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The City of Los Angeles Hyperion Wastewater Treatment Plant (HTP), located on the pacific coast, is surrounded by densely populated upscale residential communities. Odors and pollutant emissions are a prime concern for HTP and the Primary Clarifiers are a significant potential source of odors and emissions.

Currently, the Primary Clarifiers are served by three separate odor control facilities with a combined ventilation rate of 31,200 cubic feet per minute (cfm). The existing odor control facilities consist of single stage wet scrubbers, followed by carbon adsorbers. The existing facilities are old and outdated, requiring extensive and escalating maintenance and operation expenses. Furthermore, measurements indicate an average hydrogen sulfide (H2S) removal rate below of the required by the process description, is being achieved by the exiting system.

The potential for increasing odor complaints from the neighboring residential community, as well as the need to modernize the aging facilities, triggered extensive studies of the Primary Clarifier air scrubbing systems. After extensive investigations, pilot programs and studies, the City of Los Angeles Bureau of Engineering designed and is in the process of constructing a single, centralized odor control facility for its Primary Clarification process. The new facility will employ a 3-stage wet chemical scrubber followed by carbon adsorption vessels. When constructed, the new facility will exhaust and treat 120,000 scfm of foul air, providing a Primary Clarifier ventilation rate of six (6) air changes per hour.

An extensive network of fiberglass ducts and control dampers will convey foul air from each Primary Clarifier to the Centralized Primary Clarifier Air Treatment System via a main supply duct. The new centralized facility will consist of six (6) independent trains. Each train includes: a stainless steel centrifugal fan, a fiberglass reinforced plastic (FRP) 3- Stage Chemical Scrubber and two FRP double-bed Carbon Adsorption vessels.

Each fan draws foul air from the main 7-foot diameter collector duct routed 20-feet above ground. Foul air enters the first stage of the chemical scrubber where contact with a mixture of re-circulation and fresh sodium hydroxide (NaOH) and sodium hypochlorite (NaOCl) occurs. In the second stage, provisions are made to use a solution of sulfuric acid (H2SO4) & NaOCl to minimize chemical consumption. The third stage uses NaOH to reduce residual chlorine odors.

After exiting the 3-stage scrubber, the air stream enters the two double-bed carbon adsorption towers, which are operated in parallel. The activated carbon functions as a polisher to remove the remaining sulfur compounds, VOC's and odors.

HTP has a chemical distribution system, which supplies chemicals to the local tanks at this facility. These tanks hold a 5 to 7 day supply of chemicals, which are fed to the scrubbers by gravity.

Aside from the improved odor control, the benefits of this project include reduced operation and maintenance costs due to consolidation of three facilities into one. In addition, the modular design of the 3-stage scrubber simplifies design and construction of the facility. It also allows for the standardization of the equipment.

The estimated construction cost is 6,500,000 and should take approximately 12 months to build. When completed, the City of Los Angeles Hyperion Wastewater Treatment Plant will own a state of the art foul air treatment facility.
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Document Type: Research Article

Publication date: 2004-01-01

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