SHEPPARD T. POWELL
330 North Charles St., Baltimore, Md.
Adaptation of Treated Sewage for Industrial Use The treatment of liquid wastes for further use has passed the experimental stage and offers a practical solution for many industrial water problems
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T H E R E is general cognizance of industry’s growing demand for adequate water to support its rapid expansion. Records of water use in the past, as well as predictions of future needs, have been summarized and widely publicized. The need for water has been emphasized in the Hoover Commission report of June 1955, which stated that
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. . our industrial needs (including cooling water) will rise in the next 25 years by an estimated 138,000,000,000 gallons per day; and that domestic consumption will rise in the same period by another 7,000,000,000 gallons per day. By 1975 the total prospective increase for domestic and industrial use over present amounts will be 145 per centequal to the additional supply of 145 New York cities, requiring the flow of about 11 Colorado rivers. More recently, in January 1956, President Eisenhower sent to Congress several proposals for coordinating the federal water resource policies, embodied in a report of his Cabinet Committee on Water Resources Policy. The recommendations included in the report form the basis of the President’s “comprehensive legislative program for water conservation” called for in his State of the Union Message. Numerous plans for development and conservation of water, both in local areas and by river basins, have been proposed, and legislation undoubtedly will be enacted to develop realistic plans to help meet the national need for water.
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Regardless of these developments and complementary programming for meeting industry’s water requirements, the conservation and re-use of both sanitary and industrial wastes are now being recognized as a practical and economical partial solution of industry’s growing water problems. The treatment and re-use of liquid wastes have passed the experimental stage and such waters are being used in fairly large volumes, both in this country and abroad. I t may be reasonably predicted that, as water shortages become more acute, the discharge of millions of gallons of contaminated waste waters to the sea will be curtailed, and such waters will be more fully utilized at the source, thereby minimizing water shortages now threatening many areas because of concentration of industry and concurrent growth of population. The location of industrial plants depends to a large degree on the availability of water and means for the disposal of unwanted wastes. I t has been the author’s experience that sites otherwise desirable for the establishment of industries have been rejected because these two requirements could not be met. Frequently these related problems of water supply and waste disposal can be solved by treatment and utilization of waste waters. I t is natural to assume that this conservation method would be practiced only in arid and semiarid regions, but actually the use of treated wastes is no longer restricted to such areas. Sewage
INDUSTRIAL AND ENGINEERING CHEMISTRY
effluents are now being used in areas normally considered humid and semihumid. There is an increasing trend to the agricultural use of water for irrigation in many areas. Even in the relatively humid East, agriculture is rapidly becoming a significant competitor for available water supplies. In a recent symposium on supplemental irrigation, it was pointed out “that water is being lost in some tributaries, possibly from supplemental irrigation. Naturally, any industry with big production in these areas must practice conservation and economy in water usage” (5). It has been emphasized that the critical low flows in some streams in certain sections in the eastern part of the country are being seriously reduced by withdrawal of water for irrigation purposes during dry weather periods ( 9 ) . This is a disturbing development, which deserves the attention of water conservationists at all levels. Irrigation practices may have a marked impact on the equitable apportionment of available water supplies. I t may be predicted that legislation will be enacted in the near future to ensure fair distribution of available water for municipal, agricultural, and industrial requirements. I t is not the purpose to present here a discussion of the philosophy and economics of apportionment among competitive users. However, in such apportionment, the availability and use of sewage and industrial wastes must play an important part. Reclaimed waste waters
RE-USE OF WATER B Y I N D U S T R Y will have a definite effect on the over-all solution of the nation’s water supply problem. In many situations where there is competition for clean water, industry will have to turn to waste waters to fill many of its requirements.
ation from the municipal sewerage authorities, it has been possible in some cases to divert undesirable wastes from those city sewers which provide effluents for reclamation and re-use.
