lndustrl~llWastes Aeration of river waters to maintain an oxygen level to support natural digestion of pollution materials is considered feasible in some localities bg Harold R. M#irdods
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Hivm is a referee. It is the high court that decides whether a waste is tolerable for natural digestion in the waters of the stream. A river is also man’s partner. It serves as a final process plant to digest sewage and industrial ivastes wlien purged into the stream, If such wastes are exressive, the river gives silent evidence of the incompatibility by becoming foul and discolored, so that it is useless to those who have mistreated it. I n many ways a river has a person:ility, for like you and I, it is able to digest a reasonable :&mountof food well. But when the food is in excess, neither the river nor man can avoid nausea. In the November 1945 issue of INDUSTRIAL AND ENGIxmnma CHEMISTRY, this author described in the column on “M’aste Utilization,” the remarkable ability of the tidal flats in the Potomac river to digest naturally the raw sewage from the District of Columbia and Alexandria, Va. The badly polluted waters upstream entered these expansive tidal flats on the rising tide and then 12 hours later as the tide phhetl, these waters re-entered the channel substantially deaiisetl of their pollution. Optimum conditions for natural ositltioii occwrred. Green aquatic plants and multitudes of inicrowopic organisms flourished abundantly in these tidal flttts. On sunny days the dissolved oxygen averaged 103% in the w t e r and on cloudy days 75%. The Potomac river \vas a good partner to the municipalities along the river banks. Tliat \vas tibout 1910. Now, it is reported, these flats have lost their natural ability to digest wastes because they have heen overburdened with sewage, and because of that the l’:iunu is dead. 111 this column for August 1950, the author referred to studies of trheUnited States Forest Service which showed how to niiniinize nutural pollution in a river, due to soil and orgallic forest debris. by :illo~vingthe vegetative ground cover to rcni:iiii iinstwred. If iuarewed industrial and iiiunicipal water sup ly is the paramount need, then a controlled cutting of the &est with minimum disturbance of the litter and humus will give maxinium retention of rainfall and II regulated flow of water into thestrenm. \\’:tLci*scoining from such \vutersheds would be sparkling with itbuildant dissolved osygen which would persist because the stream carried a minimum amount of natural pollution loitd. Such waters, when coupled with oxygenation basins, as lemonstrated by the Potomac tidal flats, would constitute the perfect medium for any municipality or industry to utilize for natural processing of its waste. Years ago many situations such as this existed all over America. Today these situations are practically nonexistent because man fed his waste into the streams in excess and consequently lost his partner. Today there are a few feeble but tangible efforts to win back the cooperation of the river. All municipal and industrial treatment plans can be designed to use the river as a partner. Governmental authorities could require such a situation. I n this column, we wish to emphasize another approach, which is in the direction of coopei.:ition with the waters of R stream. (
Recognizing that a rive1 is pait of :i waste disposal plant, Richard G . Tyler, University of Washington, suggested in 1942 ( I ) , that rather than attempting removal or reduction of the osygen demand of a waste before it is purged into a stream, it might he better, in some cases, to add the raw waste to the stream and permit the natural biochemical process to take place within the receiving waters. Then at the point downstream where dissolved osygen became insufficient to bubble air into the river water for osygen refurnishment. This “accelerated reaeration,” according t,o Tyler’s calculationsbased on the assumption that a city of 10,000people produres 1,000,000gallons per day of raw sewage with a B.O.D. of 250 p.p.m.--a ould need 0.5 cuhic foot of air per gallon of sewage to take care of the osygen demand. Comparing this value with 1.0 to 2.0 cubic feet of air per gallon of raw sewage ais used in standard activated sludge plants, Tyler reasoned that the air consumption for accelerated river reaeration would. in his plan, be less in amount than that used for the actiwtion process. But, as he suggests, there is more to the probleni than pumping air. Because waste sulfite liquor from the wood pulp mills on the Pacific Coast has been probably the most difficult problem for disposal of any industrial w d e s and because treating methods have failed owing to the treinendous R.O.D., acid content, and volume of this waste, Tyler suggested that sulfite liquor might be :I good material to bring to the river for processing, by his plan. Tyler’s proposal aroused favorable consideration by The Sulphite Pulp Manufnct.urers Comniittee in TYisconsin, who also interested the Flambeau Paper Company, Park Falls, Wis., in the