CN115784543A - Sludge reduction device and sludge reduction method based on hydrodynamic cavitation coupled aerobic digestion - Google Patents

Abstract

The invention relates to a sludge reduction device and a sludge reduction method based on hydrodynamic cavitation coupled aerobic digestion. Placing the residual sludge in a reaction tank, starting a circulating cooling system, and keeping the temperature in the reaction tank at 25 +/-2 ℃; starting a water pump, pumping the residual sludge into the hydraulic cavitation device through a water inlet pipe by the water pump for cavitation and cracking, and adjusting the inlet pressure of the hydraulic cavitation device through a valve II; the residual sludge after the cavitation and disintegration flows back to the reaction tank along with the water outlet pipe, and the reciprocating cavitation cycle lasts for 200-240 min. And (3) closing the valve I, discharging all the residual sludge in the cavitation unit into the reaction tank, closing the valve II and the valve IV, starting the stirrer and the blower, adjusting the air flow adjusting valve, and continuously aerating and digesting for 10 days. The sludge reduction method has the advantages of simple operation, no byproduct generation, no secondary pollution, short treatment time and high treatment efficiency.

Description

A sludge reduction device and sludge reduction based on hydraulic cavitation coupling aerobic digestion method

technical field

The invention relates to the technical field of sludge treatment, in particular to a sludge reduction device and method based on hydraulic cavitation coupling aerobic digestion technology.

Background technique

As the main by-product produced in the sewage treatment process, excess sludge has the characteristics of high water content, bulky volume and complex composition. Considering the environment, economy, regulations, etc., it is very important to reduce the amount of excess sludge by cost-effective means. As the main technology to achieve sludge stabilization and sludge reduction, sludge digestion has the advantages of high stabilization degree, low investment and operation cost, convenient operation and management, odorless final product and low concentration of BOD ₅ in the supernatant.

In the process of aerobic digestion, microorganisms convert a large amount of protein, fat, carbohydrates and other macromolecular organic substances in the sludge into small molecular organic substances through decomposition. The transformation and decomposition of these organic substances are conducive to improving the dehydration performance of sludge and reducing sludge Risk of disease and reduces the release of pungent odors from sludge, resulting in a significant reduction in sludge volume. However, the structure of the remaining sludge is complex, and its extracellular polymers are difficult to be broken by conventional mechanical means, which leads to the inability of dissolved organic matter to be decomposed by microorganisms in the water phase, which eventually leads to long treatment time and excessive treatment efficiency in the aerobic digestion process. Inferior question.

Contents of the invention

Aiming at the problems of long aerobic digestion treatment time and low treatment efficiency of excess sludge at the present stage, the purpose of the present invention is to provide a simple structure, short treatment time, high treatment efficiency, no by-product generation, and no secondary pollution. The hydraulic cavitation coupled aerobic digestion technology sludge reduction device and sludge reduction method.

In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is: a sludge reduction device based on hydraulic cavitation coupling aerobic digestion, including a reaction tank, and a circulating cooling system is arranged outside the reaction tank, including a cavitation unit and Digestion unit; the cavitation unit includes a water inlet pipe, a water pump, a hydraulic cavitation device, an outlet pipe and a pressure regulating branch pipe. One end of the water inlet pipe is connected to the outlet of the reaction tank, and the other end is connected to the inlet of the hydraulic cavitation device after passing through the water pump. Valve Ⅰ, valve Ⅲ, pressure gauge and flow meter are installed on the top, one end of the outlet pipe is connected to the outlet of the hydraulic cavitation device, and the other end is connected to the inlet of the reaction tank. The other end is connected to the water inlet pipe between the water pump and valve III, and the pressure regulating branch pipe is provided with valve II; the digestion unit includes an agitator, a microporous aerator and a blower, and the agitator is installed in the reaction tank. The microporous aerator is installed at the bottom of the reaction tank, and the microporous aerator is connected with the blower through an air pipe, and an air volume regulating valve is arranged on the air pipe.

