Salty Waters

The biggest news of the year so far as saline water is concerned was the agreement between the Metropolitan Water District of Southern California (MWD) and the federal government on the financing of a nuclear desalting plant which would produce 150 million gallons per day (mgd) of water and have a net electric power output of 1,600 megawatts. The plant, which is expected to produce potable water at a cost of around 22 cents a thousand gallons, is many times larger than any existing desalting plant and is considered by the Office of Saline
Water (OSW) to be a vital experimental step in the development of desalting technology. It is to consist of three 50-mgd units, the first of which is to be in operation by late 1971. The others are to be brought in by 1976. Total cost of the complete plant estimated to be $444 million, consisting of $107 million for the water plant, $235 million for the power plant and related facilities, $24 million for location and land rights, $34 million for water conveyance, and $44 million for power transmission. Of the total plant and site cost, the participating utilities contribute $257 million, MWD $127 million and the federal government $61 million ($46 million from OSW and $15 million from the Atomic Energy Commission). In addition, OSW will contribute $11.5 million toward operation maintenance. The location is to be an artificial island to be built along the Southern California coast at a still unspecified point. Funds have not as yet been authorized by Congress.

The world currently has a desalting capacity of about 50 million gallons per day in the form of large land-based desalting plants, an increase of 100 percent in the past two years. The competition between the world's two main suppliers—the United Kingdom and the United States—for the sale of these plants has been keen, with the United States now accounting for about 40 percent and the United Kingdom 60 per cent. The major technique is flash distillation, although electrodialysis and vapor compression techniques are in use in smaller plants.

Analyses by the British Water Research Association have led that organization to conclude that the big world market for desalting plants will be in the small-to-medium-size range, with plants not exceeding 15 mgd. US and British estimates seem to be in fair agreement on the cost of water from small-to-medium flash distillation plants: for 3-, 10-, and 30-mgd single-purpose plants, about $1.00, 85 cents, and 75 cents respectively per thousand gallons. For dual-purpose electric and water plants of these sizes, depending upon the steam costs assigned to desalting, the likely ranges would be 60 to 80 cents, 52 to 70, and 48 to 65 per thousand gallons. These figures are substantially higher than the cost anticipated for the projected Southern California plant. In the small plant range of 1 to 2 mgd, it appears likely that various freezing processes may soon be capable of producing water in the 60-to-75-cent range.

The Federal Water Pollution Control Administration has been experimenting with desalting techniques as part of pollution control and water reuse systems. Electrodialysis has been used in the Research Division's water renovation pilot plant at Lebanon, Ohio. There municipal sewage, after receiving secondary treatment, is passed through a 75,000-gallons-per-day electrodialysis unit which removes 300 parts per million dissolved salts from the 700 left in the water after the secondary treatment, and thus meets the Public Health Service's standards for dissolved solids. On the basis of the perhaps shaky data now available, total process costs, including secondary treatment, have been estimated at about 54 cents per thousand gallons for larger 10-to-20-mgd plants.