Formerly, people did not understand that odors were not merely olfactory nuisances but rather higher levels of odorous chemical compounds could produce hazardous gases.  Hydrogen sulfide (H2S), for instance, can cause injury or death at 100 ppm or greater.  Odors may also stem from organic sulfur compounds (dimethyl sulfide, dimethyl disulfide, mercaptans, carbonyl sulfide, or carbon disulfide); nitrogen compounds (ammonia and amines); other volatile organic compounds (VOCs: aldehydes and ketones); and fatty acids.

Today, odor control is generally considered an essential process in municipal and industrial wastewater treatment plant design.  The Saudi government has begun requiring that newly built plants implement odor control for three main reasons.  As mentioned earlier, odor is not only a nuisance (meaning it smells bad), but in higher concentrations, it may pose a health hazard (especially to employees).  And when H2S is oxidized by bacteria, it forms sulfuric acid, which can corrode concrete sewer pipes and metal structures at a wastewater treatment plant. 

Liquid- vs. Vapor-phase Odor Control Treatment Options

There are two types of odor control treatment: liquid- and vapor-phase.  Whichever chemical compounds are causing the odor determine the best chemical, physical, or biological means of eliminating those chemicals or rendering them “odorless.”  The odor-causing compound, coupled with the point of origin, is important to selecting the right treatment method.  Costs, operational ease, and effectiveness should also be considered when assessing the correct technique for a particular application. 

Liquid-phase treatment is typically employed in wastewater collection systems or after treatment at the biosolids stage.  This type of treatment involves adding a compound directly into the wastewater to either control the formation of odor-causing compounds biologically and/or chemically or to react with odor compounds once they are formed. 
The four main types of liquid-phase treatment include: nitrates, anthraquinone, precipitants (iron salts), and oxidizers (like hydrogen peroxide).  When the cost for dealing with odor in this way gets to be too high, the upfront cost of capital equipment becomes more cost-effective. 

Vapor-phase odor control treatment differs from its liquid-phase cousin in that whereas the latter treats the entire wastewater flow, the former contains and treats odorous air that is released from a given process or area.  Odorous sources such as wet wells, headworks, clarifiers, equalization basins, sludge tanks, digesters, dewatering areas, and other treatment plant processes are covered, with a system of ducts and fans removing the odorous vapors from these areas.  Air is then pulled through a tank that contains some type of media to trap the odorous contaminant before discharging the air stream into the surrounding atmosphere.  This capital equipment falls under one of three primary categories: chemical scrubbers; bioscrubbers and biofiltration; and activated carbon systems.

Siemens Water Technologies is using all three types of vapor-phase odor control technologies successfully in projects throughout Saudi Arabia. 

Chemical Scrubbing

In Wady Al Dawasir, for instance, Siemens specified a chemical scrubber to meet the Ministry of Water and Electricity’s odor control needs.  The Ministry needed an odor control technology that could fit in a small space and respond immediately to fluctuating loads with high removal efficiencies in excess of 99%.  The Ministry opted to install a patented LO/PRO® multi-stage scrubber system that can target a range of compounds in a single scrubber system.  This multichemistry system will reduce chemical costs to less than half that required by conventional packed tower scrubbers. 

Chemical scrubbers are the most flexible, adaptable and reliable vapor-phase odor control technology that can be used to treat virtually any water-soluble contaminant.  Using a liquid to separate gaseous or particulate contaminants from a gas stream, multi-stage scrubbers can treat several odor compounds such as H2S and ammonia simultaneously.  Compared to other vapor-phase odor control technologies, scrubbers are less sensitive to variations in actual versus design H2S loadings.  Despite their small footprint, chemical scrubbers can handle air velocities of 2.5 m/s in a single vessel.  Although they can be maintenance-intensive and require chemical handling, the systems are easy to install at moderate capital costs.     

Biological Treatment

After comparing chemical and biological treatment options, Saudi Arabia’s National Guard decided that it would be more cost-effective to install two biological systems at its bases in Taif.  The ZABOCS biological treatment systems fit the military’s requirements: a green technology, it would not necessitate hazardous chemicals.  The systems would also require little maintenance, and could reduce H2S as well as other organic compounds. 

