The food industry encompasses various sectors such as meat processing, seafood processing, dairy processing, canned food production, brewing, and sugar refining. Therefore, it has a wide range of raw materials and diverse product types, resulting in significant differences in the quantity and quality of wastewater discharge. Compared to other industrial wastewater, wastewater from the food industry typically does not contain heavy metals, pesticides, and other harmful substances, but its parameters such as BOD (biochemical oxygen demand) and COD (chemical oxygen demand) are usually higher. As the primary raw materials used in the food industry are mostly digestible organic substances, its wastewater typically exhibits good biochemical properties.

The main pollutants in wastewater from the food industry include:

- Solid substances floating in wastewater, such as vegetable leaves, fruit peels, minced meat, and poultry feathers;

- Suspended substances in wastewater, including oils, proteins, starch, colloids, etc.;

- Dissolved substances in wastewater, such as acids, alkalis, salts, sugars, etc.;

- Sediments and other organic substances carried in the raw materials;

- Pathogenic bacteria, etc.

Wastewater from the food industry includes wastewater generated from alcohol, beer, monosodium glutamate, starch, lactose, citric acid, vegetable processing, and various soft drink production processes. If these wastewaters are not treated promptly, they will cause serious pollution to the environment.

The characteristics of wastewater from the food industry are high organic matter and suspended solids content, prone to spoilage, and generally not significantly toxic. Its water quality and quantity vary with the seasons, with high-concentration wastewater being more common. The main hazards are causing eutrophication of water bodies, leading to the death of aquatic organisms and fish, promoting the generation of odor-producing sediment at the bottom of water bodies, deteriorating water quality, and polluting the environment.

For such wastewater, the commonly adopted treatment process is the air flotation-anaerobic-aerobic process. Firstly, the wastewater enters the grease trap, which aims to separate most of the oil and suspended solids from the wastewater to reduce the load on subsequent treatment processes. Then, the wastewater is pumped into the air flotation tank. In the air flotation tank, microbubbles are generated by injecting air, usually air, which interact with the oils and suspended solids in the wastewater, causing them to float to the water surface and form scum, which is then removed. This step aims to further reduce the solid and oil content in the wastewater.

Next, the treated wastewater enters the anaerobic biological treatment tank. Here, microorganisms decompose organic substances in the wastewater under anaerobic conditions, producing carbon dioxide, water, and other harmless substances. This process, known as anaerobic treatment, occurs in the absence of oxygen. The microorganisms in the anaerobic treatment tank are usually anaerobic bacteria, which can effectively degrade organic substances in the wastewater.

Finally, the treated wastewater is transferred to the aerobic biological treatment tank. Here, the wastewater is exposed to an oxygen-rich environment, and aerobic bacteria are used to further decompose organic substances. The microorganisms in the aerobic treatment tank require oxygen to survive and grow, and they oxidize organic substances for growth and reproduction. The goal of this stage is to further reduce the organic matter content in the wastewater and ensure that the wastewater meets discharge standards.

After air flotation, anaerobic, and aerobic treatment, the quality of the wastewater is significantly improved, and it reaches a level where it can be safely discharged, directly into the city's sewage network.