"Coagulation-sedimentation-filtration-disinfection" conventional treatment process

Taking Guangzhou water source as an example, due to the poor water source, six of the water sources of seven water plants can't meet the five standards stipulated by the state. Therefore, before conventional treatment, potassium permanganate should be added in front of the pump (mainly through oxidation, the organic film is oxidized, and the surface properties of suspended particles or colloids change in favor of instability and coagulation, thus improving the turbidity removal efficiency, reducing the organic matter content and reducing the odor of water. Moreover, potassium permanganate reacts with reducing substances in water to produce water-insoluble intermediate product manganese dioxide, which can also promote colloid coagulation for new nucleation. Directly add it to the source water with diaphragm pump. ), activated carbon (physical adsorption and chemical adsorption, physical adsorption is mainly because its porous structure provides a large amount of surface area, so it is very easy to achieve the purpose of adsorption and collection of impurities; Chemical adsorption means that the adsorbed substance reacts with the surface substance of activated carbon, for example, with chlorite in water, so that chlorite is transformed into chloride ion, thus achieving the purpose of removing chlorite in water, so that there is no unpleasant taste and smell in water. Directly add it to the source water with screw pump. ), ammonia (mainly for residual chlorine in stable water. At the same time of chlorination, ammonia is mainly chlorine ammonia, and then other substances are gradually oxidized to reduce free chlorine in water and enhance disinfection purpose. Automatic adjustment of ammonia machine, directly added to the source water pipe). Chlorine is added after the pump (the main purpose is to kill the moss in the water, oxidize some organic matter and reduce the formation of nitrite. And this value must be added according to the residual chlorine value of the water to be considered. It is directly added to the source water pipe through a chlorinator and a water sprayer. ), alum (the main component is generally alkali aluminum or aluminum sulfate. Alkali aluminum is commonly used because of its high corrosiveness and adaptability to water temperature. Directly add it to the source water pipe with screw pump. )

After pretreatment, it enters the clarification process, that is, coagulation, precipitation and filtration. The treatment objects are mainly suspended solids and colloidal impurities in water, and the impurities in water are flocculated by drugs to form large particles (this step is completed in a flocculation tank, commonly known as a reaction tank. All the reaction tanks in our factory are grid reaction tanks, which are made up of several vertical shafts connected in series. The incoming water flows from one grid to the next, obliquely from top to bottom, until the water outlet, so that alum can fully react with suspended solids and colloidal impurities in the water. ), and then alum flower and water are separated by gravity through sedimentation tank (our factory has advection sedimentation tank and inclined tube sedimentation tank). The advection sedimentation tank uses gravity to make alum flowers sink to the bottom of the tank in parabolic form, so as to be separated from the water to be considered; The inclined tube sedimentation tank separates water from alum according to the principle that water flows upward and sludge slides downward. ), the water to be filtered enters the filter tank, so that the tiny residual impurity particles are filtered out by sand (fine sand, coarse sand and spring stone from top to bottom) (our factory has a movable hood filter tank and a common quick filter tank, and the main difference between these two tanks is the method of washing the sand layer. Movable hood filter uses siphon principle to pump away impurities on the surface of sand layer; The common fast filter adopts backwashing, including 300 seconds of air washing, mainly dispersing the sand layer, and 7 minutes of water washing to thoroughly wash the impurities in the sand layer. )。 Chlorine must be added to the filtered water (the main purpose is to kill bacteria, viruses and other pathogenic microorganisms, to ensure that there is an appropriate amount of residual chlorine in the factory water, so as to inhibit the reproduction of residual bacteria in the water and prevent the pipeline network from being polluted again, but it must be added according to the residual chlorine value of the factory water, and our factory generally controls it between 2.8 and 3.3. ), after the finished water flows into the clean water pool, it is pressurized by the water pump of the secondary pump house through the suction well and enters the urban water supply pipe network.

Second, the coagulation principle

Raw water is turbid because it contains a lot of clay particles in colloidal form. Because these clay particles generally have a certain negative charge, under the exclusion of static electricity, these particles are generally not easy to grow and precipitate, and the raw water is always turbid. One of the most effective methods is to add trivalent aluminum ions with strong sedimentation to make these particles agglomerate and precipitate. Among the derivatives of aluminum ions, polyaluminum chloride in the form of polymer has the advantages of short reaction time, good coagulation effect, large amount of alum, fast precipitation speed, adaptability to different water quality and wide PH range. In production, we use the method of adding polyaluminum chloride aqueous solution to make turbid raw water clear. The molecular formula of polyaluminum chloride can be expressed as:

We mix a certain amount of alum solution into raw water in proportion, fully mix and react in the mixing tank and reaction tank, and condense into larger particles of alum flower, which is called coagulation. Settling agent, which plays a role in coagulation, can also be called coagulant. Coagulation mechanism of water is an important subject in water treatment. Coagulation includes coagulation and flocculation. Coagulation refers to the process of making colloid unstable by electric double layer compression. Coagulation is instantaneous, just spreading chemicals into all the water. Flocculation refers to the process of colloid destabilization (or due to the adsorption bridge effect of polymer substances) to form large flocs. The flocculation process takes some time to complete. However, it is generally difficult to distinguish between the two, so agents that can coagulate and flocculate are generally called coagulants.

Note that there is an optimal range for the addition of coagulant. If the addition amount is small, the sinking effect is not great; If too much aluminum ion is added, the colloidal particles with negative charge will become positively charged, and the repulsion between particles will increase, which will lead to the decline of coagulation effect. Therefore, in the process of alum dosing, it is necessary to accurately control the dosage and often follow up the dosing effect.

Three. Chlorination process

Chlorine bottle-liquid chlorine tube-evaporator-vacuum regulator-chlorinator-sprinkler-water

Four. General process of purification process

Precipitation in source water reaction tank

Add chemicals (coagulant)

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