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Capillary electrophoresis with indirect UV detection was used to determine simultaneously arsenic, selenium, antimony and tellurium compounds. The separation was achieved in a fused silica capillary filled with an electrolyte solution containing sodium chromate and an electroosmotic flow modifier, trimethyltetradecylammonium hydroxide (TTAOH). The effect of the TTAOH concentration and electrolyte solution pH on the electrophoretic mobility of the species was studied. The best simultaneous separation of these species was achieved with 0.5 mm TTAOH and an electrolyte pH of 11.2 within 5 min. Detection limits range from 13 mg l 21 for Se VI to 509 mg l 21 for Te IV with electromigrative injection. The reproducibility was below 10% and linearity was verified in the 0-100 mg l 21 range for all species. Interferences by other inorganic ions were studied. This method was applied to the determination of metalloids in a spiked drinking water. Water extracts of industrial soils were analysed and results were compared with those of ICP-MS measurements.

Passive water treatments based on biological attenuation can be effective for arsenic-rich acid mine drainage (AMD). However, the key factors driving the biological processes involved in this attenuation are not well-known. Here, the efficiency of arsenic (As) removal was investigated in a bench-scale continuous flow channel bioreactor treating As-rich AMD (∼30-40 mg L). In this bioreactor, As removal proceeds via the formation of biogenic precipitates consisting of iron- and arsenic-rich mineral phases encrusting a microbial biofilm. Ferrous iron (Fe(II)) oxidation and iron (Fe) and arsenic removal rates were monitored at two different water heights (4 and 25 mm) and with/without forced aeration. A maximum of 80% As removal was achieved within 500 min at the lowest water height. This operating condition promoted intense Fe(II) microbial oxidation and subsequent precipitation of As-bearing schwertmannite and amorphous ferric arsenate. Higher water height slowed down Fe(II) oxidation, Fe precipitation and As removal, in relation with limited oxygen transfer through the water column. The lower oxygen transfer at higher water height could be partly counteracted by aeration. The presence of an iridescent floating film that developed at the water surface was found to limit oxygen transfer to the water column and delayed Fe(II) oxidation, but did not affect As removal. The bacterial community structure in the biogenic precipitates in the bottom of the bioreactor differed from that of the inlet water and was influenced to some extent by water height and aeration. Although potential for microbial mediated As oxidation was revealed by the detection of aioA genes, removal of Fe and As was mainly attributable to microbial Fe oxidation activity. Increasing the proportion of dissolved As(V) in the inlet water improved As removal and favoured the formation of amorphous ferric arsenate over As-sorbed schwertmannite. This study proved the ability of this bioreactor-system to treat extreme As concentrations and may serve in the design of future in-situ bioremediation system able to treat As-rich AMD.

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