CN113292216A - Method for treating excess sludge by combined process of thermokalysis, ammonium magnesium phosphate fixation of phosphorus and nitrogen and dehydration utilization - Google Patents
Method for treating excess sludge by combined process of thermokalysis, ammonium magnesium phosphate fixation of phosphorus and nitrogen and dehydration utilization Download PDFInfo
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- CN113292216A CN113292216A CN202110561973.2A CN202110561973A CN113292216A CN 113292216 A CN113292216 A CN 113292216A CN 202110561973 A CN202110561973 A CN 202110561973A CN 113292216 A CN113292216 A CN 113292216A
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/02—Biological treatment
- C02F11/04—Anaerobic treatment; Production of methane by such processes
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
- C02F11/121—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering
- C02F11/122—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering using filter presses
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
- C02F11/121—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering
- C02F11/127—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering by centrifugation
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
- C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
- C02F11/143—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents using inorganic substances
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
- C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
- C02F11/143—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents using inorganic substances
- C02F11/145—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents using inorganic substances using calcium compounds
Abstract
The invention provides a method for treating excess sludge by a combined process of thermokalolysis, magnesium ammonium phosphate fixation of phosphorus and nitrogen and dehydration utilization, belonging to the technical field of sludge treatment. According to the invention, the solid content is improved by concentrating the excess sludge, and then the excess sludge is mixed with alkali to carry out thermokalysis reaction for cell breaking, so that the cell wall of cells in the sludge is promoted to break, the substances in the cells are released, orthophosphate, ammonia nitrogen and organic matters are dissolved out, and the orthophosphate, the ammonia nitrogen and the added magnesium salt react to generate magnesium ammonium phosphate precipitate, so that a mud cake containing MAP is obtained, and the mud cake can be used as a slow release fertilizer, and the resource utilization of nitrogen and phosphorus released in the sludge is realized; the dehydrated water generated by dehydrating the thermokalysis mixture can generate methane through anaerobic digestion reaction, the generated methane is used for generating steam by a methane steam boiler, and the obtained steam is used as a heat source of the thermokalysis reaction; or the dehydrated water can directly flow back to the denitrification unit for sewage treatment to supplement carbon. The method can realize the reduction, the harmlessness and the reclamation of the excess sludge.
Description
Technical Field
The invention relates to the technical field of sludge treatment, in particular to a method for treating excess sludge by a combined process of thermokalolysis, magnesium ammonium phosphate fixation of phosphorus and nitrogen and dehydration utilization.
Background
Along with the economic development and the accelerated urbanization process of China, the discharge amount of urban sewage is increased day by day, and the amount of residual sludge generated by sewage treatment plants is increased more and more. Statistically, the residual sludge amount reaches 5432 ten thousand tons in 2020, and the value is estimated to be increased continuously in a period of time, so that the reduction of the residual sludge is urgently required. Generally, the sludge treatment and disposal cost accounts for more than 50% of the total operation cost of a sewage treatment plant, so that the resource utilization of the excess sludge amount has important practical significance.
At present, the sludge recycling technology adopted at home and abroad mainly comprises the following steps: composting sludge, digesting to prepare methane, converting sludge into fuel, and preparing building materials and the like. Chinese patent application publication No. CN 103693828A discloses a method for treating excess sludge by an integrated process of alkaline hydrolysis pretreatment-recovery of phosphorus and nitrogen by magnesium ammonium phosphate method-methane production by anaerobic digestion, wherein crude magnesium ammonium phosphate is obtained by alkaline hydrolysis while methane is recovered, but there are stuffing defects such as low release efficiency of nitrogen, phosphorus and organic matter after cell lysis, and slow reaction rate. Chinese patent application publication No. CN 110117148A discloses a low-temperature thermal alkali digestion method for biochemical sludge in a sewage plant, in which pyrolysis and alkali hydrolysis are combined at low temperature to break microbial cell bodies in sludge in the sewage plant, thereby reducing sludge yield, but nitrogen, phosphorus and organic matters after cell lysis are not further recycled. Therefore, there is a need to develop a method for treating excess sludge, which can sufficiently release nitrogen, phosphorus and organic substances in the excess sludge by cell-breaking and can recycle the released nitrogen, phosphorus and organic substances.
