NOB Repression for Mainstream Nitrite-Shunt and Deammonification: A Pilot Study

Mainstream deammonification is regarded as a paradigm shift from the conventional aerobic wastewater treatment that is capable of promoting more sustainable nitrogen removal. It is understood that for deammonification to be successful in mainstream wastewater treatment, the suppression of NOB in the cold and dilute conditions associated with mainstream applications needs to be resolved. While NOB suppression in low C/N sidestreams is generally well understood, the mainstream application remains elusive. Since known factors that favor NOB suppression in sidestream such as high free NH3, high temperature, and free HNO2 are not available in mainstream, it has been recognized that operational strategies based on a different set of parameters are needed to suppress NOB. The prospect of mainstream deammonification in treatment plants that lack anaerobic digestion (e.g., incinerator plants) and therefore the potential for sidestream-generated ammonia oxidizing bacteria (AOB) bioaugmentation (without NOB) beckons an entirely different approach that might include separating the nitritation and anaerobic ammonia oxidation (AMX) steps. To prove the viability of mainstream NOB suppression and deammonification, a pilot study was conducted. The pilot study incorporates two unique stages operated in series, known as an A/B process. The A-stage included a low solids retention time (SRT), high-rate activated sludge (HRAS) process targeted at 30-60% influent chemical oxygen demand (COD) removal. The B-stage included a two-sludge deammonification process incorporating a Nitritation-Denitritation through Modulating Aeration (NiDeMA) CSTR with a clarifier followed by a fully-anoxic AMX moving bed bioreactor (MBBR). This paper considers the B-Stage, which includes the NiDeMA CSTR operated under cyclical dissolved oxygen (DO) conditions based on a control strategy applying on-line in-situ NH4+, NO2−, and NO3− measurements and an unaerated AMX MBBR. This aeration scheme combined with aggressive SRT limitation provided NOB suppression which was confirmed through weekly nitrogen processing rate measurements coupled with targeted qPCR of the bacterial community. The fully anoxic AMX MBBR has demonstrated near complete removal of NO2−. Consequently, NOB suppression mechanisms have been postulated, and an operational framework has been put forward paving the way for mainstream deammonification in treatment plants that do not have anaerobic digestion.