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Surface Treatment

Municipal sewage

During food processing, water is needed to clean, blanch, disinfect, and excellent raw materials; containers and equipment must also be cleaned.

Therefore, food processing discharges large amounts of wastewater. However, due to the wide range of raw materials and product types used in food processing, the quality and quantity of discharged wastewater vary greatly. Therefore, food processing wastewater dramatically impacts the environment and humans, and certain technologies are required to treat and purify it before it can be discharged up to standards.

Table of contents（Click to go to where you want to see）

6.1. Physical treatment process ( Our company’s main products and cases)
6.2. Chemical treatment
6.3. Biochemical treatment
6.4. Aerobic biological treatment process
6.5 Anaerobic biological treatment process

What are the classifications of food processing ?

Different industries, food processing, can be divided into the meat products industry, dairy industry, egg industry, aquatic products industry, fermented products industry, grain and oil products industry, fruit and vegetable industry, beverage industry, food additive industry, candy industry, health food, snack food, catering industry, quick-frozen food industry, canned industry, convenience food manufacturing industry, etc.

What are the main sources of food processing wastewater ?

The primary sources of food processing wastewater are a large amount of sand and debris, leaves, skins, scales, meat, feathers, hairs, etc., which enter the wastewater during the raw material cleaning stage, causing the wastewater to contain a large amount of suspended solids;

Many ingredients in the raw materials during the production and processing stages cannot be fully utilized, and the unused parts enter the wastewater, causing the wastewater to contain a large amount of organic matter;

To increase the color, aroma, and taste of food and extend the shelf life, various food additives are used, and some of them are lost in wastewater, making the chemical composition of wastewater complex;

A large amount of grease, raw materials, and auxiliary materials produced during the cleaning stage of food processing equipment enter the wastewater.

What are the main pollutants in food industry wastewater ?

Solid materials floating in wastewater, such as vegetable leaves, peels, minced meat, poultry feathers, etc.;

Substances suspended in wastewater include grease, protein, starch, colloidal substances, etc.;

Acids, alkalis, salts, sugars, etc., dissolved in wastewater;

Silt, sand, and other organic matter entrained in raw materials, as well as pathogenic bacteria and viruses.

Characteristics of food processing wastewater

The characteristics of food industry wastewater are high content of organic matter and suspended matter, ease of putting refy, generally not very toxic, water quality and quantity change with seasons, and a lot of high-concentration wastewater.

Its main hazards are the eutrophication of water bodies, causing the death of aquatic animals and fish, causing organic matter to be deposited on the bottom of the water to produce odors, deteriorating water quality, and polluting the environment.

In addition to appropriate pretreatment according to water quality characteristics, biological treatment is generally suitable for food industry wastewater treatment.

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What are the leading pollution indicators of food processing wastewater?

The leading pollution indicators for judging food processing wastewater are physical and chemical indicators.

Physical indicators of wastewater

It mainly includes temperature, color, odor, solid content, etc. The two indicators commonly tested are colorimetric and solid content.

Color: Food processing wastewater often contains organic or inorganic dyes, biological pigments, inorganic salts, organic additives, etc., which color the wastewater.

Solid content: Most of the impurities contained in wastewater are solid substances. These solid substances exist in the water in dissolved and suspended forms. The two are collectively called total solids.
Chemical indicators of wastewater

Biological oxygen demand (BOD): the amount of dissolved oxygen consumed when organic pollutants in 1 liter of wastewater are oxidized and decomposed under the action of aerobic microorganisms within a period;

Chemical Oxygen Demand (COD): The amount of oxygen consumed during chemical oxidation by a strong oxidant used to measure the organic content in wastewater;

Total oxygen demand (TOD) refers to the amount of oxygen required for substances that can be oxidized in water, mainly organic substances, to turn into stable oxides during combustion;

Total organic carbon (TOC): the organic carbon content in the wastewater volume;

Nitrogen-containing organic matter: a general term for all nitrogen-containing organic compounds in wastewater, measured in nitrogen; phosphorus-containing organic matter.

What are the treatment technologies for food processing wastewater ?

