Sustainable biostimulant strategy through microalgae-based recycling of horticultural fertigation drainage management

The reuse of horticultural drainage water represents a promising strategy to scarcity and promote sustainability in intensive agriculture. This study evaluates the potential of a microalgae-based treatment system for fertigation management through the purification of drainage water from a hydroponic tomato crop grown in coconut fibre substrate. Using Scenedesmus sp. in raceway reactors, we analyzed the efficiency of ion removal, microbial community dynamics, and microalgal biomass productivity. Results demonstrated that microalgae treatment effectively reduced concentrations of key nutrients and trace elements—such as nitrate, phosphate, calcium, and iron—while maintaining stable electrical conductivity. Biomass productivity (15.42 ± 2.34 g m⁻2 d⁻1) was comparable to that achieved with synthetic media, confirming the viability of agricultural effluents as a growth substrate. The microbial analysis revealed that, although some beneficial microorganisms declined, the system significantly reduced pathogenic taxa and enriched microbial genes involved in carbon degradation and phosphorus cycling. These changes suggest that treated water can enhance nutrient availability, especially in soils with organic amendments or alkaline pH. Moreover, fertigation trials using the treated water on lettuce showed improved nutrient uptake and crop yield, along with mitigation of osmotic stress effects. Overall, the results highlight the agronomic, environmental, and economic benefits of integrating microalgae-based treatment systems in horticulture. This approach represents a practical model of circular economy, enhancing irrigation efficiency, reducing pollution, and promoting sustainable bioresource utilization.