Sludge total reduction and resourceful treatment process based on ultrasonic technology

Abstract

The invention provides a sludge total reduction and resourceful treatment process based on an ultrasonic technology. The method comprises the following steps: wastewater enters a secondary sedimentation tank after biological treatment, part of sludge flows back, and the rest of sludge is concentrated; 30% of concentrated sludge is taken out from the gravity concentration tank, nano bubbles with the volume ratio of 10% are introduced, ultrasonic cell dissolving treatment is conducted, the treated sludge flows back to the biological treatment device, and in-situ reduction is achieved; carrying out ultrasonic pretreatment and low-frequency pulse micro-current disintegration treatment on the residual 70% of concentrated sludge, enabling the treated sludge to enter an aerated grit chamber, discharging clean sand, and carrying out advection precipitation on the sludge to generate carbon-rich sludge; mgO2 is added into the supernate to form struvite crystals, the struvite crystals are recycled, and the carbon-rich supernate and the carbon-rich sludge are combined to serve as endogenous carbon. According to the method, in-situ reduction of the sludge is efficiently realized; comprehensive resource utilization is realized, nitrogen and phosphorus are recycled to generate struvite, and meanwhile, carbon-rich supernate and carbon-rich sludge are combined to serve as endogenous carbon.

Description

Technical Field

[0001] The patent of this invention is a method for sludge treatment and resource utilization, which belongs to the field of water treatment technology. Specifically, it relates to a sludge full amount reduction and resource treatment process based on ultrasonic technology. Background Art

[0002] The activated sludge method is one of the most widely used secondary sewage treatment processes in the world. It effectively removes organic matter, nitrogen, phosphorus and other pollutants in sewage through the action of microorganisms. However, this method also produces a large amount of residual sludge while purifying the water quality. With the acceleration of China's urbanization process and the improvement of environmental protection awareness, the number and treatment capacity of urban sewage treatment plants have continued to grow, and the resulting residual sludge production has also continued to increase. According to relevant statistics, as of the end of 2020, the total amount of wet sludge produced by urban sewage treatment facilities across the country has reached about 65 million tons, and it is expected that this figure will climb to about 90 million tons by 2025. The residual sludge is rich in organic matter and various heavy metal ions, pathogens and other harmful substances. If it is not properly disposed of, it is very likely to cause serious secondary environmental pollution problems. From an economic point of view, the cost of sludge treatment accounts for a considerable proportion of the entire sewage treatment process. Generally speaking, the cost of sludge treatment and disposal accounts for about 30%-50% of the total investment in sewage treatment plants, and in terms of operation and maintenance costs, this part of the expenditure also accounts for 20%-50%.

[0003] Currently, a variety of sludge reduction and resource utilization technologies have been developed for sludge treatment. Traditional sludge reduction methods mainly include mechanical dehydration, thermal drying, anaerobic digestion and incineration. Although these technologies can effectively reduce the volume or mass of sludge, they generally have problems such as high energy consumption, large investment and complex operation. For example, although mechanical dehydration can quickly reduce the water content of sludge, the equipment cost is high and the treated sludge still needs further disposal; the thermal drying process consumes a lot of energy and may produce harmful gases; anaerobic digestion can recover some energy (such as methane), but its efficiency is limited by the nature of the raw materials, and the remaining biogas slurry and biogas residue are difficult to handle; although incineration can achieve the greatest reduction in volume, it will generate fly ash and other potentially toxic by-products and have a great impact on the environment. For sludge resource utilization, current technical methods include composting, methanogenesis, direct brick making and thermal energy utilization. Although these methods help to increase the value of waste, they face problems such as low conversion efficiency, unstable product quality and difficulty in by-product treatment in actual applications. For example, the market acceptance of compost products is not high, especially when the heavy metal content exceeds the standard; the energy value obtained from methane fermentation is low, and the management of the residue after treatment is still a major problem; the direct use of sludge to make building materials has problems of insufficient strength and poor durability; and the use of thermal energy is affected by the combustion characteristics of sludge, and it is often impossible to completely replace conventional fuels. Although the existing sludge reduction and resource utilization technologies can alleviate the pressure of sludge management to a certain extent, there are still problems such as low proportion of sludge reduction or resource utilization, complex processes, harsh conditions, and secondary pollution.

