By David H. Paul
Summary: In this last installment of a three-part series, the author discusses four more important considerations when embarking into the choppy seas of the membrane water treatment industry. This article will expound on the final four of 10 tips for water treatment dealers to keep in mind when selecting the appropriate membrane system.
Many public and private utilities and water treatment companies are evaluating the use of membrane technologies to meet current and anticipated drinking water needs. Whether evaluating, designing or building and installing membrane water treatment equipment, there are several important factors to consider. The author has chosen 10 tips for improving the design, operation and maintenance of a membrane water treatment system. To recap, the 10 tips are:
- Identify your feed water for fouling and scaling threats;
- Select a proven membrane product;
- Be conservative in the design;
- Conduct a well-designed 2,000-hour (minimum) pilot test;
- Critically evaluate the pilot test data;
- Select an experienced designer/contractor;
- Train personnel very well;
- Don’t wet the membrane until you’re ready to run continuously;
- Take complete start-up data, and
- Implement and monitor performance trends.
Part 1, which covered Tips 1-3, discussed some important things to do and check in the feasibility evaluation phase. Part 2 covered Tips 4-6 and provided suggestions on how to ensure the best overall system design through excellent pilot testing and using experienced designers and contractors. This article, Part 3, covers Tips 7-10 and focuses on what to do during startup and operation.
Indelible first impressions
In many cases, when a new membrane system starts up, it’s a facility’s first experience with membrane water treatment. There may be up to hundreds of person-years of experience at a particular plant with conventional water treatment (clarification, filtration and chlorination), but no in-house experience with membrane water treatment. Training will be required.
There will likely be “sticker shock” for the price tag of membrane water treatment training. Supervisors and managers are used to spending a relatively small amount for conventional water treatment training.
Many managers of facilities that utilize conventional water treatment are accustomed to sending employees to “short schools” and/or buying a book or two to prepare operating personnel for certification exams. There are several reasons why conventional water treatment training is so cheap relative to membrane water treatment training. These include:
- Membrane water treatment is relatively new.
- The number of people and facilities using conventional water treatment has, to date, been huge compared to the number involved with membrane water treatment.
- Because drinking water is regulated by state and federal agencies, many of the associated training programs have been, and remain, subsidized by local, state and federal funds. (NOTE: Subsidization lowers costs.)
Perhaps a quote from a presentation by Zenon Environmental Inc., a Canadian manufacturer of membrane products and systems, best puts the status of membrane water treatment in perspective: “Membranes are to water treatment what the microchip is to information technology.”
While reverse osmosis (RO) membrane technology has been commercially available since the 1970s and may be considered the most mature of the membrane technologies, membrane water treatment as a whole, if not in its infancy, is likely no more than in its adolescence—as far as market saturation.
Less costly over time
A few years ago, when the membrane market wasn’t as large, the cost of a standard RO membrane element was around $1,200. The cost of research, development and manufacture had to be spread out over relatively few buyers. Today, with large orders, a standard RO membrane element may only cost $400. Thus, there are many more buyers today making it a much more economical option.
The same is true for membrane water treatment training. While the cost is high in comparison with conventional water treatment training, the cost of producing and delivering the training has to be spread out over relatively few facilities. The cost will drop as the membrane water treatment market expands.
Typically the best time to budget for training is during the initial bid specification for the design and/or construction of a new system. The additional funds for training are usually the most palatable at this point, because of the small percentage it represents compared to overall cost. The following are recommendations for training:
- One month prior to startup: All personnel associated with the membrane water system are trained in the fundamental process, equipment, maintenance, monitoring and basic troubleshooting of the membrane unit. The purpose of the initial training is to ensure everyone knows the purpose and function of each piece of equipment as well as the difference between acceptable and unacceptable performance. In other words, people know when to raise the alarm that performance is degrading (it isn’t always obvious) and basically know how to fix the problem (chemical cleaning in many cases).
- Three to six months after startup: All personnel associated with the membrane water treatment system receive a review of the fundamental process, equipment, maintenance, monitoring and basic troubleshooting of the membrane unit. Their level of understanding will catapult based upon their months of real-world operating experience combined with lectures and hands-on training.
