CN102284245A - Method for treating waste gas by biotrickling filter, and special device thereof - Google Patents

Abstract

The invention discloses a method for treating waste gas with a biological trickling filter tower: the waste gas is passed through the bottom of the biological trickling filter tower, treated by the biological trickling filter tower, and the treated waste gas is discharged from the top, and the biological trickling filter tower is composed of The bottom of the tower with exhaust gas inlet, the tower body, and the top of the tower equipped with exhaust gas outlet are composed. The tower body is composed of several biological treatment units stacked from bottom to top, and the biological treatment units on adjacent layers are arranged There is a liquid interlayer, and the air vents for the adjacent layers are arranged on the liquid interlayer, and each layer of biological treatment units is independently equipped with a nutrient solution spray system and a temperature control device from top to bottom. Biological packing layer and nutrient solution receiving pool; the invention increases the processing load of the unit packing; improves the plugging problem of the packing layer, avoids the occurrence of channeling phenomenon, and has uniform and sufficient gas-liquid contact; packing replacement and backwashing are more convenient; the process Economical, suitable for the purification treatment of complex volatile organic mixed pollutants.

Description

A method for treating waste gas with a biological trickling filter tower and its special device

(1) Technical field

The invention relates to a method and a device for purifying waste gas in environmental engineering, in particular to a method for treating waste gas with a biological trickling filter tower and a special device thereof.

(2) Background technology

Many industrial production processes inevitably produce a large amount of waste gas. These waste gases are not suitable for recycling. They usually contain multi-component toxic and harmful organic and inorganic substances, which are harmful to human body and environment, and cause air pollution.

At present, there are many technologies used for waste gas control. The commonly used technologies mainly include combustion method, adsorption method, chemical absorption method and biological method. Compared with other traditional treatment methods, biological method has less investment and lower operating cost. , No secondary pollution and other advantages, especially in the treatment of gaseous pollutants with low concentration and good biodegradability, it is more economical. When dealing with low-concentration organic gases and odors, the one-time investment of the biological method is 1/3 of the combustion method, 1/8-1/5 of the adsorption method, and 1/3 of the chemical absorption method; the operating cost is that of the combustion method. 1/20, 1/10 of the adsorption method, and 1/15 of the chemical absorption method. Therefore, this method is becoming a high-tech that is rapidly promoted in the field of waste gas pollution control.

Biological treatment of waste gas usually uses immobilized microorganisms to filter waste gas, and its devices mainly use the form of filter towers. Engineering practice and research show that these filter towers have defects in five aspects: ①Because the existing carrier used for microorganism immobilization in the filter tower is organic or inorganic filler, the mass transfer effect is poor and it is easy to cause short circuit. Agitating the packing or replacing the packing, the treatment effect is poor and it is not conducive to the equipment production of the filter tower; ②The surface load and mass load are small, so the removal capacity and removal rate are also small; ③The biological load is small; ④Resistance to high concentration and poisonous The performance of pollutants is poor; ⑤The structural design of the filter tower makes the empty tower residence time shorter, which affects the removal capacity and removal rate. Practice has shown that the main problems in the use of biological trickling filter towers are uneven water distribution, gas distribution and pH control in the tower, and the accumulation of dead microorganisms causes packing blockage.

In view of the above problems, the biological trickling filter tower of the present invention treats industrial waste gas, respectively controls the pH value of the nutrient solution in each packing layer and the spraying amount of the nutrient solution in each packing layer, and the spraying amount of the nutrient solution in each tower body unit can be according to The pollution treatment load can be flexibly controlled, and the pH value of the nutrient solution in each tower unit can be controlled hierarchically according to the type of pollutant treatment and the sequence of removal, which is of great significance to the engineering practice of biological purification.

(3) Contents of the invention

The object of the present invention is to provide a method and a special device for treating waste gas with a biological trickling filter tower. The treatment method and device adopt layered spraying of nutrient solution, layered control of pH value, high efficiency and economy.

