Seasonal change to TDS in water maker output

[BeBe]

I assume the Eastern Med salinity increases during the dry season.

Is my assumption correct about the Med salinity...and, if so, what should I expect for TDS in water maker output? In other words, should output TDS increase with an increase in input salinity?

I am curious as to what your Med experience is. In most places in the world, we have been able to maintain close to or under 200 TDS in product water. We presently find it difficult to get below 300. We have a 160l/hr 230v water maker with 2 each FilmTec Membranes SW30-2540 (3 years old).

Interested in any similar experiences.

Bill

 

[Marsupial]

from my experience over the last 3 years (Greece Ionian and Aegean, Turkey SW) salinity is pretty much constant all the year round (the med is in essance a saturated solution small seasonal variations are not measurable with my kit) , output from the membrance does vary in accordance with feed water temperature, TDS of product water is stable at less than 5 for the whole year - if that helps.

edit: It takes around 5 mins for the TDS to fall from 250 ish to 5 at 250 (on my metre) the water tastes very brackish so I woiuld investigate why your kit is showing a high TDS, of course TDS metres are known to be "variable" - taste is the best indicator - so mine at 5 may be the same as yours at 200 - we will never know.

 

[[81549]]

Hi

We also noticed the rise in TDS in the med, we used to get 180 in the atlantic now it averages 290.

I asked Katadyn about this, they say 300 is still a very good Tds.

I think the med is generally a much saltier sea so the product water will have a higher tds

Charlie.

 

[Marsupial]

Hi

We also noticed the rise in TDS in the med, we used to get 180 in the atlantic now it averages 290.

I asked Katadyn about this, they say 300 is still a very good Tds.

I think the med is generally a much saltier sea so the product water will have a higher tds

Charlie.

Well they would wouldn't they?


Just copied this from the webb:

"in terms of TDS, typically potable water is rated by municipal entities as 250 and below. this is actually very high and I would reccomend getting below 100. High TDS does stress kidneys and liver function. Most off the shelf bottled water will be anywhere from 5 to 100. A good reverse osmosis system will produce a water product that has a TDS below 10, even below 5 or even down to fractions"

300 is terrible, I calibrate my TDS meter with bottled and distilled water, I would suggest a clean of the membrane.

 

[crisjones]

I think it is clear from the replies in this thread that the biggest variable in TDS readings is actually the meters themselves!!!

The best indicator of product water acceptability is taste - a true TDS figure of over 600 should be easy to taste as brackish water, any product water that does no have any salty taste is likely to be fine and should be a good enough indicator that the watermaker is operating OK.

Our TDS meter gives readings between about 200 and 600ppm but the water always tastes perfectly fresh. I really must check our meter with the calibration solution!!!!

I would say that a good watermaker is unlikely to produce water at less than 10ppm, more likely would be a range of between 50 and 200ppm - these are obviously true TDS figures NOT onboard handheld meters of questionable accuracy.

Basically if your product water tastes "fresh" then all is OK. A TDS meter reading will never tell you how "clean" the product water is regarding bacteria, viruses etc - you need to employ other methods after production for this, although we never do any after treatments to our watermaker product water and we have suffered no ill effects.

 

[BeBe]

Just copied this from the webb:

"in terms of TDS, typically potable water is rated by municipal entities as 250 and below. this is actually very high and I would reccomend getting below 100. High TDS does stress kidneys and liver function. Most off the shelf bottled water will be anywhere from 5 to 100. A good reverse osmosis system will produce a water product that has a TDS below 10, even below 5 or even down to fractions"

300 is terrible...

I know that you said that you "copied from the web," but do you honestly believe that there are water makers made for yachts that will achieve less than 100? Your research is flawed. Yes, you are right for reverse osmosis product water from fresh water input, but you are wrong regarding salt water input.

Spectra (who I do not recommend and do not have) states 500 is good. From the 7 years experience of our circumnavigation in all of the oceans of the world, 150 - 250 is good...sometimes near-100 is achievable. This is based on actual experience of about 30-40 yachts around the world that absolutely have to rely on water makers for fresh water. My experience and network of experienced people is lacking now that we have arrived in the Med. I was searching for "local knowledge and experience," which I lack in the Med.

Comments and Amplifications:

• There was a comment about calibration of the meter with calibration solution. I recently did this and it is perfect.
• Another comment about the importance of taste is very good, but confirmation of taste by TDS meter is the best test.
• There was a comment in another forum suggesting cleaning/sterilizing the membranes. This will not lower the TDS, but will sometimes increase production. I do not have a production issue.

