Introduction to Common Industrial Wastewater Treatment Technologies 1

Enterprises are mainly distributed in industries such as electronics, plastics, electroplating, hardware, printing, food, printing and dyeing. From the perspective of wastewater discharge and the degree of harm to environmental pollution, the focus of treatment is on wastewater mainly composed of inorganic pollutants such as electroplating, circuit boards, and surface treatment, as well as wastewater mainly composed of organic pollutants such as food, printing and dyeing, printing, and domestic sewage. This article mainly introduces several typical industrial wastewater treatment technologies.

1. Surface treatment wastewater

1.1 Polishing and Polishing Wastewater

During the polishing process of parts, the main pollutants in the wastewater are COD, BOD, and SS due to the presence of abrasives and polishing agents.

Generally, the following processing procedures can be referred to for processing:

Wastewater → regulating tank → coagulation reaction tank → sedimentation tank → hydrolysis acidification tank → aerobic tank → secondary sedimentation tank → filtration → discharge

1.2. Oil and degreasing wastewater

Common degreasing processes include organic solvent degreasing, chemical degreasing, electrochemical degreasing, and ultrasonic degreasing. Except for organic solvent degreasing, in other degreasing processes, degreasing agents composed of alkaline substances, surfactants, corrosion inhibitors, etc., the main pollutants in wastewater are pH, SS, COD, BOD, petroleum, chromaticity, etc.           

Generally, the following processing techniques can be referred to for treatment:

Wastewater → oil separation tank → regulating tank → air flotation equipment → anaerobic or hydrolytic acidification → aerobic biochemistry → sedimentation → filtration or adsorption → discharge

This type of wastewater generally contains emulsified oil. Before air flotation, CaCl2 demulsifier should be added to break down the emulsified oil, which is beneficial for removal by air flotation equipment. When the COD concentration in the wastewater is high, anaerobic biochemical treatment can be used first. If it is not high, only aerobic biochemical treatment can be used.

1.3. Acid pickling and phosphating wastewater

Acid washing wastewater is mainly generated during the acid washing and rust removal process of steel parts. The pH of the wastewater is generally 2-3, and there is a high concentration of Fe2+and SS

The following processing techniques can be referred to for treatment:

Wastewater → regulating tank → neutralization tank → aeration oxidation tank → coagulation reaction tank → sedimentation tank → filtration tank → pH correction tank → discharge

Phosphating wastewater, also known as film wastewater, refers to the chemical treatment of iron parts in phosphate solutions containing manganese, iron, zinc, etc., resulting in a layer of insoluble phosphate protective film on the surface, which serves as a spray coating bottom layer to prevent rusting of iron parts. The main pollutants in this type of wastewater are pH, SS, PO43-, COD, Zn2+, etc.           

The following processing techniques can be referred to for treatment:

Wastewater → regulating tank → primary coagulation reaction tank → sedimentation tank → secondary coagulation reaction tank → secondary sedimentation tank → filtration tank → discharge

1.4. Anodizing wastewater of aluminum

The pollutants mainly include pH, COD, PO43-, SS, etc. Therefore, the phosphating wastewater treatment process can be used to treat the anodic oxidation wastewater.

2. Electroplating wastewater

There are many types of electroplating production processes, and due to different electroplating processes, the wastewater generated is also different. Generally, the wastewater discharged by electroplating enterprises includes pre-treatment wastewater such as acid and alkali, cyanide containing wastewater from cyanide copper plating, copper containing wastewater, nickel containing wastewater, chromium containing wastewater and other heavy metal wastewater. In addition, there are various types of electroplating waste liquids generated.           

There are different treatment methods for electroplating wastewater containing different types of pollutants, which are introduced as follows:

2.1. Cyanide containing wastewater

At present, the mature technology for treating cyanide containing wastewater is the alkaline chlorination method. It is necessary to pay attention to the strict separation of cyanide containing wastewater from other wastewater to avoid mixing with metal ions such as nickel and iron, otherwise the treatment will be difficult.           

The principle of this method is to remove cyanide from wastewater by using chlorine based oxidants under alkaline conditions. The treatment process is divided into two stages. The first stage is to oxidize cyanide into cyanide salts, which are not completely destroyed, called incomplete oxidation stage. The second stage is to further oxidize and decompose cyanide salts into carbon dioxide and water, called complete oxidation stage.

