Innovative Carbon Addition Strategies for a High Rate Step-Feed BNR System

Supplemental carbon addition strategies in response to seasonal and diurnal variations in biological nutrient removal (BNR) performance were evaluated. The seasonal carbon addition strategy evaluated using the pilot-scale step-feed BNR reactors at the New York City Department of Environmental Protection (NYCDEP) Applied Research Facility at the 26th Ward Water Pollution Control Plant (WPCP) includes the use of methanol during the warm season, and ethanol during the cold season. One of the key operational challenges in this strategy is securing the BNR performance during the transition from one carbon source to the other. The BNR performance of the pilot reactor and the specific denitrification rate (SDNR) during the transition periods were evaluated. The transition of carbon sources was achieved without compromising the BNR performance, even though the ethanol-methanol transition appeared to require some acclimation period before the SDNR of methylotrophs reached within the typical range (0.06 – 0.1 mg-N/mg-VSS/d) observed in the previous studies. Two independent studies on the evaluation of oxidation-reduction potential (ORP) as a surrogate parameter are presented. At the NYCDEP's Applied Research Facility, the applicability of ORP as a surrogate parameter for carbon control system in a step-feed BNR process was evaluated. At the Stamford Water Pollution Control Authority (SWPCA), the use of ORP for the control of an Enhanced Modified Ludzack-Ettinger (eMLE) process was evaluated. Even though ORP could potentially be used as a monitoring tool to ensure anoxic condition in the denitrification process, the carbon dose control based on ORP was not recommended based on both studies.