A comparative evaluation of sorbents for the treatment of complex metal-bearing laboratory wastewaters

This study examined the potential use of a range of sorbents (crab shell, chitosan, activated carbon, ion exchange resin, peat, sawdust, bagasse, Turbinaria conoides, Sargassum sp. and Ulva sp.) for simultaneous removal of 8 heavy metals from synthetic research laboratory effluents. The sorption experiments were conducted in both batch and continuous modes of operation. Among the sorbents used in this study, crab shell proved to be effective with a total biosorption capacity of 440 mg/g at pH 4.5. Continuous-flow experiments with crab shell loaded in an up-flow packed column were successful with a total biosorption capacity of 165 mg/g. The crab shell-based biosorption process was also identified to be superior to the commonly used hydroxide precipitation technique. This work reveals some practical issues associated with the biosorption process such as leaching of excess light metal ions, poor affinity toward anions and effluent odor. The study also highlights other shortcomings of biosorption, and proposes technical approaches to overcome them.