Evaluation of high rate ponds operational and design strategies for algal biomass production and domestic wastewater treatment

Highlights: • CO₂ addition allowed the adoption of higher depths in HRPs. • UV disinfection in 40 cm HRP provided biomass growth similar to that of 30 cm HRPs. • Chlorella sp. and Scenedesmus were the dominant genera in all evaluated conditions. • The removal efficiency of organic matter was about 40%, regardless HRPs design. • Nutrients removal was greater in 20 cm HRPs; recovery was allowed with CO₂ addition. This study evaluated the effect of high rate ponds (HRPs) depth on algal biomass production during domestic wastewater treatment. HRPs were evaluated for 20, 30, and 40 cm depths, with and without CO₂ supplementation. In addition, 40 cm deep HRP with ultraviolet (UV) pre-disinfection was evaluated. The concentration of chlorophyll-a as a function of time for each evaluated condition was represented by logistic models that were after submitted to cluster analysis. The 20 cm HRPs presented higher chlorophyll-a concentration, reaching a maximum of 5.8 and 4.3 mg L⁻¹, in the HRPs with and without CO₂ addition, respectively. Ammonia nitrogen and soluble phosphorus were greater removed in shallower HRPs. The addition of CO₂ influenced the nutrient removal processes, optimizing nutrient recovery by biomass assimilation. HRP configuration did not influence organic matter removal (~40% of removal efficiency in all HRPs), predominant microalgae genera (Chlorella sp. and Scenedesmus), and E. coli inactivation (removal of ~2 log units), except for the 20 cm HRP without CO₂ that had removal of 4 log units due to high pH values. For HRPs with CO₂ addition and UV pre-disinfection, the models for 40 cm were grouped together with those obtained for 30 cm HRPs, indicating the same behavior for chlorophyll-a production as a function of time. Thus, it can be concluded that the evaluated strategies represent alternatives for reducing HRP area requirements. Moreover, results may represent advancement and major contributions for HRP design criteria.