In 2003, USFilter provided the industry with a valuable guide to help evaluate whether membrane technologies may work for specific filtration needs. A follow-up article went one step further to answer more detailed questions pertaining to drinking water and wastewater treatment applications.
This third article in the series addresses the overwhelming industry response to the membrane technology information and includes questions contributed by customers, consulting partners, Memcor employees and others with an interest in the industry.
Q: What criteria should be considered when comparing different membrane manufacturers?
A: There are many criteria that should be considered, but some of the most important are outlined below. It is recommended that users carefully evaluate each of these for any membrane system being considered for a facility.
Lifecycle costs should factor not only the purchase price of the membrane system, but all operating costs including power, labor, chemicals, and membrane replacement. Selecting a system on capital cost alone may not—and usually does not—provide the lowest total cost of ownership. Over the life of the system, operating costs often become a greater expense than its purchase price.
Additionally, system reliability involves not only durability and system uptime, but also—and perhaps more importantly—the level of support provided by the manufacturer. It is important to understand the potential manufacturer’s demonstrated customer service experience, financial strength and commitment to the market.
Q: Membrane systems have been installed at hundreds of locations. Have there been some challenges along the way?
A: It is true that whenever a new technology is introduced to the marketplace, there is a higher probability of system underperformance than with demonstrated technologies. On the other hand, avoiding emerging technologies usually means missing out on a major opportunity for a more efficient or better performing system.
The issue then isn’t what if something happens, but rather how to be prepared to resolve a problem quickly if it does. Ask manufacturers how they would solve operational difficulties should they occur. Reputable manufacturers with an established track record, who are committed to remaining in the market and possess the financial resources to meet these obligations, are the most likely to accept the responsibility of correcting problems quickly.
Q: I know integrity testing is key to evaluating membrane performance, but I’ve heard testing isn’t standardized for all manufacturers. How can the integrity of the integrity test itself be measured?
A: A proper integrity test should measure the integrity of the entire system including valves, seals, potting interfaces, etc., not just the hollow fiber membranes themselves. The test pressure is calculated by using a membrane contact angle, which is the angle relative to the membrane surface at which an air bubble forms and escapes through a pore. One problem: contact angle cannot be measured in situ, and laboratory measurements do not reflect the wetting properties of fouled membranes in real-world conditions.
When a manufacturer allows the membrane contact angle to solely determine the pressure level, integrity tests are conducted at a lower pressure level providing a lower gauge of a membrane system’s reliability and security. Memcor performs tests at the highest and most conservative pressure; therefore, this integrity test more rigorously evaluates system performance.
Q: Pilot testing is expensive. Can we avoid pilot testing and move directly into the design phase?
A: Without regulatory approval, pilot testing is required, and in some areas it is mandatory. If the same system being considered has been piloted in the area with the same water conditions, the pilot testing phase may not be necessary.
Because testing was not required in their respective areas, some utilities have successfully designed systems based on no current or previous pilot testing. However, the design criteria are typically very conservative when pilot test data is unavailable. This often translates to an incremental increase in capital cost that can actually exceed the cost of pilot testing.
Q: As a municipal director, if I decide to invest in an MBR system to produce higher quality effluent, does that mean I can profit from the reuse capabilities?
A: This is an interesting question. There have been cases where utilities and even privately owned and operated wastewater treatment facilities have implemented MBR technology and generated a profit by reselling the high-quality effluent. The economic circumstances must be in alignment for this to occur, but when this happens, the results can be compelling.
The attributes that favor the sale of MBR treated effluent are usually present in areas where building moratoriums have limited development, where the cost of potable water is high or the cost to treat raw water is prohibitive, in areas where the need for water and the sources of supply are dislocated, and in arid climates where water is scarce. When one or more of these conditions exist, there is an opportunity to profit from high quality reclaimed water sales.
Q: I’ve heard the term “intergenerational compatibility.” It sounds great in theory, but are there any real-life examples of its positive impact?
A: Memcor uses this phrase to describe system designs that allow for future membrane improvements. As membrane technology evolves, new membrane components can be installed in existing Memcor systems. There have been several examples, but perhaps the most significant and most recent is the evolution of the Memcor CMF system to utilize a liquid backwash as opposed to a gas backwash. This new design, referred to as CMF-L, employs a highly permeable oxidant tolerant membrane to attain higher flux rate at lower pressure. The CMF-L design is not only available to new customers, it is ideally suited for retrofit into existing CMF systems.
In May 2004, Pottawatomie County, Okla., made the decision to retrofit from CMF to CMF-L. The retrofit took less than a week to complete, and it significantly improved the performance of the plant. A reduction in operating pressure and air consumption of 45%, and a reduction in wastewater of 58% resulted in lower operating costs.
In addition, the cleaning intervals have been reduced from every three or four weeks to well over four months.
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