THE REVERSE OSMOSIS PROCESS
The Reverse Osmosis (RO) process includes the following components:
- Reverse Osmosis
- One 0.5 Million Gallon Storage Tank
- RO Delivery Pumps
The production of RO water utilizes the membrane filtration process. Membrane filtration consists of a permeable membrane that allow particles smaller than the membrane pores to pass through, but captures particles that are larger than the membrane pores. In general, relatively high pressures are required to force the effluent through the permeable membrane.
The reverse osmosis process typically uses higher pressures and smaller pore sizes than microfiltration. Consequently, reverse osmosis can remove particles with lower molecular weights than microfiltration. Because of the high pressures involved in reverse osmosis, the process is capable of de-ionizing water and is typically used for desalination. Microfiltration is used as a pretreatment separation process downstream of the secondary treated effluent from the adjacent Honoluliuli WWTP secondary units. Self cleaning strainers at the Reuse Pump Station remove larger-sized particles that could clog the microfilters. The microfiltration process then removes additional residual suspended solids in the secondary effluent by utilizing a 0.2 micro hollow fiber membrane that is cleaned monthly using citric acid. This enables the reverse osmosis process to remove higher levels of ionic constituents from the effluent, thus reducing the degree of post-treatment required by RO water users to meet their water quality requirements. The microfiltration pretreatment process also prolongs the life of the reverse osmosis membranes by reducing the amount of membrane fouling and consequent cleaning required.
CURRENT USES OF RECYCLED WATER
The Honouliuli WRF currently supplies the City golf courses of West Loch and ‘Ewa Villages with 1 mgd each of R-1 water. Recycled water is pumped to the West Loch course at night, while the ‘Ewa Villages course is supplied during the day. The pumping rate to each course is 150 gallons per minute (gpm) at a pressure of 68 pounds per square inch (psi).
For more information about the Honouliuli Water Recycling Facility, please visit the official Honolulu Board of Water Supply Water. Organizations interested in touring the Facility may contact the Honolulu Board of Water Supply's Water Recycling Program at phone (808) 527-6156.