WHAT IS ZLD (ZERO LIQUID DISCHARGE)?

ZLD stands for Zero liquid discharge, this is a treatment process that removes or expels the liquid waste out of a system. ZLD produces clean and pure water thus reducing the wastewater economically. The clean water can be used for agricultural purposes.  By the use of ZLD systems, all the wastewater is recycled and purified virtually, this is done by employing advanced technologies of desalination. Thermal technologies can be used to achieve ZLD. Some examples of TT (thermal technologies) areCrystallizers, Multi Stage Flash (MSF) and Mechanical Vapor Compression (MCV) etc.

IMPORTANCE OF THE ZERO LIQUID DISCHARGE SYSTEM

1.      This system has the power to recover the resources that are in the wastewater. It lessens the volume of waste and therefore there is a decrease in the cost of waste management.

2.      Disposal cost can be decreased, this can be done by using ZLD plant.

3.      It improves the overall efficiency of ETP (Effluent treatment plant) and CETP (Common Effluent Treatment Plant), this can be done salt separation.

4.      The focus is mostly on production.

5.      ZLD can improve environmental performance.

COMPONENTS OF A ZLD SYSTEM

Zero liquid discharge is made of these components:

1.Clarifier: To precipitate out silica salts, metals and hardness

2.Biological process:Biological processes can be used or employed.It involves decomposition of the organic waste by the help of microbes. The processes like soil biotechnology treatment, Anaerobic Digestion etc. (as per COD/BOD ratio) come under biological processes

3.Chemical feed:This involves removal of suspended solids and metals by use of chemicals for precipitation, flocculation, disinfection and coagulation.

4.Filter: Secondary solid waste is concentrated after pretreatment with the help of the evaporator.

5.Filtration: To remove the suspended solids. It has three types as follows

 (a). Microfiltration.

 (b). Ultrafiltration.

 (c). Nanofilitration.

Alongwith all this, it helps to prevent corrosion.

6.Reverse osmosis: In the primary and secondary stages of concentration RO expels all dissolved solids from the stream that are present.

7.Brine concentration:  In this step, further concentration of the stream occurs which ultimately helps in decrease in the volume of waste.

8.Evaporator: The last stage in which concentrating is completed just before crystallization.

9.Crystallizer:There is a solid dry waste cake which is thrown or disposed of which has no liquid in it.

Although ZLD is a custom process, according to the need, necessity and design of the plant, other components can be added or removed which may be essential for that particular process system.

Components of a zero liquid discharge system depend on multiple factors

·       System’s adequate flow rate

·       Specific contaminants present in the stream

·       Volume of the dissolved material present in the waste stream (i.e. COD, BOD, TDS, TSS)