How does a zero liquid discharge plant works?

December 13, 2022by newebay020

Not all industrial facilities that create wastewater will need to release nothing but liquids. It is typically seen as a last option because it can be a difficult procedure with a hefty upfront cost.

It might be worthwhile to pursue if a facility is situated on a site with severe water scarcity problems and/or exorbitant discharge fees, but if it’s not required (some local and/or federal regulations might require ZLD), careful consideration must be given to whether or not it will benefit your facility.

You might be thinking, “How does it work? ” well the lengthy response to this query is condensed and explained for you below:

What is the process of a ZLD treatment system?

Although specific procedures for treatment vary, a common Zero Liquid Discharge treatment centre procedure often entails the following steps:

Pretreatment and Conditioning 

Pretreatment is used to condition the water and reduce suspended particles and materials that may otherwise scale and/or foul subsequent treatment procedures. It removes simple substances from the wastewater stream that can be filtered out or precipitated out. Usually, the clarifier and/or reactor in this treatment block precipitate out the metals, hardness, and silica.


It may be necessary to employ caustic soda or lime at this step to help the coagulation process, which entails adding various chemicals to a reaction tank in order to remove the majority suspended particles and other impurities.This procedure begins with a variety of mixing reactors, usually one or two reactors that add certain chemicals to remove all of the smaller water particles by combining them into larger particles that settle out. Aluminum-based coagulates like polyaluminum chloride and alum are the most frequently utilised coagulants. Sometimes coagulating the particles will also benefit from a slight pH adjustment. When coagulation is finished, the water enters a flocculation chamber where long-chain polymers (charged molecules that grab all the colloidal and coagulated particles and pull them together) are stirred in to combine the coagulated particles, resulting in visible, settleable particles that resemble snowflakes.


Water and flocculated material enter the gravity settler’s chamber (or the sedimentation part of the ZLD treatment process), where they flow outward from the centre. The water rises to the top and overflows at the edge of the clarifier, causing the sediments to gradually fall to the bottom and create a sludge blanket. After the solids are gradually mixed in the centre of the clarifier in a cylindrical tube, the sludge is then pushed out of the bottom into a sludge-handling or dewatering operation. The settlers can alternatively be created using a plate pack for a more compact footprint.


Alternatively, to using a gravity sand filter after the clarifiers, ultrafiltration (UF) can alternatively be utilized as a replacement for the complete clarifying process. The newest method for treatment is membranes, which bypass the entire clarifier/filtration train and pump water straight from the wastewater source via the UF (post-chlorination). This technique produces a liquid that is subsequently filter-pressed into a solid, leaving behind a solution with far less suspended particulates and no scaling-up concentration treatment options.

Phase one Concentration

Reverse osmosis (RO), brine concentrators, or electrodialysis membranes are frequently used for concentration in the early phases of ZLD.

The majority of the dissolved solids that pass through the process will be captured by the RO train, but as was we know about typical ZLD issues, it’s critical to only flow pretreated water through the RO system because untreated water will quickly foul semipermeable membranes. On the other hand, brine concentrators can typically handle brine with a much higher salt content than RO and are also used to remove dissolved solid waste. They produce a reduced volume of waste fairly effectively.

This section of the ZLD system also allows for the use of electrodialysis. It is a membrane method that may be applied in phases to concentrate the brine and employs positively or negatively charged ions to allow charged particles to pass through a semipermeable membrane. It frequently works in tandem with RO to produce incredibly high recovery rates.

Together, these technologies can concentrate this stream’s salinity down to a high level while removing between 60 and 80 percent of the water.


The process of creating a solid, which comes after concentration, is carried out by heat processes or evaporation, in which all the water is removed, collected, and used again. By adding acid now, you may neutralize the solution and prevent scaling and damage to the heat exchangers while heating it. To release dissolved oxygen, carbon dioxide, and other nonconsensual gases during this stage, deaeration is frequently used.

After that, the remaining waste is transferred from an evaporator to a crystallizer, where it continues to boil off all the water until all of the impurities in it crystallize and are filtered out as a solid.


Last but not least, Netsol has years of expertise in custom-designing and producing industrial wastewater treatment, so please feel free to contact us with any inquiries.

Contact us here on +91-9650608473 or email at if you’d like further details or to get in touch. In order to schedule a conversation with an engineer or submit a price request, you may also visit our website.

We can guide you through the process with the best solution and a reasonable price for your ZLD wastewater treatment plant’s requirements.

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