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

As part of a program to develop biological wastewatertreatment systems for cold climate areas four strainsof filamentous, mat-forming cyanobacteria isolatedfrom Arctic and Antarctic environments were evaluatedfor their nutrient stripping and growth capabilities. A tropical strain, Phormidium bohneri, known forits excellent performance in wastewater treatment, wasused as a comparison. Experiments were done inartificial media under controlled batch cultureconditions to avoid interactions with indigenousmicroorganisms such as bacteria and protozoa. Theculture medium simulated real effluents containinghigh concentrations of nitrate and phosphate.Temperatures (5, 15 and 25^°C) and irradiances(80, 210, 350, 640 and 1470 µmol photon m^-2s^-1) wereselected according to situations encountered in avariety of field conditions. For all irradiancelevels, growth was satisfactory at 15 and 25 ^°C,but limited at 5 ^°C. At 25 ^°C a satisfactory nitrogen removal rate (3.5and 4.0 mg N L^-1d^-1) was obtained forone polar strain (Phormidium tenue) and thecontrol P. bohneri. At 15 ^°C, the bestnitrogen removal rate (3.5 mg N L^-1d^-1)was measured with P. bohneri while the best ratefor the polar strains was around 2.3 mg NL^-1d^-1. At 15 ^°C, a phosphorusremoval rate of 0.6 mg P L^-1d^-1 wasobtained with P. bohneri and polar strains P. tenue and Oscillatoria O-210. Nitrogen(NO₃^-) and phosphorus (PO₄^3-)uptake rates increased as a function of irradianceover the range 80 to 350 molphoton m^-2s^-1. Our results indicate thattertiary biological wastewater treatment at lowtemperatures (5 ^°C) cannot be anticipated withthe polar strains tested, because they arepsychrotrophic rather than psychrophilic and thus growtoo slowly under conditions of extreme cold. However, it appears that these cyanobacteria would beuseful for wastewater treatment at moderately cooltemperatures (c. 15 ^°C), which are commonduring spring and fall in northern climates.