INCREASING REQUIREMENTS 219 



filtration and disinfection with chlorination. Treatment of 

 sewage in order to reuse the water for other purposes and to 

 utilize the sludge for fertilizer has been shown to be economi- 

 cal at many places. 3 



The water used but not consumed in irrigation or industrial 

 processing commonly is deteriorated in quality chiefly because 

 of increase in dissolved mineral matter but in some places be- 

 cause of addition of phenol or other organic residues. The 

 treatment processes for increasing the utility of the water after 

 use are as greatly varied as the types of contamination; they 

 generally do not achieve any great reduction in total dissolved 

 materials but remove the harmful or toxic combinations by 

 chemical neutralization or precipitation. A small but increas- 

 ing proportion of industrial water is being completely de- 

 mineralized prior to use by means of resinous ion exchangers. 

 For some contaminated waters the cost of treatment would be 

 so great that other means of disposal have been devised to 

 prevent contamination of usable water supplies. These meth- 

 ods include disposal by trunk-line sewers to the ocean and by 

 w T ells into brine-bearing formations. 



Water used for cooling becomes "polluted" with calories, 

 which does not necessarily vitiate its further use for other 

 purposes and would even be a benefit to the user who expects 

 to heat the water to high temperature. An extreme example 

 of deleterious temperature effects is offered by the Mahoning 

 River in Ohio, probably the most intensively used river in the 

 country. During December 1949 the water diverted from the 

 river was 10 times the average flow of the river, and most of 

 the water was returned after being used for cooling. The 

 temperature of the river approached 140° F during that winter 

 month, a temperature so high as to render normal sewage- 

 purification processes ineffective, so that pollution is a serious 

 problem. Here would be an excellent place for a plant that 

 could extract heat from the water. 



The potential energy of the water is used chiefly for power, 



3 Veatch, N. J., Industrial Use of Reclaimed Sewage, Jour. Am. Water Works 

 Assoc, vol. 40, pp. 1-7, 1948. 



