From water reuse to desalination, reverse osmosis plays a key role in supplying fresh water where it’s needed
Consumers may already know reverse osmosis (RO) from popular under-sink home water treatment systems, but RO is used in many applications and at many scales. Reverse osmosis can purify unusable water to the point where it’s virtually free of health risks and esthetic issues.
To understand how reverse osmosis works, a mention of osmosis is in order. Osmosis is the process by which liquids move through a semi-permeable membrane via molecular kinetic energy. Notably, it is the process by which cells transport water in biological systems.
In reverse osmosis, however, pressure is applied to liquid to force it through a semi-permeable membrane. Because of their small size, water molecules tend to move easily through a reverse osmosis membrane, while minerals and contaminants with larger molecules are stopped. Membranes are composed of a variety of materials, notably ceramic and polymers.
Reverse Osmosis Applications
Reverse osmosis is used for a host of applications such as ice-making, hemodialysis, seawater desalination, CIP water recovery, in manufacturing, and in the reuse of effluent water (a recent survey of water industry professionals rated RO highest among technologies adaptable to water reuse.
RO is frequently used as one level of treatment along with other treatment methods, including dissolved air flotation (DAF), disc filtration, ultrafiltration, ultraviolet treatment, and advanced oxidation processes. Treatment systems with an RO component may need significant customization to tailor them to specific supplies and to meet required standards.
The four types of membranes used in RO are high-rejection, low-pressure, heat-sanitized, and fouling-resistant. Fouling is a perennial problem in RO. Scale can form on membranes, so it’s common practice to condition feed water and flush membranes to increase membrane life and avoid clogging, degradation, or encrustation.
Addressing Water Scarcity
New breakthroughs in synthetic membranes have increased the efficiency of RO desalination, and decentralized treatment strategies have widened access. Now RO desalination stands poised to bring fresh water to parched areas worldwide, stabilizing nations and economies, and making deserts bloom.
High-quality and ultrapure water are required in a number of applications in the food and beverage, pharmaceutical, and microelectronics industries, as well as in power generation. For example, the Ataqa power plant in Egypt is currently using seawater demineralization for process water production, and in Israel, Fluence has created a multistage water treatment system to produce cooling system water and ultrapure water for the cutting-edge Ashalim solar plant’s steam boiler.
The containerization of modular reverse osmosis desalination and water reuse systems has been taking treatment to places where it wasn’t previously available.
One example is Fluence’s NIROBOX™ SW, a seawater desalination unit housed in a standard shipping container that can output 1,500 m3/d of fresh water from seawater. Advanced technology is engineered into a tiny footprint for easy transport and plug-and-play installation — even in remote areas — with minimal environmental disruption. One good example is the fully automated and remotely monitored Nirobox system at the Reserva Conchal resort in Costa Rica. The drought-stricken resort needed a way to ensure a freshwater supply without disrupting the area’s natural beauty.