TECHNOLOGY
Tertiary cleanup of waste water under way Chicago's 10-year study of tertiary treatment methods may be major influence on national effort At the headwaters of the Du Page River, a short drive due west of Chicago's O'Hare Field, a municipal sewage treatment plant feeding the river is undergoing a significant change. It is now a relatively small secondary treatment plant, removing most of the biological oxygen demand (BOD) by bacterial digestion of organic materials. Next year, the 2 million gallon-per-day plant will be a large tertiary treatment research facility, eliminating phosphates, organics, and pathogens from secondary plant effluent. The plant is the Hanover plant of the Metropolitan Sanitary District of Greater Chicago. It will play a decisive role in the district's water pollution control plans. As such, it will have a far-reaching effect on the inland waterways of Illinois; and, with the answers it provides the district, its influence will undoubtedly extend beyond the state to other metropolitan areas now wrestling with water pollution control problems. The district is well into a 10-year program to eliminate pollution in inland waterways under its jurisdiction. The program will cost more than $1 billion, part of which, the district hopes, will be supplied by federal and state funds. Inland waterways fit for fish habitation, irrigation, and recreation are the goal. As part of the program, the district plans to convert to tertiary treatment throughout its system. It expects to have conversion under way by 1971. Within one or two years after the Hanover plant begins operating, results should be available for scaling tertiary treatment to the district's plants of 300 million gallons per day and more. The information will come from equipment and processes designed to remove materials such as organics, phosphates, and pathogens from secondary plant effluent. The Hanover plant will use coagulation followed by rapid sand filtration. Development workers there will investigate whether, for example, top or bottom feed is most effective and what would be the most effective method of backwashing. Also to be investigated are methods of phosphate removal. Is it, for example, most effective and economical to remove phosphate 42 C&EN NOV. 27, 1967
chemically? Or is it better to do it biologically in a pond, letting algae use up the phosphates and then removing the algae? Experimental bays at the Hanover plant will include setups for studying a variety of other techniques—activated carbon adsorption, microstraining, electrodialysis, and ultrafiltration (or reverse osmosis) are examples. Even a development farm will be included at Hanover, where the sanitary district, along with the University of Illinois, will evaluate the use of activated sludge for crop fertilization. Since the plant will include sand filters and other filtration and membrane devices, good secondary treatment of feed water is important, Dr. Jerome E. Stein, director of research and control for the district, explains. Consequently, secondary treatment will be optimized, he says, and automatic control will be stressed. In the drive to halt water pollution throughout the U.S., more and more attention is being given to municipal sewage treatment facilities. Most use primary treatment methods where the bulk of organic and inorganic insoluble solids are allowed to settle out. But this usually removes only 30 to 40% of the oxygen-demanding materials. Many facilities also include secondary treatment. This makes use of biological processes—most commonly activated sludge or trickling filters—whereby suspended and dissolved organic materials are digested by bacteria in the waste water. With the large volumes of water being discharged from municipal plants, even this isn't enough in many cases to eliminate the severe polluting effects of the discharge. But few municipal plants at present carry treatment any further. In studying tertiary treatment methods on its own particular waste and in its own system, the Chicago sanitary district has a good foundation to build on. Many agencies and companies have carried out research and tests on numerous methods. The two-year-old Federal Water Pollution Control Administration, for example, has, since its formation, put more than $9 million into grants for work on advanced waste treatment
MICROSTRAINER.
Still under wraps,
this unit will be an integral part of Hanover tertiary treatment plant methods alone. Prior to the formation of FWPCA, the Public Health Service had carried on an extensive research program (now a part of FWPCA's). The advanced treatment processes or combinations that may eventually prove to be the best, both economically and for water quality, have yet to emerge in any clear-cut way. The problem of water pollution, the variety of pollutants in waste water, and the intended uses of receiving bodies make the situation complex enough that probably no one method or combination will prove best for all areas. But with research results accumulating, several methods are gaining in popularity. Chemical coagulation and filtration, for example, is finding wider use for removing suspended solids following secondary treatment. The technique is hardly new in itself, being a conventional method for treating municipal supply water. But its application to waste water is quite recent. One
such use will take place next year when the Los Angeles County Sani tation District builds a 50,000 gallonper-day plant for treating oxidation pond water. Alum will b e used for coagulation, and this will be followed by dual-media filtration using anthra cite and sand. Much newer in concept is polyelectrolyte flocculation, particularly to re move dissolved phosphates. Phos phates stimulate growth of aquatic plants in receiving waters. T h e plants, especially algae, deplete the oxygen in the water. This is one of the processes involved in the eutrofication of lakes. P o l y electrolytes—high-molecularweight anionic, cationic, or nonionic polymers—form bridges between par ticles or charged floes through ad sorption or hydrogen bonding. Thus, they can be effective in small amounts, and this has enhanced the economics of their use. One example of polyelectrolyte ap plication came this past summer when Dow Chemical conducted tests on phosphate removal in municipal plants at Grayling and Lake Odessa, Mich. (C&EN, Sept. 4, page 3 5 ) . The Grayling plant employs only primary treatment; the Lake Odessa plant has secondary treatment with a trickling filter. Detailed conclusions await a report due shortly from the state health department, but Dow says the field tests confirm its earlier labora tory findings. These show that 70 to 90% of total phosphate can be re moved by the polyelectrolyte method, depending on type of waste. The Dow method involves adding metal ions—as ferrous chloride, for example—to the raw sewage entering a treatment plant. The ions convert soluble phosphates to the insoluble state. Polyelectrolytes are : then added to flocculate the insoluble phos phate particles, which settle out of the water along with other suspended solids. Another tertiary treatment tech nique gaining wider popularity is ad sorption of organics by activated car bon. The technique is being used, for example, on the effluent from an activated sludge operation at Lake Tahoe, Calif. In Pomona, the Los Angeles County Sanitation District has been successfully operating a large activated carbon pilot plant for a couple of years. It is part of a broad spectrum of work that has been carried out jointly by the sanita tion district and FWPCA and which at times has included chemical coagula tion, diatomaceous earth filtration, ion exchange, reverse osmosis, and electrodialysis, among others. A technique introduced by Calgon Corp. earlier this year makes use of
EASTMAN Organic Chemicals 0) -C
Ο υ Έ
-Η
Maybe Eastman can make life easier for you
> Ζ Ο -Η
>
ο
Ζ
Ζ
ο
