Urban wastewater treatment by seven species of microalgae and an algal bloom: Biomass production, N and P removal kinetics and harvestability

Abstract

This study evaluates the capacity of seven species and a Bloom of microalgae to grow in urban wastewater. Nutrient removal kinetics and biomass harvesting by means of centrifugation and coagulation–flocculation-sedimentation have been also tested. Results show that the best biomass productivities ranged from between 118 and 108 mgSS L−1 d−1 for the Bloom (Bl) and Scenedesmus obliquus (Sco). Regarding nutrient removal, microalgae were able to remove the total dissolved phosphorus and nitrogen concentrations by more than 80% and 87% respectively, depending on the species tested. The final total dissolved concentration of nitrogen and phosphorus in the culture media complies with the European Commission Directive 98/15/CE on urban wastewater treatment. Regarding harvesting, the results of coagulation–flocculation sedimentation using a 60 mg L−1 dose of Ferric chloride were similar between species, exceeding the biomass removal efficiency by more than 90%. The results of centrifugation (time required to remove 90% of solids at 1000 rpm) were not similar between species, with the shortest time being 2.9 min for Sco, followed by the bloom (7.25 min). An overall analysis suggested that the natural bloom and Scenedesmus obliquus seem to be the best candidates to grow in pre-treated wastewater, according to their biomass production, nutrient removal capability and harvestability.