Surfactant removal and biomass production in a microalgal-bacterial process: effect of feeding regime

The influence of the feeding regime on surfactant and nutrient removal and biomass production was evaluated in three high rate algal ponds for primary domestic wastewater treatment. Feeding times of 24, 12 and 0.1 h d^-1 were studied in each reactor at a similar hydraulic retention time of 7.0 days and organic load of 2.3 mg m^-2 d^-1. Semi-continuous feeding at 12 and 0.1 h d^-1 showed better microalgal biomass production (0.21-0.23 g L^-1) and nutrient removal, including nitrogen (74-76%) and phosphorus (80-86%), when compared to biomass production (0.13 g L^-1) and nitrogen (69%) and phosphorus (46%) removals obtained at continuous feeding (24 h d^-1). Additionally, the removal efficiency of surfactant in the three reactors ranged between 90 and 97%, where the best result was obtained at 0.1 h d^-1, resulting in surfactant concentrations in the treated effluent (0.3 mg L^-1) below the maximum freshwater discharge limits.