Effects of fouling?

[mantispid]

What are the general effects of fouled membranes?

I'm trying to troubleshoot my situation with 150GPD residental membranes. I have one that started passing 1% sugar in the permeate. Does fouling cause sugar to pass, or does it simply slow down flow rate? I'm still fairly new at this. I'm going to try a full flush, including with peroxide, and see if that restores things.

[Clinkis]

Fouling is caused by a build up of foreign matter on the surface of the membrane (bacteria, organic matter, dirt, etc.). It is usually caused by too low a flow rate, not flushing frequently enough, plugged or contaminated pre filter and poor sanitation practices. A really good flush with permeate and peroxide and a new prefilter should fix it. The results of fouling are little to no permeate flow. It should NOT cause suger to pass. If sugar is passing then most likely you have a damaged membrane or membrane seal. Remove membrane in question and inspect seals. Any chance your RO froze? It's possible you might just have a faulty membrane.

[mantispid]

I run the membranes inside the house, so no possibility of freezing. I did have the system shut down for 2 days though and it is quite possible that there was a fair amount of bacterial growth. The odd thing is, the membrane in question was the second in a series. The other two (first and third) are working fine.

The whole system was working fine 3 days ago.

I've been putting it through a full flush and hydrogen peroxide cycle. I'm thinking I might leave the peroxide in the lines for a few hours though instead of just 15 min. Would that be a bad thing?

[mantispid]

After the full flush, it seems the problem isn't quite as bad as it was.

#2 was moved to the first position, and it is passing about 0.3%, while #1 and #3 are passing 0.1% (the permeate from all three is reading 0.2%). Concentrate line is reading about 5.7%. Until I can get a replacement membrane for #2, I can live with losing 0.2% sugar.

[Clinkis]

Interesting.....like I said, fouling will not causing suger to pass. In fact it causes nothing to pass not even water? My membranes are 2 years old and I always detect 0 to less then .1% suger in my permeate. What type of membranes are you using?

[mantispid]

Interesting.....like I said, fouling will not causing suger to pass. In fact it causes nothing to pass not even water? My membranes are 2 years old and I always detect 0 to less then .1% suger in my permeate. What type of membranes are you using?

I'm using this one:

Axeon TF Series 150GPD Residential RO Membrane (http://www.amazon.com/Axeon-Polyamide-Composite-Drinking-Membrane/dp/B005L4ZOMY/ref=sr_1_1?ie=UTF8&qid=1396036792&sr=8-1&keywords=150+gpd)

The distributor says that these won't yield 0 TDS, which is fine.. The ones that work pass about 1-2 PPM dissolved solids (basically the minerals in the sap). The bad one passes about 10-15ppm. So far I've worked out that 2-8ppm TDS correlates to about 0.1-0.2% sugar. 20ppm TDS corresponds to about 0.5% sugar (all in the permeate line). About 300-330ppm is about 5% sugar, and around 430ppm is about 6% sugar (in the concentrate line). Of course this likely only works for the sap generated by the trees on my land, as I'm sure the mineral content isn't exactly proportional to the sugar content.

[mantispid]

After talking with the manufacturer, it seems that one shouldn't use hydrogen peroxide to clean these membranes, though at 0.015% it isn't likely to damage them very quickly if used for less than 30 minutes. The manufacturer recommends using buffered sodium hydroxide at a pH of 11... then running through a buffered hydrochloric acid solution at about pH 2. Looks like I'm going to need to get a pH meter and some caustics.

[Clinkis]

I use the Dow 100gpd membranes so I can't comment on the ones you have as I'm not familiar with them. I only do a peroxide rinse a couple times a season as usually just a permeate flush will fully recover them. I don't think at that concentration level and frequency there would be any significant damage to the membranes IMHO. I do recall reading that the 150 GDP membranes were more susceptible to fouling because they require a higher flow rate. That said, there should still be no effect on the amount of suger passed. Just curious, how are you measuring your permeate? Its tough to get an accurate reading at those levels. I was told to get an accurate reading you need to concentrate a certain level of permeate and then measure that.

[mantispid]

I use two methods. One is to use an in-line TDS meter (http://www.amazon.com/HM-Digital-DM-1-In-Line-Accuracy/dp/B001EHAZGW/ref=sr_1_1?ie=UTF8&qid=1396061807&sr=8-1&keywords=in+line+tds+meter). It gives me a real time estimate of the amount of ionic material flowing through both the permeate and concentrate lines. I also have a digital refractometer (http://www.amazon.com/Milwaukee-Refractometer-Automatic-Compensation-Resolution/dp/B007Z4IN58/ref=sr_1_1?ie=UTF8&qid=1396061837&sr=8-1&keywords=digital+refractometer). It is accurate down to 0.1% (+/- 0.2%, but seems like margin of error only applies to the higher sugar concentrations). The refractometer and the TDS meter corroborate each others'r results. 3-7 ppm TDS = ~0.1% sugar in the permeate. 8-14 is about 0.2%, and 14-25 is about 0.3%. Also, I taste the permeate and concentrate. My tongue is pretty good at detecting sugar down to 0.2%.

Currently I'm concentrating 2.1% sap to 5.5% concentrate, and losing 0.3% sugar to the permeate line (I'd like to go to 6%, but I'll lose more sugar in the permeate). I have a replacement membrane on order, but it won't be here in time to deal with the sap I have now. I may run the 0.3% sugar permeate through the RO to try to recover it, but I only run about 150 gallons of unconcentrated sap at most over a weekend, so it may not be worth it.

[Clinkis]

It's might be worth taking a couple gallons of permeate and boiling it down and retesting it. As you stated, +/- .2% is a very high tolerance to be trying to make those readings at.

[mantispid]

True, but the fact that the readings fall in line with the TDS meter make believe the refractometer data. Plus, the permeate tastes like diluted sap.

[Clinkis]

True, but the fact that the readings fall in line with the TDS meter make believe the refractometer data. Plus, the permeate tastes like diluted sap.

I guess I'll have to tske your word for it! You must have a more sensitive tongue then I have. I have a hard time detecting suger at times in regular sap! Lol
I tried to find the post but can't....it went into detail about confirming sugar content in permeate and it involved boiling down some and retesting it and the various calculations. If your bored sometime may be worth searching for. It was an interesting read.

[mantispid]

I ran out of sap to concentrate, so I decided to concentrate the permeate using the system. Had to reduce the concentrate flow considerably, but it's now producing 0% permeate and 5% concentrate. Of course, that's coming from the old permeate contaminated with 0.5% sugar...

[Clinkis]

That's a good way to do it. If you are concentrating permeate down to 5% you are definitely passing suger.