Various pools are indispensable in the sewage treatment process. Let's take stock of the pools and their functions. The pools in sewage treatment generally include grit chambers, sedimentation tanks, regulating tanks, biochemical tanks, and secondary sedimentation tanks.
1. Grit chamber: Separate inorganic particles with higher density from sewage, protect water pumps and pipes from wear, reduce the volume of sludge treatment structures, increase the content of organic components in sludge, and increase the value of sludge as fertilizer. Grit chamber types Aerated grit chamber, horizontal grit chamber;
Horizontal grit chamber: It is actually a channel that is wider and deeper than the inflow channel and the outflow channel. When sewage flows through, due to the increase in the water flow section and the decrease in water flow velocity, the inorganic particles entrained in the wastewater sink under the action of gravity, thereby achieving the purpose of separating inorganic particles in the water.
Aerated grit chamber: Newly built sewage treatment plants are mainly based on aerated grit chambers. Aerated grit chambers are used to introduce air into one side of a rectangular pool to make the sewage swirl. The flow rate gradually decreases from the periphery to the center. The sand particles are separated from the water in the sand collecting trough at the bottom of the pool. The organic matter in the sewage and the sludge washed off the sand particles are still suspended and flow into the treatment structure behind with the water flow.
2. Sedimentation tank: It uses the principle that the suspended impurity particles in the water flow can be separated from the water flow when the downward sedimentation speed is greater than the downward flow speed of the water flow, or the downward sedimentation time is less than the time for the water flow to flow out of the sedimentation tank to purify the water. It can be divided into horizontal flow sedimentation tank, vertical flow sedimentation tank, radial flow sedimentation tank, inclined tube/inclined plate sedimentation tank.
Horizontal flow sedimentation tank: simple structure, good sedimentation effect, but large area, many problems with sludge discharge, currently large, medium and small sewage treatment plants have adopted it.
Vertical flow sedimentation tank: small footprint, convenient sludge discharge, and easy to manage, but the pool is too deep, construction is difficult, and the cost is high, so it is generally only suitable for small and medium-sized sewage treatment plants.
Radial flow sedimentation tank: most suitable for large water treatment plants, with standardized sludge discharge machinery, good operation effect, but requires high construction quality and management level.
Inclined plate/tube sedimentation tank: mainly suitable for primary sedimentation tanks, which are widely used in water treatment, with high sedimentation efficiency, short residence time, and small footprint.
The disadvantage is that it is easy to breed algae, etc., sludge discharge is difficult, easy to clog, and inconvenient to maintain.
3. Regulating tank: In order to ensure the normal operation of subsequent treatment structures or equipment, the water volume and water quality of sewage need to be adjusted.
＞ Acidic sewage and alkaline sewage are mixed in the regulating tank to achieve the purpose of neutralization.
＞ High-temperature sewage discharged in a short period of time can also be adjusted to balance the water temperature.
Biochemical pool: There are generally four types of biochemical pools
Anaerobic pool: Anaerobic treatment uses anaerobic bacteria to remove organic matter from wastewater, which usually takes a long time. The anaerobic process can be divided into hydrolysis stage, acidification stage and methanogenesis stage.
Aerobic pool The function of the aerobic pool is to allow the activated sludge to undergo aerobic respiration, further decompose organic matter into inorganic matter, and remove pollutants.
Facultative aerobic pool Generally speaking, a facultative aerobic pool is a sewage purification pool that has both anaerobic and aerobic microorganisms. One of the processes in the sewage treatment process, it passes through an anaerobic sedimentation tank, an aeration tank, a facultative aerobic tank, and a plant tank respectively. The first three tanks decompose organic matter in the sewage through aerobic and anaerobic respiration of microorganisms.
Biological contact oxidation pool The biological contact oxidation pool includes a pool body, filler, water distribution device, and aeration device. The working principle is: filler is set in the aeration tank and used as a carrier of the biofilm. After being oxygenated, the wastewater to be treated flows through the packing at a certain flow rate and contacts the biofilm. The biofilm and the suspended activated sludge work together to purify the wastewater.
5. Secondary sedimentation tank: The function of the secondary sedimentation tank is mainly to separate the sludge, clarify, concentrate and return the activated sludge in the mixed solution. Its working effect directly affects the effluent quality and return sludge concentration of the activated sludge system.
