CHAPTER 1. Contamination of Heavy Metals in Aquatic Media: Transport, Toxicity and Technologies for Remediation

Abstract

The presence of pollutants in aqueous solution, particularly from hazardous heavy metals and metalloids, is an important environmental and social problem. As many of these elements are stable they are bio-accumulative, and assessment of their safe limits is very difficult in the ecosystem. Few metals, such as Fe, Zn, Cu, Co, Cr, Mn and Ni, are required for biological metabolism in trace amounts; however, their higher dose may cause toxic effects. Others, such as Pb, Hg, Cd and As, are not suitable for biological functions and are positively toxic. Toxicity of these elements is of considerable concern worldwide because of their environmental burden. During the past few decades scientists have been developing cheap and environmentally friendly technologies for the treatment of wastewater generated at the household and up to the industrial scale. In this regard, methods like ion-exchange, membrane filtration, catalysts including photocatalysts and photocatalysis, microbe-assisted phytobioremediation and adsorption over low-cost biosorbents and nanomaterials have been developed and demonstrated to be successful. Because of the demand for water to feed the growing population and the needs for industrial processing, the separation and purification of generated wastewater by adsorption phenomena is gaining major relevance. Adsorption over biomass-derived biosorbents has provided the capability to treat wastewater on a large scale. Several low-cost biosorbents have been synthesized and successfully applied to remove toxic metals and metalloids from wastewater. Nanomaterials and their analogues, such as magnetic nanosorbents and layered double hydroxides, have been the focus for the development of novel materials with high surface area and low-cost synthesis to develop new generation super-adsorbents. In this introductory chapter a comprehensive appraisal over the transport, toxicity and development of removal technologies is given along with their merits and demerits.