Arsenic biosorption by psychrotrophic arctic bacteria

Abstract

Arsenic is a well-known toxic pollutant for biological systems and known human carcinogen. Its presence in the environment increased because of mining, agricultural and manufacturing activities. Use of bacterial biomass for heavy-metal removal from environment gained high interest due to the limitations and disadvantages of various existing conventional methods. The aims of this study were to isolate novel arsenic-resistant psychrotrophic bacteria from Arctic samples and study their ability to adsorb As(III) at a broad range of temperature (10°C - 40°C ) characteristic of the tropic and polar regions. Parameters affecting biosorption of arsenite: pH, time, initial As(III) concentration, temperature and adsorbent dosage were also investigated. Findings showed that among the eight psychrotrophic bacteria with high metal resistance, 12D3 (Yersinia sp. strain SOM-12D3) and 15D1 (Pseudomonas sp. strain SOM-15D1) showed the highest As(III) adsorption at pH 7 and 30 °C. Batch experiments were carried out using untreated or acid-pretreated nonliving biomass prepared from 12D3 and 15D1 isolates. The results showed that acidpretreatment of bacterial biomasses increased the ability of As(III) adsorption. Based on the value of R2 (0.959 for 12D3-UB, 0.9617 for 12D3-AB, 0.935 for 15D1-UB and 0.953 for 15D1-AB), the Langmuir isotherm model fitted the equilibrium data better in comparison to Freundlich isotherm model. The maximum biosorption capacity of the sorbents, as obtained from the Langmuir isotherm, were 33.4 mg/g for 12D3-UB, 159 mg/g for 12D3-AB, 36.63 mg/g for 15D1-UB, and 129.87 mg/g for 15D1-AB. The sorption kinetic of As(III) followed well the pseudo-second-order rate equation for all types of non-living biomass. The acquired positive values of both ?S° and ?H° suggested an endothermic reaction and increased in randomness at the solid-liquid interface. Negative ?G° values indicated a spontaneous adsorption process. High recovery efficiency of As(III) (96% for 12D3-AB and 95% for 15D1-AB) were achieved at 1.5 g/l values of solid to liquid ratio (S/L) (metal-laden biosorbent to the volume of eluent) within four cycles indicated adsorption/desorption. The involvement of functional groups (hydroxyl, amide and amine) in As(III) biosorption process was shown via Fourier-Transform Infrared spectroscopy (FTIR) analysis. FESEM-EDAX analysis of the non-living biomass revealed that acid treatment removed particles from the surface of biomass, deformed cells, and created a pore structure on the biosorbent surface. Therefore, increased As(III) biosorption was because of increased metal binding sites after acid pretreatment. This study points to the potential of using acidpretreated non-living biomass of psychrotrophic bacteria, Yersinia sp. strain SOM- 12D3 and Pseudomonas sp. strain SOM-15D1, as a new biosorbent to remove As(III) from contaminated waters at tropical and polar regions.