Reaction condition control:

First level oxidation to break cyanide: pH value 10-11; Theoretical dosage: Simple cyanide CN -: Cl2=1:2.73, complex cyanide CN -: Cl2=1:3.42. Use ORP instrument to control the reaction endpoint at 300-350mv and the reaction time at 10-15 minutes.

Secondary oxidation cyanide breaking: pH value 7-8 (adjusted with H2SO4); Theoretical dosage: simple cyanide CN -: Cl2=1:4.09, complex cyanide CN -: Cl2=1:4.09. Use ORP instrument to control the reaction endpoint at 600-700mv; The reaction time is 10-30 minutes. The residual chlorine concentration in the reaction water should be controlled at 3-5mg/1.

The treated cyanide containing wastewater is mixed with the electroplating comprehensive wastewater for treatment together.

2.2. Chromium containing wastewater

Wastewater containing hexavalent chromium is generally treated using chromium reduction method. The principle of this method is to add reducing agents such as ferrous sulfate, sodium sulfite, sodium bisulfite, sulfur dioxide, etc. under acidic conditions to reduce hexavalent chromium to trivalent chromium. Then, sodium hydroxide, calcium hydroxide, lime, etc. are added to adjust the pH value, so that trivalent chromium hydroxide precipitate is generated and separated from the wastewater.

Control of reduction reaction conditions:

Adjust the pH value to 2.5-3 by adding sulfuric acid, add reducing agent for reaction, and control the reaction endpoint at 300-330mv using an ORP meter. The specific reaction time is about 15-20 minutes, which needs to be determined through debugging. Mechanical stirring, compressed air stirring, or hydraulic stirring can be used for mixing.

Control conditions for coagulation reaction:

PH value: 7-9, reaction time: 15-20 minutes.

2.3. Comprehensive heavy metal wastewater

Comprehensive heavy metal wastewater is composed of non complex heavy metal wastewater containing copper, nickel, zinc, etc., as well as acid and alkali pretreatment wastewater. This type of wastewater treatment method is relatively simple, generally using the process of generating hydroxide precipitation under alkaline conditions for treatment.

The processing flow is as follows:

Comprehensive heavy metal wastewater → regulating tank → fast mixing tank → slow mixing tank → inclined tube sedimentation tank → filtration → pH adjustment tank → discharge

The reaction conditions are generally controlled at a pH value of 9-10, and the specific optimal pH conditions are determined during debugging. The reaction time is 20-30 minutes for fast mixing tanks and 10-20 minutes for slow mixing tanks. Mechanical stirring is the best mixing method, but air stirring can also be used.

2.4. Comprehensive treatment of various electroplating wastewater

When an electroplating plant contains multiple types of electroplating wastewater, such as cyanide containing wastewater, hexavalent chromium containing wastewater, comprehensive wastewater containing acid and alkali, heavy metals such as copper, nickel, zinc, etc., the method of wastewater diversion treatment is generally adopted. Firstly, cyanide containing wastewater and chromium containing wastewater should be separately diverted and collected from the production line, and then treated according to the corresponding methods mentioned above. The treated wastewater is mixed into the comprehensive wastewater and treated together with it using coagulation and sedimentation methods for subsequent treatment.

The processing flow is as follows:

Cyanide containing wastewater → regulating tank → primary cyanide cracking tank → secondary cyanide cracking tank → comprehensive wastewater tank

Chromium containing wastewater → regulating tank → chromium reduction tank → comprehensive wastewater tank

Comprehensive wastewater → Comprehensive wastewater tank → Fast mixing tank → Slow mixing tank → Diagonal sedimentation tank → Intermediate tank → Filter → pH callback tank → Discharge

Introduction to Common Industrial Wastewater Treatment Technologies 2

3. PCB wastewater

During the processes of grinding, etching, electroplating, hole metallization, developing, and film stripping of circuit boards, companies producing circuit boards will generate circuit board wastewater. The wastewater from circuit boards mainly includes the following types:

The chelating and chelation wastewater generated by chemical copper deposition and etching processes has a pH value of 9-10 and a Cu2+concentration of 100-200mg/l.

A large amount of acidic heavy metal wastewater (non complexed copper wastewater) is generated during the cleaning process before electroplating, grinding, and brushing, including Sn/Pb removal wastewater with a pH value of 3-4, Cu2+less than 100mg/l, Sn2+less than 10mg/l, and trace amounts of heavy metals such as Pb2+.

