ever, equipment is available and in use which can be maintained and gives acceptable assurance of working under all operating conditions. The extent of use of this and new equipment depends greatly upon the programs responsible for plumbing and water supply protection, including definite schedules for surveillance of the protective devices. installed.

THE USE OF NEW MATERIALS AND EQUIPMENT AND NEW USES OF OLDER

MATERIALS AND EQUIPMENT

Many new materials and new equipment are being developed for use in water distribution systems, and are discussed above under design and construction. All are designed to overcome one or more maintenance problems-costs, corrosion, leakage, pressure maintenance and others.

Plastic pipe.-The use of plastic pipe in the waterworks field dates from 1950 or 1951. From a maintenance standpoint, the advantages of plastic pipe are indicated to be good resistance to chemicals, electrolytic attack, and inorganic corrosive materials; lightness of weight and smoothness of surface. Disadvantages include low mechanical strength, sensitivity to temperature (brittle when cold, weak above 140° F.) and being subject to time dependent properties (low rupture stress, high creep values).

Membrane filter.-Good sanitary engineering practice requires disinfection of newly laid waterlines. Before releasing such lines forservice, a bacteriological test is necessary. The old test took up to 4 days while the new membrane filter method of bacterial analysis has reduced this period to 18 hours.

Leakage and breakage.-The new kinds of pipe jointing systems and new pipe materials show promise of alleviating the very troublesome maintenance problems caused by leaks and breaks in the distribution system. Experience thus far has shown a number of these jointing systems to be flexible, leakproof, and resistant to corrosion. New pipe materials are also being designed to reduce breakage and corrosion, and of these ductile iron is reported to show considerable promise.

Corrosion control.-Polyphosphates continue to be effective in controlling corrosion of cast iron pipe. Recently, a zinc polyphosphate has been made available and found very effective in preventing excessive corrosion of freshly cleaned cast iron pipe. A rapid method (3 to 4 hours) for laying a smooth calcium carbonate coating on the surface of pipe cleaned and mechanically scraped has also been devised. Depending on the water analysis, the chemicals used may be calcium chloride, soda ash, caustic soda, or sodium hexametaphosphate.

Great strides have been made in the control of corrosion caused by electrolysis through the efforts of cooperative area corrosion committees. This type of corrosion has in some areas been largely corrected by mechanical bonding of all underground utility structures. The change from streetcars to buses has hastened this improvement. The use of cathodic protection for steel pipe (exterior), steel water storage tanks, and steel purification facilities has greatly increased. Protection is gained through use of steel, carbon, and magnesium

anodes and rectifiers of various types, and by the use of buried anodes without current.

Paint and protective coatings.-Until recently, poor success had been obtained with paints for interior protection of steel structures such as ground-level water storage tanks, elevated tanks, and basins in purification plants. Experience with numerous steel tanks indicates that when phenolic-type paint systems are used, painting must be repeated every 2 or 3 years. Currently, red-lead phenolic paint systems are being replaced by zinc dust-zinc oxide phenolics, aluminum phenolics, vinyls and epoxies. Vinyl paints appear to be the most promising of the newer coatings, all of which provide improved protection.

For exterior tank painting, good results have sometimes been obtained in the primer coat with easy-to-use conventional paints, such as red lead-linseed oil-alkyd mixtures. For final coats, aluminum paints give excellent results, and colored aluminum is a recent introduction. Vinyl, epoxy, and chlorinated rubber paints can be used for final coats. An 8-year service life may be obtainable from vinyl paint systems.

Communications for central control.-In October 1958, there were more than 2,000 utility radio licenses involving water departments. Among the advantages of radio systems in water utility are improvement in consumer service, speedup in handling emergencies, improvement in employee morale and increased employee productivity. Transistorized equipment is replacing units with tubes which required replacement every 7 to 10 years.

Control centers for remote recording and control of pumping rates, pressures, water levels and other data, are a relatively new development in the waterworks industry being widely accepted. Equipment used for these systems includes: Electric sensing devices called transducers; various telemetering instruments from assembly points for the required electric analog signals; other devices to change analog to tone signals; microwave towers; converters for changing tone signals to microwave; equipment to reconvert microwaves to tone; and electronic deciphering equipment.

Consumer service materials.-Consumer service lines are now constructed principally of copper, although various plastic materials are extensively used also. Little trouble has been experienced with these new materials after some initial failures due to thin pipe and use of plastic adapters. Brass adapters with stainless steel clamps are now used. Type L copper is being substituted for type K, on the theory that failure of copper through corrosion will not be prevented by the slight additional thickness of type K.

