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LONG-TERM PERFORMANCE CHARACTERISTICS OF FINE PORE CERAMIC DIFFUSERS AT MONROE, WISCONSIN
Citation:
Redmon, D. R., L. Ewing, H. Melcer, AND G. V. Ellefson. LONG-TERM PERFORMANCE CHARACTERISTICS OF FINE PORE CERAMIC DIFFUSERS AT MONROE, WISCONSIN. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-94/097 (NTIS 94-200854), 1994.
Impact/Purpose:
Information.
Description:
A study of the fine pore aeration system at the Monroe, Wisconsin wastewater treatment plant was conducted to monitor, over a 2-year period, the oxygen transfer efficiency (OTE) and fouling tendencies of four different effective pore size ceramic discs. The plant treats a mixture of municipal and industrial wastes. Major industrial contributions stem from breweries, dairies, and cheese plants that account for approximately half the organic load to the plant. The average plant flow during the study was 2.2. mgd, and the average influent BOD was 400 mg/L. The plant has three, two-pass aeration tanks, each with two independent aeration grids per pass. The diffusers for all but two of the 12 grids had a specific permeability of 26 (BRV of 6). The remaining two grids contained diffusers with specific permeabilities of 38 and 50 (BRVS of 4 and 3, respectively). Four pilot test headers were installed in the aeration cells. Each header had four diffusers with different effective pore sizes equivalent to the three types in the plant grid assemblies. Frequent off-gas surveys using floating hoods and Ewing off-gas analyzers were conducted during the first weeks of operation of newly cleaned and installed diffusers to observe OTE changes and fouling tendencies. Subsequently, OTE/fouling surveys were conducted at 4-month intervals. Each survey also included the removal of diffusers from the four test headers for analysis of BRV, DWP, OTE, affective flux rate, nature of foulant, and cleanability. These analyses were used along with the full-scale off-gas evaluations to identify when diffuser cleaning should be conducted. The range of optimum effective pore size as measured by BRV ranged from 4 to 7 in. w.g. This encompasses most of the common commercial ceramic diffuser products sold in the United States. Operating parameters and wastewater characteristics such as organic loading appeared to influence aSOTE more than did diffuser pore size. Only minor charges in DWP, BRV, and OTE were observed, indicating fouling at Monroe was not progressive. SOTE appeared to be insensitive to fouling. The adverse effects of fouling with respect to backpressure, OTE, and maintenance costs were found to be less than might have been predicted from the literature. The inexpensive cleaning procedures used in the study, involving a combination of high pressure water spraying with or without liquid acid treatment and/or brushing, followed by additional spraying, resulted in nearly complete restoration of the diffusers, original characteristics. The permeability test was not as effective in characterizing diffusers as anticipated. Other, more specific tests such as BRV and its coefficient of variation should be evaluated and considered. This report was submitted in partial fulfillment of cooperative agreement No. CR912167 by the American Society of Civil Engineers under subcontract to the Ewing Engineering Co. under the partial sponsorship of the U.S. Environmental Protection Agency. The work reported herein was conducted over the period of 1985-1988. Project summary may be ordered as EPA/600/S-94/001).