LETTERS Reclam at ion Dear Sir: The article on phosphatic clays (ES&T, April 1974, p 312) was a well-written and comprehensive survey of a very difficult environmental problem, although the title ("Those Nasty Phosphatic Clay Ponds"), in my opinion, did not reflect the tone of the article. The article indicates that very little reclamation of slimes storage ponds is taking place, citing Bureau of Mines statistics that less than 1 mi2 has been returned to productive use. In actual fact, over 6000 acres of old settling areas have been reclaimed or are in the process of being reclaimed. By reclaimed, I mean put to productive use. Typical uses include: improved pasture, truck farming, municipal parks, golf courses, campgrounds, and light industry. The definition of reclamation as "generally meaning choked with wild plant growth and blending into local scenery," is not one that has been used by the industry. There are over 20,000 acres of old settling areas that meet such a description, and most of them appear to serve a useful function as thriving wildlife areas. Considering the present trends in the industry, combined with the pressures of a burgeoning population in central Florida, we can anticipate eventual reclamation of essentially all of these areas, probably within the next 10 to 20 years. Leslie G . Brornwell Florida Phosphatic Clays Research Project Lakeland, Fla. 33802
"The only effective control of the tussock moth is DDT . . ." is apparently incorrect. Van Tassel1 reported that the two biological controls tested by Nutrilite Products, tussock moth virus and Bacillus thuringiensis, seemed to provide better results than DDT without affecting other life forms. What concerns many environmentalists about DDT is its indiscriminate use when safer, biological controls exist. Granted, the use of DDT has had many beneficial effects, but its unlimited use when less damaging alternate methods exist, is like using a shotgun to kill a fly (or a tussock moth). A renaissance of DDT for uses where alternate, less harmful controls exist, would be most unfortunate and environmentally detrimental. John Musgrove Houston, Tex. 77034
Solid waste as fuel Dear Sir: The article "Liabilities into Assets" (ES&T, March 1974, p 21 0) seems unrealistically optimistic. I t gives urban refuse generation as 136 million tons per year, with a heat content of 1433 trillion Btu. This sup-
Less than $500 Completely portable permeation tube calibration system for pollution monitoring. 0
Fabric filter correction Dear Sir: ES&T published a list of air pollution control manufacturers with an indication of the various types of collectors which they had to offer (ES&T, April 1974, p 307). American Air Filter Co. was inadvertently left out as a supplier of fabric collectors. We do, indeed, offer a wide variety of fabric collectors and would appreciate being listed as a supplier of this particular type of collection equipment the next time this list is published. The other listings for American Air Filter were correct. Robert D. Moore American Air Filter Co., Inc. Louisville, Ky. 40201
posedly could produce 136 billion kWh of electrical power. The more recent studies indicate refuse generation is more like 115 million tons per year. We are aware of no data that would justify a nearterm heating value projection greater than about 4500 Btu/lb. This would give a heat content projection of roughly 1000 trillion Btu. Furthermore the conversion of heat to electrical power given implies that a Btu of energy in refuse is fully equivalent to a Btu in coal or oil. This is not true. I f refuse is fired in a form relatively near its original state all or most of its energy will be delivered to the furnace, but a smaller fraction of its heating value will be available than for coal or oil. Compared to oil or coal, the penalty due to increased moisture in the flue gas will be 8-9% of the fuel's energy. The higher excess air required to burn refuse on grates will cost another 4% under the best of conditions. The excess air penalty for firing shredded refuse probably will be much smaller. However, shredding requires energy and the net result will be no better. Therefore the upper bound of the equivalent heat control must be reduced to less than 900 trillion Btu. I f more sophisticated waste derived fuels are considered, the energy loss penalty involved in combustion becomes smaller. However, the
Mast Model 822-1 Cdhbrator
Uses stirred water as heat transfer medium.
e CaIibration standards of 0.05 ppm to 32 ppm. .. e
Designed to be used with an! instrument for mhich a permeation tube standard is available, a s well as with lMast Chlorine, Nitrogen Dioxide and Sulfur Dioxide Xlonitors.
Write for details and free data brochure.
*e%
"*
D DT
Dear Sir: I t is unfortunate that Robert Devlin ("DDT: A Renaissance?" ES&T, April 1974, p 322) did not have the benefit of the letter to the editor from Bert Van Tassel1 of Nutrilite Products, Inc., prior to writing his article. Devlin's statement that,
MAST
AIR MONITORING DIVISION
DEVELOPMENT CO. I
.
1
1
2212 East 12th St., Davenport. Iowa 52803 CIRCLE 4 ON READER SERVICE CARD
Volume 8, Number 7, July 1974
595