[0004] Therefore, it is particularly important to explore a new generation of sludge treatment solutions that are more efficient, environmentally friendly and economically beneficial. The present invention is an innovative technical solution proposed based on this background, aiming to overcome the shortcomings of the existing technology and promote the development of sludge treatment in a more sustainable direction. Summary of the invention

[0005] The present invention aims to solve the following problems: (1) The efficiency of sludge reduction and sludge resource utilization is low, which makes it difficult to meet the growing demand for sludge treatment; (2) Traditional treatment methods such as mechanical dehydration, thermal drying, and anaerobic digestion consume a lot of energy and are complicated to operate; (3) The solution to sludge resource utilization has problems such as low conversion efficiency and unstable product quality; (4) The energy consumption and carbon emissions during the treatment process are high, which does not meet the requirements of sustainable development.

[0006] The present invention proposes a sludge total reduction and resource treatment process based on ultrasonic technology, comprising the following steps:

[0007] S1: Biological treatment and sludge concentration: After the wastewater passes through the biological treatment unit, it enters the secondary sedimentation tank. Part of the sludge in the secondary sedimentation tank is returned to the wastewater biological treatment, and the remaining sludge is discharged into the gravity concentration tank for further concentration after mud-water separation;

[0008] S2: Ultrasonic lysis promotes in-situ sludge reduction: 30% of the concentrated sludge in the gravity thickening tank in S1 is taken, nanobubbles are introduced into the concentrated sludge, and ultrasonic lysis is performed. The treated sludge is returned to the wastewater biological treatment device, and the released native matrix is ​​used to promote the latent growth of microorganisms to achieve in-situ sludge reduction;

[0009] S3: Sludge ultrasonic-low-frequency pulse micro-current cracking: 70% of the concentrated sludge in the gravity thickening tank in S1 is subjected to ultrasonic pretreatment, and then subjected to low-frequency pulse micro-current cracking treatment. The treated sludge enters the aerated grit tank, and after aeration and grit settling, the clean sand is discharged, and the sludge is subjected to advection sedimentation to produce carbon-rich sludge;

[0010] S4: Sludge resource utilization: MgO2 is added to the sludge supernatant in S3, and the formed struvite crystals are precipitated and recovered. The carbon-rich supernatant is discharged and combined with the carbon-rich sludge in S3 as endogenous carbon.

[0011] Preferably, the cell lysis conditions described in S2 are an ultrasonic frequency of 20-40 kHz, an ultrasonic time of 15 min, and an acoustic energy density of 11 W / L.

[0012] Preferably, the nanobubble introduction amount described in S2 is 10%.

[0013] Preferably, the ultrasonic cracking conditions described in S3 are ultrasonic frequency 20-40kHz, ultrasonic time 15min, and acoustic energy density 33W / L.

[0014] Preferably, the current intensity of the low-frequency pulse microcurrent described in S3 is 80-100uA / cm 2 .

[0015] Preferably, the magnesium-phosphorus molar ratio of MgO2 in S4 is 1:2.

[0016] The beneficial effects of the present invention are as follows: (1) Efficient in-situ sludge reduction: by treating 30% of the concentrated sludge, 50% of the residual sludge can be reduced in-situ; concentrated sludge is selected for ultrasonic treatment, the sludge concentration is high, the volume is small, and energy consumption is reduced; the lysis ratio is increased to 30%, but the lysis degree only needs to reach 20%, saving 70% of the lysis energy consumption. (2) Comprehensive sludge resource utilization: 70% of the concentrated sludge is subjected to high-intensity ultrasonic treatment to separate the supernatant and solid residue, recover nitrogen and phosphorus and generate struvite, and at the same time use the carbon in the supernatant as endogenous carbon, thereby realizing the comprehensive resource utilization of sludge; through high-intensity lysis and cyclone aeration sand settling, the efficient release of carbon, nitrogen and phosphorus is guaranteed; the addition of horizontal sedimentation tanks improves the crystal purity of struvite; carbon-rich wastewater is mixed with carbon-rich sludge as an internal carbon source to achieve full resource utilization. (3) Reduce equipment costs: ultrasonic equipment can be shared in the process of in-situ sludge reduction and resource utilization, thereby reducing investment costs. (4) Economic and environmental protection: Compared with traditional methods, the overall cost is reduced by 30% and carbon emissions are reduced by more than 35%. This method can achieve 100% sludge reduction and resource utilization, and the final products are struvite, endogenous carbon and clean sand. (5) Maintaining effluent quality: This method maintains the sludge discharge intensity of the secondary sedimentation tank, does not affect the total phosphorus in the effluent, and avoids the need for additional phosphorus removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of a process flow for total sludge reduction and resource utilization based on ultrasonic technology. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to examples.

