3.OTEC (Ocean Thermal Energy Conversion)
Water recycling here on Oahu is an important part of ensuring a sustainable water supply for future generations. Through the natural water cycle, the earth has recycled and reused water for millions of years. Water recycling generally refers to projects that use technology to speed up these natural processes. Recycled water can reduce much of Oahu's aquifer water demands, as long as it is adequately treated to ensure water quality appropriate for the use.
The recycling of water has many benefits. The main benefit is that by recycling water, we are saving ground water for other uses. Another benefit is that recycled water is safe and has been used for over 40 years, with no negative human or environmental side effects (HWRF). Because the amount of precipitation on Oahu changes varies, sometimes the island goes through drought. With water recycling, the amount of secondary effluent available for recycling is always greater than the demand of it, therefore making it virtually drought proof. Also, recycled water can be produced at a price that is cost-effective, when compared with other methods.
Water recycling facilities on Oahu have been in place since 2000 (HBWS). The Honouliuli Water Recycling Facility in Eva, is the largest recycling plant on Oahu. The plant was built next to the City and County of Honolulu's waster water treatment plant, which provides the recycling plant with secondary effluent as the base for the recycling process. Currently, the facility has the production capacity of 12 million gallons per day and produces two grades of recycled water. R-1 water is used for irrigational uses and Reverse Osmosis (RO) for industrial uses.
The facility is currently capable of producing up to 10 mgd of R-1 water, which is the highest level of treatment as designated by the Hawaii DOH. R-1 water is used throughout the state of Hawaii for golf course irrigation, landscaping, and agriculture. The RO water is used for industrial uses such as boiler feed water for producing high-grade steam, cooling tower water, and process water for refineries. The facility currently has an RO capacity of 2 mgd. Both types of recycled water begin with the same secondary treated effluent from the Honouliuli WWTP.
According to the Honouliuli Wastewater Recycling Facility website, the basic process of producing R-1 grade water is as follows: 1.Secondary wastewater from the Honouliuli waste water plant is piped over to the recycling facility. 2.Then polyaluminum chloride is added and rapidly mixed in one of two mixing tanks. 3.Next, the effluent then flows into one of three flocculation tanks to facilitate the coagulation of suspended and dissolved particles to form larger and/or denser particles. 4.Then it the water goes through sand filters that trap all of the small particles. 5.The water moves over to the U.V. disinfection system, where it is treated with powerful U.V. lights. 6.From there the water goes through pumps into one of two, 2.5 million gallon storage tanks. 7.Finally, the R-1 water moves through pumps that ship it to customers.
The R-1 water that is produced through this process has many agricultural benefits over water that is drawn from Oahu's aquifers. The main positive attribute is that retains many of the beneficial nutrients of secondary effluent without the harmful risks to the environment. The nutrients that stay in the R-1 water allow farmers and golf courses to not fertilize as much, or at all. One of the best examples of the benefits of using R-1 water is the case of the Hawaii Prince Golf Course. Since the...