Arsenic removal by reverse osmosis

Arsenic removal by reverse osmosis

RESEARCH TRENDS matter was investigated. The performance of regenerated cellulose membrane with a nominal molecular weight cut-off of 1 kDa was examin...

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RESEARCH TRENDS matter was investigated. The performance of regenerated cellulose membrane with a nominal molecular weight cut-off of 1 kDa was examined on 20 samples from lake, river and estuary systems, characterized by contrasting dissolved organic carbon (DOC) contents and conductivity. The evaluation was based on absorbance, fluorescence and DOC measurements. Detailed protocols of membrane cleaning and conditioning are proposed. The ultrafiltration membrane can be cleaned efficiently to provide low carbon blank (less than 0.01 mg/l). Fluorescence measurements confirmed that the higher molecular weight compounds were isolated in the retentate and the lower molecular weight compounds remain in the permeate. Mass balance for natural samples show good recovery for DOC (109 ± 12%, n = 20) and fluorescence measurements (106 ± 9%, n = 13). No relation between factors of concentration and mass balance quality was observed for the factors of concentration range of 1.5–11. Moreover, high ionic strength and high DOC contents did not enhance membrane fouling. These findings demonstrate that reliable fractionations by TFF of natural organic colloids in aquatic systems can be achieved. C. Guéguen, C. Belin, J. Dominik: Water Research 36(7) 1677–1684 (April 2002).

Nitrate removal In this paper, a new method is proposed for removing nitrate from groundwater, in which elemental sulphur-based denitrification (autotrophic denitrification) and membrane separation are combined. By using a membrane, autotrophic denitrifiers (whose growth rate is considerably low) can be kept at a high concentration. The performance of the proposed process was examined through a long-term experiment using synthetic feed water. A rotating membrane disk module equipped with UF membrane (750 000 Da) was used in this study. Complete removal of nitrate (25 mg N/l) was achieved under the conditions of a biomass concentration of about 1000 mg protein/l and HRT of 160 min. Dissolved oxygen concentration and sulphur/biomass ratio in the membrane chamber were found to be the key factors in maintenance of high-process

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performance. Deterioration in membrane permeability was insignificant. It was found that membrane filtration could be continued with a water flux of 0.5 m3/m3/day for about 100 days without any chemical membrane cleaning. However, the proposed process caused a slight increase in assimilable organic carbon. Sulphide was not detected in the denitrified water. K. Kimura, M. Nakamurab, Y. Watanabea: Water Research 36(7) 1758–1766 (April 2002).

with molecular weight cut-off of 10 kDa, could be prepared successfully by the phase-inversion method. Various solvent (water, alcohols, acetone and hexane) fluxes were measured to investigate solventresistance and membrane behaviour during solvent permeation. The activation energy relationship between hexane flux and viscosity with temperature was also studied. I.-C. Kim, J.-H. Kim, K.-H. Lee, T. Moon: J. of Applied Polymer Science 85(5) 1024-1030 (1 August 2002).

Transport properties of poly(methyl-phenylsiloxane) membranes

Arsenic removal by reverse osmosis

Membranes based on dimethyl and methyl-phenylsiloxane were synthesized and then fully characterized. The transport properties and mechanical behaviour were determined as a function of different methyl/phenyl group ratios and the effects of these groups on results were then established. Membrane transport properties were evaluated from n-hexane absorption studies. Static tensile stress–strain deformation measurements, stress-hysteresis determination, and stress-relaxation studies were also performed to assess the mechanical behaviour of these membranes. The results indicate that both physical–mechanical and transport properties are strongly affected by the methyl group content. E. Erdmann, H.A. Destéfanis, R. Abalos, P.M. Frontini, G.A. Abraham: J. of Applied Polymer Science 85(8) 1624–1633 (29 August 2002).

Solvent-resistant ultrafiltration membrane Soluble copolysulphoneimides were synthesized using the thermal twostep method in solution of Nmethyl-2-pyrrolidone. The aromatic diamines which were used consisted of bis[4-(3-minophenoxy)phenyl]sulphone (BAPS-m) and 3,3´-diaminosulphone. The dianhydrides were pyromellitic dianhydride, 4,4´-oxyphthalic anhydride and 3,3´,4,4´-diphenylsulfone tetracarboxylic dianhydride. The molar ratio of diamines was changed to reduce the content of BAPS-m. The thermal and mechanical properties of polyimides were investigated. It was found that a polyimide ultrafiltration membrane,

Arsenic is widely distributed in nature in air, water and soil. Acute and chronic arsenic exposure through drinking water has been reported in many countries, especially Argentina, Bangladesh, India, Mexico, Mongolia, Thailand and Taiwan, where a large proportion of ground water is contaminated with arsenic at levels ranging from 100 µg/l to over 2000 µg/l (ppb). Public health standards of maximum of 50 ppb were been adopted by the USA and World Health Organization (WHO) during the 1970s and the 1980s. Carcinogenicity and genotoxicity led to the WHO recommendation of 10 ppb maximum level in 1993, followed by the USA’s adoption of the same in 2001. The USA estimated that 5% of all its community water systems will have to take corrective action to lower the current levels of arsenic in their drinking water. In areas of the world where arsenic is high, the need for better water treatment and resulting economic impact would be even greater. In this paper, the authors briefly review the geochemistry, natural distribution, regulation, anthropogenic sources and removal mechanisms of arsenic, pointing especially to the potential of reverse osmosis (RO) as a practical means of purification. They conclude that arsenic in the commonly high oxidation states can be removed effectively by RO. With further removal of the weakly acidic arsenic(III) species in water by RO (at sufficiently high pH levels), made possible by newer antiscalants, practical processes can be developed using RO to remove from water all major species of arsenic. Further studies are needed in the characterization of the

arsenic species that are being treated and in the design of the RO process to match the demands. R.Y. Ning: Desalination 143(3) 237–241 (10 June 2002).

Cobalt removal from aqueous solution In this research, the capacity of ion exchange resins IRN77 and SKN1, for the removal of cobalt (Co) from aqueous solution has been investigated under different conditions – namely initial solution pH, initial metal-ion concentration and contact time. The equilibrium data obtained in this study have been found to fit both the Langmuir and Freundlich adsorption isotherms. The adsorption of Co(II) on these resins follows first-order reversible kinetics. The film diffusion of Co(II) was shown to be the main rate-limiting step. The studies also showed that these cation exchange resins can be used as efficient adsorbent material for the removal of Co(II) from aqueous solutions. S. Rengaraj, S.-H. Moon: Water Research 36(7) 1783–1793 (April 2002).

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Membrane Technology October 2002