Assessment of phyto-remediation efficiency and crop productivity of castor-based rice mill effluent (RME) wetland...

For major paddy producing countries like India, rice mill effluent (RME) poses a persistent environmental challenge by dint of its high organic and nutrient loads. Among various methods of treatment of various wastewater, of late, including RME, constructed wetland has been emerging as a sustainable treatment option. Usage of Ricinus communis (commonly called Castor) has been explored herewith for being the wetland plant for remediation of RME, so as to achieve simultaneous effluent remediation and biomass production. In the present study the RME and soil samples were procured from Vallam suburb of Thanjavur district of Tamil Nadu (India) for being a part of a rich agro-belt of southern India. The biochemical analyses of the RME and soil indicate elevated TDS, EC, and nitrate levels. RME-pre-soaked castor seeds exhibited enhanced germination percentage (90%) and as high as 12-fold rise in vigor index, in comparison to controls, The results emerged from the wetland trials, moderate effluent dilution (50%) maximized plant height (52 cm), leaf area index (2.4), and removal efficiencies (65-72% for NO₃^--N and NH₄⁺-N; >70% for COD/BOD). Field validation study further confirmed enhanced plant growth and yield in effluent-enriched soils, with seed yield increasing fourfold (22 → 91 g) and harvest index rising to 60.6%. The system performance was strongly supported by enhanced microbial activity, as indicated by a 77% increase in microbial biomass carbon and a 76% increase in dehydrogenase activity. Overall, these findings suggest that castor-based constructed wetlands have the potential to integrate wastewater phytoremediation with productive land use while maintaining the chemical safety of castor seed biomass within a circular bioresource framework.