electrocoagulation

[murky]

We are designing a treatment system to treat stormwater runoff from a large industrial parcel. The treatment system will use electrocoagulation to remove suspended solids and metals. We are going to provide an equalization volume of more than 200,000 gallons, and the design treatment rate will be 250 gpm. Influent TSS ranges between 200 and 900 mg/L. Copper and zinc are usually between 0.5 and 2.0 mg/L.

We are proposing to use an inclined plate separator downstream of electrocoagulation to remove solids prior to discharge. We've done limited bench testing, and from the bench tests results, and from my limited experience with electrocoagulation, I understand that stormwater treated by EC has lots of very fine, entrained air bubbles that float some of the solids to the surface, while other larger particles settle out via gravity. How can I degas the effluent while maintaining the particle size of the coagulated solids? Also, how do I keep the solution homogenized so the inclined plate separator sees a solids load high enough to work efficiently?

I would be interested in hearing if anyone else has experience with electrocoagulation.

 

[orenda1168]

Murky:

Contact Dave Orlebeke at

http://www.eoh20.com.

He will be able to supply your need for TSS and metals removal via a system similar but superior to EC.


Orenda

 

[bimr]

Conclusions from:

http://www.isf.uts.edu.au/publications/EERE-Paper.pdf

"Electrocoagulation has successfully treated a wide range of waste streams. On-site optimization and process “tuning” had limited success, but a priori prediction for reactor operation has not been reported. Mechanisms are expected to change through the process but the dominant mechanisms and their role are yet to be identified.

The lack of a methodical approach on a mechanistic level is reflected by the lack of similarities in reactor design. No dominant reactor design exists, adequate scale-up parameters have not been defined, materials of construction are varied and operational regions fuzzy. A logical, systematic approach to a fundamental understanding of electrocoagulation is clearly required. The design phase can then proceed on solid scientific and engineering knowledge.

A large number of key mechanisms are dependent on a few operating parameters. Individual “optimizations” exist, that is, for pH and speciation of the coagulant ion (Fe3+ or Al3+) but this often conflicts with other localised optimal conditions. The electroflotation mechanism, passivation of the electrodes, economic considerations all have their own operating pH. A trade-off between the
competing factors must be evaluated to provide a global optimum operating condition."

 

[bimr]

You seem to be gambling on a technology that has limited understanding and actual field installations.

If you are really serious about applying this type of technology, why don't you consider electroflotation?

You may also look into flotation filters, involving both DAF and rapid sand filtration in the same tank. Purac has been selling this technology for over 20 years:

http://www.valleywater.org/media/pdf/DAF.pdf

In addition, some off the details that you provided are not clear.

Do you plan on operating this system intermittently? It seems that you can process the entire waste volume of 200,000 gallons in 13 hours.

How do you know that if you degas the wastewater, that the coagulation will not be effected?

In regards to your question about the fine bubbles, a simple device such as a cascading aeration should be able to remove the bubbles.

Aso, you do not have to be concerned about "homogenizing" the wastewater since you have an equalization tank.

 

[murky]

Bimr - thanks for the link to the electrocoagulation article. I briefly read the article, and I do agree that this technology needs additional research to increase our understanding of removal mechanisms, optimization, etc. Also, we hadn't evaluated electoflotation or cascading aeration, both of which are attractive ideas and worthy of some preliminary research.

To clarify our project, this is intended for stormwater treatment, so yes, the system will be operated intermittently for the most part. We do expect the system to run continuously during peak rainfall months. From July through September, the system will be shutdown.

In regards to degassification, you bring up a good point. There has been no research that I am aware of that evaluates the effects of increasing the degassification rate on the coagulation process. I'm interested in any further insight or links you may have.

And to clarify my comment on "homogenization", our objective is to keep flocs in suspension until the treated water is passed through the inclined plate separator. We're primarly concerned with the foam layer, and have looked into ultrasonic energy to collapse the foam layer.
Ultrasonic energy may also help the degassification process, but I am more concerned that this energy could break up the flocs. But your suggestion of electro floatation may provide a good fit.

 

[oxilume]

Murky,

Although EC "may" work for your application, I would not recommend it due to maintenance problems and energy usage.

Keep in mind that stormwater runoff treatment systems are normally viewed by operators as "install and forget."

If you can send me a drum or truck load of the wastewater, I will test it for you in one of our systems:
(NOTE: WE DO NOT run bench tests. That is why I require a drum or truck load.)
PlasmaWhirl
ArcWhirl, or
Hi-Temper (modified EC technology that does not plug up, but is very energy intensive - normally used for removing heavy metals at foundries.)

For pictures please see:

http://www.plasmawhirl.com

Sincerely,
Todd


Todd

http://www.oxilume.com