How to cut energy cost for ZLD evaporators with FO
When using FO for industrial wastewater management, it is possible to achieve a highly effective concentration of the effluent, which both allows you to reduce the load on your thermal evaporators in zero liquid discharge systems to save energy and to recover more clean water for reuse.
Zero liquid discharge (ZLD) systems are getting greater attention in connection with wastewater treatment for complex industrial production. The ZLD process ensures that no effluent is discharged from the facility thus eliminating the risk of contaminating the local water supply or environment. Once all liquids have been removed from the effluent, the factory can then safely dispose the remaining solid waste, often after reclaiming valuable resources like Glauber’s salt.
Despite all these benefits, ZLD systems are expensive to implement, have high OPEX and can be challenging to maintain. The main concern is the energy cost from running the thermal evaporators and crystallizer which remove the remaining water from the brine once the effluent has been through pre-treatment.
Reduced energy consumption and simpler process
Depending on the setup of the upstream effluent treatment, the quality and volume of the processed wastewater can make it necessary to employ several different types of evaporators to effectively reduce the remaining liquid before the evaporator waste brine is sent to a crystallizer for final processing.
For example, it might be relevant to have both a high-capacity evaporator like a multi-effect evaporator (MEE) coupled with an agitated thin film dryer (ATFD) which can remove a lot of water but is also energy intensive, and a low-capacity mechanical vapor recompression (MVR) evaporator dedicated to handling more complicated effluent streams.
By implementing FO in the effluent treatment process, it is possible to achieve a much higher concentration of the effluent before it reaches the evaporator stage. A FO solution can be designed to match the exact composition of the effluent and remove 70-90 % more clean water. At this point, it is possible to replace the complex multi-evaporator setup described above with a single MEE evaporator unit which would require much less energy to operate.
Usually, an initial lab-scale test followed by a pilot project ensures the best outcome.
Before embarking on the process of building or selecting and implementing a ZLD solution, take time to make these important considerations:
- What are your primary business drivers for implementing ZLD? While the need to comply with stricter regulation is the primary driver for most ZLD implementations in India, there may be other business drivers that are relevant to consider. Do you want to reduce your dependency on scarce water resources, reduce your use of chemicals, minimize your waste or simplify your effluent treatment? This information is vital for your ability to steer the ZLD implementation project in the right direction. The optimal solution depends on your plant and treatment goals.
- What are the characteristics of the incoming effluent? When selecting the ZLD solution, it is vital to take the exact characteristics of the wastewater effluent. You need to consider the total volume, pH, temperature, biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS) and salinity, to name a few.
- How can you reuse the treated water in your production? One of the main benefits of a ZLD wastewater treatment system is the ability to reuse the majority of the processed effluent – often as much as 75 percent or more, depending on the specific site and design. A forward osmosis membrane solution can improve the quality of the recycled water, by extracting clean water while rejecting difficult contaminants even with high BOD/COD/TOC levels, thereby making more available for reuse.
- Do you want to reclaim valuable solids, salts, and chemicals? A ZLD can improve your ability to recover and reuse valuable compounds like salts. This can offset some of the total operating cost of the ZLD system.
- What can you do to reduce your energy costs? One of the major expenses of running a ZLD treatment system is the cost of the energy needed to power the evaporators which remove the remaining liquid from the effluent. By integrating an forward osmosis (FO) process that uses Aquaporin Inside® FO membranes in your effluent treatment system, you can minimize waste by effluent volume and sludge reduction to save costs related to disposal or evaporation/crystallization in Zero or Minimal Liquid Discharge systems.