Validation of analysis of arsenic in water samples using Wagtech Digital Arsenator.

Groundwater, the only source of potable water for millions of people in Bangladesh during dry season, is often contaminated with arsenic (As) above the allowable drinking water limit of 50 µg/L. Testing well water--with arsenic field test kits (FTKs)--and switching to safe-wells can effectively reduce exposure to As. FTKs are low cost, provide fast results, and are commercially available. There are between 10 and 11 million shallow tubewells in Bangladesh. Approximately, 5 million have been tested using FTKs. FTKs with color comparator rely on visual identification for generating qualitative results, which may not be highly reliable at the lower range because human eyes have low sensitivity in this range and sensitivity varies from person to person. The Wagtech Digital Arsenator does not suffer from this limitation and should, in theory, be able to generate quantitative, accurate, and reliable results. The instrument has a linear range of 0-100 µg/L, an accuracy of ± 20% for the 50 µg/L quality control standards, and a detection limit of about 4.4 µg/L. All Arsenators employed in this investigation also displayed high bias for 50 µg/L arsenic standard and were calibrated in order to improve measurement accuracy and reliability. Analyses of 179 raw and 92 treated well waters in the field and in two analytical laboratories were found to be highly correlated with the Spearman rank correlation coefficient of ≥ 0.800, indicating that Arsenator results are perhaps nearly as accurate and reliable as those from analytical laboratories.

O3/H2O2 treatment of methyl-tert-butyl ether (MTBE) in contaminated waters.

The kinetics and efficiency of oxidation of methyl-tert-butyl ether (MTBE) in contaminated water employing O3/H2O2 advanced oxidation process is presented in this paper. Kinetic simulation is based on the model mechanism published in literature (Staehelin and Hoigne, Environ. Sci. Technol. 16 (1982) 676; Glaze and Kang, Ind. Eng. Chem. Res. 26 (1989) 1573) indicates that the oxidation of MTBE is primarily induced by the hydroxyl radical. The degradation of MTBE can be described by a pseudo-first-order kinetics in two phases. The first-phase covers MTBE concentrations greater than 10 mg L(-1) and the second-phase covers MTBE concentrations below 10 mg L(-1). The rate of oxidation of MTBE (at least in the first-phase) is limited by ozone mass transfer and increases with increasing ozone gas flow rate. The pseudo-first-order reaction rate constant varies from 2.0 x 10(-3) to 5.4 x 10(-3) s(-1) over the range of ozone gas flow rate employed in this investigation. An efficiency index is defined and its value for the oxidation of MTBE in different water is provided. The data provided show that remediation of MTBE-contaminated groundwater by O3/H2O2 process is more efficient and less costly than by the UV/H2O2 process.

Selective electrochemical biosensors from state-switching of bilayer and monolayer lipid membranes by lectin-polysaccharide complexes.

Interaction of the lectin concanavalin A with the polysaccharide glycogen can provide rapid spontaneous transients of the surface potential at bilayer and monolayer lipid membranes. The selective binding process can cause large, rapid potassium ion current fluctuations across bilayer membranes in a manner that is periodic and reproducible. The frequency of these transient ion current signals was shown to be related to sub-nanomolar concentrations of the reactive agents in aqueous solution. The physical mechanism responsible for ion current modulation was investigated by fluorescence methods using lipid vesicles, by the thermal dependence of the potassium ion current across planar bilayers and by pressure-area and dipolar potential measurements of lipid monolayers at an air-water interface. The mechanism is primarily associated with physical perturbations of lipid membranes by lectin-polysaccharide aggregates, resulting in the formation of localised domains of variable electrostatic potential and conductivity.