Ammonia removal in northern sewage treatment lagoons

By V. Enns, J. Kelly, and C. Butt, Environment Canada, Whitehorse, Yukon

Livingstone Trail Environmental Control Facility (LTECF), May 8, 1998.

It has been estimated that there are more than 850 sewage lagoons operating in Canada (Heinke et al., 1991). In spite of this, there have not been many comprehensive assessments of lagoon treatment performance. As communities and regulators increasingly demand higher levels of treatment, it becomes more important to improve our understanding of the factors controlling treatment efficacy.

Ammonia can be an important parameter because of: a) its toxicity to fish; b) its contribution to nutrient loading in receiving waters; and, c) it can be the limiting design factor for some land application treatment systems which can be used for polishing of lagoon effluents.

From 1999 to 2001 ammonia removal was investigated in several sewage lagoons in the Yukon. As similar trends were observed at each of the lagoons, this report will focus on the Whitehorse lagoon which was studied the most extensively.

In mechanical sewage treatment plants, ammonia removal normally is achieved by providing conditions which foster high concentrations of nitrifying bacteria. In lagoons it has been postulated that the primary ammonia removal mechanisms are volatilization and algal biomass assimilation.

At equilibrium, ammonia exists in both an ionized and unionized form in water. Volatilization occurs when ammonia is in the unionized form as shown in the equilibrium equation:

The equation proceeds to the right at high pH and, therefore, high pH favours volatilization.

The growth rate of algal biomass is regulated by photosynthesis and water temperature. The necessary carbon source can come from either absorption of atmospheric carbon dioxide or from dissolved organic carbon. Ammonia and phosphorus are assimilated into the algal biomass as essential nutrients and converted to their organic forms. The overall reaction can be approximated as shown by the following equation:

Site Description and Sampling Methodology

Whitehorse is located at 60°34'N 135°4'W. About 18,000 people are served by the Whitehorse lagoon which is known as the Livingstone Trail Environmental Control Facility (LTECF). In a typical July, this City receives approximately 256 hours of bright sunshine and has an average daily temperature of 14°C. The average annual precipitation is 269 mm.

This article was abridged from Environmental Science & Engineering magazine, which also contains many more articles not posted on our Web Site. See our home page on how to order your subscription. We regret we can only accept orders from Canada and the United States.