[0019] A sludge total reduction and resource treatment process based on ultrasonic technology, comprising the following steps: wastewater enters the secondary sedimentation tank after passing through the biological treatment unit, part of the secondary sedimentation tank sludge is returned to the wastewater biological treatment, and the remaining sludge is discharged into the gravity concentration tank for further concentration treatment after mud and water separation; 30% of the concentrated sludge in the gravity concentration tank in S1 is taken, 10% of nanobubbles are introduced into the concentrated sludge, and ultrasonic lysis treatment is performed, the lysis process is combined with nanobubbles to strengthen ultrasonic cavitation, and nanobubbles form structural defects in the sludge, reduce the surface tension of the sludge, change the viscosity of the sludge, and especially can act as cavitation nuclei, greatly promoting the generation of microjets and shock waves. The treated sludge is returned to the wastewater biological treatment unit, and the released native matrix is ​​used to promote the hidden growth of microorganisms to achieve in-situ sludge reduction; the lysis conditions are ultrasonic frequency 20-40kHz, ultrasonic time 15min, and sound energy density 11W / L. 70% of the concentrated sludge in the gravity thickening tank in S1 is subjected to ultrasonic pretreatment, and then subjected to low-frequency pulse microcurrent cracking treatment. The current intensity of the low-frequency pulse microcurrent is 80-100uA / cm 2. Concentrated sludge with a solid concentration of 2.5-4.5% can act as an electrolyte. Under the action of low-frequency pulse microcurrent, the sound-to-electron migration is greatly accelerated, charge separation is promoted, the generation of hydroxyl radicals and superoxide radicals is strengthened, and the ultrasonic cavitation effect is greatly improved. The treated sludge enters the aerated grit tank. After aeration and grit settling, the clean sand is discharged, and the sludge is precipitated to produce carbon-rich sludge; the ultrasonic cracking conditions are ultrasonic frequency of 20-40kHz, ultrasonic time of 15min, and acoustic energy density of 33W / L. MgO2 is added to the sludge supernatant in S3, and the magnesium-phosphorus molar ratio of the MgO2 is 1:2; the formed struvite crystals are precipitated and recovered, and the carbon-rich supernatant is discharged and combined with the carbon-rich sludge in S3 as endogenous carbon.

[0020] Example 1

[0021] After the wastewater is preliminarily treated in a biological treatment unit (such as an activated sludge process), it enters the secondary sedimentation tank. Part of the sludge in the secondary sedimentation tank is returned to the wastewater biological treatment unit, and the remaining sludge is discharged into the gravity thickening tank for further concentration after mud and water separation. The solid content of the concentrated sludge is about 5%. 30% of the concentrated sludge is taken out from the gravity thickening tank, and 10% volume ratio of nanobubbles are introduced into it. The concentrated sludge is treated with an ultrasonic device, and the ultrasonic frequency is set to 30kHz, the ultrasonic time is 15 minutes, and the acoustic energy density is 11W / L. The treated sludge is returned to the wastewater biological processor, and the released native matrix is ​​used to promote the hidden growth of microorganisms. The experimental results show that this process can achieve about 50% of the residual sludge in situ reduction. Take the remaining 70% of the concentrated sludge for ultrasonic pretreatment, the ultrasonic frequency is set to 30kHz, the ultrasonic time is 15 minutes, and the acoustic energy density is 33W / L. The pretreated sludge is then subjected to low-frequency pulse microcurrent cracking treatment, and the current intensity is set to 90μA / cm 2 The treated sludge enters the aerated grit chamber, where the clean sand is discharged after aeration and grit settling. The sludge is precipitated to produce carbon-rich sludge. MgO2 is added to the treated supernatant with a magnesium-phosphorus molar ratio of 1:2 to form struvite crystal precipitation and recover it. The carbon-rich supernatant is discharged and combined with the carbon-rich sludge to be used as endogenous carbon.

[0022] Example 2

[0023] After the wastewater is preliminarily treated in a biological treatment unit (such as the activated sludge method), it enters the secondary sedimentation tank. Part of the sludge in the secondary sedimentation tank is returned to the wastewater biological treatment unit, and the remaining sludge is discharged into the gravity thickening tank for further concentration after mud and water separation. The solid content of the concentrated sludge is about 6%. 30% of the concentrated sludge is taken out from the gravity thickening tank, and 10% volume ratio of nanobubbles are introduced into it. The concentrated sludge is treated with ultrasonic equipment. The ultrasonic frequency is set to 40kHz, the ultrasonic time is 15 minutes, and the acoustic energy density is 11W / L. The treated sludge is returned to the wastewater biological processor, and the released native matrix is ​​used to promote the hidden growth of microorganisms. The experimental results show that this process can achieve about 50% of the residual sludge in situ reduction. Take the remaining 70% of the concentrated sludge for ultrasonic pretreatment, the ultrasonic frequency is set to 40kHz, the ultrasonic time is 15 minutes, and the acoustic energy density is 33W / L. The pretreated sludge is then subjected to low-frequency pulse microcurrent cracking treatment, and the current intensity is set to 100μA / cm 2 The treated sludge enters the aerated grit chamber, where the clean sand is discharged after aeration and grit settling. The sludge is precipitated to produce carbon-rich sludge. MgO2 is added to the treated supernatant with a magnesium-phosphorus molar ratio of 1:2 to form struvite crystal precipitation and recover it. The carbon-rich supernatant is discharged and combined with the carbon-rich sludge to be used as endogenous carbon.

