There has been increased attention on ZLD technologies in the news over the past two years. New regulations and awareness of the water crisis have prompted businesses to adopt new technologies which treat waste water in ways that are more efficient and sustainable. ZLD, or Zero Liquid Discharge, are technologies which concentrate waste water until only solids and reusable “clean” water remains or, more broadly, which produce a “close to zero” amount of liquid waste.
Since ZLD technologies recover all, or almost all, of the waste water produced by an industrial process, they contribute to sustainable manufacturing practices and decrease the environmental impact of businesses. They also have economic advantages, such as:
- minimizing the cost of sourcing freshwater and disposing of waste,
- providing added value because valuable resources can be recovered from the “waste.”
ZLD technology maximizes the fresh water recovered and minimizes the volume of waste generated; however, there are tradeoffs. Conventional ZLD systems are based on thermal methods such as evaporators and crystallizers, which are expensive and use considerable energy. To increase the viability of ZLD technologies for both the environment and businesses, they must be further improved to minimize the amount of energy consumed by the treatment process.
One way to save energy is to reduce the amount of waste water which needs to be treated using heat. This can be done by using volume reduction technology.
Another way to save energy is to operate the treatment system at a constant temperature throughout the process. Most of the traditional volume reduction technologies do not work at high temperatures, which means that the waste water has to be cooled and then reheated during the treatment process. However, some new technologies do work at high temperatures.
Nanoscale ceramic membranes capable of dewatering are an example of a volume reduction technology that can operate at high temperatures, unlike polymer membranes. Heat resistant ceramic filters make the use of heat exchangers for the final thermal concentration step unnecessary. This reduces the total energy use of the ZLD system.
It makes no sense to use ZLD technology if the advantages of the recoverable water and resources are offset by the disadvantage of the energy use necessary for the process. Emerging nano-ceramic technologies make ZLD more energy efficient and allow more businesses to take advantage of this cost-saving and sustainable process technology.