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 (approximately 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 (approximately 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.
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