- During the first one to two years: At least two people at the plant should be trained in more advanced monitoring, troubleshooting and chemical cleaning of the membrane system. They monitor and interpret more detailed performance trend data (more on this later).
Hurry up and wait
The startup of a new system can be a crazy time. Hurry up, then wait… hurry up, then wait—over and over again. Original equipment manufacturers (OEMs) and contractors have schedules to meet. They need to hydro-test certain lines by certain dates and load membrane elements and check performance by certain dates.
A word of caution: The single-biggest potential problem with operating many membrane units is biofouling. You never want to load membrane elements into the pressure vessels, apply water to them, then let them sit for days or weeks while the computer control system, instrument loops or other equipment and sub-systems are made ready.
With the right bacteria, warm temperature and enough organic compounds (food) in the feed water, even being stagnant for less than a week can result in a subsequent dramatic reduction in performance. A biofouling process may begin that greatly increases chemical cleaning and even membrane element replacement costs.
Records, records, records
Many membrane manufacturers have software programs that provide a prediction of how a specific membrane unit will work on a given feed water and under what given conditions. This information can be very valuable. The most important data, however, are after the membrane system has been actually operating for 24-48 hours. This is called “start-up data.” All subsequent performance is referenced back to startup data.
Start-up data tell us how a new and clean unit operates on a particular feed water. These aren’t theoretical data from a software prediction program—these are real-world data. The author has, on several occasions, been hired to solve a costly performance problem at a membrane plant, only to find there are no start-up performance data. There’s no reference information as to how the unit ran in the beginning when it (supposedly) ran well.
One consulting job comes to mind where the problems cost the company nearly a half-million dollars per year in labor (overtime), membrane element replacement and cleaning chemical costs. The plant personnel were trained to monitor the RO units. They took the right data and created the right performance trends. The monitoring problem was that this was a “turnkey” job. The system wasn’t completely turned over to plant personnel for six months after the units actually began operating. The OEM took all of the data and the plant’s data were incomplete.
In the aforementioned case, the best you can do is chemically clean a unit extremely well and then, after operating for at least eight hours after the cleaning, take performance data and call it “start-up” data. You can never be sure the unit really is back to performing like new, however, without more extensive investigation and occasionally even autopsies of membrane elements.
Let’s say that we are at a large RO plant. The plant has been operating 24/7 for six months. Table 1 provides a list of a few operating parameters for one RO unit at startup and today.
How many operators do you know that would think there’s a problem when the same pressures, flows and quality of permeate are being produced? Only someone who really knows how RO membranes work might see that this unit is “really sick.”
As the temperature of the feed water increases, the amount of pressure required to produce an equal amount of permeate should decrease. That the feed pressure in the previous example remained the same indicates fouling (likely) and/or scaling is (are) occurring simultaneously with the temperature increase. If this problem isn’t caught at an early stage, cleaning back to new performance capability may be practically impossible.
As a minimum, the following must be monitored and trended:
- Normalized permeate flow (NPF)—(For nanofiltration and reverse osmosis applications). Scaling and/or fouling will cause NPF to drop. Membrane damage will cause the NPF to rise.
- Percent salt rejection (percent SR) or Percent salt passage ( percent SP)—(For nanofiltration and reverse osmosis applications). Membrane damage, o-ring leaks, and other membrane bypass problems cause the percent SR to drop or rise
- Trans membrane pressure (TMP)—the feed pressure minus permeate pressure (for ultrafiltration and microfiltra-tion applications)
- Differential pressure (DP or “delta P”) across each stage—Feed pressure minus concentrate pressure
If you’re considering membrane water treatment for the first time, there are things to watch and consider. This series of three articles covered 10 important tips. In this last installment, the need for excellent training, startup data and monitoring were emphasized.
About the author
David H. Paul is president of David H. Paul Inc, an advanced water treatment training and technical services firm in Farmington, N.M. He has over 25 years of experience in advanced water treatment, and has published over 100 technical articles and papers. He has created and administers a 4,000-page, college-accredited correspondence training program plus three on-campus college degree programs in advanced water treatment. He holds a bachelor’s degree in biology and a master’s degree in microbiology from New Mexico State University. Paul can be reached at (877) 711-4347, (505) 327-2934 (fax), email: firstname.lastname@example.org or web: www.dhptraining.com.