TDS meter testing to decide whether to mistwash

Collecting, filtering and dewatering of WVO SVO vegetable oil. For Biodiesel producers too.

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TDS meter testing to decide whether to mistwash

Postby SunWizard » Tue Mar 04, 2008 6:51 pm

17 November 2006

I am using, the 4TM model here:
http://www.tdsmeter.com/abouttds.html
still on ebay all the time for $21.99 including shipping. Its temp. compensated.

I just completed the first tests with these meters, and they are very sensitive. I think the TDS meter is better than PH since its showing acids, bases, salts and soap. The TDS meter is sensitive enough to give a reading of 150ppm with only a few grains of salt added to a glass with 3/4" of distilled water. (distilled = 0ppm.) Totally repeatable, and it also responds accurately to a tiny amount of vinegar, and a single drop of soap (reads 150ppm) added. And it works just as reliably with my tap water which starts at 60ppm TDS, the same tiny additives increase it to around 200ppm. I think TDS is much better than the PH meter, which has trouble with repeatablity, and drifts around, and only detects the vinegar.

I then did mini mistwashes on several batches of my VO, with samples that were straight from the dumpster, as well as mistwashed and centrifuged batches. They all were 0-30 ppm TDS and could probably avoid the mistwash. All of the after CF batches were near 0.

Here is how I do a mini mistwash, I add 1/4 cup VO and 1/4 cup distilled water to a quart jar. Then I shake well, and leave it settle for a few hours to separate the water. Then I use a syringe to suck the water off the bottom, avoiding the VO, put it in another glass, and measure with the TDS meter.

I think this is an accurate, cheap and quick way to see if a mistwash is needed, and if you test the mistwash water after, if it worked. It would be interesting to see some other results with nasty VO, I only have good sources. Now the trick is trying it on enough batches to know what the threshold of a bad TDS is.

The EPA says for drinking water 500ppm TDS is their recommended limit, so its also interesting to check your tap water, mine was 60. Its well water with the minerals calcium, magnesium, and iron being the main parts of TDS. (I had a engineer friend who did tests for EPA on farm wells run lab tests on my water a few years ago.)

From the instructions that came with the meter: TDS includes any inorganic element present other than the pure water molecule.
Last edited by SunWizard on Sun Sep 05, 2010 4:18 pm, edited 2 times in total.
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Postby SunWizard » Tue Mar 04, 2008 9:55 pm

An update to my TDS testing:
So far, with many different batches and testing with my TDS meter, the mistwash is only removing stuff which is removed easily on the 1st pass with my CF.

Here is an experiment that I have done: split a batch, wash half, then test the wash water. Then CF the other half 1 pass, wash, test the wash water. I find the wash is not removing a thing after CF. A wash before the CF its removing some large particles, but letting the CF remove it is much faster.

The value I see in it is if you wanted to avoid testing your VO, you could just always mistwash it to be safe. I find testing a batch with a mini-mistwash is far easier than mistwashing the whole batch. And so far I have only found 1 barrel out of 20 that needed a mistwash (and you could tell by the smell, the test confirmed my nose.) I used to always wash before I got a good test working. Now I am more in the "no-mistwash" camp, but with a way to continue to test whether a mistwash would help.
Last edited by SunWizard on Sun Apr 20, 2008 9:45 pm, edited 1 time in total.
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Postby froggo » Wed Mar 05, 2008 6:41 pm

Hi SunWizard,

thanks heaps for the info on TDS testing. I have been talking with some friends about mist washing our wvo to help remove acids, salts etc. The TDS meter will be a good place for us to start. I found a local distributor for the meters from your link.

thanks again and God bless froggo.
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Postby David » Thu Mar 06, 2008 6:38 am

Sunwizzard,

I haven't kept up on this particular technology so could you explain exactly what problem are you trying to avoid by using this TDS meter and what exactly does it tell you?

If the oil is well filtered and I believe the majority of people filter finer than they probably need to, if anything is small enough to pass through the vehicle filter, does it matter?

In reality, how likely is some one to have an oil supply that it has such a high concerntration of salt or acid to be a problem? If you determine that your oil has and amount of "Solids?" as determined by such a meter, is there a number that is a standard to know if it is acceptable or not or is each vehicle different and where does one find the number for their vehicle or does one refer to the standards for Diesel fuel?
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Postby SunWizard » Thu Mar 06, 2008 9:56 am

From my above post:
I think this is an accurate, cheap and quick way to see if a mistwash is needed.

