Study On Short Chain Fatty Acids Of Co-fermentation With Ultrasonic Pretreatment Sludge And Food Waste

In recent years,the amount of sludge is increased greatly with the increasing capacity of urban sewage treatment in China.The reduction,stabilization and resource of excess activated sludge?EAS?have become the important research topics in the field of environmental protection.The anaerobic fermentation of excess activated sludge and food waste is one of the effective solid waste disposal methods.A large amount of organic matter in the substrate,such as total volatile fatty acid?TVFAs?,could be reused as the external carbon source of sewage biological treatment system.Sequencing batch test was used to investigated the effect of ultrasonic pretreatment and sludge concentrationon on the anaerobic fermentation of excess activated sludge.The results showed that the dissolution effect of SCOD,protein and polysaccharide were proportional to the energy density.The TVFAs accumulation concentration of ultrasonic sludge was significantly increased compared with the untreated sludge.The best condition for promoting the accumulation of TVFAs was:5W/mL of energy density of sound,5 d of anaerobic fermentation time.The production of TVFAs was promoted by increasing the concentration of sludge,while there was little effect on the amount of ammonia nitrogen and phosphate from unit sludge digestion.The degradation rate of substrate and the conversion rate of acid production were better when sludge concentration was 80 g·L^-1.Then the effect of mass ratio on the co-fermentation process with excess activated sludge and food waste was investigated.The organic matter dissolution of fermentation system and the variation of organic matter degradation of substrate were also discussed.The results revealed that the co-fermentation of organic matter dissolution rate and the degradation rate of protein and carbohydrate could be promoted when excess activated sludge added with food waste.But the high proportion of food waste?>75%?was not conducive to the improvement of TVFAs production.The TVFAs concentration achived highest when the mass ratio of excess activated sludge and food waste was 50%:50%?the initial C/N ratio was 21?,while the total amount of acetic acid and butyrate acid reached 80%.Different hydrolysis rate constants lead to different VS degradation rate,the hydrolysis rate constants of the system from high to low was to follow: EAS:FW =50%:50% > 25%:75% > 0:100% >75%:25% > 100%:0,which was consistent with the law of substrate degradation rate.Response surface methodology?RSM?was used to optimize the conditions of co-fermentation with excess activated sludge and food waste in order to improve theacid production.The individual and interactive effects of pH value,substrate concentration,organic loading rate?OLR?and solid retention time?SRT?on TVFAs production were investigated in this paper.The results showed that influence order on the TVFAs production of each factor in response surface model was as follows: pH value >OLR > SRT > substrate concentration.The optimum condition derived by RSM was pH,6.72;substrate concentration,80.93 g·L^-1;OLR,8.94 g TS·?L·d?^-1 and SRT,9.68 d.Under the optimal condition,the total volatile acid production reached29.23³0.78 g·L^-1,the relative error between experiment and model predictive value was 0.022 to 0.031,and the average yield of TVFAs reached 0.46 g·g^-1 VS.Fermentation liquid of excess activated sludge and food waste was applied as external carbon source to investigate the availability of denitrification,while the effect of fermentation liquid on domestic sewage was proved.The results showed that the proportion of TVFAs in the fermentation liquid was significant on the denitrification performance.The higher the proportion of acitic acid was,the corresponding ratio of denitrification rate?? value?was higher.When the experiment condition of anaerobic fermentation was at pH value of 7.0,substrate concentration of 120 g·L^-1,OLR of 8 g TS·?L·d?^-1 and SRT of 8 d,a superior performance of denitrification was obtained when the fermentation liquid was used as external carbon source,and the maximum specific denitrification rate of ? value achived to 14.2mg·?g VSS·h?^-1.The utilization of fermentation liquid as carbon source for authentic domestic sewage denitrification was proved to be at the optimal situation when the COD/NO3--N ratio was at 6.At the optimal situation,the removal of total nitrogen was exhaustive.