Water Treatment

Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration. Osmosis is a special case of diffusion in which the molecules are water and the concentration gradient occurs across a semi permeable membrane. The semi permeable membrane allows the passage of water, but not ions (e.g., Na⁺, Ca²⁺, Cl^-) or larger molecules (e.g., glucose, urea, bacteria). Diffusion and osmosis are thermodynamically favorable and will continue until equilibrium is reached. Osmosis can be slowed, stopped, or even reversed if sufficient pressure is applied to the membrane from the 'concentrated' side of the membrane.

Reverse osmosis occurs when the water is moved across the membrane against the concentration gradient, from lower concentration to higher concentration. To illustrate, imagine a semi permeable 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.

Reverse osmosis is often used in commercial and residential water filtration. It is also one of the methods used to desalinate seawater. Sometimes reverse osmosis is used to purify liquids in which water is an undesirable impurity (e.g., ethanol).

Reverse Osmosis “What to expect”

 The semi-permeable membrane used in reverse osmosis contains tiny pores through which water can flow. The small pores of this membrane are restrictive to such organic compounds as salt and other natural minerals, which generally have a larger molecular composition than water. These pores are also restrictive to bacteria and disease-causing pathogens. Thus, reverse osmosis is incredibly effective at desalinating water and providing mineral-free water for use in photo or print shops. It is also effective at providing pathogen-free water. In areas not receiving municipally treated water or at particular risk of waterborne diseases, reverse osmosis is an ideal process of contaminant removal.

The reverse osmosis process contains several downsides which make it an inefficient and ineffective means of purifying drinking water. The small pores in the membrane block particles of large molecular structure like salt, but more dangerous chemicals like pesticides, herbicides, and chlorine are molecularly smaller than water (Binnie et al, 2002). These chemicals can freely pass through the porous membrane. For this reason, a carbon filter must be used as a complimentary measure to provide safe drinking water from the reverse osmosis process. Such chemicals are the major contaminants of drinking water after municipal treatment.

Another downside to reverse osmosis as a method of purifying drinking water is the removal of healthy, naturally occurring minerals in water. The membrane of a reverse osmosis system is impermeable to natural trace minerals. These minerals not only provide a good taste to water, but they also serve a vital function in the body’s system. Water, when stripped of these trace minerals, can actually be unhealthy for the body.

Reverse osmosis also wastes a large portion of the water that runs through its system. It generally wastes two to three gallons of water for every gallon of purified water it produces. Reverse osmosis is also an incredibly slow process when compared to other water treatment alternatives.

 Distillation “What to expect”

Aside from desalinating water, the distillation process will reliably remove bacteria and viruses and dangerous heavy metals like lead, arsenic, and mercury. Distillation is ideal for recipients of non-municipally treated water, due to the particular challenges and heavy contamination of raw, untreated water. For this reason, distillation is often used as the preferred method of water treatment in developing nations that must work with heavily contaminated, untreated drinking water. Distillation is extremely effective at the removal of bacteria and often used in areas at high risk of waterborne diseases. Distillation also removes soluble minerals like calcium, magnesium, and phosphorous that may harden water and increase the occurrence of scaling.

The distillation process contains several elements that make it undesirable for purifying drinking water. First of all, while the vaporization process will strip water of salt, metals, and bacteria, the boiling point of most synthetic chemicals, including pesticides, herbicides, and chlorine solutions is lower than the boiling point of water. Synthetic chemicals are the major contaminants remaining after municipal treatment. Distillation does not remove these harmful chemicals.

Also, distillation is a very slow process and requires a heated energy source. Though experiments in the use of solar power have been attempted, this form of energy is only able to treat small quantities of water and difficult to maintain at a constant temperature (Holland et al, 1999). The inefficiency of solar power requires the use of more costly energy forms. Also, because this process must be repeated several times to ensure significant water purity, it could take several hours to provide one gallon of cleansed water. Generally, distillation requires five gallons of tap water to generate one gallon of purified water.

Finally, distillation, like reverse osmosis, strips water of natural trace elements. When these elements are removed from water, the hydrogen composition becomes greater in proportion, making the water very acidic. Several studies have proven that drinking distilled water, stripped of minerals, can actually be harmful to the body system (Rona, 1995). Long-term consumption of such de-mineralized water can result in mineral deficiencies in the body. Though the removal of trace minerals creates water that is ideal for use in photo or print shops, it creates tasteless and even unhealthy drinking water.

 Water Filtration “What to expect”

 Filtration is the most effective type of water treatment and purification currently available. Carbon and multimedia filters build upon the treatment capabilities of reverse osmosis and distillation. They retain all of the good filtration qualities of these two systems while efficiently removing additional water contaminants. They are able to rid water of the larger compound materials, like salt, while selectively removing much smaller and dangerous chemicals, like chlorine and pesticides, that reverse osmosis and distillation systems cannot remove.

Because carbon and multimedia filters utilize both chemical and physical filtration processes, they are able to selectively remove a large number of drinking water contaminants. Water filters can remove the small, but dangerous pesticide and herbicide chemicals while allowing larger, trace minerals to safely pass through the filter with the water. The retention of trace minerals in water provides a much healthier source of drinking water. The chemical adsorption process, which carbon and multimedia filters use, is the only filtration process that can selectively filter unwanted materials from water.

Also, the slow filtration process of carbon and multimedia filters does not require costly energy sources like reverse osmosis and distillation systems. Because carbon and multimedia filtration systems do not require a heat or pressure source, they are fairly cost-effective. Carbon and multimedia water filters waste relatively little water in the filtration process.

