| In recent years,the continuous development of the economy and the continuous growth of the population have led to a continuous increase in the amount of food waste and waste activated sludge.Food waste and waste activated sludge are important components of municipal solid waste.If they are not properly handled,they will cause harm to the environment.As a mature and effective energy recovery technology,anaerobic co-digestion is usually used to treat the food waste and waste activated sludge.However,the composition of food waste varies greatly from region to region.As a vegetable and condiment,pepper is widely used in food preparation,which leads to the accumulation of capsaicin in food waste.However,the effect of capsaicin on the anaerobic co-digestion of food waste and excess sludge and its mechanism are still unclear.In this paper,the fate of capsaicin in the process of anaerobic co-digestion were investigated by using a sequencing batch reactor,and investigated the presence of different concentrations of capsaicin（2,8,20,36 mg/g VS）on methane production during anaerobic co-digestion.The kinetic model is used to fit the cumulative production of methane,and the effect of capsaicin on the kinetic parameters of the anaerobic co-digestion process is further analyzed.It was found that capsaicin was degraded by anaerobic microorganisms in the process of anaerobic co-digestion,and on the 12 day,the concentration of capsaicin in the reactor was less than 1 mg/L.As an organic matter,capsaicin could be converted into methane during the degradation process,but the conversion rate was low.Secondly,the results showed that the presence of capsaicin will inhibit the methane production during the anaerobic co-digestion of food waste and waste activated sludge,and as the capsaicin content increases from 2 mg/g VS to 68 mg/g VS,the methane production increases from 2 mg/g VS to 68 mg/g VS.274.6±9.7m L/g VS was reduced to 188.9±8.4 m L/g VS.The results of kinetic analysis show that the presence of capsaicin not only reduces the maximum methane production potential of the anaerobic co-digestion process,but also reduces the maximum methane production rate.At the same time,it extends the lag time of methane production.The half-inhibitory concentration of anaerobic co-digestion is 36.26 mg/g VS.Based on the above research,the effects of capsaicin on different stages of anaerobic co-digestion were discussed.The results show that the presence of capsaicin promotes the solubilization of organic matter,but at the same time inhibits the subsequent hydrolysis,acidogenesis and methanogenesis stages.Through the non-competitive inhibition model,the inhibition degree of capsaicin on different stages of anaerobic co-digestion was obtained in the order of acetoclastic methanogenesis>hydrogenotrophic methanogenesis>acidogenesis>hydrolysis.By analyzing the activity of capsaicin on the key enzymes involved in anaerobic co-digestion,the physiological state of microorganisms and the structure of microbial community,it is found that the presence of capsaicin will inhibit the participation of anaerobic co-digestion,especially the activity of key enzymes involved in acetylation of methanogenesis,and inhibiting effect is proportional to the concentration of capsaicin.At the same time,the presence of capsaicin can affect the physiological state of anaerobic microorganisms,destroy the cell membrane of microorganisms to induce apoptosis;it can also change the microbial community structure in the reactor.In the presence of capsaicin,the relative abundance of bacteria involved in the hydrolysis and acidification stage was reduced from 42.6%to 14.8%,and the relative abundance of bacteria with the ability to degrade organic pollutants was increased from 20.4%to42.4%.Finally,Ca O2 pretreatment was used to improve the inhibitory effect of capsaicin on anaerobic co-digestion.As a result,capsaicin could be degraded quickly and effectively,and the optimal dosage of Ca O2 was 0.05g/g.Ca O2pretreatment not only mitigates the inhibitory effect of capsaicin on methane in the anaerobic co-digestion process,but also shortens the lag time of methane production and increases the maximum methane production rate. |
