Comparative Analysis Of The Effect Of Ferrate(?) On Sludge Disintegration

In recent years,biological sewage treatment is rapid development in our country.However,the yield of excess sludge increases year by year.Therefore,the sludge treatment and final disposal becomes a serious problem.The requirements of excess sludge treatment are reduction,stabilization,harmlessness and resource utilization.While,the sludge anaerobic digestion which is one of sludge resourceful treatment is inhibited by the complex sludge structure and hard microbial cell wall,resulting in the long digestion time and low biogas production.Hence,destroying the sludge floc and microbial cell is important through the excess sludge pretreatment.To improve the disintegration degree of excess sludge,many researchers presented some methods of sludge pretreatment such as physical method,chemical method etc.Ferrate is a new kind of environmentally friendly oxidant,which has strong oxidizing property and no toxic by-products production.However,the research of ferrate in sludge disintegration and anaerobic digestion is limited.Therefore,our study will use newly prepared alkaline ferrate?NPAF?to disintegrate the excess sludge and research the anaerobic digestion performance of disintegrated sludge.In our study,we found the NPAF can effectively disintegrate excess sludge.When the addition level of NPAF was 0.15 mmol Fe⁶⁺/g VS,the sludge floc and microbial cells can be destroyed,and the sludge solubilization was improved from 0.035 to 0.361.However,Fe⁶⁺will react with the released substance which was easily degraded such as BOD,DNA when the dosage of NPAF exceeded 0.15 mmol Fe⁶⁺/g VS.Besides,the concentration of protein,polysaccharide and VFAs in the sludge supernate was improved after 0.15 mmol Fe⁶⁺/g VS NPAF pretreatment,which the concentration of protein increased by 77.2%,the concentration of polysaccharide was 31.49 times of raw sludge and the concentration of VFAs improved from 25.1 to 1317.47 mg/L.In the aspect of sludge anaerobic digestion,NPAF pretreatment can restrain the biogas production which the biogas production of NPAF treated sludge was lower than the raw sludge?245.33 mL/g VS?.However,the methane production was improved after NPAF pretreatment.When the concentration of NPAF increased from 0 to 0.15 mmol Fe⁶⁺/g VS,the methane production can increase from 81.35 to 116.14 mL/g VS.Further increasing the dosage of NPAF,more potassium ion was added into samples,which can restrain the activity of methanogens leading to the decrease of methane production.Through the contrastive analysis among NPAF,O₃ and Fe²⁺/S₂O₈^2-,we conclude that the correlation of the effect of sludge disintegration by three kind of oxidant was NPAF>O₃>Fe²⁺/S₂O₈^2-.Meanwhile,the concentration of protein,polysaccharide and VFAs in NPAF treated sludge was higher than O₃ and Fe²⁺/S₂O₈^2-.In sludge anaerobic digestion,Fe²⁺/S₂O₈^2-pretreatment had negative effects on the methane production.While,O₃ and NPAF pretreatment can improve the sludge methane production and rate.Especially,the improved effect of methane production rate after O₃ pretreatment was better than NPAF,but the improved effect of methane production was lower than NPAF.