George Rey William 1. Lacy Allen Cywin
The closed-loop cycle for waste water reuse is focused on minimal or zero
Environmental Proteci’ionAgency Washington, D.C. 20242
discharge units
Industrial water reuse: future pollution solution
T
he Water Quality Office of the Environmental Protection Agency ( E P A ) has in progress a research and development program for industrial water pollution control which touches on industrial waste water reuse as a tool for pollution control and abatement. Many others haqe also discussed the subject of water and waste water reuse, recycle, and even the zero discharge industrial plant. Man must turn from a “throwaway” economy to a “recycling” economy! I n d u s t r i a l water uses
To reduce waste water discharges from an industrial plant by implementing reuse techniques, the first step is determining the major water use requirements (water use volume balance) for the plant. The Department of Commerce “Census of Manufacturers” is a source of general water use information and distribution for industrial grou,ps. I n addition to water volume needs,, water quality requirements must also be established. At the other end of the process spectrum, the quantity of effluent water to be treated and the level of treatment must be taken into account for the plant “water balance and cost
Industry group
All (U.S. industries) Chemicals and allied products Primary metals industries Petroleum and coal products Paper and allied products Source: 1963 Census of Manufacturers.
760 Environmental Science & Technology
picture.’‘ These starting criteria are necessary to plan for the future. In general, water use within a self-supporting industrial complex is divided among three major functions: process use, cooling purposes, and steam production. The quality requirement for each function is different. F o r the year 1964, intake water requirements by selected industries were distributed by function (see below). These are the makeup requirements for each function and d o not reflect the extent of internal water reuse which occurs within any one function. Obviously, cooling water makeup needs are greatest, followed by process demands, and the requirements for steam generation. I n current practice, steam condensates are nearly always recycled, spent cooling waters are becoming more frequently recycled. and process waste waters are seldom reclcled o r reused. To reduce intake demands, and consequently waste water discharge volume. it is necessary to further recycle spent water from each function. Or, in addition to internal recycle, to reuse the spent water from one function as makeup for another function. Thus, recycle and reuse reduce and regulate water intake needs.
Water Intake Use by Function % Cooling Steam Process
26 15 22 6 64
67 80 74 a7 30
7 5 4 7 6
Reuse-recycle
Before proceeding further, multiple use, reuse, and/or recycle need( s 1 to be defined. Multiple use of watera method of reuse-implies its use more than once, but each time for a different purpose; for example, the countercurrent use of water for successively dirtier applications, but never for the same application, until it is no longer needed. This in contrast to a once-through use of water (used only once in any application). Recycle (also a method of reuse) implies using water over and over again for the same identical application from which it came. By this method, the total water intake of a plant, where reuse is practiced extensively, can be substantially less than a similar plant using water on a once-through basis (see page 7 6 2 ) . In the plant illustrated, the three major water use functions are: Process use-contacts products and raw materials in the manufacturing process; Cooling-for process operations and power production: Steam production-for process use and power production. Also assumed, in the flow plans of this hypothetical plant, is the water quality acceptability of process waste water for cooling functions and likewise cooling water blowdown as acceptable to make boiler feed. In these figures the average gross water usage is identical (i.e., 15 units of water). I n the once-through system, the water intake requirement is the same as gross water use. F o r the flow scheme of multiple use and reuserecycle, gross water use is the same 15 units as in the once-through SYStem, but intake and discharge requirements are substantially less.
