relative amounts were decreased.The analysis of GC/MS and GC showed that the aromatic pollutants were transformed into biodegradable fatty acid.The acetic,propionic and butyrate were generated during the process and the concentrations were 10,2 and 3 mg/L,respectively.Comparing Fe⁰/H₂O₂ and Fe⁰/S₂O₈^2-systems,the operate p H range of Fe⁰/S₂O₈^2-system is wider than Fe⁰/H₂O₂ system,but the leaching iron concentration of Fe⁰/H₂O₂ system is lower than Fe⁰/S₂O₈^2-system.In addition,the oxidant utilization and the COD removal and decolorization of Fe⁰/S₂O₈^2-system were higher than Fe⁰/H₂O₂ system.However,the biodegradability improve capability of Fe⁰/H₂O₂ system was higher.Based on the aforementioned results,Fe⁰/H₂O₂ and Fe⁰/S₂O₈^2-systems decreased the COD and colority of ACW bio-treated effluent and improved its biodegradability with low leaching iron concentrations.Based zero-valent iron heterogeneous Fenton technology is promising for the deep treatment of ACW.