Modifications of coconut waste as an adsorbent for the removal of heavy metals and dyes from wastewater

Abstract

Heavy metals, dyes, organic compounds and other pollutants released to the water ways without proper pre-treatment process has become a major hazard to the environment. Adsorption could be introduced as one of the most cost-effective and reliable treatment methods for the treatment of these effluents. Adsorbents play a vital role in the adsorption process and there is an increasing trend towards utilisation of the low-cost adsorbents. Among the low-cost adsorbents, coconut-based adsorbents including coconut husk, coconut shell fibre and coconut coir pith have proven to be significantly effective with the provision of satisfactory adsorption capacities for the removal of pollutants from wastewater. Although, raw, coconut-based adsorbents have been utilised in some of the adsorption experiments, research works have been conducted to investigate the modification methods for these adsorbents for achieving the optimum pollutant removal capacities from the wastewater. These modification processes include acid and alkali treatments, modification with surfactants, polymerisation and treatment with metal/metal chlorides as well as thermal treatments. The purpose of this review paper is to discuss the recent modification methods that have been applied for the coconut-based adsorbents and their effectiveness for the removal of contaminants from wastewater. Furthermore, suggestions for the improvement of these modification methods are provided.