Investigation of Denitrification Kinetics Using Various Carbon Sources in Sequencing Batch Reactors at Cold Temperature

Facilities across North America are designing plants to meet stringent limit of technology (LOT) treatment for nitrogen removal. This is in response to the Chesapeake Bay Agreement, which will limit effluent total nitrogen to 3 mg/L. Of particular interest is the use of an alternate external carbon source to replace the most commonly used carbon, methanol. Replacing methanol with an alternate external carbon source for denitrification in the winter will be particularly important since methanol utilizer growth is stunted during colder temperatures. This study focuses on three external carbon sources: methanol, ethanol and acetate. The aim of this study was to obtain the specific denitrification rate (SDNR) of the substrates in two different contexts. Sequencing batch reactors (SBRs) were set up to acclimate carbon free biomass to the specified substrate while in-situ SDNRs were conducted concurrently. Once the biomass was acclimated to the corresponding substrate, a series of ex-situ SDNRs were performed using various biomass/substrate combinations. All experiments were conducted at 13°C. The results suggest that the SDNRs for acetate (32 mgNO₃-N/gVSS/hr) and ethanol (30 mgNO₃-N/gVSS/hr) are higher than that for methanol (9 mgNO₃-N/gVSS/hr). Ethanol acclimated biomass fed with acetate resulted in the highest SDNR of 26 mgNO₃-N/gVSS/hr.