The technical scheme adopted in the present invention is:

A method for treating waste gas with a biological trickling filter tower, the method is to pass the waste gas from the bottom of the biological trickling filter tower, and after being treated by the biological trickling filter tower, the treated waste gas is discharged from the top. The biological trickling filter tower It consists of the bottom of the tower with exhaust gas inlet, the tower body, and the top of the tower with exhaust gas outlet. The tower body is composed of several biological treatment units stacked from bottom to top. There is a liquid interlayer, and the air vents for the adjacent layers are arranged on the liquid interlayer. Each layer of biological treatment units is independently equipped with a nutrient solution spray system and a temperature control device from top to bottom. The biological filler layer and the nutrient solution receiving tank, the biological filler layer is sprayed with activated sludge and nutrient solution, and the nutrient solution spray system is installed on the nutrient solution receiving tank by a sprayer installed on the top of the biological treatment unit The nutrient solution output pipe at the bottom of the pool is connected to the nutrient solution storage tank outside the biological drop tower, electromagnetic metering pump, nutrient solution input pipe, sprinkler, pH automatic control system, peristaltic pump, and sodium hydroxide liquid storage tank; The nutrient solution storage tank is connected to the nutrient solution output pipe, the nutrient solution storage tank, the electromagnetic metering pump, the nutrient solution input pipe, and the sprinkler are connected in sequence, and the pH automatic control system is connected with the nutrient solution through the peristaltic pump respectively. The nutrient solution storage tank is connected with the sodium hydroxide storage tank, and the pH automatic control system is also provided with a pH meter probe connected with the nutrient solution storage tank; the pH of the nutrient solution of each of the biological treatment units is different, and each of the described The pH value set by the pH automatic control system of the biological treatment unit is different.

The tower body is composed of three biological treatment units stacked and installed from bottom to top, and the pH values set by the pH automatic control system from bottom to top are 2-3, 4-5, 6-7 respectively.

The filler in the biological filler layer is polyurethane pellets; the filler has large porosity, high strength, and is easy to form a film. The size of the filler is 13-16mm, and the bulk density and true density are 138.9kg·m ^-3 and 1588.2 kg·m ^-3 .

The ratio of the thickness of the biological filler layer to the tower diameter is 0.8-2.0:1, most preferably 1.4:1.

The temperature of the biological filler layer equipped with a temperature control device is controlled at 30°C.

A special device for the waste gas treatment method of the present invention, the device is a biological trickling filter tower, the biological trickling filter tower is composed of a tower bottom, a tower body, and a tower top, and the waste gas filter is provided at the bottom of the tower Inlet, the top of the tower is equipped with a tail gas outlet; the tower body is composed of several biological treatment units stacked from bottom to top, and a liquid interlayer is arranged between the biological treatment units of adjacent layers. The liquid compartment is provided with air vents for adjacent layers to communicate with each other, and each layer of biological treatment units is independently equipped with a nutrient solution spray system from top to bottom, and equipped with a temperature control device that can carry activated sludge and nutrient solution. The biological filler layer and the nutrient solution receiving tank, the nutrient solution spraying system consists of a sprinkler installed on the top of the biological treatment unit, a nutrient solution output pipe installed at the bottom of the nutrient solution receiving tank, and a nutrient solution installed outside the biological drop tower Liquid storage tank, electromagnetic metering pump, nutrient solution input pipe, sprinkler, pH automatic control system, peristaltic pump, sodium hydroxide liquid storage tank connected; the nutrient solution storage tank undertakes the nutrient solution output pipe, the The nutrient solution storage tank, the electromagnetic metering pump, the nutrient solution input pipe, and the sprinkler are connected in sequence, and the pH automatic control system is connected with the nutrient solution storage tank and the sodium hydroxide storage tank respectively through a peristaltic pump, and the pH is automatically controlled. The system is also provided with a pH meter probe connected to the nutrient solution storage tank, and the tail gas outlet is provided with a through pipe connected to the sodium hydroxide tail gas absorption tank.

In the special device for waste gas treatment method according to the present invention, the vent is a tubular protrusion with a top cap arranged on the liquid compartment, and the top of the tubular protrusion is connected with a top cap whose bottom surface is larger than the tubular protrusion, The top cap is connected to the tubular protrusion through a barrier with a gap, and the gap is located above the preset liquid level of the nutrient solution receiving pool.

Further, in the special device, the top cap is conical.

Further, there are several tubular protrusions with a top cap, which are uniformly arranged radially on the liquid compartment.

Further, in the special device, the tower body is composed of three biological treatment units stacked and installed from bottom to top.