Some people are recommending to always mistwash your VO. Thats a pain that I like to avoid. Using it has also proven that my centrifuge rig is removing all the worst contaminants such as acids, bases, salt and soap. These are what a mistwash removes.

You could use this cheap meter to see if your dewatering method was removing all those water soluble contaminants. For example, it makes sense that evaporative dewatering would concentrate and not remove those contaminants, and possibly make the hot pan test stop working as an effective water test.
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Postby David » Thu Mar 06, 2008 5:58 pm

Thanks SW.

I tried washing a batch of oil the other week with no real testing other than observation. I had setteled it a couple of months and I though if istwashing it was good, blasting and mixing water through it to an emulsion must be Better! :D

A sample test showed the emuslion seperated overnight so I went ahead with 100L of oil and 50L of water. I pulverised it together for an hour and let it settle overnight. I did this 3 times in total. the taste test of the water ( gross but all I had to go on) was the same with the last wash as the first.

The oil was sat a couple of days which precious litte extra water settled out and was dried. A batch of the same oil that was taken from the settling tank and just dried as normal, showed no visual difference.

I guess this only proves if the water did anything I couldn't see it and it would have to be measured with a device as you mention or there was no benefit to the process with the oil I get. I was kind of disappointed in a way, I was hoping this extra step would give me some " super oil " that looked like it was fresh out of the bottle. Unfortunately it didn't even smell any different.

I have little doubt that the process wouldn't help with substandard oil but fortunately I get so much that I try to avoid anything less than good and any I do get below par goes to a Bio maker or gets chucked out to keep the weeds down in the neighbors paddock.

What I was interested in was the fact that despite being turned into an emulsion as everyone trys to avoid by creating a mist, the oil still separated quickly and easily. I had no trouble draining off the water and drying the oil in my normal process.
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Postby tubular031 » Tue May 19, 2009 12:51 pm

I have read this a few times and Its some good info!

I bought a CF from wvo designs last week and a TDS meter today. I hope to duplicate your findings with my setup. As soon as I have some results, Ill post them up.

Thanks again Sun for all your help and info on here!
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Postby SunWizard » Sun Aug 29, 2010 10:34 am

Update:

After many tests, some small TDS amounts 30-50ppm are showing up on my batches tested before CF. None of those are showing up after 1 pass through the CF.

What this says to me is that 1 pass through the CF is doing very good at removing acids/bases, soaps or salts that are in my VO.

Some smart guys over on the Biodiesel forums saw my posts about TDS meters and have started testing and using them on their batches with very good results:
TDS to measure how clean biodiesel is
http://www.make-biodiesel.org/index.php ... Itemid=179
Note that a TDS meter measures EC and then converts internally to PPM and you can choose to look at EC or PPM numbers.

Since biodiesel makers usually mistwash to remove soap, it works as an easy indicator of when to stop the wash process in the shortest amount of time and lose the least amount of biodiesel in the waste water. And its easier than the tests they used to perform to determine soap content.

This shows that the TDS test is also useful for those who have bad VO, and want to do a mistwash. You simply put the meter in the waste water coming off of your mistwash, and it will let you know when you have removed all the acids/bases/soaps/salts so you can know when its clean instead of simply guessing how long to mistwash for. It should be clean when the TDS of the waste water matches the TDS of your clean tap water.

It would be interesting to hear from anyone else using a TDS meter what PPM values they see on a mini-mistwash before/after doing any processing. I usually see 40-300 PPM before I CF and 0-1 after.
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Postby gozapper » Thu Jun 23, 2011 10:44 pm

at what ppm reading would require to be mist washed?
What ppm reading is safe to use.
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Postby SunWizard » Fri Jun 24, 2011 7:50 am

gozapper wrote:at what ppm reading would require to be mist washed?

Whatever level you feel safe at. Since I CF, I never mist wash now that I have shown with many tests that its removing the TDS.
What ppm reading is safe to use.

I am the only one testing and reporting results, so you would need to test your sources and decide for yourself. There isn't any testing labs to set "safe" standards for VO, and even less likely to ever be any for WVO.
YVORMV - Your veg. oil results may vary.
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Postby gozapper » Fri Jun 24, 2011 9:12 am

OK ,
I have a sample test of 017 on my next batch to centrifuge and will test after this run and report back today.
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