Seasonal isolation of microalgae from municipal wastewater for remediation and biofuel applications

Abstract

Aims: The objective of the study was to isolate the microalgae strains from treated municipal wastewater in both summer and winter seasons in order to identify strains better suited for nutrient remediation and biofuel production under either cooler or warmer temperatures.

Methods and results: Fifty-six strains in total were isolated and identified by DNA sequencing from effluent samples collected from a local wastewater treatment plant during the summer and winter of 2011. Screening of 41 isolates based on the fatty acid productivity at either 22 or 10°C resulted in the selection of 12 strains organized into two groups of 6-the M (mild) and C (cool) groups, respectively. Four of the C-group strains were isolated from the winter sample, while four of the M-group isolates were isolated from the summer sample. Fatty acid pools in M-group strains were heavily regulated in response to growth temperature while C-group strains were more insensitive. In three of the six C-group strains, the rates of biomass and fatty acid productivity at 10°C exceeded the corresponding rates at 22°C. Conversely, M group were always more productive at 22 compared to 10°C. Mixotrophic strategies to enhance productivity were generally unsuccessful in M-group strains at 22°C but proved to be more effective in C-group cultures at 10°C.

Conclusions: In general, C-group strains appeared better suited for growth in municipal wastewater at 10°C, while M-group strains were better suited at 22°C. On balance, C-group isolates were more likely to come from winter wastewater samples while M-group strains were more likely to come from the summer sample.

Significance and impact of the study: Our results demonstrate that the effects of temperature on microalgal growth for wastewater remediation can be mitigated somewhat by isolation and careful selection of strains adapted to seasonal wastewater conditions.

Keywords: CO2 capture; biofuel; biomass productivity; bioremediation; fatty acids; microalgae; temperature; wastewater.