How is the best treatment process selected for surface water treatment?
The properties of the raw water and the quality goals for the finished water serve as the foundation for selecting treatment process alternatives. Future implementation of increasingly strict drinking water quality standards, as well as possible changes and unpredictability in raw water quality, must be taken into account.
As a result, the selection of alternative processes is influenced by the aims and objectives. Furthermore, the availability of major equipmentand the capability of operators and maintenance personnel, as well as waste handling requirements and the availability and cost of water treatment chemicals, all have a significant impact on the process selection, particularly in remote areas and developing countries.
Why is surface water treated?
Before it reaches the appropriate water quality, surface water must be treated. Surface water usually contains a lot of suspended particles, bacteria, algae, and organic waste, which gives it a poor taste and smell. Surface water in some regions, such as river estuaries, can be brackish, containing up to 8000 mg/L of salts.
Common methods for treating surface water
1: Strainer for microbes:Algae and plankton should be removed from the raw water.
2: Aeration:Taste and odour-causing volatile organics and gases are stripped and oxidized, as well as iron and manganese. Gravity aerators, spray aerators, diffusers, and mechanical aerators are examples of aeration systems.
3: Mixing:Chemicals and gases are distributed uniformly and quickly into the water.
4: Pre-oxidation:In raw water and other treatment units, oxidizing agents such as ozone, potassium permanganate, and chlorine compounds inhibit microbiological growth and oxidize taste, odour, and color-causing substances.
5: Coagulation: It is the initial phase, which involves rapidly adding coagulants like aluminium sulphate, ferric chloride, and organic polymers into the water. This changes the electrical charges surrounding the suspended, unwanted particles, causing them to attract and coagulate, or clump together, forming larger particles called flocs.
6: Flocculation: It involves gently agitating the water so that the flocs or particles meet, cling together, and entrap other suspended particles, resulting in larger, heavier particles that will settle out in the following steps.
7:Sedimentation: The flocculated water travels slowly through a basin or tank during this phase, allowing the heavy floc particles to drop to the bottom and be removed.
8:Filtration:Water is filtered via a sand, coal, or similar material filter, which removes particles like silt, other very fine particulates, and some pathogens that did not settle during the sedimentation process. Filtration reduces turbidity even more, resulting in crystal clear water.
9: Use of Activated Carbon:Chemical pollutants can also be removed with activated carbon. Contaminants cling to the surface of carbon and are removed rather than being retained in the microscopic passageways between grains of sand, a process known as carbon adsorption.
10: Filtration Procedures without Clarification: Filtration processes without clarification can be swiftly overrun by filter-clogging algae in reservoirs and other surface waters with substantial algal blooms.
Algae have a density similar to water, and when they produce oxygen, they can develop their own flotation devices. As a result, dissolved air flotation (DAF), in which coagulated particulate debris, including algae if present, is floated to the top of a clarity tank, is a better procedure for algae removal.
11:Iron and Manganese removal: If unwanted levels of iron and manganese are present, aeration (the mixing of air and water) is occasionally utilized; the elements remain in solution in water in the absence of oxygen.
12:Fluoride: It is sometimes used in various systems to prevent tooth decay.
13: Membrane Filtration: It covers a wide range of processes and, depending on the membrane process employed, can be used for a variety of source water quality.
Reverse osmosis (RO) is a water purification method that eliminates pollutants from water by forcing water molecules through a semipermeable membrane under pressure. The toxins are filtered out and washed away during this process, leaving clean, tasty drinking water.The concentrated water, which contains dissolved and undissolved debris that does not flow through the membrane, is released to the drain, while purified water permeates the membrane and is collected.
14: Disinfection:In the water supply, it destroys disease-causing microbes. UV light and oxidative chemicals such as chlorine, bromine, iodine, potassium permanganate, and ozone are used to disinfect, with chlorine being the most often employed chemical.
What is the BOTTOM LINE?
When looking for surface water treatment solution, there are numerous aspects to consider.
The most successful treatment, whether biological, chemical, or physical, is determined by the site circumstances, pollutant kinds, and concentrations. Budget, timeline, and other considerations will also influence which treatment options are chosen.
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