Water Recycling
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There are many technological solutions that could potentially help to alleviate the current water shortage on Oahu. For the purpose of this paper, our group has chosen to discuss what we believe to be the top three most feasible technological solutions. In order of current usability they are;
Water recycling
Desalination
OTEC (Ocean Thermal Energy Conversion)
Water Recycling
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 Oahus 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 Honolulus 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:
Secondary wastewater from the Honouliuli waste water plant is piped over to the recycling facility.
Then polyaluminum chloride is added and rapidly mixed in one of two mixing tanks.
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.
Then it the water goes through sand filters that trap all of the small particles.
The water moves over to the U.V. disinfection system, where it is treated with powerful U.V. lights.
From there the water goes through pumps into one of two, 2.5 million gallon storage tanks.
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 Oahus 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 groundskeepers at the Hawaii Prince Golf Course switched over to R-1 water in 2002, they have stopped fertilizing their courses. They found that the nutrients that were available in the R-1 water were sufficient enough to allow them to have a healthy course, without having to buy the expensive fertilizers. The end result of no having to purchase fertilizer is an $80,000 per year savings for Hawaii Prince Golf Course, as well as a significant amount of water that was not removed from Oahus aquifers (HWRF).
Reverse Osmosis is the process in which water is passed through a semi-permeable membrane, under high pressure. The result is that the membrane allows only water molecules to pass through, while filtering out particles that are larger than water molecules. First, secondary effluent from the Honouliuli passes through microfiltration. According to GE water & process technologies, microfiltration consists of thousands of strands with pores that are 5,000 times smaller than a pinhole. The water then passes through reverse osmosis, which consists of membranes with pores that are 5 million times smaller than a pinhole.
The reverse osmosis process at the Honouliuli Water Recycling facility has a four step process for treating secondary effluent. The process is as follows;
Secondary effluent from the wastewater treatment plant is passed through microfiltration.
Next, the water is passed through the reverse osmosis filters.
The purified water is placed into storage tanks.
Then the RO water is pumped out of the storage tanks and on to customers.
The majority of the customers that use the RO water are factories in the Campbell Industrial Park. The businesses in this area prefer RO water over water from Oahus aquifers. The reasoning is because RO water is free of minerals. This allows the factories to produce what they term as “high grade steam”. High grade steam is better in factories because it boils at a slightly lower temperature, and does not leave any mineral residue that could potentially wear turbine parts down (GE water & process technologies).
Desalination
Desalination is the process of converting saline water into fresh, drinkable water. Considering the geographic location of the island of Oahu and the amount of