Effect Of Activated Sodium Persulfate Pretreatment On Anaerobic Fermentation Of High Solid Excess Sludge

In recent years,with the acceleration of urbanization in China,the sludge output has gradually increased.How to properly deal with sludge has become a widespread concern in society.The traditional anaerobic digestion technology treats low-solids sludge(Total solids,TS=2～5%),while low digestion efficiency and high operating cost limit its application in sewage treatment plants.However,the high-solids sludge anaerobic digestion system has become one of the important trends in the development of sludge anaerobic digestion technology due to its small facility size and high sludge resource efficiency.In this experiment,activated sodium persulfate(PS)technology was used to pretreat dehydrated sludge(TS≥10%)in sewage treatment plant,and the optimal pretreatment conditions were explored by measuring VFAs,SCOD and other conventional indicators;three-dimensional fluorescence spectrum analysis,kinetic model and microbial sequencing technology were used to characterize the experimental sludge,and the influencing factors of activated PS pretreatment technology on anaerobic digestion of high solid sludge were revealed.The research contents are as follows:(1)With iron powder as activator,the effect of different concentrations of PS on the acid production of sludge anaerobic fermentation was investigated under the condition of fixed PS/Fe dosage.The results showed that the production of VFAs in the sludge increased by 35.30%and the sludge disintegration rate(DD)increased by 11.62%under the conditions of pH=10,PS and Fe dosage of 1.5 and 1.875 mmol·(g TS)-1 respectively.The analysis of sludge fermentation liquid showed that the final metabolites of pyruvic acid in this experiment were short-chain fatty acids such as acetic acid,and lactic acid was completely degraded during the fermentation process,while humic acid in sludge could be effectively degraded by strong oxidizing free radicals produced by activated PS.(2)The types and dosages of activator were changed to explore the promotion effect of activated PS by Fe and FeSO4 on sludge anaerobic digestion when PS concentration was fixed at 1.5 mmol·(g TS)-1.The results showed that:the VFAs production increased by 85.13%compared with the control group when the PS/Fe ratio reached 0.5 in alkaline environment;after switching to FeSO4,the VFAs yield increased by 57.85%when the PS/Fe2+was 0.8;it was also found that the proportion of acetic acid in the sludge pretreated by activated sodium persulfate increased,while the proportion of short chain fatty acids such as propionic acid and butyric acid decreased slightly.(3)It can be inferred from the analysis of organic matter concentration that the utilization degree of protein,polysaccharide and other substances in the reactor with excellent acid-producing capacity was higher than that in the control group;when too much Fe2+existed in the reaction system,the Fe3+generated in the activation process would coagulate and precipitate with macromolecular organic matter,and reduce the concentration of soluble organic matter.(4)Chen-Hashimoto model was used to simulate the anaerobic fermentation process of high-solid sludge.It was found that activated PS pretreatment technology had a low negative effect on the activities of hydrolytic and acidproducing bacteria;and the combination of appropriate activator and PS could effectively improve the hydrolysis rate and substrate utilization simultaneously.(5)In order to reduce the cost of activated PS pretreatment of high solid sludge,coconut shell granular activated carbon was used as the activator.It was found that when the activated carbon dosage was 0.65 g·(g TS)-1,the VFAs yield in sludge was increased by 28.43%and the acetic acid concentration was increased by 48.98%compared with the control group.The concentration of SCOD in sludge increased by 19.2%,which effectively promoted the hydrolysis process of sludge to produce acid under these conditions.(6)Microbial sequencing results showed that activated PS pretreatment could change the microbial community structure.Firmicutes and other bacteria that can effectively resist the interference of external factors were enriched in the anaerobic fermentation process,which dominated the hydrolysis and acid production process of sludge;the abundance of bacteria with VFAs as substrate,such as Chloroflexi at phylum level and norank_o_MBA03 at genus level,decreased after pretreatment,which reduced the consumption of VFAs and was more conducive to the accumulation of it.