Impact of Elevated Refinery Wastewater Temperature on Nitrification Rates in the Activated Sludge Process

This paper summarizes prior research undertaken to assess the impact of elevated wastewater temperature on nitrification rates in the activated sludge process. Research work of others who have used Monod kinetics to model nitrification performance and describe the affect of temperature on nitrification rates is summarized. Observed data are presented; temperature-dependant nitrification rates calculated; and temperature correction coefficients using the Arrhenius equation are developed for the range of temperatures typically found in refinery wastewaters. Other environmental conditions, including pH, are known to affect nitrification rates, and this paper explores the role of pH in establishing a nitrification treatment strategy during periods of elevated wastewater temperature.Some of the reported observations on nitrification rates are made in the 35°C to 45°C range, the temperature range where the performance of temperature-sensitive nitrifying organisms is reported to decline. This is also the temperature range that is common for refinery wastewaters and current global environmental policies now require near complete nitrification of elevated ammonia-containing refinery wastewater, and in some cases, total nitrogen removal to less than 10 mg/L.This paper presents an empirical model for predicting the affect of wastewater temperature on nitrification in activated sludge systems and presents treatment strategies that can be used to optimize nitrification design and operation for refinery wastewaters, particularly for refineries located in warm-weather climates.