Frankly, I believe it is time to change the membranes if I want to achieve 200 or less. When they are new I usually get close to 100.

Thanks for all of your comments.

 

[crisjones]

The performance of membranes is quoted as % of stabilised salt rejection, normally over 99.7%. This obviously means that higher salinity intake water will result in slightly higher salinity (TDS) product water. Typical seawater is 35,000ppm while central Med is 40,000 and Red Sea 42,000ppm. So Med waters typically contain 14% more salt than open oceans hence your product TDS is likely to be up to 14% higher.

Water temperature is also a factor with higher intake temperatures giving higher TDS product water. Dow Filmtec recommend reducing membrane pressure slightly to compensate for higher temp and salinity in intake water to bring the product TDS down.

Performance of membranes will reduce over time and the most notable reduction is in product water flow rate - all other factors being equal. TDS will vary over time and may increase slightly but you will normally need to change membranes because of reduced output rather than increased TDS. I would not change membranes until the output TDS was consistently over 500ppm even after reducing membrane pressure.

I have just checked our records and find that our system when new and operating in cold 16 Deg C atlantic waters would produce product water at around 200PPM. Now in central med with water temps around 26 Deg and higher salinity we get around 450ppm, however I still use 800psi membrane pressure and our product water output has increased from around 2l per min to 2.25 l per min, a 12.5% increase in output. No doubt reducing the pressure will reduce output and TDS, probably back to the original parameters or close to it anyway.

I am happy with our product water, nobody we have asked is able to taste any hint of salt in the product water so we will continue as we are. If product ppm rises a bit more I will reduce membrane pressure to compensate.

 

[BeBe]

Good information

The performance of membranes is quoted as % of stabilised salt rejection, normally over 99.7%. This obviously means that higher salinity intake water will result in slightly higher salinity (TDS) product water. Typical seawater is 35,000ppm while central Med is 40,000 and Red Sea 42,000ppm. So Med waters typically contain 14% more salt than open oceans hence your product TDS is likely to be up to 14% higher.

Water temperature is also a factor with higher intake temperatures giving higher TDS product water. Dow Filmtec recommend reducing membrane pressure slightly to compensate for higher temp and salinity in intake water to bring the product TDS down.

Performance of membranes will reduce over time and the most notable reduction is in product water flow rate - all other factors being equal. TDS will vary over time and may increase slightly but you will normally need to change membranes because of reduced output rather than increased TDS. I would not change membranes until the output TDS was consistently over 500ppm even after reducing membrane pressure.

Thanks, I did not know the Med increased percentage...that accounts for some of the increase.

 

[[81549]]

Hi bebe,

I posted a similar quetion on cruising forum under water problem ?

Take a look it received several knowledgable replies similar to crisjones.

I think our watermakers are giving similar results in the med ie around 300, which is vgood, i have come to the conclusion that you have to clean your prefilter alot more in the med, which i now fo after each run and this has helped keep tds stay stable.

Charlie.

 

[BeBe]

Stabilized Salt Rejection (%)

I read the specs on the DOW FILMTEC SW30-2540 Membranes and it states, "Stabilized Salt Rejection 99.4%."

So, with input at 42000PPM and Rejection at 99.40% = 252TDS under perfect circumstances with average salinity. Some spots may be saltier.

All of this accounts for my current TDS at 250-290.

Thanks for everything...

Bill

 

[Marsupial]

I know that you said that you "copied from the web," but do you honestly believe that there are water makers made for yachts that will achieve less than 100? Your research is flawed. Yes, you are right for reverse osmosis product water from fresh water input, but you are wrong regarding salt water input.

Spectra (who I do not recommend and do not have) states 500 is good. From the 7 years experience of our circumnavigation in all of the oceans of the world, 150 - 250 is good...sometimes near-100 is achievable. This is based on actual experience of about 30-40 yachts around the world that absolutely have to rely on water makers for fresh water. My experience and network of experienced people is lacking now that we have arrived in the Med. I was searching for "local knowledge and experience," which I lack in the Med.

Comments and Amplifications:

• There was a comment about calibration of the meter with calibration solution. I recently did this and it is perfect.
• Another comment about the importance of taste is very good, but confirmation of taste by TDS meter is the best test.
• There was a comment in another forum suggesting cleaning/sterilizing the membranes. This will not lower the TDS, but will sometimes increase production. I do not have a production issue.

