Typically, odours are detected at very low concentrations of chemicals and compounds in air. The human nose is very sensitive with on average over 5 million scent receptors. Humans can detect concentrations as low as a few parts per billion (ppb), or less in air. This illustrates the difficulty of quantifying odour objectively.
The basic sensory attributes are
- Detection – Concentration of an odour when first detectable
- Recognition – Human ability to differentiate between odours, e.g. wine or vinegar
- Intensity – Perceived strength at differing concentrations, e.g. faint, distinct, strong
- Hedonic Tone – Pleasantness / offensiveness, e.g. pleasant, unpleasant, offensive
- Odour Quality or Character – Association & complexity, e.g. the many “tones” and associations we have with an odour such as flowers, coffee, waste, sewage, etc.
The concentration at which an odour is just detectable by a panel of selected human “sniffers” is defined as the detection threshold and has an odour concentration of 1 European odour unit per cubic metre (1 ouE m -3 or 1 ouE/m3 )
- 1 ouE m -3 is the point of detection
- 5 ouE m -3 is a faint odour
- 10 ouE m -3 is a distinct odour
People react to odours in different ways. Rural odours may be pleasant to one person but an anathema to another. Common odour sources and some of their possible issues are…
Increase treatment volumes & flow rates e.g. from storm conditions, increased proximity of sensitive development such as housing, inadequate maintenance of odour control systems.
Food Processing and Commercial Kitchens
Extraction system design e.g. inadequate discharge height, absence of odour control at source, poor “filtration” system maintenance.
Plants and Solvents
Odour control system’s design, building leakage and poor positioning of vents (including garages and workshops)
Animals, Livestock and Poultry
Proximity of sensitive development such as housing, waster management on-site, poor dispersions on odours during early morning and evening.
How do we combat odours?
If we split the types of sources we have those which may be enclosed; i.e. in a shed or factory or those which are open field.
The historical method of dealing with enclosed odour sources are:
- ABSORPTION – Extract the air from the enclosure and allow it to be pulled through an odour absorbing material such as Carbon granules. The downside of this is that the carbon gets filled with water and odourous chemicals and needs regular renewing. High pressure fans need lots of electrical power to run them. High ongoing costs.
- MASKING – Use other, sweeter smelling chemicals to override the noxious ones. Costly in chemical use and often locals don’t like this smell either.
- BIOBED – Large structures are built to enclose vast amounts of wet, high surface area materials, (clinker, tree bark) that are impregnated with particular bacteria strains. This sits on a porous plenum into which the odourous air is pumped. As the odours percolate upwards they are “eaten” by the bacteria and less odourous chemicals escape. This is a high capital outlay and requires the bacteria to be looked after and kept damp. Drying out will kill the bacteria and odd excesses of gasses like ammonia may result in the death one strain of bacteria leaving another to thrive that may not be as useful in odour management.
- ELECTRICAL DISCHARGE – Ozone and other vigorous radicals can be created electrically. These are projected into the space where the odour is present. The odourous molecules are broken up by the aggressive radicals and odour is reduced. An effective solution but lots of regular maintenance is required as the ozone levels slowly decrease with use.
- SIMPLEST – Extraction of the foul air through a spray wash column. A scrubber. This relies on solubility and as most scrubbers re-circulate the water they are a source of high bacterial growth, fungal growth as the water becomes warmer. As the water becomes warmer it absorbs less ammonia and odours. They are also an item which requires regular legionella testing if biocides or UV-C systems are not employed.
The iPURtech method is an attempt to find an ideal scenario.
- Destroy the odours not capture or mask them.
- Reduce maintenance by making the process very simple.
- Use as little energy as possible.
- Require little site space.
- Take known technologies and design around them.
- A system that can re-circulate air within a shed or extract the air to atmosphere.
We use a mix of catalysts anchored to a high surface area media to destroy organic molecules including odours. The catalyst is not activated by heat, as in car exhausts, but by a particular wavelength of Ultra Violet energy. We burn / oxidise odour molecules in a cold environment.
Each iPURtech Air Purification System has a series of catalyst cartridges set between layers of UV lamps. The surface area of each layer being sufficient to allow a calculated contact time of the air passing through the system. The initial stage of the process includes set(s) of filters to remove dust or any other materials which could coat the catalyst. These may be hosed clean at intervals, (monthly) depending on the environment. The unit offers little air resistance so fans are low powered. A typical large unit will take less than 3 kw of lamp energy.