Study On The Effect Of Lactic Acid-rich Fermentation Liquid Of Food Waste As A Carbon Source On Biological Denitrification Process

At present,excessive nitrate concentration in the water environment has become a global environmental problem.Excess nitrate will not only damage the normal function of water bodies,but also adversely affect the health of plants and animals.Nowadays,many wastewater treatment plants in China have a shortage of carbon source in the influent water,so it is necessary to add an additional carbon source to ensure the effect of nitrogen removal and phosphorus removal.The high lactic acid content of lactic acid-rich fermentation liquid of food waste(FLFW)can be used as an external carbon source in wastewater treatment to achieve the goal of "treating waste with waste".In this study,the denitrification performance of FLFW,sodium lactate and sodium acetate,a traditional carbon source,were compared to analyze the applicability of FLFW as an carbon source.The main research results are as follows:(1)The C/N ratio of FLFW as the denitrification carbon source was 8 to meet the denitrification demand,and the denitrification rate was accelerated by increasing the C/N ratio,and the most suitable pH condition was 8,when the COD and TN removal rate was fast and the NO2--N accumulation was less.Compared with the denitrification effect of FLFW and sodium lactate and sodium acetate,the NO3--N removal rates of FLFW and sodium lactate were higher,and the TN and COD removal rates of FLFW were 82.21%and 84.29%,respectively.(2)The SBR reactor was used in the study,and by comparing with the traditional carbon source sodium acetate,the inlet NH4+-N was 32 mg/L.When the COD was 200 mg/L,the TN removal rates of sodium lactate and sodium acetate were 51.44%and 64.45%,the denitrification effect of sodium acetate was better than that of sodium lactate;when the COD was 300 mg/L,the TN removal rate of the two systems was comparable and both reached the highest value,with 85.73%for sodium lactate and 83.04%for sodium acetate.When the COD was 400 mg/L,sodium acetate obviously inhibited the nitrification process,and the TN removal rate of the system was lower,only 56.51%,while the sodium lactate system had good denitrification effect.The microbial species and proportion were similar in the two systems,indicating that sodium lactate and sodium acetate had similar bioavailability as carbon sources.The high abundance of Ferruginibacter,which can secrete a large amount of extracellular polymer in the sodium lactate system,demonstrated that sodium lactate is prone to cause sludge agglomeration and swelling.(3)In the AAO reactor,the response time of sodium lactate and FLFW as carbon source was short,and good COD removal and nitrogen and phosphorus removal could be achieved within 10 d.The effluent could reach the primary A standard in all three stages of stabilization period.The removal effects of FLFW and sodium lactate were comparable,with COD removal rates of 92.40%and 91.59%,and TN removal rates of 96.68%and 98.27%,respectively.The N and P concentrations of the effluent increased and the water quality was not clarified by the 110th day of operation,probably because the sludge expansion led to sludge loss,sludge concentration decreased and the balance of microbial system was broken.Sludge swelling was observed in the AAO reactor on the 10th day,and the swelling increased with time.The extracellular polymeric substances(EPS)of sludge content increased and PN/PS decreased,and the sludge dewatering performance decreased;microscopic examination revealed that the sludge floc volume increased and the internal space decreased,and there were filamentous bacteria protruding from the floc,so it was inferred that the sludge swelling might be the result of the combined effect of the increase of sludge EPS and the proliferation of filamentous bacteria.(4)The dominant species in the AAO reactor were Azospira,Dechloromonas and other dominant genera with denitrifying bacteria,indicating that sodium lactate and FLFW were effective as carbon sources for denitrification and had good bioavailability.The surge of unclassified_o_Burkholderia to 43.35%at the late stage of FLFW as carbon source operation led to the destabilization of the microbial system,which might be the reason for the deterioration of the effluent.The results of macrogenomic assay showed that the abundance of genes related to denitrification such as narGHI,nirKS and norBC in the FLFW as carbon source system was comparable to that of the original sludge,which further corroborated the good utilization of FLFW as denitrification carbon source from the molecular perspective.