Frankly, I believe it is time to change the membranes if I want to achieve 200 or less. When they are new I usually get close to 100.

Thanks for all of your comments.

who got out of the wrong side of the bed today?

sorry but I am unable to conduct accurate research I dont have a lab on board, all I can say is the product from my water maker is acceptable and my TDS meter suggests its the almost the same as bottled water, sorry if that offends you.

According to my membrane supplier its time to clean the membrane when TDS rises - but not the only time, when product production falls is another.

Been drinking the stuff for a few years now - but what do I know . . . you see I have only used the machine in the atlantic and the med so yes my experience is limited.

have a nice day

 

[crisjones]

Not sure why Sulaire needs to clean his filters so often in the Med!! Med waters are generally crystal clear, there is much less plankton and bacterial organisms in Med water than in the Atlantic hence the clarity of the water.

The clear water should be ideal for watermaking, albeit with slightly higher salinity and should not cause rapid blockage of filters unless you operate the watermaker in obviously murky water.

We have a pressure guage on the inlet to the high pressure pump, a decrease in this pressure will indicate blocked or dirty filters. So far this summer with over 40hrs use the hp pump inlet pressure has remained a constant 12psi. We have a 50micron mesh filter with a clear plastic bowl as the first seawater filter and this has been cleaned twice this summer with hardly any debris found each time. We then have std industrial 10" 10 and 5 micron filters, these have not been changed or cleaned all summer, I hope to get through the whole summer without changing them. For winter the filters will be thrown away before pickling the system, new filters will be fitted in spring. I see little reason for trying to clean these filters when they can be purchased for less than 10 euros online or from plumbing suppliers - dont buy then from marine outlets!!!

 

[Sybaris]

We have a 160l/hr 230v water maker with 2 each FilmTec Membranes SW30-2540 (3 years old).

Interesting thread with a lot of good information. I have a few comments and further questions.

Production rate
Bebe states a production of 160l/h with two SW30-2540 membranes. We have the same membranes and a 60Hz 2HP electric motor connected to a 3.6GPM General Pump. When I do the calculations based on the throughput of the pump, and the 8% production figure quoted in filmtec literature I get the following:

8% of (3.6GPM) 817 lit/h is 65 liters per membrane, i.e. 130 liter/hour

This is consistent with what I have produced over the last few years in the Med.

Question to BeBe: What pump kind of pump do you have? and how much does it pump per hour.

Note: I am in the process of changing to a 50Hz generator which means that my pump will only produce around 2.9GPM and I guess I will end up with about 100 lit/hour.

Pre-filters
Someone gave me the tip to remove and sun-dry the pre-filters after each run. I have until now only used one pre-filter (10 micron) and followed that advise, but are now questioning it. Having read an extensive Filmtec manual they state that air in the system damages the membranes over time. Every time I put in a dry membrane I guess the membrane threads must contain air which is then passed through the membranes.
I am now in the process of rebuilding our watermaker and have installed 2 pre-filter housings and intend to use (as crisjones) a 10 and a 5 micron filter.

Question: What type filters do you use, thread spun? or others?

Pressure
I normally run at 800psi but have tested slightly higher settings and found that the production rate went up, AND the ppm went down (i.e. more AND better quality water). The drawback being, according to Filmtec, more wear on the membranes.

Temperature
I find that the ppm goes up with the temperature (summer vs other seasons) and the salinity (Med. vs the Red Sea)

Water Quality
Our production quality in the Med has been around 250ppm until lately which seems consistent with others on this thread. I test the TDS meter from time to time with purchased mineral water to make sure it is not way off.

Membranes
I bought two new membranes while on a visit to Florida in February but have not had time to install them yet. The box they came shipped in has been left unopened until recently, and when I opened it I noticed that the plastic wrapping of one membrane had vacuum, and the other didn't, i.e. the second wrapping must have been pierced. I am now worried about installing them because I seem to recall having read that they cannot be dry when stored. Any comments??

 

[BeBe]

Interesting thread with a lot of good information. I have a few comments and further questions.

