Study On The Key Process Of Dry Anaerobic Digestion Of Straw And Cow Dung Mixed Raw Materials

Dry anaerobic digestion（Dry AD）technology can process organic wastes with a total solid content（TS）between 20%-40%,which has the advantages of less water consumption,higher biogas production rate and less biogas slurry discharge compared with wet AD.It is one of the main research directions of agricultural waste resource utilization.However,due to the high TS of the material,dry AD technology still has problems such as difficulty in mixing,poor heat and mass transfer,and difficulty in process control.In order to solve these problems and improve biogas production efficiency,we used corn straw（CS）and cow dung（CD）as feedstock,analyzed the effect of the digestate recirculation ratio,mass ratio of feedstock,and TS on biogas production and microbial community characteristics of dry AD.This study put forward the optimization process parameters of dry AD of CS-CD mixed feedstock,and revealed the dynamic changes of microorganisms during dry AD.The main achievements of this study are as follows:1)The laboratory-scale reactor for continuous dry AD was used to optimize the digestate recirculation ratio.Under the conditions of 38℃,CD/CS was 1:1,TS of 20%,and HRT of 30 d,the maximum volumetric biogas production rate was 1.6 L L^-1d^-1 when the digestate recirculation ratio was 60%,which was 45.9%higher than the recirculation ratio was 50%.The increase of the digestate recirculation ratio is beneficial to the increase of the abundance of Vadin BC27＿wastewater-sludge＿group and Methanobacterium,so as to reduce the accumulation of volatile fatty acids and increase the biogas production rate of dry AD.2)Through orthogonal experiment[L9（3⁴）],the three process parameters of digestate recirculation ratio,CD/CS,TS were optimized.When the cumulative methane yield was used as the evaluation index,the influence of factors on biogas production was TS>CD/CS>digestate recirculation ratio.The optimal combination of process parameters was TS=30%,CD/CS=1:3,digestate recirculation ratio=40%.Under these conditions,the maximum volumetric biogas production rate can reach 3.0 L·L^-1d^-1.Both hydrogenotro-phic and acetoclastic methanogens existed in the dry AD system,and acetoclastic methanogens were predominated in this system.3)The horizontal push-flow continuous dry AD reactor（180 L）was used to optimize the mixing ratio of feedstock.Under the conditions of 38℃,TS of 20%,and HRT of 30 d,when CS:CD was 2:1,the biogas production was the largest,and the maximum volumetric biogas production rate reached 2.78 L·L^-1d^-1,which increased by 31.13%and71.78%compared with CS:CD was 1:1 and CS:CD was 3:1.