Adsorption Ability And Mechanism Of Cadmium And Zinc In Water By Extracelluar Polymeric Substances From Activated Sludge

Recently, water pollution caused by heavy metals becomes more and more serious. Heavy metal can destroy the metabolism of organism and does harm to people's health badly for they can be transferred from water into organism and accumulated. Therefore, how to control metal pollution efficiently becomes urgent. Compared with traditional method to treat metal pollution, biosorption has many advantages. Especially when it is used to deal with wastewater containing low-level metals, the efficiency is satisfying. Thus it attracts much attention.Many researches show that Extracellular polymeric substances (EPS) of microorganism have great ability to adsorption of metals, which play an important role in biosorption. EPS result from bacterial excretion, cell lysis or organic matters in surroundings and are made up of protein, polysaccharide, nucleic acid and lipids primarily. This composition endows EPS the ability to combine with metals. EPS is the third basis of activated sludge besides cells and water. It contributes to 80% of the mass of activated sludge, 50~90% of organic substances and 15% of dehydrated sludge.Three kinds of extracelluar polymeric substances from activated sludge were used as new adsorbents to adsorb Cd and Zn in water respectively. This paper focused on the influences of pH value, dosage of extracelluar polymeric substances, adsorption time and co-existed ions on adsorption ability. The results show that all of them have great efficiency on adsorption of Cd and Zn. The adsorption is fast, and can reach the balance in a short time. The adsorpition capacity can be up to 80% of total capacity in fast adsorption stage. When the mass concentration of Cd or Zn is 20mg/L, the optimal pH value for adsorption is 6 and the dosage of EPS is 375mg/L and 250mg/L respectively. At room temperature, Langmuir isotherm equations could describe the thermodynamic adsorption processes of Cd and Zn. The fit coefficient shows, the adsorption stabilization, the adsorption ability and appetency of Zn are better than Cd. The results of co-existed adsorption indicate that the selective adsorbility of EPS to...