Seawater reuse primarily involves desalination, a process that removes salt and other impurities to produce potable water. There are two main methods:
Desalination Methods:
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Thermal Desalination (Distillation): This method boils saltwater, collects the steam, and condenses it into purified water. This is a more energy-intensive process. [Reference: There are two classes of desalination: thermal or, distillation process, heats the saltwater to boiling, collects and condenses the steam producing purified water; the membrane class Reverse Osmosis (RO) and Electro-Dialysis reversal (EDR) method involves forcing salt water across a semipermeable membrane that separate ...]
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Membrane Desalination: This includes Reverse Osmosis (RO) and Electrodialysis Reversal (EDR). These methods force saltwater through semi-permeable membranes, separating the salt from the water. RO is more commonly used and has a cost ranging from $0.45 to $0.75 per cubic meter. [Reference: Costs for advanced water treatment, including Reverse Osmosis, which is needed for direct potable reuse, range between $0.45 and $0.75 /m3.] Forward Osmosis (FO) is another membrane method showing viability, needing a minimum flux of 10.5 L/m²-h to be cost-competitive with other reuse options. [Reference: A cost analysis revealed FO per se as viable technology. However, a minimum average FO flux of 10.5 L/m²-h is needed to compete with water reuse...]
Beyond Desalination: Water Reuse in Specific Contexts
While desalination focuses on making seawater potable, other forms of reuse exist:
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Reclaimed Water: Many municipalities utilize treated wastewater (effluent) for irrigation, industrial processes, or even, after further treatment, toilet flushing. The City of Ormond Beach, for example, provides over 1 billion gallons of reclaimed water annually. [Reference: The City of Ormond Beach reclaimed water (reuse) system provides over 1 billion gallons of reuse water annually to City customers. By reusing effluent for...]
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Graywater Reuse: This involves reusing wastewater from showers, sinks, and laundry, typically for irrigation. However, reuse for purposes like toilet flushing on boats requires careful consideration of tank flushing and enzyme buildup. [Reference: Furthermore, when full this gray water tank must be flushable to sea at will (but not fully to keep some water for the heads + enzyme built-up... ]
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Aquaculture: In aquaculture, used saltwater needs careful management as it becomes depleted of essential elements. Replenishing these elements can be costly. [Reference: Your used saltwater is depleted of certain useful elements, more so if you have corals. You'd spend more buying the trace elements to put back...]
The feasibility of seawater reuse depends heavily on the intended purpose, available technology, and the cost-effectiveness of treatment relative to other water sources. For example, the Panama Canal's water reuse for drought mitigation is a topic of ongoing discussion. [Reference: Is it feasible to add a system that would recycle the water during times of drought instead of dumping the fresh water into the ocean?]
