Comprehensive comparison of acidic and alkaline anaerobic fermentations of waste activated sludge

This study conducted a comprehensive comparison of acidic (R-5.0) and alkaline (R-10.0) anaerobic fermentations of waste activated sludge (WAS). The results showed that alkaline fermentation was able to increase biopolymer release and benefitted the production of volatile fatty acids (VFAs). However, large amounts of the released organic matter in the R-10.0 fermented liquid had low biodegradability unsuitable for the biological nutrient removal (BNR) process, resulting in increased C, nitrogen, and phosphorus loads in BNR effluent. Further, Al was more readily released than other metals and its maximum concentration reached 134.52 mg/L in R-10.0, 2.99 times higher than in R-5.0. The fermented sludge filterability was severely deteriorated at R-10.0, as indicated by the normalized capillary suction time and specific resistance to filtration. Considering these findings, VFAs from WAS via acidic fermentation may represent a suitable carbon source for direct use in the BNR process.

Automated summary

This study found that alkaline fermentation of waste activated sludge increases biopolymer release and benefits VFAs production. However, the released organic matter in alkaline fermentation has low biodegradability, leading to increased nutrient loads in BNR effluent. Additionally, aluminum is more readily released in alkaline fermentation, impacting the filterability of fermented sludge.