Nutrient removal from anaerobically treated pig farming wastewater by microalgae-bacteria consortia in outdoor raceway ponds

The growth of the pig farming industry has led to an increase in wastewater generation in Yucatán, underscoring the need for efficient and cost-effective treatment alternatives. Microalgae–bacteria consortia represent a viable option; however, few studies have been conducted under outdoor conditions and with raw wastewater. This study aimed to cultivate an indigenous microalgae-bacteria consortium in 100 L outdoor raceway ponds using a batch mode to treat non-sterilized, non-diluted anaerobically digested pig wastewater, evaluating its performance in terms of nutrient removal, biomass productivity, and valorization potential under real environmental conditions, which could provide critical data for scaling this technology beyond the laboratory. In the final batch, removal efficiencies reached 93.6% for total nitrogen (removal rate: 231.6 mg L ^− 1 day ^− 1 ), 94.6% for orthophosphate, and 91.6% for chemical oxygen demand (COD). The consortium exhibited auto-flocculation, facilitating biomass harvesting with a yield of 1.17 mg L ^− 1 dry weight (dw). The biomass lipid content was 268.1 mg g ^− 1 dw. Fatty acid profile showed a predominance of saturated fatty acids (SFA > 50%) with an unsaturated fatty acids/SFA ratio from 0.6 to 1.0 and a SFA/monounsaturated fatty acid ratio of 2.0 to 3.2, indicating potential for biodiesel production. The protein content of the biomass was 13.4% dw. These results demonstrated that environmental conditions did not inhibit consortium growth nor nutrient removal, supporting their viability and sustainability as an alternative for pig farming wastewater treatment.