Zero Liquid Discharge (ZLD) Plants

• Increasingly, legislation and industry demands a zero liquid discharge with a solid product that can either be sold or more readily dumped in a sealed landfill.
• This option implies a total evaporation concept without any purge to limit impurity build up. This can result in unexpected physical and chemical properties of the concentrate such as high boiling point elevation, high viscosity, foaming, poor crystal growth and increased corrosion. In the case of inorganic effluent, the final product is usually a mixed salt and of no commercial value. In the case of organic effluent, the concentrate could be a liquid or 'sludge', viscous in nature. Further drying (eg spray drying) may be required.
• The final product from an effluent plant is frequently of low or no value so that capital and operating costs are usually severely restrained.