The processes of dry film, film removal, development, ink removal, and screen cleaning produce high concentrations of organic ink waste liquid, with COD concentration generally ranging from 3000 to 4000mg/L.

According to the different characteristics of circuit board wastewater, it is necessary to separate different types of wastewater and adopt different methods for treatment.

3.1. Copper containing wastewater (copper ammonia complexation wastewater)

The heavy metal Cu2+in this type of wastewater forms a relatively stable complex with ammonia. The general method of hydroxide coagulation reaction cannot form copper hydroxide precipitate, and the complex structure must be destroyed first before coagulation precipitation. Generally, the sulfurization method is used for treatment. The sulfurization method refers to the use of S2- in sulfides and Cu2+in copper ammonia complex ions to generate CuS precipitation, which separates copper from wastewater. Excess S2- is then removed by using iron salts to produce FeS precipitation.

The processing flow is as follows:

Copper ammonia complex wastewater → regulating tank → breaking reaction tank → coagulation reaction tank → inclined tube sedimentation tank → intermediate water tank → filter → pH adjustment tank → discharge

The control of reaction conditions should be determined during commissioning based on the different water quality of each plant. Generally, the pH value is adjusted to neutral or slightly alkaline before adding chelating agents such as sulfides to prevent the generation of hydrogen sulfide. Some also adjust the pH value to slightly acidic. The dosage of sulfide is determined based on the amount of copper ammonia complex ions in the wastewater, and usually excessive dosage is added. Install an ORP meter in the rupture cell for measurement. When the potential reaches -300mv (empirical value), it is considered that there is an excess of sulfide and the reaction is complete. Excess sulfides are removed by adding ferrous salts, and the amount of ferrous added is determined by debugging and quantitatively added through a flow meter. The reaction time for the rupture tank is 15-20 minutes, and the reaction time for the coagulation tank is 15-20 minutes.

3.2. Ink wastewater

The wastewater from membrane and ink removal is generally treated intermittently due to its small water volume. Organic ink is used to separate suspended solids from the wastewater under acidic conditions for removal. After pretreatment, the ink wastewater can be mixed with comprehensive wastewater for further treatment. If the water volume is large, biochemical treatment can be used separately. The processing flow is as follows:

Organic ink wastewater → acidification and slag removal tank → discharged into comprehensive wastewater tank or subjected to biochemical treatment

When the amount of wastewater is small, the ink particles in the reaction tank float to the surface under the buoyancy of bubbles, forming floating slag that can be manually skimmed off; When the water volume is large, a plate and frame filter press can be used for dehydration, or biochemical treatment can be carried out after skimming to further remove COD.

3.3. Comprehensive wastewater from circuit boards

This type of wastewater mainly includes comprehensive wastewater containing heavy metals such as acid and alkali, Cu2+, Sn2+, Pb2+, etc. Its treatment method is the same as that of electroplating comprehensive wastewater, using hydroxide coagulation precipitation method for treatment.

3.4. Comprehensive treatment of various circuit board wastewater

When a circuit board factory contains the above-mentioned types of circuit board wastewater, the copper ammonia complex wastewater, ink wastewater, and comprehensive heavy metal wastewater should be separated and collected. After pre-treatment, the ink wastewater should be mixed with the comprehensive wastewater for subsequent treatment. The copper ammonia complex wastewater should be treated separately and then enter the comprehensive wastewater treatment system.

The processing flow is as follows:

Copper ammonia complex wastewater → regulating tank → breaking reaction tank → coagulation reaction tank → inclined tube sedimentation tank → intermediate water tank

Organic ink wastewater → acidification and slag removal tank → discharged into the comprehensive wastewater tank

Comprehensive wastewater → Comprehensive wastewater tank → Fast mixing tank → Slow mixing tank → Diagonal sedimentation tank → Intermediate tank → Filter → pH callback tank → Discharge

4. Treatment technology for common organic pollutant wastewater

4.1. Domestic sewage

The most commonly used method for treating domestic sewage is the A2/O method, and the treatment process flow is as follows:

Domestic sewage → grid tank → regulating tank → anaerobic tank → anoxic tank → aerobic tank → coagulation reaction tank → sedimentation tank → discharge

4.2. Printing and dyeing wastewater

This type of wastewater has a large volume, high color, and complex composition. Generally, the hydrolysis acidification contact oxidation physicochemical method can be used to treat printing and dyeing wastewater. The processing flow is as follows:

Printing and dyeing wastewater → regulating tank → coagulation reaction tank 1 → inclined sedimentation tank → hydrolysis acidification tank → contact oxidation tank → oxidation reaction tank → coagulation reaction tank 2 → secondary sedimentation tank → intermediate tank → filter → clean water tank → discharge

4.3. Printing ink wastewater

The characteristics of this type of wastewater are small water volume, deep color, and high concentrations of SS and COD. The following processing techniques can be referred to:

Ink wastewater → regulating tank → coagulation air flotation tank → hydrolysis acidification tank → contact oxidation tank → coagulation reaction tank → inclined sedimentation tank → oxidation tank → filter → clean water tank → discharge

5. Pre treatment in wastewater treatment of papermaking industry

The wastewater generated by the paper industry is characterized by a wide variety of types, large water volume, and high organic pollutant content, making it one of the difficult industrial wastewater to treat. The wastewater comes from various processes of pulp and paper making, with different physical properties and concentrations of organic pollutants. Effective treatment processes are determined based on the characteristics of the wastewater. Currently, the main methods used for treating wastewater in the paper industry include sedimentation, air flotation, adsorption, membrane separation, aerobic and anaerobic biological treatment methods, as well as several process combination treatment methods. Regardless of the method used, wastewater needs to be pre treated. Pre treatment is mainly aimed at improving wastewater quality to meet the inlet requirements of various processes, enhancing the overall effectiveness of wastewater treatment, and ensuring the stability of the entire treatment system. Therefore, pretreatment plays a very important role in wastewater treatment in the paper industry. The pretreatment of wastewater in the paper industry can be divided into in plant pretreatment and out of plant pretreatment. In plant pretreatment mainly involves the recovery of pulp from white water, often using filtration, air flotation, etc. for recycling and utilization, which can avoid a large amount of pulp entering the wastewater treatment system. This not only improves the yield of pulp but also saves the cost of wastewater treatment; Off site pretreatment is mainly aimed at ensuring that the wastewater entering the physical, chemical, biochemical and other treatment systems can meet the process requirements to the greatest extent possible, and enable the system to operate stably.

The pre-treatment process mainly consists of grilles, screens, fiber recovery systems, regulating water volume and quality, and other process components. Different pretreatment methods can be adopted according to the water quality of different paper industry wastewater to remove some pollutants, improve wastewater quality, and achieve the best treatment effect of the entire wastewater treatment system.

5.1. Grilles and Screens

Due to the presence of fine suspended solids such as bark, sawdust, plastic, and pulp fiber shavings in wastewater from the papermaking industry, wastewater discharged from pulp mills using wood as raw material often contains bark, sawdust, etc. During the papermaking process, a large amount of white water is produced, which contains a high concentration of fibers. These substances can cause damage to water pumps and have an impact on the main treatment process, especially causing serious blockages in the water distribution system of biological treatment processes such as UASB and hydrolysis acidification. Therefore, before entering the water pump and main treatment system, they should be intercepted by setting up grids to intercept large suspended solids and screens to intercept small suspended solids.

Grilles are generally used in the treatment of large amounts of papermaking wastewater. Due to the large amount of wastewater and the variety of suspended particles, setting up a grille can effectively intercept larger suspended particles, with high treatment capacity and low clogging. In response to the characteristics of papermaking wastewater, our company generally sets up coarse and fine grilles in engineering practice, with a gap between coarse and fine grilles usually ranging from 10-15mm and 1-5mm, respectively. Grid machines mainly include rotary mechanical grid machines, mesh rotary chain grid machines, fixed grid machines, and reverse cutting rotary fine grid machines. Our company commonly uses reverse cutting rotary fine grid machines, mesh rotary chain grid machines, fixed grid machines, etc.

Screens are usually used for relatively small water volumes and wastewater containing large amounts of fine suspended solids such as pulp. They can also remove large floating particles, with a removal rate of over 90% for suspended solids and large particulate matter. Engineering practice has shown that the gap between the screen mesh is generally 30-60 mesh, and the installation form adopts fixed installation with an installation angle of 40-50 °. The installation angle is not easy to be too large. If it is too large, it will reduce the water load, reduce the treatment capacity, and also increase some investment. If it is too small, it is easy to cause screen mesh blockage, increase the difficulty of slag removal, and affect the treatment effect.

