United States Environmental Protection Agency Risk Reduction Engineering Laboratory Cincinnati, OH 45268 Research and Development EPA/600/S-94/001 September 1994 EPA Project Summary Design Information on Fine Pore Aeration Systems Field studies were conducted over several years at municipal wastewater treatment plants employing line pore diffused aeration systems. These stud- ies were designed to produce reliable information on the performance and operational requirements of fine pore devices under process conditions. The results of the studies provided critical input to a comprehensive treatise on the subject entitled "Design Manual - Fine Pore Aeration Systems." This document, prepared by the American Society of Civil Engineers' (ASCE) Oxy- gen Transfer Committee, was published in 1989 and is available to the public. The above studies resulted in 16 separate contractor reports as part of a cooperative research agreement with ASCE. Abstracts of each contractor re- port are given here. This Project Summary was developed by EPA's Risk Reduction Engineering Laboratory, Cincinnati, OH, to announce key findings of field studies that are fully documented in separate reports (see Project Report ordering informa- tion at back). Introduction In 1985, the U.S. Environmental Pro- tection Agency (EPA) funded a coopera- tive research agreement with ASCE to evaluate the existing data base on fine pore diffused aeration systems in both clean and process waters, conduct field studies at a number of municipal waste- water treatment facilities employing fine pore aeration, and prepare a comprehen- sive design manual on the subject. This manual, entitled "Design Manual - Fine Pore Aeration Systems," was completed in September 1989 and was first distrib- uted at the 62nd Annual Water Pollution Control Federation Conference in San Francisco, CA, October 1989. Copies of the Design Manual (EPA report no. EPA/ 625/1-89/023) are available from the EPA Center for Environmental Research Infor- mation (CERI), Cincinnati, OH 45268. An earlier "Summary Report - Fine Pore (Fine Bubble) Aeration Systems" was published in October 1985 to document the early findings of this study and summarize the state-of-the-art at that time. This Sum- mary Report is also available from CERI (EPA/625/8-85/010). Data generated on the field studies con- ducted at municipal wastewater treatment plants were important sources of informa- tion for the Design Manual. These studies were undertaken as contracts under the cooperative research agreement. They were selected primarily to address techni- cal issues and data base inadequacies identified in the 1985 Summary Report. The field studies were composed pri- marily of investigations on the performance of various fine pore diffuser generic types in process waters (i.e., under field condi- tions), diffuser operating characteristics and fouling rates, and operation and main- tenance requirements including cleaning of partially fouled diffusers. In addition, an interplant diffuser fouling evaluation was carried out to relate observations and trends to wastewater characteristics and process operating conditions. A corollary interplant study used microbiologically based procedures to describe biofouling Printed on Recycled Paper ------- phenomena on fine pore aeration devices and to determine whether biofilm charac- teristics could be related to diffuser per- formance parameters. Several studies were conducted at facilities having suffi- cient prior Information to enable case his- tories to be developed. Finally, a survey of European experience with fine pore rigid porous plastic diffusers provided additional information to supplement the North Ameri- can data base on this class of diffusers. Each of the above field studies resulted in a separate contractor report. These re- ports are referenced throughout the De- sign Manual. A brief abstract of each contractor field report is given below. These abstracts are intended to provide sufficient information to identify those reports that may be of individual interest as supplements to the Design Manual. Abstract of Reports 1. "Fine Pore Diffuser System Evalua- tion for the Green Bay Metropolitan Sewerage District' (EPA/600/R-94/ 093) by J.J. Marx The Green Bay Metropolitan Sewerage District retrofitted two quadrants of their activated sludge aeration system with fine pore ce- ramic disc and plasticized PVC per- forated membrane