This is the second of a two part series on the adoption of PTFE layered EPDM membranes for wastewater aeration systems. We will continue by looking at more data. The empirical data collected by SSI to date the applications where PTFE layered EPDM has been installed as a replacement for conventional plain EPDM membranes, or side by side with conventional plain EPDM membranes is limited to two example applications, though we are attempting to collect additional information from both independent pilot studies and research, through our own tests, and through outreach to plants which replaced old technology with PTFE layered EPDM to learn from their experiences.

The two specific cases are the Agropur Dairy Cooperative in Quebec, Canada, and the Ringkobing Water Purification Plant in Denmark. In the case of Agropur, the plant has 4 basins of equal size in parallel flow, and has used EPDM membranes from 3 manufacturers, as well waxy bloom EPDM, silicone blended EPDM, and most recently PTFE layered EPDM from December 2004.

At the Agropur plant, after ten months of use the PTFE membranes showed less fouling than EDPM, as shown in the picture. With PTFE membranes maintenance frequency declined and a higher oxygen transfer for a longer time period was achieved. It is the first time the plant went more than a year without maintenance. In Figure 2 (left), the left side is typical of a plain EPDM membrane which must be acid soaked to clean, and a photo of a PTFE membrane which has been wiped clean with a stroke of a towel.

At Ringkobing another brand's diffuser had been installed.* The plant ordered SSI brand PTFE layered EPDM replacement membranes to retrofit into the existing plastic diffuser holders. We confirm that SSI PTFE membranes have been working for six months without clogging problems. Before the plant had to clean the EPDM membranes every 3-4 weeks! Figure 3 (right) shows the SSI PTFE membrane inside of the existing diffuser holder. The lines illustrate where the operator ran his finger along the surface and was able to clean the surface residue. It also illustrates that little to no fouling occurred in the slits.

Figure 4 (left) shows the PTFE membrane bubbling in a tank of clean water before the surface was wiped clean.

In both of the above cases, it was explained to SSI that the diffusers did not require cleaning, however it was the operator’s curiosity to look at the diffusers that drove them to drain the tanks and inspect them. In both cases, the surface bubble pattern was consistent with new and clean diffusers, the dissolved oxygen concentrations had not changed from new, and the diffuser headloss appeared not to have changed significantly.

It should be noted that both of the above are extreme examples of industrial plants with highly concentrated wastewater and proven foulants.

Over the course of the next few years, SSI believes that it can prove that in a typical municipal plant there is little to no change in alpha between a new PTFE and an aged PTFE membrane, and there is little to no change in delta P, with the help of independent research and the addition of further empirical examples. If this can be proven, wastewater plants of all sorts that install PTFE layered membranes will be looking at energy savings over the operating life of the plant of 30 to 40% with the added benefit of reduced maintenance and perhaps less frequent replacement requirements.

* The diffuser plastic holders shown in Figs. 2 and 3 were manufactured by the Nopon Group. SSI manufactured the membrane only and retrofitted our PTFE layered EPDM membrane into the existing holder. SSI is not related to any other diffuser company.

About the Author

Mr. Tom Frankle
Stamford Scientific International Inc.
4 Tucker Drive
Poughkeepsie, NY 12603

Telephone:  845.454.8171
Fax:  845.454.8094
Email:  info@stamfordscientific.com
Web site:  http://www.stamfordscientific.com/

Mr. Frankle is part of Stamford Scientific International Inc. which maintains production and support facilities for various products including: fine bubble diffuser, square diffuser, and tube diffuser and aeration systems.

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