Research On The Effect Mechanism Of Carbon-material Particle Size On Anaerobic Digestion Methane Production

According to the "Annual Statistical Report on Ecological Environment in 2021" released by the Ministry of Environmental Protection,China’s chemical oxygen demand emissions reached 25.310 million tons,of which agricultural wastewater accounted for 66.2%.These wastewaters are mainly medium and high-concentration organic wastewaters such as animal husbandry,and anaerobic digestion is the main treatment technology for such wastewaters.In the process of anaerobic digestion,organics can be converted into biomass renewable energy resource-biogas(the main component is methane,accounting for 55-70%)under the action of microbial groups,which can be used for heating and power generation,thereby realizing the energy conversion of pollutants.In this study,different types and particle sizes of biochar and activated carbon were added to the anaerobic digestion reactor to study the influence of these carbon materials on anaerobic digestion and the potential mechanism,in order to provide optimization strategies for adding carbon materials to improve the performance of anaerobic digestion.The main research content and results are as follows:(1)The effects of granular activated carbon(GAC),powdered activated carbon(PAC)and nano-conductive carbon black(NCB)with different particle sizes on the methanogenic process of anaerobic digestion with glucose as carbon source were investigated by batch experiments.The experimental results showed that the addition of GAC could promote the consumption of the Soluble Chemical Oxygen Demand(SCOD)during anaerobic digestion,and also could promote the consumption of VFAs,especially acetic acid and propionic acid.In addition,compared with the control,the methane production of GAC,PAC and NCB groups was increased by 24.33%,44.69% and 66.24%,respectively.The results of microbial diversity showed that methanogenes were significantly enriched in the NCB group,and acid-producing bacteria were abundantly enriched in the GAC group.The increased abundance of these functional bacteria is the main reason for the improved performance of the various stages of anaerobic digestion methanogenesis.(2)Batch experiments were conducted to study the mechanism of the addition of biochar with three particle sizes at a concentration of 10 g/L on the methanogenic process of anaerobic digestion.The experimental results showed that the addition of biochar accelerated the formation of acetic acid in the early stage and promoted the consumption of organic acids especially propionic acid in the later stage of anaerobic digestion process.Compare to the control,L and S groups could increase SCOD removal efficiency and methane production by40.48-42.41% and 81.86-82.99%,respectively.Microbial community analysis stated that microorganism associated with electron transfer and acid production were significantly enriched in the L and S groups.The improvement of anaerobic digestion system performance may be related to the relief of acid stress and the selective enrichment of functional bacteria.(3)The performance of acidified anaerobic digestion system was improved by adding 5g/L and 10 g/L biochar to the reactor,and the morphology changes of biochar in the system were investigated.The experimental results showed that the addition of biochar effectively alleviated the accumulation of organic acids in the system,the effluent p H increased to 6.8~7.1,and the removal performance of SCOD was effectively improved.The abundance of acidproducing bacteria in the reactor was significantly increased,which was speculated to be the direct reason for the efficient utilization of organic acids.In addition,the morphology of the added biochar showed that the mesh pore structure gradually broke and collapsed during the reaction.