Nutrient removal and biodiesel feedstock potential of green alga UHCC00027 grown in municipal wastewater under Nordic conditions

Integrating cultivation with wastewater treatment improves the economics of microalgal based biofuel production and allows for the sustainable reuse of nitrogen (N) and phosphorus (P) from waste streams. Batch-cultivation of a locally isolated green microalga, UHCC00027, and an indigenous algal-bacterial consortium was undertaken on screened municipal wastewater in 24 L pilot reactors. Evaluations of growth and of N and P removal were performed at different Chemical Oxygen Demand (COD) levels and N:P ratios. Lipid accumulation and fatty acid composition of the resulting biomass were also examined. Unique to the present study was the evaluation of wastewater treatment performance under cold temperatures (7-13 °C) typical of a Nordic climate. While temperature exerted little influence on heterotrophic COD removal, vigorous (temperature dependent) growth of microalgae was important in the efficient removal of N and P, with the N:P ratio playing a central role. The studied cultivation regime and organisms achieved regulatory N and P removal levels with a hydraulic retention time (HRT) of 12 days. However, biodiesel properties of the resulting biomass did not meet international standards due to a high proportion of polyunsaturated fatty acids. Possible workarounds for simultaneously increasing nutrient removal efficiency, biomass productivity, and improving biomass suitability for biodiesel under a Nordic climate are discussed.