Currently, the method widely used in food industry wastewater treatment at home and abroad is the biological treatment process, which includes aerobic biological treatment process, anaerobic biological treatment process, comprehensive biological treatment process that combines aerobic biological treatment and anaerobic biological treatment, etc.

Among the aerobic biological treatment processes are mainly activated sludge and biofilm processes. Among the activated sludge processes, the most widely used process at home and abroad is the SBR process (sequential batch intermittent activated sludge process), a biological reaction process. The pool integrates the biodegradation process, sedimentation process, and sludge return function, and the process is relatively simple;

Among the biofilm methods, the BAF method (biological aerated filter method) is relatively typical and has a certain representativeness. This process integrates various reaction processes such as filtration, adsorption, and biological metabolism.

The anaerobic biological treatment process is essential because its infrastructure investment and operation and management costs are lower than the aerobic biological treatment process. Therefore, the anaerobic biological treatment process has recently been widely developed at home and abroad. Among them, the anaerobic granular sludge expanded bed and the anaerobic internal circulation reactor are typical representatives of the third type that evolved and developed based on the UASB reactor. The third-generation anaerobic treatment is gradually applied to the food industry wastewater treatment process.

Some research results indicate that anaerobic biological treatment processes have sound treatment effects in treating food industry wastewater.

Food processing wastewater treatment technology classification

Wastewater treatment technology can be divided into primary, secondary, and tertiary treatment, depending on the degree of treatment. Primary treatment: a treatment method that mainly removes suspended solid pollutants in sewage and reduces the degree of corruption of wastewater and the load of subsequent treatment processes.

Commonly used methods include screening, sedimentation, air flotation, and pre-aeration. Generally, after primary treatment, the elimination rate of BOD is about 30%, and about 70% of the total solids are removed. The degree of wastewater purification is not high, and secondary treatment is required. Primary processing is a preprocessing of secondary processing.

Secondary treatment: a process that mainly removes colloidal and dissolved organic pollutants (i.e., BOD, COD substances) in the sewage to further purify the sewage. Generally, 80% to 90% of BOD in wastewater can be removed after secondary treatment, and the BOD content in the treated water can be less than 30ml/L. Generally speaking, after secondary treatment, wastewater has met the standards for discharge water.

Tertiary treatment: a treatment process added after primary or secondary treatment for sewage recovery and reuse. The scope of sewage reuse is broad, from industrial reuse water supply water sources to domestic water use.

Physical treatment process(Our company’s main products and cases)

Physical treatment is a method that uses physical effects to change the composition of wastewater. Physical treatment methods used for food processing wastewater include screening, skimming, conditioning, sedimentation, air flotation, centrifugation, filtration, and microfiltration.

The first five processes are mainly used for pretreatment or primary treatment, and the last three are used primarily for deep treatment. The primary function is to remove solid and large particle impurities in food processing wastewater and to achieve a certain degree of uniform wastewater quality.

Screening: Screening is the separation of dispersed suspended solids in the form of larger particles in food industry wastewater. The equipment used for screening is mainly grids and screens. Sieving is the most widely used method of pretreatment. The grid intercepts coarser suspended solids, which protects the water pump and subsequent treatment equipment. Commonly used grating screens in food processing wastewater include fixed, rotating, and vibrating screens.

Skimming: Some food industry wastewater contains a large amount of grease, which must be removed before entering the biological treatment process. Otherwise, it will cause a blockage of pipelines, water pumps, and some equipment, and it will also have a particular impact on the biological treatment process. In addition, grease removal and recovery have significant economic value. Grease in wastewater can be divided into two categories: free-floating and emulsified according to its physical state. Generally, grease traps remove floating grease, and the removal rate of floating grease in grease traps can reach more than 90%.

Regulation: The amount of wastewater discharged from food processing wastewater and the quality of sewage vary significantly over time. Therefore, setting up a physical treatment process at the beginning of the entire treatment process can make the subsequent treatment process run stably and for a long time and stabilize the change in the water quantity and water quality of food processing wastewater to a certain extent.

