Search

Odor control is similar to any other air pollution control problem. Choosing a new material with less odor potential, changing the process, using an add-on pollution control system such as a scrubber or an afterburner, or raising the stack height all achieve community odor control. When the tolerance level of a community changes, the odor control requirements also change. Odor control techniques fall into the following categories: activated carbon adsorption; adsorption with chemical reaction; biofiltration; wet scrubbing; combustion; and dispersion. Activated carbon adsorption is a viable method in many odor control problems. Biofiltration is an odor control technology that uses a biologically active filter bed to treat odorous chemical compounds. Wet scrubbing is another widely used technology for odor control. Combustion is an effective technique for odor control. The use of elevated emission points can reduce the odorant concentration at downwind ground level because of dispersion or dilution.

Unmodified and caustic-impregnated carbons were compared as adsorbents for hydrogen sulfide in the North River Water Pollution Control Plant in New York City over a period of 2 years. The carbons were characterized using accelerated H2S breakthrough capacity tests, sorption of nitrogen, potentiometric titration, and thermal analysis. The accelerated laboratory tests indicate that the initial capacity of caustic-impregnated carbons exceeds that of unmodified carbon, but the nature of real-life challenge streams, particularly their lower H2S concentrations, nullifies this advantage. As the caustic content of the impregnated carbon is consumed, the situation reverses, and the unmodified carbon becomes more effective. When the concentration of H2S is low, the developed surface area and pore volume along with the affinity to retain water create a favorable environment for dissociative adsorption of hydrogen sulfide and its oxidation to elemental sulfur, S4+, and S6+. In the case of the caustic carbon, the cata...

Odors from New York City's sewage treatment plants are controlled by activated carbon housed in 44 large towers, each holding about 11 tons of carbon. The carbons are impregnated with NaOH or with KOH, or are unimpregnated but continuously injected with ammonia gas. A study is now under way in our laboratory to monitor the progressive exhaustion of these carbon beds and to predict their useful lifetimes. The monitoring tests include a measure of the residual breakthrough capacity of the carbon for hydrogen sulfide, and an estimate of the remaining capacity for physical adsorption of other gases. For the caustic-impregnated carbons, the tests include a measure of the actual life-extension that can be realized by the retrofit of ammonia injection without interrupting the operation of the carbon vessels. A procedure to predict the results of in situ regeneration is described.

Because effluents to atmosphere from sewage treatment typically include hydrogen sulfide (H2S) among other malodors, and because H2S is a light gas, it is commonly assumed that unmodified (“virgin”) activated carbon, which acts largely by physical adsorption, is inadequate for such applications. Instead, caustic-impregnated and other modified carbons have been used in the U.S.A., Europe, and Israel for odor control where H2S is an expected airborne component. Our laboratory and full-scale comparative studies question this assumption and practice, and strongly support the advantages of virgin over impregnated or other special carbons for control of H2S as well as for general odor removal. In this report, we suggest that biofiltration in the carbon bed helps achieve such favorable outcomes.

The scope and applications of odor measurement and control are sometimes confused by various uses of the word odor. In the past, odor has been used to mean either (1) the perception of smell, referring to the sensation, or (2) that which is smelled, referring to the stimulus. To eliminate confusion, odor is best used only for the former meaning, and odorant should be defined as any odorous substance. Odor intensity, then, is the magnitude of the olfactory sensation produced on exposure to an odorant. Odor control is a term that can be used to describe any process that makes olfactory experiences more acceptable to people. The perceptual route to this objective is usually, but not always, the reduction of odor intensity. An alternative route is the change of odor quality in some way that is considered to be an improvement. When the reduction of odor intensity is accomplished by removal of odorant from the atmosphere, the process is equivalent to gas and vapor abatement, or to air cleaning, but with some special considerations. These include (1) problems related to the need to attain very low concentrations, often approaching threshold levels, (2) uncertainties with regard to the reliability of sensory or chemical analyses, and (3) difficulties associated with diffuse or sporadic sources. When an odorous atmosphere is improved by the addition of another (usually pleasant) odorant under conditions in which chemical reactions are not involved, the process is called odor modification, referring to modification of the odor perception, not of the odorant. These and other methods of odor control are considered in some detail. Keywords: Odors; Olefactory perception; Characteristics of odor; Measurement; Sampling; Surveys; Economic effects; Social effects; Control; Odor masking; Adaptation

This paper presents findings on the application of granular activated carbon as a medium for immobilizing liquid organic wastes of known characteristics.

Les essais realises en laboratoire, avec un pilote et dans une station d'epuration d'eaux usees montrent que l'injection d'ammoniac augmente d'un facteur 3 les capacites d'elimination du charbon actif

Electron spin resonance and thermal analysis have been used to investigate the catalytic oxidation of organic vapors adsorbed on activated carbon. Particular attention is given to determination of the temperature interval between oxidation of the adsorbate and burnoff of the carbon, and to the study of the oxidation states of the catalyst during repeated adsorption-oxidation cycles.

