Biological removal of hexavalent chromium in trickling filters operating with different filter media types

The purpose of the present study was to estimate Cr(VI) removal through biological mechanisms in biofilm reactors operated in SBR operating mode with recirculation using different filter media types. The choice of the support material is of great importance since chromate reduction is followed by the formation of sediments, which causes obstruction of the flow along the filter depth. In order to overcome this awkwardness, we tested the performance of two different support materials, i.e. plastic media and calcitic gravel, in pilot-scale trickling filters. The feed concentrations of Cr(VI) examined were about 5, 30 and 100 mg/l, while the concentration of the organic carbon was constant at 400 mg/l, in order to avoid carbon limitations in the bulk liquid. Plastic media showed better performance at the different Cr(VI) concentrations examined, compared to the gravel media. The removal rates for the plastic media achieved were 4.23±0.18, 3.62±0.1 and 3.3±0.08 g Cr(VI)/d, for feed concentration of Cr(VI) about 5, 30 and 100 mg/l respectively, while for the gravel media the corresponding removal rates were 4.11±0.09, 3.52±0.06 and 2.5±0.07 g Cr(VI)/d.

Chromate is a very dangerous pollutant and should be removed or transformed before wastewater disposal. Trickling filters with hollow plastic tubes as support media seem to provide a very effective process for Cr(VI) reduction from industrial wastewater. The main conclusions from this work are: • Biological Cr(VI) reduction was feasible with the use of a pilot-scale attached growth process bioreactor and an indigenous bacterial population, which was grown aerobically with sodium acetate as the sole electron donor. This work was supported by the Hellenic Aerospace Industry S.A.. The authors wish to thank Prof. K. Bourtzis and S. Siozios for their help with the identification of bacterial strains.