Effect Of Organic Modified Bentonite On Anaerobic Co-digestion Performance Of Residual Sludge And Kitchen Grease

With the rapid development of the construction of sewage treatment facilities in China,the production of residual sludge(RS)is also increasing significantly.As a by-product of the sewage treatment,the production of RS has also increased.Anaerobic digestion can achieve sludge reduction,stabilization and harmless treatment while obtaining valuable biomass energy at a lower cost at the same time.Kitchen dewatered grease(KDG)is a kind of municipal waste with high organic content.The co-digestion of RS and KDG has many advantages,such as improving the C/N ratio of the digestive system,providing more balanced nutrients,increasing methane yield,and balancing pH.As a mineral powder with the ability of ion exchange,bentonite is often used as a n ammonia nitrogen adsorbent/binding agent to buffer the inhibition of excessive ammonia nitrogen accumulation to maintain digestive system stability and improve methane production.Bentonite,especially organically modified bentonite,has a good adsorption properties for fat,oil and grease.It can avoid the adsorption of difficult-to-metabolize long-chain fatty acids(LCFA)on the surface of microbial cells,and alleviate LCFA inhibition of biological metabolism.Therefore,the addition of bentonite or organic modified bentonite on anaerobic digestion can improve the utilization efficiency of microorganisms on KDG and increase methane production.In this paper,the effects of bentonite and organic modified bentonites on anaerobic digestion were studied.Four anaerobic digestion batch experiments were carried out: the effect of organic modified bentonite on anaerobic digestion performance of RS;study of optimum dosage of bentonite and organic bentonite in anaerobic co-digestion of RS and KDG;the effect of bentonite and organic bentonite on anaerobic co-digestion performance of RS and KDG;study on the promotion of hydrolysis in anaerobic co-digestion of RS and KDG with bentonite and organic bentonite addition.In the anaerobic digestion of RS,bentonite increased the specific methane yield(SMY)by 19% and 21%,respectively,at the dosage of 0.4 and 1.0 g/g VS.The CTMAB modified bentonite increased the SMY by 5% at a dosage of 0.4 g/g VS.The SDBS modified bentonite increased the SMY by 3.2% and 20%,respectively,at the dosage of 1.0 and 2.5 g/g VS.Bentonite not only promoted the SMY,but also increased the proportion of acetic acid in volatile fatty acids(VFA),which is beneficial to improving methane production.In the anaerobic co-digestion of grease/sludge(G/S,VS)ratio = 1,the addition of bentonite has a limited improvement on gas production performance.Under the condition of G/S=2,the addition of bentonite has a obvious improvement on methanogenic performance.When the dosage of bentonite was 0,100,200,400,800 mg/gVS,the cumulative methane production was 336,513,420,468,and 637 mL,respectively.The addition of bentonite mostly increased the cumulative methane production by 89.6%.Under the condition of G/S=2,CTMAB modified bentonite promoted the digestion and methanogenesis better.It promotes cumulative methanogenesis by 44.1% and 56.8% respectively under the dosage of 0.1 and 0.2g / gVS.Through the monitoring of pH,SCOD and fatty acids in the digestion process,it can be inferred that the addition of CTMAB modified bentonite promoted hydrolysis stage of anaerobic digestion.Further experiment under the G/S=2 condition found that in the early stage of digestion(the first 3 days),the addition of natural bentonite increased the SCOD concentration by 25%,the polysaccharide concentration by 8.2%,and the protease activity by 26.3%,compared with the control group.The addition of CTMAB modified bentonite increased the SCOD by 17%,the soluble protein by 20.5%,the polysaccharide by 23.2%,and the protease activity by 29.6%.The addition of SDBS modified bentonite increased the SCOD by 51%,the soluble protein by 59%,the polysaccharide by 39.7%,and the protease activity by 46.9%.The addition of natural bentonite and SDBS modified bentonite accelerated the accumulation of LCFA by about 6.8% and 176%,respectively.The test results prove that the addition of bentonite,especially SDBS modified bentonite,helps to promote the hydrolysis of the digestive substrate.The results of three-dimensional fluorescence spectroscopy indicated that the addition of bentonites increased the concentration of various DOM in the digestive fluid,and the improvement effect was ranked as SDBS modified bentonite > CTMAB modified bentonite > natural bentonite.According to microbial community analysis,the addition of bentonite native soil to the digestive system helps to increase microbial community diversity and richness.The addition of SDBS modified bentonite helps to increase microbial community richness.The CTMAB modified bentonite effectively increased the proportion of acetic acid metabolizing methanogens in archaeal communities,which is of great significance for increasing methane content in bio gas.