Letter 128

Zero discharge, anyone? Closed loop wastewater treatment

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I am interested in how many platers and surface finishers have successfully gone over to closed loop wastewater treatment. Our shop is small, so our methods may not work for all, but we are using carbon treatment plus ion exchange on mixed rinsewaters and have no sewer discharge. Treated water is returned to the rinses. The carbon and resin are regenerated off-site. Bath dumps, strippers, etc. are also sent for outside treatment.

Bill Vins microwave & cable assemblies Mesa (what a place-a), Arizona

But in the real world, where businesspeople are beseiged by NIMBY's and bureaucrats, your approach is the best one anywhere it works. I think that production barrel platers, however, can't solve their problem this way.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

As a followup to my original post:

I am curious to see how everyone is dealing with wastes from aqueous cleaning operations. Particularly those sites that used to vapor degrease and have converted to aqueous. Are there any successful zero discharge systems for aqueous cleaner rinses?

This question would apply particularly to those who did not have a wastewater treatment system before setting up the aqueous cleaner.

Bill Vins microwave & cable assemblies Mesa (what a place-a), Arizona

I'd also like to hear from such people.

It should be no problem to counterflow three rinses to a hot aqueous cleaner, if there is room for them, and achieve zero discharge. But it will result in quicker depletion of the cleaner, and higher waste-hauling costs, as you no longer allow a percentage of the dirt, grease, and exhausted cleaner to go out the drain.

Ted Mooney finishing.com Brick, New Jersey

Zero-discharge rinsing is certainly an option for hot baths and counterflow rinses. In fact, we are setting a couple of those up in (not that sunny) Rochester, NY.

Will have more information on their performance and how much trouble they'll be giving us in a few months, when full-swing production kicks in.

Cheers from PlaterB

"PlaterB" Berl Stein NiCoForm, Inc. Rochester, NY

The writer states that regeneration occurs off-site. Do you think he really means regeneration? There are several makers of DI units that regenerate on site. As far as I know, carbon is ultimately spent and replaced, not regenerated. What do you think of DI units using on site regen processes and one made by a Califonia company ( I can't remember the name that reuses most of the regen hydrochloric and caustic).

Why do you not think DI is suitable for production barrel platers? If not DI, what is suitable for a closed loop barrel shop? I believe that, in not too distant a future, most areas will not allow any sewer discharges form plating shops, and if nothing else, closed looping helps keep the various government agencies off your back.

Richard Gilley

True zero discharge from plating shops, especially barrel plating shops, will not happen any time soon. In production barrel plating shops, tons of parts are processed per hour, and those parts came in full of scale, paint chips, shop dirt, buffing compound, oils, preservatives, metal filings, detergents, drawing compounds, fingerprints, and residues of infinite sorts. And that's only the beginning. Processes like acid dips and chromating only work because the process constituents break down into a coating plus waste products. The same with many brightener systems. These waste products can't go out on the parts, and there will never be an electroplating process which will have use for scale, paint chips, shop dirt, etc.

A plating shop releases water mixed with contaminants of various sorts. I don't like the term "closed loop", or even the concept, because it makes us focus on the water rather than the contaminants, and the water is not the problem, the contaminants are. Similarly, it is ridiculous for a regulatory agency to say that the thing that cannot be discharged is the water, and they don't really care where the real waste products go.

Ted Mooney finishing.com Brick, New Jersey

Since I seem to have raised more questions and comments than I originally expected, I would like to clarify a few points about my original posting concerning our zero discharge (to sewer) system using ion exchange.

(1) We have a small shop with relatively low flow compared to most.

(2) All plating rinses go to the system. This includes passivate, alkaline cleaner, acid activator, copper cyanide strike, nickel chloride strike, nickel sulfamate, hard acid gold, and cyanide-free silver. No concentrated solutions go to the system.

(3) The system consists of a 20 micron filter followed by three columns, each 3.5 cu ft. First is carbon, then strong acid cation, then strong base anion. Usual output is about 20-30 microsiemens, slightly basic (pH 10). The treated water goes directly back to the rinses. This water is used as makeup in all baths except sulfamate nickel, gold, and silver. We have been running this way for over a year with no problems.

(4) We have averaged one regeneration every four months. Regeneration of carbon/resin is done offsite at a RCRA Part B facility. Regenerated columns are returned to us. All metals are recycled by the regeneration facility. I can supply their name privately since I don't think they need any free advertising.

(5) I firmly believe that this type of system can be adapted to any flow, especially if you want to get out of the city sewer regulatory loop. We save enough in lab fees to help offset some of the cost. Where you can't use ion exchange (oil, chips, etc.) I am sure there are other technologies that can be applied, such as micro-, ultra-, and nano-filtration. The object is to treat RINSES, which are 90-95% or more of the treatment system flow loading, then ship concentrates off-site to a recycler, or if you have the system, do a batch treat on them, make sludge, and send the sludge to a recycler.

The term zero discharge, in my book, means zero discharge to sewer. Closed loop means closed loop on rinses. By the way, we have to add small amounts of deionized water to the system on a regular basis to make up for evaporative losses.

Bill Vins microwave & cable assemblies Mesa (what a place-a), Arizona

Some interesting points from your discussions.

First of all, my name is Mike Waite

Mr Gates has only just got his internet act together in the UK, so I've only just found the finishing.com page. Looks good.

My background is technology development for waste minimisation in the nuclear industry. One of the techniques I was involved in developing was for treating the wastes from chemical decontamination operations on nuclear power plant. A variant of this technique looks as though it offers the possibility of true closed loop operation of plating rinse baths. I'm in the process of setting up a company to develop this process for this application.

Potential benefits are:
1) Replace static rinse tank and open loop counter current rinse tanks with closed loop counter current rinse tanks (eliminates water in and effluent out to sewer)
2) 100% metal recovery as powder
3) Anion recovery as concentrate (ie SO4 or PO4), or
4) Anion destruction (CN to CO2 + N2)
5) Slight improvement in plating quality (I believe chemical suppliers have modified their chemistries to reduce drag out to reduce effleunt loading - but at the expense of slightly poorer plating)

The basic technique is to combine IX with continuous electrochemical regeneration, creating a IX column contained in ion permeable membranes within an electrochemical cell (a bit like membrane dialysis used in the chloroalkali industry, but with IX in the middle). In effect the unit operates as an unexhaustable column, with (in cation configuration) metal recovery and (in anion configuration) recovery or destruction. Initially, the carbon column would be kept, but I've got some ideas on ways to replace that - watch this space! The technique works for the nuclear power industry (taken to pilot scale), but I'd appreciate some information to help the development for this application. Any info you could provide on the following points would be great. 1) Flow rates and metal loading in efluent from countercurrent tanks for a range of plating solutions 2) Frequency of change of static rinse tank, together with metal loading and volume of tank 3) Any info on overall composition, in particular impurity levels from the workpieces and organic levels All replies will be treated confidentially. The development plan is to have a portable demonstration unit in the UK in 12 - 18 months, use this at potential client sites to establish credibility in the technology + design feedback, then look to startegic alliances / joint ventures / licencing to existing equipment / chemical suppliers to the metal finishing industry for commercial introduction. The main driving force for this in the UK is the cost of water and sewer discharge, which has increased dramatically since our water companies have been privatised. The prime market is likely to be the precious metal plating sector, purely because, until we get a mass production route sorted, the economics don't look so good on water/effluent savings alone. Best wishes, Mike, and thanks for the Gulf Stream Chris Seeley -U.K.