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The Irwin Creek and Sugar Creek wastewater treatment plants (WWTPs) operated by Charlotte-Mecklenburg Utilities (CMUD) currently use chlorine gas for effluent disinfection. Because of safety concerns and regulatory issues associated with the continued use of chlorine gas, CMUD and Camp Dresser & McKee (CDM) conducted a comprehensive study to evaluate the use of alternative disinfection techniques at both WWTPs. The alternative disinfection techniques evaluated in the study included: (1) continued use of chlorine gas with a scrubber system, (2) sodium hypochlorite, and (3) ultraviolet (UV) disinfection. Based on the results of the study, UV disinfection was selected as the preferred disinfection method at both facilities due to overall present worth costs, as well as numerous non-cost benefits including the elimination of toxicity issues related to chlorination/dechlorination by-products and the higher level of safety that UV disinfection provides to plant employees and the surrounding public.

After UV was selected as the preferred disinfection method, a detailed evaluation of the available current UV system technologies for wastewater disinfection was conducted. UV system technologies investigated included: (1) open channel, low-pressure, high-intensity systems, (2) open channel, medium-pressure, high-intensity systems, and (3) closed vessel medium-pressure, highintensity systems. A total of seven UV systems were analyzed for potential implementation at the Sugar Creek and Irwin Creek WWTPs in Charlotte, NC. Analyses included extensive coordination with each UV manufacturer through a detailed equipment questionnaire, face-to-face meetings, and correspondence with installation references. Based on company performance qualifications and experience, present worth and capital cost evaluations, and operation and maintenance (O&M) requirement comparisons, the CMUD and CDM project team determined that the Trojan 3000 Plus, WEDECO, and ODI open channel, low-pressure, high-intensity UV systems and the Aquionics closed-vessel, medium-pressure, high-intensity UV system were acceptable systems for meeting the design requirements at both facilities. After narrowing the list of pre-approved UV systems to four, CMUD proceeded with an equipment procurement process that would allow for competitive bidding for the UV supplier scope of work to be implemented at each WWTP.

This paper details how an owner and engineer can successfully provide competition in the UV market through implementation of an equipment procurement process prior to final design of the system to reduce overall project costs. In addition, the initial evaluation and determining factors leading to this decision are discussed. For this project, CMUD and CDM collaborated to produce a set of 40 percent design drawings for each of the four pre-approved UV systems. Final technical specifications for both the open channel low-pressure, high-intensity systems and the closed vessel medium-pressure, high-intensity system were developed and included within the equipment procurement bid package. Each interested UV manufacturer bid for the UV supplier scope of work detailed in the specifications that included all equipment, materials, supervisory installation and training labor, and installation testing services. Furthermore, the bid required each manufacturer to provide guaranteed components life and replacement prices for lamps, ballast, quartz sleeves, and wiper seal assemblies.

Because electrical and maintenance costs are a significant cost over the life of a UV disinfection system, the basis of award for the UV manufacturer scope of work was based not only on the capital cost of the specified UV system, but also on the 20-year present worth O&M costs and the capital cost impacts of constructing each UV system structure and/or associated buildings. The equipment bidder with the lowest total net present worth construction and O&M cost was recommended for award. Upon award, final design for each facility was completed based on the awarded low bidder. The paper will present the complete results of the competitive bid process.
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Document Type: Research Article

Publication date: 2003-01-01

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