Mechanisms of peroxymonosulfate pretreatment enhancing production of short-chain fatty acids from waste activated sludge.

Peroxymonosulfate (PMS) has been recently used as an additive to pretreat waste activated sludge (WAS) to enhance short-chain fatty acids (SCFAs) production. However, the mechanisms of how PMS enhances SCFAs production remain largely unknown. This work therefore aims to explore the mechanisms through deeply understanding its impact on the disintegration of sludge cells, the biodegradability of organics released and the bioprocesses involved in anaerobic fermentation, and differentiating the contributions of its degradation intermediates to SCFAs production. This was demonstrated by a series of batch fermentation tests using either real sludge or model organic compounds as fermentation substrates. Experimental results showed that the maximal SCFAs yield increased from 29.69 to 311.67 mg COD/g VSS with PMS level increasing from 0 to 0.09 g/g TSS. No obvious increase in SCFAs yield was observed when PMS further increased. The mechanism explorations revealed that PMS pretreatment not only enhanced the disintegration of sludge cells but also promoted the biodegradability of organics released, thereby providing more biodegradable substrates for subsequent SCFAs production. PMS pretreatment decreased the percentages of fulvic acid-like and humic acid-like substances in the released organics. Moreover, the species and total detection frequency of other recalcitrant organics such as cyclopentasiloxane, heptasiloxane, and ethylene glycol, which were hardly degraded in ordinary anaerobic condition, also decreased remarkably. Although PMS caused harms to some extents to all the microbes in the anaerobic fermentation, its inhibitions to SCFAs consumers were much severer than that to SCFAs producers, probably due to the less tolerance of methanogens. Further analyses exhibited that O, SO and •OH were the major contributors to the increased SCFAs production, and their contributions were in the order of O > SO > •OH. The findings obtained in this work provide insights into PMS-involved sludge fermentation process and might have important implication for further manipulation of WAS treatment in the future.