Januarw I952
Industrial Wastes Copper and chromium wastes except in small amounts are deleterious to biological sewage disposal methods
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memories were aroused when reading a recent story about theeffect of metal wastes on the design of a sewage treatment plant at Waterbuy, Conn. (4). In 1914,I was research chemist for a rubber reclaiming plant in Naugatuck, Corn. I n this industry old rubber shoes and boots, industrial belting, inner tubes, and bicycle, truck, and automobile tires were processed to reclaimed rubber. I n order to destroy the cotton fabric present in these wastes and t o desulfurize the rubber, the waste was ground and then digested with strong caustic soda solutions a t elevated temperatures and pressures. Following this softening process, the rubber waste was washed with copious amounts of river water. The spent cooking liquor and wash water were discharged into the Naugatuck River without treatment. Even in those early days, this stream was badly polluted with raw sewage as well as acid and metal wastes originating from the numerous brass and copper plants upstream. The rubber reclaiming plant was always pleased t o have these acid wastes in the stream for they effectively neutralized the alkaliie wastes from rubber digestions so that little evidence remained in the water from wastes created by the reclaiming plant. ADING
Current etatwa of Naugatuck R8ver But the most vivid recollection came from the statement of these recent authors that the Naugatuck River contains copper, chromium, and other metal wastes to such a degree that biological growth has been inhibited and the usual biological methods for treating raw sewage are useless. Thirty-seven years ago, t h e writer found these metal residues in the Naugatuck River to be troublesome in processing rubber. This particular investigation was originated because management learned that reclaims made at Naugatuck did not have as good stability from air oxidation as did similar reclaims made at their Indiana plant. Elimination of many factors focused attention on the quality of the raw river water. The management was advised that the Naugatuck River water contained from 10 t o 25 p.p.m. copper, and laboratory studies proved conclusively that this impurity was the source of our accelerated oxidation of rmlaimed rubber. Coppek was known to accelerate the oxidation (aging) of rubber, but manJanuary 1952
agement considered the findings to be impractical. I was chided for expecting 15 p.p.m. of copper in raw water t o be injurious. The project terminated. Stute a e d t h Department report The eventual necessity of treating raw sewage a t Waterbury was recognized when the city sewers were designed in 1905. At that time a disposal site was selected and foundations built, but for various reasons the plant was not completed. I n 1918 the Industrial Wastes Board of the Connecticut State Health Department studied such diversified methods of solving the industrial and domestic waste problem as: (1) Construction of separate treatment plants at each community. (2) Storage of water t o increase dilution of waste during low rainfall periods. (3) Construction of a Naugatuck Valley trunk sewer to discharge raw or treated sewage into Long Island Sound. (4) Pumping raw or treated sewage over the divide into another watershed. Their comprehensive report concludes that :
1. It will never be practicable t o restore the Naugatuck River t o a state even approaching its original condition as a potable stream. It must always be the main drain for a populous industrial valley and, therefore, considerably polluted. However, many of the objectionable features which now exist cari be remedied by proper treatment of the wastes at their sources. 2. Considerable latitude may be exercised in selecting the type and degree of treatment best adapted to different localities but some method of treatment should be adopted for each of the lar er towns. 3. Industrial wastes shoufid be separated into different classes and a type of treatment determined which is best suited t o each class. 4. For the reason that it is impracticable t o attempt t o restore the Naugatuck River to its original condition, i t does not seem wise t o insist on high purification of certain effluents.
