LETTERS More on Lake Erie
DEARSIR: Your feature article in the March (page 212) issue on Lake Erie pollution, reviews this problem but fails to bring forth certain facts which I believe focus on the real situation in this lake. The facts to which I refer are the following: 1. The oxygen depletion within the hypolimnion of the central basin was found, in 1964, to cover an area of 2600 square miles. The oxygen concentration in the bottom 6 to 10 feet of water was seldom above 2 mg./liter. When we convert these dimensions into oxygen deficit, at least 2.7 X lo* pounds of oxygen deficit existed at that time. 2. By using the population of the Lake Erie watershed and by applying certain factors based upon existing treatment facilities, we calculate the annual oxygen demand of the wastes draining into the watershed to be 1.8 X 108 pounds. 3. Since the annual input of oxygen demanding wastes to the drainage basin is less than the oxygen deficit found in the central basin of Lake Erie, a deficit which developed in a period of a few weeks, obviously a source of oxygen demand exists that is much larger than the total oxygen demanding discharges from the population of the basin. 4. The only other source that could create such a large deficit would be “natural” and would be based on nutrient effects. For Lake Erie, as well as the other Great Lakes, phosphate is the critical nutrient controlling the productivity of these waters. 5. A daily net fallout of phosphate into Lake Erie is 150,000 pounds which, on an annual basis, calculates to be 5.5 X lo7 pounds PO4. 6. By use of the familiar ratio of 100 C : 16 N : 1 P, for natural organic matter, the above quantity of phosphate is capable of generating 1.8 X 109 pounds of organic carbon which, upon decay, would create an oxygen demand of 4.9 x l o 9 pounds of oxygen. 7. This is 27 times the quantity of the oxygen deficit found in the lake in 1964. What is even more important, this “natural” oxygen demanding load prob446 Environmental Science and Technology
ably occurs in pulses during the warmer seasons, making its effect on the lake much greater than if it were to occur continuously throughout the year. I hope these facts will dispel the premise that no cause and effect relationship exists or that there is no solution to the oxygen deficit problem. If the recommendations of the Federal Conference on Lake Erie with reference to phosphate removal from effluents are carried out, the resulting reduction of phosphate inputs should show an immediate improvement in the oxygen deficit situation. The source of the data used in the above calculations was the “Report on Pollution of Lake Erie and Its Tributaries, Part I” (dated July 1965) and presented at the Federal Conference on Lake Erie Pollution held in August 1965, in Cleveland and Buffalo. The subsequent calculations from this data source were presented before the Natural Resources and Power SubCommittee of the House Committee on Government Operations, at Syracuse, N. Y., Aug. 19, 1966, by Mr. William Q. Kehr of the Federal Water Pollution Control Administration, my colleague at that time.
S. Megregian Director of Research Metropolitan Sanitary District of Greater Chicago, Ill. Editor’s Note: The feature article, “Lake Erie-Dead But Not Dying,” was based largely on apaper giaen by Moffett, Carr, and Kemp at the AIChE meeting in Detroit late last year. The “Report on Pollution of Lake Erie and Its Tributaries (Part I)” to which Mr. Megregian refers was published in July 1965 by H E W S Public Health SerGice, Diuisian of Wafer Supply and Pollution Control.
Foam Separation-An Additional Look
DEARSIR: I fear some readers may infer that the general subject of foam separation is circumscribed by its description in the article on foam separation that appeared
in the February issue (page 116) of ES&T. Accordingly, I think it worthwhile to point out some additional aspects. The article describes only the simple mode of operation; Le., where feed enters the liquid pool. However, as with many other methods of separation, foam separation columns can also be operated in other modes (Fanlo and Lemlich, 1965). For example, in the stripping mode, feed is injected some distance above the pool and trickles down through the rising foam. The resulting countercurrent stripping action further purifies the bottoms. In the enriching mode, some collapsed foam drains back down the column to serve as reflux. This further enriches the foam overflow. In the combined mode, both stripping and enriching are employed. For certain situations these other modes offer considerable advantage over the simple mode. It is also worth noting that foam separation can be applied to various surface inactive solutes including certain metallic ions by first adding a suitable surfactant to unite with them and/or adsorb them at the surface of the bubbles (Rubin and Gaden, 1962; Sebba, 1962; Banfield, et. al., 1965). This can sometimes be accomplished quite selectively. Thus the potentialities of foam separation are quite broad and are not necessarily limited by an initial lack of surface activity. Liieraiure Cited
Fanlo S., Lemlich, R., Am. Inst. Chem. Engrs.-Inst. Chem. Engrs., Proc. Symp. on New Chemical Engineering Problems in the Utilization of Water, (Inst. Chem. Engrs., London) Symp. Ser. No. 9 , 7 5 7 8 , 85-86 (1965). Rubin, E., Gaden, E. L., Jr., “Foam Separation”, Ch. 5 in H. M. Schoen, Ed., New Chemical Engineering Separation Techniques,Interscience, New York, 1962. Sebba, F., Ion Flotation, Elsevier, New York, 1962. Banfield, D. L., Newson, I. H., Alder, P. J., Am. Inst. Chem. Engrs.-Inst. Chem. Engrs. Joint Symp. Preprint 1.1, Inst. Chem. Engrs., London, 1965.
R. Lemlich Professor of Chemical Engineering Cincinnati, Ohio
