Description
Pre-Treatment Process:
Seawater entering the desalination plant goes through spin down screens filter to remove suspended solids and debris, then gets injected with oxidants and coagulators to purify sea water as in many parts of the world waste water is dumped into the sea, leading to the contamination of seawater. In this process, chemicals are added to the seawater to make algae, organic materials and particles bond together so they can be removed more easily in the filtration stage that follows.
In the next stage, seawater goes through automatic backwash Sand Filters to catch all the suspended solids, algae and organic materials that has bonded together.
Then Seawater goes through Automatic Backwash Activated Carbon Filters to reduce color and smell, as well adjust pH level of seawater.
Finally the seawater goes through a series of 5 micron Sediment Filters to remove silt and fine particles that may be remaining after the pretreatment process.
Seawater Desalination Reverse Osmosis Watermaker Process:
The Seawater Desalination Reverse Osmosis Process also known as SWRO process starts with High Pressure Pumps that forces the pretreated seawater through a set of semi-permeable membranes at high pressure to separate the freshwater from the seawater.
The size of the Seawater RO membrane pore is .002 microns, which is about 1/100,000th the diameter of a human hair.
Post-Treatment Process:
After the Seawater Desalination Reverse Osmosis Process, Fresh Water goes through Activated Carbon Post Filters, to improve Taste Odor and Clarity, then through pH adjust post-filters, then finally, through an Ultra Violet sterilizer to ensure water is totally disinfected and pure. Chlorine is usually added where the water is stored to stabilize the fresh water produced.
Applications
Features and Benefits
What energy does seawater reverse osmosis require, and how has that changed with energy recovery devices?
SWRO without energy recovery requires 8-12 kWh per cubic meter of product water. Modern plants using pressure exchangers or isobaric energy recovery devices reduce energy consumption to 3-4 kWh per cubic meter, recovering up to 98% of the hydraulic energy in the brine stream. AMPAC USA specifies energy recovery on all SWRO systems above 50,000 GPD because the payback period on the equipment is typically under two years at commercial electricity prices.
What is the typical TDS of seawater and what operating pressure does SWRO require?
Open ocean seawater averages 35,000 mg/L TDS with an osmotic pressure of approximately 400 psi. SWRO systems operate at feed pressures of 800-1,200 psi to overcome osmotic pressure and achieve practical flux rates of 6-14 LMH. Coastal waters with freshwater mixing may have TDS as low as 10,000-20,000 mg/L, which reduces required operating pressure significantly and improves energy efficiency.
What pretreatment is required before SWRO membranes?
Seawater contains suspended solids, biological organisms, organic matter, and scaling ions that would foul SWRO membranes within days without pretreatment. Standard pretreatment includes coagulation, dual-media filtration or ultrafiltration, and cartridge filtration to achieve a Silt Density Index below 3. Antiscalant dosing prevents carbonate and sulfate scale, and chlorination followed by dechlorination controls biological fouling while protecting the polyamide membrane from oxidative damage.
What recovery rate is achievable with seawater RO, and what limits it?
SWRO systems typically operate at 40-55% recovery, meaning 40-55% of the feed seawater becomes product water and 45-60% becomes concentrated brine at 60,000-70,000 mg/L TDS. Recovery is limited by the increasing osmotic pressure of the concentrate, the solubility limits of calcium sulfate and other scaling compounds, and the increasing energy required to maintain flux as brine concentration rises. Pushing recovery above 55-60% requires specialized scale inhibition and higher operating pressures.
What product water quality do AMPAC USA SWRO systems deliver?
Our SWRO permeate typically reaches 200-400 mg/L TDS directly from the membrane, with chloride levels around 50-100 mg/L. Most potable water applications then pass the permeate through a calcite or lime contactor to add alkalinity and hardness, raising pH and reducing the water's corrosivity toward distribution piping. For industrial applications requiring lower TDS, a second-pass RO or mixed-bed DI polishes the permeate further.