Biological treatment of water

A process for the treatment of water containing dissolved calcium ions and sulphate ions for the biological production of hydrogen sulphide, which comprises the steps of:

• adding calcium sulphate to a water supply to provide the water with dissolved calcium and sulphate ions;
• neutralizing the water containing calcium and sulphate ions in a neutralization stage;
• passing the water containing the dissolved calcium and sulphate ions at a neutral pH of 5-8.5 through an anaerobic biological sulphate removal stage wherein microorganisms utilize the sulphate ions in the water to produce hydrogen sulphide;
• passing the water from the anaerobic stage through a hydrogen sulphide removal stage where hydrogen sulphide is removed therefrom;
• passing the water from the hydrogen sulphide removal stage through an aerobic biological treatment stage wherein microorganisms cause at least partial biodegradation of any organic material remaining in the water, and wherein precipitation of calcium carbonate takes place;
• and
• recirculating the calcium carbonate precipitate from the aerobic stage to the neutralization stage to effect or assist in the neutralization of the pH of the water, the process including the step of feeding into the anaerobic biological sulphate removal stage a source of carbon which is metabolizable by the microorganisms which utilize the sulphate ions.

A process for the treatment of water to remove dissolved ions selected from the group comprising selenate ions and tellurate ions therefrom which comprises the steps of;

• adding calcium sulphate to a supply of said water to provide the water with dissolved calcium and sulphate ions;
• neutralizing the water containing sulphate ions in a neutralization stage;
• passing the water containing the dissolved calcium and sulphate ions at a neutral pH of 5-8.5 through an anaerobic biological sulphate removal stage wherein microorganisms utilize the sulphate ions in the water to produce hydrogen sulphide;
• passing the water from the anaerobic stage through a hydrogen sulphide removal stage where hydrogen sulphide is removed therefrom;
• passing the water from the hydrogen sulphide removal stage through an aerobic biological treatment stage wherein microorganisms cause at least partial biodegradation of any organic material remaining in the water, and wherein precipitation of calcium carbonate takes place;
• and
• recirculating the calcium carbonate precipitate from the aerobic stage to the neutralization stage to effect or assist in the neutralization of the pH of the water.