Evaluation des differents procedes de purification de l'air contamine: le lavage en phase liquide, l'incineration, la filtration, l'adsorption et la precipitation electrostatique appliques seuls ou en combinaison en fonction des facteurs suivants: a) le type des contamiannts (particule ou gaz); b) l'efficacite de l'unite de traitement constituee face aux polluants vises et c) le flux total d'air a traiter en rapport avec la taille de la piece et des caracteristiques du melange d'air. On compare ainsi divers types de procedes actuellement commercialises

Assessing the service life and performance of an activated carbon system requires the monitoring of carbon saturation and post-carbon air over time. For any selected environment, such performance can be predicted with the aid of an air sampler comprising 16 adsorption cartridges mounted on a manifold plate. Various methods of analysis of carbon for saturation are evaluated and compared. The partially saturated carbon can be used for sensory evaluation of the post-carbon air. The sampler can also be used for competitive tests between different kinds of adsorbents in the same environment.

Experiments are described which are designed to examine the organic vapor content of three fresh natural atmospheres. Efforts are made to determine whether or not they are comparable to each other in vapor concentration levels and/or in types of organic compounds present in vapor form. The sites selected were: the Mount Washington Observatory, Gorham, New Hampshire; the US Coast Guard Station, Sandy Hook, New Jersey; and the Black Rock State Forest, Thomaston, Connecticut. The method of sampling and analysis are described. 5 references, 15 figures, 2 tables.

Activated carbon and permanganated alumina were compared with regard to their effectiveness in reducing the odor levels of air streams containing olefin. ester, aldehyde, ketone, amine, sulfide, mercaptan, decomposed crustacean shell vapor, or state tobacco vapor. In all cases, the odor-reducing effect of the activated carbon was much faster than that of the permanganated alumina. For the odors of stale tobacco and decomposed crustacean shells, the permanganated alumina, after it was reduced to MnO2, gave evidence of prolonged partial odor reduction, probably by serving as a catalyst for oxidation by air.

The manner of preparation of BAC determines its capacity for reaction with ethylene, in the following order: slow isothermal bromination > rapid bromination > rapid bromination followed by heating at 550°C. The latter method produces unreactive BAC. It is conluded that heat supplies the activation energy for chemisorption of the bromine, and that the chemisorbed bromine is unreactive. The ability of BAC to retain its bromine was found to be related to the pore structure of the carbon. At saturation pressure, capillary condensation of the bromine occurs. Carbons with larger pore diameters desorb their bromine more rapidly and to a greater extent than do carbons with smaller pore diameters. Recommendations for applications to air purification are suggested.

Ratios of dilution or concentration of a gas sample are expressed as a pollutant quotient, or, if appropriate, an odorant quotient, Z, denoting the ratio of a pollutant (or odorant) concentration to some target concentration. The expression pZ is defined as + log10Z, so that a positive value of pZ implies dilution and a negative value concentration. The effect of particulate matter on the Z function is considered. Various examples are given, including conversions from other common dilution expressions.

The odor control performance of carbon-loaded rayon monofilaments depends on the type and proportion of activated carbon used. The filter efficiency in turn determines the rate of odor reduction in a closed space and the ultimate or equilibrium concentration when odorant generation and removal occur simultaneously. Four types of filters were evaluated: rayon loaded with air- or water-purification carbon, granular air-purification carbon, and open-lattice commercial filters. Air laden with synthetic tobacco malodor was streamed through successive increments of adsorbent bed. Sensory odor judgments were made before and after each adsorption stage by matching the effluent odors with those from mixtures of known concentrations. It was thus possible to estimate adsorption efficiencies and, by repeating the measurements after various degrees of carbon saturation, to construct adsorption waves. It was found that airpurification carbon was superior to water-purification carbon for loading in the rayon filaments, and that all the rayon-carbon compositions were much superior to the commercial open-lattice filters. The rayon-carbon filters showed efficiencies up to 70% for one pass at 0.1 sec. detention time through a 3/4-in. bed packed at 0.096 g./ml. with a filament comprising 20% rayon and 80% carbon.

It has been previously shown that the desorption of either a chemisorbed or a physically adsorbed gas can be enhanced by the subsequent introduction of a foreign gas. Under conditions in which desorption recovery of butane from activated, carbon was 50 to 65%, subsequent adsorption of CCl4 enhanced the recovery of butane to 100%. Recovery of CCl2F2, originally 79%, was enhanced to 99% by the same method. The method of enhanced desorption was applied to the recovery of samples from activated carbons exposed to atmospheres in Chicago, New Orleans, Philadelphia, Washington, D. C, and Cincinnati. Three different types of carbons, characterized by different distributions of pore diameters, were used simultaneously in the Cincinnati sampling. In general, the enhanced desorption technique was advantageous in providing analytical information on adsorbed samples recovered from carbon media. The enhancement effect is especially marked with hydrocarbon material. The effects of these structural attributes of the carb...

The various factors that play a role in the determination of ventilation requirements for odor control are described. Studies that uncovered and quantified the connection between odors and ventilation systems requirements are reviewed. They were usually motivated by interest in public hygiene and health. Recent discoveries regarding excessive levels of formaldehyde in buildings lined with chipboard, excessive levels of particulate matter in the vicinity of smokers, and excessive levels of oxides of nitrogen in homes with gas stoves, have, in conjunction with the need for energy efficiency, refocused attention on the origin and adequacy of nonindustrial ventilation rates. Subsequent to a review of the research basis for modern ventilation rates, the varieties of odor control applicable indoors are examined. The section on control deals at length with chemical and engineering considerations in the use of granular filter media, the most practical means of indoor odor control. A chapter on odor perception focuses on sensory phenomena, followed by a chapter on both chemical and psychophysical methodology. Prospects are discussed in the final chapter. (MCW)