Biological odor control systems such as biofilters, biotrickling filters, and bioscrubbers are designed to promote the growth of sulfur-oxidizing bacteria.  These organisms, in turn, break down odorous compounds.  The systems will require constant nutrient replenishment and water as well as eventual media replacement. 

Bioscrubbers have a smaller footprint than biofilters, although in general, biological treatment systems have a larger footprint than other vapor-phase odor control technologies.  Capital costs are also higher, but operating costs are minimal as biological treatment does not require an on-going chemical supply.  Operating costs are also not proportional to H2S concentration, meaning these systems are well suited to high H2S applications.

Activated Carbon

A well-known Saudi refining company was contemplating installing activated carbon systems for H2S removal at its facility in Riyadh.  The company wanted the systems to be high-quality and expandable, yet simple and low-maintenance.  It also wanted a safe-to-handle media with a very high H2S loading capacity and high tolerance levels of VOCs and carbon dioxide. 

Siemens recommended installing six carbon adsorber odor control systems containing Midas® OCM carbon media.  After entering the vessels, foul air flows through a densely packed bed of activated carbon that removes H2S and other odor-causing organic constituents.  The media is virgin bituminous coal-based and not impregnated.  It has a very high adsorption capacity exceeding 0.30 g of H2S or VOC adsorption for each cm3 of carbon, giving it a capacity four to five times greater than other types of media.  Additionally, Midas media has a high ignition temperature, no dangerous pH problem when spent, and a low pressure drop.  The media does not require water or chemicals – only electrical power, to operate.  Carbon changeout is the primary maintenance required. 

Hybrid Systems

No single odor control technology is best in all applications.  Each technology has its advantages, and will be favored in certain applications.  Although cost is important, it should not always be the deciding factor.  When performance is most important, hybrid solutions that combine multiple technologies are often the best choice.  Examples of such systems include chemical followed by carbon; biological followed by carbon; biological followed by chemical; and biological followed by chemical followed by carbon. 

An industrial facility in Dhahran, for instance, is installing seven biological systems and four carbon systems.  As with the military installation in Taif, the facility discovered that biological treatment would be more cost-effective for its odor control needs – even after adding activated carbon to the mix.  Because the facility required multiple technologies, it preferred being able to obtain them all from one provider (Siemens), as opposed to from several.  Siemens’ diverse odor control product line allows it to customize the most appropriate solution to meet the facility’s odor control needs within specified capital and operational cost parameters. 

Likewise, the Ministry of Water and Electricity has authorized installation of all three kinds of vapor-phase odor control technologies at the North Jeddah sewage treatment plant.  As the plant is located near an airport, thorough and reliable odor control treatment is a must.  The tailored solution will consist of biological, chemical, and activated carbon technologies located at five areas throughout the plant.  Once completed, this will be one of the largest odor control installations in all of Saudi Arabia. 

Conclusion

Continued population and industrial growth and an increasingly hot and arid climate will ensure that the Kingdom of Saudi Arabia’s odor control needs progress well into the future.  To find the right solution, working with a reliable and accessible product and service provider is key.  The provider should thoroughly understand the facility’s needs and ideally suggest several solution options that address the facility’s odor concerns.  The solution provider should also be willing and able to work with area contractors that are most familiar with local needs and government requirements.    

For any given application, the selection of the best technology may be based on many factors, including capital and installed cost of equipment; operating cost and maintenance requirements; and size and safety as well as reliability and performance of the system.   When the cost of applying chemicals directly into the odor-causing wastewater becomes too high, using vapor-phase odor control technology will be more pragmatic. 

Each type of vapor-phase technology has its niche.  Chemical scrubbers have a smaller footprint than the other solutions, and can treat larger air flows in a single vessel.  Comparatively, biological systems have very lower operating and maintenance costs and do not require the use of hazardous chemicals.  Activated carbon systems are the simplest and easiest to maintain (excluding carbon changeout); these systems require only electrical power to operate (and thus, no water or chemicals). 

Sometimes a combination solution is required, to meet a facility’s odor control treatment needs.  These so-called hybrid solutions might consist of chemical followed by carbon; biological followed by carbon; biological followed by chemical; or biological followed by chemical followed by carbon. 

top of page