When residential meets industrial – an introduction to air quality approaches

Rich Johnson, Senior Air Quality Consultant, has written an article introducing the most commonly applied odour abatement technologies used to ensure healthy air quality where residential areas meet industrial.

With the ever-increasing demand for both residential and commercial/industrial development the typical distance between odour producing processes (such as waste or industry) and sensitive receptors (such as residents or schools) is narrowing. As a result, SLR has seen a growing demand for assessment of odour control measures to reduce odour impacts from both existing and proposed facilities upon nearby sensitive receptors such as residents.

From my experience in odour assessments over the last decade, at a wide range of both UK-based and international facilities, the facilities at which odour issues most commonly arise are municipal waste sites, wastewater treatment works and manufacturing facilities (such as food processing, animal feed and plastics).

There are three main approaches by which to mitigate and control odour emissions from such facilities:

• containment (i.e. operating within an enclosed and ventilated building);
• dispersion (i.e. increasing dispersion stack height and/or exit velocity); and
• abatement (i.e. odour control plant).

This article will focus upon odour abatement technologies, to provide an introduction on the most commonly applied technologies. The most widely applied odour abatement technologies are wet scrubbing, biological scrubbing and adsorption.

Each of these technologies have their own distinct strengths and limitations and can also be applied in combination to achieve a greater combined effect. Application of the proper technology (or technologies) is the key to designing a system which is fit for purpose; providing both a high level of odour abatement whilst remaining cost-effective in terms of both installation and running costs.

Wet Scrubbing:

Wet scrubbing uses a liquid (water, acid, alkali) to remove odorous compounds from the airstream through contact of the foul air with the liquid media within an enclosed tower structure.

Strengths:

• suitable for airstreams with a high odour load
• typically high abatement efficiencies at high odour loads
• the type of liquid media utilised can be tailored to remove specific odorous compounds
• can handle large airflows and variable airflows

Limitations:

• relatively high installation costs
• units can require a lot of vertical space
• regular monitor and maintenance to ensure effective operation
• storage of dosing chemicals is also required, along with their subsequent disposal once used (which be classed as hazardous waste)

Overall wet scrubbing can be effective as a first stage for high load airstreams, often followed by a carbon or biofilter. It is less common at smaller facilities where budgets for odour control are typically lower.

Biological Scrubbing:

Biological scrubbing uses specifically propagated microorganisms on a solid media (typically woodchip) to remove odorous compounds from the airstream through contact of the foul air with the organisms within a flat ‘bed’ structure.

Strengths:

• suitable for airstreams with a medium-to-high odour load
• typically high abatement efficiencies at medium-to-high odour loads
• moderate installation costs
• relatively low running and maintenance costs
• popular multipurpose abatement solution

Limitations:

• poor abatement efficiency at low odour loads
• units can require a large surface area and are not suitable for highly variable airflows
• if the unit is not in use and properly maintained (even for a short period) the microorganisms can die-out, greatly reducing abatement efficiency

Overall, biological scrubbing can be an effective multipurpose solution for airstreams of a moderate odour load which aren’t highly variable.

Adsorption:

The most common odour abatement technology which uses adsorption is granular activated carbon (or ‘activated carbon’). Adsorption is the reaction by which gas molecules are retained on a solid surface, also referred to as a molecular sieve.

Strengths:

• most effectively applied on low odour loads (often as a final treatment phase following another technology)
• highly effective in a range of applications (by use of specific media types)
• low installation costs
• units generally require a small surface area compared to other technologies
• units require minimal maintenance (other than periodic media replacement)

Limitations:

• not suitable for airstreams with a medium-to-high odour load as the higher the odour load to the unit the more frequently the media will require replacement (which can lead to very expensive running costs)
• not suitable for airstreams of high moisture content without pre-treatment such as a condenser

Overall adsorption can be an effective multipurpose solution for airstreams of a low odour load and is popular as a final treatment stage in a multi-stage abatement system.

Disappointingly, it would appear that adsorption systems are often selected as a single stage treatment option for high odour load airstreams, burdening site operators with very high running costs related to the high frequency of media replacement. This is an illustration of where employing professional consultancy services in selecting an appropriate odour abatement technology (or a combination of technologies) can greatly benefit the site operator in the long-term, in regard to both running costs and abatement performance.

It should also be considered that most odour abatement technologies require some kind of pre-treatment system before the abatement plant, such as a dust filter, humidifier or condenser. Additionally, there are a wide range of other odour control technologies available to explore, such as thermal oxidisation, ultra-violet light and ionised air, however I have focused upon the most common techniques in this article.

If you would like to know more or you require professional services on a project, please get in touch. One of SLR’s Air Quality experts will be happy to discuss your project and the options available to you.