Preferably, the above-mentioned sludge reduction device based on hydraulic cavitation coupled with aerobic digestion has a pH meter, a DO meter and a sampling valve on the reaction tank.

Preferably, in the above-mentioned sludge reduction device based on hydraulic cavitation coupled with aerobic digestion, the hydraulic cavitation device is an orifice device.

A sludge reduction method based on hydrodynamic cavitation coupling aerobic digestion, using the above-mentioned sludge reduction device, comprising the following steps:

1) Hydraulic cavitation pretreatment process: put the remaining sludge in the reaction tank, start the circulating cooling system, and keep the temperature in the reaction tank at 25±2°C; start the water pump, and pump the remaining sludge into the hydraulic system through the water inlet pipe. Cavitation cracking is carried out in the cavitation device, and the inlet pressure of the hydraulic cavitation device is adjusted through the valve II; the remaining sludge after cavitation cracking is returned to the reaction tank along with the outlet pipe, and the reciprocating cycle is 200-240min.

2) Digestion process: close valve Ⅰ, discharge all remaining sludge in the cavitation unit to the reaction tank, close valves Ⅱ and Ⅳ, start the agitator and blower, adjust the air volume control valve, and continue aeration and digestion for 10 days.

Preferably, in the aforementioned sludge reduction method based on hydraulic cavitation coupled with aerobic digestion, the concentration of excess sludge added to the reaction tank is adjusted to 6000-7000 mg/L.

Preferably, in the above sludge reduction method based on hydraulic cavitation coupled with aerobic digestion, the inlet pressure of the hydraulic cavitation device is adjusted to 2.5±0.5 bar through the valve II.

Preferably, in the above sludge weight reduction method based on hydraulic cavitation coupled with aerobic digestion, in step 2) during the digestion process, the pH of the digestion system in the reaction tank is controlled at 7±0.1.

Preferably, in the above sludge weight reduction method based on hydrodynamic cavitation coupled with aerobic digestion, in step 2) during the digestion process, the DO in the digestion system is adjusted to maintain 2-3 mg/L through the gas volume regulating valve.

Preferably, in the above-mentioned sludge weight reduction method based on hydraulic cavitation coupled with aerobic digestion, in step 2) during the digestion process, the rotational speed of the agitator is set at 120-150 rpm.

Preferably, in the above sludge weight reduction method based on hydraulic cavitation coupled with aerobic digestion, in step 2) during the digestion process, keep the temperature in the reaction tank at 25±2°C.

The beneficial effects of the present invention are:

(1) The present invention overcomes the problems of long aerobic digestion treatment time and low treatment efficiency of excess sludge at the present stage, and provides a simple structure, no by-product generation, no secondary pollution, short treatment time and high treatment efficiency The sludge reduction device and method.

(2) The sludge reduction device of the present invention skillfully integrates the cavitation unit and the digestion unit into a whole, solves the problem of reciprocating transfer of excess sludge between different units, and improves the integrity of the sludge reduction device.

(3) The sludge reduction device of the present invention, the reaction tank is equipped with a circulating cooling device, and the excess heat generated by hydraulic cavitation is transferred to the outside of the system through the cooling liquid, so as to reduce the impact of high temperature on sludge cracking and enhance sludge reduction efficiency.

Description of drawings

Fig. 1 is a schematic structural view of the sludge reduction device of the present invention.

Fig. 2 is a schematic diagram of the structure of the orifice plate device in the sludge reduction device of the present invention.

Fig. 3 is the effect of hydraulic cavitation pretreatment on excess sludge SCOD and DD _SCOD in Example 2.

Fig. 4 is the effect of blank and hydraulic cavitation coupled aerobic digestion technology on sludge TCOD in Example 2.

Fig. 5 is the effect of blank and hydraulic cavitation coupled aerobic digestion technology on sludge SS and VSS in Example 2.

