Seawater Reverse Osmosis (SWRO)

It is a well-known fact that a good portion—about 71 percent to be exact—of the Earth’s surface is covered in water. However, not all of that water is usable. 97 percent of all of the water on Earth is sea or ocean water. Fresh water sources make up only about 3 percent of the world’s total water supply. One such way to lessen the stress on these precious sources of water is to use the seawater reverse osmosis (SWRO) process to desalinate water with higher than normal levels of salinity.

With the global population consuming on average over 10 billion tons of fresh water a day, it’s hard to imagine the levels of stress we place on our fresh water sources and what it could potentially do to harm us in the long-term. By desalinating seawater, we are able to provide more water to more industries, businesses, and communities where fresh water may not be readily—or easily—available.

Water Treatment for Seawater:

The SWRO process removes all existing salts and impurities from ocean water. Analysis have been done on seawater and the results state that the water contains approximately 3.5% dissolved solids and more than sixty of the chemical elements have been identified. The primary elements are sodium chloride (80% of the dissolved elements), Potassium (0.13% of the dissolved elements), Magnesium, sand / gravel, limestone, Manganese, Phosphorites, and other elements.

Since the oceans of the world contain 3.5% salt content; humans are unable to ingest this type of water to survive. There are many areas in the world where people are affected by either limited or no groundwater at their disposal. Depending on your geographic location – The Persian Gulf for instance has 45 grams of salt per liter, therefore, thermal desalination must be done while everywhere else there is a way to obtain pure and safe drinking water by the process of desalination through reverse osmosis (RO). Either process you use – thermal or reverse osmosis – the salt is cut down to 0.5 gram per liter and absolutely drinkable.

Treating seawater via reverse osmosis can be tricky because of how highly-corrosive seawater can be on the membranes, and other components. Seawater also has a range of contaminants from microorganisms, heavy metals, and insoluble salts that can cause scaling or fouling of the RO membranes.

Pre-treatment for SWRO can consist of:

• Pre-chlorination
• Multimedia Filters
• Dechlorination
• Antiscalant injections

Post-treatment for SWRO can consist of:

• pH adjustment
• Calcite filter

Since seawater is so highly-corrosive parts made of special components are needed to make sure the system is performing at optimal levels and without issues. We at Pure Aqua, Inc. use only high-standard parts for our seawater reverse osmosis systems.

The SWRO Process

Desalination is the process of removing dissolved minerals from seawater, treated wastewater, and brackish groundwater by using a system called Reverse Osmosis (RO). The RO process removes approximately 95% to 99% of the salts and inorganic material found in the seawater which results in safe, healthy, and salt free drinking water.

Seawater Reverse Osmosis Systems is a process that desalinates with the use of membranes and has been commercially used since the early 1970s. They found that since no heat or phase changes were needed, the requirements for energy were lower as compared to the process of desalination.

The largest Seawater Reverse Osmosis (SWRO) desalination plant in the world is based in Israel. This enormous plant consists of the typical single-pass (SWRO) system which consists of an intake, pretreatment, high pressure pump, membrane assembly, remineralization adjuster, pH adjuster, disinfection (UV / Ozone), and a control panel.

The procedure starts with a high-pressure pump that pumps seawater into a module that is divided into two volumes by a semipermeable membrane. The membrane allows water to pass through while blocking salts, resulting in desalination of the water beyond the membrane, known as the permeate, as well as desalination of the salt that was left behind at the front of the membrane. A pressure control valve allows the concentrated salt water to exit. The flow rate is determined by the membrane's characteristics and area. The osmotic pressure of the concentrated sea water in the module is generated by the pump and controlled by the pressure valve.

The pump pressure must be higher than the osmotic pressure in order to force the seawater through the membrane and the permeate water out of the module. The flow rate is proportional to the difference between the two pressures. When the pressures are equal, water will not flow through the membrane. Also, if the pump pressure is lower than the osmotic pressure, permeate will flow back toward the concentrated salt water.