Electric field reinforced sludge dewatering method

Abstract

The invention discloses an electric field reinforced sludge dewatering method, which comprises the following steps: biological enzyme pretreatment, gradient electric field dewatering, electrode self-cleaning, electric field self-adaptive adjustment, mud cake collection and water resource recovery. Through the multistage synergistic effect of acidification pretreatment, composite biological enzymolysis and gradient electric field dehydration, the sludge floc structure is effectively cracked, extracellular polymeric substances are degraded, bound water is released, the dehydration efficiency is remarkably improved, a three-step gradient pulsed electric field is adopted, progressive increase voltage is applied in stages, energy consumption is optimized, efficient migration of water is promoted, and the dehydration efficiency is improved. The rotating electrode is combined with ultrasonic and reverse pulse technologies, electrode passivation is prevented, stable operation of the system is kept, active magnesium oxide or magnesium hydroxide is added to construct an alkaline environment, ultraviolet irradiation and ozone photocatalysis are assisted, generation of toxic by-products is effectively inhibited, and secondary pollution is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sludge treatment, in particular to a method for sludge dewatering by electric field enhancement. BACKGROUND

[0002] Sludge dewatering is a key link in the process of wastewater treatment, and its dewatering effect directly affects the cost and environmental impact of subsequent incineration and landfill treatment. The traditional dewatering methods of mechanical pressure filtration and centrifugal dewatering have limited efficiency, and the moisture content of the treated sludge is usually between 70%-80%, which is difficult to meet the increasingly stringent environmental protection requirements and the demand for resource utilization.

[0003] In recent years, electric field enhanced dewatering technology has attracted attention because it can effectively destroy the structure of extracellular polymeric substances in sludge and promote water release. However, the existing electric field dewatering technology still has many problems:

[0004] Low dewatering efficiency: single electric field treatment has poor permeability for dense sludge, and the water migration rate is slow, resulting in long dewatering cycle and high energy consumption;

[0005] Easy electrode passivation and pollution: under the action of electric field for a long time, the electrode surface is easy to form an oxide layer or be covered with organic / inorganic matter, resulting in a decrease in electrode activity and a decrease in dewatering efficiency;

[0006] Risk of secondary pollution: for sludge containing chloride ions, electrochemical reactions may occur under the action of electric field, producing toxic by-products such as halogenated organic compounds or free chlorine, causing secondary pollution;

[0007] Lack of adaptive control: existing systems are mostly operated with fixed parameters, and cannot adjust the operation strategy according to the real-time changes of sludge resistance, making it difficult to achieve optimal dewatering effect;

[0008] To overcome the above problems, chemical conditioning or physical pretreatment is often combined. However, chemical conditioning may introduce new pollutants, and single biological enzyme treatment has limited ability to break down sludge structure and is easily affected by environmental conditions. Therefore, we propose a method for sludge dewatering by electric field enhancement. SUMMARY

[0009] The purpose of the present application is to provide a method for sludge dewatering by electric field enhancement to solve the problems in the background art.

[0010] To achieve the above purpose, the present application provides the following technical solution: a method for sludge dewatering by electric field enhancement, which comprises the following steps:

[0011] Step one: biological enzyme pretreatment: the sludge to be treated is homogenized, and a composite biological enzyme preparation is added to the homogenized sludge, the biological enzyme preparation is stirred and mixed, the stirring and mixing temperature is 35-40℃, the stirring and mixing pH value is 6.5-7.5, and the stirring and mixing time is 20-30min;

[0012] Step two: gradient electric field dewatering: the sludge after step one pretreatment is sent to a rotating electrode dewatering device, and then a three-step gradient electric field is applied for gradient dewatering treatment, the three-step gradient electric field is applied with pulse frequencies of 30-50Hz, 50-80Hz and 80-150Hz respectively, and the gradient electric field dewatering process treatment temperature is 40-50℃;

[0013] Step three: electrode self-cleaning and electric field self-adaptive adjustment: the electrode rotates at a speed of 5-10rpm / min during the gradient electric field dewatering of step two, and an ultrasonic generator is additionally added, the ultrasonic generator is started to work for 5-10s every 30min;

[0014] Step four: sludge cake collection and water resource recycling: the sludge after electrode treatment is dewatered by a filter press, the dewatering treatment is carried out until the moisture content of the sludge cake is less than 55%, and the water after the filter press filtration is adsorbed by activated carbon and then flows back to the gradient electric field electrode dewatering device in step two.

