Treament of water

A process for treating sulphate-containing water, which process includes

• feeding sulphate-containing water into a primary biological sulphate reduction stage containing a complex carbon source;
• subjecting the water to biological sulphate reduction in the primary biological sulphate reduction stage, thereby to reduce sulphates in the water to sulphides, to produce alkalinity and to mobilize the complex carbon source;
• withdrawing partially treated sulphide-rich, alkalinity-rich and dissolved carbon-rich water from the primary biological sulphate reduction stage;
• feeding the partially treated sulphide-rich, alkalinity-rich and dissolved carbon-rich water into an enclosed primary sulphide removal stage;
• subjecting the water to chemical and/or biological sulphide oxidation in the primary sulphide removal stage, thereby removing at least some of the sulphides present in the water as sulphide precipitates or as elemental sulphur;
• withdrawing partially treated sulphide-depleted water but still alkalinity-rich and dissolved carbon-rich from the primary sulphide removal stage;
• feeding the partially treated sulphide-depleted, alkalinity-rich and dissolved carbon-rich water into an enclosed anaerobic secondary biological sulphate reduction stage containing carbon material;
• subjecting the water to further biological sulphate reduction, under anaerobic conditions, in the secondary biological sulphate reduction stage, utilizing the carbon material present in the stage and the dissolved carbon material produced in the primary biological sulphate reduction stage, thereby further to reduce sulphates in the water to sulphides;
• withdrawing sulphide-rich and alkalinity-rich treated water from the secondary biological sulphide reduction stage;
• feeding the sulphide-rich and alkalinity-rich treated water into a secondary sulphide removal stage;
• subjecting the sulphide-rich and alkalinity-rich treated water to sulphide removal in the secondary sulphide removal stage;
• and
• withdrawing treated water from the secondary sulphide removal stage.

A water treatment installation which comprises

• a primary biological sulphate reduction unit which contains a bed of carbon-containing material;
• a first water transfer conduit leading from the primary biological sulphate reduction unit;
• a primary biological or chemical sulphide removal unit from which precipitated sulphides or sulphur can be removed, with the first water transfer conduit leading into the primary sulphide removal unit;
• a second water transfer conduit leading from the primary sulphide removal unit;
• a secondary sealed biological sulphate reduction unit which also contains a bed of carbon-containing material, with the second water transfer conduit leading into the secondary biological sulphate reduction unit at or near its lower end;
• a third water transfer conduit leading from the secondary biological sulphate reduction unit at or near its upper end;
• a secondary sulphide removal unit, with the third water transfer conduit leading into the secondary sulphide removal unit;
• and
• a fourth water conduit leading from the secondary sulphide removal unit.