Summary of sewage treatment technology

1. Sewage treatment level

Sewage treatment levels include primary treatment (including primary intensive treatment), secondary treatment (including secondary intensive treatment) and advanced treatment.

2. Composition of sewage treatment process

(1) Physical processing section. (2) Biochemical treatment section.

The principle of sewage treatment process selection

The main technical and economic indicators of process selection include: investment per unit of water treatment, investment reduction per unit of pollution, power consumption and cost per unit of water treatment, power consumption and cost reduction per unit of pollutants, land area, reliability of operation performance, management and maintenance difficulty, overall environmental benefits, etc.

The municipal sewage treatment process should be optimized according to the treatment scale, water quality characteristics, environmental functions of receiving water bodies and local actual conditions and requirements after comprehensive technical and economic comparison.

The influent water quality of sewage should be determined realistically, the process design parameters should be optimized, the current water quality characteristics of sewage and the composition of pollutants must be investigated or determined in detail, and a reasonable analysis and prediction should be made. When the water quality composition is complex or special, the dynamic test of sewage treatment process should be carried out, and pilot study should be carried out if necessary.

The new process applied for the first time in China must go through pilot and production tests to provide reliable design parameters before being applied. When the same sewage plant is constructed in stages, the same process should be adopted in each stage as far as possible, and the construction scale of each stage should be as same as possible.

Sewage treatment method

Modern sewage treatment methods are mainly divided into four categories: physical treatment, chemical treatment, physical chemical treatment and biological treatment.

1 Physical treatment method

The physical treatment method is to separate and recover the insoluble and suspended pollutants (including oil film and oil beads) in sewage through physical action, without changing their chemical properties during treatment. Commonly used are filtration, precipitation, flotation and so on.

(1) Filtration method: The use of filtration media to intercept suspended matter in sewage. Filter media have screen, gauze, particles, commonly used filtration equipment such as grille, screen, microfilter and so on.

1) Grille and screen. In the drainage project, the waste water flow through the sewer to the water treatment plant, should first pass through a group of metal vertically parallel frame (grid), perforated plate or filter (screen) in the channel, so that the floating matter or suspended matter can not pass and is blocked in the grid, fine screen or filter material.

Grille plate

This step is the pretreatment of wastewater, the purpose of which is to recover useful substances; Initial flushing of wastewater to facilitate subsequent treatment and reduce the load on settling tanks or other treatment equipment; Protect pumping machinery from failure due to particulate matter blockage. Protect water pumps and other treatment equipment. The effect of grille interception mainly depends on the sewage quality and the size of the grille gap. There are two kinds of slag cleaning methods: manual and mechanical. Grid slag should be cleaned and treated in time.

The screen is mainly used to intercept fine suspended debris with a particle size of a few millimeters to tens of millimeters, such as fibers, pulp, algae, etc., usually woven with metal wire, chemical fiber, or perforated steel plate, the aperture is generally less than 5mm, the minimum can be 0.2mm. The screen filter device has rotary drum type, rotary type, rotary disk type, fixed vibration inclined screen and so on. No matter what kind of structure, it should not only be able to trap dirt, but also easy to discharge and clean the screen surface.

2) Granular media filtration (also known as Tong, filter, surprise material filtration). When the wastewater passes through the granular filter material (such as quartz sand) bed, the fine suspended matter and limbs are trapped in the surface of the filter material and the internal void. Commonly used filter media are quartz sand, anthracite and garnet. In the filtration process, the filter material also acts on physical retention, sedimentation and adsorption of suspended matter. The effect of filtration depends on the size of the pore size of the filter material, the thickness of the filter material layer, the filtration speed and the nature of the sewage.

When the waste water flows through the granular filter layer from top to bottom, the suspended particles with larger diameter are first trapped in the gap of the surface filter material, so that the gap of the filter material of this layer is smaller and smaller, and gradually form a filter membrane mainly composed of the trapped group particles, and it plays the main filtration role. This action belongs to the resistance trapping or screening action.