Adsorption study of micropollutants by biosorbents from different rice harvest residues for large scale applications

Abstract

A large-scale removal of micropollutants from residual waters is an urgent problem to be tackled. In this work, three biomasses from agricultural residues, produced by different processes, were compared in terms of the adsorption efficiency of toxic species in water. The biosorbents used were rice husk ashes (RHA), leached rice husk silica (SRHA), and rice straw ashes (RSA). Two representatives of the most common micropollutants present in the effluent waters, 2-nitrophenol and the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D), were chosen as probing molecules. The biosorbents were characterized by SEM, X-Ray FRX, FT-IR, BET, pHcpz, and hydrophobicity; surface areas of 175.81 m2 g-1(SRHA), 66.11 m2 g-1 (RHA) and 42.77 m2 g-1 (RSA) were found, together with a microporous morphology. Firstly, the efficiency of removal was evaluated through adsorption isotherms: RHA and SRHA proved to be more efficient, with an adsorption capacity of 29.14 mg g-1 and 23.75 mg g-1 of 2-nitrophenol and 10.82 mg g-1 and 10.55 mg g-1 for 2,4-D. In particular, the removal of more than 90% for both 2-Nitrophenol and 2,4-D stands out as a very promising result. In light of these results, pillow-shaped filters with RHA were fabricated and tested for the first time for 2-Nitrophenol removal on a larger scale. The positive outcome (removal efficiency of 73%) demonstrates the possibility of producing filters based on sustainable and cheap biosorbents that could be implemented industrially to improve water purification as well as to implement the concept of circular economy.