I am trying to remove PAHs (poly aromatic hydrocarbons) from the contaminated water while passing through a column treated with bio adsorbbents. i have tried different spiking times. But need to verify that, is their any standead time duration which i need to keep PAHs mixed water before start the experiment or due to the volatility of PAHs is it advisible to start just after mixing them?
Your problem is common whenever you carry out tests or experiments with water solution of lipophilic compounds. The problems are: compounds do not solve in water and film on the surface; because of their increased fugacity, they can evaporate or adsorb on the surface of the container.
How to prevent this problems? it is not a matter of increased contact time, because increased time favours even evaporation and/or surface adsorption. You have to take these compounds in solution adding them in a co-solvent (a water soluble solvent such as methanol-acetonitrile-DMSO-acetone); or the best solution to get a steady state concentration is to equilibrate water with a polymer layer which releases the organic compounds (a passive sampler used in the reverse way). The latter is the best solution to garantee a constant solution in water.
The last recommendation: it is mandatory to measure the actual concentrations in water before and after the experiments, do not trust in the nominal concentration.
Dear sir, thank you so much for the answer! yes i am measurring the initial and final actual concentrations. to be more clear, kindly in second option i can use such polymer to release the PAHs to water in a constant rate? if can name a polymer , too. Best regards!
I agree with Stefano Polesello that it can be a good idea to dose the PAHs by equilibrium partitioning from a loaded polymer. Such "passive dosing" is most often done with a silicone polymer and many different silicone formats have been used sucesfully sofar. Several papers about passive dosing applied for maintaining constant exposure in toxicity testing are collected in the following project (see references), where you can read more about this technique:
https://www.researchgate.net/project/Passive-Dosing-Controlling-Exposure-of-Hydrophobic-Organics-in-Toxicity-Tests
The following paper gives an example on how to load a silicone with a mixture of PAHs at concentrations that are high enough for the analytical work, but still well below the saturation level:
https://www.researchgate.net/publication/51859155_Measuring_Binding_and_Speciation_of_Hydrophobic_Organic_Chemicals_at_Controlled_Freely_Dissolved_Concentrations_and_without_Phase_Separation
I can suggest a suited silicone format if you let me know how much water you need to dose with PAHs. Silicone rods are likely a very good format. Best regards.
Article Measuring Binding and Speciation of Hydrophobic Organic Chem...
Dear Sir,
Thank you very much for the very informative answer. I'll go through the paper and let you know for any doubt. :)
Sir, for the moment i am using either 20 liters or 10 liters of PAHs mixed water (depending upon the quantity of different PAHs that we have) in order to pass through our experimental column. But later i am expecting to do the same with crude oil and some PAHs in bulk quantity of water , say around 200L. Therefore, kindly tell me suited silicone format/s for 10L and 20L for the current work .
thanks once more for your valuable answer and kind concern for further.
Best regards!
Anusha
For contaminating such large volumes of water to be used for a column retention experiment, I would spike the water with a water miscible solvent containing the PAHs. I would be very careful with the materials in contact with the spiked solution (only glass, steel, Teflon) and I would keep the spiking level below 10% of the solubility for each of the PAHs in order to avoid problems near the solubility limit. For several of the PAHs this means that you need to work in the ng/L range. In many cases it will also be ok to spike the water right at/before doing the retention experiment. If you want to do passive dosing, I would recommend the use of silicone rods but this would require a very large mass of silicone e.g. 200g -1000g of silicone for high performance passive dosing of 20 L of water. I can send you more information by mail if you are interested.
thank you very much Sir! i have replied you yesterday. but then while sending net was falure and now realized that it has not published:).
Anyway, yes sir, i am using glass and teflon bottel type containers that can be closed so that to minimize the evaporation of PAHs during the experimental time.
Ya, sure i want to know more details and kindly send through my mail mentioned bellow.
Thanks with best regards,
Anusha
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