5.2. Fiber Recycling System

Papermaking wastewater contains a large amount of pulp fibers. If pulp fibers are not recycled, a large amount of pulp will enter the wastewater treatment system, seriously affecting the treatment effect of the wastewater treatment system and causing pulp waste. The fiber recycling system inside the factory is mainly used for fiber recycling of papermaking white water. On the one hand, it reduces the discharge of white water through white water circulation. On the other hand, it uses methods such as screen filtration, multi disc filtration, air flotation, and sedimentation to recover pulp fibers. Off site fiber recycling often uses screen filtration to recover pulp fibers.

The main types of screen filtration include gravity flow screen filtration, ordinary rotary filter, reverse shear unidirectional flow rotary filter, bidirectional flow rotary filter, etc.

Gravity flow screen filtration is a process in which wastewater is evenly distributed onto a screen through an overflow weir in a collection tank. Due to gravity, the filtrate flows out through the gaps of the screen, and pulp fibers flow into the slag collection tank along the screen under the action of gravity and water impact, achieving the separation of pulp and water.

The ordinary rotary filter has an angle between the filter drum and the installation ground. Wastewater enters the drum from the top, and the inner wall of the inlet filter screen has a 90 degree angle. During the rotation of the filter drum, the filtrate is discharged from the gap of the filter screen, and the pulp is automatically discharged to the other end of the drum.

The reverse cutting unidirectional flow rotary filter adopts a horizontal drum structure, and the transmission mode can be divided into chain type and gear type. The wastewater is evenly distributed to the inner wall of the filter screen in the opposite direction of water flow. The water flow and the filter screen form a reverse cutting relative motion, and the filtrate is discharged from the gaps of the net. The pulp fibers are trapped on the inner wall of the net and automatically discharged from the slag discharge end under the action of the guide plate. Thus achieving the separation of pulp and wastewater; The principle of reverse cutting bidirectional flow through a filter is the same as unidirectional flow.

5.3. Adjustment

Due to the diversity of wastewater discharge in the production process of the paper industry, the water quality and quantity of the discharged wastewater may vary within a day. Therefore, it is required to regulate the wastewater, balance the water quality, and ensure that it can enter the subsequent treatment units evenly to improve the treatment effect. The regulation of wastewater mainly includes water quantity regulation and water quality regulation.

Wastewater treatment equipment and structures are designed according to a certain water volume standard, requiring uniform water inflow, especially for biological treatment systems. In order to ensure the normal operation of the subsequent treatment system, the water volume should be adjusted in advance before the wastewater enters the treatment system to meet the design requirements.

According to the different processes in the paper industry, the amount and quality of wastewater vary, and the residence time of the regulating tank also varies. When the treated water volume is relatively small, the residence time can be selected to be larger. When the treated water volume is relatively large, the residence time can be selected to be smaller according to the specific situation, generally 4-8 hours.

Although most of the suspended solids in the wastewater are removed through measures such as grilles and fiber recovery before entering the regulation tank, there will still be a portion of suspended solids, especially pulp, flowing into the regulation tank. To prevent sedimentation and enhance the uniformity of the wastewater, it is recommended to consider adding aeration devices in the regulation tank, which can effectively improve the water quality characteristics of the wastewater.

5.4. Conclusion

In short, paper industry wastewater is a difficult to treat organic wastewater with large water volume, high color, high suspended solids content, high organic matter concentration, and complex components. Through extensive engineering practice, it has been proven that the pretreatment process of wastewater in the comprehensive treatment process of paper industry wastewater is very important. It is related to the stable operation and standard discharge of the entire system, and also involves the high or low operating costs. Pre treatment of wastewater can greatly improve the water quality of wastewater, which is conducive to further treatment of paper industry wastewater and ultimately achieves the goal of removing pollutants. Therefore, pretreatment process is one of the essential key technologies in the treatment of wastewater in the paper industry.