Precipitation: The primary function is to remove inorganic solids and organic solids from food processing wastewater, which separates the liquid and biological phases in the biological treatment process.

Air flotation: Air flotation is mainly used to remove emulsified oil, surface active substances, and other suspended solids from food processing wastewater. There are vacuum air flotation, pressurized dissolved air flotation, and diffuse tube (plate) air flotation. Before the wastewater enters the flotation tank of the container, adding chemical coagulants or coagulants to the water can improve the removal rate of emulsified grease and colloidal suspended particles.

Other processing techniques. The commonly used method for in-depth treatment of secondary treatment effluent is filtration, which can use sand or composite filter media filters. According to the filtration speed, it is divided into slow sand filter and fast filter. Generally, the filtration speed of a single-layer sand filter is 8 to 12m/h.

Application case(Preprocessing-physical method)

Angel-(Yichang)-Co.,-Ltd.-Yeast-Products-Green-Manufacturing-Project.jpg

Case Studies-Yeast Product Wastewater Treatment

This project is Angel (Yichang) Co., Ltd yeast product wastewater. After flotation treatment, the effluent is added with a phosphorus removal agent, pH adjustment, and PAM. After sufficient mixing, it is precipitated in an inclined plate sedimentation tank to achieve the effect of phosphorus removal.

Case Studies-Thailand Seafood Processing Wastewater Treatment Plant Project

Case study-This case describes the application of Yosun Environmental Protection Equipment's high-efficiency dissolved air flotation in a wastewater treatment project at a seafood food processing plant in Thailand.

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Chemical treatment

Chemical treatment methods refer to applying chemical principles and effects to convert pollutant components in wastewater into harmless substances so that sewage can be purified. Pollutants change their chemical nature after undergoing chemical treatment, and chemical changes always accompany the treatment process. Chemical treatment methods used for food processing wastewater include neutralization, coagulation, electrolysis, redox, ion exchange, membrane separation, etc.

Coagulation method

The primary chemical treatment process used in food processing wastewater treatment is coagulation.

The coagulation method cannot be used alone. It must be combined with the sedimentation, clarification, or air flotation method of the physical treatment process to form coagulation sedimentation or air flotation. Coagulation sedimentation can be used as a pretreatment for biological or biological treatment—post-depth processing.

Coagulation and sedimentation is an essential method of water treatment. For some wastewater with small colloidal particles or some colloidal solutions that are difficult or impossible to settle, chemical coagulants are added to form large particles that are easy to pay for and remove. Proteins and polysaccharides in the colloid state in wastewater can be effectively removed through coagulation and precipitation by adding drugs. Commonly used agents include lime, ferrous sulfate, ferric chloride, and aluminum sulfate. Lime is generally not used alone but is often combined with other chemicals. The optimal dosage and pH value should be determined through experiments.
Redox

Chemical redox is an effective method for transforming pollutants in wastewater. Dissolved inorganic and organic substances in sewage are oxidized or reduced to slightly toxic or non-toxic substances through chemical reactions or converted into forms that are easily separated from water, thereby achieving the purpose of treatment.
Ion exchange

Ion exchange mainly uses ion exchangers to exchange and remove harmful ions (including organic and inorganic) in water.

Biochemical treatment

Biochemical treatment is one of the most essential processes in organic wastewater treatment systems.

In food processing wastewater treatment, biological treatment processes can be divided into aerobic, anaerobic, stabilization ponds, land treatment, and various combination processes formed by the above processes.

Food wastewater is organic wastewater, and biological treatment is the primary secondary treatment process, aiming at degradation.
COD, BOD5.

Aerobic biological treatment process

Aerobic biological treatment processes are divided into activated sludge and membrane processes according to the growth form of the microorganisms utilized.

The former includes the traditional activated sludge method, staged aeration method, biological adsorption method, complete mixing method, delayed aeration method, oxidation ditch, intermittent activated sludge method (SBR), etc.

