Mainstream nitritation and denitritation in a pilot-scale multi-cycle sequencing batch reactor

Abstract

Addition of external carbon sources for deep nitrogen removal highly increased the cost of municipal wastewater treatment. In this study, a carbon-saving nitritation and denitritation process was developed in a pilot-scale multi-cycle sequential batch reactor over 230 days. In the first three stages, the effluent total nitrogen (TN) concentration of the pilot plant without external carbon addition was similar to that of the on-site cyclic activated sludge system with external carbon addition. A highest nitrite accumulation rate (57.3%) and TN removal rate (85.1%) was observed, respectively, under conditions that temperature of 28.3 °C, dissolved oxygen concentrations of 2.0 mg/L and COD/N ratios of 4.5:1 as well as a short oxic phase (32.8 min). As the influent TN decreased after heavy rain, NOB could still be suppressed by shortening oxic phase and lowering DO (1.5 mg/L). In winter, slight nitrite accumulation was still obtained by adding glucose in stage IV. Nitrite competition between NOB and denitrifiers was indeed the key to NOB suppression. It should be a good choice for wastewater treatment plants to achieve high discharge standard and save carbon source using such a proposed process.