Effects Of Citrus Pulp And Garden Waste On Anaerobic Digestion Of Excess Sludge

The anaerobic digestion experiments were carried out on the citrus waste and the campus leaves,representing the urban fruits and vegetables waste and the garden garbage,respectively,and the excess sludge,so as to improve the biogas production efficiency of the digestive system for the proplem of the excess sludge digestion rate is low and the waste of municipal organic waste is serious.The factors that affect the stability of digestive system,the rate of gas production after CO digestion,and the change of sludge dewatering performance at the end of digestion were studied.16 S rDNA sequencing techniques were used to detect the digestion of sludge and garden garbage at the end of digestion,the microbial population abundance and species diversity were analyzed from the perspective of environmental microbiology,and the structural components of methanogens in different digestive groups were determined.①The ratio of sludge to waste citrus is the key parameter affecting the digestion process.When the VS ratio of excess sludge and citrus waste was 2:1,the synergistic effect was obvious,at this time,the biogas yield and methane yield were 1522.3 mL/g VS and 574.5 mL/g VS,which was 58.3% and 91.2% higher than that of excess sludge and citrus pomace.When the ratio of citrus waste and sludge is too large,the system tends to acidification,and VFAs accumulates to 8968.8 mg/L and pH is as low as 5,meanwhile,the biogas yield and methane yield decreased to 593.9 mL/g VS and 188.6 mL/g VS.When the ratio of sludge to citrus waste VS was 1:4,the CST time of digestive products was the longest,112.7 s,which was 9.2 times that of sludge digestion alone,and 3.1 times of that of citrus waste.The dehydration properties of digestive products decreased with the increase of the amount of citrus waste.②Synergistic anaerobic digestion of excess sludge and garden garbage contributes to the increase of biogas production and methane production in the system.The yield of digestive gas was the most obvious in group 1:2(628.9 mL/g VS),which was nearly 8.1% higher than that in sludge digestion group;the most obvious increase in methane yield was 1:1 group(299.9 mL/g VS),which was nearly 27.2% higher than sludge digestion alone.When the garden waste was digested alone,the pH was always below 5.5,and the VFA concentration of the system accumulated to 2909.1 mg/L.After adding to the excess sludge,the pH in the co digestion group decreased and VFA concentration accumulated more easily.There was a negative correlation between the amount of garden garbage and the dehydration performance of digestive products.The CST of digestive products in 1:4 group was the largest(203.7 s),which was 16.6 times that of excess sludge alone.In addition,three dimensional fluorescence detection showed that there were more organic compounds in garden garbage,which could increase the content of organic substance in digestive substrate,but the humus contained in it could lead to the difficulty of hydrolysis of organic compounds.③16S rDNA amplicon sequencing showed that the microbial biomass in the excess sludge digestion was greater than that in the other groups.It was possible that the garden waste inhibited the growth of some microorganisms.The main methanogens in the 1:0 and 1:0.5 groups of sludge and garden waste were Methanobrevibacter,Methanobacterium and Methanosaeta,the major methanogens in the 1:2,1:4 and 0:1 groups are Methanobrevibacter and Methanoculleus,and this shows that the addition of garden garbage will change the major types of methanogens in the digestive system.