Study On Thermally-Activated Persulfates Coupled With Magnesium Ammonium Phosphate Method Of Excess Sludge Treatment

Annual output of excess sludge is nearly 60 Mt in China up to 2018,which contains abundant pollutants and nutrients.The output of excess sludge is growing at an annual rate of10～15%and becomes a severe problem.The combination of thermally-activated persulfates and magnesium ammonium phosphate（MAP）method——a novel technology to attain reduction and reutilization of excess sludge simultaneously is pointed out.Optimal conditions of sludge reduction,sludge conditioning and MAP reaction are determined by single factor experiment.Mechanism of enhanced dewaterability of excess sludge conditioned by thermally-activated persulfates is determined by characterization methods such as 3D-EEM and Zeta potential.The barrier between thermally-activated persulfates and MAP method is broken through by cation exchange.The conclusions as followed are the theoretical basis of practical application and novel insights into sludge reduction and sludge conditioning（1）Optimal conditions of sludge conditioning by thermal-activated persulfate is found to be 80℃,persulfate 2.0 mmol/g TS,initial p H 4～7 and reaction time 40 min,which demonstrated that CST falls from 94.2 s to 28.5 s.（2）Mechanisms of enhanced dewaterability of excess sludge conditioned by thermally-activated persulfates as follow:sulfate radical anions（E⁰=2.5～3.1 V）activated at more than80℃attack LB-EPS和TB-EPS in sludge and do not broke sludge particle into massive tinier ones,which enhances sludge dewaterability.During the process,H⁺,the by-product of persulfate reduction reaction,acidizes reaction system to cause thermal acidolysis of sludge,which makes hydrolysis of polysaccharide possible and accelerate hydrolysis of protein to break LB-EPS和TB-EPS further.Rapid H⁺transfer processes in 80℃reduces the negative charge of sludge particle surface and increases Zeta potential to more than-5 m V,which benefits enhanced dewaterability of sludge.（3）Optimal conditions of sludge reduction by thermal-activated persulfate is found to be80℃,persulfate 1.5 mmol/g TS and reaction time 40 min,which demonstrated that the release of TN,NH₄⁺-N,TP and PO₄^3--P is 854.48 mg/L,287.22 mg/L,177.71 mg/L and 177.71mg/L,respectively.Released COD 10754 mg/L,DD_SCOD21.95%。Thermally-activated persulfates release more NH₄⁺,PO₄^3--P and COD,and retain the concentration of NH₄⁺.（4）Optimal conditions of MAP reaction is found to be p H 10,n(Mg²⁺):n(PO₄^3-)=1.4 and reaction time 10 min,which demonstrated phosphorus recovery rate of 95.06%,ammonia nitrogen removal rate of 39.09%and product purity of 95.03%.