Synergic role of potassium ferrate pretreatment and zero valent iron for enhancement of waste activated sludge anaerobic digestion

Abstract

Potassium ferrate (PF) pretreatment can effectively promote the hydrolysis and acidification of waste activated sludge (WAS), but the high ammonia nitrogen and oxidation-reduction potential (ORP) resulting from it will be unfavorable to the subsequent methanogenesis. In this study, zero-valent iron (ZVI) was added into the PF pretreated sludge to minimize the inhibition and enhance the methanogenesis. Results showed that WAS pretreated with suitable amount of PF (4 g/L) could effectively improve CH4 production, which was about 34.3 % higher than that in control. And the addition of ZVI into pretreated sludge anaerobic digester could further improve the CH4 production, which was about 9.8 % higher than the reactor pretreated solely with PF. Mechanisms exploration indicated that ZVI could effectively improve the activity of the enzyme related to methane production. And the genes encoded enzymes involved in methanogenesis were significantly unregulated in ZVI added reactor. Besides, the hydrogenotrophic methanogens and homoacetogens were enriched in ZVI added reactor, which was beneficial for H2 partial pressure decline and methane production improvement.