Studies On The Operation Characteristics Of Anaerobic Reactor For Kitchen Waste Regulated By Zero-valent Iron And Microbial Community Metabolism

Kitchen waste is an important part of municipal solid waste,because of its high organic matter content,good biodegradability,and great potential for anaerobic methane production.Anaerobic digestion,especially thermophilic anaerobic system,has the advantages of strong metabolic activity of microorganisms,high treatment efficiency,and more harmless.In this study,zero valent iron（ZVI）was used to improve the stability of anaerobic digestion of kitchen waste and its biogas production performance,and the anaerobic digestion-microbial electrolysis coupled reactor（AD-MEC）with zero valent iron as electrode was further explored to eliminate and control the phenomenon of“excessive acidification”during mesophilic and thermophilic anaerobic digestions in kitchen waste,and its mitigation effect was evaluated.The experiment of dosing ZVI to eliminate the“excessive acidification”phenomenon of anaerobic digestion of kitchen waste in the thermophilic reactor was firstly proposed,which included solid contents of 4%,6%,8%and 10%.The results showed that under thermophilic conditions,H-ZVI reactor could shorten the lag period caused by acid accumulation.At TS conditions of 4%and 6%,thermophilic anaerobic reactors with dosing ZVI quickly recovered biogas production,and the methane yield compared with the low organic loading reactor increased by 52.05%and 10.51%respectively,which reached 335.95 and 355.66m LCH₄/g VS.But as the solids content increased,the time required to recover the biogas production was also increasing.The addition of ZVI effectively reduced the hydrogen partial pressure of the system and accelerated the transition from butyric acid fermentation to propionic acid fermentation.Hydrogenotrophic methanogen Methanothermobacter interacted with the syntrophic acetate-oxidising bacteria Syntrophaceticus to achieve the syntrophic acetate oxidation and hydrogenotrophic methanogenesis（SAO-HM）pathway and recovered the methanogenesis metabolism.The effect of ZVI in eliminating the“excessive acidification”phenomenon in mesophilic and thermophilic anaerobic digestions was compared and analyzed,and it was found that the thermophilic condition accelerated the elimination of the"excessive acidification"phenomenon,but the final methane yield was not as good as the same loaded mesophilic reactor,the difference between the two was more than 100 m LCH₄/g VS.The absolute dominant methanogenic archaea in mesophilic and thermophilic anaerobic digestion system were Methanoculleus and Methanothermobacter respectively.Dosing ZVI promoted the mutual metabolism of these two hydrophilic methanogenic archaea with Syntrophaceticus.The anaerobic digestion-microbial electrolysis coupled reactor（AD-MEC）was used to further improve the electron transfer efficiency between methanogens and syntrophic bacteria when zero-valent iron eliminated“excessive acidification”.However,in the high-load reactor,only the Fe-C（0.3V）reactor’s biogas production performance improved by 14.92%compared with the control group,while only the Fe-Fe（0.3V）reactor in the low-load reactor improved the methane yield.The anaerobic digestion in the low organic loading reactor was dominated by propionic acid fermentation;the Fe-C（0.3V）reactor in the high-load reactor had the fastest hydrolysis rate of VFAs,and the main acid-producing metabolism type changed from butyric acid fermentation to propionic acid type Fermentation,and then recovered normal biogas production.This study provided corresponding technical measures to improve the operation stability of anaerobic reactors,and explained the metabolic differences between thermophilic and mesophilic anaerobic methanogenesis under the control of ZVI,which further enriched the relevant theory of anaerobic methanogenesis technology from kitchen waste.