Recovering biodegradable carbon from a thermophilic aerobic digestion supernatant for biological nutrient removal

The biological nutrient removal (BNR) process usually requires external carbon supplements for enhanced phosphorus and nitrogen removal. It has become popular for full-scale wastewater treatment plants to implement carbon addition and optimization, to ensure best system performance. Thermophilic aerobic digestion (TAD) is operated at elevated temperatures to achieve sludge stabilization, volatile solids destruction, and pasteurization. Preliminary tests indicated that the volatile fatty acids (VFAs) accumulation in the TAD sludge supernatant, under a microaerated operation (system oxygen demand exceeds the supply), was a potential carbon source for BNR enhancement.; The objectives of this study were to investigate the feasibility of using the TAD supernatant as a carbon source for BNR enhancement, and the potential impacts of the TAD supernatant addition on the system performance. Furthermore, due to the nature of VFA variance in TAD supernatant. TAD supernatant addition must be optimized in practice to obtain the benefits of carbon supplement and eliminate the potential nutrient overloading. A new control and monitoring technique was developed in this study using the headspace gaseous monitoring to estimate the VFA concentrations in TAD supernatant, and assess the BNR system performance.; In this study, TAD supernatant was proven to be a potential carbon source for BNR enhancement in both batch and continuous feed studies. The VFAs in TAD supernatant resulted in comparable phosphorus release and denitrification. In addition, substrates other than the VFAs in the TAD supernatant were also found to be available for both P release and denitrification. The extra nutrient load (nitrogen and phosphorus) was significant, requiring mitigation and dosing optimization to reduce treatment system deterioration.; The “headspace carbon dioxide (CO₂) monitoring” method proposed in this study was proven feasible in estimating the VFA equivalent in the TAD supernatant. The duration of CO₂ changes shown on the CO₂ profile (between the point of CO₂ starting to increase, and the point starting to decrease after the peak) of the phosphorus release and denitrification enhancement, due to the external carbon source addition, was defined as the “E Time” in this study. The duration of “E Time” was found to be proportional to the available carbon source concentration at the time of addition.; This “E Time” approach using the headspace CO₂ monitoring can be an attempt to replace the current oxygen utilization rate (OUR) method for readily biodegradable substrate determination. (Abstract shortened by UMI.)...