Study On Efficient Degradation Of Waste Cooking Oil And Biobutanol Production By Mixed Fermentation

The development and wide utilization of new biomass energy has been supported by the national policy and has become the focus of national attention.During the period of energy reform,biofuels such as biobutanol are replacing fossil fuels and rebuilding the energy consumption structure.At present,using kitchen waste as butanol fermentation raw material effectively reduces the fermentation cost,which is reflected in: No complex pretreatment required.Kitchen waste is rich in nutrients and do not need fermentation additives.With the production of biobutanol,the fermentation process produces a amount of biohydrogen.Compared with western countries,China’s unique cooking culture and cooking habits promoted the consumption of edible oil,and the content of oil components in the kitchen is higher than western countries.However,the fermentation strain cannot use the oil in kitchen waste,and the oil and its hydrolysate were also the inhibitors of fermentation.Reduce the pretreatment steps of raw materials and the fermentation cost,increasing fermentation intensity,increasing yield and relieving fermentation inhibition have become urgent problem to be solved in biobutanol fermentation industry.The purpose of this study was to explore a new fermentation way to effectively hydrolyze waste cooking oil as a usable fermentation substrate for Clostridium,so as to reduce the cost of biobutanol fermentation.The results could provide a scientific basis for the application of biobutanol fermentation in the production of oily kitchen waste.In this study,a facultative anaerobic strain WO2 was rapidly isolated from the oil sludge polluted by waste cooking oil by anaerobic enrichment-aerobic screening method.It was identified as Pseudomonas aeruginosa WO2 by 16 S r DNA molecular biology.Through morphological observation and investigation of basic physiological characteristics,Pseudomonas aeruginosa WO2 could grow at 6% salinity and has great salt tolerance.It was found that under the initial culture conditions,the utilization rate of waste cooking oil could reach 86.5%,and the by-product was rhamnolipid,a glycolipid biosurfactant.The conversion rate of waste cooking oil was improved by studying the salt tolerance and oil treatment ability of bacteria,optimizing the culture temperature,inoculation amount,system p H,types of carbon and nitrogen sources.Under the condition of optimal utilization of waste cooking oil,the fermentation kinetics of the whole process was studied,and the p H of fermentation broth,lipase activity,cell biomass,utilization rate of waste cooking oil and rhamnolipid production were measured.The final results showed that when the inoculation amount was 4%,at 37℃,the p H of the system was 7.0 and the nitrogen source was peptone,the utilization rate of 1% waste cooking oil by Pseudomonas aeruginosa WO2 reached 92.25% and 3.03g/L rhamnolipid was produced.Considering the product yield,the optimal fermentation time is 96 h.Pseudomonas aeruginosa WO2 could quickly utilize 77.76% of waste cooking oil within 48 h.At 96 h,the utilization rate of waste cooking oil,rhamnolipid concentration and yield were 87.56%,3.08 g/L and 0.032 g/L /h respectively.Meanwhile,Pseudomonas aeruginosa WO2 has excellent utilization rate of waste cooking oil and salt tolerance and shows higher resistance to harmful environmental conditions.Pseudomonas aeruginosa WO2 has poor ability to use soluble starch and prefers to use oil component as its own growth substrate.This also means that when Pseudomonas aeruginosa WO2 is used to treat mixed substrates(such as oily kitchen waste),it can directionally consume oil and preserve starch component.After measure the component proportion of mixed school kitchen waste,it was found that the higher total sugar content means that Clostridium with strong starch utilization ability could use kitchen waste as the substrate for ABE fermentation.However,the content of waste cooking oil(also include fat)in kitchen waste was high,reaching 28.61 g/kg,and the content of protein(41.2 g/kg)was lower than that reported in other studies.The fermentation kinetics and kitchen treatment capacity of Clostridium sp.M6 were studied,and the kitchen concentration selected for co-culture strain M6 and WO2 was 270 g/L.Finally,the mixed fermentation system of Pseudomonas aeruginosa WO2 and Clostridium sp.M6 was constructed.The stability and fermentation mechanism of biobutanol production system by mixed fermentation were explored by investigating the difference of inoculation time between the two strains and the effect on fermentation performance.The results showed that when oxygen was not expelled from the interior of the serum bottle,the total amount of fermentation ABE solvent(Acetone,Butanol and Ethanol)was close to zero after the simultaneous inoculation of Pseudomonas aeruginosa WO2 and Clostridium sp.M6,and there was no hydrogen production.In the experimental group with treatment time of 12-48 h,obvious fermentation inhibition was observed.Only 0.27-0.43 g/L biobutanol was produced,and the production of ethanol,acetone and hydrogen approached zero.The fermentation inhibition of Clostridium sp.M6 could not be relieved by secondary sterilization and passivation of long-chain fatty acids in Pseudomonas aeruginosa WO2 fermentation broth at each pretreatment time.After 120 h of fermentation,0.32-0.56 g/L of biobutanol and very low concentrations of acetone and ethanol were detected.The concentration of biobutanol increased by 18-30% compared with that before secondary sterilization,while the hydrogen production of each control group was almost 0 mmol,which was not improved.The preliminary experimental results show that the pretreatment step of using Pseudomonas aeruginosa WO2 to remove oxygen from the medium and partially degrade waste cooking oil to virtual fatty acids inhibited the fermentation of Clostridium sp.M6.