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| Trickling filter odor control system. |
Winnipeg, Canada -- Hydrogen Sulfide (H2S) based odors emanating from wastewater treatment plants and lift stations are not only a source of concern for operator safety, but are an extreme nuisance for residential homeowners or users of near-by public facilities or property. The negative publicity and hassle caused by persistent nuisance odor complaints are costly in both time and money for cities or industries that own the odor-producing infrastructure.
H2S as well as numerous other odor causing compounds are generated as a result organic material decomposition in an anaerobic environment such as sewer force mains, lift stations, digesters or wastewater treatment plant head works.
The distinctive odor (rotten egg smell) of H2S gas is easily perceptible at very low levels (< 1ppm in air). Exposure to moderate H2S levels (10-50ppm) can cause headaches, dizziness, nausea and vomiting, coughing and breathing difficulty. Exposure to H2S Levels above 50ppm can result in severe respiratory tract and eye irritation and in extreme cases even death.
In addition to safety and nuisance odor concerns, the H2S can lead to the formation of sulfuric acid, which is very corrosive to all exposed steel and can lead to reduced life of concrete piping and structures.
UV Odor Control Process
Various technologies and processes such as ozone generators, chemical oxidizers (hydrogen peroxide, chlorine etc.) activated charcoal filters, essential oils (masking agents), and biofilters have been used in an attempt to reduce H2S levels. Problems associated with these processes typically revolve around high capital or operation costs and in some cases limited effectiveness.
Nelson Environmental Inc.’s Sol-Air UV based odor control system is a compact footprint process that utilizes patented multi–frequency Ultraviolet (UV) light. The technology harnesses the UV light in the UV-C and UV-V frequencies. The wavelength frequency is particularly “tuned” to produce highly radical hydroxyls, which rapidly oxidize a wide range of airborne odor producing compounds such as ammonia, H2S and mercaptans.
Ambient air is directed through the systems UV chamber. The ultraviolet light acts as a catalyst, breaking down the ambient oxygen and water vapor molecules into O- and OH- (hydroxyl) radicals. These short-lived free radicals go on to oxidize the more complex molecules found in the contaminant, while the radicals themselves are used up in the process. The end result is a sequential and instantaneous gas breakdown with very little by-product, in the form of odor and elemental traces, but mostly simple, harmless CO2, water vapor, molecular oxygen, trace ozone, elemental forms of N, S, CL, and weak mineral acids.
Because of the way that UV reacts with the water in the ambient air (to form oxygen radicals), it is not necessary to pass the contaminated air through the unit. The hydroxyls formed by passing ambient air through the system are dispersed throughout the contaminated air, either by injecting them into a lift station, or by placing the unit inside an odor filled room in a wastewater treatment plant. In some cases, such as a gas collection system, the contaminated air may be passed through the UV unit, but since the process relies only on moisture in the air passing through the UV lamps the method of treatment remains the same. In this way, a relatively small unit can treat the air in a large space, since a full air exchange is not required.
The UV process is easily adaptable for use in existing treatment plants or lift stations. It is also ideal in the treatment of odors originating in urban collection systems.
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| UV odor control system at a WWTP sludge loading facility |
For typical lift station applications the footprint of the process requires less than one square metre of floor space. The unit can either be installed inside a building or in most cases the system can simply be set outside with treated air injection piping running to the lift station or manhole. A standard 30-amp 110V electrical service is adequate to operate all but the largest custom built units.
The system does not require any on-going chemical costs or disposal of contaminated odor adsorption media.
Wastewater Treatment Plant Odor Control Case Study
A 13,000 m3/day wastewater treatment plant in Vernon, British Columbia experienced citizen complaints regarding offensive odors. The headworks area and the trickling filter were identified as the sources of H2S.
In 2001, a total of 8 Sol-Air UV units were installed in the City of Vernon Reclamation Plant. Four modified off-the-shelf units were installed in the grit room and head works, which re-circulate the air in each room. Four larger custom units were installed around the perimeter of the trickling filter, exhausting processed air to the atmosphere.
The UV process proved to be extremely effective in reducing odor levels at these locations, at a fraction of the cost of other odor control technology considered. Offensive odors were eliminated from the grit room/compressor and the trickling filter.
Lift Station Odor Control Case Study
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| Direct injection of UV produced oxgen radicals into a lift station wet well. |
An existing lift station in Kamloops, British Columbia is located several meters from a new condominium development. Sulfurous odors were escaping from lift station into the development, prompting complaints by neighbors. The odors were so severe, that the condominium developer temporarily relocated condo owners to local hotels. Previous attempts with other technologies had failed to stem the problem.
A carbon filter was installed, but results did not meet expectations. In addition, maintenance was difficult, and disposal of contaminated filter medium was an ongoing issue.
The City purchased an eight-lamp UV odor control unit for the lift station. It was installed in the existing building, which previously housed the carbon filter and brought the odor under control very quickly. Reduced odor was reported within minutes of turning on the system. Residents are back in their condominiums and odor complaints have ceased.
Summary
Sol-Air’s UV system is a cost effective way to eliminate odors from sewage lift stations and treatment plants. A well-designed system can eliminate odor complaints from residents and reduce workplace hazards for operators in addition to reducing in-plant corrosion resulting from excessive H2S. For more information on UV based odor control contact: mkroeker@nelsonenvironmental.com or call 1-888-426-8180.
About Nelson Environmental Inc.
Nelson Environmental Inc. and associated companies have more than 75 years of construction and 35 years of wastewater design experience. Hundreds of systems have been installed in Canada, the USA and Mexico. We have successfully completed projects from simple restoration of back yard ponds to full “turn-key” design and construction of large industrial wastewater treatment plants.
For more information contact:
Lionel Ens, P.Eng.
Nelson Environmental Inc.
101 Dawson Road
Winnipeg, MB
Canada, R2J 0S6
Telephone: 204-949-8731
Fax: 204-237-0660
Web site: http://www.nelsonenvironmental.com/
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