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IWC 21-33: Xcel Cherokee near ZLD Wastewater Treatment System Design Considerations
Paul Brandt, Burns & McDonnell

Given new NPDES permit limits for chlorides, sulfates, total inorganic nitrogen (TIN) and other constituents for the plant’s common outfall. Meeting the new chloride and sulfate concentrations became the limiting factor for technology selection and compliance. Wastewater produced at the plant includes cooling tower blowdown, reverse osmosis (RO) system reject, stormwater, and other miscellaneous plant wastewaters. Due to the new NPDES limits, Xcel Energy, with the assistance of Burns & McDonnell, determined that a near-ZLD wastewater treatment system was the best option for the plant to replace an existing conventional clarification system. Treated water from the new system is returned to the plant for reuse and concentrated brine is routed to new evaporation ponds. Various options were evaluated in the study phase to help select the most economical treatment configuration including: Makeup water softening, High efficiency reverse osmosis, Nanofiltration, Closed-circuit reverse osmosis, Forward osmosis, Ultra-high pressure reverse osmosis, Membrane electrodialysis, Osmotically enhanced reverse osmosis, Mechanical vapor 15

recompression evaporator, Forced circulation crystallizer, Alternative thermal evaporator designs, Evaporation ponds, Waste heat cooling tower, Bypass evaporator spray dryer, Operational changes, Discharge to a nearby POTW facility

The wastewater system ultimately selected and designed includes:

Equalization ponds, High rate softening clarification, Multimedia filtration, Closed circuit reverse osmosis with 98% recovery of wastewater for reuse, Evaporation ponds for concentrated brine wastewater, Filter press for sludge dewatering, Required startup in Fall of 2021

The WWT project is currently under construction and is planned to complete startup at the end of 2021. This paper will cover the following aspects of the study and detailed design phases of the wastewater treatment system:

• Study phase options considered and drivers for the near ZLD system selected.
• Process description and design considerations/limitations of equipment selected.
• Operational changes to reduce wastewater flow requiring treatment.
• Challenges of elevated TOC in wastewater, effects on selected wastewater equipment, and TOC removal methods evaluated.
• Challenges and recommendations of locating new equipment in existing water treatment building
• Methodical approach to evaporation pond selection/sizing.

Paul Brandt is a Senior Chemical Engineer with Burns & McDonnell.  His 15 years of power industry experience include water and wastewater aspects of various systems such as: physical/chemical/biological treatment with ZLD for wet scrubber blowdown, demineralized water treatment, air quality control equipment, bottom ash handling, and CCR pond closures.

IWC 21-34: Power Plant Water Balance Tool Optimizes Load Leveling and Achieves ZLD
Dan Carey, Ph.D., P.E., Worley

Orlando Utilities Commission (OUC) operates two coal fired boilers in the Stanton Energy Center and has recently announced they will repower both units with natural gas. OUC had a need for a water balance model to guide dispatch, maintain ZLD, and understand the site wide salt balance. A calibrated model was created to predict evaporation rates, pond storage volumes, chloride and TDS. The model has been useful for optimizing current operation and predicting future conditions.

Dr. Carey has over 11 years of experience in biological and chemical wastewater treatment in industrial, municipal, and academic settings. At Worley, he serves as an environmental process engineer; his primary role is consulting and design in oil refineries, power plants, chemical manufacturing, and other industries.