Reverse osmosis, or membrane desalination, is a type of desalination treatment that removes impurities from saline water. In reverse osmosis systems, saltwater is passed through a semi-permeable membrane to separate all dissolved and undissolved substances -- including salts, minerals and chemicals -- to make it fit for industrial and residential consumption. Reverse osmosis systems are regularly used in the car washing, food and hydrogen production industries. Despite their widespread use and effectiveness, reserve osmosis desalination systems do have some problems.
One of the main problems with reverse osmosis systems is their high purchase, operating and maintenance costs. According to Remco Engineering, as of September 2010, a reverse osmosis system that provides 1 gallon of pure water per minute costs between $3,000 and $9,000. Membranes cost another few hundred dollars. Furthermore, reverse osmosis systems are liable to malfunction, warranting expensive repairs.
According to Yiu H. Hui and Stephanie Clark in “Handbook of Food Products Manufacturing,” impure water may require pretreatment before it is run through a reverse osmosis system. This involves treating the water with various chemicals, such as antiscalants, acids and chlorine removals -- which increase the operating costs of the unit. Membranes and carbon filters used in reverse osmosis systems have limited lives and need to be frequently replaced, which further adds to maintenance costs.
Require Constant Maintenance
Reverse osmosis systems require constant maintenance to ensure bacterial biofilms, scaling and solid impurities do not accumulate and the system is allowed to perform optimally, according to Takashi Asano in the book, "Water Reuse."
Reverse osmosis membranes deteriorate after constantly collecting suspended solid impurities and must be thoroughly cleaned after each individual desalination process. The system's membranes are also prone to scaling. Scaling is due to the accumulation of excessive levels of calcium sulfate, barium sulfate, silica, calcium carbonate and calcium fluoride ions. These salts precipitate on surface of the membranes, producing scale.
Bacteria colonize and form tough biofilms over the surface of reverse osmosis membranes, according to Richard William Baker in the book "Membrane Separation Systems." These films decrease the energy efficiency of reverse osmosis systems.
Reverse osmosis systems waste a considerable amount of water. According to Skye Weintraub in the book “The Parasite Menace,” reverse osmosis systems use between 3 to 6 gallons of water for every gallon of pure water produced. Reverse osmosis systems also take a minimum of an hour to produce a gallon of pure water. Reverse osmosis systems are ineffective at eliminating hard mineral deposits of magnesium and calcium.
- Remco Engineering: Small Reverse Osmosis System Design
- "The Parasite Menace"; Skye Weintraub; 1998
- NDSU: Reverse Osmosis Water Treatment
- Photo Credit water splash - bottle and water in a moment image by Stasys Eidiejus from Fotolia.com
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