Deterioration of the anammox process at decreasing temperatures and long SRTs

The implementation of autotrophic nitrogen removal in the mainstream of a municipal wastewater treatment plant is currently pursued. Among the crucial unknown factors are the kinetic properties of anaerobic ammonium oxidising (anammox) bacteria at low temperatures. In this study we investigated the adaptation of a fast-growing anammox culture to a lower temperature. In a membrane bioreactor a highly enriched anammox community was obtained at 30°C, 25°C and 20°C. This culture was exposed to long- and short-term temperature changes. In short-term experiments the decrease in biomass-specific activity due to decrease in temperature can be described by an activation energy of 64 ± 28 kJ mol⁻¹. Prolonged cultivation (months) implies that cultivation at low temperatures resulted in deterioration of biomass-specific activity (Ea^LT 239 kJ mol⁻¹). The growth rate and specific anammox activity in the system decreased from 0.33 d⁻¹ and 4.47 g NO₂-N g VSS⁻¹ d⁻¹ at 30°C to 0.0011 d⁻¹ and 0.037 g NO₂-N g VSS⁻¹ d⁻¹ at 20°C. The reason for the deterioration of the system was related to the required long SRT in the system. The long SRT leads to an increase of non-active and non-anammox cells in the reactor, thereby decreasing the biomass-specific activity.