Common domestic water treatment process

Currently, many water plants still apply the following basic steps to treat groundwater and surface water into drinking water. However, in fact, the water quality after treatment is still contaminated with heavy metals or arsenic. The trend of groundwater and surface water sources is becoming more and more seriously polluted, so the supply water treatment process will require more stages as well as better treatment efficiency than existing technology.

Reservoir and Pre-settlement:  Create favorable conditions for the self-cleaning process: settle suspended sediments, reduce the amount of bacteria due to environmental conditions, perform oxidation reactions due to the effect of dissolved oxygen. soluble in water and is responsible for regulating the flow between the flow from the source and the consumption flow by the raw water pump station supplying the water treatment plant.
Screens and screens: Eliminates floating objects in the water stream to protect equipment and improve the cleaning efficiency of treatment works. Floating objects and objects suspended in water can be as small as toothpicks, when passing through the pump into the treatment works, they may be dispersed or rot, increasing the color and sediment content of the water.
Sand settling tanks: In surface water sources with high turbidity (>250mg/L) behind the screen, the inorganic suspended particles are small in size, have a larger density than water, are hard, and have the ability to settle quickly. kept in the sand settling tank.
Chemical treatment of water at source: To limit the growth of algae and water microorganisms, eliminate color, odor, and taste caused by dead bodies and substances. The commonly used chemical is CuSO4, the dosage is 0.12 – 0.13 mg/l. The dosage and interval between treatments depends on the raw water composition as well as the concentration of organisms and algae, temperature, alkalinity and CO2 content.
Aeration: Dissolve oxygen from the air into water to oxidize divalent iron, divalent Manganese to Iron III, and manganese IV to form Fe(OH)3  hydroxide compounds capable of precipitation and settling.
Pre-chlorination: Add chlorine to the water before the settling tank and filter. Extend the contact time for sterilization when the water source is heavily contaminated. Oxidation of dissolved iron in the form of organic compounds, oxidation of dissolved manganese to form the corresponding precipitate. Oxidation of organic substances to decolorize. Prevents the growth of algae in the reaction and settling tanks, destroys the cells of microorganisms that produce viscous mucus on the filter surface, increases the filter cycle time.
Mixing chemicals: Facilitates rapid and even dispersion of chemicals into the entire volume of water to be treated because the hydrolysis reaction creates flocculation very fast (usually less than 1/10s), if not mixed well and prolonged mixing will not produce sufficient, firm and uniform flocculation in the water volume, the sedimentation efficiency will be poor and alum expensive. Other chemicals require mixing while mixing requires less rigorous mixing time than alum.
Coagulation and flocculation reaction: Creates nuclei capable of binding dissolved dissolved water contaminants into a floc capable of settling in settling tanks and adhering to the grain surface of the layer. filter material with the fastest speed and most economic. When alum is mixed with treated water, chemical and physical-chemical reactions occur immediately, forming a positive colloidal system that is evenly dispersed in water. When neutralized, this positive colloidal system is the nuclei that are able to adhere to other substances. Negative colloids disperse in water to form flocs. Therefore, the process of agglomeration is called flocculation, and the process of agglomeration and flocculation is called flocculation reaction. Usually use aluminum alum and iron alum
Sedimentation: The process of reducing the amount of suspended solids in the source water by the following measures: Gravity sedimentation in the settling tanks, then the particles with a higher density than the water in the appropriate hydraulic regime will settle; By centrifugal force acting on sediment particles, in centrifugal settling tanks and hydraulic cyclonics; By buoyancy force due to air bubbles clinging to sediment particles in flotation tanks. Along with sedimentation, the finished settling process reduces 90-95% of bacteria in the water because the bacteria are always adsorbed and adhered to the floc particles during the settling process.
Filtration: The process that not only retains the suspended particles in the water larger than the pores created between the filter particles, but also retains the colloidal iron and organic colloidal particles that cause turbidity and coloration. The size is many times smaller than the pore size but has the ability to stick and absorb on the surface of the filter material layer.
Absorbing odor causing substances, causing color: Activated carbon powder particles have a very large active surface, have the ability to absorb gas molecules and substances in liquid form dissolved in water, making water taste and color. to the surface of this coal grain out of the water. Water is deodorized and colorless.
Fluorination of water: Because after the water purification process, the amount of fluorine present in the water is lower than the standard, so it is necessary to add more fluorine to the water.
Disinfection: To ensure microbiological safety, water must be disinfected prior to consumption. Disinfection measures include: Boiling water, Using ultraviolet rays, Using substances with high sterilization effect such as ozone, chlorine, etc.
Water stabilization: The process of reducing the aggressiveness of water and simultaneously inoculating the surface