Yaser, A. Z., Cassey, T. L., Hairul, M. A., & Shazwan, A. S. (2014). Current review on the coagulation/flocculation of lignin containing wastewater. Int. J. Waste Res, 4(3), 153-159.
There are a lot of techniques that you can use. I recommend to you the electroflotation. you can see my paper, that it's about a wastewater from mine .