In the figure: 1-reaction tank, 2-water pump, 3-blower, 4-stirrer, 5-valve Ⅰ, 6-valve Ⅱ, 7-valve Ⅲ, 8-pressure gauge, 9-hydraulic cavitation device, 10- Valve IV, 11-sampling valve, 12-outlet pipe, 13-pressure regulating branch pipe, 14-flow meter, 15-water inlet pipe, 16-microporous aerator, 17-circulating cooling system, 18-DO meter, 19- Gas delivery pipe, 20-air volume regulating valve, 21-pH meter.

Detailed ways

Example 1 A sludge reduction device based on hydraulic cavitation coupled with aerobic digestion

As shown in Figure 1, a sludge reduction device based on hydraulic cavitation coupled with aerobic digestion includes a reaction tank 1, a cavitation unit and a digestion unit.

A circulating cooling system 17 is provided outside the reaction tank 1 to avoid overheating of the system due to too long operation time.

The cavitation unit includes a water inlet pipe 15 , a water pump 2 , a hydraulic cavitation device 9 , a water outlet pipe 12 and a pressure regulating branch pipe 13 . One end of the water inlet pipe 15 is connected to the outlet of the reaction tank 1, and the other end is connected to the inlet of the hydraulic cavitation device 9 after passing through the water pump 2. The water inlet pipe 15 is provided with a valve I5, a valve III7, a pressure gauge 8 and a flow meter 14, and one end of the water outlet pipe 12 It is connected to the outlet of the hydraulic cavitation device 9, and the other end is connected to the inlet of the reaction tank 1. The outlet pipe 12 is provided with a valve IV10. One end of the pressure regulating branch pipe 13 is connected to the reaction tank 1, and the other end is connected to the water inlet pipe 15 between the water pump 2 and the valve III7. The pressure regulating branch pipe 13 is provided with a valve II6.

The digestion unit includes an agitator 4 , a microporous aerator 16 and a blower 3 . The agitator 4 is installed in the reaction tank 1, and the microporous aerator 16 is installed at the bottom of the reaction tank 1. The microporous aerator 16 is connected with the blower 3 through an air pipe 19, and the air pipe 19 is provided with an air volume regulating valve 20.

Preferably, in this embodiment, the reaction tank 1 is provided with a pH meter 21 , a DO meter 18 and a sampling valve 11 .

As a preference, in this embodiment, the hydraulic cavitation device 9 uses an orifice device, as shown in Figure 2, the structure of the orifice device is: the main body plate 9-1 is provided with 10 through holes 9- 2. The hole diameter is 2mm, and the thickness of the main plate is 30-40mm.

Example 2 A sludge reduction method based on hydraulic cavitation coupled with aerobic digestion

Using the sludge reduction device of embodiment 1, the sludge reduction method based on hydraulic cavitation coupling aerobic digestion comprises the following steps:

1) Hydraulic cavitation pretreatment process: put excess sludge in reaction tank 1, adjust the concentration of excess sludge added in reaction tank 1 to 6000-7000 mg/L, start circulating cooling system 17, and keep the reaction tank 1 The temperature is 25±2°C; start the water pump 2, pump the remaining sludge into the hydraulic cavitation device 9 through the water inlet pipe 15 through the water pump 2 for cavitation cracking, and adjust the inlet pressure of the hydraulic cavitation device 9 through the valve Ⅱ6 to 2.5±0.5 bar; the remaining sludge after cavitation cracking is returned to the reaction tank 1 along with the water outlet pipe 12, and the reciprocating cycle is 200-240 minutes to complete the cavitation cracking.

2) Digestion process: close valve Ⅰ5, discharge all remaining sludge in the cavitation unit to reaction tank 1, close valve Ⅱ6 and valve Ⅳ10, start agitator 4 and blower 3, and set the speed of agitator to 120 ~150rpm, adjust the gas volume regulating valve 20 to maintain the DO of the digestive system in the reaction tank 1 at 2~3mg/L, and continue aeration for 10 days. During the overall digestion process, keep the temperature in the reaction tank 1 at 25±2° C., and maintain the pH in the reaction tank 1 at 7±0.1.

(1) The effect of hydrodynamic cavitation pretreatment on the dissolved chemical oxygen demand (SCOD) of sludge.

