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FINE PORE DIFFUSER CASE HISTORY FOR FRANKENMUTH, MICHIGAN
Citation:
Allbaugh, T. A. AND S. J. Kang. FINE PORE DIFFUSER CASE HISTORY FOR FRANKENMUTH, MICHIGAN. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-94/100 (NTIS 94-200888), 1994.
Impact/Purpose:
Information.
Description:
Frankenmuth is a community of 4,000 people in central Michigan. bout 25-3O% of the flow and 50-70% of the BOD load to the wastewater treatment plant are contributed by a brewery. In January 1986, conversion from a stainless steel broad band coarse bubble diffuser system to fine pore aeration was completed in all of the six existing aeration tanks. The Frankenmuth retrofit was designed with in-situ wastewater oxygen transfer efficiencies (OTE) at average air flow and peak flow based on off-gas tests at other location. These values were adjusted to account for the significant high strength industrial component of the influent wastewater. he design OTE at 2 scfm/diffuser was only two-thirds that used at 1 scfm/diffuser (aSOTEs of 16.9% and 11.0%, respectively). In spite of lower than expected OTES, the Frankenmuth retrofit to fine pore diffusers was an economic success. he actual capital cost of installation was slightly more than estimated during the evaluation period, but the projected energy savings appeared to be slightly greater as well. TEs were measured by off-gas testing on selected aeration cells on 13 different days between April 1987 and May 1988. Some of the off-gas tests were carried out on consecutive days before and after gas cleaning of the diffusers. No relationship could be developed between gas cleaning and OTE. The rate of diffuser plugging and fouling at Frankenmuth is significant. The plant staff has employed different methods of determining when cleaning should be done since the fine pore equipment was installed. These have included cleaning when the dynamic wet pressure (DWP) reached 16-18 in. w.g., cleaning with small doses of gas every 2 weeks, and operating at higher air rates than required for oxygen demand to hopefully inhibit biological growth on the diffusers. The first two methods employed in 1986 and 1987 appear to have been successful in maintaining acceptable levels of DWP and system performance. Operating at elevated air flows (January through June 1988) was probably successful in limiting DWP but resulted in a significant increase in system operating cost. The hydrogen chloride gas used was approximately one-third of a pound per diffuser per year during the evaluation state. The condition of the fine pore diffusers was monitored over the long term by measuring DWP and pressure drop across air distribution orifices in test diffuser assemblies. Four diffusers were placed in one of the six aeration cells, and measurements were obtained at 1 to 2 week intervals. No relationship could be developed between DWP and OTE. However, gas cleaning was effective in controlling diffuser DWP. This report was submitted in partial fulfillment of Cooperative Agreement No. CR812167 by the American Society of Civil Engineers under subcontract to McNamee, Porter & Seeley, Inc. under the partial sponsorship of the U.S. Environmental Protection Agency. The work reported herein was conducted over the period of 1986-1988. Project summary may be ordered as EPA/600/S-94/001).