The Mechanism Of Sludge Organic Toxicity Formation And Reduction Of Activated Sludge Treating Wastewater With High Organic Contents

The organic toxicity of sludge in land applications is a critical issue.However,minimal attention has been paid to the mechanism of toxicity formation and distribution during high-strength wastewater treatment.This study focused on the distribution of toxic organics in liquid and solid phases in wastewater activated sludge treatment process and the accumulation distribution of organic toxicity in activated sludge.Traditional activated sludge studies only focused on water phase and studied the pollutants removal in water as well as activated sludge treatment.In this study,the influent COD of blank group was only constituted with peptone,and control groups were constituted with peptone and BPA/N,N-dimethylformamide(DMF).The SBRs were controlled to a range of 3000?3500mg L-1.The activated sludge was obtained from the Chang Qiao wastewater treatment plant in Shanghai,which was acclimatised with synthetic wastewater.The effluent COD,concentrations of BPA/DMF in different phase(water phase,sludge phase),and the organic toxicity in activated sludge were monitoring in wastewater treating processes.The mechanism of toxicity formation and distribution during high-strength wastewater treatment was studied.HPLC was used to measure the concentrations of BPA and DMF in liquid and sludge flocs.The results indicated that degradation ability was stronger in acclimated activated sludge.BPA and DMF could be completely biodegraded in the wastewater treatment processes.The organic toxicity of sludge increased with increasing concentrations of BPA/DMF.During different acclimation ways,the organic toxicity of high-concentration shocked sludge was higher than the organic toxicity of gradually acclimated sludge that under the same influents BPA/DMF control groups.It indicated that the fonnulation of high organic toxicity of sludge in high-concentration shocked wastewater treatment processe was due to the weaker biodegradation ability of microorganism.The variations of organic toxicity of sludge were different between blank groups and control groups.The organic toxicity of sludge in blank group was the most stable and lowest in all groups.The organic toxicity inside sludge flocs of control groups increased with increasing concentrations of BPA/DMF.The formation mechanism of organic toxicity was due to the biodegradation of BPA/DMF by microorganisms in activated sludge.The toxic by-products in biodergradation processes accumulated in sludge flocs increased the toxicity of sludge.To study the correlation between organic toxicity and diversity of microorganisms,Pearson correlation analysis was conducted that there was correlation between organic toxicity and H.In BPA control groups,the correlation between organic toxicity and H was 0.482,and in DMF control groups,the correlation between organic toxicity and H was-0.550.In the gradually acclimated processes,it showed highly negative correlation between organic toxicity and similarity of microorganisms in BPA and DMF control groups.In other words,there was less similarity of microorganisms between blank groups and BPA/DMF control groups as the increasing of total organic toxicity of sludge.The results showed that the protein composition of BPA control groups were obviously different between different acclimated wastewater treatments by the protein two-dimensional electrophoresis test.Pseudomonas was dominant bacterial community in BPA degradation processes.The protein composition of DMF control groups were no significant differences between different acclimated wastewater treatments.A lot of same high quantity of protein expression was founded in DMF groups.It indicated that there was obviously correlation between microorganism and organic toxicity of sludge.Compared to organic toxicity distribution of in SBRs under the gradually and impact acclimation,the organic toxicity predominantly accumulated inside of sludge flocs.Compared to the distribution of organic toxicity of sludge in SBRs and continuous flow systems,the organic toxicity inside sludge flocs in continous flow systems was higher then which in SBRs.Otherwise,a little organic toxicity accumulated in outer section EPS of sludge flocs.Compared to organic toxicity distribution of different operation conditions in SBRs,the organic toxicity was reduced and also predominantly accumulated inside of sludge flocs in shorter HRT.Compared the organic sludge toxicity in continuous flow systems and SBRs,the organic toxicity of BPA/DMF control groups in continuous systems were higher than which in SBRs.It indicated that SBR was temporal plug flow mode,and the organic matter would be biodegradation completely.Changed the operational parameters such as shorten HRT and SRT,the effluents COD and residual pollutant were no obvious changed.The variations of sludge toxicity were similar to initial operation conditions.The microorganism activity is obvious enhanced due to high metabolic rates.Dosing PFS was an effective degradation method to reduce sludge toxicity,effluents COD and BPA/DMF.There was positive correlation between PFS concentration and reduction of sludge toxicity.Sludge toxicity is negative correlated with germination rate of clover by clover germination rate test.PFS was contributed to promote seed germination,reduce sludge toxicity and offer essential element Fe for plant.This study showed that formation and distribution of organic sludge toxicity,and explored effective methods to reduce toxicity.It was benefit to saving cost of excess sludge treatments and reducing environmental risk of sludge resource utilization.