Mechanism On Improving Methane Production Efficiency From Anaerobic Digestion Of Pig Manure By Adding Attapulgite

The rapid development of livestock cause increasingly outstanding prominent environmental contradictions.Anaerobic digestion has proved an effective way to carry out reduction and harmlessness of pig manure,moreover it can produce clean energy production.Pig manure wastewater contains high concentrations of COD(Chemical Oxygen Demand)and total nitrogen.In the early stage of process,the accumulation of ammonia nitrogen and volatile acid will reduce the methane production efficiency.Studies have shown that the addition of zeolite,montmorillonite and bentonite to the anaerobic system can increase anaerobic digestion methane production rate and efficiency.Attapulgite clay is also a kind of natural non-metallic clay mineral with strong adsorption and ion exchange properties.However,the effect of attapulgite on the methanogenic efficiency of anaerobic digestion of pig manure and its mechanism of action are still lacking.In this study,the batch anaerobic digestion experiment was started with swine manure as the substrate under medium temperature conditions.In this study,changes in methane production efficiency,methane production kinetic,process stability,microbial activity,and key enzymes were evaluated under different amounts of attapulgite.Mechanism on improving methane production efficiency from anaerobic digestion of pig manure by adding attapulgite were investigated.And theoretical basis for engineering application of pig manure were also obtained.(1)Attapulgite changed the methane production rate and efficiency of anaerobic digestion of pig manure.Low-concentration(<10g/L)attapulgite increases the methane production and methane production rate,and high concentration(30g/L)inhibits methane production from pig manure,the optimal attapulgite dosage of pig manure in anaerobic digestion is 10g/L.The attapulgite shortened the delay period of anaerobic digestion,but there was inhibition in 30g/L attapulgite group.(2)Attapulgite improved the stability of anaerobic digestion process of pig manure.In the early stage of digestion,attapulgite has a buffering effect on p H,and the buffering capacity was higher with increasing dose of attapulgite,30g/L attapulgite had the largest buffering capacity.Attapulgite addition(10g/L)could accelerated the hydrolysis stage and methanogenesis.During the entire anaerobic digestion,the ammonia nitrogen concentration in the group with attapulgite addition was lower than that in the blank group.The concentration of FA(free ammonia)in the 30g/L experimental group was higher than that in the other groups,especially in the initial stage.High concentration of FA in 30g/L group has inhibitory effect.(3)Attapulgite improved key enzyme activity in anaerobic digestion of.pig manure.Adding attapulgite can significantly increase the activities of protease,β-glucosidase,dehydrogenase and coenzyme F420,but the dosage of 30 g/L inhibited protease and coenzyme F420 in the early digestion stage.(4)Attapulgite changes microbial commucities in anaerobic digestion of pig manure.The results showed that Methanomicrobia and Methanosarcinales have high ammonia nitrogen tolerance.The attapulgite can increase the relative abundance of Methanomicrobia and Methanosarcinales.Attapulgite enhances the relative abundance of Clostridiales,Lactobacillales and Desulfobacterales,which accelerates hydrolysis and acetogenic stages of anaerobic digestion,improved the production of methane and methane production rate.