Biological chlorate removal was studied on a laboratory and a pilot scale with the aim of optimizing process design and operating conditions with respect to process efficiency, stability and economy.

The results showed a suspended-carrier biofilm process design to be suitable for biological chlorate removal. In the laboratory tests, at pH 7 and 37°C, a complete removal of chlorate could be maintained at hydraulic retention times (HRTs) as short as 24 min. A longer HRT (1.5 h) was required for complete chlorate removal in the pilot test, due to a lower degree of filling with carrier material (25% versus 50% of the reactor volume), higher process temperature, and leakage of oxygen into the process. However, it is assumed that the loading capacity of a large-scale process would approach that of the laboratory system if the operating conditions were the same.

Laboratory tests showed chlorate reduction to be possible within a wide range of pH values and temperatures, although the process stability and loading capacity were strongly affected by changes in these parameters.

The results of the laboratory and pilot scale studies, using a suspended-carrier process design, show biological treatment to be an economically viable and efficient process for the removal of chlorate from bleaching plant effluents.

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