Method: The residual sludge in the secondary sedimentation tank of the sewage treatment plant was used as the substrate, and the sludge concentration was adjusted to 7000mg/L. Put the adjusted excess sludge in the reaction tank 1, start the circulating cooling system 17, and keep the temperature in the reaction tank 1 at 25±2°C; start the water pump 2, and pump the excess sludge into the hydraulic system through the water inlet pipe 15 through the water pump 2. Cavitation cracking is carried out in the cavitation device 9, and the valve II6 on the pressure regulating branch pipe 13 is adjusted so that the inlet pressure of the hydraulic cavitation device 9 is 2.5 ± 0.5 bar, and the remaining sludge after cavitation cracking flows back with the outlet pipe 12 In the reaction tank 1, the circulation reaction was carried out for 240 minutes, and the SCOD concentration of the sludge in the reaction tank 1 was measured at 0, 30, 60, 90, 120, 150, 180, 210, and 240 minutes respectively. The results are shown in Figure 3.

Sludge SCOD is used to characterize the chemical oxygen demand of sludge extracts. It can be seen from Figure 3 that with the increase of cavitation time, the SCOD value shows a clear upward trend, indicating that cavitation has a significant effect on sludge cracking.

(2) Effect of hydraulic cavitation pretreatment on sludge disintegration rate (DD _SCOD )

Method: The residual sludge in the secondary sedimentation tank of the sewage treatment plant was used as the substrate, and the sludge concentration was adjusted to 7000mg/L. Put the adjusted excess sludge in the reaction tank 1, start the circulating cooling system 17, and keep the temperature in the reaction tank 1 at 25±2°C; start the water pump 2, and pump the excess sludge into the hydraulic system through the water inlet pipe 15 through the water pump 2. Cavitation cracking is carried out in the cavitation device 9, and the valve II6 on the pressure regulating branch pipe 13 is adjusted so that the inlet pressure of the hydraulic cavitation device 9 is 2.5 ± 0.5 bar, and the remaining sludge after cavitation cracking flows back with the outlet pipe 12 In the reaction tank 1, the circulation reaction was carried out for 240 minutes, and the DD _SCOD of the sludge in the reaction tank 1 was measured at 0, 30, 60, 90, 120, 150, 180, 210 and 240 minutes respectively. The results are shown in Figure 3.

DD _SCOD is an important index to reflect the degree of sludge disintegration. As shown in Figure 3, the DD _SCOD values of the sludge supernatant were measured at 0, 30, 60, 90, 120, 150, 180, 210, and 240 min, respectively. It can be seen that with the increase of cavitation time, the DD _SCOD of the sludge showed an obvious upward trend. The increase rate of the DD _SCOD of the sludge was the fastest at 30-90 minutes, and the increase of the DD _SCOD of the sludge gradually became flat at 210 minutes. The DD _SCOD of the sludge reached 8.89% at 240 minutes. This shows that under the influence of mechanical effects, thermal effects and chemical effects caused by cavitation, the internal structure of sludge is broken, and the dissolved organic matter in sludge flocs is released, which eventually leads to the continuous increase of sludge SCOD and DD _SCOD .

(3) Effect of blank and hydraulic cavitation coupled aerobic digestion technology on total chemical oxygen demand (TCOD) of sludge.

Method: After the cavitation cracking is completed, close the valve Ⅰ5, discharge all the remaining sludge in the cavitation unit to the digestion reaction tank 1, close the valve Ⅱ6 and valve Ⅳ10, start the agitator 4, and set the speed at 120-150rpm , start the blower 3, adjust the gas volume control valve 20 to maintain the DO in the reaction tank 1 at 2-3mg/L, keep the temperature of the digestion system at 25±2°C, and use 1mol/L sodium hydroxide (NaOH) or 1mol/L Hydrochloric acid (HCl) maintains the pH of the digestive system at about 7, and continues aeration for 10 days. Record 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10d sludge TCOD degradation rate respectively, and compare with the blank group directly treated with aerobic digestion without cavitation treatment, the results are shown in the figure 4.