Filtration, like reverse osmosis and distillation, is a fairly slow process as it requires several stages of water purification. Although the process is slow, once the water has been through the required stages, it is freer from contaminants than the water product of any other purification technique.

Besides the relatively slow process, there are a few other aspects to filtration that may make it less than ideal. Depending upon the type of filter used, water may have limited contact time with the filter media, resulting in only partial removal of drinking water contaminants. Also the type of filter media may affect the number of contaminants that can pass through the filtration process. Rapid filters and granular filters are less effective than solid block carbon filters. Rapid filters allow for only brief contact time with the filter media, limiting the amount of contaminants that may be removed through the adsorption process. Granular filters contain fairly large pores and allow several contaminants to pass through the filter media. For the most reliable and efficient filtration, solid block carbon or multimedia filters should be used.

 Osmosis and Distillation “Chemical removal”

 Reverse osmosis will generally remove any molecular compounds smaller in size than water molecules. Such compounds include salt, manganese, iron, fluoride, lead, and calcium (Binnie et al, 2002). Reverse osmosis is extremely efficient at stripping minerals from water, and it is highly valued as a water purification process in the printing industry, in which mineral-free water must be used.

Although reverse osmosis supplies useful, mineral-free water for printing purposes, it does not provide the healthiest drinking water. Reverse osmosis will remove several mineral and chemical materials from water, including salt, fluoride, lead, manganese, iron, and calcium. Reverse osmosis, because it removes minerals according to physical size, is non-selective in its removal of dangerous and beneficial minerals. Clearly, mineral contaminants like salt, fluoride, and lead should be removed from drinking water, but minerals like iron and manganese, because they are essential to natural body processes and important components of drinking water, should be left in that water. Iron builds and maintains healthy red blood cells while manganese helps in regulating protein, fat, and carbohydrate metabolism. Manganese, like calcium, is also an essential component in the building of bones and the clotting of blood. Though many foods contain these minerals, drinking water can and should be a major source for their intake.

Distillation removes chemicals similar to those removed by reverse osmosis, but in a different manner. Distillation, through its water evaporation process, will remove any chemicals or organic materials with higher boiling points than water. Such chemicals and organic materials with higher boiling points include bacteria, minerals, trace amounts of metals, many volatile organic chemicals (VOCs), and nitrate (Binnie et al, 2002). Clearly, distillation is valuable in its removal of the potentially deadly VOCs and nitrate. It strips water of nearly all of its natural minerals, though. Many of the minerals the distillation process removes are vital to the body’s natural processes. The distillation process is not selective in its removal of minerals, and it strips water of both dangerous and valuable mineral compounds.

 Filters “Chemical removal”

 Single media filters, typically constituting carbon or sand, absorb impurities from water, through both physical and chemical processes, as the water passes through the filter cartridge. Single media filters will generally remove undesirable tastes, colors, and odors from water as well as such chemicals as hydrogen sulfide, radon, chlorine, volatile organic compounds (VOCs), pesticides, and benzene (Ramstorp, 2003). Drinking water filters will also remove lead and other chemicals transferred from plumbing systems to water. Filtration is the only water purification process that will remove chlorine and chlorine byproducts from water. It is also the only water purification process that reliably and completely removes harmful pesticides from water. Single media filters will not remove mineral compounds from water.

The true power of the filtration process lies in multimedia filtration technology. By using multimedia filters, select minerals can be retained in water while more harmful or useless minerals and chemicals can be removed. The magic of multimedia filters lies in their use of chemical processes, as well as physical processes for the removal of undesirable ground and surface water contents. As more media elements are added to the filter cartridge, the filter is able to remove more of the dangerous mineral contents. Multimedia filter cartridges can remove such harmful mineral deposits and chemical additives as arsenic and fluoride from drinking water. Though arsenic levels are generally low in most ground and surface water, the mineral can be deadly. Fluoride, while useful in maintaining healthy teeth, is a reactive and dangerous chemical that should be taken with care.

 What Is The Difference Between Softeners And Filters

 Technically, the term "water treatment" refers to any modifications made to raw water (water from the original source, i.e. rivers, lakes, streams, etc.). Included under the umbrella term "water treatment" are both water softeners and water filters. For this reason, the functions of the two different technologies are often seen as interchangeable. Water filters and softeners do, in fact, serve very different purposes. The main goal of a water filter is to provide clean, contaminant-free water for drinking and other purposes. The main goal of a water softener is to remove "hardening" minerals like calcium and magnesium from the water. Water softeners do not remove dangerous chemicals or bacteria.

 Water is termed "hard" if it contains large amounts of dissolved calcium and magnesium. Hard water causes two major problems. First, it can initiate scaling on the inner surface of pipes, water heaters, and/or tea kettles. When scaling occurs, the calcium and magnesium separate from the water and form a hard, thin layer on the inside of such appliances, causing the appliances to clog and reducing their ability to conduct heat. Second, hard water causes soap scum to build up on dishes and tile. Hard water also reduces the soap’s ability to lather.

In order to remove calcium and magnesium from water, water softeners chemically replace the calcium and magnesium ions with sodium ions. Because sodium does not separate and scale on pipes or react badly with soap, both problems of hard water are solved. From a health perspective, calcium and magnesium are better and healthier for our body systems than sodium. Water filters will generally solve the same problems as water softeners, without adding sodium to the water.