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Ask the Expert Question-and-Answer Archive
(Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
March, 2008

Total Organic Carbon Reduction

Q. This question is not related to wastewater treatment; so I would understand if you are unwilling or unable to reply. For readability, only the most relevant information is provided.

Our small potassium sulfate manufacturing plant (at Wynyard, Saskatchewan, Canada) uses sodium sulfate lake water as feed for an ion exchange process. The lake water contains high total organic carbon (TOC) content i.e., 40-50 mg/L in summer and 100-150 mg/L in winter, the majority of which is in the dissolved form. We have tried several pilot studies (including aeration, coagulation/flocculation, advanced oxidation processes, and hydrogen peroxide treatment) to find a cost-effective solution that would reduce the TOC content to 20-25 mg/L (especially in winter) to prevent production loss. Due to the massive volume of lake water in use, activated carbon filtration is not considered a feasible option. Hydrogen peroxide treatment is the only effective solution that we have discovered; however, the cost of treating such large volumes is the deterrent.

From your experience, can you offer any suggestions for this problem or direct to other people who might have better insight on issues of this nature?

Appreciate your time.

A. I would try ozone treatment followed by sand filtration first. Ozone acts as an oxidizer, just like hydrogen peroxide, but also if used in small enough doses it acts as an organic flocculant. The Sand filter then collects and removes the flocculant thus removing a substantial portion of the TOC, COD, BOD and CBOD, which is later back washed to regenerate the sand filter. This has been done successfully before with lake water, and even published at past IOA (International Ozone Association) Conferences. Ozone does not add any TOC to the water, and generally reduces the COD, BOD and CBOD under the right conditions, right conditions meaning a limited amount of ozone, just enough to form a floc followed by filtration, and not enough ozone to increase the BOD or CBOD. The half life of ozone is 20 minutes at typical ambient conditions.

Pretreatment of the sand filter with Diatomaceous Earth might improve the process above in your case.

Another option to consider is ultrafiltration to remove the TOC with out removing the sodium sulfate. Once again pretreatment with ozone followed by ultrafiltration might do the job very cost effectively.

If you try these out and get good results, I would appreciate your letting me know the results. If you need help with the design , layout or hardware please let me know.

Sincerely,

Mike McGinness



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