Potential of Crystalline and Amorphous Ferric Oxides for Biostimulation of Anaerobic Digestion

• Published in: ACS sustainable chemistry & engineering 2019-01, Vol.7 (1), p.697-708
• Main Authors: Wang, Mingwei, Zhao, Zhiqiang, Niu, Junfeng, Zhang, Yaobin
• Format: Article
• Language: English
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.8b04267

Iron oxides have been widely investigated to accelerate the conversion of organic wastes to methane. However, the potential mechanism involved with different types of iron oxides is a controversial topic. In this study, crystalline Fe2O3 and amorphous Fe (OH)3 were respectively supplemented to explore the effects of the crystal form of Fe­(III) on anaerobic digestion. The results showed that the addition of Fe2O3 and Fe­(OH)3 both significantly enhanced COD removal and biomethanation compared with the control. The reason was related to that the supplement of Fe­(OH)3 induced an efficient microbial dissimilatory iron reduction to enhance the decomposition of complex organics into simples. Consistently, 28.3% of Fe­(OH)3 dosed at the initial stage were reduced into Fe­(II), while no obvious iron reduction was observed with the Fe2O3 supplement. Interestingly, Fe2O3 significantly stimulated the secretion of protein and humic acid-like substances in EPS, leading to an electron-transfer capacity higher than that for Fe­(OH)3 and control reactors, which seemed to be an important reason for the improved anaerobic performance. The gene function prediction also showed a different degree of expression of functional genes involved in amino-acid, polysaccharides, and inorganic ion transport and metabolism in the presence of Fe2O3 and Fe­(OH)3. This study helped to give a more comprehensive insight for the mechanisms of ferric oxides on the improvement of anaerobic digestion.