The special device for the method of treating waste gas with a biological trickling filter tower according to the present invention is composed of multi-layer biological treatment units as a whole, and each biological treatment unit can independently control the pH value and the spraying amount of nutrient solution, and is suitable for use in biodegradable It is especially suitable for multi-component mixed exhaust gas.

Compared with the prior art, the beneficial effects of the present invention are mainly reflected in: (1) The present invention uses a biological trickling filter tower to treat waste gas, and the special device for treating waste gas consists of several biological treatment units stacked and installed from bottom to top , the strength of the nutrient solution in each biological treatment unit can be individually controlled according to the processing load, which increases the processing load of the unit packing; improves the plugging problem of the packing layer, avoids the occurrence of channel flow, and the gas-liquid contact is uniform and sufficient; (2) adopts Separate biological treatment unit structure makes packing replacement and backwashing more convenient; (3) the use of a separate pH automatic control system can obtain highly efficient degrading bacteria under different pH conditions, and the amount of alkali solution required to stabilize the pH of the nutrient solution is reduced. It is more economical and can adapt to the purification treatment of complex volatile organic mixed pollutants.

(4) Description of drawings

Figure 1 The exhaust gas purification system of the biological trickling filter tower: 1. Waste gas inlet, 2. Tower body, 3. Exhaust port, 4. Packing sampling port, 5. Gas sampling port, 6. Electromagnetic metering pump, 7. pH meter probe, 8. Nutrient solution receiving pool, 9. pH automatic control system, 10. Peristaltic pump, 11. Sodium hydroxide liquid storage tank, 12. Sodium hydroxide tail gas absorption tank, 13. Tail gas discharge port 14. Liquid compartment, 15. Baffle structure, 16, biological filler layer, 17, sprinkler, 18, nutrient solution input pipe, 19, nutrient solution output pipe, 20, through pipe, 21, biological treatment unit;

Fig. 2 baffle structure diagram: 22, tubular protrusion, 23, air vent, 24, top cap, 25, fence;

Fig. 3 Investigation of the performance of hydrogen sulfide purification by the exhaust gas purification system of the biological trickling filter;

Fig. 4 The change of the removal load of each layer when the exhaust gas purification system of the biological trickling filter purifies hydrogen sulfide for a long time;

Fig. 5 The performance investigation of purifying dimethyl sulfide by the exhaust gas purification system of the biological trickling filter;

Fig. 6 Performance investigation of purifying tetrahydrofuran by the exhaust gas purification system of the biological trickling filter;

(5) Specific implementation methods

The present invention is further described below in conjunction with specific embodiment, but protection scope of the present invention is not limited thereto:

Example 1

The waste gas to be treated is simulated with the mixed waste gas containing hydrogen sulfide, methyl sulfide, and tetrahydrofuran, and the waste gas is treated with the biological trickling filter tower according to the present invention. The tower body 2 of the biological trickling filter tower consists of a tower bottom, a tower body, The tower top is composed of a waste gas inlet 1 at the bottom of the tower, and an exhaust gas outlet 3 is installed at the top of the tower; the tower body is composed of a plurality of biological treatment units 21 stacked from bottom to top. A liquid interlayer 14 is arranged between the biological treatment units of adjacent layers, and a vent 23 for adjacent layers to communicate with each other is arranged on the liquid interlayer, and the vent is arranged on the liquid interlayer with a The tubular protrusion 22 of the conical top cap, the top of the tubular protrusion is connected with the conical top cap 24 whose bottom surface is larger than the tubular protrusion, and the top cap and the tubular protrusion are connected by a barrier 25 with a gap, the gap Located above the preset liquid level of the nutrient solution receiving pool, there are 15 tubular protrusions with top caps, which are evenly arranged on the liquid compartment. Each layer of biological treatment unit is independently provided with a nutrient solution spray system from top to bottom, a biological filler layer 16 that can carry activated sludge and nutrient solution with a temperature control device, and a nutrient solution receiving pool 8. The liquid spray system consists of a sprinkler 17 installed on the top of the biological treatment unit, a nutrient solution output pipe 19 installed at the bottom of the nutrient solution receiving tank, an electromagnetic metering pump 6 outside the biological drop tower, a nutrient solution input pipe 18, and a pH automatic The control system 9, the peristaltic pump 10, and the sodium hydroxide liquid storage tank 11 are connected to form; the nutrient solution receiving pool 8 is connected to the nutrient solution output pipe 19, and the nutrient solution receiving pool 8, the electromagnetic metering pump 6, Nutrient solution input pipe 18 and sprinkler 17 are connected successively, and described pH automatic control system 9 is respectively connected with nutrient solution receiving pool 8 and sodium hydroxide liquid storage tank 11 by peristaltic pump 10, and pH automatic control system 9 is also provided with The pH meter probe 7 that is connected with the nutrient solution receiving pool 8, the tail gas exhaust port 3 is provided with the through pipe 20 with the sodium hydroxide tail gas absorption tank 12, and the sodium hydroxide tail gas absorption tank 12 is provided with the tail gas discharge port 13 , as shown in Figure 1 and Figure 2.