tube diffusers to evaluate and compare the savings in energy use with that of the sparged turbine aerators originally installed. Because significant dif- fuser fouling was expected, the two diffuser types were closely moni- tored over an 18-mo period. The oxygen transfer efficiencies (OTEs) of the full-scale systems were mea- sured by using off-gas techniques. The effects of diffuser fouling and the effectiveness of diffuser clean- ing procedures were evaluated in the laboratory with the use of dy- namic wet pressure (DWP) and steady-state clean water oxygen transfer tests. Although significant fouling was encountered on both types of dif- fusers, cost-effective cleaning pro- cedures were developed. The ceramic disc diffusers provided bet- ter long-term performance with pe- riodic cleaning than did the plastidzed PVC membrane tube dif- fusers, which irreversibly lost OTE with time in use. Collectively, the fine pore diffuser systems provided a 30% savings in electrical power use compared with that of the origi- nal sparged turbine aerators. 2. "Oxygen Transfer Efficiency Sur- veys at the Jones Island Treatment Plants, 1985-1988" (EPA/600/R-94/ 094) by R. Warriner Ceramic plate diffusers were among the earliest forms of fine pore diffusers used for oxygen transfer in activated sludge treat- ment. They have been successfully used for over 60 yr in the Jones Island West Plant of the Milwaukee Metropolitan Sewerage District (MMSD) and in the MMSD Jones Island East and MMSD South Shore Plants since 1935 and 1974, re- spectively. Results of off-gas sam- pling surveys carried out at the original Jones Island West Plant, which was scheduled for rehabilita- tion in 1988-90, and in the newly rehabilitated East Plant are re- ported. Twenty-one (21) basin sur- veys were carried out in the West Plant and 30 in the East Plant. For the West Plant basins, equipped with the original ceramic plate diffusers installed in 1923 and 1924, the median value of stan- dardized oxygen transfer efficiency under field conditions, aF(SOTE), was 11.8% at 15 ft of submergence. For the East Plant basins, which contained new plate diffusers in- stalled in 1983, the median value of «F(SOTE) was 15.3% at a sub- mergence of 14 ft. Cleaning history was noted for each basin at the time of each off- gas survey. A relationship between time-in-service since cleaning and OTE was not established in these surveys; however, a short-term im- provement in OTE following clean- ing was indicated in the East Plant. Because alpha was unknown and varied widely between surveys, and possibly during surveys, it was dif- ficult to separate alpha effects from fouling effects on OTE. For the most part, extended periods of basin op- eration had no measurable effect on performance. 3. "Fine Pore Diffuser Fouling: The Los Angeles Studies" (EPA/600/R- 94/095) by M.K. Stenstrom and G. Masutani Fine pore diffuser evaluations conducted at three different waste- water treatment plants located in the greater Los Angeles area are described. The overall goal of the study was to evaluate the perfor- mance of fine pore diffusers by us- ing selected cleaning methods for extended periods of time at selected treatment plants. The major part of this study was conducted at the Whittier Narrows Water Reclama- tion Plant, operated by the Los An- geles County Sanitation Districts. This study evaluated fine pore ce- ramic disc and dome aeration sys- tems using HCI acid gas cleaning and a ceramic dome aeration sys- tem without acid gas cleaning over a 25-mo period. A second study, smaller in scope and effort, was conducted at the Valencia Water Reclamation Plant (also operated by the Districts). This study evalu- ated fine pore rigid porous plastic disc diffusers over a 13-mo period. A third study, also smaller in scope and effort than the Whittier Nar- rows study, was conducted at the Terminal Island Wastewater Treat- ment Plant, operated by the City of Los Angeles. In this study, the per- formance of a perforated membrane tube system and a parallel nonrigid porous plastic tube system was evaluated over a 12-mo period. The principal indicator of the per- formance of the different aeration systems was OTE, as measured by off-gas analysis. For the Whittier Narrows study, changes in diffuser characteristics were also reported. The fine pore ceramic disc aera- tion system at Whittier Narrows, which was acid gas cleaned, per- formed better than both the