Abstract
The health impairment caused by ingestion of arsenic contained in groundwater is serious in areas, such as Bangladesh and India. In order to improve the efficiency of coagulation or adsorption process for arsenic removal, arsenite (As (III)) needs to be oxidized to arsenate (As (V)) by chemical oxidizer as a pretreatment. For the purpose of developing an economical arsenite oxidation method, this research examined continuous oxidation of As (III) to As (V) using a bioreactor where arsenite-oxidizing bacteria enriched from activated sludge were fixed in the Down-Flow Hanging Sponge (DHS). The inorganic media with the As (III) concentrations of 0.5 mg/L and 1.0 mg/L were supplied to two sets of the reactor, respectively. The As (III) and As (V) concentrations were analyzed with an HPLC-ICP-MS. At HRTs of 3 - 0.5 h, more than 95% of As (III) was oxidized to As (V). Moreover, at an HRT of 0.5 h, the bacterial density showed the maximum at the top of 25 sponges and gradually decreased downward. Furthermore, a model of biological As (III) oxidation in the sponge was developed and it could describe the variation of As (III) concentration in the reactor by using the data of cell concentration in the sponge and rate constant obtained in batch experiment.
