letters Wastes-from membrane processes
DEARSIR: The article by Jacob I. Bregman, “Membrane processes gain favor for water reuse,” EMT, April 1970, page 296, describes most of the favorable applications of reverse osmosis and related membrane techniques for separating purified water from contaminants. Unfortunately, it fails to state that the contaminants are discarded along with a substantial fraction of the water. A conventional aim is 90% water recovery which means that the contaminants are concentrated up to tenfold. Disposal of this waste stream is a n important part of the problem which has been totally neglected by most workers. Consider the case of salt removal from a waste stream containing initially 1500 mg./l. total dissolved solids (TDS) and producing 90% of a product stream containing 500 mg./l. TDS. The waste stream will contain 10,500 mg./l. TDS and each pound of salt carries with it 9 5 pounds of water.
The cost of moving this much water to the ocean where it could safely be disposed of depends, of course, on the location of the plant and will obviously be highest in the interior parts of the country. Disposal in deep wells is applicable only where the local geology is particularly favorable and should not be looked upon as a general solution. Even disposal to the ocean requires enough treatment to ensure that the wastes will not interfere with the ecology of the near-shore environment. Discharge of brines to local surface waters will rarely be permitted. If organic wastes such as primary effluents are treated by reverse osmosis, it is still necessary to remove the organic matter and nutrient salts from a concentrated stream by processes which have not yet been developed.
Robert B. D e a n
Ultimate Disposal Research Program Federal Water Quality Administration Cincinnati, Ohio 45226
Air pollution sources reevaluated
DEARSIR: The determination of the sources of air pollutants precedes, logically, efforts to eliminate air pollution. As an expediency, the accounting often has been on a mass basis with particular classes of sources identified by the mas5 of pollutants emitted per year or day. Although the distribution among different pollutant species usually has been stated, the practice has been to sum the pollutant masses to arrive at a grand total for the purpose of comparing the contributions of different air pollution sources. The estimates of air pollution due to various sources on such a basis are now generally well accepted. The numbers cited most often are the 1965 figures published by the Department of Health, Education, and Welfarc. Similar distributions among sources can be arrived at for particular localities from more recent data. The distri(Continued on page 454)
Heed reliable. chemical feedinfl? -
The finest water and wastewater treatment chemicals are only as good as the feeder that feeds t h e m . If you have feeder problems . , , overtreatment, undertreatment, breakdown . . . contact BIF for reliable liquid and dry chemical feeders, performance-proved in thousands of treatment installations! Dry materials? The answer is Omega@helix feeders. Compact, low-cost models for volumetric feeding from 1 ounce to 1 ton per hour. Liquids? Only BIF’s Proportioneers@line includes all three types of metering pumps: mechanical diaphragm, , . hydraulically balanced diaphragm.. . and packed plunger p u m p . These three handle virtually anything that flows. . . efficiently, economically, reliably. Send details on chemicals to be fed, feed range, and number of feeders needed. BIF, A u n i t of General Signal Corporation, 326 Harris Ave., Providence, R. I. 02901 Tel. (401) 421-4302.
Balanced Diaphragm Pump Capacity to 300 gph
Packed Plunger Pump Capacity to 600 gph
Dry Material Helix Feeder Capacity from 1 oz to 1 tonlhr
1
“Dependableperformance that pays
foritself”
Circle No. 4 on Readers’ Service Card
Volume 4, Number 6 , June 1970 453