mature
Water use methods
To reduce waste water discharge 93+% by reuse-recycle, the waters used must be continually purged of waste materials which accumulate (build u p in concentration) with usage. It is this buildup which affects water quality and limits the extent of water reuse achievable. The concentration of salinity, hardness, alkalinity, organic matter, and suspended solids must be controlled in such a system by their selective removal at appropriate locations and in appropriate amounts. I n this manner water quality may be controlled to meet reuse or recycle requirements. A hypothetical plan for purging limiting waste materials from the reuse-recycle system is described above. It is assumed that cooling, process, and boiler feed makeups are produced by a multieffect evaporation method; that alkalinity is removed by chemical methods; and that organic and suspended solids are removed by conventional techniques. In addition to providing high quality makeup water, a multieffect evaporator controls salinity and hardness buildup in the system. To accomplish this, the evaporator blowdown would need to be taken to dryness, o r near dryness, by some appropriate method which prevents uncontrolled release of the materials in the blowdown to the environment. In addition to salinity and hardness, this single blowdown effluent would be expected to contain many
other accumulated nonvolatile (possibly toxic) substances from each water use function. Toxic substances could include heavy metals from process and corrosion products and toxic organic and inorganic inhibitors and catalysts. If the ratio of gross water to water intake is an index of reuse, the oncethrough system would have a reuse ratio of 1.00. The multiple use system would be 1.50, and the reuse-recycle system would be 15.00. I n a total reuse system the ratio would be infinite. In practice, this can never be achieved due to water consumption (evaporation and drift losses, leaks, etc.) and the final fluid blowdown requirements imposed by salinity buildup and sludge removals. Some water intake will always be necessary. Industry trends
Water reuse in industry is increasing. The trends of two major industry groups since 1954 are shown on page 763. The reuse ratio shown is the effective number of times water is reused by the industries. Although reuse has been increasing, a much higher reuse ratio is potentially possible, under appropriate circumstances. The past trends have been motivated by the pressures of limited water supply, poor water supply quality, and, more recently, environmental considerations. The latter should accelerate the trend in the near future.
762 Environmental Science & Technology
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.,..
As practiced today, cooling waters and condensed recoverable steam are largely reused waters. Reusing steam condensates for direct boiler feed and new steam production, practiced since the industrial revolution, was motivated by engineering factors related t o boiler operations and construction. Waste waters are and can be used, directly or indirectly, as feed waters for boiler feed makeup. Similarly, process waste waters have also been utilized as cooling waters and for cooling water makeup. Accordingly, a plan for a waste water recycle system is not a pipe dream and is within the realm of engineering reality. Water quality standards established by states should sharply increase industrial efforts to reduce water pollution discharges within the next few years. However, even if discharges per capita were held constant, increasing population and consumption would dictate increasingly stringent standards since the assimilation capacities of the receiving environment are rather constant. Therefore, farsighted industrial management should consider a water use plan which results in the zero discharge, or as close to this goal as is possible. Engineers have pointed out that a closed cycle for water use in which no outfall returns effluent either to local supplies o r groundwater can eliminate the cost of continuous mon-
Reuse-recycle treatment system Intake 1 unit 4
3
1
Salinity
+ hardness
itoring. which may, in addition to being costly, be required within a few years. Add to these aldvantages cost reductions from eliminating outfalls and lesser intake water supply facilities for new plants. Now, the dream starts to look like a reality. In xiew of current and prospective environmental standards, each industrial plant should ask itself which \v;iy is best to proceed to comply with regulator!. demands. In considering the alternatives, there are really only t h o : no discharge. or discharge conipl!-ing with currenr and future requirements of the regulatory agency. Where conditions may initially dictate treatment for discharges, the resulting effluent might be suitable for reuse within an industrial plant ---either as cooling wate.r and/or boiler feed makeup. So why throw it away? Especially when perrnits may be needed to d o so. Recent developments indicate waste waters of very high salinity, hardness. and containing organic matter can be successfully utilized directly as boiler feed without prior treatment. This i \ particularly significant since boiler feed water normally requires high quality water. In some cases boiler feed water is indirectly produced by an evaporator generating a distillate for boilers. LTiider this condition evaporators may be considered as waste water concentrators, which have a wide operating- latitude of ac-
Alkalinity
Suspenhd teiids
ceptable feed quality. In fact, evaporators operating on low quality water can still produce a high quality distillate suitable for boiler or cooling tower makeup. R&D-the
key
The Water Quality Office program for industrial water pollution control views closed-cycle water use as an ultimate goal for industrial plants to control water pollution. Accordingly, water pollution control reuse-recycle projects are high priority areas for R&D support. Basic technology for technically and economically feasible closed-cycles is generally accepted as available. More often than not it is practiced in piecemeal fashion in specific applications. Now the time has arrived to consider putting the pieces together to de-
velop totally engineered systems suitable for typical industrial plants, and to research water quality parameters which are controlling factors in water reuse and the affected economies. How can this be done? A planning guide for an industrial water reuse R&D program (page 764) was prepared by using three major industrial water use functions as a basis for the closed-cycle system which must effectively minimize water intake, waste water discharge, and treatment (water supply as well as waste water) costs. Interconnecting functions (hydraulically I and more fully utilizing capabilities of waste water treatment facilities of each water use function (normally expected to be required) follow these guidelines. Also, expanding each operation’s capabilities to serve a multiple purpose would further take into account the economies involved. But i t is not that simple since operation and maintenance of cooling towers and boiler systems are very sensi tive to water quality. Furthermore, experience with total reuse-recycle systems in industrial complexes is rare. which indicates R&D efforts are needed in this area. As a consequence, future R&D emphasis should establish more firmly engineering feasibility. This particular concept is predicated on maximizing waste water reuse-recycle, and the water reuse plan is essentially the same as shown previously (pages 762-3) in more general terms. Even the more detailed pitanning guide must be considered as general with respect to specific needs of typical industries with different operating characteristics. Therefore, actual plans which will evolve in industry can only be expected to be “of the kind” shown in the general scheme. However, the time is now to plan for the future.
