Four mainstream treatment processes for domestic sewage plants

（1） Physical method

1. Sedimentation method: mainly removes inorganic particles and SS from wastewater;

2. Filtration method: mainly removes SS and oil substances in wastewater;

3. Oil separation: Remove floating and dispersed oil;

4. Air flotation method: oil-water separation, recovery of useful substances, and suspended solids with a relative density close to 1;

5. Centrifugal separation: Remove SS and colloids that are difficult to remove by precipitation method.

（2） Chemical method

1. Coagulation sedimentation method: remove colloids and fine SS;

2. Neutralization method: treatment of acid-base wastewater;

3. Oxidation-reduction method: removal of toxic substances and difficult to biodegrade substances;

4. Chemical precipitation method: removal of heavy metal ions, sulfur ions, sulfate ions, phosphate ions, ammonium ions, etc.

（3） Physicochemical method

1. Adsorption method: small amounts of heavy metal ions, difficult to biodegrade organic matter, decolorization and deodorization, etc;

2. Ion exchange method: recovery of precious metals, radioactive wastewater, organic wastewater, etc;

3. Extraction method: difficult to biodegradable organic compounds, heavy metal ions, etc;

4. Blowing off and stripping: Removal of soluble and volatile substances.

（4） Biological method

1. Activated sludge method: A general term for various methods of microbial suspension in wastewater biological treatment.

(1) SBR method

Sequential batch activated sludge method, also known as sequencing batch activated sludge method, is an activated sludge wastewater treatment technology that operates in an intermittent aeration manner.

The core of SBR technology is the SBR reaction tank, which integrates functions such as homogenization, initial sedimentation, biodegradation, and secondary sedimentation in one tank, without a sludge reflux system. Water treatment equipment PP cotton softening equipment

(2) CASS water treatment equipment PP cotton soft water equipment

The CASS method is an improved version of the SBR method, characterized by small footprint, low operating costs, mature technology, and stable process.

The CASS method involves setting up a biological selection zone in the front of the CASS reaction tank and an automatic decanting device that can be lifted and lowered in the rear. Water treatment equipment PP cotton softening equipment

(3) AO method

This process, also known as anaerobic aerobic process, is an anaerobic stage used for nitrogen and phosphorus removal; O (Oxic) is an aerobic stage used for removing organic matter from water. Water treatment equipment PP cotton softening equipment

(4) AAO method

This method, also known as A2O method, is the abbreviation for the first letter of Anaerobic Anoxic Oxic in English. It is a commonly used sewage treatment process that can be used for secondary or tertiary sewage treatment, as well as reclaimed water reuse, with good nitrogen and phosphorus removal effects.

(5) Oxidation ditch method

The oxidation ditch is a variant of the activated sludge method, with its aeration tank in a closed ditch type. Therefore, it is different from traditional activated sludge methods in terms of hydraulic flow state. It is a circulating flow aeration ditch connected from end to end, in which sewage seeps into and is purified. The earliest oxidation ditch was not built of reinforced concrete, but a soil ditch with slope protection treatment, which was intermittent inflow and intermittent aeration. From this perspective, The oxidation ditch was originally a technology for treating wastewater in a sequential batch process.

2. Biofilm method: A method of treating wastewater or waste gas using membrane like biological communities fixed on the surface of inert materials. The biological filter method, biological contact oxidation method, and biological rotary disc method all belong to this method. Water treatment equipment PP cotton softening equipment

(1) Biological filter

A bioreactor used for treating wastewater, filled with inert filter materials, with a surface growth of biological communities for treating pollutants. Water treatment equipment PP cotton softening equipment

(2) Biological turntable

A bioreactor for aerobic treatment of wastewater, consisting of a water tank and a set of disks. The lower part of the disk is submerged in water, while the upper part of the disk is exposed to air. The surface is covered with biological communities, and the rotating disk repeatedly contacts the wastewater and oxygen in the air, purifying the wastewater.

(3) Biological contact oxidation tank

The structure includes the pool body, filler, water distribution device, and aeration device. The working principle is to set up fillers in the aeration tank as carriers for the biofilm. The wastewater to be treated flows through the filler at a certain flow rate after being oxygenated, and comes into contact with the biofilm. The biofilm and suspended activated sludge work together to purify the wastewater. Water treatment equipment PP cotton softening equipment

3. Anaerobic biological treatment method: including anaerobic digestion, hydrolysis acidification tank, UASB, etc.

Anaerobic biological treatment method is an organic wastewater treatment method that utilizes facultative and specialized anaerobic bacteria to degrade macromolecular organic compounds in wastewater into low molecular compounds, and then convert them into methane and carbon dioxide. It is divided into two stages: acidic digestion and alkaline digestion.

In the acidic digestion stage. The external enzyme action secreted by acid-producing bacteria transforms macromolecular organic matter into simple organic acids and alcohols, aldehydes, ammonia, carbon dioxide, etc; In the alkaline digestion stage, the metabolites of acid digestion are further decomposed into biogas composed of methane, carbon dioxide, etc. under the action of methane bacteria.

4. Biological treatment under natural conditions

(1) Stable pond

Properly manually trim the land, build ponds, and set up embankments and anti-seepage layers, relying on microorganisms growing in the ponds to treat sewage. Water treatment equipment PP cotton softening equipment

(2) Soil treatment method

A general term for methods of improving water quality using soil and plants, while utilizing the water and nutrients of wastewater to nourish the land. Soil treatment methods mainly include irrigation, flood irrigation, and high irrigation rate infiltration. Modern sewage treatment technology can be divided into primary, secondary, and tertiary treatment according to the degree of treatment. Water treatment equipment PP cotton softening equipment

Primary treatment mainly removes suspended solid pollutants from wastewater, while most physical treatment methods can only meet the requirements of primary treatment. After primary treatment of sewage, BOD can generally be removed by about 30%, which does not meet the discharge standards. The primary treatment belongs to the pretreatment of Secondary treatment;

Secondary treatment is mainly used to remove organic pollutants (BOD, COD) in colloidal and dissolved state in sewage, with a removal rate of more than 90%, so that organic pollutants can meet the discharge standard;

Tertiary treatment, further treatment of refractory organics, nitrogen, phosphorus and other soluble inorganic compound substances that can lead to eutrophication of water body. The main methods include biological nitrogen and phosphorus removal, coagulation precipitation, sand filtration, activated carbon adsorption, ion exchange, and electroosmotic analysis.