The Stabilization Of Heavy Metals In Municipal Sludge

With the urbanization progress speeding up,the urban sludge quantity are growing rapidly. Safetily treating and disposing of this sludge have become a solved urgently problem which may affect the steadily development of city.However,the reduction,harmless,stabilization and reusing of sudge was restricted by the high moisture of sudge.Meanwhile, the poisonous heavy metal ions of sludge are hidden trouble for reusing of sudge.The study shows that excess sludge of the moisture exceeding90%could be disposed under50%by technology of wet oxidation and coagulation which are the best technology of sludge treatment at the dehydration effect. According to the detection result,this technology could play an effective stabilization for heavy metals of sludge.merely,there are rare reports on the mechanism of satbilization.If we can explore the mechanism of satbilization,which may provide theoretical support for the technology,supplying a scientific basis to resourceful and security of the sludge disposal.This paper completed the study on stabilization of heavy metals(Zn,Cu,Pb,Cd) in sludge which was disposed by technology of wet oxidation and coagulation,with the purpose of confirming the stablization of heavy metals.EPS exttracting from residual activated sludge and oxidizong medium(ozone) were used for adsorbing heavy metals(Zn,Cu,Pb,Cd).In addition,IR was intended for characterizing EPS which adsorbed heavy metals,SEM was intended for characterizing sludge before and after oxidation disintegration-membrance.In these basis,we will explore the stabilization mechanism of heavy metals.Main works as follow:(1) The total contents and chemical fractions of heavy metals (Zn,Cu,Pb,Cd) in sludge were analyzed with Tessier’s procedure.The acid leaching test and stability assessment were also applied to analyze stabilization of heavy metals.The results showed that the total amount of these heavy metals were less than the acidity limit value in the pollutant control standards in the agricultural sludge and accorded with the grade B of the sludge shale requirements,which is only apply to oil-bearing crops,fruit trees,fodder,fiber and other crops.Unstablestate of these heavy metals were converted into stable state at varying degrees after treatment.The leasting content and ratio of these heavy metals were small;The average reduction of bioavailability attained to67%.The above analysis shows that the heavy metals (Zn,Cu,Pb,Cd) in sludge were evidently stablized by technology of wet oxidation and coagulation.(2) EPS comblining with ozone were used to adsorb heavy metals.This paper invastigated the infulances of oxidation time,pH value,dosage of EPS and dosage of ozone on adsorption ability.The result shows that adsorption process experienced a rapid adsorption,slow adsorption and the balance of adsorption.The pH value shoud be6.5. the best dosage of EPS with the ratio of the quality of benchmark solution is eighteen to one for adsorption of Zn2+,Cu2+and Pb2+,compared with twenty to one for Cd2+.When the optimal dosage of ozone was0.004gO3·g-1SS,the absorption level of EPS was more than22.1%as the ozone dosage of zero,it declared that ozone disintegrating EPS is beneficial to adsorb heavy metals. In addition,Langmuir isotherm equations could describe the thermodynamic adsorption processes of these heavy metals.(3)The IR of EPS’s result show that amidogen,hydroxyl,carboxyl,amidogroupand C-O-C group are pivotal functional groups for the adsorption of EPS.While the technology of wet oxidation and coagulation destroyed the organic matter membrane and extracellular polymeric strucure from the SEM figure.(4)Based on the above study,the stabilization mechanism of heavy metals were discussed.The analysis think that have a variety of possible stabilization mechanism.Because the organic matter membrane and extracellular polymeric strucure were destroyed,generated even more bonding active groups,increaced the specific surface area and mugmented the functional groups involved in the reaction which produced more metal adsorption sites;Moreover,Particle surface adsorption and exocellular adsorption of heavy metals were transformed into the adsorption of intracellular activity and the adsorption of active groups.There are another mechanism that the·OH were produced in the process of oxidation,which can translate the heavy metals into be highly-charged with stronger complexing and bonding capacity.It can form MOHn+with hydroxyl.