Batch and continuous feeding of thermophilic aerobically digested sludge supernatant as a carbon source for biological nutrient removal

Abstract

Short chain volatile fatty acids (VFAs), namely acetate and propionate, are among the most available carbon sources for biological nutrient removal (BNR) enhancement in wastewater treatment. The thermophilic aerobic digestion (TAD) of sludge under a "microaerated" condition, whereby the system oxygen demand exceeds the system supply, has been found to accumulate high concentrations of VFAs. Since the sludge supernatant will be returned to the main treatment stream in most cases, using the TAD supernatant as the carbon source for BNR enhancement is a potential benefit for energy and resource conservation purposes. Batch and continuous feeds of TAD supernatant in BNR anaerobic and anoxic zones, as the carbon supplement for phosphorus and nitrogen removal, were investigated in this study. Results showed that the TAD supernatant was capable of enhancing the phosphorus release and denitrification, similar to the sodium acetate (NaOAc). Carbon sources in the TAD supernatant other than the VFAs were also utilized in the BNR processes; this indicated that the TAD supernatant consisted of other available carbon sources, not just the VFA concentrations detected by chemical analyses. Volatile fatty acid maximization and nutrient mitigation in the TAD supernatant are seen as crucial in this recovered carbon source application. Key words: biological nutrient removal, carbon source, digested sludge supernatant, thermophilic aerobic digestion, volatile fatty acids.