Effect Of Ferrate Solution-A/O Process On Sludge Reduction And Effluent Quality

Activated sludge process is widely used in wastewater treatment plant,but the biggest drawback is the production of large amount of excess sludge,which can easily cause secondary pollution without improper handling.In view of the disadvantages of activated sludge process,combined with the theory of cell lysis and latent growth,this paper used ferrate solution to crack sludge and took the cell lysate return to the A/O process anoxic tank.The influence of ferrate solution-A/O process on sludge reduction and effluent quality of the system were investigated.The effects of initial sludge pH value,reaction time,sludge concentration and ferrate solution dosage on sludge cracking were investigated by single factor method.The response surface method was used to analyze and optimize the influencing factors of sludge cracking.The results showed that the sludge concentration and ferrate dosage had significant effect on the sludge cracking,and their influence degree were the same.The reaction time had less effect on the reaction.When the pH value was 6.94,the highest operating conditions of organic matter dissolution were as follows:sludge MLSS concentration 10000 mg/L,reaction time 24 h,ferrate solution dosage 50 mgFe/gSS,under this condition,SCOD dissolution rate was 37.96%.Ferrate solution could effectively destroy sludge floc and dissolve cell structure,resulting in dissolution of intracellular substances.With the increase of ferrate dosage,the contents of SCOD,nitrogen and polysaccharide in the supernatant increased significantly,while TP and protein showed a trend of increase first and then decrease.The value of BOD₅/COD increased from 0.28 to 0.44,which indicated a significant improvement in biodegradability.After sludge cracking,MLSS and MLVSS were significantly reduced,sludge settleabilityb and dewatering performance were significantly improved.Microscopic examination showed that when the ferrate dosage was 50 mgFe/gSS,filamentous bacteria in the sludge were completely broken,and the sludge floc was fragmented.The ferrate solution-A/O process was designed and used to treat simulated domestic sewage.The effect of different excess sludge disintegration amount on the system operation was studied.The results showed that when 50%of the cracked excess sludge was returened to the A/O reaction tank,the sludge MLSS in aeration tank was 4500⁵500 mg/L,and the sludge activity and sedimentation performance were improved.The removal rates of COD,BOD₅,TN,NH₃-N and TP in sewage were 93.45%,97.75%,71.78%,88.91%and 39.08%respectively,which improved 5.58%,5.47%,14.76%,9.65%and 14.91%compared with A/O process,and the effluent concentrations of NO₃-N and NO₂-N were low.Continuous operation for 20 days under this condition,sludge reduction reached 42.30%.The results showed that the ferrate solution-A/O process could operate stably,which not only realized sludge reduction,but also improved the effluent quality of the system.The ferrate solution-A/O process had certain application value.