Alkalinity enhanced hydrolysis of primary sludge for carbon source recovery and its impact on denitrification in wastewater treatment.

Primary sludge can serve as an internal carbon source for denitrification in wastewater treatment plants (WWTPs). This study explores the use of alkaline treatment to produce a fermentation broth from primary sludge, which predominantly contains short-chain volatile fatty acids (VFAs), with acetic acid and propionic acid making up over 65% of the total VFAs. The performance of this fermentation broth as a sole carbon source for denitrification was compared with that of sodium acetate, acetic acid, methanol, and ethanol in both biofilm and activated sludge systems. The results revealed that the denitrification rate achieved using the fermentation broth was as high as 2.1661 mg NO3--N/(g MLSS·h), which was slightly lower than that of sodium acetate and acetic acid but higher than that of methanol and ethanol. The fermentation broth demonstrated a high heterotrophic yield (0.7183), an equivalent specific carbon requirement for denitrification as acetic acid and sodium acetate, and a rapid denitrification start-up. Moreover, variations in the VFAs/SCOD ratios in the fermentation broth did not significantly impact the denitrification rate or substrate biodegradation rate. However, the yield coefficient and specific carbon requirement for denitrification were found to vary significantly depending on the carbon source used. This study concludes that with appropriate treatment, fermented broth from primary sludge can be an effective carbon source comparable to commercial external carbon sources, significantly reducing carbon emissions.