Swine wastewater treatment in high rate algal ponds: Effects of Cu and Zn on nutrient removal, productivity and biomass composition.

This study aimed to evaluate the simultaneous interferences of Cu and Zn found in swine wastewater (SW) in the development of microalgae considering real conditions of cultivation in high rate algal ponds (HRAPs). Ten HRAPs on a pilot scale were fed with SW with different mixtures of Cu (0.5-3.0 mg/L) and Zn (5.0-25.0 mg/L). The interferences of these metals in removing nutrients (N-NH and soluble phosphorus (Ps)) from the SW were determined. In addition, this study evaluated the effects on biomass growth and biochemical composition. Chlorella sp. was dominant in all HRAPs and the condition that potentiated its growth occurred in medium containing 1.8 mg Cu/L + 15.0 mg Zn/L, while higher concentrations conferred inhibition. Only Cu compromised the removal rates of N-NH while the effects of Zn were not significant. Contrary, Zn interfered with Ps removal rates, but the impact of Cu was not significant. The greatest Cu applications increased the protein levels by biomass (50.5-55.2 %). Carbohydrate accumulation was favored by conditions that inhibited the development of microalgae due to either limitation or excess of metals. Copper and Zn compromised the levels of lipids, and the control treatment had the highest content (24.5 %). The presence of Cu and Zn changed the dynamics of HRAPs regarding nutrient removal, productivity, and biochemical composition of the biomass.