Distribution Of Heavy Metals In Solid-Liquid During Dewater Process Of Sewage Sludge

With the development of wastewater treatment,the amount of sewage sludge,which is one “product” during the metabolic and physical-chemical settlement process,has being increasing dramatically.It is one kind of hazardous substance attributed to its complex containing which has an enormous threat to environment.Finding an appropriate method to treat sludge and regarding it as a resource for sustainable recycling has attracted attention for both environmental and economic reasons.At present,heavy metals in sludge are supposed to be the biggest obstruction for sludge recycling and limit its applications.Even in mant wastewater treatment plants nationwide,excessive problem occurs frequently.This article has investigated the distribution and potential transitivity of heavy metals between solid and liquid two phases under various conditions.Sewage sludge used in this study was sampled from Qige municipal and Linjiang industrial wastewater treatment plants.The effects of pH?extraction time?coagulants and flocculants?novel dehydrating agents from Guotai(GT-15,the same below),were established to have a much deeper research exploring heavy metals in sludge.Qige sludge under the condition of a neutral encironment or with the addition of CaO 250 mg/g DS(Dry Sludge,the same below)or PAM 4~6 mg/g DS exhibits excellent dehydration performance.The statistical result showed all of the 6 heavy metals distributed more in solid phase with the increase of pH value,while had a more fixation ability with the addition of dehydrating agents from Guotai.The heavy metals content followed an order:Zn>Cu>Cr>Pb>Ni>Cd,and the potential ecological Risk Index(RI)followed another: Cu>Zn>Pb>Ni>Cr>Cd.Copper?Zinc are more easily transferred by the environment change and apt to cause environmental issues.The distribution of heavy metals from Linjiang sludge generally followed a similar result to Qige's.However,all the expriments evidently demonstated Chromium was retatively stable in sludge,especially in the solid phase.In other words,it had a poor potential transitivity which was low-risk to the environmental safety.The heavy metals content followed an order: Zn>Cr>Cu?Ni>Pb>Cd,and the potential ecological Risk Index(RI)followed another: Zn>Ni>Cu>Pb>Cr>Cd.This study also implied the dehydrating agents from Guotai were superior to chelate more heavy metals in sludge and prevent them transferring into environment,which proved to be promising for practical application.