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I am working in a construction company which is building hydropower plants in Northern Norway. We are monitoring the Total Hydrocarbon Content (THC) of our process waste water. This particularly important during tunneling as the machines are likely to leak.

At the moment we are sending waste water samples to an analysis company and there are some disadvantages of that, including the price, the delay in information, and the risk of volatile hydrocarbons evaporating during transportation.

I would like to take weekly samples in the field and do the analysis myself. I am an environmental engineer with some background in the laboratory from my time as a student, but I have never tried to find THC before.

I have been trying to find a simple and inexpensive way of measuring the THC in the water, but most of the instruments I have seen on various company websites are very sensitive (measuring in the ppm range) and meant to measure the THC continuously on some industrial flow (like this).

The measuring range should be something like 1-100 mg/L, and I simply cannot find any method or instrument that suits those needs. Do you know of any kind of instrument that can perform this analysis, or a manual method? I am looking for an inexpensive, portable, and simple solution.

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  • $\begingroup$ The continuous THC monitor you linked can't be repurposed to suit your needs? I would think that you can convert ppm to mg/L, and continuous sampling of a static sample should still give you a result. $\endgroup$
    – grfrazee
    Apr 4 '16 at 16:34
  • $\begingroup$ It's possible. I could even dilute samples to make it match any measuring range. But wouldn't I then be paying for some accuracy that I don't need? I don't want to use a sledgehammer to crack a nut. The price is central. $\endgroup$ Apr 4 '16 at 16:43
  • $\begingroup$ It may be overkill, sure. But if you don't get any good answers on how to do this is a less-expensive manner, there's always this to fall back on. $\endgroup$
    – grfrazee
    Apr 4 '16 at 16:44
  • $\begingroup$ That's true. BTW thanks for the language edits :) $\endgroup$ Apr 4 '16 at 16:45
  • $\begingroup$ This comment is only slightly tongue-in-cheek: At those concentrations, can't you do a field test by how well a sample burns? I'm having trouble thinking of a situation where such a large volume of sample would contain hydrocarbons, yet you care about the (relatively) exact ratio. $\endgroup$
    – hazzey
    Apr 4 '16 at 17:53
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The only or vastly major source of chemical oxygen demand (COD) should be your dissolved or suspended hydrocarbons, so a COD test could be the way to go. . I don't know hw confident you are in your analytical chemical and labwork skills. COD determintation requires handling of strong acids and oxidizers, would avoid without proper training. However, there exist micro vials for safe, quick test for people with little training. Search for micro vial COD quick test. These are marketed to WWTP operators without proper labs or labwork training.

You will need check the following:

  • Chloride content of sample, Chloride can distort the result and would need to be masked.
  • COD equivalent to your 20mg/l THC - either derived from stochiometry of your hydrocarbons (that you likely don't know exactly), or maybe you find a code you can reference. Or you measure the COD of samples with known THC and map these.
  • Not that engine oils are often modified (-H substituted) heavily and you may underestimate the THC/COD ration if you take the stochiometry of straight petrol or Diesel as a baseline

Either way, I suggest you define a COD equivalent to THC value way less than 20mg/l and then laboratory test only sample above this treshold to be sure.

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Measure the water and distilling container separately and together. Subtract the added weight left behind in the distiller after distilling all the water out. You could count the hydrocarbons in a drop of water under a microscope and multiply. Get a microscope.

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