ceramic dome system that was acid gas cleaned and the control ceramic dome aeration system that received no cleaning. Part of the differences in performance between the disc system and the two dome systems was attributable to mechanical prob- lems with the domes. The cleaned and uncleaned dome systems had comparable OTEs during the study. Relatively consistent performance was observed for the rigid porous plastic disc system at Valencia over the 13-mo study period. The tube systems at Terminal Island exhib- ited high variability because of op- erational differences, and one tube system experienced significant foul- ing over a relatively brief period. The variability in performance of ------- the several aeration systems dur- ing day-to-day changes in plant load and operating mode was an impor- tant finding of the study. 4. "Oxygen Transfer Studies at the Madison Metropolitan Sewerage District Facilities" (EPA/600/R-94/ 096) by W.C. Boyle, A. Craven, W. Danley, and M. Rieth Field studies at the Madison Met- ropolitan Sewerage District facilities were conducted over a 3-yr period to obtain long-term data on the per- formance of fine pore aeration equipment in municipal wastewater service. The studies were con- ducted on several basins in the East Plant containing ceramic domes in- stalled in 1977 and two sets of first- pass basins in the West Plant containing newly installed ceramic discs. The performance of the domes was excellent even after 10 yr of service. This conclusion was based on OTE as measured by off-gas analysis, alpha calculations, and dif- fuser characterization. Reasons for excellent performance included rou- tine maintenance of the diffusers and the use of high quality ceramic diffusers and hardware. Evidence was presented for this plant that operation at high solid retention times (SRTs), i.e., low food-to-mi- croorganism loadings, which pro- duced complete nitrification, resulted in higher aF(SOTE) val- ues than did operation at low SRTs. Results of studies on the impact of diffuser cleaning and hydraulic flow patterns on performance are also reported. The ceramic discs in the West Plant were monitored for 800 days. In that period, no perceptible de- crease in diffuser performance was observed based on aF(SOTE) measurements. The mean first-pass «F(SOTE) values over 800 days were about 11.5% at a submer- gence of approximately 15 ft. The mean-weighted «F(SOTE) for all three passes ranged from 12.1% to 15.3%. The West Plant aeration system was operated at high SRT values to achieve complete nitrifi- cation. As seen in the East Plant, some evidence of improved aera- tion performance [aF(SOTE)] with increased SRT was noted. Brief ex- aminations of diffusers in these low- loaded basins suggested that fouling was not a problem in this plant. 5. "Long-Term Performance Charac- teristics of Fine Pore Ceramic Dif- fusers at Monroe, Wisconsin" (EPA/ 600/R-94/097) by D.T. Redmon, L Ewing, H. Melcer, and G. V. Ellefson A study of the fine pore aeration system at the Monroe, Wl, Waste- water Treatment Facility was con- ducted over a 2-yr period to monitor the OTE and fouling tendencies of ceramic discs with four different permeabilities. The plant, which treats a mixture of municipal and industrial wastewaters, consisted of three two-pass aeration tanks, each containing two independent aera- tion grids per pass. In 10 of the 12 passes, disc diffusers with a spe- cific permeability of 26 were em- ployed. The remaining two grids contained disc diffusers with spe- cific permeabilities of 38 and 50. OTE was monitored by off-gas analysis. Fouling tendencies and ef- fectiveness of cleaning were deter- mined by using diffusers obtained from separate pilot test headers, which were then analyzed in the laboratory. Results of this study indicated that the clean diffuser bubble re- lease vacuum (BRV) and its coeffi- cient of variation were better measures of effective pore size of ceramic diffusers than was perme- ability. Although OTE increased with decreasing permeability (increasing clean diffuser BRV) in clean water, the operating conditions of the plant and its wastewater characteristics appeared to influence aF(SOTE) more than did effective pore size. Although fouling was visually ob- served on the ceramic discs under certain operating conditions, it had little apparent effect on a F(SOTE), BRV, or DWP. Little correlation was shown between fouling tendencies and permeability at this plant over the range of permeabilities tested. Inexpensive cleaning procedures were used in the laboratory. These involved a combination of high pres- sure water spraying with or without liquid acid treatment and/or brush- ing, followed by additional spray- ing. Laboratory cleaning resulted in nearly complete restoration of the diffusers' original characteristics. 