Study On Anaerobic Co-digestion And Rheology Of Food Waste And Sludge

This paper systematically studied the physico-chemical properties（soluble organic matter,methane production,dewatering,particle size,etc.）,rheological properties（apparent viscosity,yield stress,thixotropy,etc.）and changes in the microbial community（archaea and bacteria）of anaerobic digestion under different mixing ratios of 170℃thermally hydrolyzed sludge and food waste.A linear relationship was established between rheology and physico-chemical properties.Besides,the mechanism of methane production was analyzed from the perspective of microorganisms.The main conclusions are as follows:（1）During the anaerobic digestion,the dissolved organic matter is reduced,and the proportion of food waste is larger,the release amount is greater.The p H and alkalinity in the system gradually increase.After the anaerobic digestion,the particle size of the material becomes smaller,the range of distribution becomes narrower,and the distribution becomes more concentrated.Compared with the single-substrate anaerobic digestion of thermally hydrolyzed sludge,the dewatering is improved when the mixture ratio of the thermally hydrolyzed sludge and the food waste is 3:2,and the dewatering of other ratios becomes worse,and the larger the proportion of food waste,the dewatering worse.（2）The gas production after mixing food waste and sludge is higher than that of sludge single-substrate anaerobic digestion.Moreover,the mixed matrix will reach the peak of gas production earlier than the single-substrate anaerobic digestion of thermally hydrolyzed sludge.The single-substrate anaerobic digestion of thermally hydrolyzed sludge showed a gas production peak on the 13th day,while the mixed substrate produced two or three gas production peaks during the AD process.The reactor with the largest cumulative gas production is the reactor with a VS ratio of sludge to food waste of 1:1.The gas production is 14.46 times higher than that of the single-substrate anaerobic digestion of thermally hydrolyzed sludge.（3）In the process of anaerobic digestion,at the same shear rate,the apparent viscosity of the A、C、D、E and F reactor gradually decreases with the time of anaerobic digestion,while the apparent viscosity of the food waste and the independent anaerobic digestion reactor B,the viscosity first decreases and then increases.After the end of anaerobic digestion,for the ABDEF reactor,the apparent viscosity is significantly reduced at a lower shear rate(0-200s^-1).At higher shear rates(200-1000s^-1),the apparent viscosity basically stabilizes.For the C reactor,the apparent viscosity is very small in the entire shear range.（4）After anaerobic digestion,the yield stress in the reactor where food waste and sludge are mixed is reduced compared with that of a single substrate.In addition,the flow behavior index n increases,the consistency coefficient k decreases,and the thixotropy disappears.This shows that co-digestion improves the fluid flow performance better.In addition,the release of soluble COD is positively correlated with the flow behavior index n,and negatively correlated with the consistency coefficient k.Dewatering is linearly related to yield stress.The greater the yield stress,the worse the dehydration performance.（5）The mixed digestion of food waste and thermally hydrolyzed sludge reduces the diversity of archaea and bacteria,and the greater the content of food waste,the lower the diversity of microorganisms.In addition,there is a big difference in the microbial community between the reactor for anaerobic digestion of food waste and other reactors.（6）Archaea at the genus level are mainly Methanothrix,Methanomassiliicoccus,Methanobacterium,Methanomethylovorans,unclassified＿Euryarchaeota,Methanosarcina,Methanosphaera,Methanoculleus and Methanospirillum.In the ACDEF reactor,Methanothrix is the first genus and the dominant species.It is a methanogen with acetic acid as the nutrient type,which can produce methane through the decarboxylation of acetic acid.Methanosarcina is the dominant strain in the B reactor.It can use acetate,H₂,CO₂,and methylated one-carbon compounds as substrates to produce methane.It is a mixed high-efficiency methanogen（7）Firmicutes,Bacteroidetes,Proteobacteria,Cloacimonetes,Synergistetes,Chloroflexi,Atribacteria,Actinobacteria and unclassified＿Bacteria are the main bacteria at the phylum level.unclassified＿Bacteria is the dominant bacteria species in the reactor for anaerobic elimination of thermally hydrolyzed sludge.Proteobacteria are the dominant bacteria in food waste and the B reactor for separate anaerobic digestion.For other reactors,Firmicutes is the dominant strain.