Production rate
Bebe states a production of 160l/h with two SW30-2540 membranes. We have the same membranes and a 60Hz 2HP electric motor connected to a 3.6GPM General Pump. When I do the calculations based on the throughput of the pump, and the 8% production figure quoted in filmtec literature I get the following:

8% of (3.6GPM) 817 lit/h is 65 liters per membrane, i.e. 130 liter/hour

This is consistent with what I have produced over the last few years in the Med.

Question to BeBe: What pump kind of pump do you have? and how much does it pump per hour.

Note: I am in the process of changing to a 50Hz generator which means that my pump will only produce around 2.9GPM and I guess I will end up with about 100 lit/hour.

BeBe:
Dessalator D160 system at this link:http://www.dessalator.fr/en/products/d90-d200-range/
CAP Pump #277
Flow 3.5 GPM or 13.2L/M
RPM 1450
Electric 2.4hp, 230v, 50htz

Pre-filters
Someone gave me the tip to remove and sun-dry the pre-filters after each run. I have until now only used one pre-filter (10 micron) and followed that advise, but are now questioning it. Having read an extensive Filmtec manual they state that air in the system damages the membranes over time. Every time I put in a dry membrane I guess the membrane threads must contain air which is then passed through the membranes.
I am now in the process of rebuilding our watermaker and have installed 2 pre-filter housings and intend to use (as crisjones) a 10 and a 5 micron filter.

Question: What type filters do you use, thread spun? or others?

BeBe:
20 micron in front of 5 micron. These are accordion-made with a film-like material, that I bought in New Zealand...easy to clean. Before these I used string 25 and 5. I think you may want to consider 20 or 25 instead of 10. 10 micron in front of 5 may not give you the flow you need. A 20 micron will stop anything from passing that is larger than 20 micron. It will pass to the 5 micron which will stop anything that is larger than 5. I think using 10 micron as your first filter should be reconsidered.

Pressure
I normally run at 800psi but have tested slightly higher settings and found that the production rate went up, AND the ppm went down (i.e. more AND better quality water). The drawback being, according to Filmtec, more wear on the membranes.

BeBe:
800psi

Temperature
I find that the ppm goes up with the temperature (summer vs other seasons) and the salinity (Med. vs the Red Sea)

Water Quality
Our production quality in the Med has been around 250ppm until lately which seems consistent with others on this thread. I test the TDS meter from time to time with purchased mineral water to make sure it is not way off.

BeBe:
I agree and have similar experience, except that I recently tested the TDS meter with testing solution that, if I remember correctly was set to 300PPM. Also, note that I recently bought a new TDS meter and, out-of-the-box, it reads 100PPM high, assuming that my old TDS meter is correct...I need to get some more test solution...

Membranes
I bought two new membranes while on a visit to Florida in February but have not had time to install them yet. The box they came shipped in has been left unopened until recently, and when I opened it I noticed that the plastic wrapping of one membrane had vacuum, and the other didn't, i.e. the second wrapping must have been pierced. I am now worried about installing them because I seem to recall having read that they cannot be dry when stored. Any comments??

BeBe:
I have dealt with airwaterice.com in Florida. I asked what the shelf life is of membranes because I was interested in purchasing a spare. I was told 6 months, but it is important that they stay wet. I cannot vouch for this...this is what I was told.

A hint for anyone transporting membranes or shipping membranes:
Membranes come packaged in plastic with a small amount of fluid to keep them wet until installed. Cut a piece of 3" PVC pipe the length of the membrane, secure PVC end-caps with tape and drill a small breather hole in one of the end-caps. The hole will make removal of the end-cap much easier. This is important if you are inserting the membranes in a duffel bag as checked luggage on an airplane. You want the inspectors to be able to open the PVC tube easily. If you are checking them in luggage, place a copy of your receipt and a product information sheet on the outside of the tubes.

Hope this helps...

Bill

 

[crisjones]

Just checked my pre-filters and we use 20 and then 5 micron, not the 10 and 5 I said earlier!! This works fine together with the 50micron wire mesh filter. I never dry the filters out - I usually run the watermaker every 2nd or 3rd day so I just leave the system with seawater in it so it never gets any air in. If I plan to leave the system longer than 3 days without use then I will flush the system with 25ltrs fresh product water and leave this in the system, this is ok for up to 7 days.

Our membranes were vacuum packed when new and I stored them in the original packaging for over 2 years before installing and commissioning - performance seems exactly as the factory specs so the 6 month shelf life quoted is pretty conservative.

