Preparation Of External Carbon Source For Wastewater Treatment By Anaerobic Fermentation Of Kitchen Waste And Its Denitrification Performance Evaluation

At this stage,the carbon source in raw water can not meet the requirements of denitrification and denitrification,so it is necessary to add carbon source.The commonly used additional carbon sources include sodium acetate,methanol,etc.However,the cost of such additional carbon sources is high and there is a risk of deteriorating the tail water of the sewage treatment plant.The cost of preparing carbon source by anaerobic fermentation of food waste is low,and the volatile fatty acids(VFAs)in the fermentation products are excellent additional carbon source substances.At this stage,different processes and technologies are often used for the treatment of food waste and kitchen waste.Mixing food waste and kitchen waste according to a certain proportion as anaerobic fermentation substrate can solve the problem of limited hydrolysis and acidification in the separate anaerobic fermentation of food waste,and provide a new way for the resource utilization of food waste and kitchen waste.Based on the analysis of the basic physical and chemical properties of kitchen garbage and kitchen garbage,the optimal proportion of carbon source prepared by mixing them was determined,and the key process parameters of carbon source preparation were optimized.Finally,the denitrification performance of the prepared carbon source was evaluated based on denitrification test.The conclusions are as follows:1)In this study,the C/N ratios of kitchen waste and kitchen waste were 30.52 and15.44,respectively.The C/N ratio in the fermentation system could be adjusted by mixing the two,and the two substrates were suitable for the preparation of carbon sources for anaerobic fermentation.The higher the proportion of kitchen garbage,the higher the VFAs concentration,hydrolysis rate and acidification rate in the fermentation system.When the proportion of kitchen garbage was more than 20%,the ratio of COD/NH₄⁺-N in the fermentation system decreased rapidly,indicating that the mixed anaerobic fermentation of kitchen garbage and kitchen garbage has advantages in preparing carbon sources.However,the larger the proportion of kitchen garbage is,the worse the mass transfer effect of the system is,so 8:2 is determined as the optimal mixing proportion.After the end of anaerobic fermentation,the Thick-Walled Fungi and Actinomycetes related to hydrolytic acidification in the system occupied an absolute advantage,indicating that the fermentation process remained at the hydrolytic acidification stage.2)By optimizing the p H in the fermentation process,the results showed that under the condition of p H 9,the acidification rate(13.30%)and hydrolysis rate(32.15%)were higher,and the hydrolysis and acidification rates were significantly higher than those under other conditions.Based on the carbon source preparation efficiency,the optimal p H of the fermentation system was controlled at p H 9.By optimizing the initial organic load in the fermentation process,the results showed that when the initial organic load TS was 6%,the acidification rate was 19.67%,but the hydrolysis rate was greatly improved,up to 91.13%,indicating that the initial organic load in the system was the main reason to limit the hydrolysis rate.Therefore,the initial organic load TS=6%is determined as the optimal initial organic load.By optimizing the fermentation temperature,the results showed that when the fermentation temperature was 35°C,the acidification rate and hydrolysis rate of the system were the best,which were 45.19%and 98.23%,respectively.When the fermentation time was controlled to 4 d,the hydrolysis rate in the fermentation system was up to 68.57%,and the acidification rate was only reduced to 31.50%.The fermentation time was controlled to 4 d from the perspective of fermentation efficiency and acidification rate.3)The SCOD content in the fermentation broth was 27996.45 mg/L,which was a high organic matter liquid.The content of N and P in the fermentation broth was relatively low,which were 398.66 and 27.29 mg/L,respectively,which could ensure that sufficient carbon source was provided for the biological treatment of sewage without reducing the effluent quality.Based on the denitrification performance evaluation experiment,at the end of denitrification,when the COD/N of fermentation broth and sodium acetate were 6,the average denitrification rates of the two were 7.28mg NO₃-N/(g MLVSS·h)and 8.77 mg NO₃-N/(g MLVSS·h),respectively.Under the same COD/N,the average denitrification rate of fermentation broth was lower than that of sodium acetate.When the COD/N ratio was 6,the fermentation broth could provide sufficient energy for NO₂-N reduction,and the utilization rate of COD reached83.67%.The TN removal rate was almost the same as that of sodium acetate,and the difference of denitrification capacity was small.Considering the yield,yield and cost of fermentation broth,fermentation broth can be used as an alternative denitrification carbon source for sodium acetate.