Polymers and defoamers

The short answer is, it depends on the characteristics of the waste stream; your question is way too broad. My suggestion would be to contact your suppliers to find the optimum solution (which should include what and how much to add).

You are certainly right, Jim, that a treatability study on the actual waste stream is important. But for the purpose of Su's general education, the polymers used in metal finishing wastewater treatment are predominantly anionic polyelectrolytes, and the defoamers are silicone-based. Silicone is a disaster if it gets on parts you are trying to plate, so I would be very wary of using a silicone defoamer if there is any recycling of water after its use.

There are more polymers than there are polymer suppliers. Finding the "best" can be a lifelong effort requiring thousands of jar tests. The anionic polymers are best for metals, but that barely narrows the search.

Foam should not be detrimental to the electrocoagulation process and is a natural product of electrolysis in impure water. Mechanical agitation after reaction is the most effective, although you can destroy the natural floc and then need a polymer. If foaming inside the reactor is a problem then it is a problem of reactor design. Re-design.