Project Summary
This project upgraded the water treatment plant to 100% reverse osmosis (RO) by adding one more 500-GPM RO unit (four total) and eliminating greensand treatment. Previously, about 20% of the water had been treated only with the greensand filters and then blended with the RO-treated water (also known as "permeate"). Eliminating the greensand filters had been necessary because they did not remove the excess salt and hardness from the new "deep" well. The production rate for the upgraded treatment system became 2,000 GPM (2.88 MGD). The future production rate was planned to be 3,000 GPM (4.32 MGD) with six RO units.
RO permeate contained very low concentrations of minerals and was very soft water, which made remineralization with calcium carbonate a necessity. A new building and remineralization tanks were constructed to achieve optimal hardness and alkalinity levels of between 50 mg/L and 70 mg/L (as CaCO₃).
New Building
A new 52 feet by 38 feet, 24-foot tall building was constructed to house the remineralization system, including two 20-ft by 10-ft calcite contactor tanks, a carbon dioxide injection system, and a pH adjustment system.
Carbon dioxide (CO₂) was used to dissolve the calcite into the permeate. A 6-ton capacity CO₂ tank (16-ft tall) was installed outside the new building. A CO₂ dosing system, using 15-GPM water and the CO₂ supply, injected dissolved CO₂ into the permeate discharge piping. A backup CO₂ supply consisted of twelve CO₂ gas cylinders.
Final pH was adjusted by injecting a soda ash solution into the remineralized water. This system included two new 3,000-gallon tanks, a mixing pump, and the existing repurposed dosing pumps. A bridge crane was installed in the new building for loading calcite and soda ash into the tanks.
Existing Water Treatment Plant Improvements
Improvements included one new RO unit and modifications to the three existing RO units to improve water production and decrease the rate of membrane scaling. The greensand filter tanks and chlorine contact tank were demolished to make room for new equipment.
A new permeate flush system was installed. This system was used daily to flush the RO filter membranes with permeate, which was necessary to extend the useful life of the membranes. This system included a 4,000-gallon water tank and a 380-GPM pump. The existing CIP/Permeate Flush system was retained for CIP (clean-in-place), which was a semi-annual chemical cleaning of the membranes.
The existing RO antiscalant dosing system was rebuilt, adding two more dosing pumps (for a total of six). Antiscalant was used to maximize water production and protect the membranes from scaling. The existing greensand filter backwash pump was reused and repurposed for the remineralization tanks. Three chlorine injection points were included: (1) the permeate discharge pipe, (2) before, and (3) after the clear well. A new distribution system flow meter was installed to replace the old meter for the discharge to the distribution system. A new bridge crane was installed in the existing building for servicing the Distribution System Pumps and the new RO Unit(s).