Problems at Waterbury One third of the brass and copper products produced in the United States are made in the Naugatuck Valley. Waterbury is the oldest and largest city engaged in this activity. In addition t o three large brass and copper mills, there are over 100 smaller plants that use chemicals in cleaning, pickling, plating, and finishing nonferrous metal goods. I n 1949, these industries of Waterbury consumed Xi%
ducers and some smaller ones now exclude their industrial waste from the city sewer system. Their waste enters adjacent small streams which eventually reach Naugatuck River. Most of the smaller metals plants, however, are situated in densely populated sections of Waterbury where no access t o natural watercourses are available and limited space is afforded for installation of treatment facilities. The city sewers are considered essential for these plants for disposition of their waste waters. Industrial wastes of Waterbury are, therefore, either purged directly t o the Naugatuck River and its tributaries or added to the city sewage system. I€the river is t o keep its category of a government-recognized pollution basin, then no treatment, by those concerns discharging t o the river waters may be expected. However, such a policy deprives the river basin the privilege of industrial expansion and soon this antiquated policy will have t o be abandoned for an equitable waste treatment plan in order t o create a healthy stream for others than industry to enjoy. In ,1943, /Waterbury engaged an engineering firm t o study the sewage treatment facilities of the city (4). They reported the presence of a considerable amount of copper in the sewage and recommended the construction of an ample capacity primary sewage treatment on the Naugatuck River below the city. Digestion of sludge wm recommended, based on a program of excluding industrial wastes from the sewers. The Waterbury Board of Aldermen passed anordinancewhich gave the city the power t o exclude from the sewers any waste deemed undesirable for the sewage system or treatment. This procedure placed the smaller plants in a difficult position, particularly those not able to discharge their waste into t h e watercourse directly. I n 1949,the State Water Commission ordered the city t o call for bids on the sewage plant designed b y the engineering h. The plant which is expected t o be complete early in 1952 will use a nonbiological treatment method for handling the sewage (Continued on page 106 A sludge.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Industrial Wastes Effect o f mtaZ wmtes on 8ew-e treatments The literature contains adequate data t o show that the sewage from these cities cannot be processed normally. Mohlman ( 5 ) discussed the presence of copper in sewage at New Haven, Conn., in 1917. Few data on the actual effect of metal wastes on sewage treatment were published, however, prior to 1940. In the Eighth Biennial Report of the Connecticut State Water Commission (193840), Hoover ( 2 ) reports that 0.5 p.p.m. of copper in sewage produced a sludge containing over 100 p.p.m., and when the amount of copper in sewage exceeds 1 p.p.m., a decrease in the efficiency of digestion is noticeable. He also found that when 200 p.p.m. of precipitated chromium is present in the sludge, the digestion rate is lowered and when the concentration of chromium in the sewage exceeds 1 p.p.m., its effect i:: similar to that of copper. Rudgal ( 7 ) reported in 1941 a concentration of 3000 p.p.m. of copper in the digestion tanks a t Kenosha, Wis., with daily additions of raw sludge, containing 50 to 100 p.p.m. of copper. He confirmed experimentally that digestion would stop a t 200 p.p.m. copper. Later (8) he added that 0.7 p.p.m. of copper in the raw sewage concentrated to 226 p.p.m. in the raw sludge on the wet basis and 3710 p.p.m. on the dry basis. I n the digesters the copper concentration reached 50,000 p.p.m. on a dry, solid basis and no gas was produced. These Kenosha difficulties originated from a large copper and brass plant similar to, those in Waterbury. The trouble was overcome by eliminating this waste from the seqage by the use of a long pipeline disposal into Lake Michigan. Riehl (6) experienced similar conditions in Ohio where a raw sewage contained 8.8 p.p.m. of copper and 56 p.p.m. of zinc, and produced a raw sludge containing 691 p.p.m. of copper and 1934 p.p.m. of zinc which concentrated in the digester to 978 p.p.m. of copper and 8508 p.p.m. of zinc in the sludge. Digestion stopped completely. Coburn ( 1 ) considers that the allowable limit of copper is 1 p.p.m. for primary treatment with sludge digestion or for secondary treatment. For primary treatment without sludge digestion, he sets a limit of 3 p.p.m. Both Coburn and Laboon ( 3 ) set the upper limit of chromium for primary treatment a t 5 p.p.m. With this historical data before them, the engineering consultants had only to study the Waterbury sewage to determine that sufficient copper or chromium was present in order t o eliminate the digestion method of treatment. An &hour composite sample taken on the main sewage line within the city contained (Contantied OR page 1 0 8 A )
42 p.p.m. of copper and 30 p.p.m. of
chromium. Grab samples showed even higher values. Taking all the intensive sampling periods into consideration, they estimate that the copper averaged about 2.6 p.p.m. during a week’s sampling. Because these values were well above the allowable limits and it had proved impracticable to expect the smaller plants to separate or treat their wastes to any great extent, they abandoned biological methods for treating the sludge from the city sewers. Our sympathy resides with the heavily burdened Naugatuck River which has never been in good health for over 50 years and now is condemned permanently to become a sewer line for the entire Naugatuck Valley. The cities will process their sewage by nonbiological methods, but industry will continue to pollute the stream without treatment. Surely, there must be a more practical, corrective answer.
Literature cited ( 1 ) Coburn, S . E., Sewage Works J., 21,522
(May 1949). State Water Commission. Hartord, Conn., Eighth Biennial Report (1938-1940). (3) Laboon, J . F., Sewage W o r k s J . , 21, 197 (March 1949). (4) Mitchell, R. D., Cassanos, J. G., and
. , Connecticut
(2)
Okun, D. A., Sewage and Ind. Wastes, 23, 1001 (August 1951). ( 5 ) Mohlman, F. W., IND.ENG.CHEM.,9,
1093 (1917). (6) Riehl, M. L., Sewage Works J., 20, 629 (July 1948). (7) Rudgal, H. T., Ibid., 13, 1248 (November 1941). (8) Zbid., i8, 1130 (November 1946). Correspondence concerning this column will be forwarded promptly if addressed t o the author, c/o Editor, I N D U ~ T R IAND A L ENGINEEBING CHEMISTRY, 1155-16th St., N.W., Washington 6. D. C:
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