By: Tom Higgins, Global Technology Leader for Power Water and Process
The newly promulgated Steam Electric Power Effluent Limitation Guidelines (ELGs) for flue gas desulfurization (FGD) wastewater are based on biological treatment to remove selenium and nitrates. Consistently achieving these ELG limits with biological treatment can be challenging. As water quality standards and ELGs become more stringent, utilities are examining alternatives that do not require discharging FGD wastewater. For utilities inclined toward zero liquid discharge (ZLD) alternatives, the key to achieving ZLD is finding the optimal scenario that overcomes site-specific challenges, while also making evaporative technology costs competitive with physical/chemical plus biological treatment costs.
CH2M has evaluated ZLD for several different wastewater applications and developed an approach to achieving ZLD by maximizing the natural evaporative capacity of the FGD system. Our MEGA Symposium presentation shares CH2M’s experience working for a confidential client’s plant and our approach in successfully getting the plant to zero discharge of its FGD wastewater.
CH2M assisted the case study plant in developing a comprehensive plan to address future compliance with new National Pollutant Discharge Elimination System (NPDES) permit discharge limitations. In addition to meeting the strict requirements of the ELG limits, the plant had a strong likelihood of receiving a boron limit in its next NPDES permit cycle.
Through our comprehensive approach, we were able to lower the overall capital cost of FGD treatment by approximately 23 percent and the annual operations and maintenance (O&M) cost by 18 percent compared to all FGD wastewater going directly to advanced treatment. Additionally, reduced flow and partial lime softening lowered ZLD costs to make this technology cost-competitive with biological treatment, allowing the regulated utility to more easily recover costs for installing a ZLD system. Furthermore, our laboratory testing showed that the simulated treatment process removed approximately 62 percent of soluble boron, 92 percent of mercury and 90 percent of selenium. Finally, an evaporator vendor verified our estimates of lime dosage, magnesium removal and boiling point rise to brine production.
For more detailed information on this case study, join me at MEGA Symposium! If you can’t attend and have questions about ZLD at your facility, please reach out to me.
Dr. Thomas E. Higgins, PhD, PE, is a Vice President, Technology Fellow and Global Technology Leader for Power Water and Process at CH2M. He earned three degrees in Environmental Engineering at Notre Dame, was an Associate Professor of Civil Engineering at Arizona State University and has 40 years of experience developing technologies for and designing wastewater treatment systems for power plants, particularly for metals removal. He is the author of more than 100 publications, including three books and three patents. </br>
Krystal Perez, PE, is a senior chemical process engineer at CH2M experienced in water chemistry, industrial wastewater treatment, groundwater treatment and waste-to-energy technologies. Krystal’s background includes a wide-range of service areas including treatment alternative evaluations, treatability and optimization studies, detailed design, services during construction and plant operations. Most recently, Krystal has led process engineering for several coal-fired power plant wastewater design evaluations with an emphasis on zero liquid discharge (ZLD) technologies.
Dennis Fink, PE, brings more than 20 years of experience in water/wastewater treatment and characterization, pollution prevention and groundwater remediation projects. He specializes in power plant and refinery wastewater treatment and management. Dennis’s recent work includes leading development of wastewater compliance strategies at seven power plants in the past two years.