Introduction Water makes up seventy percent of our body and covers three quarters of the Earth. It is also part of the water cycle. Evaporation of the oceans occurs, and water condenses to form clouds. Water then falls back to earth again, as precipitation. But less than one percent of Earth's water is fit for human consumption. A study by the United Nations states, that about 1.2 billion people around the world, will experience a lack of safe drinking water, in the next twenty five years.
Introduction Using reverse osmosis technology, Singapore’s scientists have perfected the process of transforming sewage water into new, clean, safe drinking water. And since every corner of this city is connected to a single sewerage system, Singapore will never run out of sewage water as long as its residents keep flushing.
NEWater Branded NEWater, this reclaimed or recycled water is one of Singapore's �four national taps� or freshwater sources providing 7% of the country’s water demands. The other taps are: Local catchments: providing 50% of water needs Imported water : from Johor, Malaysia, supplying 33% of water needs, made available through a 1961 agreement, and pumped through pipelines across the 2km causeway separating the two countries Desalinated water : or converted seawater, addressing 10% of water needs
NEWater NEWater is a product of stringent purification and treatment processes capable of making sewage water clean, clear, and sparkling. PUB has even dared put NEWater into plastic bottles for public consumption
Reclaiming water Singapore is now a global city�a prime destination of tourists, world entrepreneurs, and hopeful migrants from its Asian neighbors since its successful emergence as an international financial hub after the 1997 Asian Financial Crisis. The 4.5 million people in singapore consume about 300 million gallons of water per day. The lack of water in this small, multi-cultural, city-state could have serious repercussions. It was a good thing, then, that the country foresaw its freshwater sources problem as early as the 1970s.
Reclaiming Water PUB built a pilot water reclamation plant in 1974, but implementation plans were shelved because of huge costs and unreliable technology. It wasn�t until 1998 that the project was revived through a joint initiative between PUB and the Ministry of Environment and Water Resources. The 1998 Singapore Water Reclamation Study (or NEWater Study) clinched the deal on NEWater as a raw water resource to supplement the country’s water supply. With the agreement with Malaysia expiring in 2011 and water demands expected to rise to 400 million gallons a day by 2012, the development of NEWater is very timely.
Reverse Osmosis Reverse osmosis is a filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be "selective," this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.
Reverse Osmosis Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and other substances from the water molecules. This is the reverse of the normal osmosis process, in which the solvent naturally moves from an area of low solute concentration, through a membrane, to an area of high solute concentration. The movement of a pure solvent to equalize solute concentrations on each side of a membrane generates a pressure and this is the "osmotic pressure." Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis.
Reverse Osmosis Reverse osmosis is similar to membrane filtration. However, there are key differences between reverse osmosis and filtration. The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration. Reverse osmosis, however involves a diffusive mechanism so that separation efficiency is dependent on solute concentration, pressure and water flux rate
Process The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs. In most cases, the membrane is designed to allow only water to pass through this dense layer, while preventing the passage of solutes (such as salt ions). This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 2–17 bar (30–250 psi) for fresh and brackish water, and 40–70 bar (600–1000 psi) for seawater, which has around 24 bar (350 psi) natural osmotic pressure that must be overcome.
Process Osmosis describes how solvent moves between two solutions separated by a semi-permeable membrane to reduce concentration differences between the solutions. When two solutions with different concentrations of a solute are mixed, the total amount of solutes in the two solutions will be equally distributed in the total amount of solvent from the two solutions. Instead of mixing the two solutions together, they can be put in two compartments where they are separated from each other by a semi-permeable membrane.
Process The semi-permeable membrane does not allow the solutes to move from one compartment to the other, but allows the solvent to move. Since equilibrium cannot be achieved by the movement of solutes from the compartment with high solute concentration to the one with low solute concentration, it is instead achieved by the movement of the solvent from areas of low solute concentration to areas of high solute concentration. When the solvent moves away from low concentration areas, it causes these areas to become more concentrated.
Process On the other side, when the solvent moves into areas of high concentration, solute concentration will decrease. This process is termed osmosis. The tendency for solvent to flow through the membrane can be expressed as "osmotic pressure", since it is analogous to flow caused by a pressure differential. Osmosis is an example of diffusion.
Process In reverse osmosis, in a similar setup as that in osmosis, pressure is applied to the compartment with high concentration. In this case, there are two forces influencing the movement of water: the pressure caused by the difference in solute concentration between the two compartments (the osmotic pressure) and the externally applied pressure.
Reverse osmosis plant At 110,000m3/day, the Tuas seawater reverse osmosis (SWRO) plant has sufficient capacity to meet around 10% of the national demand - and at a price which challenges the notion that desalination is a high-cost option. Based on a pre-defined formula, the water sale price varies monthly with prevailing fuel cost and annually with inflation. The initial tender figure was $0.78/m3 for 2005; in practice the plant's efficiency has meant that the actual first year selling price approaches half that.
Interesting facts In 1946, some maple syrup producers started using reverse osmosis to remove water from sap before being further boiled down to syrup. The use of reverse osmosis allows approximately 54-42% of the water to be removed from the sap, reducing energy consumption and exposure of the syrup to high temperatures.
Interesting facts Many reef aquarium keepers use reverse osmosis systems for their artificial mixture of seawater. Ordinary tap water can often contain excessive chlorine, chloramines, copper, nitrogen, phosphates, silicates, or many other chemicals detrimental to the sensitive organisms in a reef environment. Contaminants such as nitrogen compounds and phosphates can lead to excessive, and unwanted, algae growth. An effective combination of both reverse osmosis and deionization (RO/DI) is the most popular among reef aquarium keepers, and is preferred above other water purification processes due to the low cost of ownership and minimal operating costs. Where chlorine and chloramines are found in the water, carbon filtration is needed before the membrane, as the common residential membrane used by reef keepers does not cope with these compounds.