Economic evaluation of a microalgae-based pig manure treatment: a model involving the circular economy and bioeconomy

This study evaluates the economic and environmental performance of a microalgae-based process for pig manure treatment using thin-layer reactors within the framework of the circular bioeconomy. The system was tested at pilot scale for one year, achieving consistent nutrient recovery and biomass production. Results show that the process removes on average 86% of nitrogen and 80% of phosphorus, equivalent to recovery rates of 2.0 g N/m 2 /day and 0.33 g P/m 2 /day, thereby reducing nitrate pollution and eutrophication risks. When scaled to a 1-ha facility, the model achieves an annual productivity of 109,500 kg of biomass, produced from 15 m 3 of slurry per day, with a unit operating cost of €2.35/kg. This biomass can be transformed into biofertilizers and biostimulants, directly substituting chemical inputs and contributing to soil health and emission reduction. A techno-economic analysis demonstrated profitability under multiple market conditions, with a positive Net Present Value (NPV) of up to €2.4 million over 15 years, and a break-even point of only 39,000 kg in year one, highlighting economic resilience. Environmentally, the model provides significant climate benefits by reducing greenhouse gas emissions associated with conventional manure management and by recycling nutrients into productive agricultural applications. This research demonstrates that microalgae-based pig manure treatment offers a viable and scalable solution for sustainable agriculture and waste valorization. By simultaneously addressing nutrient recovery, greenhouse gas mitigation, and economic feasibility, the system aligns with circular economy principles and provides a competitive alternative to energy-intensive conventional practices.