[0015] The existing electric field dewatering has low dewatering efficiency: single electric field treatment has poor permeability for dense sludge and slow water migration rate, resulting in long dewatering period and high energy consumption; the electrode is easily passivated and contaminated: under the action of electric field for a long time, an oxidation layer is easily formed on the surface of the electrode or covered by organic / inorganic matter, resulting in decreased electrode activity and dewatering efficiency; secondary pollution risk: for sludge containing chloride ions, electrochemical reaction may occur under the action of electric field, producing toxic byproducts such as halogenated organic matter or free chlorine, causing secondary pollution; lack of adaptive control: the existing system is mostly operated with fixed parameters, which cannot adjust the operation strategy according to the real-time changes of sludge resistance, etc., and it is difficult to achieve optimal dewatering effect, the present application significantly improves the dewatering efficiency and system stability through multi-link cooperation. First, the composite biological enzyme is used to pretreat the sludge under suitable temperature and pH conditions, effectively degrading extracellular polymeric substances, destroying the sludge floc structure and releasing bound water, creating favorable conditions for subsequent dewatering, secondly, a three-step gradient pulse electric field is introduced, the electric field force is applied in stages, promoting directional water migration, avoiding energy waste and improving dewatering kinetic efficiency, at the same time, the electrode rotation combined with periodic ultrasonic waves can prevent sludge deposition and maintain electrode activity. The sludge cake after dewatering has a moisture content of less than 55% after filter pressing, realizing deep dewatering; the filtrate is adsorbed by activated carbon and then reused, realizing water resource recycling and reducing emissions.

[0016] Further description of the above technical solutions:

[0017] The biological enzyme preparation added in the step one is composed of cellulase, protease and lipase, the mass fraction of the cellulase, protease and lipase is 2:1:1, the added amount of the biological enzyme preparation is 0.1%-0.3% of the weight of the sludge, and the temperature is raised to above 60℃ after the homogenization and stirring treatment of the biological enzyme preparation.

[0018] As a further description of the above technical solution:

[0019] In the three-step gradient electric field in the step two, the first step gradient electric field applies a voltage of 80-120V, and the treatment time is 40-60min; the second step gradient electric field applies a voltage of 150-220V, and the treatment time is 30-50min; and the third step gradient electric field applies a voltage of 200-250V, and the treatment time is 30-50min.

[0020] As a further description of the above technical solution:

[0021] The sludge resistance detection sensor in the step three electrode self-cleaning and electric field self-adaptive adjustment is used to detect the change of sludge resistance, and when the change rate of sludge resistance exceeds 15% / min, the pulse frequency of the ultrasonic generator is adjusted to 80-150Hz.

[0022] As a further description of the above technical solution:

[0023] The rotating electrode dewatering device includes a cylindrical anode and a cylindrical cathode, the cylindrical anode is arranged inside the cylindrical cathode, the cylindrical anode adopts an iridium dioxide coated porous electrode, the cylindrical cathode is made of stainless steel mesh, and the cylindrical anode and the cylindrical cathode are coated with a titanium dioxide photocatalytic layer outside.

[0024] As a further description of the above technical solution:

[0025] The gradient electric field dewatering process in the step two applies ultraviolet light irradiation at the same time, the wavelength of the ultraviolet light is 254-365nm, and the light intensity is 10-50mW / cm².

[0026] As a further description of the above technical solution:

[0027] Before the composite biological enzyme preparation is added in the step one, the sludge is mixed and treated by sulfuric acid to adjust the pH value of the sludge to 4.5-5.5, and the pH value of the sludge is adjusted to 4.5-5.5 for 10-15min.

[0028] As a further description of the above technical solution:

[0029] In the step two gradient electric field dewatering, active magnesium oxide or magnesium hydroxide is added to the sludge to be treated, so that the sludge generates an alkaline environment with adsorption and neutralization in situ during the gradient electric field treatment.

