improving the quality of existing water. These 
needs stem from the rapid depletion of available 
natural sources of water, severity varying with 
specific locality. In addition, the quality of exist- 
ing water is being degraded in many places. 
Desalination techniques applied to sewage treat- 
ment and brackish water represents a powerful 
tool for meeting these needs. 
2. Technology Status and Problems 
Desalination processes can be divided into four 
broad categories: distillation, crystallization, mem- 
branes, and advanced processes in initial develop- 
ment. Four operating plants in the continental 
United States have capacities of at least one 
million gallons per day; all use the distillation 
technique. Three are OSW demonstration plants. 
Indeed, the distillation technique, in a very ad- 
vanced state of development, is being used widely 
and will be the basis for all very large plants (SO to 
100 mgd) in the near future. 
Nevertheless, no single technique is best for all 
kinds of water. While distillation will produce 
fresh water from any kind of water, it may not be 
economical. It should not be used to desalt water 
with 9,000 parts per million or less. At present, 
numerous small communities use electrodialysis on 
available inland brackish water supplies. Yet even 
electrodialysis cannot process all kinds of brackish 
water, nor can reverse osmosis, the newer mem- 
brane technique being developed. This is because 
there are certain kinds of contaminants in water as 
silicates, calcium, and iron which will foul the 
membranes very quickly. 
The freezing process, operating at low tempera- 
tures, is not fouled by contaminants in certain 
kinds of brackish water. For all the processes 
mentioned for brackish water, pretreating may be 
an important key, rather than attempting to design 
a plant to treat all kinds of water. 
While the reverse osmosis membrane process is 
in the pilot stage, the technique is being consid- 
ered as an advanced technology to be used 
ultimately in converting of polluted water to fresh. 
A major challenge to the Nation is the capa- 
bility to build giant desalination facilities (100-200 
mgd) to augment water supplies for large popula- 
tion centers and as a forerunner to large agro- 
industrial complexes producing 1,000 mgd. Sup- 
plying such large water capacities might require 
VI-212 
full-scale model testing of critical parts to improve 
reliability levels. Engineering problems include 
heat transfer rates, suitable materials (materials 
presently constitute up to 20-30 per cent of total 
capital cost), and scale control techniques. As an 
example, long period operating experience with 
several types of materials is needed urgently, under 
varying conditions of temperature, oxygen con- 
tent, brine concentration, and flow velocity. 
3. Outlook 
Desalination is in an embryonic stage with a 
very optimistic future. Many ideas are being 
advanced to bring costs down, some either about 
to be or already in practice. These include dual 
plants for simultaneous electricity generation and 
desalting, the use of waste heat from incinerator 
plants, the ability to concentrate the brines suffi- 
ciently to extract useful chemicals economically, 
and the use of chemically pretreating brackish 
water. Finally, low-cost, small desalination plants 
for islands and hotels appear to be a promising 
source as soon as improved technology permits 
costs and reliability to improve. 
Recommendations: 
The OSW research and development program 
should continue to be directed toward solution of 
two problems: 
—Development of technology to supply large-scale 
regional water needs, including those of metropol- 
itan areas near the coast, utilizing such tools as 
dual-purpose power plant-sea water conversion 
complexes. As a long-range consideration, efforts 
should be continued on technology requirements 
to meet agricultural water needs. 
—Development of processes to make use of brack- 
ish water supplies adjacent to inland communities 
and to purify waste water from industries and 
municipalities for reuse. 
Greater emphasis should be placed on solving 
engineering problems in those processes now tech- 
nically feasible in order to maximize plant relia- 
bility, lengthen plant life, and minimize water 
costs. Development of hardware for prototype 
plants ranging up to 50 million gpd and more 
should be pursued. 
