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the COz climate problem. 1 very much enjoyed reading it. There is one minor point which I would like to bring to your attention. 1 -D radiative-convective models have played a limited but useful role in climate studies, primarily by providing estimates of the effect of changes in atmospheric composition on global thermal structure. However, it is anticipated that the role will be expanded because the realism of the model is improving. For example, recently it has been shown that the ice-albedo feedback can be realistically incorporated into the model ( J . Atnzos. Sci., March 1980, p 545). It is also possible to incorporate the cloud feedback which may be used to explicitly study the dependence of the global surface temperature on the cloud vertical distribution and optical properties. Such model studies are needed to develop and test cloud parameterizations for the multidimensional climate models. Wei-Chyung Wang Atmospheric and Environmental Research, Inc. Cambridge, Mass. 021 39

Pollutant treatability Dear Sir: Concerning Dr. M. P. Strier’s article “Pollutant treatability: a molecular engineering approach” ( E S & T , January 1980, p 28), the practical limitations on the attainability of the theoretical effluent concentrations must not be overlooked. Mass transfer (diffusion) limitations are much more likely to be controlling in practical steam strippers than theoretical thermodynamic limitations. Tray efficiencies are often quite low in actual distillation equipment at very low residual concentrations. Reliance on oil-water separation devices for other than rough-cut separations is highly questionable. In large systems, thermal currents and other short-circuiting effects can easily override any separation achievable under “ideal” conditions. Consistent, year-round maintenance of ideal operating conditions with these devices is highly unlikely. I n extrapolating single-compound biological treatability data to realistic, multicomponent wastes, both antagonistic and synergistic effects may be encountered. Some compounds may be metabolized for energy but will not sustain microbial growth without the presence of another carbon source (a potential for synergism in multicomponent wastes). Other compounds

have been observed to be biodegradable only in the absence of other, more readily degradable compounds (a potential for antagonism in multicomponent wastes). Extrapolation from model compound treatability is particularly uncertain for biological treatment. In our experience, multicomponent interactions are extreme11 important in carbon adsorption s1stems. Whatever the underlying phqsical cause, adsorption of a particular compound from mixtures is less than predicted from single-compound adsorption data. In continuous column adsorbers treating multicomponent wastes. a chromatographic separation/elution phenomenon is frequently encountered. The less readily adsorbed solute is frequently adsorbed for a time, then eluted as a “chromatographic band” at concentrations higher than the influent. My point here is not to question the usefulness of the theoretical considerations in Dr. Strier‘s article. I t is to emphasize that these single-compound treatability limits cannot be taken as attainable performance levels (or effluent permit limits) for actual systems treating tjpical, multicomponent wastewaters. The caveat should be emphasized to put Dr. Strier’s article in practical perspective. Cyron T. Lawson Union Carbide Corporation Technical Center, R / D Dept. South Charleston, W.V. 25303

Corrections May 1980, p 509. The process for removing heavy metals and certain anions from mixed acidic planting wastes involves precipitation in addition to activated-carbon adsorption. March 1980, p 276. In “The N - B y’s of wastewater treatment” article, the biomass balance equation is misprinted. Unfortunately, a second typo may persuade the reader that a new) mass balance relationship is proposed which is not the case. p 278, COI.3 should be p 278, col. 3 should be

1 -NAF/AT-P -

-

SA M I -&FIAT -SA M

-P

(Ib biomass/lb M ) ( 1 /days)

p 279, col. 2 /3 = 0.18 should be 0.018 Figure 5 OC should be

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CIRCLE 4 ON READER SERVICE CARD

Volume 14, Number 7, July 1980

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