TCOD is mainly used to characterize the content of organic matter in sludge, and can indirectly reflect the change of biomass in sludge. Therefore, in the sludge reduction experiment, the substantial increase in the removal rate of TCOD can reflect that the process has a significant sludge reduction effect. volume effect. Figure 4 a) shows the changes of sludge SCOD and TCOD before and after hydraulic cavitation pretreatment. It can be seen that after 240 minutes of hydraulic cavitation treatment, sludge SCOD increased from 148.65 mg/L to 529.59 mg/L, and TCOD increased from The original 4383.25mg/L was reduced to 2082.81mg/L. The increase of the former is caused by the breakdown of sludge flocs, and the decrease of the latter can be explained by the following theory: when the sludge passes through the hydraulic cavitation device, a large number of cavitation bubbles are generated inside the fluid, and these cavitation bubbles collapse in the pressure recovery zone And produce extreme conditions such as hot spots, high-speed jets, and strong shear forces, which can cause a large number of water molecules (H ₂ O) in the sludge to break bonds and form hydroxyl radicals (·OH) and hydrogen radicals (· H) etc. These free radicals have a high oxidation potential and can oxidize the organic molecules in the sludge, resulting in a degradation reaction. It can be seen from b) in Figure 4 that after 10 consecutive days of aerobic digestion, the TCOD removal rate of the sludge after hydrodynamic cavitation pretreatment reached 52.36%, which was higher than the blank group's 47.99%. In addition, the total removal rate of sludge TCOD reached 78.2% by the degradation system of hydrodynamic cavitation coupled with aerobic digestion technology, which is in line with the aerobic digestion of organic matter in sludge stipulated in the "Pollutant Discharge Standards for Urban Sewage Treatment Plants" (GB18918-2002) Removal rate greater than 40% requirement.

(4) Effect of blank and hydraulic cavitation coupled aerobic digestion technology on sludge SS and VSS.

Method: After the cavitation cracking is completed, close the valve Ⅰ5, discharge all the remaining sludge in the cavitation unit to the digestion reaction tank 1, close the valve Ⅱ6 and valve Ⅳ10, start the agitator 4, and set the speed at 120-150rpm , start the blower 3, adjust the gas volume control valve 20 to maintain the DO in the reaction tank 1 at 2-3mg/L, keep the temperature of the digestion system at 25±2°C, and use 1mol/L sodium hydroxide (NaOH) or 1mol/L Hydrochloric acid (HCl) maintains the pH of the digestive system at about 7, and continues aeration for 10 days. Record 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10d sludge SS and VSS degradation rates respectively, and compare with the blank group directly aerobic digestion without cavitation treatment, the results Figure 5.