scheme. A joint research study wns made at the Institut’e of Paper Chemistry, Appleton, 1T-k. ; this was followed by a full scale esperinientd installation on the F1:rnibeau river downstream from where the paper company dumps the waste sulfite liquor from its GSton-per-dny pulp mill. haeration studies were st:trted in September 1943 and were continued each year during the sunmer months. The National Council of Stream Iniprovenient purchased rights and interest8 in the process in 1945 and supervised the Flsnibeau studies. Aeration facilities are located at the Pisley hydroelectric dam, some 6.2 miles downstream from the pulp mill. Critical conditions of low dissolyed osygen content were found to start a t this point. The original installation of aeration equipment was placed in the tailrace of the pomerhouse. Seventy-five Carborundum diffusion plates, 1-foot square, with a permeability of about 29, were fitted into :I steel frame so that there was a bed of porous plates 15 x 5 feet in area, across the floor of each of the two main tailraces. Remodeling of this design was necessary as experience justified. In August 1945 a different type of equipment w.w installed in the headrace. These were tube-type diffiisers mounted in four sections of 16 tubes each on stationary holtlers, just in front of the racks (Confinned oti page 74 .4)
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Industrial Wastes above the two mairl turbines Both the headrrtce and tailrace aerators were placed 12 feet below the surface of the water. For further details of the equipment and tests refelence should be made to the published report (2). The folloning conclusions sufficeour purpose: Reaeration of the Flambeau river. which had 1945 summer low flows of 720 to 1100 cubic feet per second and a B.O.D. loading from sulfite waste liquor in excess of 40,000 pounds per day, showed definite improvement in the condition of the stream. With efficiency of the reaeration equipment in excess of 5% in terms of the ratio uf oxygen absorbed to oxygen delivered, the present installation was shown capable of aiding stream recovery to the point of normal &day B.O.D. leve h a t Babcock’s landing and to maintain the dissolved oxygen at 3 pap.m. or more at that location some 18 miles from the point of discharge of sulfite waste liquor. A biological SUP vey tended to show that normal aerobic biota of the stream were recovering from the effects of pollution at Crowley dam 11.5 miles from the point of pollution. The equipment at Flambeau has operated every season since 1943 but without extensive modification. It has been difficult to show outstanding advantages according to private information. This author congratulates those who have been engaged in this cooperate study. It is a step forward. However, these experiments have not fulfilled the requirements which this author believes essential and has outlined in the first part of this column. By operating the reaeration unit only in the summer the aquatic plants, fish, and microbiological components of the river have a difficult, if not impossible, time to exist. Consequently the experiments during the summer are without the full assistance of the nstural habitat in a stream. The Flambeau report indicates that this assistance is desirable and that a minimum of 2.0 p.p.m. dissolved oxygen is absolutely essential, if not inadequate, to allow growth and sustain life. No suggestion is made to partially treat the waste before purging to the stream in order to keep the dissolved oxygen in the stream at all times at the minimum value, unless this thought is implied in the follawingsummary:
It is plainly evident that the practical evaluation of river reaeration as a method of treatment of fermentable organic wastes is dependent on: 1. Local conditions determining the degree of waste treatment required. 2. A thorough preliminary survey supervised by competent engineers to determine local conditions of stream flow. B.O.D. loading, degree of natural reaeration, oxygen saturation values, nutrients as nitrogen and phosphorus necessary in maintaining biological life, and the chemical composition of the waste to be treated. 3. Adequate design based on the above data. 4. Adequate determination of performances and development of standards as a requisite to routine operations. New methods for treating water with oxygen or air by simple cheap operations are on the horizon. With such equipment the disposal of man-made wastes into the river will probably require, first, primary settling to remove suspended solids, then oxygenation of the waste to dispose of quick B.O.D. demand, and then further reaeration a t the waste sources adequate to permit adding the modified waste to the stream so that the waters are never below the minimum to support aquatic life because of controlled rmeration.
Literatare cited (1) Tyler, Riohsrd G., Sewage Works J., 14, No.4,834 (1942).
L.,Gehm, H. W., Wiwiewski, F., and Bartsch, A. F., Paper Trade J . . 124, No.12, 123 (1947).
(2) Wiley, Averill J., Parkinson,
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