6. "Case History of Fine Pore Diffuser Retrofit at Ridgewood, New Jersey" (EPA/600/R-94/098) byJ.A. Mueller and P.O. Saurer In April 1983, the Ridgewood, NJ, Wastewater Treatment Plant was partially retrofitted from a coarse bubble to a fine pore ceramic dome diffused aeration system. The pro- cess was also modified from a con- tact stabilization to a tapered aeration activated sludge treatment regime. A case history of plant and aeration system performance from 1981-1986 is presented. Extensive aeration studies were conducted on the fine pore system in 1985 and 1986 to observe changes in OTE with time and evaluate cleaning fre- quency requirements to maintain efficiency at a viable level. An eco- nomic evaluation including bid prices, maintenance costs, and pay- off period based on power savings is included. Over the 6 yr of study, the coarse bubble system exhib- ited an average aF(SOTE) of 4.8% (at a submergence of approximately 13 ft) with an average «F value of 0.55. Over 3.75 yr of operation, the fine pore dome diffusers produced an average aF(SOTE) of approxi- mately 9.5% (at a submergence of approximately 14 ft) during normal operation with an average a F value of 0.4. A significant improvement in effluent quality with respect to nitri- fication in the summer months was observed with the fine pore system when compared with the coarse bubble system, which achieved no nitrification. 7. "Oxygen Transfer Efficiency Sur- veys at the South Shore Wastewa- ter Treatment Plant, 1985-1987" (EPA/600/R-94/099) by R. Warriner Ceramic plate diffusers were among the earliest forms of fine pore diffusers used for oxygen transfer in activated sludge treat- ment. They have been successfully used for over 60 yr in the Jones Island West Plant of the Milwaukee Metropolitan Sewerage District (MMSD) and in the MMSD Jones island East and MMSD South Shore ------- Plants since 1935 and 1974, re- spectively. Twenty basin off-gas sampling surveys were carried out at the South Shore Plant, yielding a median aF(SOTE) value of 18.9% at a submergence of 15 ft. When evidence of nitrification was present, aF(SOTE) values were higher than on other survey dates. A diffuser cleaning history was ob- tained at the time of each off-gas survey; however, no correlation be- tween the number of months-in-ser- vice since cleaning and aF(SOTE) could be identified. 8. "Fine Pore Diffuser Case History for Frankenmuth, Michigan" (EPA/ 600/R-94/100) by T.A. Allbaugh and SJ. Kang In 1986, the Frankenmuth, Ml, Wastewater Treatment Facility, which treats a mixture of municipal and industrial wastewaters, was ret- rofitted with fine pore ceramic discs. Significant flows received by the plant from a brewery and a large restaurant produced high soluble or- ganic loadings on the aeration tanks. Off-gas tests were conducted over a 1-yr period on 13 different days to determine the effects of acid gas cleaning and operation at elevated airflow rates on the per- formance of the fine pore system. The rate of diffuser fouling at the plant was significant. Acid gas cleaning was typically initiated when the DWP reached 16 to 18 in. (wa- ter gage). Gas cleaning was effec- tive in controlling the DWP at this plant, but little effect was observed on OTE. 9. "Off-Gas Analysis Results and Fine Pore Retrofit Information for Glastonbury, Connecticut" (EPA/ 60Q/R-94/101) by R.G. Gilbert and R.C. Sullivan The Town of Glastonbury, CT, retrofitted one of its two aeration tanks in 1983 with rigid porous plas- tic tube fine pore diffusers in a spi- ral roll configuration. These tubes were placed on existing swing arms used for the original coarse bubble spargers. An extensive aeration system performance evaluation us- ing off-gas analysis was conducted involving six separate investigations over a 35-mo period. The ccF(SOTE) measurements aver- aged 6.6.