tity reflects total water reuse not just of process 

 water. The consumption of water4)y the industry 

 amounted to approximately 240 billion gallons in 

 1964. No corresponding calculation may be made 

 at this time for process water only because no 

 data on process water discharge are available. 



Significant indicators of water quality 



The water quality indicators which will be con- 

 sidered are settleable, suspended, and dissolved 

 solids, acidity and alkalinity, hardness, pH, chlo- 

 rides, dissolved oxygen, temperature, oil, and 

 floating material. In the judgment of the task 

 force, this short list incudes those process water 

 qualities that are considered important to the 

 industry. 



The quality of surface waters that are being 

 utilized by the iron and steel industry varies con- 

 siderably from plant to plant. Ranges of values for 

 the selected quality characteristics for existing 

 supplies are listed in table V-16. The quality of 

 the water available has been much less important 

 than the quantity in determining where a steel mill 

 should be built and even severe limitations on 

 water availability have not precluded the building 

 of new mills where the controlling economic 

 factors were considered favorable. 



TABLE V-16. Quality Characteristics of Surface 



Waters That Have Been Used by the Iron and 



Steel industry (SIC 33) 



[Unless otherwise indicated, units are mg/l and values are 



maximums. No one water will have all the maximum values 



shown.] 



NOTE. — Application of the above values should be based on 

 Part 23, ASTM book of standards (1), or APHA Standard 

 methods for the examination of water and wastewater (5). 



The desired quality of water for various process 

 use in the iron and steel industry is difficult to 

 define. For a few processes, using relatively small 

 quantities of water, limits on some constituents 

 are known. For most of the process water used, 

 however, only a few of the water quality char- 

 acteristics have been recognized as a cause of 

 operational problems. For the other characteristics 

 or properties neither the technological nor eco- 

 nomical limits are known. 



Water treatment processes 



Most integrated steel plants have two or more 

 process water systems. One system is the general 

 plant water supply. It receives only mechanical 

 skimming and straining for control of floating and 

 suspended materials which could harm pumps and 

 possibly internal conditioning. This water is used 

 for such diverse tasks as coke quench, slag 

 quench, gas cleaning, and in the hot rolling opera- 

 tions. For some of these operations, many mills 

 use effluent from another process or recycle water 

 in the same process and the water might actually 

 be of very poor quality. However, the only limits 

 for these process uses which could be established 

 based on present knowledge are those listed in 

 tableV-17. 



The other process waters used by the steel in- 

 dustry comprise only 2 to 5 percent of the total 

 volume but often require considerably improved 

 quality. Almost universally, one of these two im- 

 proved supplies is clarified while the second is, in 

 addition, either softened or demineralized. 



The clarified water is usually a coagulated, 

 settled, and filtered supply that is either treated by 

 the steel company or purchased from a municipal- 

 ity. The use for this water is mainly in the cold 

 rolling or reduction mill where surface properties 

 of the product are particularly important. 



The softened or demineralized water is required 

 for rinse waters following some pickling and 

 cleansing operations. The more particular proc- 

 esses from a water quality point of view are the 

 coating operations such as tin plating, galvanizing, 

 organic coating, etc. Some plants use_softened and 

 others demineralized water for identical purposes. 

 The quality limits desired for these two types of 

 water, softened and demineralized, are given in 

 table V-17. The quantity of these waters required 

 is less than 1 percent of the total process water 

 supply. 



206 



