What is Water Treatment?
Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, agriculture and aquaculture, transportation, water recreation and many other uses, including being safely returned to the environment.
The purpose of water treatment is to remove contaminants and undesirable characteristics, or reduce their concentration so that water becomes more suitable for its desired end-use.
What does Water Treatment Allow you To Remove?
In its natural state, there are many substances that can be found in water. These include Microorganisms, Organic and Inorganic compounds, Particulate matters, Dissolved Gases etc. These impurities often have a profound and far-reaching effect on humans, environment, and products being made and on manufacturing cost.
How do You Identify the Condition of Your Water?
You will never be able to tell the purity levels of water through visual inspection alone, testing the water in a certified water testing laboratory is a necessity. This is the only way to know what substances are present and the right water treatment solutions to apply.
Water Treatment Technologies used
Technological advances have made water treatment highly scientific. For about 85 years or there about, chemical clarification, granular media filtration, and chlorination were virtually the only treatment processes used in municipal water treatment. However, the past 30 years have seen a dramatic change in the water industry’s approach to water treatment in which water utilities have started to seriously consider alternative treatment technologies to the traditional filtration/chlorination treatment approach.
Removal of Inorganic Contaminants
The water treatment technologies for inorganic contaminants are;
Ø Clarification
Ø Filtration
Ø Membrane Filtration
Ø Ion Exchange System
Typical inorganic contaminants of concern in water include suspended metals, dissolved metals, nitrate, sulfate, calcium, magnesium, phosphorus, fluoride, and cyanide. Common metals and metalloids such as arsenic, antimony, selenium, lead, copper, cadmium, and zinc.
Clarification: Clarification utilizes multiple processes to remove suspended particles, i.e., contaminants that are present in particulate form rather than dissolved. These processes include coagulation, flocculation, and settling. Precipitation reactions create particles from dissolved contaminants. They involve adding a chemical coagulant to form particles which settle and remove contaminants from water. These techniques are used in softening of water as well as to remove impurities like phosphorus, fluoride, arsenic, ferrocyanide and heavy metals, etc.
Filtration: In filtration, water passes through a filter, which is made to take away particles from the water. Such filters are composed of gravel and sand or sometimes crushed anthracite. Filtration gathers together impurities that float on water and boosts the effectiveness of disinfection. Filtration methods include bag filters, cartridge filters, sand filters, and media filters.
Membrane Filtration: The most common membrane technologies are microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. These have been listed in order of decreasing pore size, increasing removal efficiency, and increasing pressure requirements.
Microfiltration (MF) utilizes pore sizes of 0.05 to 3 microns and removes most suspended solids but not dissolved contaminants.
Ultrafiltration (UF) is a “tighter” membrane technology than MF in that it removes colloidal particles, polymers, and bio-molecules. UF utilizes pore sizes of 0.03 to 0.1 micron and operates at pressures of 30 to 150 psi. UF also does not remove dissolved contaminants.
Nanofiltration (NF) membranes have pore sizes of 0.001 to 0.006 micron. It removes solids, bacteria, high-molecular weight contaminants, and divalent or larger ions such as sulfate. Therefore, it removes some dissolved contaminants. However, NF will not remove monovalent ions such as nitrate and sodium.
Reverse osmosis (RO) is the tightest membrane technology, with pore sizes of 0.0001 to 0.001 micron. It removes solids, bacteria, viruses, and dissolved solids. RO removes 95 to 99 percent of inorganic salts and charged organics, with higher-valence ions having higher rejection rates. Monovalent ions such as nitrate are only partially rejected.
Ion Exchange System: Ion exchange is a chemical reaction by which ions are exchanged between the solution and an ion exchange resin. It used for removal of hardness (calcium and magnesium) as well as removes impurities such as silica, heavy metals, fluorides, phosphate and TSS (total suspended solids).
Removal of Organic Contaminants
Organic contaminants such as pesticides, VOCs (such as toluene, benzene, styrene etc.), petroleum hydrocarbons, trihalomethanes, haloacetic acids, industrial wastes etc., from water and waste water are removed by a number of methods. These include;
Ø Ion Exchange
Ø Reverse Osmosis
Ø Advanced Oxidation Process
Ø Adsorption
Among the possible techniques for water treatments, the adsorption process by activated carbon shows potential as one of the most efficient methods for the treatment and removal of organic contaminants in water and wastewater treatment. Adsorption has advantages over the other methods because of simple design and can involve low investment in term of both initial cost and land required.
Removal of Biological Contaminants
Water and waste water treatment technologies for killing microorganisms such as bacteria, viruses, cysts, and protozoa today are;
Ø The use of chlorine-based such as chlorine gas, sodium hypochlorite, monochloramine and chlorine dioxide
Ø Ozonation: Ozone is a powerful oxidizing agent which, when dissolved in water, produces a broad spectrum biocide that destroys all microorganisms.
Ø Ultraviolet (UV) radiation: The microorganisms in the water are inactivated through exposure to the UV light in the wavelength range of 250 to 270 nm.
Ø Membrane Filtration such as ultrafiltration, nanofiltration and reverse osmosis
Removal of Radiological Contaminants
Radiological contaminants in water and waste water are removed using the following treatment technologies;
Ø Reverse Osmosis
Ø Ion Exchange
Ø Activated Carbon Filtration
Reverse osmosis: Reverse osmosis is one of the most effective ways to remove radioactive materials from water. Pressure forces water through a membrane with very tiny pores. These pores allow water molecules through. These pores are so small that many molecules and even larger atoms cannot get across. As a result, the membrane catches radioactive particles. Reverse osmosis membranes can remove up to 99% of radioactive elements such as uranium and radium from water. This makes reverse osmosis highly effective for the treatment of radioactive water.
Ion exchange: Ion exchange is another effective method of removing radioactive materials from water. Water passes through a resin that contains exchangeable ions. These stronger bonding ions are exchanged with the weaker radioactive materials in the water. Thus, the radioactive materials stay in the resin. Radium, which is a cation (a positively charged ion), is exchanged for other cations like potassium or sodium. Uranium, which is an anion (a negatively charged ion) is exchanged for other anions like chloride.
Activated Carbon filtration: Carbon filtration is also effective at removing radioactive materials from water. Water passes through a filter made of activated carbon. In doing so, the carbon absorbs and fixes radioactive contaminants in the water. Active carbon is inexpensive. The cost makes this method of radioactive water treatment readily available. Eventually, the activated carbon must be replaced once its load capacity is reached. At this stage, it loses its ability to absorb contaminants.
Any one of these technologies is effective at removing radioactive contaminants from water. You can never remove 100% of radioactive contaminants from water. You can, however, remove more of them if you combine the use of these technologies. For example, you could pass water through a carbon filter. You could then follow it with a reverse osmosis membrane. Doing so would be more effective than using either of these technologies on their own.