When the biotrickling filter tower system is started, the filler is soaked for 24 hours before being loaded into the tower, and the gas-liquid circulation is carried out on it to obtain the biological filler. The biological trickling filter tower is composed of upper, middle and lower biological treatment units. The inner diameter of the tower is 140mm. The thickness of the biological filler layer in each biological treatment unit is 200mm. For cross-flow contact, the nutrient solution spray volume is controlled the same, that is, the spray volume is 100mL·min ^-1 , and the pH of the upper, middle, and lower biological treatment units is controlled to 6.5, 4.5, and 2.5 respectively; the biological filler of the upper biological treatment unit The dominant microorganisms in the layer are bacilli, the dominant microorganisms in the middle layer are bacilli and filamentous bacteria, and the dominant microorganisms in the lower layer are filamentous bacteria; the air velocity in the empty bed is 0.02～0.004m ³ ·s ^-1 Under the conditions of 14-28s and nutrient solution temperature of 30°C, the waste gas is passed into the biological trickling filter tower from the waste gas inlet, and the treated clean gas is discharged from the tail gas discharge port.

The change of the hydrogen sulfide removal rate of the biological trickling filter tower is shown in Figure 3. In the initial stage of membrane-hanging start-up (imported hydrogen sulfide concentration is maintained at 50mg·m ^-3 ), the biological trickling filter has no significant purification effect on hydrogen sulfide. On the 5th day, the removal rate of hydrogen sulfide gradually increased, and the removal rate reached 92.3% on the 8th day. Since then, despite the increase in the concentration of imported hydrogen sulfide, the biotrickling filter system can still maintain a high purification performance. On the 14th day, when the concentration of hydrogen sulfide was 94.3mg·m ^-3 and the residence time (EBRT) was 28s, the removal rate of hydrogen sulfide by the biological trickling filter reached 100%. This shows that more hydrogen sulfide-degrading bacteria have been attached to the filler, and the film-hanging start-up of the biological trickling filter system has been basically completed. Since then, although the hydrogen sulfide concentration was gradually increased to 250mg·m ^-3 and the EBRT was shortened to 17s, the removal rate remained stable at 100%.

The change of the removal rate of dimethyl sulfide by the biological trickling filter is shown in Figure 5. At the initial stage of film formation (the concentration of imported dimethyl sulfide is maintained at 10 mg·m ^-3 ), the biological trickling filter has no significant purification of dimethyl sulfide Effect, on the 6th day, the removal rate of methyl sulfide gradually increased, and the removal rate reached 66.7% on the 8th day. Since then, the concentration of imported methyl sulfide has been gradually increased, and the removal rate of the biological trickling filter has also gradually increased. On the 17th day, when the concentration of dimethyl sulfide was 25.9mg·m ^-3 and the EBRT was 28s, the removal rate of dimethyl sulfide in the biological trickling filter reached 100%. This shows that there are more methyl sulfide degrading bacteria attached to the filler, and the start-up of the biotrickling filter tower has been basically completed. After that, the concentration of dimethyl sulfide was gradually increased to 50mg·m ^-3 and the EBRT was shortened to 17s. Although the removal rate decreased, the removal rate was basically stable at 90%.

The change of the removal rate of THF by the biological trickling filter is shown in Figure 6. In the initial stage of film formation (the concentration of imported THF was maintained at about 10 mg·m ^-3 ), the removal rate did not change significantly. The removal rate of the bio-trickling filter increased significantly from the 7th day, and reached 100% on the 11th day, which indicated that the number of THF-degrading bacteria in the filler increased and the biofilm gradually formed. In order to determine whether the biofilm growth is mature, the concentration at the inlet of the biotrickling filter was increased to 20mg·m ^-3 on the 13th day, and the removal rate gradually increased and stabilized at about 80%; when the concentration was increased to 50mg·m ^-3 At about ³ , the removal rate has been maintained at about 81% (removal load remains unchanged), which shows that the start-up of the biotrickling filter is basically completed.

