Sodium reduction in effluent streams

[Klen]

I am interested in any processes that are being employed to control (minimise) Sodium content in effluent streams, particularly from food and beverage processing plants. At present a major contributor to the overall Sodium content is the Caustic based cleaning system and and there seem to be few alteratives available. Is anyone aware of "new technologies" either at the front end of the problem with alternative cleaning systems (enzymes have been considered) or at the effluent treatment stage where a DAF is currently used?
Regards
Greg

 

[DeltaCascade]

Hello Greg:

Perhaps KOH could replace NaOH? .. although for CIP (clean in place) you may have "code or regulation" requirements for NaOH. KOH will also likely be more corrosive. I'd double-check CIP recommended best practices, starting with the web, if you havn't already (eg: multiple stage countercurrent rinsing, use conductivity meters to improve CIP process control, etc).

Also, of course, a site-wide water audit to ensure that recycling and re-use opportunities are being taken advantage of would be helpful, while confirming that the cleaning agent is really the major sodium source (which it appears you have done). Perhaps other sources can be reduced, for example from sodium zeolite water softener (which you likely have as CIP water is often softened to prevent scaling in alkaline conditions, unless you use chelants; changing your make-up water quality with lime softening or other process may also reduce its buffering ability and caustic demand) or water demineralization plant (possibly used for boiler make-up water treatment, etc, where reduction in boiler make-up water requirement may significantly reduce sodium to waste (eg: increase steam condensate recovery, reduce % blowdown, etc)), if any.

Re-using the water as much as possible would reduce overall lb/day of sodium discharge (which you are likely already doing). At a beverage distillery, we reused our 4% caustic solution over and over again, occassionally topping up the caustic strength, before neutralizing and discharging to waste; this minimized total lb sodium to waste.

Membrane systems can be used to enhance recycling ability (eg:

http://www.kochmembrane.com/APPLICATIONS/Specialty.html)

You may even end up with a high organic stream free of caustic that could be sold as animal feed.

Ironically, perhaps caustic recycling is causing high sodium concentrations, even though lb sodium/day to waste is lower with recycling. In this case dilution is a solution, or, less recycle. Preferably, in this case, the stream's sodium content could be diluted with another waste stream so as not to increase total waste or supply water demand. Perhaps there is opportunity to use the waste caustic to neutralize waste acids so that fresh caustic need not be used for that purpose.

Alternatively, slowly discharging waste over a long period, as "opposed to all at once" would eliminate high sodium "spikes", if that is a problem.

Of course, heating the caustic cleaning solution may enable you to use less; ideal temperature is typically 160F

Unfortunately, the sodium added must go somewhere, unless you have evaporators (not likley) and can send it to landfill as a solid. So, yes, reducing caustic, or sodium in whatever form, input to the site's processes appears desirable. Perhaps a process audit to ensure caustic use is minimized ... minimize pooling, etc...

To answer your questions more direclty, it looks like membrane technology may be a new approach for you to consider.

Interesting challenge. Good luck.

PS: I am a consultant specializing in water treatment, based in Calgary, Alberta. Feel free to let me know if you have more questions.

Wayne//

 

[DeltaCascade]

Ion collider? Ions in solution always collide. You still have the sodium atoms to deal with.