Bio-fouling in ground-water / LNAPL remediation system piping 2

[banana1701]

Anyone out there who knows of effective additives or methods for reducing bio-fouling in piping from GW remediation systems?

Our contaminants are BTEX/naphthalene from coking by-product LNAPL. pH is neutral, and we have carbon steel pipe from our sump to treatment plant. We probably have SOME iron-fouling bacteria, but we see a substantial slime layer at our GW/LNAPL interface, which is the fouling that's likely causing our problems (greatly reduced flow rate due to pipe fouling).

We have tried shock treatments with muriatic acid & dissolved chlorine pellets, and scheduled system shutdowns (1-2 weeks) to reduce fouling, each of which helps somewhat, but we're hoping to find something that is more effective, and hopefully is less corrosive to our piping than the acid and chlorine treatments.

Any suggestions for anti-bacterial products or other techniques or lessons learned? Could we expect better results from isolating & jetting out our pipes?

 

[aspearin1]

Have you ruled out local natural flora feeding on BTEX? Why pump and treat if nature is doing it right?

ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee

 

[banana1701]

Yes, we believe it is natural flora feeding on the organics, and we are glad they are present in the subsurface. As you say, nature is helping us clean up the subsurface already. But we are trying to reduce clean-up time and help nature along, so we are pumping and treating to remove the bulk of the free product plume which, after 15,000 gallons reclaimed to date, is still up to a foot thick in the area. After we have substantially removed the free product, we are planning on letting biotreatment finish the job for us, as you suggest.

Basically, for now, we're just looking for ways to effectively reduce the biomass in our pipes so we can continue to pump at a rate sufficient to draw the LNAPL to our sump. We have dropped from >30 gpm to <9 gpm and are thus reducing our cone of depression and LNAPL recovery rates. So, I was just curious to see if anyone out there had similar experiences or knew of a bactericide or other alternative for our application. If we keep using HCl, we will have to dig up and replace our (carbon steel) pipes soon, and we would like to avoid this if possible.

 

[4tuna]

banana1701 -

Your problem is a common one, and there are no easy solutions. One method is to use low-dose acid more frequently, to prevent buildup. Another is the use of high-pressure jetting for well redevelopment. This technique doesn't use any acid, and prolongs the life of your pipe. However, this may not be economical if biofouling occurs rapidly - you will generally need a well-qualified drill contractor, and your pump will have to be pulled each time.

You might want to try one of the books below (I have not read them). Good luck.

Alford, G. and D.R. Cullimore. 1999. The Application of Heat and Chemicals in the Control of Biofouling Events in Wells. CRC Press Lewis Publishers, Boca Raton, FL, 181 pp.

Alford, G., S.A. Smith and R.L. Leach. 2000. Engineering and Design - Operation and Maintenance of Extraction and Injection Wells at HTRW Sites, EP 1110-1-27, U.S. Army Corps of Engineers.

 

[banana1701]

Thanks for the great advice and book recommendations! I will take a look at these.

We're planning to try your lower dose/higher frequency approach unless we find something more effective. We also found a biocide on-line called Oxygenics 2002 that we bought a sample of to try. If we have any luck with this product, I'll post our results in case it can help someone else out there.

 

[mbph]

You may get better success if you know what your dealing with. Depending on the contamination and the site specifics, the microorganisms can be very different. There are labs that can profile your biomass. Once you know what you've got you may be able to target the bad actors.

 

[agsgeophysics]

Adjusting pH is probably the best way. Unfortunately you are using the wrong technology for the job - P&T is so '80s!!! Perhaps you should look into converting your system to a multi-phase extraction system where you are only moving enough gw to lower the water table below the smear zone and "bioslurp" free product. Then, you will be treating the bulk of your contaminants in the vapor phase - much more efficient than P&T and you will have less rebound effects in the long run.