Abstract: A water quality improvement process is provided for acid water containing sulphate and/or sulphite ions. The water is continuously fed into a fluidized bed containing calcium carbonate particles. The water consumes calcium carbonate and has its pH increased while calcium sulphate CaSO.sub.4 and/or CaSO.sub.3 are produced.

Abstract: The invention provides a chemical process for the treatment of water containing dissolved calcium and sulphate ions, so as to produce a purified product water having a reduced sulphate ion concentration. Barium sulphide is added to the water to cause precipitation of barium sulphate from the water. The water from which the barium sulphate has been precipitated is then treated with carbon dioxide to form hydrogen sulphide in the water, and the hydrogen sulphide is stripped from the water.

Abstract: The invention provides a process for the treatment of water containing dissolved calcium ions and dissolved sulphate ions. The water is passed at a pH of 5-8,5 through an anaerobic biological sulphate removal stage wherein microorganisms utilize sulphate ions in the water to produce hydrogen sulphide. The water from the sulphate removal stage is then passed through a hydrogen sulphide removal stage where hydrogen sulphide is removed therefrom. Water form the hydrogen sulphide removal stage is passed through an aerobic biological treatment stage wherein microorganisms cause at least partial biodegradation of any organic material remaining in the water and wherein calcium carbonate is precipitated.