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Biological odor control has gained acceptance in the US municipal odor control marketplace during the past decade.

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Biological odor control has gained acceptance in the US municipal odor control marketplace during the past decade. Varying strength and contaminants make no one technology appropriate for all odor control problems. As more is known about the processes that control these systems, the designs have moved from basic pit and pile compost biofilters to biological reactor systems that provide an order of magnitude reduction ten times in footprint with more control and predictability.

The Zero Acclimation Biological Odor Control System (ZABOCS®) Bio-Trickling Filter (BTF) from USFilter RJ Environmental Products reflects this evolution in the design process. The system is an advanced, non-hazardous biological air treatment system which combines gas absorption and biological oxidation to capture and then eliminate organic and inorganic odors from wastewater process air streams.

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The system consists of a Biotower and the Nucirc Process skid. The BTF vessel design integrates a resilient synthetic media in a vinyl ester fiberglass reinforced plastic (FRP) vessel. The Nucirc Process Skid is a standalone skid mounted system, which provides for ease of installation and process flexibility. The unique design allows for the operation of one or multiple BTF vessels. In addition, the system can be operated in recirculation or once through modes for accelerated acclimation and optimum performance.

The system has been tested in a number of successful pilot plant trials, with demonstrated 99% + removal efficiency of hydrogen sulfide (H2S) up to 300 ppm.

The Process

The ZABOCS biological odor control systems use bacteria to deodorize odorous airstreams. The BTF system first starts by inoculation with activated sludge. The activated sludge contains millions of bacteria species of sulfur-oxidizing bacteria. As the sulfur is oxidized, the pH of the recirculating water decreases, and only bacteria that can survive in low pH conditions remain active. The system preferentially favors the growth of sulfur-oxidizing, acidophilic bacteria. As the sulfur-oxidizing bacteria population increases, the H2S removal improves.

The system uses custom manufactured synthetic media which is well suited for growing target bacteria. The bacteria adhere to the media and thus come into intimate contact with the contaminants in the air stream. The odorous air flows upward through the media, while water containing nutrients and bacteria is trickled down over the top of the media. The media maximizes the mass transfer surface area and provides the rigidity for the support and growth within the biological film. The counter current flow enhances mass transfer to the wet surfaces, where the biological processes take place. Soluble sulfates are the byproducts of the biological reaction, and are absorbed and removed with the irrigation water.

There are seven standard sizes of ZABOCS BTF available, in addition to custom designs. The systems range from mid- to large-size capacity. They are pre-assembled, skid-mounted systems for compact, flexible operation and lower installation costs. The Nucirc Skid adjacent to the biotower contains nutrient and recirculation tanks, recirculation pump(s), nutrient metering pump, piping complete with irrigation water diffuser assemblies, and a three-way valve to allow for effluent reuse water and potable make-up water. The skid can accommodate operation of multiple BTF vessels.

Case Study

The Padre Dam Municipal Water District manages the water and wastewater supply for more than 125,000 people in the San Diego, CA, suburbs. The district has been operating a chemical scrubber at its wastewater treatment facility to control odors from the facility’s headworks. Significant chemical costs necessitated the district to identify alternative technologies. After investigating several odor control options, the district management decided to run a pilot test of a biological system in parallel to its existing system.

After consultation with USFilter RJ Environmental Products, the district chose to pilot test the ZABOCS BTF. In partnership with the engineers at Padre Dam, USFilter has been monitoring results for performance and maintenance requirements since October 2004. The system is constructed of FRP and plastic components for complete corrosion protection. The pilot system is capable of operating at 350 cfm and can treat H2S levels as high as 200 ppm.

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The pilot BTF started on October 11, 2004. After an expected four-week acclimation period the H2S removal efficiency stabilized at better than 99%. Following continued excellent performance over the next few months, Padre Dam concluded that the ZABOCS BTF was the most appropriate technology for this application. A full-scale system will replace the existing pilot system and will be operational in October 2005.

For more information about the ZABOCS BTF system, USFilter RJ Environmental Products at 858-486-8500. Or visit the company’s website at

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