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Information Sheet
WORLD ENZYMES AUSTRALIA
PO Box 348
Yarrambat
Victoria 3091
Phone / fax: 03 9717 0200
email: [email protected]
www.enzymatic.biz
Enzymatic and Odour Control
Degradation of organic compounds in the absence of oxygen is a principle cause of foul odours. Organosulphur compounds which
are naturally present in all organic waste materials break down in the absence of oxygen to yield hydrogen sulphide (H2S) gas
associated with the smell of rotten eggs.
Incomplete degradation of organic compounds under anaerobic conditions also produces volatile organic compounds (VOC’s).
These compounds can vary enormously in chemical composition and are characteristic of the waste from which they are derived.
Under anaerobic conditions organosulphur compounds generally degrade to simpler substances containing a sulphur-hydrogen
moiety (S-H bond), known as thiols or mercaptans. The mercaptans can further degrade under anaerobic conditions to hydrogen
sulphide.
If oxygen is available then aerobic digestion takes place. Under these conditions, the biochemical processes lead to the conversion
of organosulphur compounds to water and sulphate (H20 and SO4) which are odourless. Also, under aerobic conditions, VOC’s
are not produced because organic compounds are completely degraded to carbon dioxide and water which are odourless.
The odour that is perceived and that enables humans to differentiate between different odours is the result of a complex interaction
between the particular spectrum of VOC’s and the hydrogen sulphide that a given waste produces.
Hydrogen sulphide is detectable at extremely low concentrations (the recognition threshold is 0.47ppb). The detectable
concentration of many malodorous VOC’s is similarly very low. Thus, although a particular smell may be subjectively identified as
“strong” this does not necessarily indicate a high concentration of odour causing compounds. It is a reflection of the response to
the particular spectrum of VOC’s that is present.
It is rarely possible to detect hydrogen sulphide alone. The assessment of odour resulting from the interplay of hydrogen sulphide
and VOC’s is highly subjective. Even a small alteration in the composition of VOC’s or the concentration of VOC’s relative to
hydrogen sulphide can result in substantial changes in the subjective assessment of odour.
Enzymatic suppresses or controls odour by two different mechanisms. Firstly, it is able to complex with or “capture” volatile organic
compounds producing a practically instantaneous reduction in perceived odour. This effect explains why odour may be controlled
subjectively even though hydrogen sulphide is still detectable by objective chemical methods of analysis.
Secondly, Enzymatic affects digestion of organic contaminants in two ways:
1. Direct enzymatic catalysis of catabolic processes to breakdown complex molecules into progressively smaller less complex
molecules.
2. The smaller less complex molecules act as food substrate for microbes which can then proliferate and further promote
biochemical breakdown of the organic substrate.
For hydrogen sulphide control, it is primarily the first method of action that is at play. Mercaptase enzymes break the hydrogensulphur bonds of the mercaptans and thiols that are generated at the surface of the organic waste, thus suppressing the generation
of hydrogen sulphide. This is the most effective means of controlling the hydrogen sulphide component of the odour.
Hydrogen sulphide itself is a stable and potentially toxic gas. By eliminating the mercaptans and thiols from which it is produced,
and thus preventing its formation, Enzymatic eliminates the need for the more difficult task of degrading H2S after it has formed.
It is for this reason that a fine aerosol spray onto the surface is the best way to deal with odor. This needs to be repeated as
frequently as required to maintain odor control at the surface once the Enzymatic has been absorbed from the surface into the
organic waste or has biodegraded.
A fine aerosol spray is also the most effective way for Enzymatic to capture volatile organic compounds. An aerosol spray
generates a large surface area allowing the VOC’s to be efficiently and rapidly absorbed.
When a more comprehensive Biotechnology Solution is implemented in a waste water situation, aeration increases the available
oxygen to ensure that efficient full aerobic digestion of the organic waste takes place. This ensures that no H2S is produced and all
of this substrate is fully aerobically digested to produce H20 and SO4. In addition, under aerobic conditions, malodorous VOC’s are
reduced or eliminated.