Every industrial facility that originates wastewater will not require zero liquid discharge system or ZLD Manufacturers & ZLD Suppliers.
ZLD Manufacturers & ZLD Suppliers
It is usually looked to as end resort because it can be a complex process that requires a massive investment.
If a facility is settled on a site that has major issues of water scarcity or astronomical discharge fees, it might be serviceable to seek, but in the instances some federal regulations or local might require zero liquid discharge. So a proper and effective decision must be made as to whether it will benefit your facility or not.
If your industrial facility does is looking for ZLD, this article will help you to find out “what is zero liquid discharge and how does it work?
Table of Contents
What is a Zero Liquid Discharge or ZLD system?
Zero Liquid Discharge System or ZLD System is a system that uses highly advanced technological water treatment processes to limit all the liquid waste at the end of your industrial process.
A well-designed and efficient ZLD treatment system should be able to:
- Handle all essential variations in waste contamination and flow
- Allow for needed chemical volumes adjustments
- Recover and reuse around 95% of your liquid waste
- Treat and retrieve valuable products like salt and brines from your waste
- Create a dry, solid cake for disposal
A proper ZLD treatment system will also help your industry facility to meet severe effluent requirements.Just keep one thing in your mind is that the requirements of your facility will vary upon whether you are releasing into a publicly owned treatment works (POTW) or to the environment under a NPDES permit called as National Pollutant Discharge Elimination System.
What compnents are included in a basic ZLD system?
The basic and exact components of a ZLD treatment system will entirely depend on (1.) the volume of material which is dissolved and present in the waste, (2.) the required flow of system’s rate, and (3.) what specific and essential contaminants are present. But in general, a basic zero liquid discharge treatment system includes some type of:
- clarifier and/or reactor to carry out metals, hardness, and silica
- chemical feed to help facilitate the flocculation, precipitation, or coagulation of any suspended solids and metals.
- filter press to gather secondary solid waste alongside an evaporator or after pretreatment
- ultrafiltration (UF) to eliminate all the remaining trace amounts of suspended solids and prevent scaling,corrosion, and fouling down the line of treatment
- reverse osmosis also caled (RO) is used to extract the majority of diffused solids from the water stream in the main phases of concentration
- brine concentrators to further reject from electrodialysis or concentrate the reject RO stream further to reduce waste volume
- evaporator for evaporating access water in the last phases of waste concentration before crystallizer.
- crystallizer to boil off any leftover liquid, leaving you with a dry like a solid cake for disposal
Depending on all the needs of your plant and process, these general standard components are usually sufficient.
However, if you are looking for a plant that requires bit more customization for a system, there might be some technologies or features that you will need to add on.
Because wide range of industries use zero liquid discharge and the various waste streams produced/
ZLD is a highly and straight forward custom process and these add on’s will entirely depend on the individual needs of your facility.
How does a ZLD System work?
The typical facility process of ZLD treatment will usually include the following steps:
Pretreatment and conditioning
Pretreatment is used to execute simple things from the wastewater stream that can be easily filtered or precipitated out, conditioning the water and decreasing the suspended materials and solids that would otherwise foul or scale the following treatment steps.
Typically this treatment block contains of some type of reactor or a clarifier to precipitate metals, hardness, metals, and silica.
Sometimes it is called an essential step because it requires the addition of caustic lime or soda to help with coagulation.
Now what does coagulation means, well it is a process where different chemicals are added to a reaction tank to remove the majority of various contaminants and other suspended solids.
This process generally starts off with an assortment of mixing several reactors, typically one or maybe two reactors that add certain chemicals to take out all the clear and finer particles in the water by joining them into heavier particles that settle out. The most coagulates that are widely used are aluminum-based such as polyaluminum and alum chloride.
Sometimes a slight adjustment of pH will help to coagulate the particles, as well.
When coagulation is fully complete, the water invades a flocculation chamber where the coagulated particles are slowly mixed together with long-chain polymers and creates a visible, settleable particles that follow snowflakes.
The sedimentation part of the ZLD treatment process is also called as gravity settler. This setter is typically a big circular device where flocculated material and water stream into the chamber and circulate the material from the center out.
In a very slow and settling process, the water ascents to the top and overflows at the clarifier’s parameter, allowing all the solids to settle down to the base of the clarifier into a sludge blanket.
The solids are then raked to the middle of the clarifier into a cylindrical tube where a slow stirring takes place and the sludge is pushed out of the base into a dewatering operation or sludge-handling.
The settlers can also be designed carefully by using a plate pack for smaller footprint.
Depending on the material in the feed, extra reactors or chemistry may be required for the reduction of silica or metals. Careful precaution must be given to the pretreatment step to turn into a successful ZLD system.
Ultrafiltration (UF) can also be used to replace the entire clarification process altogether.
Membranes have become the latest technology for treatment that is pumping water directly from the wastewater source through the post-chlorination and removing the entire clarifier/filtration train.
Out of this process generates a liquid that is then converted and filter-pressed into a solid, resulting in a solution that is much lesser in suspended solids and without the capacity to rise up concentration treatment.
Phase-one concentration
Concentrating in the beginning stages of ZLD is usually done with membranes like brine concentrators, electrodialysis, or reverse osmosis (RO).The RO train will seize the majority of dissolved solids that move through the process, but it’s essential to move only pretreated water through the system of RO as allowing untreated water to flow through the semipermeable membranes will impure them quickly.
On the other hand, Brine concentrators, are also majorly used to eliminate dissolved solid waste but they are usually easy to handle brine with a more important salt content than RO. They are pretty proficient for turning out a decreased-volume waste.
Electrodialysis can also be effectively used at this part of the zero liquid discharge treatment system. It’s a process of membrane that uses negatively or positively charged ions to allow charged particles to move through a semipermeable membrane and can be used in several stages to concentrate the brine. It is often used in connection with RO to carry out extremely high recovery rates.
Combined, all these technologies take this stream and focus it down to a high salinity while pulling out up to majority 60–80% of the water.
Evaporation/crystallization
After the concentration step is entirely completed, the next step is producing a solid, which is done through evaporation or thermal processes where you evaporate all the water collect it, and then reuse it.Adding acid at this stage will help to neutralize the solution so, when scalding it, you can avoid harming and scaling the heat exchangers.
Deaeration is usually used at this stage to release all the carbon dioxide, dissolved oxygen, and other noncondensible gases.
The leftover waste then goes directly from an evaporator to a crystallizer, which resumes to boil off all the water until all the contaminations present in the crystallized water and are filtered out as a solid.
Recycled water distribution/solid waste treatment
If the treated water is being used again in an industrial process, it’s typically pumped directly into a holding tank where all the water can be used based on the facility demand.The ZLD treatment system should have clean and enough purified the water to be reused safely in your process.
The solid waste, at this point, will invade into a dewatering process that will take out all the water of the sludge with belt presses, filter or yielding a solid cake.
The sludge is instantly put onto the press and runs between two belts that influence the water out, and after that the sludge is then put into a vast hopper that goes to either a place or landfill that reuses it. The water carried out from this process is also typically reused.
Here is video that will help you understand The ZLD System More Clearly
In conclusion
Savas has over 20 years’ experience in manufacturing and custom-designing industrial wastewater treatment.
So feel free to reach out to us with all your doubts and questions. For additional information or to get in touch, contact us here.
You can also request a quote or take a tour to our website to set up a call with an engineer. We can walk you through all the essential steps for developing the effective solution and realistic cost for all the needs of your ZLD wastewater treatment system.