Dear,

I read one article to treat the tannin in Japanese. They used some coagulants, or coagulation settling. I think coagulants is useful for treatment contains tannin wastewater using membrane system, too. Coagulants make suspended solid bigger, so it would be convenient for membrane treatment.

And I think ozone treatment and electrolysis are useful for decolorizatio, but they might cost a little bit high.

Best regard.

For ozone and tannins see this referenc and references within:

https://www.ncbi.nlm.nih.gov/m/pubmed/28651322

Basically, full removal of tannins by ozonation takes a lot of ozone, so it really depends what quskirt of water you are looking for.

Yoram

Tannins can be precipitated by some polyacrylamide flocculants. It is a trial and error process to identify the most appropriate product. Dose rate is typically tannin x 2.5 .

Gelatin will also usually offer a similar effect.

The addition of Ferrous or Ferric iron and pH adjustment to pH 7 - 8.0 should also produce good results.