SBR treatment

The SBR method is developed from the original intermittent activated sludge method. The SBR method has a secondary sedimentation tank and activated sludge return equipment compared to other activated sludge treatment methods. The entire reactor combines the biodegradation process sedimentation. The process and sludge return functions are integrated into one, the treatment process and infrastructure building structure are simple, the whole process occupies less area, the operation and management costs are low, and it is not easy to cause problems such as activated sludge expansion.

The operation process of the SBR process to treat food processing wastewater generally includes five steps: water inflow, oxygenation and aeration, static sedimentation, drainage, and sludge discharge.
Aerated biological filter method

The BAF method is a wastewater treatment technology developed in Europe and the United States in the late 1980s. This treatment method integrates multiple functions such as the filtration process, adsorption process, and biological metabolism process, making the process occupy a small area; the effluent water quality is good and has many advantages, such as not quickly causing activated sludge expansion.
MBR method (membrane bioreactor)

The MBR method is a wastewater treatment technology developed in the 1990s. This method uses membrane modules to replace the secondary sedimentation tank in the traditional solid and liquid phase separation process. Compared with the conventional activated sludge method, this method treatment method has the advantages of a small footprint, relatively high removal efficiency, good effluent quality, large device volume load, low activated sludge yield, and simple management and operation.
Biological contact oxidation method

The biological contact oxidation method of the coal slag packing tower device is selected. The coal slag packing biological contact oxidation tower device with a flow rate of 220l/h, the treated water quality COD≦100mg/l, BOD≦30mg/l, SS≦30mg/l, fully meets the requirements—emission standards.

Anaerobic biological treatment process

The main reason anaerobic biological treatment technology is suitable for food processing wastewater is that the wastewater contains high concentrations of organic matter that is readily biodegradable and non-toxic.

In addition, the power consumption of anaerobic treatment is low, the biogas generated can be used as energy, and the amount of residual sludge generated is negligible. The anaerobic treatment system is completely sealed, which is conducive to improving environmental sanitation. It can be operated seasonally or intermittently, and the sludge can be stored for a long time.

UASB (Upflow Anaerobic Sludge Bed)

Invented by Professor Lcttinga of Wageningen Agricultural University in the Netherlands, the main structure of the process is divided into four parts: water distribution system, reaction area, gas phase, liquid phase, solid phase two-phase separation area, and biogas collection area.

This process has many advantages, such as a small land area, low investment and operation costs, high biological treatment efficiency, and is conducive to the formation of anaerobic granular sludge. Therefore, it has apparent advantages in food processing wastewater treatment.
EGSB reactor

The EGSB reactor combines the advantages of FB (fluidized bed) and UASB (up-flow anaerobic sludge bed). This technology mainly relies on anaerobic granular sludge to treat organically polluted wastewater.

Food processing wastewater enters the reactor from the bottom of the EGSB reactor and slowly passes through the main sludge area of anaerobic granular sludge. A large amount of organic pollutants are removed under the action of anaerobic granular sludge, and a large amount of biogas is generated. Biogas and effluent are discharged separately through the separator at the top of the EGSB reactor, while the anaerobic granular sludge settles back into the main sludge area.

This reactor maintains a very high inlet water rising flow rate (<6 m/h-12 m/h) during operation, thereby keeping the anaerobic granular sludge in the sludge area of the reactor body in a highly suspended state. The high concentration of suspended state ensures complete and adequate contact between organic pollutants in food processing wastewater and anaerobic sludge particles, thereby significantly improving the removal effect of organic contaminants in food processing wastewater.
IC reactor

The IC reactor has many advantages when treating food processing wastewater, such as small floor space and long-term stable operation. The IC reactor eliminates the reflux process in the traditional method and saves operation and management costs to a certain extent.
ASBR (anaerobic sequencing batch activated sludge process) reactor

It is an anaerobic treatment process characterized by intermittent operation. The operation process is divided into four stages: water inlet, reaction, precipitation, and drainage.

The ASBR reactor is an anaerobic treatment process that integrates the removal of organic matter and solid-liquid phase precipitation. This process has the characteristics of a small footprint, low operation and management costs, and strong resistance to impact loads of organic pollutants. It has obvious advantages in food processing wastewater treatment.

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