Biosorption of heavy metals from water: mechanism, critical evaluation and translatability of methodology

ABSTRACT The presence of heavy metals in drinking water is a serious global issue. Sustainable methods for treating drinking water such as biosorption are gaining popularity. The maximum permissible limits of most metal ions in drinking water are in the range from 0.003 to 2 mgL−1, however, the elevated concentrations in the range 0.01–2.5 mgL−1 are reported in contaminated waters in various regions of the world. Therefore, selecting the initial metal ion concentration range, and an optimum pH suitable for treating drinking water (pH 6.5–8.5) for laboratory experiments is a challenge for multi-ion biosorption studies. For the quantification of metal ions, ICP-MS is often used owing to its many advantages, however, the high operational costs of this instrument limits its use in research laboratories. Surface characterisation techniques such as TEM, NMR, ESR and related techniques are often ignored in biosorption studies although, these give valuable information pertaining to the mechanism of biosorption. Many theoretical models for explaining the biosorption mechanism have been proposed in the literature, one often contradicting the other. One of the major drawbacks of published biosorption studies is that too much emphasis has been laid on the theoretical explanation of biosorption mechanism and too little has been done to address the lack of practical application in terms of translatability of the methodology for commercial use. The present review highlights such issues while giving an insight on the processes, parameters and models used in biosorption reactions. GRAPHICAL ABSTRACT