Challenge
A 250-megawatt power plant in the Western United States utilized evaporation ponds to hold large volumes of wastewater discharged from their operations. The powcs-power-plant-saveser plant operated three ponds, capable of holding 35 million gallons of water each. The customer experienced two major issues with their evaporation ponds: contaminant levels and capacity. The plant experienced an unexpected large increase in the amount of total dissolved solids (TDS) in its well water, which rose from 500 TDS to 2,500 TDS in the space of three years. Additionally, levels of wastewater production – and subsequent discharge – were much higher than anticipated, doubling the expected amount of water within the evaporation ponds. Although initially planned to last for 15 years, the ponds had reached maximum levels after just three years. While naturally-occurring evaporation could help decrease water levels over time, it would not remove a substantial amount of water quickly enough to help the plant. In addition, the customer did not have the physical space, building permit, or budget to build additional evaporation ponds. At this point, the customer was faced with having to shut down operations or de-rate until the excess water could be hauled away in trucks. However, the hauling cost was significant: at nearly $0.50 per gallon, the cost to empty only one of the three ponds was estimated at $17 million dollars. To avoid this massive expense, as well as the need for immediate help, the customer turned to Veolia to find a solution.
Solution
After reviewing the situation, wastewater reuse was deemed to offer the most value to the customer while also avoiding costly hauling expenses. The pond water would be treated to remove contaminants and then fed back into the plant for use in its boiler system. Upon closer inspection, the pond water was found to be extremely dirty: 100 NTU turbidity and 40,000 ppm salt content, containing a mix of cooling tower blowdown, water treatment polymers, organic chemicals from the plant operations, wash water from the plant, enormous seasonal algae blooms, potentially toxic algae and bacteria, anoxic conditions, sulfate, nitrate-reducing bacteria, and Hydrogen Sulfide gas. In addition, hot summer temperatures of over 100 degrees Fahrenheit and variable weather conditions including wind, rain, and sun also contributed to other issues such as pond stratification, turnover, and huge variability swings. Page 2 CS1589EN.docx In order to effectively treat this challenging water supply, and reuse it within the power plant, Veolia introduced a customized wastewater recovery system. The system was designed to process 1,000 gallons of water per minute using a combination of Veolia equipment and chemistry, including:
- Coagulation
- Oxidation
- Filtration
- Scale and biological control
- High salinity reverse osmosis
- Automation and recycle
- Concentration RO, plus various other adjunct, proprietary technologies.
The entire system was delivered in just days, and functioned as a self-contained operation in containerized water treatment units protected from wind, sun and rain. It did not require any power lines from the power plant. The solution also included 24/7 on-site Veolia service personnel to monitor and control the water treatment system.
Result
The wastewater treatment system was extremely effective in cleaning the pond water for reuse. The system produced 60 million gallons of pristine boiler feed water to feed the power plant, and reduced demand on the plant’s wells by over 90 million gallons over a period of two years. More importantly, the solution enabled the power plant to continue operations and avoid an unplanned shutdown. By avoiding uninterrupted power production, as well as costs to haul away the excess water, the customer saved over $20 million.