Scorodite Cystallization through GAC-catalyzed As(III) Oxidation in a Thermoacidophilic Airlift Reactor

Arsenite at a concentration of 0.62 g.L-1 was immobilized as crystalline scorodite (FeAsO4.2H2O) in a continuous laboratory-scale airlift bioreactor fed with Fe(II) as electron donor. The reactor was operated at a pH of 1.2 and a temperature of 70°C to facilitate scorodite crystallization. Arsenite oxidation to arsenate was catalyzed by granular activated carbon (GAC), added to the reactor at a concentration of 4 g.L-1. Fe(II) was probably oxidized by both a thermoacidophilic ferrous iron oxidizing mixed microbial culture inoculated to the reactor and by GAC catalyzed oxidation. After 13 days of batch mode at the start, the reactor was operated in continuous mode at a HRT of 3.1 days for 18 days and at a HRT of 2.2 days for 68 days. Stable arsenite oxidation efficiencies of 96% were reached while total arsenic removal reached 86%.