[0030] As a further description of the above technical solution:

[0031] In the step three electrode self-cleaning and electric field self-adaptive adjustment, after the gradient electric field dewatering treatment is continuously operated for 2-4 hours, a reverse pulse current is applied to the cylindrical anode and the cylindrical cathode, the voltage of the reverse pulse current is 50%-80% of the original dewatering voltage, the pulse frequency is 20-40 Hz, and the reverse pulse duration is 1-3 minutes.

[0032] As a further description of the above technical solution:

[0033] In the step two gradient electric field dewatering, ozone gas is introduced into the cylindrical cathode while the gradient electric field is applied, the ozone gas is introduced at a frequency of 1-2 times per dewatering cycle, the ozone introduction time is 30-60 seconds, and the ozone gas introduced has an ozone concentration of 10-50 mg / L.

[0034] Compared with the prior art, the present application has the following beneficial effects:

[0035] 1、The present application can systematically break down the sludge structure through the multi-stage synergistic effect of acidification pretreatment, biological enzymolysis, gradient electric field and photocatalytic oxidation, and greatly improve the dewatering efficiency; the acidification step is introduced before biological enzyme treatment, which can preliminarily dissolve metal ions and colloids, change the sludge floc structure, and create favorable conditions for subsequent enzymolysis, and the composite biological enzyme preparation used can efficiently degrade organic components in extracellular polymeric substances and release bound water, and in the gradient electric field dewatering stage, three-step pulse electric field and increasing voltage are used to apply electric field force of different intensities in stages, which effectively drives water migration and avoids energy waste and local overheating caused by high initial voltage, at the same time, ultraviolet light can excite the titanium dioxide photocatalytic layer on the electrode surface to generate strong oxidizing free radicals, further destroying the EPS structure, and the synergistic effect of the above series of physical, chemical and biological processes fundamentally improves the sludge dewatering performance, and finally the filter pressing can obtain a mud cake with a water content of less than 55%;

[0036] 2. Secondly, the rotating electrode is arranged to cooperate with the periodically started ultrasonic generator to prevent the sludge from being cemented on the surface of the electrode through mechanical disturbance, and the resistance change is monitored in real time through the sludge resistance detection sensor, the ultrasonic frequency is automatically adjusted, intelligent response is realized, and the electrode activity is restored through the reverse electrochemical reaction; at the same time, ozone is periodically introduced into the cathode, which can oxidize and decompose the organic pollutants on the surface of the photocatalytic layer to prevent the inactivation, thereby significantly prolonging the service life of the electrode to a certain extent and reducing the downtime maintenance time.

[0037] 3. Finally, active magnesium oxide or magnesium hydroxide is added to the sludge to build an alkaline environment, which can effectively capture and neutralize the halogenated organic by-products and free halogens that may be generated under the action of the electric field, thereby controlling the generation and release of toxic substances from the source and solving the environmental protection hidden danger of the electrochemical treatment of the sludge containing chlorine. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The figure is a schematic diagram of the system flow of the present application. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0040] Embodiment one:

[0041] Please refer to Figure 1 The present application provides a technical solution: a method for strengthening sludge dewatering by electric field, which comprises the following steps:

[0042] Step one: biological enzyme pretreatment: the sludge to be treated is subjected to homogenization treatment, and a composite biological enzyme preparation is added after the homogenization treatment of the sludge, the biological enzyme preparation is stirred and mixed, the stirring and mixing temperature is 35-40℃, the stirring and mixing pH value is 6.5-7.5, and the stirring and mixing time is 20-30min;

[0043] Step two: gradient electric field dewatering: the sludge after the pretreatment in step one is sent into a rotating electrode dewatering device, and then a three-step gradient electric field is applied for gradient dewatering treatment, the pulse frequencies of the three-step gradient electric field are 30-50Hz, 50-80Hz and 80-150Hz respectively, and the treatment temperature of the gradient electric field dewatering process is 40-50℃;

[0044] Step three: electrode self-cleaning and electric field self-adaptive adjustment: the electrode rotates at a speed of 5-10 rpm / min during the gradient electric field dehydration in step two, and an ultrasonic generator is additionally added, which is started to work for 5-10 s every 30 min;

[0045] Step four: sludge cake collection and water resource recycling: the sludge after electrode treatment is subjected to dewatering treatment by a filter press, and the water after pressure filtration of the filter press is recycled to the inside of the electrode dewatering device in step two after being adsorbed by activated carbon.

