Medicinal plant ashwagandha in hydroponics: Pioneering greywater remediation using response surface methodology along with plants’ physiological and phytochemical attributes for sustainable resource recovery

Abstract

This study aimed to investigate greywater treatment through hydroponically growing ashwagandha, often referred to as "Indian Ginseng," which is rich in secondary metabolites and bioactive compounds that enhance its medicinal properties. The research examines the effect of input parameters, such as initial chemical oxygen demand (300–1500 mg/L), phosphate (0–120 mg/L), and nitrate (15–75 mg/L) and their optimization utilizing response surface methodology (RSM) with central composite design (CCD). The interactive effects are analysed with model fit through analysis of variance. The optimized parameters are investigated as 600 mg/L chemical oxygen demand (COD), 37 mg/L phosphate, and 35 mg/L nitrate, with maximum removal efficiencies of 97.74% COD, 93.62% total phosphorus, and 89.68% nitrate-nitrogen while preserving ashwagandha's medicinal qualities. The study assesses growth improvements through physiological traits, showing increase of 72.2% in wet biomass, 20% in plant height, 60% in leaf number, and total chlorophyll content of 45.45 μmol m⁻². It also examines phytochemical characteristics, including fourier transform infrared spectroscopy analysis (-OH peaks within 3500-3000 cm⁻¹) and total phenolic content of leaf and root extracts, measuring 7.14 mg gallic acid equivalents for leaves and 2.155 mg GAE for roots. Additionally, the extracts demonstrated radical scavenging activities of 73.26% for leaves and 83.74% for roots after treatment, highlighting ashwagandha's adaptability and resilience in greywater conditions. Lastly, scanning electron microscopy analysis to assess the impact of wastewater on the root structure. This research presents significant economic potential of the greywater treatment within 6 days by cultivating ashwagandha with the preservation of its medicinal properties.