Influence of flue gas sparging on the performance of high rate algae ponds treating agro-industrial wastewaters

Abstract

The influence of flue gas sparging (7% CO 2) on the performance of two 465 L High-Rate Algal Ponds (HRAPs) treating diluted swine manure at 10 days of hydraulic retention time was evaluated under continental climatic conditions (Castilla y León, Spain). COD, NH 4 +, and PO 4 3− removal efficiencies were not significantly affected by flue gas input (at 2.2 and 5.5 L min −1), which suggests that CO 2 sparging does not compromise wastewater treatment in HRAPs. In this particular study, COD and NH 4 + removal efficiencies of 56 ± 31% (near to maximum swine manure biodegradability) and 98 ± 1%, respectively, were consistently maintained, regardless of the environmental and operational conditions. CO 2 sparging resulted however in lower pH values (≈2 units lower) and an enhanced NH 4 + nitrification (higher NO 3 − and NO 2 − concentrations) compared to the system operated in the absence of flue gas supply. Biomass concentration was only higher (≈30% than in the control HRAP) when flue gases were supplied at 5.5 L min −1, probably due to the fact that the higher irradiances and temperatures prevailing within this experimental period resulted in an inorganic carbon-limited scenario in the control HRAP. Therefore, it can be concluded that CO 2 assimilation would be ultimately dependent on the occurrence of inorganic carbon limitation and will never occur in light, COD or nutrients-limited scenarios.