Volume 5, Number 9, September 1971 763
How can industry start? Before a plant considers how to move toward the no-discharge system, it must first m:ike a water use and materials (affecting water quality) balance. For new plant designs, industry should locate water use and distribution systems to the best advantage for a closed-cycle system. For old plants, obvious reuse possibilities should be implemented along with other capital plant improvement projects. For either type plant, existing supply water quality and receiving water standards should be evaluated to identify the water quality parameters which limit existing systems from achieving greater reuse and/or pollution control. Finally, plans should be developed to use the minimum number of treatment operations and to handle the least amount of pollutants inherent to the industrial operation and treatment processes applicable for use. This system (below) also includes considerations for environmental factors other than water pollution control. These factors, also to be considered in the future, concern use of waste waters for air and thermal pollution control functions and waste residue usage for heat and power production and /or water treatment ( a s h ) . However, even an ideal plant system will have a net discharge of waste niaterial. In the system discussed, this includes excess ash from thermal power production and a waste water blowdown of high salinity, hardness,
and toxicity. These wastes may be blended for some beneficial purpose. to ease proper handling, or for controlled assimilation by the environment in appropriate disposal sites. These areas have to be given consideration as man proceeds to meet future environmental demands. Economics
Numerous unit operations and processes may be applied to waste water treatment. Several publications have listed the various methods and treatment costs by respective unit processes or operations employed. Such information can be very useful, but also misleading because it does not present less obvious factors which can influence costs considerably (for example, the concentration of pollutants, scale of operation, etc.). Rather than discuss economics with typical costs based on amount of water treated (i.e., cents per 1000 gallons) or on specific processes employed, it may be more beneficial, at least initially, to look at total cost potential in a simpler, more general way. Water treatment costs are primarily related to volume of water treated; amount of suspended solids, alkalinity, hardness. organic matter, and dissolved salts removed. Barring any unusual waste water ingredient, constituents that are controlling factors in industrial water usage and waste water treatment fall into the above major categories. These
controlling factors and their approximate cost of removal from hypothetical waste water system are shown on page 765 (on the basis of amount removed), To obtain water pollution control costs for an industrial plant, the amount of these materials to be remo\ed in various reuse schemes and water volume to be handled should be calculated. Employing this approach should increase understanding of what each industr). faces as potential water pollution cost. and alternatives of by-product recovery vs. disposal or treatment can be approximated more easily. Total uater reuse schemes may a1.o be evaluated on a more manageable basis. h’hen making complete niaterial and cost balances, the removal cost of the same components from intake water supplies as well as Lvaste wateri should be included. In poor ivater quality areas the total water recycle method may provide minimum cost for pollution control since these water supplies bring into a plant several of the same materials whose removal is required when the water is treated for use or discharge. The net effect is that more suspended solids, organic materials, and dissolved salts would be handled on a once-through hasis than if only net increases due to internal (closed-cycle) plant functions were to be handled. This point should be kept in mind when industrial water pollution control planr are being made.
Industrial waste water reuse scheme
-
Ash for waste water treatment
Sfudges (Resourcerecovery, land assimilation, incineration, etc.)
