Utilization of agriculture waste materials as sustainable adsorbents for heavy metal removal: A comprehensive review

Low cost-adsorbent has been a good candidate as an alternative for commercial activated carbon in the application of water treatment. As they possess the capability of adsorbing contaminants, from wastewater and their use minimizes waste in the environment. Heavy metals have been a primary water pollutant since the increase in processing and production of several materials such as steel, copper, etc. Therefore, research has been conducted on the utilization of agricultural wastes which may serve as low-price adsorbents. In this paper, four main categories of agricultural waste materials, namely nut shells/stones, hulls/husks/seed coats, agroforestry peels, and others were investigated and compared as adsorbents to remove or minimize several wastewater impurities described in previous research. The results showed that the Nut shells/stones, such as green coconut single component, demonstrate effective adsorption capacities for lead and cadmium, while hulls/husks/seed coats, including soya bean hulls and modified Lentil husk, exhibit remarkable adsorption of copper and lead. The utilization of agroforestry peels, including chemically modified orange peel and orange peel, shows promising results in the removal of cadmium and nickel. Furthermore, the cost analysis shows variations in the estimated expenses associated with the utilization of these waste materials. Agroforestry peels demonstrate slightly lower estimated expenses, while Nut shells and hulls/husks exhibit comparable cost estimates. Future research should focus on the optimization of adsorption capacities, the exploration of practical applications, and the assessment of economic feasibility for potential large-scale implementation.