[0046] Among them, the dehydration efficiency and system stability are significantly improved through multi-link cooperation. First, the composite biological enzyme is used to pretreat the sludge under suitable temperature and pH conditions, effectively degrading the extracellular polymer, destroying the sludge floc structure, and releasing bound water to create favorable conditions for subsequent dehydration. Second, a three-step gradient pulse electric field is introduced to apply electric field force in stages, promote directional migration of water, avoid energy waste, and improve dehydration kinetics efficiency. At the same time, electrode rotation combined with periodic ultrasonic waves can prevent sludge deposition and maintain electrode activity. After dehydration, the sludge cake is filtered to a water content of less than 55%, achieving deep dewatering; the filtrate is recycled after being adsorbed by activated carbon, achieving water resource recycling and reducing emissions.

[0047] Example two:

[0048] The biological enzyme preparation added in step one is composed of cellulase, protease and lipase, and the mass fraction of the cellulase, protease and lipase is 2:1:1. The amount of the biological enzyme preparation is 0.1%-0.3% of the weight of the sludge. After the homogeneous stirring treatment of the biological enzyme preparation is completed, the temperature is raised to above 60°C.

[0049] Among them, the composite enzyme preparation is composed of cellulase, protease and lipase in a mass fraction of 2:1:1, achieving the synergistic degradation of different types of organic matter in the sludge. The cellulase mainly decomposes the cellulose structure in the cell wall, the protease efficiently degrades the protein skeleton of the extracellular polymer, and the lipase acts on the lipid substances. The synergistic effect of the three can more comprehensively destroy the extracellular polymer and cell membrane structure of the sludge, release bound water more thoroughly, significantly improve the subsequent dehydration performance, and raise the temperature to above 60°C after the pretreatment is completed, which can effectively inactivate the biological enzyme and terminate the enzymolysis reaction in time to prevent excessive degradation and produce too much soluble organic matter, which is beneficial to the subsequent electric field dehydration and water quality control.

[0050] The first step of the three-step gradient electric field in the second step applies a voltage of 80-120V, and the treatment time is 40-60min; the second step of the gradient electric field applies a voltage of 150-220V, and the treatment time is 30-50min; and the third step of the gradient electric field applies a voltage of 200-250V, and the treatment time is 30-50min.

[0051] The first step uses a lower voltage for a long time to gently start the electrodialysis and electrophoresis process, so that the free water and part of the bound water in the sludge gradually migrate at low energy consumption, avoiding excessive current, local overheating and energy waste caused by directly applying high voltage at the beginning. With the decrease of the water content of the sludge and the increase of the resistance, the voltage is increased to 150-220V in the second step to overcome the resistance and further drive the migration of deep water. In the third step, a higher voltage is used for deep dewatering to strongly destroy the structure of the remaining bound water, significantly improve the dewatering rate and the final dewatering effect. The thick gradient voltage boosting mode slows down the polarization and wear of the electrode, reduces the impact on the power supply system, and is beneficial to maintain the stable operation of the system and prolong the service life of the electrode and equipment. The overall process is scientific and reasonable, and takes into account the dewatering efficiency, energy consumption control and equipment safety.

[0052] The sludge resistance detection sensor is used to detect the change of sludge resistance, and when the change rate of sludge resistance exceeds 15% / min, the pulse frequency of the ultrasonic generator is adjusted to 80-150Hz.

[0053] The sludge resistance detection sensor is used to detect the change of sludge resistance, and when the change rate of sludge resistance exceeds 15% / min, the pulse frequency of the ultrasonic generator is adjusted to 80-150Hz.

[0054] The rotating electrode dewatering device comprises a cylindrical anode and a cylindrical cathode which are communicatively connected, the cylindrical anode is arranged inside the cylindrical cathode, the cylindrical anode is a porous electrode coated with iridium dioxide, the cylindrical cathode is made of stainless steel mesh, and the cylindrical anode and the cylindrical cathode are both coated with a titanium dioxide photocatalytic layer on the outside.

