Contribution identification of hydrolyzed products of potassium ferrate on promoting short-chain fatty acids production from waste activated sludge.

Potassium ferrate (KFeO) has been extensively employed to promote short-chain fatty acids (SCFAs) production from anaerobic fermentation of waste activated sludge (WAS) because of its potent oxidizing property and formation of alkaline hydrolyzed products (potassium hydroxide, KOH and ferric hydroxide, Fe(OH)). However, whether KFeO actually works as dual functions of both an oxidizing agent and an alkalinity enhancer during the anaerobic fermentation process remains uncertain. This study aims to identify the contributions of hydrolyzed products of KFeO on SCFAs production. The results showed that KFeO did not execute dual functions of oxidization and alkalinity in promoting SCFAs production. The accumulation of SCFAs using KFeO treatment (183 mg COD/g volatile suspended solids, VSS) was less than that using either KOH (192 mg COD/g VSS) or KOH & Fe(OH) (210 mg COD/g VSS). The mechanism analysis indicated that the synergistic effects caused by oxidization and alkalinity properties of KFeO did not happen on solubilization, hydrolysis, and acidogenesis stages, and the inhibition effect caused by KFeO on methanogenesis stage at the initial phase was more severe than that of its hydrolyzed products. It was also noted that the inhibition effects of KFeO and its hydrolyzed products on the methanogenesis stage could be relieved during a longer sludge retention time, and the final methane yields using KOH or KOH & Fe(OH) treatment were higher than that using KFeO, further confirming that dual functions of KFeO were not obtained. Therefore, KFeO may not be an alternative strategy for enhancing the production of SCFAs from WAS compared to its alkaline hydrolyzed products. Regarding the strong oxidization property of KFeO, more attention could be turned to the fates of refractory organics in the anaerobic fermentation of WAS.