CONTINUOUS HIGH-RATE REMOVAL OF CHROMATE IN A FLUIDIZED-BED WITHOUT SLUDGE GENERATION

The objective of the work presented here was to investigate the catalysing effect of iron oxyhydroxide on the redox reaction between ferrous iron and chromate. This was done in a bench-scale upflow reactor containing an expanded sand medium (fluid-bed reactor), where continuous chemical addition, reaction and solid-liquid separation take place. Removal efficiencies of chromate in excess of 99% were attainable on spiked tapwater corresponding to an outlet concentration of 0.01 mg/l. Chromate polluted groundwater from a fly-ash disposal site was treated in the first full-scale plant (3 m3/h) with good results as well. The waste product generated by this method is a very compact granulate with a specific density of approx. 3 kg/l and low water content. Operation of the compact plant is simple and chemicals cost very little (approx. US D 1/400 per m3). The method (patent pending) is recommended for remediation purposes, but may also be applied in treatment of industrial wastewaters.