Stimulating short-chain fatty acids production from waste activated sludge by nano zero-valent iron

• nZVIa accelerated the solubilization and hydrolysis of WASb.
• SCFAsc production was enhanced greatly due to nZVI addition.
• The highest SCFAs production from WAS was 1307.8 mg COD/L with 5.0 g/L nZVI.
• The activities of key enzymes related with SCFAs production were improved by nZVI.
• The fermentative bacteria producing SCFAs were highly enriched in nZVI reactor.

An efficient and green strategy, i.e. adding nano zero-valent iron into anaerobic fermentation systems to remarkably stimulate the accumulation of short-chain fatty acids from waste activated sludge via accelerating the solubilization and hydrolysis processes has been developed. In the presence of nano zero-valent iron, not only the short-chain fatty acids production was significantly improved, but also the fermentation time for maximal short-chain fatty acids was shortened compared with those in the absence of nano zero-valent iron. Mechanism investigations showed that the solubilization of sludge, hydrolysis of solubilized substances and acidification of hydrolyzed products were all enhanced by addition of nano zero-valent iron. Also, the general microbial activity of anaerobes and relative activities of key enzymes with hydrolysis and acidification of organic matters were improved than those in the control. 454 high-throughput pyrosequencing analysis suggested that the abundance of bacteria responsible for waste activated sludge hydrolysis and short-chain fatty acids production was greatly enhanced due to nano zero-valent iron addition.