The Improvement Of Dry Anaerobic Digestion Of Swine Manure

The large-scale development of swine breeding leads to the concentrated production of swine manure in local regions.Swine manure contains a lot of organic matter,which can be converted into clean renewable energy-biogas by the technology of anaerobic digestion.Based on the solid content of the substrate,the anaerobic digestion can be divided into wet and dry anerobic digestion.Compared with wet process,dry anaerobic digestion has many advantages,such as no need to dilute with water and convenient use of the digestate.However,the efficiency of anaerobic digestion is not high,and ammonia inhibition is the main limiting factor.Therefore,aiming at the problem of ammonia inhibition,this paper studied the improvement approach of dry anaerobic digestion efficiency by using swine manure with total solid?TS?> 20% as feedstock.?1?The effect of granular activated carbon?GAC?and acclimated sludge with high content of ammonia nitrogen on continuous dry anaerobic digestion of swine manure was studied.The results showed that the addition of GAC increased the volumetric biogas production rate by 10.6%,and the removal efficiency of TS and VS were enhanced by 5.30% and 6.58% respectively.In the GAC group,the concentration of total ammonia nitrogen?TAN?was 15.3% higher than that of the control group,while the content of total volatile acids?TVFA?was 30.3% lower.In the treatment group inoculated with acclimated sludge,the reactor could operate stably under the conditions of TAN and TVFA concentration up to 5200 and 8800 mg/L respectively,but the improvement effect on biogas production performance was not obvious.?2?Since adding GAC could promote gas production,the mechanism of adding GAC to improve the dry anaerobic digestion of swine manure was explored.The Scanning Electron Microscope?SEM?observation showed that the surface of GAC was rough,and there were abundant pores and large specific surface area with GAC before the test.After the test,microorganisms attached and grew on the surface and near the pores of GAC,which indicated that GAC was beneficial to microbial attachment.GAC was conducive to the degradation of insoluble organic macromolecules,and the hydrolysis efficiency of crude protein by was increased by 27.7%.Adding GAC in dispersion was better than in wrapping on improving the methane production of dry anaerobic digestion of swine manure.The maximum methane production rate of the dispersed GAC group was 10.9% higher and the lag time was 22.2% shorter than that of the wrapped GAC group,which was possibly because the dispersed GAC provided more “electron transfer bridges”.Microbial community analysis showed that adding GAC could enrich more functional microorganisms which were beneficial to the anaerobic digestion of swine manure,such as acidogen of Clostridium_sensu_stricto₁,aceticlastic methanogen of Methanosaeta,hydrogenotrophic methanogen of Methanospirillum and so on.Moreover,it may establish a direct interspecies electron transfer?DIET?pathway between Clostridium_sensu_stricto₁ and Methanosaeta.?3?Based on the promoting effect of GAC on biogas production,the effect of GAC on the dry batch anaerobic digestion of swine manure was studied under different temperatures and ammonia concentration.The methane production periods of 35°C and 55°C were obviously shorter than that of 20°C.The lag time of 20°C and 55°C was longer than that of 35°C,the main reason for slow methane production at 20°C was the low microbial activity,and microorganisms?especially methanogens?had long adaptation time at 55°C.At 20°C,35°C and 55°C,the maximum methane production rate decreased with the increase of ammonia nitrogen concentration.The addition of GAC could reduce the ammonia nitrogen concentration by 64⁴40 mg/L,reduce the accumulation of volatile fatty acids?VFAs?,and increase the methane production rate by 8.40%⁴5.6%.?4?The effect of GAC on the dry anaerobic digestion efficiency of swine manure under different organic load rates?OLR?was investigated.The reactors were started-up at the initial TAN concentration of 3600 mg/L and the OLR was gradually increased to 9.0 gTS/L/d.The results showed that adding GAC could increase the volumetric methane production rates of dry anaerobic digestion of swine manure by 13.7%,2.91%,6.44%,9.28%,7.75% and 9.35% respectively under the OLR of 1.0,1.5,3.0,5.0,7.0 and 9.0 gTS/L/d,and increase the removal efficiency of VS by 0.631%,2.23%,1.21%,3.04%,2.13% and 3.18% respectively.The concentrations of ammonia nitrogen and VFAs in the GAC treatment group were lower than that in the control group,and the content of methane was slightly higher than that in the control group.In short,the addition of GAC could accelerate the start-up of dry anaerobic digestion of swine manure and improve the biogas production efficiency,especially under high OLR.