The increase in industrial, agricultural practices and several anthropogenic activities adds a significant amount of heavy metals in soil and water. Presence of these metals beyond threshold limit is toxic for the flora and fauna of the surroundings. So, there is a need for removing the harmful heavy metals from the environment. Several methods such as precipitation, evaporation, electroplating, ion exchange, membrane processes etc. have been developed for the decontamination of heavy metals from environment. These methods have several disadvantages like unpredictable metal ion removal, high reagent requirement, generation of toxic sludge and many more. To avoid such environmental problem, biosorption has been getting momentum for the removal of pollutants from aqueous medium and soil by the help of biosorbents (bacteria, algae, fungi, plants). Sometimes biosorbents are modified physically, chemically and genetically for the enhancement of their biosorption capacity. The mechanism of biosorption is affected by temperature, pH, bacterial activities and kinetics. This review paper describes the bacterial adsorbents, their modification and mechanism for removal of copper. By comparing previous studies it was observed that highest copper uptake was carried out by chemically modified Thiobacillusferroxidans (198.5 mg/g at pH 5.5 and temperature 30°C) and naturally occurring Pseudomonas putida (96.9 mg/g at pH 6.0 and temperature 37°C).
Keywords: Bioremediation, biosorption, adsorbent, bacteria, heavy metals, copper.
Metals are inorganic form of pollutants which are added globally through military, mining, metallurgical, electroplating, metal finishing, agricultural processes and waste disposal. The extensive use of heavy metals has caused significant environmental pollution that mainly affects soil, watercourses, atmosphere and living systems1. Mercury, lead, cadmium and chromium (VI) are considered as toxic metals; whereas, copper, nickel, cobalt and zinc are not as toxic, but their extensive usage and increasing levels in the environment are of serious anxieties2.
Copper is extensively used in mining, materials processing, paper making, printing, and so on. It is necessary to flora and fauna, but at high concentration it causes diseases in them3. The conventional methods such as ion-exchange, reduction, ultrafiltration, oxidation, precipitation etc. used for copper removal are generally ineffective because of technical or economic limitations4. So, bioremediation of copper through bioreduction and biosorption is considered as an alternative method for removal and recovery of metals5. Biosorption is the physicochemical mechanism of inactive metal uptake or selective sequestering of metal soluble species by microbial biomass. It depends on the affinity between the metallic species or its ionic forms and the binding sites on the molecular structure of the cellular membrane, cell wall and capsule6.
Biosorbents are the biological...