Example 2

The structure and experimental operation of the biological trickling filter tower are the same as those in Example 1. After the film coating in the reactor is completed, the hydrogen sulfide concentration at the inlet is 250-300 mg·m ^-3 , and the EBRT is 14s. The results of hydrogen sulfide gas purification are shown in Figure 3. It can be seen that when the hydrogen sulfide concentration is 250mg·m ^-3 and the EBRT is 14s, the hydrogen sulfide removal rate is always maintained at 100%; when the hydrogen sulfide concentration is suddenly increased to 300mg·m When ^-3 , the hydrogen sulfide removal rate is stable above 99.9%, indicating that the biological trickling filter system has a good and stable removal effect on hydrogen sulfide.

It can be seen from Figure 4 that when the EBRT is 14s, the hydrogen sulfide entering the biotrickling filter system is mainly removed in the lower and middle packing layers, and the removal load of the upper packing layer is small. The contribution of the upper packing layer to the hydrogen sulfide removal load gradually increased; with the continuous operation of the reactor, the removal load of the lower and middle packing layers gradually increased, and the two packing layers accounted for more than 90% of the hydrogen sulfide purification contribution. Under the condition of equal inlet concentration, EBRT directly determines the intake load of hydrogen sulfide. To sum up, the contribution of each packing layer to the removal of hydrogen sulfide varies with the fluctuation of the intake load.

After the film coating in the reactor was completed, the operation of the biotrickling filter system was investigated under the condition that the concentration of dimethyl sulfide at the inlet was increased sequentially from 10 to 100 mg·m ^-3 and the EBRT was 14s. The results are shown in Figure 5. When the inlet concentration is about 60mg·m ^-3 and the EBRT is 14s, the removal rate of dimethyl sulfide is always maintained at 90%; when the concentration is suddenly increased to above 70mg·m ^-3 , the removal rate of dimethyl sulfide is stable above 90% . For the removal of dimethyl sulfide, the contribution of the middle packing layer is relatively large, which can reach about 60%, and the contribution of the lower packing layer and the upper packing layer is equal. As the intake load changes, the contribution of each layer to the removal rate also changes accordingly.

After the completion of film coating in the reactor, the change of THF removal load and removal rate with the inlet concentration in the biotrickling filter system was investigated. The inlet concentration of THF increased sequentially from 10 to 80 mg·m ^-3 , as shown in Figure 6. When the inlet concentration is low (below 40mg·m ^-3 ), the removal efficiency of THF in the biotrickling filter system can reach 95%, and the removal load increases with the increase of the inlet concentration. After the inlet concentration was further increased to 50 mg·m ^-3 , the removal rate gradually decreased, and the removal capacity of the biotrickling filter tower system for THF no longer increased, but remained at a fixed value (about 60%). At this time, the biotrickling filter The degradation performance of the tower system reaches a maximum. For the removal of THF, the removal effect of the lower packing layer is not ideal, THF is mainly removed in the upper packing layer, and the middle packing layer also shows a certain removal effect (10-20%).

When the bio-trickling filter system is started, the microorganisms are in the film-hanging stage, and the overall pressure drop in the bio-trickling filter tower is very small. After the completion of the film-hanging process and entering a stable operating state, the total pressure drop gradually increases and then tends to be stable. Due to the different contributions of each layer of packing layer to the exhaust gas removal rate, the growth of microorganisms is also different, resulting in different pressure drops in each layer. It can be seen that the pressure drop of the lower packing layer is the largest, the middle packing layer is the smallest, and the upper packing layer is the smallest.