6. Research progress on treatment and utilization technology of beer industry wastewater

The content of organic matter in beer wastewater is relatively high. Direct discharge not only pollutes the environment but also reduces the utilization rate of raw materials in the beer industry. Therefore, many scholars and manufacturers have studied the treatment and utilization technology of beer wastewater. Based on the explanation of the sources and characteristics of beer wastewater, this article compares several common treatment and utilization technologies. The conclusion is that a single treatment and utilization technology cannot fundamentally solve the pollution problem of beer wastewater. Only by combining multiple technologies can economic and environmental benefits be achieved

Keywords: Beer industry wastewater treatment, comprehensive utilization of wastewater

With the improvement of people's living standards, China's beer industry has made significant progress, and its output has been increasing year by year. In 1988, there were over 800 breweries in China with an annual production of 6.63 million tons of beer, ranking third in the world; After nearly a decade of development, the number of beer producers has reached over 1000, with an annual production of more than 10 million tons of beer, making it the second largest beer producing country in the world. However, while beer production has significantly increased, a large amount of organic wastewater has also been discharged into the environment. According to statistics, for every 1 ton of beer produced, 10-30 tons of fresh water are required, resulting in 10-20 tons of wastewater. The annual discharge of beer wastewater in our country has reached 150 million tons. Due to the high concentration of organic and non-toxic components such as protein, fat, fiber, carbohydrates, waste yeast, and hop residue in this type of wastewater, when discharged into natural water bodies, it consumes dissolved oxygen in the water, causing oxygen deficiency and promoting anaerobic decomposition of sedimentary compounds at the bottom of the water, producing foul odors and deteriorating water quality. In addition, the above ingredients mostly come from beer production raw materials. Abandoning them not only causes huge waste of resources, but also reduces the utilization rate of raw materials in beer production. Therefore, in today's world of food scarcity and tight water and resource supply, how to effectively treat beer wastewater while fully utilizing its useful resources has become an important research topic in environmental protection. This article summarizes the current status of beer wastewater treatment and utilization based on previous research results, in order to provide reference for further exploring efficient resource-based treatment technologies.

6.1. Generation and Characteristics of Beer Wastewater

The beer production process includes two parts: malt making and brewing. Both parts produce cooling water, which accounts for about 65% of the total drainage of the brewery. The water quality is good and can be recycled for the malt soaking process. The wastewater with medium and high pollution loads mainly comes from the soaking process in wheat production and the saccharification, fermentation, filtration, and packaging processes in brewing. Its chemical oxygen demand is between 500 and 40000 mg/L. Except for the continuous discharge of wastewater from the packaging process, all other wastewater is discharged intermittently (see Table 1).

Table 1 Sources and concentrations of high pollution wastewater in the beer industry

The total drainage of the brewery belongs to medium to high concentration organic wastewater, which is acidic with a pH value of 4.5-6.5. The main pollutants are chemical oxygen demand (CODcr), biochemical oxygen demand (BOD5), and suspended solids (SS), with concentrations of 1000-1500, 500-1000, and 220-440mg/L, respectively. The biodegradability (BOD5/CODcr) of beer wastewater is relatively high, ranging from 0.4 to 0.6, so the main part of many treatment technologies is biochemical treatment.

6.2. Beer wastewater treatment technology

At present, biochemical methods are widely used to treat beer wastewater both domestically and internationally. Depending on whether aeration is required during the treatment process, biological treatment methods can be divided into two categories: aerobic biological treatment and anaerobic biological treatment.

6.2.1 Aerobic biological treatment

Aerobic biological treatment is the process of utilizing the life activities of aerobic microorganisms to oxidize organic matter in beer wastewater under conditions of sufficient oxygen. The products are carbon dioxide, water, and energy (released into the water). This type of method does not take into account the utilization of organic matter in wastewater, resulting in higher treatment costs. Activated sludge method, biofilm method, and deep well aeration method are representative aerobic biological treatment methods

6.2.2 Activated Sludge Process

The activated sludge process is the most commonly used and reliable method for treating medium and low concentration organic wastewater, with advantages such as low investment and good treatment efficiency. The main components of this treatment process are aeration tanks and sedimentation tanks. After the wastewater enters the aeration tank, it is mixed with activated sludge (containing a large number of aerobic microorganisms). Under the condition of artificial oxygenation, the activated sludge absorbs and oxidizes and decomposes the organics in the wastewater, while the separation of sludge and water is completed by the sedimentation tank. the Pearl River Brewery, Yantai Brewery, Shanghai Yimin Brewery, Wuhan West Lake Brewery, Guangzhou Brewery and Changchun Brewery in China all use this method to treat beer wastewater. According to reports, when the influent CODcr is 1200-1500 mg/L, the effluent CODcr can be reduced to 50-100 mg/L, with a removal rate of 92% -96%. The disadvantage of using activated sludge method to treat beer wastewater is that it consumes a lot of power and often leads to sludge swelling during the treatment process.