[0055] The cylindrical anode and the cylindrical cathode are coaxially arranged to form a ring-shaped reaction cavity, so that the electric field is uniformly distributed in the radial direction, the sludge is more uniformly stressed under the action of the electric field, and the water can be efficiently migrated to the cathode in the radial direction, thereby effectively shortening the mass transfer path and improving the electrodialysis dewatering rate. When the cylindrical anode and the cylindrical cathode rotate, the driving motor can be used to drive the cylindrical anode and the cylindrical cathode to rotate. In addition, the anode is a porous electrode coated with iridium dioxide, which can maintain stability during long-term operation of the device. Moreover, the titanium dioxide photocatalytic layer coated on the surface of the electrode can generate active free radicals under ultraviolet light irradiation, which can synergistically degrade organic pollutants attached to the surface of the electrode or in the sludge, prevent the catalytic sites from being blocked, and maintain the activity of the electrode.

[0056] The gradient electric field dewatering process in step two is irradiated with ultraviolet light at a wavelength of 254-365 nm and an intensity of 10-50 mW / cm².

[0057] The titanium dioxide photocatalytic layer on the surface of the electrode generates strong oxidizing free radicals under ultraviolet light excitation, and cooperates with the electric field to further destroy the structure of the sludge extracellular polymeric substance, thereby improving the dewatering efficiency.

[0058] Before the composite biological enzyme preparation is added in step one, the sludge is mixed with sulfuric acid to adjust the pH value of the sludge to 4.5-5.5, and the sludge is maintained at a pH value of 4.5-5.5 for 10-15 min.

[0059] The acidification pretreatment can initially dissolve part of the metal ions and colloidal substances, change the sludge floc structure, and better create processing conditions for the subsequent biological enzyme action. Therefore, this acidification and enzyme hydrolysis treatment method can obtain better cell wall breaking and organic matter dissolution effect.

[0060] In the gradient electric field dewatering of step two, active magnesium oxide or magnesium hydroxide is added to the sludge to be treated, so that the alkaline environment with adsorption and neutralization effect is generated in situ during the gradient electric field treatment of the sludge.

[0061] When toxic by-products such as halogenated organic compounds or free chlorine are generated during the electric field treatment, the gradient electric field environment in the alkaline environment is used to capture and neutralize the halogenated organic by-products and free halogen generated under the action of the electric field, thereby preventing secondary pollution.

[0062] The electrode self-cleaning and electric field self-adaptive adjustment in step three applies a reverse pulse current to the cylindrical anode and the cylindrical cathode after the gradient electric field dewatering treatment is continuously operated for 2-4 h. The voltage of the reverse pulse current is 50%-80% of the original dewatering voltage, the pulse frequency is 20-40 Hz, and the reverse pulse duration is 1-3 min.

[0063] The electrochemical reaction generated by the reverse current can strip the deposits and oxide layer on the surface of the electrode and restore the activity of the electrode.

[0064] In the step two gradient electric field dehydration, the ozone gas is introduced into the cylindrical cathode while the gradient electric field is applied, the frequency of the ozone gas introduction is 1-2 times per dehydration cycle, the ozone introduction time is 30-60s, and the ozone concentration of the introduced ozone gas is 10-50 mg / L.

[0065] The strong oxidizing property of the ozone can be used to oxidize and decompose the organic pollutants attached to the surface of the titanium dioxide photocatalytic layer, so as to prevent the active sites from being covered and cause the photocatalytic efficiency to decrease.

