| Anaerobic digestion is a biological process,which is widely used in organic waste treatment with production of methane.However,the functional microorganisms that convert organic matter to methane are susceptible to a variety of inhibitory substances or factors,leading to a reduced methane production and even process failure.More and more studies showed that the ammonia inhibition is one of the main problems which would lead to system instability,whose mechanism and recovery strategy should be payed more attention,especially in the anaerobic digestion of nitrogen-rich substances.In response to the above problems,this paper is mainly consisted with the following three parts:1.Take chicken manure,a typical nitrogen-rich raw material,as the object to explore the recovery strategy of co-digestion.It was indicated that adjusting Rs/c(the ratio of VS of sheep manure and chicken manure)could avoid ammonia inhibition at the source.The well-fitted kinetic results illustrated that the optimal co-digestion was obtained at the Rs/c of 0.4 with the highest methane yield(219.67 mLCH4/gVSadd)and significantly improved bioCH4 production rate(0.378 mLCH4/gVSadd/h).The migration and transformation of dissolved organic matter(DOM)based on three-dimensional fluorescence(EEM)analysis was closely related to the methanogenesis process.Additionally,a significant variation of DOM was detected at the Rsec of 0.4 with a consistent degradation of soluble microbial byproduct-like and protein-like organics.Microbial community analysis based on 16S rRNA showed that the co-digestion proved positive synergy effects on acetogens and acetolactic methanogens of Methanosaeta(occupied by 92.07%)activity,beneficial to methane production.2.Take chicken manure as the target to explore the recovery strategy of adding biochar.(a)Mild ammonia inhibition studies based on batch experiments demonstrated that the addition of appropriate biochar had a slow-release effect on ammonia nitrogen in the early stage of digestion.At the same time,it could improve fermentation performance by participating in the effective conversion of organic matter.The kinetic analysis and organic matter conversion analysis indicated that the efficiency of hydrolysis,acidogenesis,acetogenesis and methanogenesis would be greatly improved with 0.3 g/L biochar added.While,adding 30 g/L biochar could lead to the rapid release of ammonia nitrogen in the early stage of digestion and reduce the performance by adsorbing a large amount of easily degradable organic matter(reduced by 25-48%).Microbial community analysis implied that the addition of biochar was conducive to the enrichment of electricity-producing microorganisms and its interaction mechanism with methanogens benefited to improving the system stability under mild ammonia inhibition.(b)Severe ammonia inhibition studies based on continuous stirred fermentation tank(CSTR)experiments showed that the continuous feeding of chicken manure and biochar could improve the ammonia resistance of microorganisms.It was also indicated that even if the ammonia nitrogen concentration was higher than 9800 mg/L,the system could still operate effectively.3.Using starch as a single carbon source and taking varied concentrations of ammonium bicarbonate as variables,kinetic simulation,enzyme activity measurement,fluorescence spectroscopy,molecular docking,high-throughput sequencing and metagenomics were combined to reveal the methanogenesis mechanism of starch under ammonia inhibition.(a)The relevant research based on batch experiments showed that the reduction rate of the maximum methane production rate was as high as 51.51%,the lag phase would be extended by 5 times;the activity of a-Amylase and ATPase were severely weakened in the hydrogen-production and hydrogen-consumption stage,but the activities of coenzymes F420 and NADH in the methane-production stage were enhanced when the feed ammonia concentration was 5500 mg/L.Besides,the content of protein in the extracellular polymer(EPS)was increased by 77.1%to drive detoxification.The abundance of synergistic oxidizing bacteria was greatly reduced,which hindered the process of acetogenesis(50%reduced).In addition,the enrichment of bacteria of Marinilabiliaceae,which was considered to ammonia-resistant,might be one of the reasons why the system could run inefficiently and would not collapse directly.(b)The relevant research based on the up-flow anaerobic sludge bed(UASB)reactor implied that when the ammonia nitrogen concentration was higher than 3800 mg/L,the reactor would run down.Metagenomics analysis showed that the abundance of genes encoding key enzymes in the methanogenic pathway was reduced to varying degrees,while the abundance of genes encoding ATPase(F type and V/A type)was significantly enhanced(1.0-1.3 folds)with ammonia inhibition.(c)The molecular docking results showed that ammonia nitrogen and amylase were hydrogen-bonded,which had the greatest impact on arginine and lysine especially.The weak force of hydrogen bonding could provide a theoretical basis for the recoverability of ammonia inhibition potentially. |
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