Polyacrylamide is used for sewage treatment in food industry, which converts pollutants in wastewater into harmless substances and purifies wastewater. Commonly used reagents are: polyacrylamide, lime, ferrous sulfate, ferric chloride and aluminum sulfate. Generally speaking, lime is not used alone, but often combined with other chemicals. The optimum dosage and pH value should be determined by experiments. Due to the wide variety of foods and wide sources of raw materials, the sewage from food industry has many suspended solids, high oil content, heavy metal ions and large COD and BOD values. Sludge, waste oil, waste acid, waste alkali, animal and plant wastes produced in the sewage treatment process of food industry can also be treated harmlessly.
Food wastewater treatment technology ※
Food wastewater treatment processes mainly include biochemical methods and physical and chemical methods:
1. Chemical treatment method
Chemical treatment refers to the application of chemical principles and chemical action to transform pollutants in wastewater into harmless substances and purify wastewater. The chemical properties of pollutants have changed after chemical treatment, and chemical changes are always accompanied during the treatment process. Chemical treatment methods of food industry wastewater include neutralization, coagulation, electrolysis, redox, ion exchange, membrane separation and so on.
Food wastewater treatment process (1) redox
Chemical oxidation-reduction is an effective method to transform pollutants in wastewater. Dissolved inorganic 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, so as to achieve the purpose of treatment.
Food wastewater treatment process (2) Coagulation method
Coagulation is the main chemical treatment process for wastewater treatment in food industry. Coagulation can not be used alone, but must be combined with precipitation, clarification or air flotation of physical treatment process to form coagulation precipitation or coagulation air flotation. Coagulation and sedimentation can be used as pretreatment of biological treatment or 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 to settle or cannot settle, chemical coagulants are added to form large particles that are easy to settle and remove. Coagulation and sedimentation can effectively remove colloidal protein and polysaccharide from wastewater.
Commonly used chemicals are: lime, ferrous sulfate, ferric chloride and aluminum sulfate. Generally speaking, lime is not used alone, but often combined with other chemicals. The optimum dosage and pH value should be determined by experiments.
Food wastewater treatment process (3) ion exchange
Ion exchange is mainly a method to remove harmful ions (including organic and inorganic) from water by ion exchanger.
2. Biological treatment methods
Biochemical treatment is one of the most important processes in 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 composed 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 high concentration of organic matter, which is easy to biodegrade and non-toxic. In addition, the power consumption of anaerobic treatment is low, the generated biogas can be used as energy, the amount of excess sludge 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 therapy method
Physical treatment refers to the treatment method of changing the composition of wastewater through physical action. Physical treatment methods for food industry wastewater treatment include screening, skimming, adjustment, precipitation, 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.
Overview of Food Wastewater Treatment Process (1)
Some food industry wastewater contains a lot of oil, 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 oil recovery have great economic value.
Oils in wastewater can be divided into two types according to their physical state: free state and emulsified state. Usually the grease trap will remove floating grease. The removal rate of floating oil in the oil separation tank can reach above 90%. 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 relevant technical documents for details.
Food wastewater treatment process (2) Screening
Screen filtration is a widely used method in pretreatment. Its main function is to separate coarse and dispersed suspended solids from wastewater. The equipment used is a grid and a grid screen. Grille intercepts coarse suspended matter, and its function is to protect water pump and subsequent treatment equipment. Fixed screen, rotating screen and vibrating screen are commonly used in food industry wastewater, and the aperture of the most commonly used grid screen is 10-40 mesh.
Adjustment of food wastewater treatment process (3)
For food industry wastewater with great changes in water quality and quantity, a regulating tank is often set up to regulate the water quality and quantity of wastewater, and the regulating time is generally 6-24 hours, mostly 6- 12 hours. The capacity of the regulating tank is 05%-50% of the daily sewage treatment capacity of 65438+.
Food wastewater treatment process (4) air flotation
Air flotation is mainly used to remove emulsified oil, surfactants and other suspended substances 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, adding chemical coagulant or coagulant aid into the water can improve the removal rate of emulsified oil and colloidal suspended particles. According to the data, air flotation can remove more than 90% oil and 40%-80% BOD5 and SS. HRT of air flotation tank is generally 30 minutes.
(5) Treatment process of precipitated food wastewater
Precipitation is used to remove inorganic solids and organic solids from raw wastewater, and to separate solid and liquid phases during biological treatment. Removing inorganic solids from raw wastewater through a grit chamber; Removing organic solids in the raw wastewater through a primary sedimentation tank; The secondary sedimentation tank is used to separate biological phase and liquid phase in biological treatment process, and the grit chamber is generally located behind the grid and mesh screen. In order to remove the organic matter on the surface of inorganic solids in wastewater and avoid the deposition of organic solids in wastewater in grit chamber, aerated grit chamber can be used. The use of 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 raw materials and products treated. 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. The general precipitation time is1.5-2.0h. ..
Features of food sewage treatment equipment: ※:
Food sewage treatment equipment is applied to algae removal and turbidity reduction in water plants with lakes as water sources; Used in industrial wastewater treatment engineering, such as petrochemical industry, textile, printing and dyeing, electroplating, tanning, food industry and other fields; It is applied to the recovery of useful substances in sewage, such as fiber recovery in papermaking and batik water. The advantages of food sewage treatment equipment mainly include the following aspects:
(1) The technical 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 main process adopts biological contact oxidation process, and the treatment effect is stable and reliable.
(4) The food sewage treatment equipment adopts coagulation air flotation, which can remove most of the suspended solids, organic matter and most of the oil, make the pretreatment effect more perfect, and provide a superior environment for the follow-up process.
Scope of application of food sewage treatment equipment: ※:
It is suitable for the treatment of domestic sewage and similar industrial organic wastewater in residential quarters, hospitals, sanatoriums, office buildings, shopping malls, hotels, restaurants, institutions, schools, military units, aquatic products processing plants, animal storage processing plants, dairy processing plants and other industries. The main purpose is to treat domestic sewage and similar industrial organic wastewater to meet the requirements of reuse water quality, so as to achieve the purpose of treating wastewater.