POLAR CYANOBACTERIA VERSUS GREEN-ALGAE FOR TERTIARY WASTE-WATER TREATMENT IN COOL CLIMATES

Forty-nine strains of filamentous, mat-forming cyanobacteria isolated from the Arctic, subarctic and Antarctic environments were screened fo r their potential use in outdoor waste-water treatment systems designe d for cold north-temperate climates. The most promising isolate (strai n E18, Phormidium sp. from a high Arctic lake) grew well at low temper atures and formed aggregates (flocs) that could be readily harvested b y sedimentation. We evaluated the growth and nutrient uptake abilities of E18 relative to a community of green algae (a Chlorococcalean asse mblage, denoted Vc) sampled from a tertiary treatment system in Valcar tier, Canada. E18 had superior growth rates below 15 degrees C (mu = 0 .20 d(-1) at 10 degrees C under continuous irradiance of 225 mu mol ph oton m(-2) s(-1)) and higher phosphate uptake rates below 10 degrees C (k = 0.050 d(-1) at 5 OC) relative to Ve (mu=0.087 d(-1) at 10 degree s C and k=0.020 d(-1) at 5 degrees C, respectively). The green algal a ssemblage generally performed better than E18 at high temperatures (at 25 degrees C, mu=0.39 d(-1) and k=0.34 d(-1) for Vc; mu=0.28 d(-1) an d k=0.33 d(-1) for E18). However, E18 removed nitrate more efficiently than Vc at most temperatures including 25 degrees C. Polar cyanobacte ria such as strain E18 are appropriate species for waste-water treatme nt in cold climates during spring and autumn. Under warmer summer cond itions, fast-growing green algae such as the Vc assemblage are likely to colonize and dominate, but warm-water Phormidium isolates could be used at that time.