Granular activated algae for wastewater treatment

摘要

The study used activated algae granules for low-strength wastewater treatment in sequential batch mode. Each treatment cycle was conducted within 24 h in a bioreactor exposed to 235 mu mol/m(2)/s light intensity. Wastewater treatment was performed mostly in aerobic conditions, oxygen being provided by microalgae. High removal efficiency of chemical oxygen demand (COD) was achieved (86-98%) in the first hours of the reaction phase, during which the indicator's removal rate was 17.4 +/- 3.9 mg O-2/g h; NH4+ was removed during organic matter degradation processes with a rate of 1.8 +/- 0.6 mg/g h. After almost complete COD removal, the NH4+ remaining in the liquor was removed through nitrification processes promoted by the increase of the liquor's oxygen saturation (O-2%), the transformation rate of NH4+ into NO3- increasing from 0.14 +/- 0.05 to 1.5 +/- 0.4 mg NH4+/g h, along with an O2% increase. A wide removal efficiency was achieved in the case of PO43-(11-85%), with the indicator's removal rate being 1.3 +/- 0.7 mg/g h. In the provided optimum conditions, the occurrence of the denitrifying activity was also noticed. A large pH variation was registered (5-8.5) during treatment cycles. The granular activated algae system proved to be a promising alternative for wastewater treatment as it also sustains cost-efficient microalgae harvesting, with microalgae recovery efficiency ranging between 99.85 and 99.99% after granules settling with a velocity of 19 +/- 3.6 m/h.