Biosorption is the binding andconcentration of heavy metals from aqueoussolutions (even very dilute ones) by certain typesof inactive, dead, microbial biomass. Biosorption can be defined as theselective sequestering of metal soluble speciesthat result in the immobilization of the metals bymicrobial cells.
Heavy metals are chemical elements with a specific gravity that is at least 5times the specific gravity of water Arsenic 5.7Cadmium 8.65 Three countries, the Unitediron 7.9 States, Germany and Russia,lead with only 8% of the world’s 11.34 population consume about 75%mercury 13.546. of the world’s most widely used metals.
Heavy metals become toxic when they are not metabolized by thebody and accumulate in the soft tissues. Toxic metals are Cr, Cu, Mn, Ni, Sn and Zn. once dispersed in therebiosphere, these metals cannot be recovered or degraded. Hence, environmentaleffects of metal pollution are said to be permanent.Symptoms of Heavy metal Toxicity: mental confusion gastrointestinal upsets food intolerances allergies or headaches short term memory loss pain in the muscles and joints chronic fatigue vision problems Arsenic poisoning
Biological treatment technologies are available for remediation ofmetals-contaminated sites. These technologies are commonly used forthe remediation of organic contaminants and are beginning to beapplied for metal remediationBiological treatment exploits natural biological processes that allowcertain plants and microorganisms to aid in the remediation of metals.These processes occur through a variety of mechanisms, includingadsorption, oxidation and reduction reactions and methylation
Heavy metal, present in differenttypes of industrial effluents, isresponsible for environmentalpollution. Traditionally, metalremoval was made by chemicalprecipitation.Biosorption is a process in whichsolids of natural origin are employedfor binding heavy metals. It is apromising alternative method fortreating industrial effluents, mainlybecause of low cost and high metalbinding capacity.
Biosorption is a rapid phenomenon of passive metal sequestration bynon-growing biomass.Biosorption is possible by both living and non-living biomass.Bioaccumulation is a growth dependent process and Biosorptioninvolves mechanism like ion exchange, chelation and complexation .Metal binding appears to be at least a two step process, Where stoichometric interaction between the metal and the reactive chemical groups in the cell wall an inorganioc deposition of increased amount of metal.
Biosorption Bioaccumulation Biosorption is a Bioaccumulation ismetabolically passive an active metabolicprocess, and the amount process driven byof contaminants a sorbent energy from a livingcan remove is dependent organism andon kinetic equilibrium and requires respirationthe composition of thesorbents cellular surface. It occurs by absorbing contaminants which reversible process are transferred onto occurs at a faster rate and within the cellular surface. produce higher concentrations
According to the dependence on the cells metabolism, biosorption mechanisms can bedivided into:1.Metabolism dependent2.Non -metabolism dependent. Physical adsorption: Physical adsorption takes place with the help of van der Waals forces. In 1998, Kuyucak and Volesky hypothesized that uranium, cadmium, zinc, copper and cobalt biosorption by dead biomasses of algae, fungi and yeasts takes place through electrostatic interactions between the metal ions in solutions and cell walls of microbial cells.
Ion Exchange Reduction PrecipitationComplexation Chelation
Bioremediation of heavy metals by algaeCladophora species,are best bioindicatorsChlorella & ScenedesmusScenedesmus acutus Scenedesmus acutus tolerant to the Cr & Cu , not to Znred alga porphyra.cell wall of brown algaecontains fucoidin andalginic acid.
Bioremediation of heavy metals by plants Plants have a unique ability to concentrate essential and non essential elements from the soil, through the roots. Phytoremediation includes several subsets such as phytoextraction phytostabilization rhizofilteration phytovolatilisationHyperaccumulator: Brassicaceae, such as Alyssum species, Thlaspi species and Brassica juncea,, Violaceae, such as Viola calminariaa, Leguminous , such as Astragalus racemosus Thlaspi caerulescens Phytoceratophyllum
Fungi streptoverticillum saccharomyces Aspergillus terreus Filamentous fungi Rhizopus Arrhizus Bacteria Bacillus subtilius B.licheniformisPseudomonas species , zooglea ramigera andstreptomyces species are used for biosorption ofmetals . In B.subtilus, teiochoic acid and inB.licheniformis, teiochoic acid and teichuronic acidwere found to be prime sites for metal binding.
Some of the key features of biosorption compared to conventional processes include:1. competitive performance2. heavy metal selectivity3. cost-effectiveness4. regenerative5. no sludge generation. Biosorption is particularly economical and competitive for environmental applications in detoxifying effluents from, for example:1. metal plating and metal finishing operations2. mining and ore processing operations3. metal processing4. battery and accumulator manufacturing operations5. thermal power generation (coal-fired plants in particular)6. nuclear power generation.