Volume reduction technologies come in many shapes and sizes and can be combined with custom process engineering to provide a solution to suit specific wastewaters.
Membrane systems are usually the most cost-effective at volume reduction: nanofiltration (NF), reverse osmosis (RO), and ultra high-pressure reverse osmosis (UHP RO) provide increasing volume reduction. All produce a concentrated liquid brine reject. More advanced systems, such as Saltworks’ XtremeRO/NF can achieve reduction and reliability on challenging fluids, such as those with scaling ions and organics, however total dissolved solids (TDS) need to be below 90,000 mg/L for RO systems to be applicable.
When further reduction is required, or when TDS is greater than 90,000 mg/L, thermal evaporator-crystallizers are available to squeeze wastewater volumes even further. Thermal systems are more energy intensive than membrane systems, and achieving zero liquid discharge can be challenging for highly impaired wastewaters. Saltworks’ SaltMaker MultiEffect is an example of a modernized evaporator-crystallizer providing reliable solids production, and available in several options to meet energy, chemistry, and capacity requirements. Some wastewaters have volatile organic compounds (VOCs). An air-safe evaporator, such as the SaltMaker AirBreather, can ensure air emission standards are met.
Thermal systems generally have higher total cost than membrane systems, so it is advantageous to maximize membrane volume reduction first, to reduce the size of downstream thermal systems. Volume reduction can also be achieved incrementally, only taking the next process step if warranted by the treatment economics. In some cases, if water chemistry is suitable, ultrahigh recoveries could be achievable with membrane systems, which would reduce volumes needing disposal or going to an evaporation pond, eliminating the need for a thermal system.