The product output is a determined by high pressure pump pressure and flow rate, our CAT pump is driven by a 2hp 1350rpm motor so our output is less than the above because of the lower flow rate, we get about 120ltrs / hr. Obviously you need more power to give more flow so the limiting factor is you drive motor. The technical data on the CAT Pumps website gives very detailed information about flow rates and power requirements.

 

[Sybaris]

BeBe:
CAT Pump #277
Flow 3.5 GPM or 13.2L/M
RPM 1450
Electric 2.4hp, 230v, 50htz

I checked out your pump specifications and yes it is rated for 3.5GPM @ 1450rpm.

My pump was purchased for our old generator and electrical setup (110V, 60Hz). The pump is a General Pump WM3615C rated at 3.6GPM @ 1750rpm.

According to my calculation if I run it at 50Hz instead that will bring down the speed to 1425rpm and hence only a flow rate of 2.95GPM - a slight "bummer".

I am still quite surprised about your production of 160lit/h given your pump. Your pump throughput in ideal conditions is 792lit/h which gives a production rate of 10% for each membrane. This is much more than stated by Filmtec.

BeBe:
I think you may want to consider 20 or 25 instead of 10.

Ok, gottcha.

BeBe:
It is important that they stay wet.

I have studied the very extensive manual found on the Filmtec site and found somewhere a comment indicating that a shipped membrane which has become dirty can be cleaned in sodium metabisulphite before installing it. I will follow your tip about the PVC pipe and clean the one without vacuum in there first and hope it will work as good as the one still in vacuum.


Here is a summary of a few things I have figured out, read, and been advised while working with our home built watermaker system.

** Filmtec is quite clear about the importance of slowly increasing the pressure from 0psi to 800psi at startup (and the reverse at shutdown). A quick pressure change will damage the membranes over time.

** I used a combination of stainless and brass fittings on the HP side until now. This is discouraged by Filmtec so I am now in the process of making sure all fittings are Stainless.

** I used a white teflon cream type thread sealer (purchased in Turkey) in all pipe fittings until now. When I disassembled the setup a few weeks ago I found that the thread sealer had crumbled up in a few places (where there was excess amounts) and might have been pushed into the membranes on the HP side. I am just guessing that this might not be healthy for the membranes and have found a much better liquid thread sealer now.

 

[silver-fox]

Why does the salinity of the water affect the quality of the fresh water produced?

My conceptual understanding is that RO is forcing water through a fine filter (membrane) at high pressure and I would have expected that the quality of the water produced depends on the membrane's characteristics only with perhaps reduced production if the membrane becomes clogged.

What am I missing?

 

[BeBe]

I checked out your pump specifications and yes it is rated for 3.5GPM @ 1450rpm.

My pump was purchased for our old generator and electrical setup (110V, 60Hz). The pump is a General Pump WM3615C rated at 3.6GPM @ 1750rpm.

According to my calculation if I run it at 50Hz instead that will bring down the speed to 1425rpm and hence only a flow rate of 2.95GPM - a slight "bummer".

I am still quite surprised about your production of 160lit/h given your pump. Your pump throughput in ideal conditions is 792lit/h which gives a production rate of 10% for each membrane. This is much more than stated by Filmtec.

I misstated my psi at 800.
The Dessalator D160 operates at a pressure 60 to 65 bars, or about 870 - 940 psi. The Fimtec membrane operates at 800 - 1000psi with a Maximum Operating Pressure 1,000 psi (69 bar). http://www.dessalator.fr/en/technical-questions/reverse-osmosis/


Bill

 

[BeBe]

Why does the salinity of the water affect the quality of the fresh water produced?

My conceptual understanding is that RO is forcing water through a fine filter (membrane) at high pressure and I would have expected that the quality of the water produced depends on the membrane's characteristics only with perhaps reduced production if the membrane becomes clogged.

What am I missing?

I believe that the Filmtec SW membranes remove a percentage of the salt from the water. The spec sheet states, "Stabilized Salt Rejection (99.4%)"

See attached spec sheets.

Bill

 

[noelex]

Why does the salinity of the water affect the quality of the fresh water produced?

My conceptual understanding is that RO is forcing water through a fine filter (membrane) at high pressure and I would have expected that the quality of the water produced depends on the membrane's characteristics only with perhaps reduced production if the membrane becomes clogged.

What am I missing?

The membrane and seals are never perfect so a small amount of salt gets into the product water. The amount is dependent on the initial salt concentration.