Study On Characterization And Mechanism Of Biochar Alleviating The Inhibition Of Ammonia During Anaerobic Digestion Of Organic Waste

Anaerobic digestion（AD）technology has the ability to convert organic matter in organic waste into methane which is clean energy,the AD is widely used in organic solid waste resource treatment.However,the AD process is often inhibited by the high concentration of ammonia,which leads to the decrease of methane production and the accumulation of volatile fatty acids（VFAs）.Meanwhile,biochar is a low-cost,widely available and environmentally friendly biomass-based carbon material,and its rich pore structure and surface functional groups as well as excellent acid-base buffering capacity are conducive to enhancing AD performance,and its abundant redox functional groups on the surface provide redox intermediates for anaerobic digestion,thus accelerating the interspecies electron transfer process of syntrophic oxidizing microorganisms.In this study,the inhibition of AD process by different ammonia concentrations and the efficacy of biochar in alleviating the inhibition of ammonia were investigated by batch model,and analyzed in depth from various aspects such as electron transfer,microbial changes and extracellular polymer substances,in order to clarify the mechanism of biochar in alleviating the ammonia inhibition of AD process.The main contents and conclusions are as follows:1.the efficiency of anaerobic methanogenesis production decreased significantly with the increase of ammonia dosing.At the total ammonia nitrogen（TAN）concentrations of 2000,4000 and 6000 mg/L,biochar increased the maximum methanogenic rate of the system by 27.2%,51.2%and 108%,respectively,and methanogenic lag time were shortened by 41.7%,44.4%and 71.8%,respectively.The control group（CT）showed complete inhibition at 8000 mg/L,while the biochar group（BC）achieved methane production after a 25 days lag duration.In addition,the cumulative methane production and maximum methane production rate of the CT and BC groups were linearly and negatively correlated with ammonia concentration,while the lag time was exponentially correlated with ammonia concentration.2.The accumulation of VFAs was observed in both the BC and CT groups under ammonia stress,and the maximum accumulation of VFAs in BC group was 43.1%,22.5%,32.9%and 3.20%lower than that in the CT group under the conditions of TAN at 2000,4000,6000 and 8000 mg/L,respectively,and the rapid degradation of acetate and butyrate was observed in the BC group,which indicated that biochar under high ammonia concentration stress promoted the syntrophic oxidation process of acetate and butyrate while alleviating the further increase of acidification.3.The results of microbial population analysis indicated that biochar promoted the enrichment of electroactive microorganisms such as Mathanosarcina,which suggested that biochar might accelerate the direct interspecies electron transfer（DIET）process between VFA syntrophic oxidizing bacteria and methanogenic bacteria.In addition,biochar firstly enriched ammonia-tolerant archaea such as Mathanosarcina,and over time,and the syntrophic oxidation methanogenic pathway gradually replaced the acetoclastic methanogenic pathway,the dominant genus gradually changed to Methanoculleus,and the pathway shift also confirmed that biochar promoted the syntrophic oxidation process among microorganisms.4.Analyzed from the electron transfer activity of systemic microorganisms,the INT-ETS activity experiment showed that the ETS of BC group was enhanced by 12.8%,32.2%,83.0%and 156.2%compared to CT group at ammonia concentration of 2000-8000 mg/L,respectively.The extracellular electron transfer activity was characterized by using WO₃electrochromic measurement,and the rate of color change was significantly faster in BC group than in CT group at ammonia concentrations of 6000-8000 mg/L.The addition of biochar could enhance the extracellular electron transfer between electroactive bacteria and promote the DIET process between syntrophic bacteria.Therefore,biochar greatly promoted the electron transfer capacity of the system under ammonia stress,and the abundant oxygen-containing active functional groups on its surface might have facilitated the DIET process and contributed to the syntrophic partner between VFA-oxidizing bacteria and methanogenic archaea.In addition,the rich pore structure and slightly alkaline conditions on the surface of biochar provided good conditions for microbial enrichment,which enriched the dominant genera of methanogenic bacteria more quickly under ammonia stress,and accelerated the recovery of methanogenic efficiency.