High TDS in Vegetable Processing Effluent

We are running ​a vegetable ​processing ​industry and our ​process ​includes ​washing ​gherkins and ​vegetables. ​ The effluent with initial ​TDS of 3200 ppm ​is directed to ​an effluent ​treatment ​plant where it is aerated and passed through ​the sand filter. ​The TDS then drops ​to around ​2900 ppm which is very high. How can ​we reduce ​the TDS to less ​than 1000 ppm?​