Enhanced short chain fatty acids production from anaerobic fermentation of primary sludge using free ammonia pretreatment

This study is the first to report a new free ammonia (FA) pretreatment technique to recover short-chain fatty acids (SCFAs) from primary sludge (PS). The results showed FA pretreatment (240 mg N/L) largely enhanced the SCFAs production from PS to 355.8 mg chemical oxygen demand (COD)/g VSS, which was about 4.5-fold that of control (i.e., 80 mg COD/g VSS). Mechanism investigations showed that FA pretreatment greatly accelerated the PS solubilization and destroyed the integrity of EPS, and the easily biodegradable substrates in the fermentation broth increased significantly, providing microorganisms with more organics to convert into SCFAs. Further analyses displayed that FA greatly inhibited the methane production during fermentation, resulting in further accumulation of SCFAs. Given that the NH4+-N released during the fermentation can be converted into FA in situ, this could facilitate the transition of wastewater treatment plants operation from linear to circular mode.

Automated summary

This study introduces a new FA pretreatment technique for recovering SCFAs from PS. The results show that FA pretreatment significantly enhances SCFAs production, resulting in a 4.5-fold increase compared to the control group. Mechanism investigations reveal that FA pretreatment accelerates PS solubilization, destroys EPS integrity, and increases easily biodegradable substrates in the fermentation broth. FA also inhibits methane production, leading to further SCFAs accumulation. The conversion of NH4+-N released during fermentation into FA facilitates the transition of wastewater treatment plants operation from linear to circular mode.