Communities served.-There are over 9,900 separate systems treating water for towns and cities in the United States in addition to the 7,900 which do not treat their supply. Even though there is a wide range in skills required, each plant must have at least one competent person in charge. Water treatment requires scientific supervision and one of the problems facing the waterworks industry in this area. is the recruitment and training of qualified personnel. Since public water supply is usually a local undertaking adds to this problem because the number of qualified personnel needed is much larger than if centralized water supply systems served many communities.

New chemical contaminants.-Many references have been made to the growing complexity of the water treatment problem. Hundreds of new chemical substances are being marketed annually, among them being detergents, pesticides, and industrial chemicals of a wide variety. After use, may of these compounds find their way into watercourses where it is hoped no toxic effect results to either humans, aquatic life, or animals. Since conventional water treatment processes do not remove many of these chemicals or only partially, there is reason for concern. This concern is rising as the concentration of these new chemicals at water supply intakes is increasing each year.

The newly adopted (April 5, 1962) Public Health Service drinking water standards prescribe limits for the concentration of some types of synthetic chemicals but it was not deemed feasible at the time of adoption to include limits for the many chemicals with a toxic potential that may get into water supplies. Specific limits were not set for the more common chlorinated hydrocarbons and organophosphate insecticides but it was recognized that pollution of water suppies with such contaminants can become significant. Simple and practical analytical methods to identify and measure these latter organic materials in water are not yet available, although several can be measured with difficulty at concentrations as low as a fraction of a part per billion. Synthetic detergent problem.-Under drought conditions, detergents have been found in streams used for public water supply in concentrations sufficiently high to cause foaming, taste and odor, and to cause difficulty with coagulation. These compounds have also been found frequently in ground water supplies. Activated carbon in high dosages will remove detergents but this process is not presently being used in public water supply practice. Removal of detergents by an ionexchange resin has been demonstrated in the laboratory but it has not yet been shown to be practical for use in a municipal water treatment plant. ABS, the most common detergent chemical, has not been concentrated enough in most streams used for water supply to cause difficulty with coagulation but the phosphate builders used in household detergents have caused such interference.

Radioactive materials. The presence of radioactivity in higher than background concentrations in both ground and surface waters has become a matter of concern to the waterworks industry. Radioactive fallout, the growing use of radioactive isotopes, and the use of radioactive materials for power production present opportunities for contamination of water supply sources. Instruments and methods of analysis for radioactivity are available but not widely used, and a number of problems connected with radioactivity remain to be solved. Tastes and odors.-Activated carbon is most generally used for controlling tastes and odors. Chlorine dioxide, potassium perman

ganate and breakpoint chlorination are also used. In most situations, these treatment methods have been effective in removing the tastes and odors usually encountered. However, in an increasing number of instances, threshold odors and new chemical contaminant problems are being reported where such treatment has not been effective, or is expensive.

As the streams and rivers become more highly regulated, problems of tastes and odors are expected to increase. This will require the development of much more effective control measures and removal processes than are presently available.

Coagulation problems.-Coagulation of colloidal turbidity with alum or an iron coagulant is an empirical process and difficulties are often encountered in water treatment. Fundamental studies are needed to develop a science of coagulation in water treatment; also in the development of new coagulant chemicals and processes.

Chemical handling, storage, and feeding. Many of the advances in the industrial handling of materials have not found their way into the waterworks industry. Newer plants take advantage of bulk delivery by either truck or railroad but in many older plants chemicals are handled bag by bag, without pallets, lift-trucks, etc. Alum in liquid form has become increasingly common and used in this form greatly simplifies unloading, storage, and accuracy of feed. Troubles have been experienced with crystallization of the alum at lower temperatures and when it contains potassium aluminum sulfate. Dust difficulties are common with powdered activated carbon and hydrated lime. Hydrated lime slurries are difficult to handle because of their tendency to plug lines.

Pipelines, meters, valves at treatment plant.-Plastic pipe is now commonly used for conveying solutions of water treatment chemicals and difficulties with breaking of the lines, leaky joints and bending are common. Meters and metering pumps for control of treatment chemical solutions are available, but lack flexibility and a wide enough range to meet the load requirements of a treatment plant. Valves used in treatment plants are subject to corrosion and graphitic deterioration.

Source protection

TRADITIONAL PRACTICES

The time-tried procedures of using the least polluted sources available and protecting the source from further pollution remains an accepted sanitary engineering procedure in the waterworks field. Source protection varies from the elaborate watershed policing arrangements of cities like Boston, New York, and Seattle to cleanup programs of severely polluted streams like the Ohio, Delaware, and Potomac. The clean streams program of Pennsylvania is an example of the benefits of pollution control which accrue to water supply.

