Reverse osmosis is found to be successful and about 70-80 % colour can be removed regardless of the type of dye stuffs. Decolourisation in the range of 95-100 % has been achieved by the use of zirconium oxide/ polyacrylate membranes.

Use of Physico-chemical & Tertiary Polishing Treatment

This article explores an appropriate treatment scheme for removing the dyestuff and other impurities from the segregated dye effluent by adopting physico-chemical and tertiary polishing treatments. This process helps in achieving commercial zero hardness and low level of metal content in the recovered water, providing an excellent scope for its reuse in the dyeing process itself. The waste inorganic chemicals were also recovered in the concentrated form or in pure crystalline form and were reused in the dyeing operation. The fastness properties such as light, washing and rubbing of the yarn after dyeing with recovered water and salt have been found comparable to the original samples dyed using fresh chemicals and soft water The repeated recirculation does not cause any significant enhancement of TDS or metal content in the recirculated water. This helps in the indirect control of TDS limit for the remaining major segregated water as prescribed by the concerned pollution boards in its disposal into the outside environment, after repeated recycling.

Role of Pump in Zero-discharge

The pumps used in the recovery system behind this nickel/chromium plating operation must handle acidic and alkaline plating and cleaning solutions over a broad pH range, commingled chemical waste streams, and DI high purity water recovered from the ion exchange system.

A zero discharge resource recovery treatment system designed, built and installed by CASTion Corporation (Worcester, MA) and Columbia. This system is a custom-engineered Controlled Atmosphere Separation Technology (CAST) packaged concentrated wastewater and valuable chemicals recovery system. CAST can be furnished as a stand-alone wastewater and chemical recovery system, or as part of an integrated plant-wide program to minimize or completely eliminate costly disposal of hazardous waste or process effluent.

The turnkey wastewater and product recovery system has resulted in the following advantages:

1. All recovered wastewater is returned to the rinse baths, and plating solutions that are recovered are returned directly to the plating tanks.
2. Concentrated wastewater from the cleaning and plating lines have their own CASTion ion-recovery systems and are recovered as DI water and are then recycled for use in the rinse tanks.
3. 98 percent of the nickel and chromic acid plating chemicals are recovered and re-used.
4. There is no discharge into sewer or air, so the company needs no permits from DEP, and is exempt from RCRA permits.
5. Six hundred pounds of chromium trioxide are recovered each week and returned to the plating tank. As a result of these changes and installation of the recovery systems.