Study On Carbon Source Recovery From Food Waste Fermentation And Its Application In Nitrogen Removal Enhancement

Insufficient carbon source is an important barrier for high nitrogen removal efficiency,and supplying carbon source is a reasonable solution for this issue.Food waste is one of the main organic components of municipal solid waste,and contains high content of organics.Based on the principle of “use waste to treat waste”,carbon source production from food waste has become a hot topic in the field of water environment.Accordingly,food waste from a university campus was used as the substrate to produce carbon source in this study,which was systematically explored during the thermophilic free fermentation and mesophilic lactic acid fermentation.The denitrification features of the fermentation products were discussed,and their application in an A/O-MBR system was also investigated focusing on the nitrogen removal efficiencies and membrane fouling behaviour.The main results were:(1)The strategies for carbon source recovery were provided: controlling the anaerobic fermentation at hydrolysis and acidogenesis stage to efficiently produce the carbon source.The thermophilic free fermentation(55°C and uncontrolled pH)could promote the hydrolysis,and the carbohydrates were the main products;the mesophilic lactic acid fermentation(37°C and pH adjusted to 6 intermittently)was favor for acidogenesis,lactic acid bacteria(Lactobacillus)accumulation,and could reach the highest LA yield at the organic loading rate(OLR)of 14 g-TS/L·d.Higher OLR was not suitable for lactic acid fermentation.(2)Lactic acid fermentation using different types of inocula was compared.It was found that the highest lactic acid yield and lowest organics loss were obtained using raw food waste as inocula.Based on the analysis of microbial community structures,it was clarified that although the huge microbial diversity existed in the inocula,the Lactobacillus could be accumulated and became the dominant cultures under the optimized conditions,which promoted the transformation rate of substrate into carbon source.(3)The dynamic membrane-assisted lactic acid fermentation technique was investigated.It was found that the dynamic membrane(DM)could retain the particulate organics,lengthen the retention time of the substrates,accumulate the bacterial population,enhance the microbial enzymes,and significantly promote the lactic acid yield.Additionally,the DM fermenter could continuously separate the soluble fermentation products and promote the fermentation efficiency.(4)The transformation pathway of the organics(“carbohydrate?lactate?VFAs”)during the mesophilic acidogenic fermentation and the variations of microbial community structures were investigated.With the non-fermented,partially fermented fermentation products,and fermentation products mainly containing lactic acid and VFAs as carbon sources in denitrification tests,it was found that the fermentation products mainly containing lactate exhibited higher denitrification rate and potential,and could realize complete denitrification at a C/N ratio over 6.With this type of fermentation product as carbon source in a SBR for low C/N municipal wastewater treatment,it was found that the SBR could be stably operated with high nitrogen removal,the bacterial metabolic capacity was obviously enhanced,and the microbial diversity was very high.(5)The fermentation products of thermophilic free fermentation mainly contains carbohydrates,and could exhibit satisfactory denitrification potential.Moreover,the particulate organics in the fermentation product could also be completely degraded,showing a high nitrogen removal rate.Using the fermentation products in a pilot-scale A/O-MBR system for treating low C/N ratio wastewater,it was found that the reactor could be stably operated,the microbial metabolic capacity obviously increased,and the nitrogen removal efficiency obviously increased.Some facultative bacteria which could degrade the SMP and other complicated organics enriched in the reactor,and the relative abundance of denitrifying bacteria obviously increased.After adding the FLFW,no obvious accumulation of EPS was observed,and the DOM decreased along the reactor array.The cake layer could effectively retain some foulants and the membrane was not irreversibly fouled during the long-term operation.