In addition to the processing stages pickling, tin phosphatisation, borax coating and associated rinsing stages, the order also included a complete wastewater treatment facility. Apart from recovering water, which is fed back into the process as fresh water, the plant recovers metals contained in the spent solutions and wastewater together with acids, which are concentrated in the form of dry salt crystals. Thanks to this comprehensive wastewater treatment system, the entire surface treatment process produces no wastewater (ZLD= Zero Liquid Discharge).
The water recovery process incorporates processing stages that perform metal separation, ultrafiltration and reverse osmosis. Besides residual water, the solution accumulated following water recovery contains salts dissolved during the metal separation stage. This water is evaporated off using the previously unused production exhaust gas and the dissolved salts converted into salt crystals (dust). The salt crystals are then separated from the exhaust gas stream using a fabric filter and either re-used or disposed of.
In addition to operating without generating any wastewater (ZLD), the entire Steuler process is characterised by low operating costs, which are well below those associated with conventional methods of wastewater treatment, such as neutralization, precipitation, drainage and discharge into receiving waters or a sewer system. There is an increasing demand for surface treatment plants that operate without generating wastewater from China, India and other Asiatic countries where there is a focus on significantly reducing the impact on the environment and water pollution.
The surface treatment plant is scheduled to start operation in the 2nd quarter of 2016.