% at a submergence of approximately 12 ft; this represents a 57% increase in OTE compared with the average 4.2% aF(SOTE) value estimated for the original coarse bubble spargers. The retro- fit simple payback period was less than 18 mo. 10. "Off-Gas Analysis Results and Fine Pore Retrofit Case History for Hart- ford, Connecticut' (EPA/600/R-94/ 105) by R.G. Gilbert and R.C. Sullivan In 1986, the Hartford Water Pol- lution Control Plant in South Mead- ows, CT, was retrofitted from a coarse bubble, spiral roll system to a fine pore ceramic dome, grid-con- figured system. Four of six aeration tanks were involved in the retrofit. Extensive off-gas studies were con- ducted over 18 mo to evaluate the performance of the new system and to determine the effectiveness of diffuser cleaning. The aF(SOTE) measurements averaged 10.0%; this is more than double the aver- age a F(SOTE) value estimated for the original coarse bubble, spiral roll aeration equipment. The retrofit simple payback period was less than 3 yr. 11. "The Measurement and Control of Fouling in Fine Pore Diffuser Sys- tems" (EPA/600/R-94/102) by E.L. Barnhart and M. Collins The purposes of this study were to define the efficiency of various methods of cleaning fine pore dif- fusers and to develop a methodol- ogy that could be used to evaluate the efficiency of several cleaning techniques. Fouled ceramic dome diffusers from the North Texas Mu- nicipal Water District were cleaned with these techniques, and the im- provement in OTE was measured. The domes were reinstalled in the aeration tanks and withdrawn at various time intervals thereafter. The deterioration in OTE was then noted. The cleaning techniques were repeated, and the improve- ment in transfer was recorded. Overall, the domes from the North Texas Plant did not exhibit severe fouling. Low-pressure hosing ap- peared to be as effective as any other method in cleaning the domes. The domes deteriorated promptly after they were reintro- duced into the aeration tank, and aF(SOTE) stabilized. The technique of using an off- line aeration tank for studying dif- fuser cleaning techniques provided mixed results. The comparative ef- fectiveness of cleaning techniques appeared to be properly described in this small test tank. The break- down of slimes and fouling materi- als during dome transportation and handling, however, may have caused an underestimation of the degree of fouling. 12. "Fouling of Fine Pore Diffused Aera- tors: An Interplant Comparison" (EPA/600/R-94/103) by C.R. Baillod and K. Hopkins The objective of this study was to assess the relative fouling ten- dencies of fine bubble diffusers at nine activated sludge treatment plants. A secondary .objective was to relate fouling to mixed liquor and process parameters. A standardized diffuser test header containing four removable diffusers was installed at each of the participating plants. Diffusers were periodically removed and tested for OTE, BRV, DWP, foulant accumulation, and increase in OTE after acid cleaning. The results of this study showed that an increase in BRV was gen- erally accompanied by a decrease in OTE, an accumulation of foulant, and an increase in DWP loss through the diffuser. The plants were classified according to their degree of fouling (as measured by BRV). The classifications were heavily fouling (Jones Island West, Wl and Frankenmuth, Ml), moder- ately fouling (Green Bay, Wl, North Texas, TX, and Whittier Narrows, CA), fouling (South Shore, Wl and Portage Lake, Ml), and lightly foul- ing (Madison, Wl and Monroe, Wl). Observations at individual plants suggested that high organic loads enhanced fouling, although inter- plant comparisons suggested a weak association between fouling and organic load. 13. "Case History Report on Milwau- kee Ceramic Plate Aeration Facili- ties" (EPA/600/R-94/106) by LA. Ernest Ceramic plate diffusers were among the earliest forms of fine pore diffusers used in activated sludge treatment. They have been used for 60 yr in the Jones Island West Plant of the Milwaukee Met- ropolitan Sewerage District (MMSD) and in the MMSD Jones Island East and MMSD South Shore Plants since 1935 and 1974, respectively. The Jones Island East Plant aera- tion basins were completely reha- bilitated in 1982-83, and the West ------- 14. Plant basins were scheduled for re- habilitation in 1989-90. In both cases, alternative fine pore systems were evaluated and ceramic plate diffusers were again selected. Three separate case history reviews are presented: the Jones Island East Plant, the Jones Island West Plant, and the South Shore Plant. All of the historical reviews dis- cuss the conceptual