SYSTEM FOR TREATING SELENIUM-CONTAINING WASTEWATER, METHOD FOR TREATING SELENIUM-CONTAINING WASTEWATER, AND METHOD FOR RECOVERING SELENIUM FROM SELENIUM-CONTAINING WASTEWATER

摘要

A system for treating a selenium-containing wastewater is provided in which, in the case where the wastewater has a high selenium concentration and a high concentration of substances that inhibit selenium removal, a cost reduction can be made by effectively utilizing an iron-containing substance for selenium removal and by further recovering the selenium. The system for treating a selenium-containing wastewater is equipped with a sulfuric acid removal step (1) in which sulfuric acid ions (SO4 2-) are mainly removed from the wastewater and with a COD matter removal step (2) in which dithionic acid ions (S2O6 2-) are mainly removed from the wastewater. The system is further equipped with a selenium removal step (3) in which selenium is removed from the wastewater. In the removal of selenium in the selenium removal step (3), hexavalent selenium is reduced by iron to produce tetravalent selenium. The thus-oxidized iron becomes iron hydroxide to sediment as sludge, during which the tetravalent selenium coprecipitates with the iron sludge. Some of the resultant sludge is circulated to the COD matter removal step (2) and introduced into the selenium-containing wastewater. Thus, effective utilization of iron and selenium recovery can be achieved.