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The effect of different concentrations of Cu (II) on microbial scorodite (FeAsO4⋅2H2O) formation was investigated by using thermo-acidophilic iron-oxidizing archaeon, Acidianus brierleyi. In the presence of 8-16 mM Cu (II) microbial Fe (II) oxidation and cell growth was only marginal. Its As (III) oxidation ability was especially severely inhibited by the presence of Cu (II), consequently disabling scorodite formation. However, when scorodite seed crystals were fed, Ac. brierleyi readily oxidized Fe (II) and As (III) even in the presence of 8.0 mM Cu (II), forming crystalline scorodite within 24 days in shake flasks. All Cu (II) remained in the solution phase during scorodite crystallization, with or without the presence of seed crystals. Increasing the seed crystal concentration (from 0.015 to 0.15%) slightly improved the As immobilization (from 96 to 98%). This study demonstrated that scorodite can be crystallized from the model As (III)-bearing wastewater containing Cu (II).

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