Cost of Reclaiming Sewage Treatment of Sewage
Eefore a sewage effluent can be used directly for industrial purposes, it usually requires treatment. The degree of conditioning depends in part on the water quality required for specific uses and also on the quality of sewage available. In order to take advantage of every economy, the used water shQu1d be treated stepwise, with provision for supplying less demanding purposek with a water of relatively low quality. The advanced treatment steps should be reserved for water needed for more exacting uses. The actual treatment processes for producing industrial water from a sewage effluent must take over where sewage treatment stops. Municipal sewage may be available only in a raw or untreated state, or it may have been already treated to a degree required by pollution control or health regulation. Where treated, sewage usually is given either primary or “complete” treatment-namely, reduction of biochemical oxygen demand (B.O.D.) by about 35 or 85%, respectively. Obviously, the more highly treated the effluent, the less additional treatment is necessary to produce a satisfactory water supply for“any specific industrial use. Basically, however, there is very little difference between treating a sewage effluent and any other water supply. Many of our rivers which are used extensively as water sources for all purposes are nothing more than sewage diluted to a greater or lesser degree. General treatment methods available for sewage conditioning prior to re-use as an industrial water supply are well known. Most municipal sewage contains both sanitary and industrial wastes. Consequently, a given effluent may contain a wide variety of constituents not normally found in sanitary sewage, which if not removed may be highly objectionable for certain. industrial processes. Toxic materials will interfere with biological treatment; volatile substances may be dangerous to personnel; and acid wastes will corrode pipelines, pumps, and other equipment. Where such harmful contaminants are present, special treatment may be required to assure satisfactory re-use of either sanitary or industrial wastes. However, before expensive facilities are installed for such treatment, the possibility of removing the unwanted substances a t their sources should be thoroughly investigated. With cooper-
The cost of treatment of any waste, whether for stream pollution abatement or for water reclamation, varies greatly. Its economic justification necessarily depends on the urgency to meet statutory requirements or to supply water of desired quality, as well as on the comparative costs of alternative water supplies. The cost of collection, treatment, distribution, and application of sewage for any purpose must be analyzed on the .same basis as would any other water supply. A few examples of costs for existing sewage reclamation projects are presented in Table I. I t is emphasized, however, that judgment must be used in applying these cost figures a t different installations and for different uses. Such data may be misleading if not meticulously examined and interpreted. Acceptable costs of treatment must be evaluated and re-evaluated as often as necessary in the light of the ever-changing situation of water supply and demand. Examples of Industrial Use of Sewage
The largest and most publicized industrial use of municipal sewage is the Bethlehem Steel Corp’s installation a t Sparrows Point, Md., on Chesapeake Bay, a few miles from the city of Baltimore (70). This is a very large and expanding operation, embodying all the departments of a complete mill of this type. Large quantities of water are used for cooling, boiler feed, quenching, and other purposes. Brackish water from the bay is used for cooling and condensing, but fresh water is also necessary for
Table 1.
many services. The only available fresh water supply a t this location is ground water of limited supply and inadequate for the demand to meet the plant’s expansion. After a comprehensive study, it was decided to obtain treated sewage from the municipal plant a t Baltimore, retreat it, and pump it to the mills, about 10 miles away. The city sewage receives complete treatment by activated sludge and trickling filters. This installation has been widely publicized and requires n o description here. At the present time the steel company is purchasing about 70,000,000 gallons of sewage per day. At the company’s. treatment plant the sewage is coagulated, settled, chlorinated, and then pumped. through a concrete conduit to the millsThe steel company plans eventually to increase the use of water from this sourceThe present discharge from the city plant amounts to about 140,000,000 gallons per day and will probably increase, offering an ample supply for expanded use. Wolman (70) estimated the cost of the’water to be 1.73 cents per 1000 gallons, exclusive of interest and amortization on the investment, during the year 1946. This figure includes the purchase of the effluent and operation of the company-owned treatment and pumping facilities. This project deserves attention because it is an outstanding example of a realistic and economical solution of a large industry’s water problem. Its success should encourage the consideration of sewage reclamation by other industries. Another example of waste water reclamation is afforded by the Kaiser steel plant in Fontana, Calif. (7). Although much smaller than the Sparrows Point installation, it is similar in importance because it points u p the growing value of re-use of sewage. At this location the domestic supply furnishes water for fire, sanitary, drinking, and irrigation purposes, All wastes
Cost Data for Use of Reclaimed Water“
Quantity cost of Alternative Used, cost, Water, AcreLocation Ft./ Yr. $/Acre-Ft. $/Acre-Ft. of User Type of Use (APWOX.) (APPTOX.) ( A p ~ 0 s . Z Grand Canyon, Ariz. Power plant * 200 $120 $650 40 Los Angeles, Calif. Sewage plantc, Hyperion 12.000 60,000 4d 3 3% Baltimore, Md. Steel plant, Bethlehem Amarillo, Tex. Refinery, Texas Co. 1,700 14 e 45 2,200 16 57 Big Springs, Tex. Refinery, Cosden Reproduced by permission of State Water Pollution Control Board (3). b EBuent aIso used for irrigation. Pumping and chlorination are only costs. Approximate cost does not include additional treatment and pumping, and amortization of $2,000,000 investment. Does not include amortization costs paid by refinery, which would raise cost to approximately that of city water at minimum use.
