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

ABSTRACT Anaerobic digested pig-farming wastewater was treated in 100 L raceway ponds by microalgae-bacteria consortia under uncontrolled outdoor conditions. Removal of ammonia, nitrate, nitrite, phosphate and COD was achieved. Harvesting was facilitated by autoflocculation of the consortia. Lipids were extracted and a fatty acid profile was performed. Growth of pig farming industry has increased wastewater generation, underscoring the need for efficient, cost-effective treatment alternatives. This study aimed to cultivate an indigenous microalgae-bacteria consortium in 100 L outdoor raceway ponds (RWP) operated in batch mode to treat non-sterilized, non-diluted pig wastewater effluent from an anaerobic lagoon. RWP performance was evaluated in terms of nutrient removal, biomass productivity, and biomass valorization potential under real environmental conditions, which could provide critical data for scaling this technology beyond laboratory. Removal efficiencies of 93.6% for total inorganic nitrogen (removal rate: 231.6 mg/L·day), 94.6% for orthophosphate, and 91.6% for chemical oxygen demand (COD) were achieved in the final batch. The consortium exhibited auto-flocculation, facilitating biomass harvesting with a yield of 1.17 mg/L, as dry weight (DW). Biomass lipid content was 268.1 mg/g, as 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 2.0–3.2, indicating potential for biodiesel production. The dry-weight content of the protein was 13.4%. Environmental conditions did not inhibit consortium growth nor nutrient removal, supporting their viability and sustainability as an alternative for pig farming wastewater treatment.