Abstract
Heavy metal refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations. Examples of heavy metals include mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), thallium (Tl) and lead (Pb). Little amounts of some heavy metals are needed by living organisms, however excessive levels of these metals can be harmful to the organisms due to their level of toxicity and accumulation behaviour. Different methods such as electrodeposition, electrocoagulation and nanofiltration system have been used to decontaminate the environment from adverse effect of these pollutants yet most of the methods used are ineffective. Biosorption is the removal of organic and inorganic substances from solution by biological material. Cheap biosorbents for the removal of metals are bacteria, fungi, algae, plants, industrial wastes and agricultural wastes. There are many mechanisms involved in biosorption some of which are not fully understood, examples are precipitation, ion exchange, complexation and adsorption. The efficiency of biosorption depends on many factors such as, temperature, characteristics of the biomass, pH, surface area to volume ratio, metal affinity to the biosorbent, concentration and characteristics of the biomass. Compared to other methods biosorption is operated over a wide range of physiochemical conditions and it uses naturally rich renewable biomaterials that can be cheaply produced. However, the potential for biological process improvement (for example through genetic engineering of cells) is restricted because cells are not metabolizing. Biosorption is in its developmental stages and further improvement in both performance and costs can be expected in future.
Highlights
Heavy metals are natural components of the earth’s crust which cannot be degraded or destroyed
Biosorption mechanism may be classified according to dependence on the cell's metabolism which is called metabolism dependent or according to the location where the metal removed from solution is found which is called non -metabolism dependent or metabolism independent; this is based on physical adsorption, ion exchange and chemical sorption, which is not dependent on the cells' metabolism
Biosorption uses naturally rich renewable biomaterials that can be cheaply produced, it involves less need for additional expensive reagent, which typically cause disposal and space problems, biosorption have high selectivity when it comes to the removal and recovery of certain heavy metals
Summary
Heavy metals are natural components of the earth’s crust which cannot be degraded or destroyed. Biosorption being a physicochemical process and includes mechanisms such as; absorption, adsorption, ion exchange, surface complexation and precipitation.
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