Is it possible to have greater Electric Conductivity (EC) value for Waste Water than Total Dissolved Solid (TDS)?

Hello. I am facing a problem with our waste water treatment setup. The TDS found in waste water is 1200 mg/l whereas the EC calculated for the same waste water is around 1600dS/m. My experience says that EC has relation with TDS, which is EC = 0.67 x TDS. In our factory we process waste water generated from Personal Care Cosmetics and Soaps . I know that EC varies with temperature and ionic compounds, but what we are experiencing is confusing. So I need your advice. It is normal to have greater EC value for waste water than TDS ? If not, what could be the possible reasons behind it? Thanks in advance. Regards, Forhad, Chemical Engineer, BUET.