designs and selection processes involved for each of the plants. The review of the Jones Island West Plant covers the period from the start-up of the activated sludge plant in 1915 through the planned rehabilitation in 1989-90. The Jones Island East Plant history begins with start-up in 1930 and discusses in some detail the comparisons of optional fine pore diffuser layout patterns with the original ridge-and-furrow full floor diffuser coverage pattern. The East Plant review also includes the history of the 1982-83 retrofit to diffuser plates installed in concrete containers placed at right angles to the basin flow and with the diffuser surface flush with the floor. In the South Shore history, the concept of the layout and design of the con- crete containers is discussed. The South Shore Plant history, covers the time from initial plant start-up in 1974 to 1988 and describes how the results at South Shore formed the basis for the Jones Island East and West Plant rehabilitations. "Survey and Evaluation of Porous Polyethylene Media Fine Bubble Tube and Disk Aerators" (EPA/600/ R-94/104) by D.H. Houck Historically, although alternative media materials have been em- ployed over the years with varying degrees of success, the principal fine pore diffuser medium has been porous ceramic. In the early to mid- 1970s, diffusers with rigid porous plastic media were installed in sec- ondary treatment plants in Europe, primarily in Finland and Sweden. To document operation and main- tenance experiences with rigid po- rous plastic media diffusers, 11 plants in Europe were visited. Observations made at each site and the review of on-site, long-term operation and maintenance infor- mation are discussed. In general, it was concluded that the rigid po- rous plastic diffusers were perform- ing satisfactorily. It was also concluded that the use of ferrous sulfate for precipitation of phospho- rus in wastewater treatment facili- ties was the most adverse fouling condition encountered in applica- tions of these diffusers. The most effective cleaning method for this type of fouling was found to be formic acid gas treatment followed by an air/water backwash with spe- cialized equipment. The effective- ness of similar cleaning for biofouling was inconclusive. The design and application of aeration systems using rigid porous plastic media diffusers appeared to be similar to those employing ceramic media diffusers. 15. "Investigations Into Biofouling Phe- nomena in Fine Pore Aeration De- vices" (EPA/600/R-94/107) by W. Jansen, J.W. Costerton, and H. Melcer Microbiologically based proce- dures were used to describe biofouling phenomena on fine pore aeration devices and determine whether biofilm characteristics could be related to diffuser process per- formance parameters. Fine pore dif- fusers were obtained from five municipal wastewater treatment plants in Wisconsin, one in Michi- gan, and one in California. Biofilm thickness and carbohydrate content were measured as was each film's ability to retain air bubbles. Scan- ning electron microscopy (SEM) procedures were used 1o examine biofilm structure. The effect of four different laboratory cleaning proce- dures on diffuser characteristics was also measured. A parallel labora- tory-scale investigation simulated microbially induced fouling of small- scale diffusers and the effects of bleach and acid cleaning. Microbial fouling of the diffusers occurred irregularly at all seven sites. The thickness of a biofilm and its distribution over a diffuser appeared to vary randomly. Highly structured biofilms were observed by SEM and were thought to inter- fere with the passage of air bubbles such that the size of the bubbles released from a fouled diffuser sur- face was probably not the same as those from a cleaned and unfouled diffuser surface. Two types of biofoulant were observed. One ap- peared to reduce OTE with mini- mal impact on diffuser headless as measured by DWP. The second appeared to increase DWP with minimal impact on OTE. Although measurements of biofilm thickness and carbohydrate content did not appear to be directly related to mea- surements of OTE, DWP, and BRV, the microbiological measurements contributed to an improved under- standing of diffuser operation and performance. The laboratory investigations showed that the progressive devel- opment of a bacterial biofilm on the surface of a fine bubble diffuser could increase the size of bubbles