Secondary functions of ammonia oxidising bacteria and their impact on the environment

Ammonia oxidising bacteria (AOB) play an important role in the Earth’s ecosystem by being the only known autotrophic bacteria to be able to convert ammonia to nitrite, the first step in nitrogen removal. Besides their primary function and ability, AOB also have secondary functions that have an effect on our climate. Under aerobic conditions, AOB can produce nitrous oxide which is a greenhouse gas with warming effect 260 times that of carbon dioxide. Hence, even low amounts of nitrous oxide are unwanted. Another secondary function of AOB is their ability to co-metabolise toxic organic compounds due to the unspecific nature of the ammonia monooxygenase enzyme. This uncanny ability allows them to play a major role in the bioremediation of organic compounds which is an economical and environmentally friendly method. In recent years, a new type of organic solvent called ionic liquids (IL) has emerged due to favourable properties over traditional organic solvents. Their increase in usage inevitably allows them to find their way into the environment via different routes such as effluent of wastewater treatment plants. This is because traditional wastewater treatment plants are not equipped to deal with such new emerging contaminants. This thesis examines the secondary functions of AOB mentioned above. Firstly, an investigation of nitrous oxide emission between an enriched partial and full nitrification AOB culture revealed that the full nitrification culture produced significantly more nitrous oxide which is contrary to most literature. Secondly, the potential removal of ILs by AOB in short and long-term studies were explored. Soluble microbial products, extracellular polymeric substances and nitrogen removal performance were also monitored. And thirdly, the effects of various ILs on the ammonia oxidation rate (AOR) were also examined. Results indicated that biosorption played a major role in removal for ILs with long alkyl chain however, it had an adverse effect on the AOR. Biotransformation pathways for various ILs were also investigated.Doctor of Philosoph