Nitrogen and phosphorus removal by high latitude mat-forming cyanobacteriafor potential use in tertiary wastewater treatment

As part of a program to develop biological wastewater treatment systems for cold climate areas four strains of filamentous, mat-forming cyanobacteria isolated from Arctic and Antarctic environments were evaluated for their nu trient stripping and growth capabilities. A tropical strain, Phormidium boh neri, known for its excellent performance in wastewater treatment, was used as a comparison. Experiments were done in artificial media under controlle d batch culture conditions to avoid interactions with indigenous microorgan isms such as bacteria and protozoa. The culture medium simulated real efflu ents containing high concentrations of nitrate and phosphate. Temperatures (5, 15 and 25 degrees C) and irradiances (80, 210, 350, 640 and 1470 mu mol photon m(-2)s(-1)) were selected according to situations encountered in a variety of field conditions. For all irradiance levels, growth was satisfac tory at 15 and 25 degrees C, but limited at 5 degrees C. At 25 degrees C a satisfactory nitrogen removal rate (3.5 and 4.0 mg N L(-1)d(-1)) was obtain ed for one polar strain (Phormidium tenue) and the control P. bohneri. At 1 5 degrees C, the best nitrogen removal rate (3.5 mg N L(-1)d(-1)) was measu red with P. bohneri while the best rate for the polar strains was around 2. 3 mg N L(-1)d(-1). At 15 degrees C, a phosphorus removal rate of 0.6 mg P L (-1)d(-1) was obtained with P. bohneri and polar strains P. tenue and Oscil latoria O-210. Nitrogen (NO3-) and phosphorus (PO43-) uptake rates increase d as a function of irradiance over the range 80 to 350 mu mol photon m(-)2s (-)1. Our results indicate that tertiary biological wastewater treatment at low temperatures (5 degrees C) cannot be anticipated with the polar strain s tested, because they are psychrotrophic rather than psychrophilic and thu s grow too slowly under conditions of extreme cold. However, it appears tha t these cyanobacteria would be useful for wastewater treatment at moderatel y cool temperatures (c. 15 degrees C), which are common during spring and f all in northern climates.