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from these uses are treated and then added to the system supplying water for industrial process. I t has been reported that the re-use of waste domestic water, with maximum recirculation of all industrial water streams, enables this mill to limit its water intake to 1400 gallons per ton of steel produced. In evaluating such statistics, the design and operation of the plant and the type of products manufactured must be taken into consideration. However, when compared to the usually quoted national average for steel mill requirements, 65,000 gallons per ton, the Fontana plant’s water use stresses the great value of re-use of waste water as a conservation measure. The Shell-Oil Co. at Ventura, Calif.. recently designed a sewage recovery plant which will treat the effluent from that city‘s disposal plant. In the past, this effluent has been wasted into the Pacific Ocean. The company plans ultimately to obtain 2,000,000 gallons per day from this source. After treatment in the recovery plant, the water will be of potable quality but is intended for industrial purposes only. After 20 years of operation, the plant will be conveyed to the city. When the plant is turned over to the city, The Shell Co. will retain the right to purchase water for 10 years. During the initial 20 years, Shell will receive water from the city without charge. but will pay for the operation of the recovery plant. It is predicted that this installation will eliminate water shortage problems for all the company’s operations at this location. One of the earliest industrial plants to use sewage effluent was the Cosden Petroleum Corp. refinery at Big Spring, Tex. The city-owned activated sludge plant delivers approximately 1.OOO,OOO gallons per day of effluent to a lagoon a t the sewage plant ( 8 ) . The company pays approximately 4.4 cents per 1000 gallons at the lagoon and conveys it to the refinery through its own pipeline. The use of sewage as a substitute for ground water in this case results in substantial savings to the company and pays a large portion (about 90y0)of the city’s cost for operating the treatment plant. A few years ago the author studied several possible methods of supplying water for make-up for a proposed very large cooling tower installation in an area of severe water shortage. Investigation revealed a large trunk sewer adjacent to the plant site, which carried raw sanitary sewage to a municipal disposal plant. Comparative studies of costs for alternative water sources showed a decided advantage in using the treated sewage as make-up water. A complete treatment plant was designed to convert the waste into a satisfactory cooling water. The design included an activated sludge plant, unique in that the aeration tanks were covered and vented for odor control. The primary and
secondary sludge was to be returned to the trunk sewer for ultimate disposal at the municipal treatment works. Although shown to be practical, this recovery plant was never built, because another site having ample water was finally selected. Precautions in Re-use of Sewage
,4ny discussion of the industrial uses of reclaimed sewage would be incomplete without mention of certain precautionary measures which are indicated for the protection of personnel, equipment, and products. The health hazards inherent in the use of sewage, as well as the applicable preventive steps, are fairly well known. Suffice it to say that this phase of personnel protection should be an important part of the over-all safety program in any plant using this type of water. The hazards to plant equipment related to sewage re-use are not so widely understood. Among the great variety of constituents found in municipal sewage, especially where industrial wastes are combined with sanitary wastes, a number of substances are potentially damaging to pipelines and other manufacturing equipment. For this reason? the installation of any waste-reclamation system should be preceded by a careful study to determine possible detrimental effects and means of elimination. One of the principal objectionable characteristics of sewage is the frequently high ammonia content. Ammonia in several forms, especially in the presence of oxygen, can readily attack copper alloys and other metals The damage may be in the form of pitting, general wastage of metal, or stress corrosion causing cracking. Relatively small amounts of ammonia in the presence of oxygen have been known to cause rapid loss of tubes in heat exchangers, condensers, and other equipment. In one of many similar occurrences in the writer’s experience, the intake water of a large mill was excessively contaminated for a short while with municipal sewage. As a result of the ammonia contained in the mixed waters, corrosion cracking with heavy tube losses occurred in several exchangers. The tube material in this case was a good grade of Admiralty. This type of failure is greatly accelerated if the tube material contains locked up stresses or is subject to vibration. Recently brass corrosion by chloramines has been reported (6). A sudden rise in the number of faucet-seat replacements by one large plumbing contractor was attributed to the presence of chloramines. Similar damage occurred at one location after a change in water treatment to facilitate iron removal which provided for prechlorination, replacing the previous practice of