Water make ups Boiler Process
Air
\
--
A-
m
Ash
blowdown Wet scrubbers Landfill or building materials
I
Clean flue gases
- - --
,-
Normal route Alternatlve
I
L---.r-.l.--.
R10 needrd Deletions
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764 Environmental Science & Technology
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, , , , , , , , , , , , ~
Evaporation & drift losses
uevrge n e y
13
~
Costs of using evaporation techniques for pollution control can be misleading. -. at first dance, when consicb e d in terms of cc)st per volume urlit directly treated. However, the gr oss water quantities in a plant - ~ ~ _ treated . oe enureiy by this n e.>w IIUL L~ method, but rather only a small fraction of the total. If this cost is spread over overall water and waste water management costs, it then does not appear unreasonable-particularly if using the resulting water lowers other water operations' costs. Toxic, hard-totreat, nonvolatile pollutants may still be present in process effluents and cooling tower blowdowns even after some conventional treatment; therefore, the effectiveness of a n evaporation-concentration method to accumulate and concentrate these contaminants should be considered. The value of high quality water produced for reuse should be subtracted from the cost of its production. Using "new" water can maximize the water reuse ratio within an industrial complex. I
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Future demands
Closed-loop industrial waste water and water systems are vitally necessary to maintain continuity in future industrial expansion. The huge water demands and high water usage growth rate of American industry cannot continue to rely solely on traditional water supply sources. Even in waterabundant areas, intake Water supplies for industrial use are fast becoming restrictive. Trends toward water re-
have been started and must be accelerated now-if an adequate base for future industrial expansion is to be provided.
Current and future environmental standards for waste water discharges are expected. to increase the pressure on industry to reduce both the pollution discharge loads and the magnitude of effluent volumes in. order to minimize environmental impact, Industrial water quality requirements for reuse ,are less demanding as a general rule, than for municipal supplies. Accordingly, industrial water reuse should be technically and economically achievable earlier than comparable
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Waste water reuse is not only a resource conservation measure, but also a method of pollution control-a step in tune with future demands. Adequate R&D activity in this area is the key to accelerating implementation of extensive waste water reuse systems and, eventually, the total closed-loop cycle. The latter, with no effluent discharge, would comply with any quality standards now or in the future.
ucLL,Lg cnrr,, I n u U J I r L u L
Pollution Control Branch, EPA, Ofice of Research and Monitoring. He received his BS and MS in chemical engineering (University of Idaho). Prior to his EPA position, Mr. Rey worked with air and water pollution from hazardous chemical and nuclear materials and atomic waste handling, dimoral. A d d r e s .~~ in.treatment. ~ . ......, . ~ ~nnd .... ~ quiries to Mr. Rey. ~~~~
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William . I . Lacy, a graduate of tht? University of Connecticut (BS in chemistry), is presently acting director of EPA's Division of Applied Science and Technology. Mr. Lacy has worked in the area of waste treatment and wafei decontamination since 1951. He joined the Federal Water Quality Administration in 1967 and assumed his present post in May.
Additional Reading
Brooke, Maxey, "Water," Chem. Eng., 77, Dec. 14, 1970. Cywin, Allen, "Engineering Water Re-
zirFD.:f hyv,F;2J::c, New York, N.Y.
",",":,::;
Cywin. Allen, "The Urban Hydrological Cycle," EASCON 1970, American Conference Of ,ProfessionalGroup on Aerospace and Electronics Systems UEEE.) October 26-28. Washington, D.C. ~ ~ D. R., k B ~~ 7., s., ~ ~ ,f i c.~ H., ~ , "Water Management a Fashionable Topic," Environ. SCi. Technol.. 1 (lo), 1967. Lacy, William J., "The Industrial Water Pollution Control R&D Program," National Association of Corrosion Engineers, 26th National Conference, Mar. 2-6, 1970, Philadelphia, Pa. Symons, George E.,"lndustrial Wastewater Management-A Look Ahead." Water Wastes Eng., 6, January 1969.
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Allen Cywin is a mechanical engineering graduate of Rensselaer Polytechnic Institute. A s acting chief of Water Quality Research in EPA, Mr. Cywin plans, directs, and implements R&D programs in preventing, controlling, and abating pollution from storm and sewer overflows, industrial, agricultural, mining, and other sources o f pollution. Volume 5, Number 9, September 1971 765
