Abstract: A method of treatment of an arsenic sludge obtained from a solid-liquid separation step on arsenic waste water by adjusting the value of pH to 12 or higher by adding a calcium compound is disclosed. The method is characterized by addition of hydrated lime and calcining the sludge.

Abstract: In a flue gas desulfurization process based on the wet lime-gypsum method, the controlled oxidation of sulfites, by comparison of the redox potential of an absorbing fluid in a sample tank and the redox potential of the absorbing fluid in a completely oxidized state in a reference tank, and adjustment of the rate of air flow through the absorbing fluid, is improved by removing peroxides from the absorbing fluid in the reference tank before passing air therethrough to effect oxidization to a completely oxidized state. The method avoids instability due to the presence of peroxides in the absorbing fluid.

Abstract: The present invention provides a process for treating arsenic-containing waste water, comprising adding an oxidizing agent, if necessary, to arsenic-containing waste water to oxidize trivalent arsenic in the waste water into pentavalent arsenic; adding a calcium compound to adjust the pH to 12 or higher; separating it into solid and liquid (first solid/liquid separation); calcining the resulting sludge, while adding a ferric salt to the treated solution to adjust the pH to 6-9 after the solid/liquid separation; and separating it into solid and liquid (second solid/liquid separation). According to the present invention, it is possible to remove arsenic from waste water efficiently to yield treated water satisfying various tolerance limits under various regulations, while the arsenic-containing sludge separated from the waste water can become harmless in subsequent continuous steps.

Abstract: A method of controlling the oxidation of sulfites in a flue gas desulfurization process involves treating the exhaust gas with an absorbing fluid containing a calcium compound and controlling the oxidation of sulfites by regulating oxygen flow into the absorbing fluid. Oxygen flow is controlled by continuously monitoring the oxidation-reduction potential (ORP) of the absorbing fluid relative to the same fluid in a completely oxidized state using a detector with a plurality of fluid tanks, one of which functions as a reference tank at any particular time. The fully oxidized reference tank is periodically switched, reducing adherence of oxidizing substances to the ORP electrodes, resulting in more accurate measurements and reduced chemical oxygen demand of the waste water.

Abstract: A flue gas treatment system is provided for which is capable of easily treating Se contained in flue gas, comprising an extractor 13 for extracting soluble components in the dust removed by a dry-type dust precipitator 5 into water to slurry the dust; insolubilizer supply 16 for supplying an insolubilizer for insolubilizing at least tetravalent Se to the dust slurry which has been slurried from the dust by the extractor 13; adsorbent supply 14 for supplying an adsorbent composed of an organism material for adsorbing at least hexavalent Se in the dust slurry; and separator 15 for solid-liquid separating the dust slurry to which the insolubilizer and the adsorbent have been supplied by said supplies.