Low-alkaline fermentation for efficient short-chain fatty acids production from waste activated sludge by enhancing endogenous free ammonia

• Published in: Journal of cleaner production 2020-12, Vol.275, p.122921, Article 122921
• Main Authors: Ye, Min, Ye, Jiongjiong, Luo, Jinghuan, Zhang, Sitong, Li, Yu-You, Liu, Jianyong
• Format: Article
• Language: English
• Subjects: Carbon source; Endogenous free ammonia; Low-alkaline fermentation; Short-chain fatty acids; Waste activated sludge
• ISSN: 0959-6526; 1879-1786
• DOI: 10.1016/j.jclepro.2020.122921

Alkaline fermentation at pH 10 is an effective method of producing short-chain fatty acids from waste activated sludge, but requires high cost of alkali. In this study, low-alkaline fermentation at pH 9 with enhanced endogenous free ammonia was proposed to improve sludge hydrolysis and short-chain fatty acids production for the first time. The results showed that the release of 210.6 ± 5.9 mg/L of endogenous free ammonia was sufficient for sludge hydrolysis, with a soluble chemical oxygen demand production of 6303.8 ± 45.9 mg/L within 24 h. Following the increase in sludge hydrolysis, ammonia stripping was employed to further improve acidogenesis by eliminating free ammonia inhibition. The final short-chain fatty acids production was 431.4 ± 1.7 mg chemical oxygen demand/g volatile suspended solid, which was even higher than that of regular alkaline fermentation. Furthermore, the theoretical availability of the produced short-chain fatty acids as a carbon source for denitrification was improved by 56.7%. A schematic of a wastewater treatment process employing low-alkaline fermentation of sludge considering carbon neutrality and nutrients recovery was proposed. [Display omitted] •Free ammonia was enhanced for low-alkaline fermentation of sludge to produce SCFAs.•SCOD increased by 211.0% due to 210.6 mg/L endogenous free ammonia release in 24 h.•SCFAs yield of pH 9 was higher by around 15% than reported results of pH 10.•A promising way was raised for carbon-neutral and nutrients recovery from sludge.