REFERENCES

(1) Ingram, W. T. and Moore, G. W.: Fluoridation in Major Cities of The United States, Table 3-Characteristics of Distribution Systems. J. Am. Water Works A., September 1959, p. 1098.

(2) Arnold, G. E.; Clerk, E. J.; Remus, G. J.; Niemyer, H W.: Experience with Main Breaks in Four Large Cities-Panel Discussion. J. Am. Water Works A., August 1960, pp. 1041-1058.

(3) Barracos, A.; Hurst, W. D.; Leggett, R. F.: Effects of Physical Environment on Cast Iron Pipe. J. Am. Water Works A., December 1955, p. 1195.

(4) National Bureau of Standards: Summary of Technical Report-A Study of Causes and Effects of Underground Corrosion. J. Am. Water Works A., December 1958, p. 1581.

(5) Flentje, M. E.: Control of Red Water Due to Pipeline Corrosion. J. Am. Water Works A., December 1961, p. 1461.

(6) Jordan, H. E.: Costs of Corrosion to the Water Industry. J. Am. Water Works A., August 1947, pp. 773-778.

(7) AWWA Committee Report: Design and Installation of Steel Pipe Lines, Chapter 5—Hydraulics of Pipelines. J. Am. Water Works A., June 1961, p. 762. (8) Hawkins, E. D.: Water Problems in Freezing Weather. J. Am. Water Works A., February 1959, p. 264.

(9) U.S. Public Health Service: Municipal Water Facilities Inventory, Public Health Service Pub. 775, No. 4, January 1958, Washington, D.C.

(10) Cast Iron Pipe Research Association: Advertisement in Water and Sewage Works Magazine, February 1962, p. 23A.

(11) Flentje, M. E., and Sweitzer, R. J.: Further Study of Solution Effects on Concrete and Cement in Pipe. J. Am. Water Works A., November 1957, p. 1441. (12) Aldrich, E. H., Editor: A Training Course in Water Distribution. American Water Works Service Co., Philadelphia, Pa.

(13) AWWA Task Group Report: Study of Domestic Water Use. J. Am. Water Works A., November 1958, p. 1408.

(14) Sweitzer, R. J.: Basic Water Works Manual. Chapter IV, p. 6, Lock Joint Pipe Co., East Orange, N.J.

(15) Shillinger, W. D., and Fassnacht, G.: Cross Connections and Controls. J. Am. Water Works A., January 1960, p. 36.

(16) Ongerth, H. J.: Control and Elimination of Cross Connections. Panel Discussion. J. Am. Water Works A., January 1960, p. 46.

(17) Holzer, R. W.: Installation and Maintenance of Gate Valves in St. Paul. J. Am. Water Works A., February 1960, p. 269.

(18) Flentje, M. E.: Control of Red Water Due to Pipeline Corrosion. Water Works A., December 1961, p. 1461.

J. Am.

(19) Sweitzer, R. J.: Basic Water Works Manual. Lock Joint Pipe Co., East Orange, N.J.

(20) Socha, M. K.: Plastic Pipe in Water Supply Use. Panel Discussion. Installation Methods in Los Angeles. J. Am. Water Works A., April 1957, p. 427.

(21) Flentje, M. E.: Plastic Pipe in Water Works Service. Paper delivered before Iowa Section, AWWA, October 1958.

(22) Seymour, R. B.,: Materials of Construction Review-Plastics. trial and Engineering Chem. Magazine, December 1960, p. 1038.

Indus

(23) Flentje, M. E.: Committee Report of Plastic Pipe Research Council published as article "Plastic Pipe for Water Systems." Water Works Engineering Magazine, January 1960, p. 36.

(24) Sweitzer, R. J.: Developments in Plastics and Plastic Pipe. J. Am. Water Works A., October 1960, p. 1251.

(25) Flentje, M. E., Editor: Material for Plastic Pipe Manual. Soc. Plastics Industry.

(26) AWWA Distribution Manual: Pipe System, chapter 5, J. Am. Water Works A., September 1961, p. 1181.

(27) Clow, S. C.: The Properties of Ductile Iron. Paper presented before Pennsylvania Section, AWWA. June 1961 (unpublished).

(28) Monie, W. D.: Metaphosphate Protection After Pipeline Cleaning. Journal Pennsylvania Water Works Operators Association, 33: p. 57 (1961). (29) McCauley, R. E.: Controlled Deposition of Protective Calcite Coatings in Water Mains. J. Am. Water Works A., November 1960, p. 1386.

