Swine wastewater-cultivated Chlorella sorokiniana reduces cadmium accumulation in rice grown on contaminated paddy soil

Cadmium (Cd) contamination in acidified paddy soils poses a major threat to rice safety and necessitates practical remediation strategies compatible with flooded rice cultivation systems. In this study, a Cd-tolerant microalgal strain, Chlorella sorokiniana T003, was isolated and evaluated for its potential to reduce Cd accumulation in rice through a microalgae-based remediation strategy integrated with swine wastewater utilization. Strain T003 maintained growth at Cd concentrations up to 25 mg L⁻¹ and removed over 90% of dissolved Cd at 5-25 mg L⁻¹, with a removal efficiency of 62% at 50 mg L⁻¹. T003 also showed robust growth in untreated swine wastewater, reaching 1.5 × 10¹¹ cells L⁻¹ after 9 d, supporting its suitability for wastewater-based biomass production. In pot experiments, application of T003 cultivated in swine wastewater increased soil pH from 5.61 to 6.60 and reduced rice shoot Cd concentration by up to 75.9% compared with the alkalized control. Field application similarly increased soil pH from 5.60 to 6.11, reduced exchangeable Cd by 49.7%, and decreased grain Cd concentrations by 72.7% and 98.7% in two rice cultivars, respectively. These findings indicate that C. sorokiniana T003 cultivated in swine wastewater can reduce Cd accumulation in rice under field conditions and may provide a biologically based strategy for Cd mitigation in acidified paddy soils while supporting nutrient recycling in crop-livestock systems.