a b s t r a c tAdsorptive removal of paraquat from aqueous solution is performed in continuous mode using packed beds of RHA and BFA. The packed-bed parameters of RHA and BFA are determined and compared at different influent concentrations, flow rates, and bed heights. The maximum saturation capacity of RHA (6.96 mg/g) is found at 2 mL/min (flow rate) and 6.4 cm (bed height), whereas that of BFA (20.55 mg/g) is found at 5 mL/m in (flow rate) and 8.8 cm (bed height) for 20 mg/L (concentration). The volume of paraquat solution treated using RHA and BFA for the aforementioned experimental conditions is 2380 mL and 7800 mL, respectively. The bed saturation time and fractional bed utilization of BFA are higher than those of RHA. The bed depth service time (BDST), Thomas, and Yoon-Nelson models are applied to predict the behavior of breakthrough curves. The BDST model reveals the complex mechanism comprising more than one rate-limiting step for the adsorption of paraquat on RHA and BFA. The value of effluent concentration predicted by the Thomas model is in accordance with the experimental value. The lower value of standard deviation between the experimental and predicted times for 50% saturation indicates the applicability of the Yoon-Nelson model for packed-bed adsorption of paraquat on both RHA and BFA.

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As a regular farming practice in India, especially in Vidarbha, biomass ashes (BMAs) are spread on farmland. BMA forms a protective layer on the soil surface and acts as a barrier, thereby preventing direct contact between pesticides and soil. BMA acts: (i) as an adsorbent for removal of pesticides; (ii) as a soil additive and water enhancer, and (iii) as a micronutrient source for plants. In this study, paraquat, a representative chemical was selected to prove the hypothesis that BMAs are the most efficient adsorbents of herbicides used in Vidarbha. The adsorption capacity (mg/m 2 ) of BFA for removal of paraquat was found to be greater than that reported for natural adsorbents. Based on adsorption capacity, RHA and BFA dosages per hectare of land are recommended for different crops and fruits.