Claims (10)

1. A method for treating waste gas with a biological trickling filter, characterized in that the method is that the waste gas is passed into from the bottom of the biological trickling filter, and through the treatment of the biological trickling filter, the treated waste gas is discharged from the top. The biological trickling filter tower consists of a tower bottom with a waste gas inlet, a tower body, and a tower top with an exhaust gas outlet. The tower body is composed of several biological treatment units stacked from bottom to top. A liquid interlayer is arranged between the biological treatment units, and the air vents for adjacent layers are arranged on the liquid interlayer, and each layer of biological treatment units is independently provided with a nutrient solution spray system from top to bottom, A biological filler layer and a nutrient solution receiving pool provided with a temperature control device, activated sludge and nutrient solution are sprayed on the biological filler layer, and the nutrient solution spray system consists of a sprinkler installed on the top of the biological treatment unit, The nutrient solution output pipe installed at the bottom of the nutrient solution receiving tank, the nutrient solution storage tank located outside the biological drop tower, the electromagnetic metering pump, the nutrient solution input pipe, the pH automatic control system, the peristaltic pump, and the sodium hydroxide liquid storage tank are connected. The nutrient solution storage tank is connected to the nutrient solution output pipe, the nutrient solution storage tank, the electromagnetic metering pump, the nutrient solution input pipe, and the sprinkler are connected successively, and the pH automatic control system is connected by a peristaltic pump Connect with the nutrient solution storage tank and the sodium hydroxide storage tank respectively, the pH automatic control system is also provided with the pH meter probe that is connected with the nutrient solution storage tank; The pH of the nutrient solution of each described biological treatment unit is different, the described The pH values set by the pH automatic control system of each biological treatment unit are different. 2. The method according to claim 1, characterized in that the tower body is composed of three biological treatment units stacked from bottom to top, and the pH value set by the pH automatic control system from bottom to top They are 2~3, 4~5, 6~7 respectively. 3. The method according to claim 1, characterized in that the filler in the biological filler layer is polyurethane pellets; the diameter of the filler is 13-16mm, and the bulk density and true density are respectively 138.9kg·m ^-3 and 1588.2 kg·m ^-3 . 4. The method according to claim 1, characterized in that the ratio of the thickness of the biological filler layer to the tower diameter is 0.8 to 2.0:1. 5. The method according to claim 1, wherein the temperature of the biological filler layer provided with a temperature control device is controlled at 30°C. 6. A special device for waste gas treatment method as claimed in claim 1, characterized in that said device is a biological trickling filter tower, and said biological trickling filter tower is composed of a tower bottom, a tower body and a tower top, and said The bottom of the tower is provided with an exhaust gas inlet, and the top of the tower is equipped with an exhaust gas outlet; the tower body is composed of several biological treatment units stacked from bottom to top, and the biological treatment units of adjacent layers are provided with Liquid interlayer, the liquid interlayer is provided with air vents for adjacent layers to communicate with each other, and each layer of biological treatment units is independently equipped with a nutrient solution spray system from top to bottom, and a temperature control device that can The biological packing layer and the nutrient solution receiving tank carrying activated sludge and nutrient solution, the nutrient solution spraying system is composed of a sprinkler installed on the top of the biological treatment unit, and a nutrient solution output pipe installed at the bottom of the nutrient solution receiving tank. The nutrient solution storage tank, electromagnetic metering pump, nutrient solution input pipe, pH automatic control system, peristaltic pump, and sodium hydroxide storage tank connected outside the biological drop tower are composed; the nutrient solution storage tank undertakes the described nutrient solution The output pipe, the nutrient solution storage tank, the electromagnetic metering pump, the nutrient solution input pipe, and the sprayer are connected successively, and the described pH automatic control system is respectively connected with the nutrient solution storage tank and the sodium hydroxide storage tank through a peristaltic pump , the pH automatic control system is also provided with a pH meter probe connected with the nutrient solution storage tank, and the exhaust gas outlet is provided with a through pipe connected with the sodium hydroxide tail gas absorption tank. 7. The special device according to claim 6, characterized in that the vent is a tubular protrusion with a top cap arranged on the liquid barrier, and the top of the tubular protrusion is connected with a bottom surface larger than the tubular protrusion. A top cap, the top cap is connected to the tubular protrusion through a barrier with a gap, and the gap is located above the preset liquid level of the nutrient solution receiving pool. 8. The special device according to claim 7, characterized in that said top cap is conical. 9. The special device according to claim 7, characterized in that there are several tubular protrusions with top caps, which are evenly arranged on the liquid barrier. 10. The special device according to claim 6, characterized in that the tower body is composed of three biological treatment units stacked and installed from bottom to top.

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