Study On Three Different Valence States Of Iron In Mesophilic Anaerobic Digestion Of High-solids Content Sludge

Trace metal elements have important effects on microbial growth and metabolism.Many studies found that iron element could promote the anaerobic digestion process.However,there are few systemic researches to investigate the effects of iron element on high-solids sludge anaerobic digestion process,whose solid content is between 8²0%.The solid content of sludge was about 10%in this research.This paper primarily investigated the effect of iron-carbon micro electrolysis on high-solids sludge anaerobic digestion system and discussed the behind mechanism by batch experiment.In addition,this study has comparatively studied the effects and mechanisms of FeCl₃and FeCl₂ on high-solids sludge anaerobic digestion system through batch experiment and continuous stirred tank reactor?CSTR?continuous flow experiment.The main results are as follows:?1?The addition of iron powder and active carbon could improve the methane production and the organics degradation in high-solids sludge anaerobic digestion.When the Fe/C ratio reached10:1,the methane content in biogas reached up to 68.8%,and the highest total chemical oxygen demand?TCOD?and soluble chemical oxygen demand?SCOD?degradation rate in sludge were80.4%and 70.2%,respectively.?2?Dosages of the FeCl₃ or FeCl₂ could effectively enhance methane production and organic matter degradation in high-solids sludge anaerobic digestion system.With the dosage concentration of 200 mg/L FeCl₃,the methane accumulation yield was increased by 28.9%and the degradation rate of volatile solid?VS?/total solid?TS?reached 40.1%.When FeCl₂ concentration was 250 mg/L,the cumulative methane production was increased by 6.4%and the degradation rate of VS/TS reached 58.7%.However,the methane production performance of high-solids sludge anaerobic system was inhibited with high concentration FeCl₃ and FeCl₂,especially with excessive FeCl₃.These results indicated that the best dosages of FeCl₃ and FeCl₂ for high-solids sludge anaerobic system were 200 mg/L and 250 mg/L,respectively.High concentration of FeCl₃ could intensify the hydrolysis of Fe³⁺,which resulted the decline of pH value in the system.However,methane production process could be gradually restored with the high concentration of NH₄⁺-N.?3?The sludge retention time played an important role in high-solids sludge anaerobic system.The organics showed better decomposition performance with the longer sludge retention time.The results suggested that high-solids sludge anaerobic digestion showed stronger tolerance at the shorter sludge retention time,compared to the traditional sludge anaerobic digestion process.?3?Microbial community diversity analysis showed that FeCl₃ could improve relative abundance of Anaerolineae and Clostridia in microorganism,and FeCl₂ could improve the relative abundance of Cloacamonae in microorganism.In addition,the suitable concentration of FeCl₃ and FeCl₂ could improve relative abundance of Methanobacterium and Methanomassiliicoccus,while excessive FeCl₃ could inhibit the activity of both.These results indicated that adding suitable concentration of FeCl₃ or FeCl₂ was beneficial to the microbial community of high-solids sludge anaerobic system,which could promote the methane production process.But high concentration of FeCl₃ could inhibit the activity of methanogens.