Treatment practices

The water treatment plant operator has found it necessary, because of increasing pollution, to improve the efficacy of the water treatment procedures with which he has to work. These differ little from those in use 50 years ago except for slight modifications.

1. Coagulation and sedimentation.-Coagulation is accomplished mostly by the use of alum compounds although a significant amount of other chemical coagulants are used, such as iron salts and lime. By

improvements in flocculation equipment and settling efficiency, plant operators are able to produce water with turbidity of 5 or less before filtration, whereas in former years, they were limited to reductions to 20 to 35. Improved coagulation and better sedimentation, together with effective prechlorination, have eliminated in many plants the need for periodical filter cleanings often carried out annually at some plants. Coagulation difficulties remain a problem but with the introduction of activated silica and the new coagulant aid, these difficulties can be made less troublesome.

2. Filtration. The rapid sand filter is called upon to do only a very small percentage of the total removal work of a water purification plant. Where some years ago, the filters removed 90 percent of the bacteria and 20 to 30 units of turbidity, in present day practice prechlorination decreases the filter load (bacteriological) to almost zero, and the turbidity removal is 25 to 30 percent of that formerly required of these units. Filtration rates remain at the original 2 gallons per minute per square foot loading although many new plants are designed hydraulically to exceed this rate by 50 percent. Rapid sand filters, almost identical with those originally installed, now produce water with turbidity of less than one and length of filter runs between washings has been extended to 50 to 100 or more hours. Previously a 24-hour filter run was often a goal to be strived for.

Filter washing has seen little change except for increased rise rates and an awareness that 50-percent sand expansion is necessary for proper cleaning. Surface filter wash systems are common. Wash control is passing from manually controlled hydraulic valves to pushbutton initiated, timed-sequence automatic washing. Filter wash water and sedimentation basin sludges cannot now, in some States, be returned freely to the rivers from which they come.

3. Disinfection.-Chlorine is still the principal chemical used for disinfection; however, many plants now rely on prechlorination as well as postchlorination. This introduces a definite, additional factor of safety for assuring adequate disinfection.

Laboratory control procedures have shown little change in the past 25 years, but there has been some equipment change. Electrometric pH determinations are now the rule rather than colorimetric procedures, and colorimeters, and photometers are rapidly replacing visual colorimetric and turbidity determinations. The membrane filter technique of bacteriological analysis is rather slowly becoming standard practice.

NEW MATERIALS, EQUIPMENT, AND DESIGNS AND NEW APPLICATIONS OF OLDER MATERIALS AND EQUIPMENT

While traditional practices in water treatment have not changed. greatly, many procedure modifications and improvements have been made in recent years.

Clarification

1. New chemical coagulants and aids. Some compounds of a class of chemical materials called polyelectrolytes have been found to be effective coagulants aids. Spectacular results have in some cases achieved through the use of extremely low concentrations of these materials. These compounds are synthetic polymers of high molecular

weight, analogous in general properties to naturally occurring polymers carrying electric charges or ionizable sites. These naturally occurring polymers are called biocolloids, among which are starch and starch derivatives, cellulose compounds, and polysaccharide gums. Three general classes of polyelectrolytes are available: (a) Negatively charged compounds, called anionic polyelectrolytes; (b) positively charged compounds, called cationic, and (c) compounds having both charges, called polyampholytes. Approximately 29 manufacturers' products have been approved for use as coagulants aids (with restrictions) for public water supply treatment.

2. Coagulant control with zeta potential. Chemists and operators have long searched for a control test or signal that would indicate proper coagulation of a water being treated for clarification and filtration. Zeta potential is one of the potential values associated with colloids in suspension in a solution. It is reported that the magnitude of the zeta potential can be rapidly and accurately determined. Since rapid coagulation of a colloid takes place shortly before the zeta potential has been completely neutralized, it is hoped these values can be used for determining when coagulation dosages are correct. However, considerable work remains to be done before a reliable procedure can be developed and incorporated in waterworks practice.

3. Chemical coagulants. While liquid alum has been available for a number of years, and has been used quite extensively by the paper industry, little or no alum in this form was used in the waterworks industry before approximately 1955. Since that time numerous small alum manufacturing plants have been installed at various convenient locations throughout the country. Stored in lead-lined or rubberlined tanks (steel, concrete, wood), the use of the liquid material has resulted in lower costs, elimination of dust, savings in unloading costs and better dosage regulation. A new form of dry alum designed to eliminate dust and feed more easily is said to have been recently placed upon the market. Also, alum from coal-mining wastes will soon be available.

4. Increased filter rates.—There is a gradual tendency toward somewhat higher filtration rates in conventional rapid sand filters. The Torresdale plant of the Philadelphia City Water Department operates under peak demand conditions at 3 gallons per minute per square foot as do all filters designed for the American Water Works Co. system in the past decade.