[0066] Although the embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, changes and alterations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. An electric field enhanced sludge dewatering method, characterized by: The method comprises the following steps: Step one: biological enzyme pretreatment: the sludge to be treated is homogenized, and a composite biological enzyme preparation is added to the homogenized sludge, the biological enzyme preparation is stirred and mixed, the stirring and mixing temperature is 35-40°C, the stirring and mixing pH value is 6.5-7.5, and the stirring and mixing time is 20-30 min; Step two: gradient electric field dewatering: the sludge pretreated in step one is sent to a rotating electrode dewatering device, and then a three-step gradient electric field is applied for gradient dewatering treatment, the pulse frequency of the three-step gradient electric field is 30-50 Hz, 50-80 Hz and 80-150 Hz respectively, and the gradient electric field dewatering process treatment temperature is 40-50°C; Step three: electrode self-cleaning and electric field self-adaptive adjustment: the electrode rotates at a speed of 5-10 rpm / min during the gradient electric field dewatering of step two, and an ultrasonic generator is additionally added, the ultrasonic generator is started to work for 5-10 s every 30 min; Step four: sludge cake collection and water resource recovery: the sludge treated by the electrode is dewatered by a filter press, the dewatering treatment is performed until the moisture content of the sludge cake is less than 55%, and the water filtered by the filter press is recycled to the inside of the gradient electric field electrode dewatering device in step two after being adsorbed by activated carbon.

2. The method of electrocoagulation enhanced sludge dewatering according to claim 1, wherein: The biological enzyme preparation added in step one is composed of cellulase, protease and lipase, the mass fraction of the cellulase, protease and lipase is 2:1:1, the added amount of the biological enzyme preparation is 0.1%-0.3% of the weight of the sludge, and the biological enzyme preparation is heated to above 60°C after the homogenization and stirring treatment.

3. The method of electrocoagulation enhanced sludge dewatering according to claim 2, wherein: In step two, the first-step gradient electric field applies a voltage of 80-120 V, the continuous treatment time is 40-60 min, the second-step gradient electric field applies a voltage of 150-220 V, the continuous treatment time is 30-50 min, and the third-step gradient electric field applies a voltage of 200-250 V, the continuous treatment time is 30-50 min.

4. The method of electrocoagulation enhanced sludge dewatering according to claim 3, wherein: In step three, the electrode self-cleaning and electric field self-adaptive adjustment further comprises a sludge resistance detection sensor, the sludge resistance detection sensor is used to detect the change of sludge resistance, and when the sludge resistance change rate exceeds 15% / min, the pulse frequency of the ultrasonic generator is adjusted to 80-150 Hz.

5. The method of electrocoagulation enhanced sludge dewatering according to claim 4, wherein: The rotating electrode dewatering device comprises a cylindrical anode and a cylindrical cathode arranged in communication, the cylindrical anode is arranged inside the cylindrical cathode, the cylindrical anode adopts an iridium dioxide coating porous electrode, the cylindrical cathode is made of a stainless steel mesh, and the outer part of the cylindrical anode and the cylindrical cathode is coated with a titanium dioxide photocatalytic layer.

6. The method of electrocoagulation enhanced sludge dewatering according to claim 5, wherein: In step two, the gradient electric field dewatering process is irradiated with ultraviolet light at the same time, the wavelength of the ultraviolet light is 254-365 nm, and the light intensity is 10-50 mW / cm².

7. The method of electrocoagulation enhanced sludge dewatering according to claim 5, wherein: The step one is to adjust the pH value of the sludge to 4.5-5.5 by mixing the sludge with sulfuric acid before adding the composite biological enzyme preparation, and the duration of the pH value adjustment is 10-15 min.

8. The method of electrocoagulation enhanced sludge dewatering according to claim 7, wherein: In the step two, active magnesium oxide or magnesium hydroxide is added to the sludge to be treated to generate an alkaline environment in situ during the gradient electric field treatment.

9. The method of electrocoagulation enhanced sludge dewatering according to claim 8, wherein: The step three is to apply a reverse pulse current to the cylindrical anode and the cylindrical cathode after the gradient electric field dewatering treatment is continuously operated for 2-4 h, the voltage of the reverse pulse current is 50%-80% of the original dewatering voltage, the pulse frequency is 20-40 Hz, and the reverse pulse duration is 1-3 min.

10. The method of electrocoagulation enhanced sludge dewatering of claim 8, wherein: In the step two, ozone gas is introduced into the cylindrical cathode while the gradient electric field is applied, the frequency of the ozone gas introduction is 1-2 times per dewatering cycle, the ozone introduction time is 30-60 s, and the ozone concentration of the introduced ozone gas is 10-50 mg / L.

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