Urban wastewater photobiotreatment with microalgae in a continuously operated photobioreactor: growth, nutrient removal kinetics and biomass coagulation–flocculation

The aim of this study was to investigate the growth, nutrient removal and harvesting of a natural microalgae bloom cultivated in urban wastewater in a bubble column photobioreactor. Batch and continuous mode experiments were carried out with and without pH control by means of CO2 dosage. Four coagulants (aluminium sulphate, ferric sulphate, ferric chloride and polyaluminium chloride (PAC)) and five flocculants (Chemifloc CM/25, FO 4498SH, cationic polymers Zetag (Z8165, Z7550 and Z8160)) were tested to determine the optimal dosage to reach 90% of biomass recovery. The maximum volumetric productivity obtained was 0.11 g SS L−1 d−1 during the continuous mode. Results indicated that the removal of total dissolved nitrogen and total dissolved phosphorous under continuous operation were greater than 99%. PAC, Fe2(SO4)3 and Al2(SO4)3 were the best options from an economical point of view for microalgae harvesting.