released from the fouled surface. Five-percent bleach was found to be more effective in removing the biofilm than 14% HCI on both artifi- cially induced and naturally occur- ring biofilms, and a combination of bleach followed by acid returned the diffusers to their original condi- tion. 16. "Characterization of Clean and Fouled Perforated Membrane Dif- fusers" (EPA/600/R-94/108) by L Ewing and J. Kitzinger Laboratory analyses were con- ducted on plasticized PVC perfo- rated membrane tube diffusers after varying periods in service at two different municipal wastewater treat- ment facilities. One set of diffusers from Cedar Creek, NY, was in ser- vice for 26 mo. The other set from the Green Bay Metropolitan Sew- erage District facility was in service for approximately 47 mo. Tests on the membranes included DWP, flow uniformity, weight, dimensions, ten- sile modulus of elasticity, hardness, and OTE. Results of this brief study indi- cate a significant increase in DWP and decrease in flow uniformity and OTE after service. Following mem- brane cleaning, measurements in- dicated: a nonrecoverable reduction in DWP below that of a new mem- brane; an increase in specific grav- ity, durometer hardness, and circumferential modulus of elastic- ity; and a decrease in weight, length, and strain at failure. These findings were in good agreement with other field tests performed with these diffusers. The full reports were submitted in par- tial fulfillment of Cooperative Research Agreement CR812167 by the American Society of Civil Engineers under the par- tial sponsorship of the U.S. Environmental Protection Agency. ------- 7?7/s Project Summary was authored by The Steering Subcommittee of the ASCE Committee on Oxygen Transfer. ASCE headquarters are in New York, NY 10017. Richard C. Brenner is the EPA Project Officer (see below). The complete reports are entitled: "Fine Pore Diffuser System Evaluation for the Green Bay Metropolitan Sewerage District," (Order No. PB94-200813; Cost: $27.00, subject to change); "Oxygen Transfer Efficiency Surveys at the Jones Island Treatment Plants, 1985-1988," (Order No. PB94-200821 Cost: $19.50, subject to change); "Fine Pore Diffuser Fouling: The Los Angeles Studies," (Order No. PB94- 200839; Cost: $27.00, subject to change); "Oxygen Transfer Studies at the Madison Metropolitan Sewerage District Facilities," (Order No. PB94-200847; Cost: $27.00, subject to change) ; "Long-Term Performance Characteristics of Fine Pore Ceramic Diffusers at Monroe, Wisconsin," (Order No. PB94-200854; Cost: $27.00, subject to change); "Case History of Fine Pore Diffuser Retrofit at Ridgewood, New Jersey," (Order No. PB94-200862; Cost: $27.00, subject to change); "Oxygen Transfer Efficiency Surveys at the South Shore Wastewater Treat- ment Plant, 1985-1987," (Order No. PB94-200870; Cost: $17.50, subject to change); "Fine Pore Diffuser Case History for Frankenmuth, Michigan," (Order No. PB94-200888; Cost: $19.50, subject to change); "Off-Gas Analysis Results and Fine Pore Retrofit Information for Glastonbury, Connecticut," (Order No. PB94-200896; Cost: $27.00, subject to change); "Off-Gas Analysis Results and Fine Pore Retrofit Case History for Hartford, Connecticut," (Order No. PB94-200938; Cost: $27.00, subject to change); "The Measurement and Control of Fouling In Fine Pore Diffuser Systems," (Order No. PB94-200904; Cost: $27.00, subject to change); "Fouling of Fine Pore Diffused Aerators: An Interplant Comparison," (Order No. PB94-200912; Cost: $19.50, subject to change) ; "Case History Report on Milwaukee Ceramic Plate Aeration Facilities," (Order No. PB94-200946; Cost: $19.50, subject to change); "Survey and Evaluation of Porous Polyethylene Media Fine Bubble Tube and Disk Aerators," (Order No. PB94-200920; Cost: $19.50, subject to change); "Investigations into Biofouling Phenomena in Fine Pore Aeration Devices," (Order No. PB94-200953; Cost: $19.50, subject to change); and "Characterization of Clean and Fouled Perforated Membrane Diffusers," (Order No. PB94-200961; Cost: $17.50, subject to change). These reports will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Risk Reduction Engineering Laboratory U.S. Environmental Protection Agency Cincinnati, OH 45268 ------- ------- United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 Official Business Penalty for Private Use $300 EPA/600/S-94/001 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 ------- |