Brief Introduction of Process Flow in Waterworks

1. How is tap water produced?

It is well known that raw water contains various impurities due to natural and human factors. From the point of view of water treatment, these impurities can be divided into three categories: suspended matter, colloid and dissolved matter. The purpose of water treatment in urban waterworks is to remove these suspended substances, colloidal substances, bacteria and other harmful ingredients in raw water, which will endanger human health and industrial production, so that the purified water can meet the needs of drinking and industrial production. The Waterworks of Municipal Water Supply Corporation adopt conventional water treatment process, which includes mixing, reaction, precipitation, filtration and disinfection.

(1) Coagulation treatment:

After the raw water is lifted by the intake pump house, it is first treated by coagulation process, that is, raw water + water treatment agent mixing reaction alum water;

The whole process is called coagulation from the uniform mixing of the reagent and water until the formation of large particles of flocculants. Commonly used water treatment agents are polyaluminium chloride, aluminium sulfate, ferric chloride and so on. According to the chemical properties of aluminium, there are ionized aluminium ions in the water after being put into the reagent, and there are the following reversible reactions with the water molecule:

Al3 + 3H2O_Al (OH) 3 + 3H+;

Aluminum hydroxide has adsorption function, which can destabilize and coalesce the colloidal particles and micro-suspended substances which are not easy to precipitate in water, and then adsorb and build bridges, thus forming larger flocs, which are conducive to separation and sedimentation from water. The mixing process needs to be completed quickly after dosing. The purpose of mixing is to make the medicament disperse rapidly and evenly in water by means of hydraulic and mechanical stirring.

The water treated by coagulation reaction flows into the sedimentation tank through pipeline and enters the second stage of water purification.

(2) Precipitation treatment:

The flocs formed during the coagulation stage are separated from the water by gravity, which is called precipitation, and the process is carried out in the sedimentation tank. When water flows into the sediment area, it distributes along the whole section of the water area, enters the sediment area, and then flows slowly to the outlet area. The particles in the water settle at the bottom of the pond, and the sludge accumulates and concentrates continuously, and is discharged out of the pond regularly.

(3) Filtration treatment:

Filtration generally refers to the process of clarifying water by intercepting suspended particles in water by means of granular filter material layer with voids such as quartz sand through adhesion, thus further removing fine suspended impurities, organic matter, bacteria and viruses in water.

(4) Disinfection after filtration:

After filtration, the turbidity of the water is further reduced, and the residual bacteria and viruses lose the protection or attachment of the turbidity, creating good conditions for disinfection after filtration. Disinfection does not eliminate all microorganisms, it only requires the elimination of pathogenic microorganisms. Although most bacteria and viruses can be removed by coagulation, precipitation and filtration of water, disinfection plays a role in guaranteeing that drinking water reaches the bacteriological indicators. At the same time, it keeps a certain amount of residual chlorine at the end of urban water pipes to control bacterial reproduction and prevent pollution. The amount of chlorine added to disinfection (liquid chlorine) ranges from 1.0 to 2.5 g/m3. Hypochlorite produced by chlorine reacting with water plays an oxidative role in bacteria, destroying the enzyme system of bacteria and causing bacterial death. After disinfection, the water from the clear pool is elevated to a certain water pressure through the water supply pump room, and is delivered to millions of households through the water transmission and distribution network.