-Which are the most common problems with water?
-What is Reverse Osmosis?
-My membrane is rated at 75 GPD but I only get 50 GPD out of it. Why?
-What factors affect my R.O.Unit´s performance?
– How does water temperature affect membrane performance?
– How does water pressure and TDS affect membrane performance?
Question: Which are the most common problems with water?
HARDNESS – A common water quality problem caused by dissolved calcium and magnesium (limestone) in water. Hard water causes scaling of pipes and hot water heaters, plumbing fixtures, etc. It makes cleaning and laundering more difficult.
LEAD – Commonly used in plumbing installation material until the late 1980´s. U.S. Safe Drinking Water Act (SDWA) standards have since set limits on the amount of lead that may be used in solder materials. Lead has been found to occur in drinking water primarily due to leaching. Lead exposure has been linked to learning deficiencies in children and, at higher levels, has been associated with hypertension in adults.
MICROBIOLOGICAL PATHOGENS – Waterborne organisms that are known to cause disease in humans. Common waterborne pathogens include fecal coliform, dysentery, cholera, hepatitis and microbial cysts such as Crytosporidium and Giardia Lamblia.
NITRATES: Nitrogen compounds are ussually found in surface and well water, in rural zones. It appears as a concecuence of the use of nitrogen based fertilizers. High nitrogen levels can interfer in the oxygen transport process, mainly in babies.
HEAVY METALS: Mercury, zinc, copper and cadmium are present in water due to industrial trash. These metals can cause physiological demage in the human, including central nerviuos system deterioration.
ORGANIC CHEMICALS – A group of chemicals commonly referred to as Volatile Organic Compounds (VOCs). There are over 80 VOCs regulated by the SDWA. Typical VOCs include benzene, trichloethylene, and chlordane. High levels of exposure to VOCs have been linked to a variety of cancers and organ damage.
TRIHALOMETHANES (THMs) – THMs are the first organic chemicals regulated by the SDWA. THMs are a byproduct of the chlorine disinfection process. THMs are formed when chlorine reacts with other organic compounds in water. THMs are known carcinogens and have been linked to bladder cancer. Arsenic: Arsenic enters in water naturally or due to insdustrial process. It is realted to several kind of cancer, can demage circulatory system and central nervous system.
SULPHUR – A naturally occurring objectionable substance which contributes a “rotten egg” like odor to drinking water and is also known to be very corrosive to plumbing products and materials.
RADIOLOGICAL SUBSTANCES – Radium and its related cousins may be found in groundwater supplies. They are known cancer causing substances in humans. Radium exposure is through drinking and cooking while radon exposure is normally through inhalation.ASBESTOS – A construction material commonly used in insulation, building materials, or certain types of water piping. However, it has been linked to lung and bladder cancer in humans. pH: Is related to the acidity and alkalinity of th ewater. High acidity is corrosive and high alkalinity can arise in aestetic problems.
Question: What is Reverse Osmosis?
Osmosis is a natural selective process, on which some materials can pass through a semipermeable membrane, others cannot. Living cells are natural membranes. The water can pas much more readily than the dissolved minerals, from the more diluted solution to the more concentrated solution.
Reverse osmosis process is observed when a pressure is applied to the concentrated solution, the direction of water passage through the membrane is reversed and the process that we refer to as reverse osmosis is established. The direction of the water flow is changed.
In order to keep the membrane from fouling it is important to continually flush the brine side. As the water is squeezed through the membrane, leaving most of the salts behind, the brine side solution becomes increasingly concentrated. Without the reject flow to drain, the brine side mineral concentration would eventually exceed the solubility limits of the salts present and they would precipitate, forming a scale on the membrane. To avoid excessive brine side concentrations, the permeate volume recovered, in a low pressure system, is usually kept in the range of 1- to 30 percent of the feed stream volume. For example, if for each five gallons of water fed to the membrane, one gallon of permeate is recovered, the membrane is operating at 20% recovery.
The general operation of all RO modules is the same. The feed stream is supplied to the membrane and split into the permeate which has diffused through the membrane, and the concentrate which passes over the membrane, carrying away the minerals to waste.
Question: My membrane is rated at 75 GPD but I only get 50 GPD out of it. Why?
A variety of things can cause performance problems. Variables such as the choice of membrane material, the operating pressure, temperature, the pH of the water, and the type and concentrations of ions present in the water.
Question: What factors affect my R.O.Unit´s performance?
The quality of water produced by a reverse osmosis system is affected by such variable as the choice of membrane material, the operating pressure, the pH of the water, and the type and concentrations of ions present in the water.
Divalent ions like calcium, magnesium and sulfate are generally more effectively rejected than monovalent ions like sodium and chloride.
The percent recovery at which a membrane is operated will directly affect the quality and quantity of permeate, in that as the recovery is increased so is the TDS of the brine as it exits the membrane. Though, from water conservation point of view, higher recoveries are attractive, there are limits imposed both by the membrane manufacturers´ specifications and by the solubility of the species in the feed water.
The elimination of non-ionic contaminants such as organics, pyrogens, cysts, viruses, and bacteria is simply a filtration process. They cannot pass through the pores in the membrane if they are of a molecular weight of greater than about 100. This cutoff limit is not to be construed as absolute, as it varies with membrane selection and the shape of the molecule in question.
Question: How does water temperature affect membrane performance?
Temperature is one of the main factors to be considered in RO performance. An increase in feed water temperature increases the permeate flux, but does not affect permeate quality. For some membranes it is also recommend that they not be allowed to freeze.
Question: How does water pressure and TDS affect membrane performance?
The operating pressure for a reverse osmosis system depends on the total dissolved solids in the feed water and the desired permeate delivery pressure. It is the TDS which determines the osmotic pressure of a solution. In order for a system to deliver water, the feed pressure must be greater than the sum of the osmotic pressure difference plus the permeate pressure.