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split chlorination. The new scheme resulted in more than 2 p.p.m. chlorine residual in water leaving the plant, all in the form of chloramine. Both oxygen and chlorine residuals were found at the ends of the distribution system where formerly chlorine had been virtually absent. Controlled corrosion tests on brass- and Monel-seated faucets showed rapid deterioration of the brass seats, all of which failed within 27 days. The Monel was reported to have suffered no damage during the tests, one of which was continued for almost a year. The investigators concluded that “excessive replacement of faucet seats resulted from the presence of appreciable chloramine residuals in a greater portion of the distribution system.” These experiences should serve to warn anyone proposing to use a water likely to contain significant quantities of chloramine. Reclaimed sewage is usually chlorinated for slime control, with possible formation of chloramines. Detergents and Foaming
With the increased use of detergents during the past decade, difficulties with excessive foaming have been experienced at sewage disposal works. Where treated sewage is to be used, its foaming characteristics should be carefully studied, Where detergents are found in the wastes, reclaimed water is likely to foam badly if used in spray ponds or cooling towers, resulting in an unsightly condition or objectionable atmospheric pollution. The responsibility of household detergents for foaming troubles at sewage treatment plants is still being debated. Temperature
Because the most probable use of reclaimed sewage is for cooling purposes, its temperature is significant. Most sewage plant effluents contain considerable quantities of heat and so, as a coolant, compare unfavorably with surface or ground water, especially for use in a once-through system. However, the growing practice of recirculating cooling water as a conservation and economy measure will lessen the temperature advantage of other water supplies over sewage. Effect on Wood
Among coolant-recirculating systems, cooling towers: constructed mainly of wood, are important. Therefore, the possible effect of sewage on wood should not be ignored. Until a relatively short time ago, the deterioration of wood in cooling towers, though widely observed, was not well understood. Baker ( 7 ) has pointed out that both chemical and biological attack are re-
RE-USE OF WATER B Y I N D U S T R Y sponsible for damage to wood in towers. He reported that cellulose, able to resist most chemicals, is readily attacked by many microorganisms, especially fungi. He indicated further that most fungi which attack cellulose are inhibited by lignin, and removal of the lignin renders the cellulose more digestible by microorganisms or higher animal life. These studies appear to lead to the conclusion that any material in water which delignifies wood could accelerate deterioration. These and other damaging effects are possible with the use of sewage in contact with wood, because of the potentially high content of microorganisms or delignifying agents. However, no such difficulties have been observed at two installations where reclaimed waste waters are cooled in wood towers. The towers at the Cosden Refinery in Big Springs, Tex., and a t LOSAlamos, N. M., are reported to be in excellent condition after several years of operation with sewage make-up (3).
Radioisotopes in S e w a g e In February of this year, President Eisenhower, acting on the recommendation of Lewis Strauss, chairman of the Atomic Energy Commission, authorized the designation of 88,000 pounds of uranium-235 for research and development purposes and for fueling nuclear power reactors. When compared with the largest previous amount assigned for peaceful purposes-only 440 pounds -this new allocation emphasizes the increasing use of radioactive materials in industry, science, and medicine. The greatly increased use of radioisotopes will automatically result in massive quantities of radioactive wastes. For the protection of the general environment, high-level wastes must be disposed of by special and complicated procedures. Low-level wastes, on the other hand, are being discharged into many of our sewers, and it is a safe prediction that this practice will continue to grow. A word of caution should be given, therefore, on the reuse of sewage that may contain any radioactive material. Although the level of activity in municipal sewage will generally be sufficiently low to avoid hazard to humans, it may exceed the levels that can be tolerated in some industries, especially where the isotopes are concentrated by evaporation or other means. There are many processes in which radioactive material, even in extremely low concentrations, may be objectionable. Among such processes are the manufacture of all types of photographic film and of chemicals entering into such manufacture. Even the paper used
in wrapping films must be free of radioactivity to prevent damage to the film. At least one case is on record where such damage has occurred. These cautionary comments are not intended to cover all possible complications which may arise in the use of reclaimed sewage, nor to promote pessimism or discourage such use. They have been included primarily to direct attention to the need for careful and thorough study when planning to use treated sewage for any of industry’s varied water requirements.
