Study On Mechanism Of Effect Of Fiber And Activated Persulfate On Dewaterability Of Paper Mill Sludge

The composition of paper mill sludge is complex and the water content is high.Sludge dewatering is a necessary step to achieve the minimization of paper mill sludge.A further understanding of the characteristics of paper mill sludge and a reasonable choice of the advanced dewatering technology will help to achieve the strategic goal of sludge reduction and resource development,which is of great significance to the country’s sustainable development strategy.In this paper,the influence mechanism of fiber and activated persulfate on the dewaterability of the simulated paper mill sludge were studied.Firstly,the effects of fiber properties including content,average length,fibrillation and type on the dewaterability(i.e.SRF and compressibility)of simlutated paper mill mixed sludge(the mixture of fiber and activated sludge)were studied.The influence mechanism of fiber on the dewaterability of the mixed sludge was revealed in according to fiber-sludge particle adhersion,filter cake permeability and SEM image.The results showed that the fiber can improve the dewaterability of the mixed sludge.The higher the fiber content,the better the sludge dewaterability.Generally,when the average fiber length was more than 0.303 mm.the sludge filterability increased with the decrease of fiber length,and the filterability of the mixed sludge with fines(0.189 mm)was dropped.Chemical mechanical pulp(PRC-APMP)fiber was more effective than chemical pulp(HBKP)fiber to improve sludge dewaterability.Fiber properties(including fiber content,average length,fibrillation and type)have little influence on the compressibility of the sludge cake.The mechanism of the influence of fiber on the dewaterability of the mixed sludge can be explained by the intrinsic relationship between fiber-sludge particle adhersion,the floe(fiber-sludge particle aggregates)size,the permeability of the sludge cake and sludge filterability.Secondly,the oxidative degradation kinetics of sulfate radicals on polysaccharide models(glucose and dextran)and protein model(bovine serum albumin,BSA)in extracellular polymeric substances(EPS)by thermal activation were studied.The results showed that when the PDS was excessive,the degradation of glucose and BSA or a mixture of both systems by thermal activated PDS followed a pseudo-first-order reaction kinetics model with or without fiber.The pseudo-first-order reaction rate constant kobs increases as the PDS concentration increases.When the initial concentration of PDS is the same,the degradation rate of protein model(BSA)is much greater than the degradation rate of polysaccharide models(glucose and dextran).The presence of fiber slightly increased the pseudo-first-order reaction rate constants of glucose or BSA at the same initial concentration of PDS,but the degree of influence was insignificant.Finally,Fe(Ⅱ)-activated persulfate technology was used to imprved the dewaterability of the simulated mixed sludge and activated sludge,and the Zeta potential,the size of floes and the changes of polysaccharides(PS)and protein(PN)in EPS were analyzed.From the perspective of kinetics,the mechanism of activated persulfate technology to improve sludge dewaterability was analyzed.The results showed that after the activated sludge or mixed sludge was pretreated by Fe(Ⅱ)-activated PDS(PDS:Fe(Ⅱ)was fixed at 0.8),the dewaterability of the actvated sludge and the mixed sludge deteriorated at low PDS dosage(such as 0.16 mmol/g VSS).When the PDS dosage was high(such as>0.4 mmol/g VSS),the sludge dewaterability were significantly improved.The effect of Fe(Ⅱ)-activated PDS on the sludge dewaterability was related to the Zeta potential of sludge,floe size and PS/PN variation(especially PN in TB-EPS and PS in S-EPS).The influence mechanism can be explained by the oxidative degradation of EPS by sulfate radicals and the flocculation of Fe(Ⅲ)on sludge particles.