Research On The Removal Of Heavy Metals In Sewage Sludge By Microwave Cooperated With Compound Leaching Agent

On account of the long time for the citric acid leaching of heavy metals inmunicipal sludge and large sum of pharmaceutical dosing is becoming a problem forindustrial applications and sludge for agricultural. This paper used the citric acid as themain method with microwave radiation of leaching of heavy metals in the sludge. Onthe basis of above, combination of H2O2, EDTA, EDDS leaching agent, in a properrange of compound reagents, by orthogonal experiments,chosing efficient and readilybiodegradable green compound leaching agent formulations.Adopting relatedcharacterization methods studied the impact of sludge properties after addingcomposite reagents.The main findings are as follows:（1）Microwave synergistic separate citric acid experiments investigated theheating rate of removal of heavy metals, pH, stirring time on the leachingrate.Optimum conditions was adding2mol/L citric acid, adjusted pH to3, stirring for30minutes under25oC with microwave treatment at the P1power (170W), the heatingrate of15oC/min, heated to60oC, keep warm in water bath and stir for3h. The heavymetals in the sludge of zinc, copper, nickel, lead leaching rate were47.84%,11.05%,43.83%,23.97%. Comparing microwave synergy with no microwave synergisticexperiments showed that sure of microwave assisted in leaching of heavy metals inpromoting and strengthening effect, under other conditions were the same, microwavecooperate with citric acid treatment so average leaching rate of heavy metals leachingis28.9%higher than a separate citric acid;（2）Firstly, examined by the leaching agent and citric acid complex,thendetermined the optimal formula was formula3by orthogonal experiment,which wasmicrowave cooperate with H2O2, EDTA, EDDS and CTA compound for addingconcentrations were0.5mol/L,0.1mol/L,0.1mol/L,2mol/L and dosage were0.1mL,0.8mL,0.5mL,0.65mL respectively. PH was adjusted to4with citric acid, otherconditions associated with microwave cooperate with citric acid， Zn,Cu,Ni,Pb leaching rate reached47.03%,53.38%,44.89%,46.94%;（3）Distribution of heavy metals in the original sludge has certain effect onheavy metals leaching. By contrast the mud mixture stage microwave-citric acidtreatment and microwave-formula treatment showed that for Cu, microwave-formulahandling of the iron and manganese oxidation state, organic binding and residualconversion into the exchangeable and carbonate-bound,while the microwave-citricacid treatment can only convert a small amounts of other four forms intoexchangeable; For Pb, microwave-formula handle more iron and manganeseoxidation state transformed into exchangeable state, conversion of the iron andmanganese oxidation state in the microwave-citric acid treatment is much lower thanthis. After treatment of heavy metals in the exchangeable fraction increased, the otherfour types of content were reduced;（4）Microwave-Formula treatment significantly improved sludge settling anddewatering performance, the SV30decreased from98%of untreated sludge directfiltration to86%, the water content of vacuum filtration decreased from83.04%to69.7%. Step-by-step experiment showed that formula treatment on the sludge settlingand dewatering properties improvement is better than only microwave treatmentresults, illustrated the formula on the sludge settling and dewatering propertiesimprovement of contribution to a greater degree. Through electronic scanninginstrument showed that, after the microwave-formula treatment, sludge agglomerationcompared to the original sludge particle size, compact structure, which was processedby settling and dewatering properties improvement of reason. Sludge was measuredbefore and after treatment,N,P,K content showed that,compared to the originalsludge,the treated sludge’s total nitrogen content increased, total phosphorus and totalpotassium loss rate was only6%and7.3%, the sludge had better fertilizer effect.