Re-hydrolysis characteristics of alkaline fermentation liquid from waste activated sludge: Feasibility as a carbon source for nitrogen removal

Abstract

To overcome the issue of substandard nitrogen and phosphorus discharge, resulting from the low carbon/nitrogen (C/N) ratio of municipal wastewater, immobilized filler was used to re-hydrolyze the alkaline fermentation liquid of waste activate sludge (WAS) as a nitrogen removing carbon source. The complex organic matter was further hydrolyzed and its denitrification efficiency as a carbon source for nitrogen removal was improved. Volatile fatty acids increased from 1605 ± 5 mg/L to 2546 ± 37 mg/L after re-hydrolysis of mixed-alkali sludge fermentation liquid, and complex organic matter, such as fulvic acids, humic acids, class I aromatic proteins, and soluble microbial products were hydrolyzed into small-molecule organics. When the re-hydrolysis fermentation liquid (RH-SFL) was used as the carbon source for nitrogen removal, the nitrogen removal effect was close to sodium acetate and the nitrogen removal rate (NRR) was up to 98.5 ± 0.5%. According to the NOX--N removal curve, the reaction rate of RH-SFL was significantly higher than before re-hydrolysis (nRH-SFL) (0.486 > 0.38). This technology can significantly improve the effective organic quality in the alkaline fermentation liquid of WAS, which can be more easily utilized by denitrifying bacteria. This provides a feasible and effective solution for nitrogen removal in municipal wastewater with insufficient carbon.