ODOUR CONTROL

ABSTRACT

In this lecture we will be looking at odour, the different sources of odour, and the materials that causes odour in our environment. The various types of odour, causative element and its concentration and the various ways of eliminating or reducing its concentration will also be looked at.

                                  INTRODUCTION

Odour removal or suppression from air is absolutely necessary for comfort air conditioning. The odour creates dullness and reduces working efficiency. Sources of odours are so many and so diverse that it is difficult to suggest specific remedies for the emission they create. Many of the product causing odours are self oxidizing and disappear in a short period when the time interval and mixing volume are sufficient.

CLASSIFICATION OF ODOUR

Odours can be classified into two groups based on the source they are emitted from. These sources can also be divided into two based on the element that produce the emission. Our domestic odours are different from the odour from industrial area because of the constituent element that makes up the odour, this is because the industrial odour main constituents are toxic chemicals, gases and compound.

·        Domestic odour

This type of odour is classified as domestic because of the source it is emitted from. This type of odour is basically found in our home environment, offices, in public places, in trains, flight and cars. These types of odour are very common and their source of emission is all around. They are self oxidizing and they disperse or disappear in a short period of time when the concentration, time interval and mixing volume are sufficient.

·        Industrial odour

This type of odour is classified as industrial because it sources is mainly from industrial or company environment. Industrial areas like Guinness, Nigeria brewery and the entire Ogba area which is an industrial layout has this characteristic smell in the environment. These types of odour are not self oxidizing and they do not disappear on time as domestic odour does. These type of odour require an additional addictive or oxidizing agent for their effect in the environment to be reduced to the bearest concentration and comfortable minimum.

ODOUR REMOVAL:

 Control of odour in occupied spaces is a health as well as a comfort necessity. The principle sources of air contamination are body odours resulting from breathing, insensible perspiration and product of organic decomposition. Contamination of the air occur either directly from the bodies of occupants and from their clothes. The seriousness of the odour problem varies with the personal cleanliness, density of occupancy and degree of exertion of the occupants. Odours emitted from manufacturing plants are usually complex because they are made up from the mixture of many materials, compound and gases. Some odour bearing materials and vapours carried with the air are removed by absorbing materials. The activated carbon placed in perforated container is used for removing odours. Whenever the activated carbon becomes ineffective, it can be made effective by heating it to a temperature of 550^oc.

            The use of ozone for the treatment of odours is made successful from many years. The unwanted odours are suppressed by the masking effect of ozone. The ozone has pleasing effect when it is added 0.1 parts per million parts of air. Greater concentration of ozone is rather harmful and the quantities of the order of 15parts per million are exceedingly irritating to respiration membranes and the eyes. The use of ozone is not universally accepted as a desirable odour suppressing element for comfort air conditioning systems.

Sources of odours are so many and so diverse that it is difficult to suggest specific remedies for the emission they create. Many of the product causing odours are self oxidizing and disappear in a short period when the time interval and mixing volume are sufficient.

The different types of materials which are responsible for odour carried into air are given in table a below. If the odour is from outside air (industrial area then the odour absorber is placed in the path of outside air supply before entering into the room, but if the odour is from the conditioned space itself, then the absorber is placed in the return recirculated air.

ODOUR CAUSING ELEMENT	SOURCES	CONCENTRATION IN KG PER MILLION CU M. OF AIR
Butyric acid Valeric acid Pyridine Iodoform Cresol Aerolein Essential oils	Body odour Body odour Burning tobacco - - Frying fat Perfumes	1.5 0.01 0.035 0.0255 0.85 1.00 1.00

Only small portion of the total air recirculated needs to pass through the absorber as the activated carbon is practically 100% efficient and the resultant mixture of odour free air with the balance of the recirculated air is of sufficient low concentration to give satisfactory results. The arrangement of the system is shown in fig B.

 

            In a restaurant and similar installations, the minimum outside air is 0.35m³/min. per person for keeping the effect of odour below tolerable concentration. This increased outdoor air quantity will always require a large cooling in summer and a large heating in winter with resultant increased operating cost. This can be minimized by introducing inside odour absorber system.

METHOD OF ELIMINATING ODOUR

Most odours are either eliminated or reduced in concentration by the following methods.

·         Modification of the process.

·         Dilution with outdoor air.

·         Masking and neutralization.

·         Absorption.

·         Combustion and incineration.

·         Condensation.

·         Scrubbing.

·         PROCESS MODIFICATION.  Many times, slight changes in process minimize odour generation and are more effective and more economical than control devices. Modification in manufacture process could involve lowering the process temperature or such parameters. This is commonly done in foundry ovens, mineral wool plants, vanish cookers and paint baking ovens. The temperature in fertilizer plant using brewery waste is adjusted to assure that there is no vaporization.

                                                 

·         DILUTION METHOD. The odour can be eliminated at or near the source whenever possible. If the odour is not dangerous, it can be diluted until the concentration is below the objectionable level. This is very common approach in many industries.  For example in producing poly urethane foam, the tolylene –disocynate is soon diluted to a non detectable concentration.

·         SENSORY MODIFICATION METHOD. There are two sensory modification methods. Masking does not alter the composition of the original odour where does not modify the original odour. In sensory modification, perfume or deodorant may be added directly to the process. Perfume, colognes and deodorant are odour masking elements which release a pleasant odour/ fragrance to overcome an unpleasant smell.

