The Influence Of Bioleaching On Heavy Metals And Dehydration Performance Of Municipal Sewage Sludge

In recent years,with the accelerating pace of urban and industrial development in our country,the increasing urban and industrial water consumption will inevitably lead to a large amount of sewage.In order to solve the pollution problem of domestic sewage and industrial production wastewater on the environment,a large number of sewage treatment plants are constructed in various cities.As of 2016,a total of more than 3,900 sewage treatment plants have been built in our country,and a large amount of surplus sludge will be generated during the operation of the sewage treatment plants.Residual sludge in cities has the characteristics of high water content,large volume and many pollutants,which can lead to environmental pollution.Therefore,the safe and effective treatment of sludge is getting more and more attention.It is of great practical significance to develop a cost-effective sludge disposal technology for the future development of sewage treatment in China.Decreasing heavy metals in sludge and improving sludge dewatering performance are the key problems in sludge disposal.Reducing the risk of heavy metal pollution in sludge can promote the process of sludge land use.Improving sludge dewatering will reduce the intensity of subsequent sludge treatment while saving on sludge transport costs.In this study,the remaining sludge of a sewage treatment plant in Suzhou is as the research object.Analysis of the nature of the recovered sludge shows that the sludge has high organic matter content,abundant total nitrogen and total phosphorus,and has high agricultural value.However,the content of Cu,Zn,Cr and Ni in the sludge is large,and the water content of the sludge is high and the flocs are loose,so the sludge belongs to the hard dewatered sludge.Therefore,before the land use,the sludge must reduce the content of heavy metals such as Cu,Zn,Cr and Ni to make it reach the standard of heavy metal control of agricultural sludge in our country.At the same time,the sludge dewatering performance should be adjusted for the subsequent disposal of the sludge.The results show that bioleaching treatment technology can effectively reduce the heavy metals in sludge.The experimental group with the composite substrate FAS+S⁰ had the best leaching effect.The removal rates of Cu,Zn,Cr and Ni in the treated sludge were 86.7%,88.2%,76.2%and 65.0%,respectively.The contents of Cu,Cr and Ni in the sludge were 78.61mg/Kg,69.05mg/Kg and28.72mg/Kg,respectively,all of them are within the implementation standard of GB4284-84 acidic soil.Zn content was 720.37mg/Kg reaching alkaline soil Implementation standards.At this time,the centrifugal dewatering rate of sludge was89.5%,and the specific resistance of sludge decreased from 1.51×10¹³m/Kg of original sludge to 0.46×10¹³m/Kg.Sludge dewatering performance has been significantly improved.Ferrous sulfate ammonium（FAS）,ferrous sulfate（FS）and elemental sulfur（S⁰）were selected as biological leaching substrates.Acidophilus thuringiensis inoculum was prepared from the recovered sludge samples for leaching experiments.Focus on the type of substrate and dosage on the biological leaching effect of sludge.The study also found that the stability of heavy metals Cu and Zn in biologically leached sludge increased,and the bioavailability of heavy metals decreased.However,the contents of TN and TP in the experimental sludge all had different degrees of loss,of which FAS had the least effect on the total nitrogen and total phosphorus loss in the sludge,and the residual TN and TP in the leached sludge Contents were 21.20g/Kg,14.31g/Kg.Therefore,the use of bioleaching sludge should be considered the dissolution of heavy metals,the improvement of sludge dewatering and sludge total nitrogen loss of total phosphorus.Different substrates are used according to the specific conditions of the sludge.When the content of heavy metals in the treated sludge is high,the composite FAS+S⁰ can be used to obtain a higher removal rate of heavy metals and the dewatering performance of the sludge is also greatly improved.However,if the content of heavy metals in the sludge to be treated is low,the single substrate FAS can be used to minimize the TN and TP losses in the sludge under the premise of reaching the standard of heavy metals after bioleaching.