Zero Liquid Discharge (ZLD) Wastewater Treatment
An advanced technology from ENCON.
What is Zero Liquid Discharge?
Zero Liquid Discharge (ZLD) is a wastewater treatment process developed to completely eliminate all liquid discharge from a system. The goal of a zero liquid discharge system is to reduce the volume of wastewater that requires further treatment, economically process wastewater and produce a clean stream suitable for reuse. Companies may begin to explore ZLD because of ever-tightening wastewater disposal regulations, company mandated green initiatives, public perception of industrial impact on the environment, or concern over the quality and quantity of the water supply.
Zero Liquid Discharge Technology for Wastewater Treatment
The first step to achieving ZLD is to limit the amount of wastewater that needs to be treated. Once wastewater generation is minimized and the volume of wastewater that needs to be treated is known, you can then explore what equipment is needed, which depends on the characteristics of the wastewater and its volume. A traditional approach to ZLD is to use filtration technology, funnel the reject waters to an evaporator, and send the evaporator concentrate to a crystallizer or spray dryer. However, the equipment to de-water the concentrated slurry tends to be very large and extremely expensive, which limits the cost effectiveness to only those with very large waste streams.
- ZLD Process Step-by-Step Explanation - Read More
Feed In
This could be wastewater direct from a process or it could be reject from an initial wastewater treatment step such as Reverse Osmosis.
Pre-TreatmentPretreatment of the feed wastewater may be necessary. Possible treatment could include pH adjustment, Antifoam or antiscalent.
MVR EvaporatorThis step performs the initial dewatering of the wastewater. The result of this step will be two streams, condensate (i.e. distilled water) and a concentrated wastewater residue. The amount of wastewater reduction will vary by application, but the average is around 90% condensate, 10% concentrated wastewater residue.
Holding TankThe concentrated residue from the MVC is pumped into this holding tank where the residue separates into two layers: slurry (solids) and supernatant (liquids). The slurry is fed into the centrifuge for final dewatering and the supernatant is fed into the thermal evaporator.
Thermal EvaporatorThe concentrated wastewater residue is fed into the thermal evaporator for further dewatering. Water vapor is exhausted to the atmosphere and the residue is pumped back to the holding tank. Once again, the additional reduction percentage varies by application, but it generally further reduces the concentrated wastewater residue by an additional 40 - 70%. For example, if we had a 90% reduction in the MVC step and an additional 60% in the Thermal step, for every 100 gallons of wastewater we started with we would have 4 gallons of concentrated residue remaining.
CentrifugeThe remaining concentrated wastewater residue is fed into a centrifuge for final dewatering. After this, you are left with solids. The liquid removed by the centrifuge is then sent back into the holding tank.
Why choose ENCON?
The ENCON approach is unique because it uses cost-effective, time-tested equipment that makes it economically feasible for even moderately sized waste streams. At the core of the ENCON zero liquid discharge solution is evaporation technology. Evaporation always figures prominently in most ZLD solutions because it has always been more “hands off” than other wastewater treatment methodologies resulting in a dramatically lower labor cost. Evaporation technology can handle a much wider range of waste streams compared to membranes and traditional physical / chemical treatment methodologies. Finally, evaporation does a much better job of concentrating waste streams compared to other methods, thereby yielding a lower cost for disposal.
Two types of evaporation technology are used in the ENCON ZLD solution. First, at a typical operating cost $0.01 - $0.02 per gallon of distillate, the ENCON Mechanical Vapor Compression (MVC) Evaporator is also very energy efficient and yields a high quality distillate. Models are available that can process 40 to 4,000 gallons of distillate per hour. Second, the ENCON Thermal Evaporator can be used with a variety of heat sources, such as natural gas, propane, #2 fuel oil, waste oil, steam, and electricity. Capacities range from 8 to 400 gallons per hour.
Achieving Zero Liquid Discharge Over Time
The ENCON approach to Zero Liquid Discharge is that it can be implemented in stages over time. For example, a company may choose to install an ENCON MVR Evaporator to minimize their wastewater hauling expenses. A year or so later, they find that feeding an ENCON Thermal Evaporator from the MVC’s concentrate holding tank to further reduce the volume of liquid waste makes financial and environmental sense. When the company finally decides to become a Zero Liquid Discharge facility, it is a simple matter of adding a filter press and accessories to the current wastewater process.