Effects of waste rusted iron shavings on enhancing anaerobic digestion of food wastes and municipal sludge
2020
Cheng, Jiehong | Zhu, Cheng | Zhu, Jun | Xue, Jing | Kong, Feng | Zhang, Chunyong
In this study, rusted iron shavings with Fe⁰ and iron oxides were added to the mixture of food wastes and municipal sludge to improve methane (CH₄) production in the fermentation system. The effectiveness of such treatments was evaluated based on methane yield, biogas production, and production of volatile fatty acids (VFAs) and Fe²⁺ in the sludge supernatant. The results showed that the maximum daily methane yield (DCH₄) and specific methane production potential (SCH₄) for the group treated with the rusted iron shavings reached 13.28 mL g⁻¹VSS₀·d⁻¹ and 408.1 mL·g⁻¹VSSᵣₑₘₒᵥₑd (on day 36), respectively. These values were 12.2% and 41.2% higher than those obtained from the control group (nothing added). During digestion, the highest VFAs level of the rusted iron shavings group was 13,694 mg L⁻¹ on day 3, which was 48% higher than that of the control group. The volatile suspended solids (VSS) removal rates of the group with rusted iron shavings (45.8%) were 18.0% higher than that of the control group (27.8%). The Fe²⁺ content of the rusted iron shavings group was 132% and 282%, respectively, higher than those of the clean iron shavings and non-rusted iron shavings groups on day 5. Analysis data showed that the rusted iron mainly consisted of FeOOH with 53.5% hydroxyl groups and 41.4% Fe₂O₃ due to the porous and loose structures in the sludge system. These results indicated that rusted iron shavings, as a reductive material, could produce a more reductive environment that promoted methanogenic activity in the system, leading to improved methane yield.
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