5. Automatic filters.-Many new filter installations are of the semiautomatic, pushbutton type in which the operator initiates the wash. cycle but from there on, the filter washing operation is automatic. Automation has also been extended to iron removal plants in some locations, and to resin exchange softening plants where hardness of the raw water is reasonably constant.

Removal of objectionable chemical substances

1. Softening. Lime-soda softening plants have shown little change in a number of years. However, there has been an advance in the knowledge of softening to gain greater efficiency and a trend in large softening plants to recalcining for recovery of lime.

2. New ion-exchange resins. The introduction of high capacity, styrene base resins has made possible smaller base-exchange softening plants, because of the much greater exchange capacity of these resins

(16 to 45 kilograms per cubic feet) and the higher throughput rates possible without deterioration of the effluent water. Many such softening systems operate at 10 gallons per minute per square feet and even higher rates are possible with some loss of capacity.

3. Iron and manganese removal.-The new coagulation-filtration process developed at Hanford shows promise of rates up to twice the normal for iron removal plants. Manganese removal with potassium permanganate is efficient and practical. In a moderately low hardness well water, high in manganese (up to 9 parts per million) an ionexchange plant for manganese removal proved more economical in first cost and in operation than a conventional type plant, because of ease of automation and control. Potassium permanganate has also been used recently in less than normal dosages in zeolite beds, a new development in iron and manganese removal processes.

REFERENCES

(A) Wertz, C. F.: Water Supply-A Continuing Challenge. Journal AWWA, January 1961, p. 1. (1) Jenkins, K. H.: 1958 Inventory of Water Supply Facilities in U.S. Communities with Populations of 25,000 or More. Journal AWWA, January 1961, p. 31.

(2) USPHS Publication Proceedings The National Conference on Water Pollution. December 12-14, 1960 (G. Klassen, p. 136).

(3) Cohen, J. M.; Kamphake, L. J.; Lemke, A. E.; Henderson, C; Woodward R. L.: Effect of Fish Poisons on Water Supplies, Part 1. Journal AWWA, December 1960, p. 1551.

(4) Idem, Part 2: Odor Problems.

Cohen, J. M.; Rourke, G. A.; Woodward,

R. L. Journal AWWA, January 1961, p. 49.

(5) Idem, Part 3: Field Study at Dickinson. Cohen, J. M.; Pickering, Q. H.; Woodward, R. L.; Van Heuvelen, W. J. Journal AWWA, February 1961, p. 233. (6) USPHS Drinking Water Standards: Anonymous. Journal AWWA, August 1961, p. 935.

(7) Hindin, E.; Hatten, M. J.; May, S. M., Jr.; Skrinde, R. T.; Dunstan, G. H.: Analysis of Synthetic Organic Pesticides in Water. Journal AWWA, January 1962, p. 88.

(8) Vaughn, J. C.: Detergents and Other Contaminants in Water Supplies. Journal AWWA, August 1961, p. 994.

(9) Higgins, F. B., Jr., Grune, W. N.; Smith, B. M.; Terrill, J. G., Jr.: Methods for Determining Radon 222 and Radium 226. Journal AWWA, January 1961, p. 63.

(10) Lyon, W. A.: Nature and Control of Radioactive Wastes in Pennsylvania Waters. Journal AWWA, January 1961, p. 89.

(11) Anonymous: America's Largest "Push-Button" Water Treatment Plant Dedicated. Water Works Engineering, November 1959, p. 988.

(12) Records American Water Works Service Co., Inc., Philadelphia, Pa. (13) Flentje, M. E.: Auxiliary Uses of Disinfection and Oxidizing Agents in Water Treatment, Proceedings 3rd Sanitary Engineering Conference, JanuaryFebruary 1961, p. 57.

(14) Eld, E. F.; Flentje, M. E.: Quality Improvements Resulting From Industrial Needs at Hopewell. Journal AWWA, March 1961, p. 283.

(15) Ryckman, W. W.; Burbank, N. C.; Edgerly, E.: Methods of Characterizing Missouri River Organic Materials of Taste and Odor Interest. Journal AWWA, November 1961, p. 1392.

(16) Symposium-Progress in Water Supply Research. Journal AWWA, September 1960, p. 1085. Idem: Faber, H. A.; p. 1102.

(17) Kalinske, A. A.: Advances in Water Supply Technology. Journal AWWA, February 1960, p. 199.

† (18) Black. A. P.: Basic Mechanisms of Coagulation. Journal AWWA, April 1960, p. 492.

(19) Black, A. P.; Hannah, S. A.: Electrophoretic Studies of Coagulation of Turbidity Removal Coagulation with Aluminum Sulfate. Journal AWWA, April 1961, p. 438.