Nitrification in cold climate – impact of sudden temperature change in a wet weather event

摘要

Strong dependence of the growth rate of nitrifying bacteria on temperature has receivedconsiderable attention as the nitrification process defines the size of reactors. The temperature correctionfactor (TCF) for autotrophic growth rate is typically set at the default value of 1.072 in the Arrheniusequation. Recent studies however have reported higher temperature sensitivity in case of suddentemperature drops, such as caused by cold shock due to wet weather and snow-melt events. Thepurpose of this study was to investigate the effect of temperature on nitrification growth rate in case of asharp decrease of temperature and to model the impact of the TCF on the nitrification rate during coldshock and wet weather flows, using BIOWIN simulation software. It was found that a sudden temperaturedecrease impacted nitrification much more than predicted. The immediate decrease of temperature by10°C led to 20% larger decrease of specific nitrification rate than predicted by the temperature correctionfactor of 1.072. BIOWIN simulation compared the effluent NH4-N concentrations for different TCFs, one ofwhich is found from the conducted experiment, in cold shock condition. Higher TCF would result in higherpredicted effluent concentration during cold-shock days and slower recovery, which translates to a longerperiod of autotrophs washout. This study showed that a nitrifying activated sludge will suffer from the coldshock more seriously than predicted by the current default TCF. The washout of nitrifiers will be severe atlower solid residence time (SRT) but can be mitigated by increasing the biomass inventory.