The reason for sludge swelling is that the carbohydrate content in beer wastewater is too high, and nutrients such as N, P, Fe are lacking, resulting in an imbalance in the proportion of each nutrient, which leads to the inability of microorganisms to grow normally and death. The solution is to add chemical agents containing N and P, but this will increase the processing cost. A more economical method is to mix domestic sewage (with high concentrations of N and P) with beer wastewater.

The intermittent activated sludge process (SBR) can significantly reduce the power consumption through intermittent aeration, and at the same time, the wastewater treatment time is also shorter than the ordinary activated sludge process. For example, the Pearl River Brewery introduced the Belgian SBR patent technology, and the wastewater treatment time is only 19~20h, 10~11h shorter than the ordinary activated sludge process, and the CODcr removal rate is also more than 96%. Yangzhou Brewery and Datian Brewery in Sanming City have also achieved the same effect by using SBR technology to treat beer wastewater. The SBR method has low dilution of wastewater, high concentration of reaction substrate, and high adsorption and reaction rates, thus enabling sludge regeneration in a short period of time.

6.2.3 Deep well aeration method

In order to improve the utilization rate of oxygen and save energy during the aeration process, Barrie Brewery in Ontario, Canada, Shanghai Brewery in China, and Wuxing Brewery in Beijing all use deep well aeration (ultra deep water aeration) to treat beer wastewater. Deep well aeration is actually an activated sludge method that uses underground deep wells as aeration tanks. The aeration tank consists of a downcomer and an riser. The wastewater and sludge are introduced into the downcomer and circulated in the well. Air is injected into the downcomer or both pipes at the same time. The mixed liquid is discharged from the downcomer to the solid-liquid separation device, that is, the wastewater circulation is carried out by the static water pressure difference between the downcomer and the downcomer. Its advantages are: small footprint, high efficiency, high utilization rate of oxygen, no odor generation, etc. According to measurements, when the influent BOD5 concentration is 2400mg/L, the effluent concentration can be reduced to 50mg/L, with a removal rate of up to 97.92%. Of course, deep well aeration also has its shortcomings, such as high construction difficulty, high cost, and inadequate anti leakage technology.

6.2.4 Biofilm method

Unlike the activated sludge process, the biofilm process involves adding soft fillers to the treatment tank and using microorganisms that grow on the surface of the fillers to treat wastewater without the problem of sludge expansion. The biological contact oxidation tank and biological turntable are representative of this method and are used in beer wastewater treatment to reduce BOD5 in beer wastewater.

The biological contact oxidation tank is artificially aerated while microorganisms are firmly growing. This method can achieve high concentrations of biological solids and high organic loads, resulting in high treatment efficiency and a smaller footprint than the activated sludge method. This technology has been adopted in the wastewater treatment of domestic manufacturers such as Zibo Brewery, Qingdao Brewery, Bohai Brewery, and Xuzhou Brewery. After secondary biological contact oxidation and coagulation air flotation treatment, Qingdao Brewery achieved removal rates of CODcr and BOD5 in beer wastewater of over 80% and 90%, respectively. On this basis, Shandong Environmental Science Institute changed atmospheric aeration to pressurized aeration (P=0.25-0.30MPa), aiming to enhance oxygen mass transfer and effectively increase the dissolved oxygen concentration in wastewater to meet the needs of microbial and organic matter oxidation and decomposition in medium and high concentration wastewater. The results showed that when the volumetric load was ≤ 13.33 kg/m3. d and the COD residence time was 3-4 hours, the average removal rates of COD and BOD reached 93.52% and 99.03%, respectively. Due to the shortened stay time to 1/3 to 1/4 of the original, the operating costs are also lower. The biological turntable is an early method used to treat beer wastewater. It mainly consists of a disc, an oxidation tank, a rotating shaft, and a driving device. It relies on the rotation of the disc to achieve contact and oxygenation between the wastewater and the biofilm on the disc. This method operates stably and consumes less power, but low temperature has a significant impact on operation. When treating high concentration wastewater, it is necessary to increase the number of disc groups. This method is widely used in the United States, and is also used by Hangzhou Brewery, Shanghai Huaguang Brewery, and Zhejiang Cixi Brewery in China. According to reports, the removal rate of BOD5 in wastewater is over 80%.