Valorization of swine manure-derived effluent using Arthrospira (Limnospira) maxima: pilot-scale nutrient removal and biomass utilization as livestock feed

Although physical, chemical, and biological wastewater treatment technologies have improved in recent years, their overall effectiveness remains limited by various challenges. This study evaluated the potential application of swine manure aerobic digestate effluent (SME) as an alternative medium for cultivating the cyanobacterium Arthrospira (Limnospira) maxima to meet the requirements for sustainable microalgae cultivation. A pilot-scale study was conducted using a 200-L photobioreactor to test the efficacy of SME dilutions of 30%, 50%, and 70% (v/v) over 30 days. The objective was to identify the optimal concentration for microalgae growth and nutrient removal. The 30% SME group showed the highest biomass productivity (1.04 ± 0.02 g L⁻1) and superior nutrient removal, with total nitrogen (T-N) and phosphate (PO₄-P) reduction rates of 42.46 ± 3.96% and 46.19 ± 1.36%, respectively, and chemical oxygen demand removal efficiency of 50.05 ± 6.04%. These findings indicate effective organic matter reduction under high-load conditions. The harvested biomass exhibited high protein content (~ 52%) and stable amino acid composition, supporting its potential as a protein-rich livestock feed. However, trace metal accumulation (Zn and Cu) increased at higher SME concentrations, highlighting the need for optimized dilution strategies. These results demonstrate the feasibility of integrating nutrient removal and biomass valorization using microalgae and show that swine manure-derived SME can be directly used without pretreatment as a scalable, eco-friendly approach in circular agriculture.