indirect Use of S e w a g e Most of the foregoing discussion is primarily concerned with the direct use of sewage for industrial purposes. However, the writer does not wish to ignore the great potential means of using sewage indirectly by treating it adequately and then adding it to existing water sources, both surface and underground. This practice is by no means new; it has been carried on for centuries, for the simple reason that it could not be avoided. I t has resulted from the dual use of streams and underground formations for waste disposal and water supply. Every water intake located downstream from a sewer outfall receives sewage, more or less diluted and purified by natural processes in the stream. Similarly, wells tapping aquifers fed in part by septic tank drain fields, sewage seepage pits, or sewage-polluted surface streams, supply water that contains diluted sewage. In the past this unintentional use of sewage has been generally considered an unavoidable evil. However, with growing water shortages, far-sighted planners have been looking for ways to assist nature in the purification of sewage, not just to get rid of it, but so that it can be used intentionally and deliberately to augment scarce water supplies. Much pioneering has been done in California in the use of waste waters to recharge underground aquifers. I t was reported in 1951 that the average dry-weather sewage flow to the Pacific Ocean from the south coastal area of California totaled some 400,000 acrefeet during the calendar year 1949 (4). A 1954 report stated that 112 sewage treatment plants in California were recharging ground waters with treated effluent (Z),indicating that considerable quantities of usable water are being conserved which formerly were wasted into the ocean. Water thus conserved remains available for industrial and other uses. The experience in California provides valuable lessons for use in other areas in the development of similar water conservation measures.
Conclusions The expanding water requirements in many areas may be satisfied only by wise apportionment of existing supplies and by the practice of strict economy. Granting that such conservation of our water resources is essential, it follows that re-use of water must be practiced whenever possible. This, in turn, entails curtailment of our present-day practice of discharging to waste large volumes of sanitary sewage and industrial effluents which, if treated, would greatly minimize water shortages. Many problems must be solved in the collection, treatment, and re-use of sewage, but this can be done by intelligent appraisal and engineering knowhow. Our present need at both the local and national levels is for publicizing the value of this type of water conservation, its adaptability, and means for processing. The use of waste waters must be considered from many angles, but if treatment systems are intelligently planned, adequately designed, and properly operated, successful re-use will be realized. The California State Water Pollution Control Board, which has sponsored extensive research in the reclamation of waste waters, has clearly stated the value of sewage re-use in its 1954 report, from which the following comments are quoted (2): There appears to be no physical reason for treating waste water as being fundamentally different from any other water source. The uses to which it can be put are the same, and the precautions taken before using it are the same.
literature Cited (1) Baker, R. D., Industry and Power 59 (3), 94 (1950). (2) Bush, A. F., S. F. Mulford, “Studies
of Waste Water Reclamation and Utilization,” California State Water Pollution Control Board, Publ. 9 (1954). (3) California State Water Pollution Control Board, “Survey of Direct Utilization of Waste Waters,” Publ. 12 (1955). (4) California State Water Resources Board, “Water Resources of California,” Bull. l(1951). (5) Interstate Commission on the Potomac River Basin, Symposium on Supplemental Irrigation, 1955. ( 6 ) Larson, T. E., others, J . Am. Water Works Assoc. 48, 84 (January 1956). (7) Riegel, H. I., Sewage and Znd. Wastes 24, 1121 (September 1952). (8) Veatch, N. T., Sewage Works J . 20, 3 (January 1948). ( 9 ) Wiseman, J. W., Sewage and Znd. Wastes 27, 1284 (November 1955). (10) Wolman, Abel, Sewage Works J . 20, 15 (January 1948). RECEIVED for review April 10, 1956 ACCEPTED September 29, 1956
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