Study On The Performance And Mechanism Of Mn (Ⅲ) Conditioning-Horizontal Electro Dewatering Of Activated Sludge

With the rapid increase of municipal wastewater and the improvement of wastewater treatment capacity,a large number of excess sludge generated by municipal wastewater treatment plants poses a serious threat to the environment,which has become an urgent problem.In this study,a Mn(Ⅲ)conditioning-horizontal electro-dewatering(Mn(Ⅲ)C-HED)process was established to improve activated sludge(AS)dewaterability.The optimum operating conditions were determined by response surface methodology(RSM)optimization and the dewatering effect of the sludge under typical conditions and the economic feasibility of the process were evaluated.In addition,the physical and chemical properties,moisture distribution and the variation characteristics of organic matter in different extracellular polymeric substances(EPS)layers of typical AS samples were analyzed.The mechanism of Mn(Ⅲ)conditioning-horizontal electro-dewatering was discussed.The results are as follows:After conditioned by Mn(Ⅲ),with the best dosage:KMnO4 0.09mol/L AS,NaHSO3 0.45mol/L AS.The capillary suction time(CST)of the conditioned sludge increased by 25.4%than the raw activated sludge,while the sludge dewatering rate decreased by 11.93%.The oxidation effect of Mn(Ⅲ)could led to the cell disruption and EPS disintegration,which induced partial bound water release.Additionally,the flocculation effect induced by Mn2+and MnO2 skeleton building also benefited AS dewaterability.Therefore,the dewatering performance of sludge could be improved by using Mn(Ⅲ)conditioning.The effect of horizontal electric field on sludge dewatering is verified separately.Under the effect of the horizontal electric field,the sludge particles with negative electricity were gathered to the anode,and the water of the sludge was moved from the anode to the cathode.The water content of the sludge decreased from 97.99%to 91.33%,and the water content of the sludge at anode side was lower than that of the cathode.The change of pH and temperature caused by electric field also caused sludge cell cracking and water release.In the process of Mn(Ⅲ)conditioning-horizontal electro-dewatering,the activated sludge was conditioned by Mn(Ⅲ)first,then the horizontal electro-dewatering was used to reduce the water content of the sludge.The optimum dewatering conditions for Mn(Ⅲ)C-HED process were determined as the combination of KMn04 0.01 mol/L AS and NaHSO3 0.05 mol/L AS at 20 V for 120 min.During the whole Mn(Ⅲ)C-HED process,the total water content,free water content,and bound water content decreased to 85.86%,87.62%,51.68%(anode),82.64%,85.08%,36.55%(cathode).As a result,the volume of the sludge reduced significantly.Mn(Ⅲ)oxidation led to the cell disruption and EPS disintegration,which induced partial bound water release.And the inner EPS fractions transformed to the outer ones,which was beneficial to AS dewatering.Moreover,Mn2+ions could play an important role in AS flocculation through bridge formation between biopolymers of microbial cells.Under the effect of horizontal electric field,EPS and AS cells were further disrupted,then their cytoplasm were released together with part of bound water.As for the MnO2,which could act as skeleton builders and lead to a more porous and incompressible structures of AS,provided passages for water removal.