[0024] Example 3

[0025] After the wastewater is preliminarily treated in a biological treatment unit (such as an activated sludge process), it enters the secondary sedimentation tank. Part of the sludge in the secondary sedimentation tank is returned to the wastewater biological treatment unit, and the remaining sludge is discharged into the gravity thickening tank for further concentration after mud and water separation. The solid content of the concentrated sludge is about 4%. 30% of the concentrated sludge is taken out from the gravity thickening tank, and 10% volume ratio of nanobubbles are introduced into it. The concentrated sludge is treated with an ultrasonic device, and the ultrasonic frequency is set to 20kHz, the ultrasonic time is 15 minutes, and the acoustic energy density is 11W / L. The treated sludge is returned to the wastewater biological processor, and the released native matrix is ​​used to promote the hidden growth of microorganisms. The experimental results show that this process can achieve about 50% of the residual sludge in situ reduction. Take the remaining 70% of the concentrated sludge for ultrasonic pretreatment, the ultrasonic frequency is set to 20kHz, the ultrasonic time is 15 minutes, and the acoustic energy density is 33W / L. The pretreated sludge is then subjected to low-frequency pulse microcurrent cracking treatment, and the current intensity is set to 80μA / cm 2 The treated sludge enters the aerated grit chamber, where the clean sand is discharged after aeration and grit settling. The sludge is precipitated to produce carbon-rich sludge. MgO2 is added to the treated supernatant with a magnesium-phosphorus molar ratio of 1:2 to form struvite crystal precipitation and recover it. The carbon-rich supernatant is discharged and combined with the carbon-rich sludge to be used as endogenous carbon.

Claims

1. A sludge total reduction and resource treatment process based on ultrasonic technology, comprising the following steps: S1: Biological treatment and sludge concentration: After the wastewater passes through the biological treatment unit, it enters the secondary sedimentation tank. Part of the sludge in the secondary sedimentation tank is returned to the wastewater biological treatment, and the remaining sludge is discharged into the gravity concentration tank for further concentration after mud-water separation; S2: Ultrasonic lysis promotes in-situ sludge reduction: 30% of the concentrated sludge in the gravity thickening tank in S1 is taken, nanobubbles are introduced into the concentrated sludge, and ultrasonic lysis is performed. The treated sludge is returned to the wastewater biological treatment device, and the released native matrix is ​​used to promote the latent growth of microorganisms to achieve in-situ sludge reduction; S3: Sludge ultrasonic-low-frequency pulse micro-current cracking: 70% of the concentrated sludge in the gravity thickening tank in S1 is subjected to ultrasonic pretreatment, and then subjected to low-frequency pulse micro-current cracking treatment. The treated sludge enters the aerated grit tank, and after aeration and grit settling, the clean sand is discharged, and the sludge is subjected to advection sedimentation to produce carbon-rich sludge; S4: Sludge resource utilization: MgO2 is added to the sludge supernatant in S3, and the formed struvite crystals are precipitated and recovered. The carbon-rich supernatant is discharged and combined with the carbon-rich sludge in S3 as endogenous carbon.

2. According to claim 1, a sludge total reduction and resource treatment process based on ultrasonic technology is characterized in that: The cell lysis conditions described in S2 are ultrasonic frequency 20-40 kHz, ultrasonic time 15 min, and acoustic energy density 11 W / L.

3. The sludge total reduction and resource treatment process based on ultrasonic technology according to claim 1 is characterized in that: The nanobubble introduction amount described in S2 is 10%.

4. The sludge total reduction and resource treatment process based on ultrasonic technology according to claim 1 is characterized in that: The ultrasonic cracking conditions described in S3 are ultrasonic frequency 20-40kHz, ultrasonic time 15min, and acoustic energy density 33W / L.

5. The sludge total reduction and resource treatment process based on ultrasonic technology according to claim 1 is characterized in that: The current intensity of the low-frequency pulse microcurrent described in S3 is 80-100uA / cm 2 .

6. The sludge total reduction and resource treatment process based on ultrasonic technology according to claim 1 is characterized in that: The magnesium-phosphorus molar ratio of MgO2 in S4 is 1:2.

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