Synergistic effects of iron and persulfate on the efficient production of volatile fatty acids from waste activated sludge: Understanding the roles of bioavailable substrates, microbial community & activities, and environmental factors

Evident synergistic effects of iron activated persulfate (Fe/PS) on the marked promotion of volatile fatty acids (VFAs) from waste activated sludge during anaerobic fermentation were reported. The maximal VFAs concentration was up to 2255 mg COD/L with the proportion of 72.8% acetic acid in the Fe/PS reactor while it was merely 120 and 517 mg COD/L in Fe and PS reactors, respectively. Fe/PS treatment could substantially improve the solubilization and hydrolysis processes via the combined chemical and biologic effects to provide sufficient bioavailable substrates for acidogenic bacteria. Meanwhile, the presence of Fe in Fe/PS reactors could alleviate the adverse effects of PS on environmental factors (i.e. ORP and pH) and simultaneously involve in the regulation of microbial growth and activities. The fermentative bacteria responsible for VFAs production were highly enriched and the activities of key acid-forming enzymes and ATP concentration were greatly improved in Fe/PS reactors. It was the overall improvement of bioavailable substrates, abundance and activities of acidogenic bacteria, and fermentation conditions that led to the high VFAs accumulation in Fe/PS reactors.