Enhanced Dewaterability Of Waste Sludge By Nickel Ferrite Activated Sodium Persulfate Process

With the continuous development of China’s industry,more and more wastewater treatment plants have been built and put into operation,and the volume of wastewater treatment is increasing day by day.Accordingly,the amount of sludge produced after sewage treatment is rapidly increasing,which also causes more and more pressure on sludge treatment in China.The sludge floc structure is complex,and the water wrapped inside the sludge is difficult to be discharged and removed.Therefore,improving sludge dewatering performance is a major measure for sludge treatment.In this study,advanced oxidation processes based on sulfate radicals（SO₄·^—）were used to enhance the dewatering performance of sludge by conditioning.Advanced oxidation processes based on sulfate radicals have more obvious advantages than those based on hydroxyl radicals（·OH）.The storage and transportation of persulfate are easier,safer and cheaper,and the activation of persulfate is varied.In this study,magnetic nickel ferrate（NiFe₂O₄）material was prepared,and all metal ions on the surface of NiFe₂O₄could participate in the process of activating persulfate,and the sludge extracellular polymer（EPS）was cleaved by using NiFe₂O₄ to activate sodium persulfate（Na₂S₂O₈）to strengthen the sludge dewatering performance.NiFe₂O₄ was prepared by the co-precipitation method and the effects of different reactants on the catalytic performance of the prepared NiFe₂O₄ were investigated.The results showed that when Ni Cl₂·6H₂O and Fe Cl₃·6H₂O were used as reactants for the preparation of NiFe₂O₄,the NiFe₂O₄ particles were more regular,more uniformly distributed,with better crystallization,higher purity,larger specific surface area(86.462m²·g^-1),and free of impurity functional groups.In addition,the prepared NiFe₂O₄ had the strongest ability to activate the oxidative degradation of Na₂S₂O₈ when the curing temperature was 80℃,the curing time was 2 h,the calcination temperature was 500℃,and the calcination time was 3 h,respectively.The sludge from the secondary settling tank of a municipal wastewater treatment plant in Shenyang,Liaoning Province,was used as the experimental object to investigate the optimal reaction conditions for dewatering NiFe₂O₄ activated sodium persulfate（Na₂S₂O₈）conditioned sludge.The optimum sludge conditioning conditions were determined by measuring the parameters of the water content of filter cake（Wc）,specific resistance to filtration（SRF）,and soluble chemical oxygen demand（SCOD）before and after sludge conditioning.In the free radical quenching experiment,it was confirmed that the SO₄·^—generated during the conditioning of sludge dewatering using NiFe₂O₄-activated Na₂S₂O₈ was the main factor in enhancing sludge dewatering and improving sludge dewatering performance.The results of the single-factor experiments can be obtained that the optimal reaction conditions for NiFe₂O₄ activation of Na₂S₂O₈ to enhance sludge dewatering with a reaction time of 20 min,no additional adjustment of sludge p H,a dosing ratio of 0.6 between NiFe₂O₄ and Na₂S₂O₈ and a Na₂S₂O₈ dosing rate of 400 mg·g^-1 TSS.The recovery rate of NiFe₂O₄ and the effect of the recovery on sludge dewatering conditioning were tested,and the results showed that the experimentally produced NiFe₂O₄ is magnetic,the recovery rate of the material is close to 80%after four cycles,and it can maintain good catalytic activity,which can enable the reuse of NiFe₂O₄.The mechanism of NiFe₂O₄-activated Na₂S₂O₈ enhanced sludge dewatering was investigated by testing and analyzing the sludge EPS structural components,basic physical and chemical properties of sludge,sludge microscopic morphology and other indicators.It is known that after advanced oxidation of sludge conditioning based on NiFe₂O₄-activated Na₂S₂O₈,the internal macromolecules of sludge are oxidized and cracked into small molecules by the action of SO₄·^—.The surface of sludge particles becomes loose and forms a pore structure that facilitates the drainage of water inside the sludge.More bound water inside the sludge is released.The bound water is reduced from4.84 kg·kg^-1 to 2.60 kg·kg^-1,which effectively improves the sludge dewatering performance.