Zero Liquid Discharge System Plant or ZLD(Zero liquid discharge) is an engineering approach to water treatment where all water is recovered and contaminants are reduced to solid waste.
Such treatment plant ensures that the contaminated and polluted water from industries get treated and become reusable before being released back to nature. Without this treatment, it won’t be possible for humans to get clean usable water for household chores.
Several methods of waste management are classified as zero liquid discharge, despite using different boundaries to define the point where discharge occurs. Usually, a facility or site property line that houses the industrial process is considered the border or ‘boundary condition’ where wastewater must be treated, recycled, and converted to solids for disposal to achieve zero liquid discharge.
Certain facilities send their liquid waste off-site for treatment, deep well disposal, or incineration and they consider this to qualify as zero liquid discharge. This approach to zero liquid discharge eliminates continuous discharge of liquids to surface waters or sewers, but can significantly increase cost.
In a world where freshwater is an increasingly valuable resource, industrial processes threaten its availability on two fronts, unless the water is treated. Many industrial processes require water, and then reduce the availability of water for the environment or other processes, or alternately contaminate and release water that damages the local environment.
Another important reason to consider zero liquid discharge is the potential for recovering resources that are present in wastewater. Some organizations target ZLD for their waste because they can sell the solids that are produced or reuse them as a part of their industrial process. For example, lithium has been found in USA oil field brines at almost the same level as South American salars. In another example, gypsum can be recovered from mine water and flue gas desalinization (FGD) wastewater, which can then be sold to use in drywall manufacturing.
Regardless of an organization’s motivations to target zero liquid discharge, achieving it demonstrates good economics, corporate responsibility and environmental stewardship. By operating an in-house ZLD plant, disposal costs can be reduced, more water is re-used, and fewer greenhouse gases are produced by off-site trucking, which minimizes impact on local ecosystems and the climate.
Conventional treatment methods discussed above are unable to treat purge streams high in chlorides, evaporation of the purge stream is favored. The attractiveness of evaporation as a way to treat wet FGD blowdown is that, in theory, all of the dissolved species, whether benign, hazardous, or toxic, can be separated completely from the water. Also, the process produces a stable solid that can be landfilled, and a high-quality distilled water is returned for reuse in the plant.