·         MASKING & NEUTRALIZATION. Use of ozone for odour control is also a masking method. The concentration of ozone required to destroy odours is normally toxic. The toxic qualities of ozone cause drowsiness and headaches and reduce the ability to perceive odours. Ozone treatment has been employed in processing of fish and other foods, paints and vanish, plastic and petroleum, paper and fertilizers plants as well as in breweries.

Odour neutralization is the method used to eliminate or diminish the intensity of the original odour. Selection of neutralization agents depends mainly on the experience of the person in that field. A series of precatalogued agents is available for treating a variety of specific odours.

·         ABSORPTION. Charcoal (active carbon) is used mostly in locations where noxious gases are plentiful. Coal is an absorbent of odour in the same way that silica gel is an absorbent for moisture except that odour absorption does not generate heat. Charcoal is able to absorb condensable vapour and gases which come in contact with its surface and hold them until released by reactivation. It has a strong affinity for organic gases and hydrocarbons, the small charcoal container are capable of handling 1 cu. m of air with a pressure drop of 0.5cm. of water.

·         DEODORANT.  This method is used in removing odours by neutralization or masking. This method acts like a blind fold or blanket which shields the odour from emitting. Deodorant, preparation used on the body to eliminate or reduce the odor of perspiration. Deodorants are available in the form of powders, liquids, creams, lotions, sprays, and solid sticks. Perspiration itself is almost odorless, and the unpleasant smell of stale sweat is due to the bacterial release of ammonia. Deodorants reduce this odor by killing the bacteria, by preventing the secretion of perspiration, or by masking the smell of sweat with a pleasant-smelling scent.

Deodorants that kill or inactivate bacteria contain antiseptic substances, such as alcohol, formaldehyde, and boric acid. Deodorants that prevent the secretion of perspiration contain antiperspirants, chemical compounds that block the pores in the skin through which perspiration is secreted. The oldest forms of deodorants are those that contain perfumes to mask perspiration odor; they borrow from the ancient use of materials such as frankincense and myrrh, and distilled rosewater.

·         COMBUSTION. This method is used in removing odours from industrial exhausts. The gases containing objectionable odours are passed over catalyst which is maintained at 300^oc. the odour is removed by catalytic combustion. Direct combustion at 650^oc is also used for destroying odour from gases.

The combustion of air pollutants that are organic and gaseous in nature converts pollutants to harmless products as carbon dioxide and vapour which can be vented into the atmosphere. The carbon dioxide is colourless and odourless and the water vapour present in the exhaust is simply superheated steam.

The advantage of using catalytic oxidation technique is that the same performance can be obtained at comparatively lower cost through saving in fuel as provided with thermal oxidation.

A catalyst is an agent that accelerates a chemical reaction but is unchanged by itself. As the catalyst reaction proceeds, the catalyst returns repeatedly to its original state. Catalyst occasionally retains activity for 5 to 10 years. The most common useful life of an oxidation catalyst is about 15000 hours.The reduction in temperature necessary for oxidation that catalyst make possible is often surprising which is noted below:

Emission                      Catalytic Oxidation                  Auto Ignition

Carbon monoxide        205^OC                                       650^Oc

Hydrogen                     95^OC                                         650^Oc

Methane                       510^OC                                       650^OC  

                             CONCLUSION

Odours are very unpleasant and uncomfortable to human and can be very fatal to health when exposed to harmful and toxic odours. Odours are always around and they pose a threat to community and personal health and more still has to be done to improve the already existing means of eliminating or reducing its effect on human’s personal health and longetivity.

THANKS AND GOD BLESS YOU.

Deodorant, preparation used on the body to eliminate or reduce the odor of perspiration. Deodorants are available in the form of powders, liquids, creams, lotions, sprays, and solid sticks. Perspiration itself is almost odorless, and the unpleasant smell of stale sweat is due to the bacterial release of ammonia. Deodorants reduce this odor by killing the bacteria, by preventing the secretion of perspiration, or by masking the smell of sweat with a pleasant-smelling scent.

Deodorants that kill or inactivate bacteria contain antiseptic substances, such as alcohol, formaldehyde, and boric acid. Deodorants that prevent the secretion of perspiration contain antiperspirants, chemical compounds that block the pores in the skin through which perspiration is secreted. The oldest forms of deodorants are those that contain perfumes to mask perspiration odor; they borrow from the ancient use of materials such as frankincense and myrrh, and distilled rosewater.

REFERENCES

 Young, Christopher A. (2010). "What Smells?". Pollution Engineering 42 (5).

 Dalton, P (2002). "Odor, irritation and perception of health risk". International Archives of Occupational and Environmental Health 75 (5): 283–90. doi:10.1007/s00420-002-0312-x. PMID 11981666.

 Engen, Trygg (1991). Odor sensation and memory. New York: Praeger. ISBN 0-275-94111-6.

  What's Happening to My Body? Book for Boys: Revised Edition – Lynda Madaras, Area Madaras, Simon Sullivan – Google Boeken. Books.google.com. 2007-06-08. ISBN 9781557047694. Retrieved 2012-12-30.