Environmental regulations, higher water demand on industrial ends create the need for ZLD. ZLD systems employ the most advanced wastewater treatment technologies to purify and recycle virtually all of the wastewater produced. ZLD technology includes pre-treatment and evaporation of the industrial effluent until the dissolved solids precipitate as crystals. These crystals are removed and dewatered. The water vapor from evaporation is condensed and returned to the process. Biological and suspended impurities present in the effluent are removed using combination of primary, secondary and tertiary treatment
In some cases this treated effluent still consists of higher content of dissolved solids. These dissolved solids are removed using Reverse osmosis technology. Reverse osmosis generates concentrated brine solution as a waste/ reject. Using evaporation, rejected water can be recovered and reused.
By this way zero liquid discharge can be achieved.
ZLD is generally used for desalination or for the process effluent with higher TDS.You can also achieve ZLD without using RO membranes by following activities
- Try internal process recirculation
- Try maximum possible recycling of water back into the process.
- Try segregation of waste streams at source and try treating them separately rather than mixing everything.