Water Treatment Process

Collection

First, raw water is transported to the water treatment plant via pumps and pipelines. Water treatment facilities within water treatment plants are often designed to utilize gravity flow whenever possible to reduce the cost of pumps. Many water treatment plants utilize water from more than one source. Groundwater is blended with surface water to improve the quality of the final product.

Screening and Straining

Water contains different amounts of suspended and dissolved substances, including Turbidity, color, taste, odor, microorganisms, fish, plants, trash, etc. Some of these larger items can obstruct the equipment in the treatment process, such as tree branches getting stuck in the pump impeller. Therefore, the first process in conventional water treatment is to screen or filter out these larger volumes of debris. This is usually done by a bar screen, which is placed in front of the water source inlet. As the water passes through the screen, the larger items are trapped on the screen. As water passes through it, large items are trapped on the screen. These screens must be raked or cleaned off periodically.

Aeration

After screening, the water is aerated (supplied with air) to absorb oxygen from the air. This process helps to expel soluble gases such as carbon dioxide and hydrogen sulfide (both are acidic, so this process makes the water less corrosive) and any gaseous organic compounds that are detrimental to the water. Aeration also removes iron or manganese by oxidizing these substances to insoluble forms. Once in the insoluble form, these substances can be removed by filtration.

Aeration

Aeration is the process of bringing water and air into close contact to remove dissolved gases, oxidize dissolved metals and volatile organic chemicals.

Chemical Addition

Once raw water is received at the treatment plant, chemicals are added to help cause suspended particles floating in the water to clump together and form heavier, larger colloidal particles, often called flocs.

Chemical Dosing

Chemical dosing is the addition of chemicals to the water to achieve the desired conditioning. Make the treatment effective through various mechanisms.

Coagulation and Flocculation

Usually fast mixing equipment (mixer agitator) is used to add coagulants (alum, polymer, etc.) to the water to speed up the mixing. The water is allowed to come in contact with the flocs formed to increase their volume. The continuous mixing must be gentle to allow the floc to grow and gain weight, but fast enough to keep it in suspension until it is ready to be allowed to settle in the clarifier. The process of adding a chemical to keep the suspended material in suspension is known as flocculation or coagulation.

Sedimentation and Clarification

Once the flocculation process is complete, the water flows over the weir in the flocculator to the center of the clarifier, or settling tank. As the water flows toward the weir, the larger flocculent particles are allowed to settle to the bottom of the clarifier. A rake continuously passes through the bottom of the clarifier, scraping the settled floc to the center of the clarifier. The settled floc is scraped into the center of the unit. A pump is used to pull the settled “sludge” out of the clarifier and send it to the settling tank. The water passing through the weir is collected and transferred to a filter.

Sludge Treatment

Accumulation of residues is called sludge in sewage treatment plant. Sewage sludge is a solid or slurry residue produced in the process of wastewater treatment.

Filtration

The clarified water enters the filter from the top. Gravity pulls the water down and through the filter to collect in the drainage system at the bottom of the unit. The most common materials used in filters are sand and gravel. Many conventional plants now use granular activated carbon as the preferred media because it not only provides excellent mechanical filtration of particulate matter, but also removes organic compounds that can cause taste and odor problems.

Disinfection

The filtered water becomes very clear and clean. But there are still bacteria and viruses left. For this reason disinfection is required. The most common disinfection process is chlorination. Chlorine gas comes in many different forms, including chlorine gas, chlorine dioxide, and hypochlorite (bleach). Waterworks continuously monitor the chlorine levels in treated water to ensure that the water is thoroughly disinfected.

Disinfection

Disinfection is usually the final stage of the water treatment process to limit the effects of organic matter, suspended solids and other contaminants.

Finally Distribution

The final water is pushed through the distribution system (underground pipes) throughout the city. Distribution System The system consists of large pumps at the treatment plant, overhead storage tanks, piping, hydrants, valves and other equipment.