LETTERS Bugs and AWT Dear Sir: As specialists in activated carbon systems, we must necessarily agree with your article, "Debugging physical-chemical treatment" (p 984 of your November 1972 issue). Having reviewed some of the designs, we are scratching our heads in amazement about the engineering parameters. Some of them will really have bugs and not just those growing around the activated carbon. One design actually looks like it was lifted lock, stock and barrel from a sugar refinery. W. F. Heneghan W. F. Heneghan Associates Greenwich, Conn. 06830
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Environmental Science & Technology
Dear Sir: In an article in the November 1972 issue of ES&T (p 984) you express concern about operational problems which may be associated with physical-chemical treatment of waste waters. I share this concern to the extent that care must be used in selecting the process sequence. I very much prefer the tertiary sequence of treatment in which chemical treatment, filtration, carbon adsorption, and other unit processes for more complete treatment follow conventional secondary biological treatment. This process chain retains the low cost advantages of biological treatment but adds greater reliability and greater ease of control associated with certain AWT unit processes. I disagree with the thought that physical-chemical processes are unavoidably more difficult to operate than biological processes. Our experience in two years of operating a 2.5-mgd AWT plant, and five years of operating the plant expanded to 7.5mgd capacity at South Tahoe, is exactly the opposite. The AWT processes are much more reliable and very much easier to operate and control than the biological processes in our plant. Our activated sludge treatment is more complicated and erratic in its operation than any of the seven AWT processes included in the plant, which produce very uniform results with little difficulty. Fortunately, the reliability inherent in the AWT processes and their proper selection and sequencing provides backup for the biological treatment so that there is no loss in the quality of the finished reclaimed water during biological upsets. While our process is a tertiary sequence rather than strictly a physical-chemical plant, I see no reason why the proper selection of pro-
cesses for physical-chemical processes, as specifically tailored to a particular waste w a t y by proper analysis of pilot plant test results, cannot result in the design of a physical-chemical treatment plant which would be easier to operate and control than a biological plant and as reliable as our tertiary AWT plant has proved to be. On the other hand, I would certainly agree wholeheartedly that improperly combined physical-chemical processes can produce a plant which might be totally unsatisfaQory and completely incapable of operation. Some chemical treatment plants built in the 1930's are good examples of this. Your words of caution in this regard are certainly appropriate and quite timely. It might be good to add a similar warning regarding certain new complicated series of biological processes which are proposed. Despite the many advantages of physical-chemical treatment methods for certain applications, biological processes also have advantages under many conditions which warrant their inclusion in waste water treatment flow sheets. It is just as great a mistake to overlook the advantages of biological treatment as it is to ignore the benefits of physical-chemical processes. R. L. Culp, Genetal Manager
South Tahoe Public Utility District South Lake Tahoe, Calif. 95705
Who pays the fine? Dear Sir: You reported in your September issue (p 785) that New Jersey will be checking auto exhaust emissions as part of its annual state inspection, starting in mid 1973. Now that we are going to such types of control, I wonder who is going to pay the fines when a car is not conforming to the standards. 1 submit that, as an ordinary motorist who went to my mechanic when requested after failing tests, I am not responsible if my car does not conform afterwards-the mechanic is. Indeed, this is coming into such specialized technology that as a layman I cannot recognize whether the work was done properly. We are not anymore dealing here with something that anybody can check, such as the proper functioning of a tail light. I hope legislators will understand that. Andre J. Lebrun, M.D. The Medical College of Wisconsin Department of Environmental Medicine Milwaukee, Wis. 53226
