Biosorption and metal removal through living cells

Abstract

Unicellular and higher organisms have a variety of properties that can affect chemical speciation, mobility and toxicity of metals and radionuclides. Apart from their importance in the environmental cycling of elements, the passive and active interactions of microbes, fungi, algae and plants with metals and radionuclides could have beneficial consequences in context of bioremediation of polluted water, soils and sediments. The capacity of living cells to remove metals and radionuclides from waste waters is well documented. Besides biosorption, the bioremediation using living organisms may exploit their bioaccumulation capacity or metabolic pathways. Useful microbial properties exploited to immobilize or volatize metals and radionuclides involve mainly production of phosphates, carbonates of sulphides that precipitate soluble toxic species and reductive transformations to insoluble ionic or metallic forms, including production of catalytically active nanoparticles directly from waste water. Various bioprocesses, bioreactor setups or in situ bioremediation approaches employing isolated microbes or microbial consortia were proposed and brought to pilot scale. One of the approaches achieving compliance using mixed-function consortia at low cost is construction of artificial wetlands, the systems that rely on collective action of physical, chemical and biological processes. Besides the microbial activities promoting in wetlands formation of insoluble metal sediments, the heavy metal removal performance of wetland is largely contributed by plants, namely through metal biosorption, root uptake and precipitation induced by changes in redox potential within the rhizosphere. The possibility of altering the microbes and plants to improve their bioremediation potential by genetic engineering is under study in many laboratories. © 2011 Springer Science+Business Media B.V.