Performance and Kinetics of Nitrification of Low Ammonia Wastewater at Low Temperature.

  The objective of this study was to investigate the effect of dissolved oxygen on nitrification in a sequencing batch reactor (SBR) treating low ammonia wastewater (40 mg N/L) at a low temperature (14 °C). During the 130 days of operation, three dissolved oxygen levels (5-6 mg dissolved oxygen/L, 2-3 mg dissolved oxygen/L, and 0.8-1.0 mg dissolved oxygen/L) were tested. Dissolved oxygen reduction resulted in lower ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) activity, with decreasing ammonia conversion ratio and increasing nitrite accumulation ratio. The maximum growth rates of AOB and NOB determined in this study (0.28 and 0.38 d-1) were below the median values from the literature (0.47 and 0.62 d-1), whereas the oxygen half-saturation coefficients of AOB and NOB (1.36 and 2.79 mg/L) were higher than those found in the literature. The kinetic model explained the SBR performance well. Low dissolved oxygen, together with long solids retention time, was recommended for partial nitrification at a low temperature.