Often times selecting membranes can be a confusing task. Most producers pick membranes on word of mouth suggestions or look up manufacturer's specification sheets. To compare membrane specifications directly, in one simple table, MES has compiled side by side specifications for select manufacturers, including MES. Are you tired of flipping through membrane spec. sheet after spec. sheet? Are you concerned about which salt rejection specification to look at? MES brings all of the pertinent specifications for all of the common membranes used in the maple industry into one simple table.
* Membrane specification were published without the addition of flow distributor technology. Flow increases in addition to test flow rate are proven.
One of the biggest questions we get here at MES is “what do you suggest I do for washing my membrane?” As a result, we are happy to provide this page to address this question as well as potential other membrane-related suggestions and ideas. This allows the user to access this type of information at any time. Ever been in the sugarhouse for the first RO cleaning of the year and find yourself asking, “how did I do this last year?”, and after 8 months or so away, it is common to feel rusty.
The MS2 membrane we offer can be washed for short periods of time up to a pH of 12 and as low as a pH of 1. During this time the maximum allowable temperature of the solution in contact with the membrane is 113°F (45°C).
Each operator chooses to wash their RO skid a little differently. During the season when a hot caustic wash is needed (sodium hydroxide, Ultrasil 10), we suggest starting the circulation of a wash solution from a wash tank, through the RO skid, and back to the wash tank. The friction of the fluid through the membrane coupled with recirculation pumps, naturally raises the temperature of the fluid. To protect the membranes, all traditional OEM machines have high temperature switches that will shut the RO skid off when it hits a preset temperature.
As the wash solution is circulated within the system, generally the pH of the solution will decrease over time. This is from the removal of organic fouling that counteracts the caustic solution. In addition, with a change of temperature of the solution, the pH will adjust with respect to this as well. It has been shown that pH and temperature play the largest part in cleaning of membranes within the maple syrup industry. Therefore, it is critical that the operator check and monitor the pH of the solution to make sure the desired pH is achieved. Ultrasil 10 is designed with a buffer that will not allow the solution to rise much above a pH of 12. This is our suggested membrane cleaning product and is available from MES or most OEM RO manufacturers within the maple syrup industry.
Basically what we do is thoroughly purge and rinse the RO skid of any sugar using permeate. Then fill the wash tank with the desired amount of permeate to wash with. Add the membrane soap to the wash water and bring up to a pH of 11 +/-. Let the RO skid circulate until the temperature reaches 90°F. Check the solution with your pH strips or a digital pH meter. Readjust the solution to the desired pH at this point. Allow the system the system to wash until the RO skid shuts off at the set temperature. Again thoroughly rinse the RO skid with permeate. If you are organic there are guidelines for the amount of permeate volume that needs to rinse out the RO skid after a wash.
For an acid wash of the membranes it is suggested that the same procedure is followed: monitor the pH of the solution over time and there may also be some temperature requirements to follow. Of course you should always be mindful of the cleaning suggestions that accompany your RO skid.
During the Offseason:
There are also many questions that involve what to do with membranes during the offseason. Some producers keep their membrane(s) in sap and allow fermentation to occur, then they wash the membrane prior to use for the next year. Others do a full cleaning regimen and store them in containers containing sodium solutions. Other operations add sodium solutions to their RO skids directly and leave the membranes installed. There is much controversy surrounding offseason storage and cleaning. Here at MES we suggest a full washing routine, with a caustic and an acidic solution, and then storage in a sodium solution. It is the opinion of MES that the best results have been proven with these steps. For further questions about offseason storage and cleaning, feel free to Contact Us today.
How do I know I need a wash?
Here at MES we suggest that you monitor your benchmarks. You may ask, "what is a benchmark?" Upon receiving a new membrane, a benchmark test should be performed on the membranes with permeate. We are able to tell the membrane flow rates when leaving the factory, but each RO skid is different and may produce a different flow. Documenting this benchmark is very important. By having this benchmark at any time during the season an operator can see what the flows are in relation to when they performed new. We suggest a wash when flows dip below 15% of the original flows.
How do I benchmark?
Benchmarking is a relatively simple practice and can be done very quickly. Just follow the following steps:
- Rinse the RO skid with permeate for approximately 15 minutes. Check for sugar coming from the system. Rinse time may need to be adjusted to remove the sugar.
- Change your RO skid parameters so that the skid will operate at 150 psi.
- Record permeate flows for each membrane. On some OEM skids this is not possible. Record what can be recorded in the most accurate way possible.
- Record the water temperature. You will need to refer to the correction chart to adjust your benchmark. (Link Provided Below)
What do I do with the benchmark data?
Now that you are successful in documenting the benchmark flows and temperature, its time to do some math calculations. This is how we can figure out if we need to clean the membranes or not.
Benchmark initial=10 gpm, 150 psi, 77°F
Benchmark Current=4.5 gpm, 150 psi, 43°F
Benchmark=permeateflow / temp correction factor
Benchmark= 4.5gpm / 0.54=8.3 gpm
Benchmark Loss=1-(corrected benchmark/initial benchmark)*100%
Our Suggestions would be to clean the membranes. If you as the operator follow the suggestions of 15% reduction in flows before washing, and you have taken the time to rinse the sugar from your RO skid, it would be an ideal time to wash. This of course may not be applicable to everyone due to undersizing an RO skid, high volume sap flows, etc.