Effect Of Feeding Frequency On Stability And Kinetic Characteristics Of Mesophilic Co-digestion Of Food Waste And Waste Activated Sludge

With the rapid development of modern industry and the acceleration of urbanization,the food waste?FW?and waste activated sludge?WAS?has also increased.Although the co-digestion of FW and WAS can effectively overcome the drawback of mono-digestion,stable performance was still difficult to be achieved at high organic loading rate?OLR?.In many researches,continuously stirred tank reactor?CSTR?with low feeding frequency?one or more times a day?is a common choice for organic waste digestion.However,the low feeding frequency often leads to a high loading shock at the initial stage of feeding thus aggravates the imbalance between hydrolysis,acidogenesis and methanogenesis,and subsequently results in the severe accumulation of volatile fatty acid?VFA?.Therefore,in this study,in order to explore whether the load impact at the initial stage of feeding can be alleviated by increasing the feeding frequency,thus inproving the stability of the system,the continuous co-digestion experiments and the batch tes were used to analyze the efficiency,stability and kinetic characteristics of the feeding frequency to the co-digestion.in order to determine the optimal feeding frequency for efficient and stable co-digestion.Meanwhile,the kinetic characteristics of methanogensis of individual VFA were also analyzed to know the reason for instable performance.the specific methanogenic activity experiment were also analyzed to explore the influence of feed frequency on VFA accumulation process in the system,main results were shown belowand:?1?When the feeding frequency is high,the gas production,methane production and ts removal rate increased slowly with the decrease of feed frequency,and CH₄ and CO₂ content,pH alkalinity and VS removal rate did not fluctuate significantly.When the feed frequency was reduced to 2 times/d,the gas production,methane production and ts removal rate reached the highest,15.95 L·d^-1,9.44 L·d^-11 and 54.19%,respectively,The alkalinity was significantly reduced.When the feed frequency was further reduced,the alkalinity was further reduced,and the removal rates of ts and vs were rapidly reduced.vfa accumulated in the system,with an average concentration of4.25 g-COD·?L·d?^-1,which was much higher than VFAs inhibition concentration(1.4g·L^-1).propionic acid accounted for 53.20%of TVFA,and valeric acid began to accumulate in a small amount.?2?Through the efferts of loading shock on mesophilic co-digestion of FW and WAS,it was showed that in a feeding period,the variation of gas composition,SCOD and pH were not significant,biogas production increased almost linearly without VFA accumulation at the high feeding frequency.With the decrease of feeding frequency,the fast hydrolysis and acidogenesis led to the increase of SCOD and VFA concentration at the beginning of the feeding period,then gradually decreased,and resulted in the significant fluctuation of p H and methane percentage in biogas.At the feeding frequency of 1 time/d,the content of methane dropped to 45.4%.The concentration of propionic accounted for 87.9%of TVFA.?3?By comparing the kinetics of methanation of sodium acetate and sodium propionate at each feed frequency,it can be seen that the maximum methanogenesis rates of acetic acid and propionic acid increased first and then decrease as the feed frequency decreases.The maximum methanogenesis rates reached the highest at the feed frequency of 3 times/day,which was 9.06 mL·h^-1 and 6.20 mL·h^-1.At the same time,the maximum methanation rate of acetic acid is significantly higher than that of propionic acid,which should be one reason for the poor stability in low frequency feed systems that cause the accumulation of propionic acid.