Nitrifying biofilms at cold temperatures: Kinetics and in-situ characterization

The biological process of nitrification is currently the most economical and commonly employed means of removing ammonia from wastewater. Although nitrification is cost-effective and has been used in many treatment facilities in North America, the temperature sensitivity of suspended growth nitrifying bacteria is of considerable concern when designing wastewater treatment facilities in many North American cities. Notwithstanding the limited ability of suspended growth treatment systems to achieve nitrification at low temperature, there is evidence that attached growth nitrification processes have the potential to consistently achieve ammonia removal at low temperatures.;The laboratory experiments demonstrated significant rates of attached growth nitrification at 4°C for the approximate span of a cold climate, North American winter. Specifically, significant nitrification rates were confirmed after 115 days at 4°C. A pronounced kinetic reduction of the rate of nitrification occurred immediately after the acclimatization period, with the kinetics approaching steady state values after approximately 90 days. The field experiments revealed significant rates of nitrification within laboratory-scale and pilot-scale treatment systems configured as nitrification-upgrades to a lagoon treatment system during winter conditions.;The analytical protocols developed in this research demonstrated that attached growth ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) populations are capable of surviving exposure to 4°C for 118 days within wastewater treatment environments. The RNA content of the AOB cells remained sufficient for FISH enumeration throughout the 118 days at 4°C, while the RNA content of the NOB cells decreased significantly with exposure to 4°C and therefore prevented their enumeration using FISH.;The objective of this dissertation is to investigate the effect of prolonged exposure to cold temperatures on the kinetics of attached growth nitrification in wastewater treatment facilities as well as the subsequent consequences on the nitrifying bacterial community. Methodological techniques to characterize the weight, nitrogen content and volume of the biofilm along with the volume of nitrifying biomass were developed that minimize loss of mass and manipulation of the biofilm samples. Subsequently, laboratory experiments were performed on attached growth nitrifiers at 4°C. In addition, field experiments were conducted on attached growth laboratory-scale and pilot-scale treatment systems at 4°C.