Why do we sometimes smell foul odors around wastewater treatment plants?
Odors are a natural part of the substances that are delivered to and treated at any wastewater treatment plant.
Odors are typically contained within the wastewater treatment plant site; but occasionally odors drift from the plant site depending on weather conditions and wind direction.
Routine processing operations are designed to reduce the amount of odors present; however, certain weather conditions and equipment maintenance may lessen the effectiveness of these routine odor control measures.
What causes these foul rotten-egg odors?
Most of the odors detected in and around wastewater treatment plants are signals that the natural organic treatment process is working. Organic matter is decomposing with the assistance of good bacteria and pollutants are being removed from the wastewater.
As the following table Odorous Compounds In Wastewater shows, three major odorous compounds naturally occurring in the treatment process, hydrogen sulfide, amines and mercaptans(see Mercaptan definition from Brittanica in the following column), are detectable by the human nose at extremely low concentrations:
Odorous Compounds In Wastewater
| Compound Name |
Recognition Threshold parts per million |
Odor Description |
Allyl mercaptan |
0.0015 |
Disagreeable, garlic |
Ammonia |
37 |
Pungent, irritating |
Amyl mercaptan |
---- |
Unpleasant, putrid |
Diisopropyl amine |
0.38 |
Fishy |
Dimethyl amine |
---- |
Putrid, fishy |
Ethyl amine |
1.7 |
Ammonialike |
Ethyl mercaptan |
0.001 |
Decayed cabbage |
Hydrogen sulfide |
0.0047 |
Rotten eggs |
Indole |
---- |
Fecal, nauseating |
Methyl amine |
---- |
Putrid, fishy |
Methyl mercaptan |
0.0010 |
Rotten cabbage |
From Table 2.1, Odor Control in Wastewater Treatment Plants, 1995, WEF & American Society of Civil Engineers |
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Definition of MERCAPTANS (Thio-alcohols), organic chemical compounds of the type R.SH (R = an alkyl group).
The name is derived from mercurium captans, in allusion to the fact that these compounds react readily with mercuric oxide to form crystalline mercury derivatives. The mercaptans may be prepared by the action of the alkyl halides on an alcoholic solution of potassium hydrosulphide; by the reduction of the sulpho-chlorides, e.g. C 2 H 5 SO 2 C1 (chlorides of sulphonic acids), by heating the salts of esters of sulphuric acid with potassium hydrosulphide, and by heating the alcohols with phosphorus pentasulphide.
They are colourless liquids, which are insoluble in water and possess a characteristic offensive smell.
On oxidation by nitric acid they yield sulphonic acids.
They combine with aldehydes and ketones, with elimination of water and formation of mercaptals and mercaptols. (See Sulphonal.) Methyl mercaptan, CH,.SH, is a liquid which boils at 5.8° C. (752 mm.), and forms a crystalline hydrate with water.
Ethyl mercaptan, C 2 H 5 .SH, is a colourless liquid which boils at 36.2° C. It is used commercially in the preparation of sulphonal. The mercury salt, Hg(SC2H5)2, crystallizes from alcohol in plates. When heated with alcohol to 190° C. it decomposes into mercury and ethyldisulphide.
Sulfree™ from FreshAWL is safe, stable, non-corrosive, does not require special handling or training, and is not subject to spikes due to temperature or loading factors. It is your answer for a green solution to hydrogen sulfide, acid gases, mercaptans and the associated odors.
For more information, schedule an on-site demonstration or request a quote, call or email to speak to a representative:
(707) 494-5758
steve@freshawl.com
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