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Reverse Osmosis Purification Technology

The Origin of RO

RO, also known as hyper-filtration is an advanced water purification technology. It was first developed in the late 1950s with the successful invention of semi-permeable membranes and was initially used by the US government for their armed forces. This semi-permeable membrane effectively rejected dissolved solids (salt / inorganics) in ionic form but allowed the passage of water molecules and was therefore a revolutionary separation process. Initially, this technology was applied to desalinate sea water as an alternative technology to the energy-intensive, thermal-based separation (Heating-Evaporation-Condensation). With the progress of the space race, NASA invested heavily into membrane technology as the solution for providing drinkable water during space flight.

In the early 1970's, the first commercial low-pressure semi-permeable membrane was developed and was capable of producing 1 to 5 gallons per day of clean, safe drinking water for small households. Later, as a result of technology advancements, the capacity of membrane systems was augmented to produce enough water for whole communities. However, one issue that had remained a challenge was scaling. Scaling is the physical process that occurs when sparingly soluble salts come out of the solution and form a solid scale on the membrane surface. This occurs in membrane filtration due to the fact that when dirty or salty water enters the membrane most of the water molecules are removed, leaving behind many salts in a reduced amount of water. As fresh water sources are reduced and the demand for higher recovery systems increases, the likelihood for scaling of the membrane also increases.

In the late 1970's when polyamide membrane-also known as thin film composite (TFC) - was introduced into membrane separation applications, Sodium Hexametaphosphate (SHMP) was introduced to control the potential scaling. Due to the limitations of SHMP (high dosage rates), like quick degradation, limited control of carbonate scale liquid anti-scalants primarily made of polyacrylic acid (borrowed from cooling tower technology) was introduced and was found to be much more stable than SHMP. However, these chemistries also had limitations such as limited control of carbonate scale and precipitation in the presence of metal hydroxides.

In the mid-to-late 80's, phosphate-based anti-scalants were introduced to the application, and many formulations used today are derived from phosphate-based materials. These too carry many limitations like overdosing (which can exacerbate phosphate scaling and have limited control over silica precipitation) along with increased prohibitions by US and many other countries. Phosphate is the primary ingredient in many fertilizers and therefore, can greatly increase the risk of algal blooms and bacterial proliferation of the discharge stream.

The new generation of antiscalants is unique in molecular structure. Phosphate-free and made in concentrated form, this technology is an evolutionary step in the science of RO operation. This technology eliminates the concern of fouling caused by overdosing and adheres to most discharge regulations of various countries.

Today, aboard the space shuttle, RO forms a critical component to recycle waste water and provides drinking water to the astronauts. Currently, this technology is used for purification of many water sources - brackish well water, reuse of agriculturally contaminated ground sources, production of drinking water from sea water and ultra-purification of water for microelectronics and pharmaceutical manufacturing.