(continued from page 287) Phosphate removal process
DEARSIR: W e would like to call attention to two aspects of the Environmental Currents item on the PhoStrip phosphate removal process published in your January 1971 issue, page 15. The diagram you prepared does not provide for sludge return from the anaerobic tank to the aeration basin. Sludge return is an essential part of the overall process, as it is of the activated sludge process itself. The text refers to phosphate being concentrated in “an anaerobic digestion process.” The step in which the phosphate taken up by the microorganisms is released is not digestion but merely the imposition of anaerobic conditions for a brief period, to induce the living organisms to release phosphate. Finally, if the process centers on any step, it is not the “higher-than-normal aeration rate” cited, but, we think, the cycling of the microorganisms through the anaerobic tank.
Gilbert V. Levin, president Biospherics Inc. Rockville, Md. 20853 Joseph Shapiro Lirnnologicnl Research Center University of Minnesota Minneapolis, Minn. 55455 Unloading system designed by Sargent 8, Lundy Engineers, Chicago.
Unobtainable insurance
for Unloading Coal Cars To capitalize o n unit t r a i n savings power plants have developed methods to quickly unload coal cars. Wisconsin Electric Power Co.’s Oak Creek Plant, for example, unloads unit trains using enclosed r o t a r y c a r d u m p e r s . Naturally, as the coal is dumped, float dust billows into the unloading enclosure. This dirty air problem is controlled by a 126,000 C F M Sly Shaker-type Dust Filter mounted on the enclosure‘s roof. The filter ~ u l l sin the dust-laden air, filters o u t t h e coal fines a n d exhausts clean air to the atmosphere. Collected fines are hopper t r a n s f e r r e d to dual screw conveyors for return to the coal
handling system. This automatic dust removal system reduces dust conditions and returns clean air to the atmosphere. If you have a similar dust control problem, put our experience to work on it. We’ve been engineering wet and dry dust and a i r pollution c o n t r o l equipment for over 95 years. Ask your Sly Sales Engineer for our catalog and help in handling your problem. Or contact us direct. The W. W. Sly Manufacturing Company, 4813 Train Ave., Cleveland, O h i o 44102. Overseas: Aeronca lnternational Ltd., Maidenhead, Berks, England; Mideco (Sales) Pty., Ltd., Nunawading Victoria, Australia.
SLY M A N U F A C T U R I N G Manufacturers of Dust Filters and Impinjet” Gas Scrubbers Circle NO. 11 on Readers’ Service Card
288 Environmental Science & Technology
DEARSIR: In the article, “Is pollution insurable?” that appears on page 1103 of your December 1970 issue, you report on the exclusion endorsement which the insurance companies of America have added to all of their liability insurance policies outstanding. W e would like to point out that this is not the only type of exclusion the insurance companies have made in regard to their potential liability involving pollution suits. Enviro-Trol, Inc. was formed last year to help industries solve their pollution problems. Since we are offering both a testing and consulting service, we feel the need for professional liability insurance. However, even though we are owned by a much larger company with considerable insurance coverage, liability insurance has SO far been denied our operation. We are for the time being operating without this coverage, but it is very risky business to say the least.
