Selection Enhanced Nutrient Removal from Pig Farm Wastewater Using Co-Immobilized Chlorella vulgaris and Azospirillum brasilense Azo09 in Alginate Beads

The livestock industry in Vietnam significantly contributes to agricultural production but also generates severe environmental pollution, particularly from untreated wastewater. Pig farm effluents contain high concentrations of nitrogen (N) and phosphorus (P), far exceeding regulatory limits. This study investigates an innovative wastewater treatment approach using co-immobilized Chlorella vulgaris microalgae and Azospirillum brasilense bacteria in alginate beads. The combination aims to enhance the removal of ammonium (N-NH4+), total nitrogen (TN), phosphate (P-PO43−), and total phosphorus (TP), while also facilitating easier biomass recovery. Experimental wastewater, diluted tenfold, exhibited high pollutant concentrations: TN (540.7 mg/L), TP (185.7 mg/L), N-NH4+ (157.5 mg/L), P-PO43− (19.3 mg/L), and BOD5 (189.4 mg/L). Over 12 days, different treatment setups were evaluated, with the most effective being the co-immobilized microalgae-bacteria system (VTVK treatment). Results showed significant reductions: N-NH4+ decreased by 93.8% (to 9.71 mg/L), TN by 85.9% (to 76.24 mg/L), P-PO43− by 77.7%, and TP by 66%. These removal rates exceeded those of treatments using only C. vulgaris immobilized in alginate beads, confirming the beneficial role of A. brasilense in stimulating microalgal growth and nutrient assimilation. This bioremediation method effectively reduces nutrient loads in pig farm wastewater, meeting Vietnam’s national discharge standards (QCVN 01-79:2011/BNNPTNT and QCVN 62-MT:2016/BTNMT). The study highlights the potential of microalgae-bacteria co-immobilization as a sustainable and scalable solution for livestock wastewater treatment, offering improved efficiency and simplified biomass recovery.