For my first regular post (I plan to normally publish on a weekly basis, probably on Thursdays), I decided to look back at the research I did for my master's degree at the NSERC Chair in Water Treatment at the University of Waterloo. Two years ago, I submitted my thesis, titled,
An Investigation of Nitrification Predictors and Factors in Two Full-Scale Drinking Water Distribution Systems
As a brief explanation, most drinking water utilities in North America add a persistent disinfectant chemical so that the water is protected from harmful bacteria all the way to the tap. Chlorine has traditionally been the disinfectant of choice. However, many utilities are now choosing chloramines (mono-, di-, tri-), made from reacting free chlorine with ammonia. Chloramines have some notable advantages, such as often being longer-lasting in distribution system environments and not producing as much byproducts (at least not as many tri-halomethanes). One downside they have is that when they decay, ammonia is released; ammonia is a food source for some microorganisms so under some circumstances chloramines can promote the growth of microorganisms in distribution systems—the opposite of a disinfectant's purpose. The microbial conversion of ammonia to nitrite, and subsequently nitrate, is known as nitrification and is something that distribution system operators want to avoid/minimize. I'm deliberately using the term "microorganisms" rather than simply "bacteria", because there is another kind of microorganism, archaea that can be involved; this was an aspect of my research.
Not counting literature review, there were three main parts to my thesis research:
- Collecting samples from different locations in two distribution systems that use chloramine as a disinfectant and analyzing them for characteristics that are related (or may be related to nitrification). One thing that was analyzed was the abundance of nitrifying microorganisms, both ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) at each site over the course of the sampling campaign (which was long enough to encounter different seasonal conditions).
- Applying—and adapting—an easy-to-use test method, based on the batch decay of chloramine residuals, that previous authors had proposed for studying distribution system nitrification.
- Reviewing some models on distribution system nitrification.
If you'd like to see a copy, here are links for: