Sewage from food industry mainly comes from food processing and production processes such as raw material treatment, washing, dehydration, filtration, various separation and refining, deacidification, deodorization and cooking. Sewage contains a lot of protein, organic acids and carbohydrates. Due to the existence of many plankton, the dissolved organic matter in water increases rapidly, and it is easy to produce humus, accompanied by unpleasant gases; At the same time, there are many metal ions such as copper, lead, manganese and chromium in these sewage, and bacteria and coliforms often exceed the national discharge standards, so the wastewater from food factories can only be discharged after treatment.

Polyacrylamide used for wastewater treatment in food industry can convert pollutants in wastewater into harmless substances, so that wastewater can be purified. Commonly used reagents are: polyacrylamide, lime, ferrous sulfate, ferric chloride and aluminum sulfate. Generally, lime is not used alone, but often used in combination with other chemicals. The optimum dosage and pH value should be determined by experiments. Due to the wide variety of foods and the wide sources of raw materials, food industry sewage has suspended solids, high oil content, many heavy metal ions and large COD and BOD values. Sludge, waste oil, waste acid, waste alkali, animal and plant wastes generated in the processing of food industry sewage can also be treated harmlessly.

※ Pollutants have changed their chemical nature after chemical treatment, and chemical changes are always accompanied in the treatment process. Chemical treatment methods used in food industry wastewater include neutralization, coagulation, electrolysis, redox, ion exchange, membrane separation and so on.

food wastewater treatment process (1) redox

chemical redox is an effective method to transform pollutants in wastewater. Dissolved inorganic substances and organic substances in wastewater are oxidized or reduced to slightly toxic or non-toxic substances through chemical reactions, or converted into forms easily separated from water, thus achieving the purpose of treatment.

food wastewater treatment process (2) coagulation method

the chemical treatment process used in food industry wastewater treatment is mainly coagulation method. Coagulation can not be used alone, but must be combined with precipitation, clarification or air flotation of physical treatment process to form coagulation sedimentation or coagulation air flotation. Coagulation sedimentation can be used as pretreatment of biological treatment or as advanced treatment after biological treatment.

Coagulation and sedimentation is an important method of water treatment. For some wastewater with small colloidal particles, or some colloidal solutions that are difficult or unable to settle, chemical coagulants are added to form large particles that are easy to settle and removed. Protein and polysaccharide in colloidal state in wastewater can be effectively removed by coagulant sedimentation.

The commonly used chemicals are lime, ferrous sulfate, ferric chloride and aluminum sulfate. Lime is generally not used alone, but often used in combination with other chemicals. The optimum dosage and pH value should be determined through experiments.

food wastewater treatment process (3) ion exchange

ion exchange is mainly a method of removing harmful ions (including organic and inorganic) in water by ion exchanger.

2. Biological treatment

Biochemical treatment is one of the most important processes in the organic wastewater treatment system. In the wastewater treatment of food industry, biological treatment processes can be divided into aerobic process, anaerobic process, stabilization pond, land treatment and various combined processes formed by the combination of the above processes. Food wastewater is organic wastewater, and biological method is the main secondary treatment process to degrade COD and BOD5.

aerobic biological treatment process can be divided into activated sludge process and membrane process according to the growth form of microorganisms used. The former includes traditional activated sludge process, stage aeration process, biosorption process, complete mixing process, extended aeration process, oxidation ditch, intermittent activated sludge process (SBR) and so on. The latter includes biological filter, tower biological filter, biological rotary table, active biological filter, biological contact oxidation method, aerobic fluidized bed and so on. General aerobic treatment has a good effect on low concentration wastewater.

Anaerobic biological treatment process is suitable for food industry wastewater, the main reason is that wastewater contains biodegradable high-concentration organic matter and is non-toxic. In addition, the power consumption of anaerobic treatment is low, the generated biogas can be used as energy, the amount of residual sludge generated is small, the anaerobic treatment system is completely closed, which is beneficial to improving environmental sanitation, can be operated seasonally or intermittently, and the sludge can be stored for a long time.

3. ? Physical treatment method

Physical treatment method refers to the treatment method of changing the composition of wastewater by physical action. Physical treatment methods used for food industry wastewater treatment include screening, skimming, regulation, sedimentation, air flotation, centrifugal separation, filtration and microfiltration. The first five processes are mostly used for pretreatment or primary treatment, while the last three are mainly used for advanced treatment.

food wastewater treatment process (1) skimming

Some food industrial wastewater contains a lot of grease, which must be removed before entering the biological treatment process, otherwise it will cause blockage of pipelines, pumps and some equipment, and will also have a certain impact on the biological treatment process. In addition, oil removal and recovery have great economic value.

