Odour control in the Kingdom
Siemens looks at the challenges in Saudi Arabia
By Georgios Ioannou
Georgios Ioannou, odour control technical sales manager at Siemens Water Technologies, examines the challenges in the Saudi water market
Odour control in Saudi sewage treatment plants has become more of a concern in the last decade. In previous years, this issue was considered more of a luxury rather than a necessity. Plants were located further out of town and, as a result, odours were not as noticeable. But odour complaints are now rising as population growth near existing plants and outside temperatures are increasing.
In the past, people did not understand that odours were not merely olfactory nuisances but rather that higher levels of odorous chemical compounds could produce hazardous gases. Hydrogen sulfide (H2S), for instance, can cause injury or death at 100 parts per million (ppm) or greater. Odours 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, odour 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 odour control for a number of reasons. A key concern is that when H2S is oxidised by bacteria, it forms sulfuric acid, which is able to corrode concrete sewer pipes and
metal structures at wastewater treatment plants.
Liquid- vs. Vapour-phase
There are two types of odour control treatment: liquid- and vapour-phase. Whichever chemical compounds are causing the odour determine the best chemical, physical, or biological means of eliminating those chemicals or rendering them “odourless.” The odour-causing compound, coupled with the point of origin, is important in 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 odour-causing compounds biologically and/or chemically or to react with odour compounds once they are formed.
The four main types of liquid-phase treatment include: nitrates, anthraquinone, precipitants (iron salts), and oxidisers (like hydrogen peroxide). When the cost for dealing with odour in this way becomes too high, the cost of capital equipment becomes more cost-effective.
Vapour-phase odour 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, equalisation 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.
In Wadi Al Dawasir, for instance, Siemens has specified a chemical scrubber to meet the Ministry of Water and Electricity’s odour control needs. The Ministry needed an odour-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 vapour-phase odour 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 odour compounds such as H2S and ammonia simultaneously. Compared to other vapour-phase odour 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 need chemical handling, the systems are easy to install at mild capital cost.
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 odour control systems such as biofilters, biotrickling filters, and bioscrubbers are designed to promote the growth of sulfur-oxidising bacteria. These organisms, in turn, break down odorous
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 vapour-phase odour 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.
A well-known Saudi refining company was contemplating installing activated carbon systems for H2S removal at its facility in Riyadh.
Siemens recommended installing six carbon adsorber odour 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 odour-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 cubic centimetre 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.
No single odour control technology is best in all applications. Each technology has its advantages, and will be favoured 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.
The Ministry of Water and Electricity has authorised installation of all three kinds of vapour-phase odour control technologies at the North Jeddah sewage treatment plant. As the plant is located near an airport, thorough and reliable odour control treatment is a must. Once completed, this will be one of the largest odour control installations in the whole of Saudi Arabia.
Continued population and industrial growth and an increasingly hot and arid climate will ensure that the Kingdom of Saudi Arabia’s odour 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 odour concerns. The solution provider should also be willing and able to work with those area contractors that are most familiar with local needs and government requirements.
Siemens Water Technologies’ Odour Control Capabilities
Siemens Water Technologies (formerly USFilter RJ Environmental Products) has been designing and building odour control systems for municipal and industrial customers since 1991. The company’s principal engineers have been working in the odour control field since its inception in the 1970s. Siemens offers a full range of vapour-phase odour control technologies including biological systems, biotrickling filters, chemical scrubbers, and a variety of activated carbon adsorption systems.
About the Author
Georgios Ioannou, PE, is an odour control technical sales manager at Siemens Water Technologies. His territory includes Europe, the Middle East, and Africa. He holds a MSc degree in Mechanical Engineering, and has worked for Siemens since 1998. Georgios is located in Athens, Greece, and can be contacted at (+30) 6936101300 or at Georgios.Ioannou@siemens.com.