July 2011, Vol. 23, No.7


Experience with dual nutrient control in Canada

I was very interested to read the article “Algae wars: Is dual nutrient control necessary to curb algal blooms?” in WE&T (May 2011).

Based on our practical experience, to curb algal blooms, one should control both nitrogen and phosphorus.

In 1984 and 1985, the City of Saskatoon, in Saskatchewan, carried out a very comprehensive study assessing the effects of the city’s effluent, which was treated by primary treatment only, on the water quality of the South Saskatchewan River. Results indicated that the city’s effluent contributed as much as 80% of the total phosphorus and 50% of the total nitrogen to the river downstream of the plant outfall. This resulted in relatively dense weed growth beginning 1.0 km downstream of the outfall and excessive growth 4.0 km downstream.

In 1996, the City of Saskatoon Wastewater Treatment Plant upgraded its treatment process with a biological nutrient removal system. The state-of-the-art tertiary treatment system removes biochemical oxygen demand, suspended solids, nutrients (phosphorus and nitrogen), and minerals.

In 2001, Environment Canada published a report entitled “Ecological Survey of the South Saskatchewan River Downstream of the City of Saskatoon Wastewater Treatment Plant” and concluded that nutrients have been reduced considerably in the river and overall the South Saskatchewan River appeared to be very clean and affected little within the first 26 km downstream of the City of Saskatoon’s effluent.


C. P. Hwang
Retired branch manager of wastewater treatment for the City of Saskatoon
Saskatoon, SK



The May Problem Solver on the use of fiber optic temperature measurement to monitor sewers neglected to mention that the work was performed by Olivier Hoes of Delft University and SelkerMetrics (Portland, Ore.). 




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