According to its physical state, the oil in wastewater can be divided into two categories: free floating and emulsified. Usually the grease trap removes floating grease. The removal rate of floating grease in the grease trap can reach above 91%. If there is a regulating tank or sedimentation tank in the treatment process, the oil separation tank can share a unified structure with the regulating tank or the primary sedimentation tank, which can save investment and land occupation. For small treatment systems, an oil-water separator can be set to skim oil. See more related technical documents for details.

food wastewater treatment process (2) sieve filtration

sieve filtration is a widely used method in pretreatment. Its main function is to separate coarse dispersed suspended solids from wastewater. The equipment used is a grid and a grid screen. Grille intercepts coarse suspended solids, and its function is to protect water pump and subsequent treatment equipment. There are fixed screens, rotating screens and vibrating screens commonly used in food industry wastewater, and the most commonly used aperture of the grid screen is 11-41 mesh.

food wastewater treatment process (3) adjustment

for food industrial wastewater with large changes in water quality and quantity, adjustment tanks are often set up to adjust the water quality and quantity of wastewater, and the adjustment time is generally 6-24 hours, mostly 6-12 hours. The capacity of the regulating tank is 1.5%-51% of the daily wastewater treatment.

food wastewater treatment process (4) air flotation

air flotation is mainly used to remove emulsified oil, surfactant and other suspended solids from food industry wastewater. There are vacuum air flotation, pressurized dissolved air flotation and air diffusion tube (plate) air flotation. Before the wastewater enters the container air flotation tank, chemical coagulant or coagulant aid is added to the water, which can improve the removal rate of emulsified oil and colloidal suspended particles. According to the data, air flotation can remove more than 91% oil and 41%-81% BOD5 and SS. HRT of air flotation tank is generally 31min.

food wastewater treatment process (5) sedimentation

sedimentation is used to remove inorganic solid and organic solid in raw wastewater, and to separate solid phase and liquid phase in biological treatment process. Removing inorganic solids in the raw wastewater by a grit chamber; Removing organic solids in the raw wastewater by a primary sedimentation tank; The secondary sedimentation tank is used to separate the biological phase and the liquid phase in the biological treatment process, and the grit chamber is generally located behind the grid and grid screen. In order to remove the organic matter on the surface of inorganic solids in wastewater and avoid the organic solids in wastewater from depositing in grit chamber, aerated grit chamber can be used. Using the primary sedimentation tank can reduce the load of the subsequent process. The effect of removing suspended solids in the primary sedimentation tank is related to the processed raw materials and products. According to the direction of water flow in the pool, it is divided into advection sedimentation tank, vertical sedimentation tank and radial sedimentation tank. In order to improve the sedimentation efficiency of the sedimentation tank, parallel inclined plates or inclined tubes can be arranged in the sedimentation tank to form an inclined plate (tube) sedimentation tank. Generally, the precipitation time is 1.5-2.1h..

※ Features of food sewage treatment equipment:

Food sewage treatment equipment is used to remove algae and reduce turbidity in water treatment of waterworks with lakes as water source; Used in industrial wastewater treatment projects, such as petrochemical industry, textile, printing and dyeing, electroplating, leather making, food industry and other fields; It is applied to the recovery of useful substances in sewage, such as paper making, fiber recovery in batik water and other fields. The advantages of food sewage treatment equipment mainly include the following aspects:

(1) The technological route of food sewage treatment equipment is mature, reliable, advanced and reasonable.

(2) paying full attention to pretreatment has created favorable conditions for the normal operation of the main process.

(3) The biological contact oxidation process is adopted as the main process, and the treatment effect is stable and reliable.

(4) Coagulation air flotation is adopted in the food sewage treatment equipment, which can remove most of the suspended solids and organic matter as well as most of the oil, making the pretreatment effect more perfect and providing a superior environment for the subsequent process.

※ Application scope of food sewage treatment equipment:

It is suitable for treating domestic sewage and similar industrial organic wastewater in residential quarters, hospitals, sanatoriums, office buildings, shopping malls, hotels, restaurants, institutions, schools, troops, aquatic products processing plants, animal storage processing plants and dairy processing plants, such as organic sewage in textile, beer, paper-making, leather-making, food, chemical and other industries. The main purpose is to