Power plants—whether fossil-fuel or nuclear—generate wastewater from multiple sources, including flue gas desulfurization, ash handling, boiler and cooling tower blowdown, and stormwater runoff. Each stream contains different contaminants at varying levels of total dissolved solids (TDS) and total suspended solids (TSS), creating complex treatment challenges. Facilities pursuing zero liquid discharge (ZLD) aim to recover and treat this wastewater while meeting permit requirements, sustainability goals, and contaminant limits defined by effluent limitation guidelines (ELG).
ZLD systems typically integrate pre-treatment, evaporation, and crystallization processes to concentrate and recover water while converting residual contaminants into solid waste. Pre-treatment removes suspended solids and hardness to prevent scaling, while thermal or mechanical evaporators separate water from dissolved salts. The concentrated brine is then processed in crystallizers to generate solid salts suitable for safe disposal or reuse. By eliminating liquid discharge, ZLD not only ensures regulatory compliance but also maximizes water reuse, reduces freshwater intake, and minimizes environmental impact.
Power generation facilities pursuing ZLD must manage multiple wastewater streams while maintaining regulatory compliance
Advanced ZLD treatment
Water chemistry will determine which solutions comprise the treatment train. For some applications requiring ZLD, Xylem will combine the Vacom One-Step solution with a reverse osmosis (RO) system or a type of clarification such as a dissolved air flotation (DAF) or CoMag® ballasted clarification system to manage the total dissolved solids (TDS). This is especially true if the water has ~5,000 mg/l containing arsenic and selenium or other contaminants.
Xylem’s Vacom One-Step ZLD system combines evaporation and crystallization in a single process, allowing it to treat wastewater with a wide range of TDS. High-flow operation ensures efficient processing, and as contaminants crystallize, they scour the system interior, preventing scaling and fouling.
Treatment by TDS range
- Below 30,000 mg/L TDS: Wastewater in this range may require pretreatment—such as reverse osmosis (RO), dissolved air flotation (DAF), or other clarification processes—prior to treatment with the Vacom One-Step system.
- Above 30,000 mg/L TDS: Xylem’s Vacom One-Step zero liquid discharge (ZLD) solution can effectively treat effluent in this range without the need for pretreatment.
Treatment outcomes
The Vacom One-Step process produces two types of material:
- Treated water – Clear water that can be discharged in compliance with regulations or recycled through the process for further treatment.
- Crystallized solids – Depending on water chemistry, solids may be dry or form a slurry with varying consistency.
Dry solids can be sent offsite for disposal. Slurry can undergo further treatment and liquid separation using a filter press to produce drier solids. In some cases, slurry from fossil-fueled power plants can be combined with fly ash and repurposed for commercial applications, such as asphalt or gypsum for drywall manufacturing.
With Xylem’s Vacom One-Step, power generation facilities can:
- Minimize or eliminate liquid discharge
- Recover water for reuse
- Reduce waste management and disposal costs
- Support regulatory compliance and sustainability goals
