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

This study conducted a comprehensive comparison of acidic (R5.0) and alkaline (R10.0) 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 R10.0 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 R10.0, 2.99 times higher than in R5.0. The fermented sludge filterability was severely deteriorated at R10.0, 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.

A novel strategy for improving volatile fatty acid purity, phosphorus removal efficiency, and fermented sludge dewaterability during waste activated sludge fermentation.

Volatile fatty acids (VFAs) from waste activated sludge (WAS) via alkaline fermentation have been shown to provide an effective alternative carbon source for biological nutrient removal in wastewater treatment plants (WWTPs) that promotes the subsequent release of phosphorus (P) and refractory dissolved organic matter. The dewatering ability of fermented sludge is known to decrease during alkaline fermentation. Here, a novel strategy of initiating fermentation at a pH of 10 was developed to improve VFA purity, P removal efficiency, and fermented sludge dewaterability during WAS fermentation. Although VFAs concentration was lower (1.69 ± 0.09 g COD/L) when the pH was only initially adjusted to pH 10 (RIA) relative to when the pH was maintained at 10 on a daily basis (RDC), the purity of VFAs in the fermented liquid was improved (58.48%). Furthermore, the release of total phosphorous (TP) in RIA was 5.90 times lower than that in RDC (139.37 mg/L). The normalized capillary suction time and specific resistance to filtration in RIA decreased to 42.23% and 40.70%, respectively, suggesting that the dewaterability of fermented sludge also improved. The amount of alkali needed was 17.44 kg for each ton of total solid (TS) in RIA, which was 5.49 times lower than that in RDC. Thus, approximately 45.44 USD was saved in operational costs for each ton of TS processed in RIA. These results indicated that VFAs production via initial pH 10 fermentation was a robust and cost-efficient way for providing carbon resources in WWTPs.

Effects of individual volatile fatty acids (VFAs) on phosphorus recovery by magnesium ammonium phosphate.

Volatile fatty acids (VFAs) are a major component of dissolved organic matter in alkaline fermentation supernatants. In this study, effects of different VFAs (acetate, propionate, and butyrate) on phosphorus recovery, as magnesium ammonium phosphate (MgNH4PO4·6H2O, or MAP), were studied. Results showed that optimal pH was 9.5 and MAP purity was ∼70% in VFA-free wastewater. With VFA addition, MAP purities of precipitates were higher, reaching 75%-85%. The crystalline characterization of precipitates suggested that VFAs had a weak complexation ability with Mg2+ and NH4+. Further, pH changes during the MAP crystallization process were monitored and results indicated VFAs only contributed to the alkalinity condition, which, in turn, improved the MAP crystallization process. These data provide for a better understanding of P recovery by MAP precipitates from VFA-rich fermented supernatants.

Multiple uses of magnesium chloride during waste activated sludge alkaline fermentation.

Multiple uses of magnesium chloride during waste activated sludge (WAS) alkaline fermentation was investigated. The results revealed that a higher MgCl2 concentration inhibited acidogenesis, while the purity of volatile fatty acids (VFAs) improved and the maximum percentage of VFAs accounted for 52.92% (w/w) of soluble chemical oxygen demand (SCOD) at 120 mmol/L Mg2+. A phosphate removal efficiency of 81.22% was obtained at 15 mmol/L MgCl2 concentration, while only a 14.77% increase was observed when further MgCl2 was added (120 mmol/L MgCl2). Capillary suction time (CST) values decreased sharply from 4410.20 s to 207.30 s with the increase of MgCl2. A similar trend was observed in bound water and the minimum value was 85.56 ±â€¯0.06%. The distribution of extracellular polymeric substances (EPS) and rheological profiles of the fermented sludge were also analyzed and the results confirmed that a high MgCl2 concentration had a positive effect on sludge dewatering.