I am unsure of Electrocoagulation use in this stream but I do know of a process that will concentrate the solution generating a distilled quality product.  The concentrate can be sent through a follow up technology to scavange out the Nickle/Zinc creating a closed loop process.  I do know that electrocoagulation will be limited on the solids (phosphate) for blinding of the electrodes will cause the system to lose its ability to transfer the voltage plate to plate.  
I can provide information on the technology.  Email me.

grrun

Thank you for your comments - we have considered this , however, we are using RO water cascaded and mixed with process water  from final rinse through polishing rinses to the primary rinse.  We are considering diverting all rinse wastewater back to the RO as an option.  Reject from the RO (which is used to generate additional RO for other processes as well) however still goes to the pretreatment plant and is a significantly higher flow than the phosphate rinse wastewater making the collection and treatment more capital intensive.  We settled on microfiltration as a point source concept instead of RO due to the pH sensitivity of the RO process which would have to run at a pH 6-8 and the potential to need for Iron or Alum chemistry to treat prior to filtration.  Still trying to determine if the microfiltration will work at the pH 9 - 9.5 we expect to need to precipitate the metals (our lime softened process water usually runs about pH 9.5 to 10).   Additionally  although we are considering it we are hesitant to reintroduce the treated water to the phosphating tank as there are significant opportunities for contamination to the phosphating solution doing so and still may be more cost effective to dispose the metal solids rather than recalim.  Still an idea to consider after we have all the kinks worked out. Thanks again.

JMJ:  Thanks for the thoughts - on the microfiltration were you refering to the cloth type pressure filter or membrane/concentrator  type of microfiltration.

Rudydog
All rinses we are considering for treatment are post phosphating. We do not use any surfactants/cleaners post phosphate so I do not see that as an issue.  I have heard that there is a process similar to electrocoagulation that uses non-sacrificial anodes (electrocatalytic precipitation). Any experience with that?  Also could you clarify your thoughts on the zinc/nickle being less soluable above pH 7.5 - Standard practices I have dealt with have always been to precipitate them as an hydroxide with lime or caustic at pH 9-9.5.

Thanks - Dbrock

Dear Rudydog,

I just wanted to discuss the 'surfactant issue'.
The problem obviously refers to anionic surfactants. Nonionic surfactants are greatly unaffected by pH. Further only in case of soaps the dispersing effectivity drops with the pH, because other common anionic surfactants show a high dissociation degree also at low pH.
It seems to me that the real problem is the interaction of the anionic surfactants with metal ions or their insoluble  complexes.

Addition of a cationic polyelectrolyte should be very effective in avoiding interference from anionic surfactants and to some degree from nonionic too.

Kind regards
T. Sobisch

Back in 05 I responded to this original question and since then we have done a lot of research and we have a definate answer for you now.  Cal-Neva has developed a new electrode that allows us to flow water through our new Anode and not around it.  This has improved the the removal of hard to remove metals such as your lead and zinc and Boron and Selinium from such sources as your rinse water.  This new Anode allows us to increase the residence time of the water containing the contaminants and since the water flows through the Anode it stays in contact with the Electron Cloud that is formed in the water by the addition of the DC power source.  In Texas we have proved to Chesapeake Oil that we can remove up to 98% of these heavy metals from their Produced Water and Flow Back Water.  In helping us to accomplish this we have also developed a new additive that is put in the water flow prior to the EC tubes and what happens is that we are able to start phase separation of the contaminants by specific gravity which assists the EC unit in delivering the correct amount of Electrons to the contaminants so that they will become complete atomic particles of the metals instead of being a colloid of the metal and being unstable.  By the addition of our metals in the Anodes we combine the small flock particle of Aluminum which is what starts the coagulation process in this water and then we charge the Iron Anode and this allows the flock of the contaminant to adhear to this larger particle and when it emerges the end of the EC system into a tank the flock is floated to the surface on the Hydrogen bubbles that are created within the system and the flock can be paddled off of the top of the water in a decant mode.  This same technology is proving very successful in the removal of Boron and Selinium from sewage plant discharge waters and we are getting up to 99.7% removal of these contaminants with our system.  I realize that this is almost three years after your question but these kind of problems don't go away and maybe this answer will assist someone else in the removal of these contaminants.  I do not want to divulge too much about our studies without having non-disclosure in place but if anyone needs more info on this subject call me or email and we will talk and can give you more with docs in place.