Formation of algal flocs from activated sludge in synthetic medium and secondary treated wastewater

BACKGROUND: Photogranules seem to be an alternative solution for wastewater treatment and biomass harvesting. The aim of our work was to investigate the formation of algal flocs as an efficient method for the treatment of wastewater and separation of algal cells. RESULTS: The progressive change of activated sludge to algal flocs was evaluated under static and stirring conditions using a synthetic substrate (modified Blue Green-11 medium) and the secondary effluent from an activated sludge wastewater treatment plant. Algal flocs were observed in all cultures by day 10 and a high chlorophyll concentration was detected in all cases reaching values up to 610-630 mu g L-1 at the end of the experiment after 30 days. The size of flocs in all cultures at either static or mixing conditions ranged from 330 to 994 mu m, resulting in biomass concentration from 330 to 660 mg L-1. The cultures in secondary effluent at static conditions presented the greatest size, and the mean diameter on days 10 and 30 was 250 and 994 mu m, respectively. The cultures were efficient in nutrient removal and, by the end of the experiment, nitrates and phosphates were completely consumed. CONCLUSIONS: Algal flocs were developed from activated sludge without adding any other flocculant and a highly efficient biomass was developed, which can easily settle and remove nutrients from the medium. (c) 2022 Society of Chemical Industry (SCI).