Effect Of Electrochemical Pretreatment On Volatile Fatty Acids Production From Anaerobic Fermentation Of Waste Activated Sludge

Waste Activated Sludge(WAS)is a by-product of the wastewater treatment process,and its production is increasing year by year,and the reduction,environmentally sound and resourceful disposal of residual sludge is receiving more and more attention.Anaerobic Fermentation(AF)can achieve sludge reduction and resource utilization,and can produce high value-added Volatile Fatty Acids(VFAs).However,the hydrolysis stage is considered as the rate-limiting stage in the anaerobic fermentation process.Electrochemical pretreatment can disrupt the sludge cell wall and promote the leaching of organic matter from the sludge,thus increasing the rate and yield of acid production.Therefore,this paper investigated the effect of different factors(electrolyte type,electrolyte NaCl dosing,current intensity and pretreatment time,etc.)on the efficacy and mechanism of electrochemical pretreatment WAS stage and anaerobic fermentation VFAs production stage,and the main conclusions of this paper are as follows.Firstly,different influencing factors such as electrolyte type(e.g.,NaCl,CaCl2,Na2SO4),electrolyte NaCl dosage(M)(0,0.5,1,3 g/L),current intensity(I)(0,0.5,1,3A),and pretreatment time(T)(0,30,60,90 min)were investigated in the electrochemical pretreatment stage on the The effect of WAS efficacy.The results showed that NaCl as the electrolyte was the most effective;different settings of NaCl dosage,current strength and pretreatment time were positively correlated with the dissolved chemical oxygen demand(SCOD),dissolved protein and polysaccharide concentrations of the sludge supernatant.Multiple Linear Regression(MLR)simulations showed that the effects of different factors on the efficacy of WAS organic solubilization were in the following order: Current strength >electrolyte NaCl dosing > pretreatment timeSecondly,in the anaerobic fermentation stage,the effects of different current strengths(0,0.5,1,3 A),electrolyte NaCl dosage(0,0.5,1,3 g/L)and pretreatment time(0,30,60,90 min)on the effect of anaerobic fermentation of WAS on VFAs production were firstly investigated using single factor analysis;then the Box-Behnken model was used to investigate the effect of anaerobic fermentation of The Box-Behnken model was then used to simulate the relationship between the effect of anaerobic fermentation and the factors;finally,the changes of microbial community structure were compared;and the mechanism of electrochemical promotion of VFAs production from anaerobic sludge fermentation was investigated.The results showed that the optimum electrochemical pretreatment conditions were determined by single-factor analysis: current intensity of 1 A,electrolyte NaCl dosage of 1 g/L,and pretreatment time of 60 min.Under these conditions,the maximum yield of VFAs from anaerobic fermentation was 2625.79 mg COD/L on day 9,which was 51.55%higher than that of the non-pre-treated group.The results showed that the order of influence of each factor on the yield of VFAs was: pretreatment time > current intensity > electrolyte NaCl dosing.The response surface analysis showed that the appropriate range of factors was 1.0-1.3 A for current intensity,1.0-1.7 g/L for electrolyte NaCl,and 55-75 min for pretreatment time.The results showed that electrochemistry was beneficial to the screening and enrichment of acid-producing bacteria such as Proteobacteria,Firmicutes and Bacteroidetes.The above results indicated that under the optimal electrochemical pretreatment conditions,more total residual chlorine would be produced,which promoted the leaching of WAS organic matter and facilitated the screening and enrichment of acidproducing bacteria,and finally improved the yield of VFAs.