Abstract: Brine produced in an interfacial polycarbonate plant can be treated to render it useful for recycle to the electrolytic cell, which is used in the production of chlorine. The waste brine stream is combined with ozone to produce an ozonated brine in which the amounts of organic contaminants such as phenol, bisphenol A and chloromethyltrimetlhyl ammonium chloride is reduced. The ozonated brine is then acidified to remove carbonates and produce a decarbonated brine which is then concentrated to produce a treated brine in which the concentration of NaCl is at least 10 wt % NaCl. A filtration step may be included prior to the ozonation to remove particulate impurities. When used in an interfacial polycarbonate plant in combination with chlorine, phosgene and polycarbonate producing facilities, this allows recycling of the brine waste stream and this provides an environmentally superior and highly cost effective method for the producing polycarbonate.