Microalgae growth and phosphorus uptake in wastewater under simulated cold region conditions

Abstract

Facultative waste stabilization ponds (WSP) are a common form of wastewater treatment in cold regions. However, cold region WSPs have been found to have highly variable and inconsistent microalgae growth and phosphorus removal. This study investigated whether facultative WSPs can be used to provide biological phosphorus removal in cold regions by evaluating maximum specific growth rates and phosphorus removal pathways under simulated cold region summer (ice-free) conditions. A factorial experiment was conducted in order to determine the main effects and interactions of temperature (10, 15°C), photosynthetically active radiation (PAR) (100, 150μmol/m2/s) and initial phosphorus concentration (7.5, 15mg P/L) on microalgae growth and phosphorus uptake. Maximum specific growth rates varied from 0.029 to 0.058/h. PAR and temperature had a statistically significant negative and positive effect, respectively, on growth rates. Initial phosphorus concentration had no statistical effect on growth rates under the studied ranges. Growth rates were similar to those observed at temperate climates. Luxury uptake was a significant phosphorus removal mechanism as it accounted for 53±8% (g P/g P) of biomass phosphorus. Biomass phosphorus concentrations were positively affected by PAR and initial phosphorus concentration while temperature had no effect. A crossover interaction between temperature and initial phosphorus concentration was found to have a negative effect on biomass phosphorus concentration. Under cold region conditions biomass phosphorus concentrations were 45% greater than under warm climate conditions. Ultimately, it is expected that climate should not hinder microalgae production in cold region WSPs during the summer months when temperatures exceed 10°C and the surface is ice-free. Cold region conditions appear to aid in phosphorus removal by increasing biomass phosphorus concentrations.