Study On Anaerobic Co-digestion Characteristics Of Municipal Wastewater Treatment Plant Sludge With Dairy Manure And Food Waste Respectively

Anaerobic digestion can obtain both environmental and economic benefits.However,there are the problems of poor biogas production in anaerobic digestion of single sludge.Therefore,dairy manure and food waste,the most important organic solid wastes in cities and towns,were selected for the substrate of anaerobic co-digestion with sludge in this study.The effects of dairy manure and food waste on methane production of waste sludge and hydrolysis of organic matter were evaluated.Moreover,the synergistic effect of biogas production and the reaction kinetics was analyzed.The main results and conclusions are as follows:（1）The cumulative methane production in the mesophilic and thermophilic anaerobic digestion of single sludge was 154.8 and 179.4 m L/g VS,respectively.By contrast,when dairy manure was added at 10%,20%,30%and 40%,the cumulative methane yield decreased by 7.7,12.1,28.8 and 28.7 m L/g VS in the mesophilic anaerobic digestion respectively,and the cumulative methane yield by 5.6,7.1,13.5 and21.8 m L/g VS in the thermophilic anaerobic digestion respectively.The results showed that the addition of dairy manure had an adverse effect on the cumulative methane production of the co-digestion reactor.The main reason is the poor hydrolysis effect of organic matter in dairy manure.However,the addition of dairy manure significantly improved the buffer capacity of the reactor,reduced the risk of ammonia inhibition.Therefore,the co-digestion of dairy manure and sludge can reduce the methane production of sludge,but it can play a positive role in the acid-base balance and ammonia concentration control of the co-digestion system.（2）Compared with anaerobic digestion of single sludge,when 25%,50%and 75%food waste were added to the reactor,the cumulative methane production increased by110.8,221.0 and 264.7 m L/g VS respectively in the mesophilic anaerobic digestion,and103.5,178.8 and 280.4 m L/g VS in the thermophilic anaerobic digestion,The results showed that the addition of food waste promoted the cumulative methane production of the reactor,and the cumulative methane production was the largest when 75%of food waste was added in both the mesophilic and thermophilic anaerobic digestion.The main reason is that the organic matter of food waste is hydrolyzed and released well.However,adding too much food waste will lead to the accumulation of organic acids（mainly n-butyric acid）,which may cause acidification of the reactor.Therefore,food waste can provide rich organic matter for the reactor,but excessive food addition may lead to the accumulation of organic acids,which is not conducive to the stability of the reactor.（3）The analysis of synergistic effcet of biogas production shows that there was 4.4%～17.1%negative synergistic effect in the mesophilic anaerobic digestion when 10%～40%dairy manure was added to the co-system.However,50.2%～92.1%positive synergistic effects were achieved in the mesophilic anaerobic digestion when 25%～75%of food waste was added to the reactor.（4）The analysis of reaction kinetics showed that adding 10%～40%dairy manure to the reactor increased the hydrolysis rate constant k by 18.9%,and the lag periodλaverage shortening was 0.8 d,but the maximum methane production potential P₀decreased by 9.6%.On the other hand,the addition of 25%～75%food waste increased P₀ of the reactor by 124.9%,but theλwas delayed by 2.9 d.