Mechanism Research On Anaerobic Fermentation Process Of Edible Oil In Domestic Sewage

To solve the current oily domestic sewage and farm manure treatment and energy shortage problem,this research proposed to use the oily domestic sewage and farm cattle manure for anaerobic fermentation.The effects of oil in domestic sewage on the biogas properties,pH.biodegradation,enzyme activity and microbial community structure were studied to reveal the mechanism of oil in domestic sewage on anaerobic fermentation process.The results showed that:(1)The biogas property of oil addition promoted the efficiency of anaerobic fermentation process of sewage and cow manure at low concentrations while inhibited the process at high concentrations.The modified Gompertz equation well fitted the cumulative biogas yields curve.The cumulative biogas yield of sewage+2 g oil group was the highest,which was similar to that of sewage+1 g oil group.The biogas yield rate of sewage+1 g oil group was maximum,and the lag period was shorter-than that of sewage+2 g oil group.Therefore,the sewage+1 g oil group was more in line with the requirements of engineering practice.(2)Compared with the oil-free group,the cumulative biogas yield and CH4 content of the sewage+1 g oil group in anaerobic fermentation were increased,in spite of the lower peak daily biogas yield.In the ear-ly stage of fermentation,the hydrolysis and acidification of oil in the sewage+1 g oil group produced a large number of acids,which induced lower pH values than the oil-free group,and further impacted the system stability of anaerobic fermentation.With the progress of the reaction,the pH values of both groups rose and eventually stabilized.During the whole anaerobic fermentation process,the average NH4’-N content of the sewage+1 g oil group was lower than that of oil-free group,however,the total VFA concentration was higher.The lignocellulose content of the sewage+1 g oil group was higher than that of oil-free group,which indicated that the degradation of lignocellulose in the oil-free group was more efficient than the sewage+1g oil group.The addition of oil changed the enzyme activity during the anaerobic fermentation process.In the sewage+1 g oil group,the biogas yield and CH4 content were enhanced by increasing the activity of coenzyme F420.(3)The addition of oil led to the variation of microbial community structure.The diversity of bacteria and archaea in the sewage+1g oil group was higher than that in oil-free group,indicating that the introduction of oil promoted the metabolic growth of microorganisms.The relative abundance of bacteria and archaea in sewage+1 g oil group was higher in phylum and genus than in oil-free group,which manifested that oil addition promoted the development of microbial community.During in the anaerobic fermentation process.acid-producing CH4 was dominant in both groups.(4)The actual domestic sewage was pretreated by ozone,and the domestic sewage before and after pretreatment was fermented with cow manure.The results showed that in the absence of oil,the biogas yields of the pretreated group without oil addition were higher than the group without pretreatment,indicating that ozone pretreatment effectively improved the biogas yields of anaerobic fermentation by increasing the soluble organic matters in the pretreated sewage.However,in the presence of oil,ozone pretreatment went against the biogas production,which meant that sewage without treatment was more suitable for anaerobic fermentation.This study explored the mechanism of oil in domestic sewage on anaerobic fermentation process.The results showed that the introduction of oil effectively improved the biogas properties of anaerobic fermentation.This research further revealed the variaiton of fermentation indexes during in the anaerobic fermentation process and the mechanism of oil in domestic sewage on anaerobic fermentation process,which provided a new idea for the treatment of oil polluted domestic sewage and the development of clean energy.