反渗透的应用英文论文.doc

Reverse Osmosis Water Treatment Technology andIts Application ProspectForeword:Water resources are indispensable to human natural resources, but also studentsMatter to the survival of environmental resources. As the water crisis intensifies.And deteriorating water quality of the environment, water resources has evolved into much the whole.The worlds environmental concerns. Department of industrial and domestic wastewaterManagement and thus converted into drinking water has become to solve the water crisisAn important way. The worlds most advanced water treatment technology.The surgery is a thin-film reverse osmosis (RO) filter. Reverse osmosis filtration process fromPhase change and does not require acid-base regeneration does not occur in the energy crisisToday has very important significance; and reverse osmosis technology to studentsAcid, alkali and other environmentally harmful substances are not used in the production process.Abstract:The meat industry is characterized by high water consumption. Since this wastewater is highly loaded,it should be thoroughly pre-treated prior to its discharge into receiving water. Our investigations revealedthat a hybrid system of ultrafiltration and reverse osmosis is a promising purification method. Its applicationresulted in a 100% and 98.8% removal of phosphorus and nitrogen compounds, respectively. The efficiencyof COD and BOD removal exceeded 99%.Keywords:membranes, ultrafiltration, reverse osmosis, wastewater produced by the meatindustryReverse osmosis occurs when the water is moved across the membrane against the concentration gradient, from lower concentration to higher concentration. To illustrate, imagine a semipermeable membrane with fresh water on one side and a concentrated aqueous solution on the other side. If normal osmosis takes place, the fresh water will cross the membrane to dilute the concentrated solution. In reverse osmosis, pressure is exerted on the side with the concentrated solution to force the water molecules across the membrane to the fresh water side.Dont feel stupid if youve ever seen a news story about a terrible drought, then turned to your computer to see your pretty ocean beach screensaver and thought, Why dont they just use that?Of course, within a moment, you probably made a few points to yourself. One, the sea is salty. Two, salty water isnt so great for drinking or growing plants. Three, you cant just take the salt out of water, just like you couldnt dissolve the sugar out of your tea. Or can you?Reverse osmosis is one of the processes that makes desalination (or removing salt from seawater) possible. Beyond that, reverse osmosis is used for recycling, wastewater treatment, and can even produce energy.Water issues have become an extremely pressing global threat. With climate change come unprecedented environmental impacts: torrential flooding in some areas, droughts in others, rising and falling sea levels. Add to that the threat of overpopulation - and the demand and pollution a swelling population brings - and water becomes one of the paramount environmental issues to watch for in the next generation.Water treatment plants and systems are now adapting reverse osmosis to address some of these concerns. In Perth, Australia (notably dry and arid, yet surrounded by sea), nearly 17 percent of the areas drinking water is desalinated sea water that comes from a reverse osmosis plant source: The Economist. Worldwide, there are now over 13,000 desalination plants in the world, according to the International Desalination Association.But while knowing that reverse osmosis can convert seawater to drinking water is useful, what we really need to understand is how the heck the process occurs. Assuming that you have a fairly good grasp on the definition of reverse, we better start by taking a look at how osmosis works before we put the two together.Reverse osmosis (RO) is a membrane-technology 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.In the normal osmosis process, the solvent naturally moves from an area of low solute concentration (High Water Potential), through a membrane, to an area of high solute concentration (Low Water Potential). The movement of a pure solvent to equalize solute concentrations on each side of a membrane generates osmotic pressure. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. 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.1 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.DisinfectionPost-treatment consists of preparing the water for distribution after filtration. Reverse osmosis is an effective barrier to pathogens, however post-treatment provides secondary protection against compromised membranes and downstream problems. Disinfection by means of UV lamps (sometimes called germicidal or bactericidal) may be employed to sterilize pathogens which bypassed the reverse osmosis process. Chlorination or chloramination (chlorine and ammonia) protects against pathogens which may have lodged in the distribution system downstream, such as from new construction, backwash, compromised pipes, etc.Regular chemical cleaning of RO membranes will ensure that they continue to perform and extend their useful life. If cleaning is neglected for prolonged periods of time the membrane is at risk of becoming irreparably fouled. As such, cleaning should be undertaken whenever the normalised permeate flux reduces by 10 15% or whenever either the normalised differential pressure or permeate conductivity increase by 10-15%. In many instances the implementations of a programme of regular preventive cleaning would be advisable.Depending on the characteristics of the water supply membrane fouling may be inorganic, organic, colloidal or microbiological in nature and often a combination. Each type of fouling requires a different cleaning strategy.10DisadvantagesHousehold reverse osmosis units use a lot of water because they have low back pressure. As a result, they recover only 5 to 15 percent of the water entering the system. The remainder is discharged as waste water. Because waste water carries with it the rejected contaminants, methods to recover this water are not practical for household systems. Wastewater is typically connected to the house drains and will add to the load on the household septic system. An RO unit delivering 5 gallons of treated water per day may discharge anywhere between 20 upwards of 90 gallons of waste water per day.11 For household use, however, and based on consumption of half a gallon per day, this may amount to less than a toilet-flush per day.Large-scale industrial/municipal systems have a production efficiency typically 75% - 80%, or as high as 90%, because they can generate the high pressure needed for more efficient RO filtration. On the other hand, as efficiency of waste-water rates increases in commercial operations effective removal rates tend to become reduced, as evidenced by TDS counts.Due to its fine membrane construction, reverse osmosis not only removes harmful contaminants that may be present in the water, it also strips many of the good, healthy minerals from the water as well, thereby making the water quite acidic.12 Reverse Osmosis water is, in fact, so chemically unstable and acidic that in many countries national plumbing codes restrict water that has been filtered via reverse osmosis from being reintroduced into copper pipes due to its corrosiveness on the copper. This also has implications for reverse osmosis filtration systems that use steel storage tanks, as the acidity of the water can lead to the steel rusting over time and contaminating the post-filter water.A number of Peer-reviewed studies have looked at the long term health effects of drinking demineralized water, including the following:Health risks from drinking demineralised water. However, demineralized water, can be remineralized, and this process has been done in instances when processing demineralized water for consumption. An example of this process is Dasani.13Types of Reverse Osmosis MembranesTwo common types of household RO membranes are the Thin Film Composite (TFC or TFM) membrane and the Cellulose Triacetate (CTA) membrane. The main differences between the two types are filtration ability and chlorine tolerance. The CTA membrane is chlorine tolerant, but is more susceptible to fouling from bacteria, and it only rejects 93% of standard contaminants. The TFC/TFM membranes reject 98% of standard contaminants on average, are less susceptible to organic fouling, but it can only treat chlorine free water. Carbon pre-treatment filters must be used with a TFC/TFM membrane when purifying chlorinated municipal water supplies. Brackish water, saline water, and brine water membranes are available for marine, industrial, and municipal desalinization projects.Before water filter reviews, consult our buying guide to home water filtration systems. Topics on process, stages, purity, efficiency, more. Know before buying.reverse osmosis systemi