Water Treatment Process
Collection
The source of water for a municipal surface water treatment plant is typically a local river, lake, or reservoir. The water is transported through a series of pumps and pipelines to the treatment plant. At the water plant, large pumps are used to transfer the water up to the treatment facility. Treatment facilities are often engineered to utilize gravity water flow as much as possible to reduce pumping costs. Many water treatment plants utilize water from more than one source. Blending groundwater with surface water is a method often used to improve the quality of the final product. (Rinkesh, 2016)
Screening and straining
Surfaces water sources such as lakes, rivers, and reservoirs, contain various amounts of suspended and dissolved materials. This material may include turbidity, color, taste, odor, microorganisms, fish, plants, trees, trash, etc. Some of the larger items can impede equipment in the treatment process, so screening or straining out the larger items is a required step. This is often accomplished using a large metal screen, often called a barscreen, which is placed in front of the water source intake. Large items are tapped in the screen as the water passes through it. These screens must routinely be cleaned off. (Rinkesh, 2016)
Chemical Addition
Once the screened source of water is received into the treatment plant, chemicals are added to help make the suspended particles that are floating in the water clump together to form a heavier and larger gelatinous particle, often called floc. In this process, a chemical is added that reacts with the natural alkalinity in solution to form an insoluble precipitate. There are many different chemicals on the market that are used in this process. These chemicals are called coagulants. One of the most common that has been used for many years is aluminum sulfate, or alum. Regardless of which coagulant or combination of coagulants is used, they must be mixed very well with the water before they can form a heavier floc. (Water Treatment, 2015)
Coagulation and Flocculation
A rapid mixing unit is usually used after the coagulant (aluminum sulphate) is added to provide a very quick and thorough mix. As the coagulant meets water, the particles in the water (e.g., natural organic matter, including algae and dissolved organics) will be attracted to each other and allows the organic matter to increase in size, making removal easier. The continued mixing must be gentle to allow the floc to grow and gain weight, but fast enough to keep it in suspension until you are ready for it to settle in the clarifiers. The process of adding a chemical to cause the suspended material to “clump” into larger particles is called flocculation or coagulation. The treatment unit where coagulation and flocculation are performed is called the “flocculator”. ( Hunter Water Corporation, 2019)
Sedimentation and Clarification
As the water and the floc particles progress through the treatment process, they move into sedimentation basins where the water moves slowly, causing the heavy floc particles to settle to the bottom. A rake continuously travels across the bottom of the basin and scrapes the settled floc to the center of the unit. Pumps are used to pull the settled “sludge” (Floc which collects on the bottom of the basin) out of the basin and it is sent to a disposal pond. The water that passes is collected and transferred to the filters. The reason clarification occurs before filtration is so the majority of suspended material can be removed prior to filtration, which avoids overloading the filters and thus allowing much more water to be filtered before the filters must be backwashed. (Hunter Water Corporation, 2019)
Filtration
Water flows through a filter designed to remove particles in the water. The filters are made of layers of sand and gravel, and in some cases, crushed anthracite. Filtration collects the suspended impurities in water and enhances the effectiveness of disinfection. (Hunter Water Corporation, 2019)
Disinfection
Water is disinfected before it enters the distribution system to ensure that any disease-causing bacteria, viruses, and parasites are destroyed. The most common disinfection process is chlorination. Chlorine is a very effective disinfectant and are added to water to ensure all microorganisms are destroyed. Water plants monitor the chlorine levels continuously and very carefully in the treated water. They must add enough chlorine to ensure thorough disinfection of the water but avoid adding excesses that can cause taste and odor problems when delivered to the consumer. (Water Treatment, 2015)
Distribution
So how does the water come out of your kitchen tap? The stored water is pushed through underground pipelines all over town in what is called a “distribution system”. The distribution system consists of large water pumps at the treatment plant, overhead water storage tanks, large pipelines, smaller pipelines, fire hydrants, valves, and water meters in your front yard. (Water Treatment, 2015)
