Water treatment can be defined as any procedure or method used to alter the chemical composition or natural “behavior” of a water supply. Water supplies can be classified as either surface water or groundwater. The majority of water comes from surface water such as rivers, lakes, and reservoirs.
MUNICIPAL OR UTILITY WATER TREATMENT SOLUTIONS
Most municipal water found in a city or community today has been treated extensively. Specific water treatment solutions and steps taken by municipalities to meet local, state, national, or international standards vary but are categorized below.
A coarse screen, usually 50 to 100 mesh, at the intake point of a surface water supply, removes large particular matter to protect downstream equipment from clogging, fouling, or being damaged.
Clarification is generally a multi-step water treatment solution to reduce turbidity and suspended matter. Steps include the addition of chemical coagulants that react to form floc. The floc settles by gravity in settling tanks and is removed as the water percolates through a gravity filter.
The addition of lime (Ca) and soda ash (Na2CO3) reduces the level of calcium and magnesium and is referred to as “lime softening.” The purpose of lime softening is to precipitate calcium and magnesium hydroxides and then clarify the water.
Disinfection is one of the most important steps to municipal water treatment solutions. Usually, chlorine gas is fed into the supply after the water has been clarified and/or softened. The chlorine kills bacteria. In order to maintain the “kill potential”, an excess of chlorine is fed into the supply to maintain a residual. The chlorine level must be constantly monitored to assure that no harmful levels of chloramines or chlorinated hydrocarbons develop.
ON-SITE WATER TREATMENT SOLUTIONS
After the water is delivered from the utility or the well, there are many on-site options for further water treatment solutions to meet specific end-use requirements.
• pH adjustment. Certain chemicals, membranes, ion exchange resins and other materials are sensitive to specific pH conditions.
• Dispersants. Dispersants are added when scaling may be expected due to concentration of specific ions in the stream. Dispersants disrupt the scale formation, preventing growth of precipitate crystals.
• Sequestering (chelating) agents. Sequestering agents are used to prevent the negative effects of hardness, preventing the deposition of Ca, Mg, Fe, Mn and Al.
• Oxidizing agents. Oxidizing agents have two distinct functions: as a biocide, or to neutralize reducing agents.
• Potassium permanganate. Potassium permanganate (KMnO4) is a strong oxidizing agent used in many bleaching applications. It will oxidize most organic compounds and is often used to oxidize ferrous iron to ferric for precipitation and filtration.
Tank-type pressure filters
A typical filter consists of a tank to house the filter media and a valve or controller to direct the filter through its various cycles–typically service, backwash and rinse.
Some examples of pressure filters and their applications are:
• Sand filters. Sand or other filtration media are used to remove turbidity. However, the location of the fine media on top of the coarse media causes the sand filter to clog quite quickly and the coarseness of sand allows many smaller impurities to pass through.
• Neutralizing filters. Neutralizing filters usually consist of a calcium carbonate calcite medium to neutralize low pH water.
• Oxidizing filters. Oxidizing filters use a medium treated with oxides of manganese as a source of oxygen to oxidize and precipitate iron, manganese, hydrogen sulfide, and others.
• Activated carbon filters. Activated carbon (AC) is similar to ion exchange resin in density and porosity. It absorbs low molecular weight organics and reduces chlorine or other halogens from water, but does not remove any salts.
Water Treatment Solutions | Disinfection