SS (sludge suspended solids concentration) and VSS (sludge volatile suspended solids concentration) are mainly used to characterize the concentration of activated sludge and the number of microorganisms in the sludge. Figure 5 a) shows the sludge before and after hydraulic cavitation pretreatment. The changes of SS and VSS, it can be seen that after 240min of hydraulic cavitation pretreatment, the sludge SS decreased to 4405mg/L; the sludge VSS decreased to 3090mg/L, this phenomenon is caused by the active free radicals and Shear stress is caused by the decomposition of sludge. It can be seen from b) in Figure 5 that after 10 consecutive days of aerobic digestion, the sludge SS and VSS removal rates after hydrodynamic cavitation pretreatment reached 61.5% and 67.2%, respectively, much higher than that of the blank group 15% and 42.5%. In addition, the overall removal rates of sludge SS and VSS reached 75.1% and 83.8% respectively by the hydrodynamic cavitation coupled aerobic digestion technology degradation system. This shows that the addition of hydraulic cavitation increases the upper limit of sludge reduction of aerobic digestion technology and overcomes the problem of low efficiency of aerobic digestion treatment. has a significant effect.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A sludge reduction device based on hydrodynamic cavitation coupled aerobic digestion comprises a reaction tank (1), wherein a circulating cooling system (17) is arranged outside the reaction tank (1), and is characterized by comprising a cavitation unit and a digestion unit; the cavitation unit comprises a water inlet pipe (15), a water pump (2), a hydraulic cavitation device (9), a water outlet pipe (12) and a pressure regulating branch pipe (13), one end of the water inlet pipe (15) is connected with an outlet of the reaction tank (1), the other end of the water inlet pipe is connected with an inlet of the hydraulic cavitation device (9) through the water pump (2), a valve I (5), a valve III (7), a pressure gauge (8) and a flow meter (14) are arranged on the water inlet pipe (15), one end of the water outlet pipe (12) is connected with the outlet of the hydraulic cavitation device (9), the other end of the water outlet pipe is connected with the inlet of the reaction tank (1), a valve IV (10) is arranged on the water outlet pipe (12), one end of the pressure regulating branch pipe (13) is connected with the reaction tank (1), the other end of the water outlet pipe is connected to the water inlet pipe (15) between the water pump (2) and the valve III (7), and a valve II (6) is arranged on the pressure regulating branch pipe (13); the digestion unit comprises a stirrer (4), a microporous aerator (16) and an air blower (3), wherein the stirrer (4) is installed in the reaction tank (1), the microporous aerator (16) is installed at the bottom of the reaction tank (1), the microporous aerator (16) is connected with the air blower (3) through an air pipe (19), and an air quantity regulating valve (20) is arranged on the air pipe (19).

2. The sludge reduction device based on hydrodynamic cavitation coupled aerobic digestion as claimed in claim 1, characterized in that the reaction tank (1) is provided with a pH meter (21), a DO meter (18) and a sampling valve (11).

3. The apparatus for sludge reduction based on hydrodynamic cavitation coupled with aerobic digestion according to claim 1, characterized in that the hydrodynamic cavitation apparatus (9) is an orifice plate apparatus.

4. A sludge reduction method based on hydrodynamic cavitation coupled aerobic digestion, which is characterized in that the sludge reduction device of any one of claims 1 to 3 is utilized, and comprises the following steps:

1) The hydrodynamic cavitation pretreatment process comprises the following steps: placing the residual sludge in a reaction tank (1), starting a circulating cooling system (17), and keeping the temperature in the reaction tank (1) at 25 +/-2 ℃; starting the water pump (2), pumping the residual sludge into the hydrodynamic cavitation device (9) through the water inlet pipe (15) by the water pump (2) for cavitation and breaking, and adjusting the inlet pressure of the hydrodynamic cavitation device (9) through the valve II (6); returning the residual sludge after cavitation and breaking to the reaction tank (1) along with the water outlet pipe (12), and performing reciprocating circulation for 200-240 min;

2) And (3) digestion process: and (3) closing the valve I (5), discharging all residual sludge in the cavitation unit into the reaction tank (1), closing the valve II (6) and the valve IV (10), starting the stirrer (4) and the blower (3), adjusting the air flow regulating valve (20), and continuously aerating and digesting for 10d.

5. The method for sludge reduction according to claim 4, wherein the concentration of the excess sludge added to the reaction tank (1) is adjusted to 6000 to 7000mg/L.

6. The method for sludge reduction according to claim 4, wherein the inlet pressure of the hydrodynamic cavitation device (9) is adjusted to 2.5 ± 0.5bar by means of the valve II (6).

7. The method for sludge reduction according to claim 4, wherein the pH of the digestion system in the reaction tank (1) is controlled to be 7 ± 0.1 during the digestion in step 2).

8. The method for sludge reduction according to claim 4, wherein the DO in the digestion system is adjusted to be maintained at 2-3 mg/L by the air volume adjusting valve (20) during the digestion process in the step 2).

9. The method for sludge reduction according to claim 4, wherein the rotation speed of the stirrer (4) is set to 120 to 150rpm during the digestion in step 2).

10. The method for sludge reduction according to claim 4, wherein the temperature in the reaction tank (1) is maintained at 25 ± 2 ℃ during the digestion in step 2).

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