Outsourced Water Treatment Plant – USA
To meet the client’s ultra-high pure demineralized water specifications, Veolia Water Technologies designed an outsourced water treatment plant (OWTP) to reduce the TOC to less than 10 ppb.
Southeast USA – A large U.S. based power generation company operating nuclear power facilities in the Southeast U.S. contacted Veolia Water Technologies to develop a competitive solution to design, build, install, operate and maintain two new 400 GPM ultra high purity demineralized water plants that would replace their internally operated, 25+ year old, demineralized water plant at each of the two separate stations.
The Client’s NeedsAs part of the upgrade and replacement, the client required higher quality demineralized water (parts-per-trillion concentration level of metals), low Total Organic Carbon (TOC) and low dissolved oxygen levels. In addition, the client also required a specialized contingency for mobile water to back-up the installed system.
The Southeast Nuclear Power Utility had been operating each of their demineralized water plants with conventional technology: media and carbon filtration, reverse osmosis, and mixed bed demineralization. Both stations had a capacity of approximately 2200 MW, and operated pressurized water reactors. Plant 1 originally had Diatomaceous Earth Pre-coat Filters, while Plant 2 had been utilizing Veolia’s L’Eau Claire™ Upflow Filter for the initial filtration step.
Project & Technology SolutionsTo meet the client’s ultra-high pure demineralized water specifications, Veolia Water Technologies designed the following outsourced water treatment plant (OWTP) to reduce the TOC to less than 10 ppb.
Veolia Water Technologies included ultrafiltration (UF) for clarifiation/filtration of the lake water because it is superior to the media fitration that was currently being used. The UF offered a nominal pore size of 0.03 μm (30 nm) versus 10 – 50 μm for media. The second step in the OWTP was single pass reverse osmosis (RO) with a 5:3 array. This was chosen due to the low total dissolved solids (TDS) of the source water. Continuous electro-deionization (CEDI) was selected for the next step because it works by capturing the charged particles on ion exchange resin and then transfers them through ion exchange membranes to produce high quality water. In this case, not only does CEDI provide a higher quality of water than a 2nd pass RO, but the exchange resin also provides reduction in TOC through charge attraction and adsorption.
Process DescriptionBy the time the water stream reaches the pure water storage tank, it has been through several steps reducing the TOC to a very low level where it is practical to use a UV TOC destruct system. The UV TOC destruct system utilizes UV lamps that emit short wave lengths of UV light, approximately 185 nm, which carry a higher amount of energy as compared to 254 nm typical of disinfection UV systems. The UV energy generates hydroxyl-free radicals from the water molecules that destroy the remaining organic molecules, such as the low molecular weight THMs.
Finally, downstream of the UV is the worker / polisher mixed bed DI (MBDI). The exchange resin in the MBDI removes the trace TDS and byproducts of the UV system through charge attraction and adsorption. The majority of the MBDI run lengths will be replaced based on time in service rather than exhaustion as dictated by best practices. This prevents compaction of the resin, which will happen well before ionic exhaustion in this system design. This low ionic load is due to the multi-step RO + CEDI approach in reducing the load on the MBDI as well as the nitrogen blanking on the pure water tank to prevent contamination from atmospheric carbon dioxide and particles.