(30) Cristofferson, D. W.: Coatings in Steel Water Storage Tanks. J. Am. Water Works A., June 1961, p. 725.

(31) Hetzberg, L. W.: Radio Communications for Water Utilities. J. Am. Water Works A., May 1959, p. 598.

(32) Philadelphia's New Electronic Load Center is Now "On Stream." Works Engineering Magazine. November 1960, p. 988.

Water

THE DESIGN AND CONSTRUCTION OF WATER

TREATMENT PLANTS

GENERAL

No matter whether the source of a municipal or industrial water supply is surface water or ground water, it is almost impossible to meet all modern requirements of water quality without some form of treatment. These requirements will vary, depending upon the use of the water, but ideally they would be as follows:

1. The water shall be free from disease-producing organisms. 2. The water shall be sparkling clear and colorless.

3. The water shall be palatable, free from odors, and preferably cool.

4. The water shall be reasonably soft.

5. The water shall be neither scale-forming nor corrosive.

6. The water shall be free from objectionable substances, such as hydrogen sulfide, iron, and manganese.

7. The water shall not contain substances in quantities which are toxic or which have adverse physiological effects.

8. The water shall be available in ample quantities and at a reasonable cost.

THE PROBLEMS INVOLVED

Supply requirements.-One of the first steps to be taken in the design of a water treatment works to meet the above criteria is the estimation of the quantity of water required. This estimate must, of necessity, be an approximation since it applies to some future date. The factors to be taken into account include domestic usage, commercial and industrial usage, public usage and losses, variations in water demand, fire demand, and the amount of storage available or to be provided.

The quality of the water required by the consumers and the quality of the source are the next consideration. These factors determine the type of plant which must be designed and constructed. Generally, the plant must be designed to produce treated water which will at least meet the U.S. Public Health Service drinking water standards, as revised in 1961. Also to be considered are certain industrial uses which have higher quality requirements.

Treatment needs. The problems involved in meeting these criteria have been magnified in recent years. The lack of adequate sewage treatment in some areas and the resulting deterioration of surface waters have made the treatment of these waters much more difficult. These waters now contain chemical compounds which were not present in the past. Some of these chemicals will impart objectionable tastes and odors to the water and some resist removal by conventional treatment processes. For example, synthetic detergents as used in the household cannot be completely removed by the water treatment.

processes normally used. Therefore the treated water may have a tendency to foam when agitated, depending upon the concentration of the detergents.

As the population of this country continues to grow and increase in density, the problems of water treatment will become greater. The available good quality water resources will continue to be depleted, and water reuse will need to be practiced to a greater degree than at present. Many of the techniques needed for the production of satisfactory water are known but their application may be costly. In other cases, such as the problems of synthetic organic chemicals, the techniques for removal must be developed by research in the near future.

TRADITIONAL DESIGN AND CONSTRUCTION PRACTICES

In general, there are eight well-known combinations of processes used for water purification:

(1) Prolonged storage.

(2) Filtration through slow sand filters.

(3) Coagulation and filtration through rapid sand filters.

(4) Water softening.

(5) Iron and manganese removal.

(6) Combined water softening and iron removal, coagulation, and filtration through rapid sand filters.

(7) Disinfection.

(8) Fluoridation.

In addition to these, there are a number of special treatment processes and modifications. Very often it is necessary that a combination of treatments be used in order to obtain the desired results.

Prolonged storage.-Prolonged storage involves storage in basins or reservoirs for an extended period of time, thereby affording an opportunity for subsidence of silt and clay, reduction in color, and the death of bacteria. Considerable time is required for these results to be accomplished by storage alone, and even then bacteria and finely divided particles of clay are not entirely removed. The size of the basins or reservoirs required normally makes this method very expensive. The tendency toward stagnation and the multiplication of low forms of animal and vegetable life often makes this type of treatment undesirable. Even though many days of storage are provided, additional treatment usually is required to insure a satisfactory product. Slow sand filters.-Slow sand filters are beds of sand 30 to 40 inches deep, contained in concrete basins, each about 1 acre in area. sand filters are used extensively abroad, but few have been built in the United States since the development of the rapid sand filter around 1890. The slow sand filter is adapted to water having a turbidity not exceeding about 30 parts per million and of low color. The chief disadvantages of slow sand filters are

(1) The large area required.

Slow

(2) Their successful operations is limited to clear water with low color.

(3) The first cost is relatively high.

Rapid sand filters.-To obtain a high rate of filtration through sand filters, it is usually necessary to treat the water ahead of the filters.