Disclosure of Invention
The invention aims to provide a method for treating excess sludge by a combined process of thermokalysis, ammonium magnesium phosphate fixation of phosphorus and nitrogen, and dehydration utilization.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a method for treating excess sludge by a combined process of thermoalcalinization-magnesium ammonium phosphate fixation phosphorus nitrogen-dehydration utilization, which comprises the following steps:
(1) concentrating the residual sludge to obtain concentrated sludge;
(2) mixing the concentrated sludge obtained in the step (1) with alkali, and carrying out thermokalysis reaction to obtain thermokalysis mixture;
(3) mixing the thermal alkaline hydrolysis mixture obtained in the step (2) with magnesium salt, and carrying out magnesium ammonium phosphate precipitation reaction to obtain a mixture containing MAP;
(4) dehydrating the mixture containing MAP obtained in the step (3) to obtain dehydrated water and a mud cake containing MAP;
(5) refluxing the dehydrated water obtained in the step (4) to a denitrification unit for sewage treatment for carbon supplement;
or, carrying out anaerobic digestion on the dehydrated water obtained in the step (4) to produce methane, then using the obtained methane in a methane steam boiler to produce steam, and using the steam as a heat source of the thermoalkaline hydrolysis reaction in the step (2).
Preferably, the concentration treatment in the step (1) comprises gravity concentration, air flotation concentration or centrifugal concentration.
Preferably, the solid content of the concentrated sludge in the step (1) is 2.0-5.0%.
Preferably, the base in step (2) comprises sodium hydroxide or calcium hydroxide.
Preferably, the temperature of the thermal alkaline hydrolysis reaction in the step (2) is 70.0-90.0 ℃, and the time of the thermal alkaline hydrolysis reaction is 30.0-90.0 min.
Preferably, the initial pH value of the thermoalkaline hydrolysis reaction in the step (2) is 10.0-11.0.
Preferably, the magnesium salt in step (3) comprises magnesium chloride, magnesium sulfate or magnesium carbonate.
Preferably, the ratio of the amount of the magnesium salt to the amount of the phosphorus in the thermal alkaline hydrolysis mixture in the step (3) is (1.5-1.8): 1.
Preferably, the initial pH value of the magnesium ammonium phosphate precipitation reaction in the step (3) is 9.4-9.9, and the time of the magnesium ammonium phosphate precipitation reaction is 30.0-60.0 min.
Preferably, the dewatering in step (4) comprises pressure filtration or centrifugation.
The invention provides a method for treating excess sludge by a combined process of thermoalcalinization-magnesium ammonium phosphate fixation phosphorus nitrogen-dehydration utilization, which comprises the following steps: concentrating the residual sludge to obtain concentrated sludge; mixing the obtained concentrated sludge with alkali, and carrying out thermokalysis reaction to obtain thermokalysis mixture; mixing the obtained thermal alkaline hydrolysis mixture with magnesium salt, and carrying out magnesium ammonium phosphate precipitation reaction to obtain a mixture containing MAP; dehydrating the obtained mixture containing MAP to obtain dehydrated water and a mud cake containing MAP; refluxing the obtained dehydrated water to a denitrification unit for sewage treatment for carbon supplement; or carrying out anaerobic digestion on the obtained dehydrated water to produce methane, then using the obtained methane in a methane steam boiler to produce steam, and using the steam as a heat source of the thermokalysis reaction. According to the invention, the excess sludge is concentrated, the solid content of the excess sludge is increased, then the excess sludge is mixed with alkali, and then cell breaking is carried out through thermal alkaline hydrolysis reaction, so that cell walls of cells in the excess sludge are broken, intracellular substances are released, and orthophosphate, ammonia nitrogen and organic matters in the excess sludge are dissolved out; performing magnesium ammonium phosphate precipitation reaction on orthophosphate, ammonia nitrogen and an additional magnesium salt to generate a mixture containing MAP, dehydrating to obtain an alkaline mud cake containing MAP, and using the alkaline mud cake as a slow release fertilizer to realize resource utilization of nitrogen and phosphorus in the residual sludge; dehydration product of mixture containing MAPThe produced dehydrated water can be used for producing methane through anaerobic digestion reaction, the produced methane is used for producing steam by a methane steam boiler, the obtained steam is used as a heat source of thermokalysis reaction, or the obtained steam can directly flow back to a denitrification unit for sewage treatment to supplement carbon, so that the reduction, harmlessness and reclamation of the residual sludge are realized. The results of the examples show that the method for treating excess sludge provided by the invention comprises the following steps: the ammonia nitrogen release rate is 422.6 percent, the orthophosphate release rate is 94.4 percent, and the COD release rate is 957.5 percent; after the MAP reaction: the ammonia-nitrogen conversion rate is 22.3 percent, and the orthophosphate conversion rate is 53.3 percent; after dehydration of the MAP-containing mixture: the recovery rate of ammonia nitrogen is 54.0 percent, and the recovery rate of orthophosphate is 93.1 percent; producing methane by using a UASB reactor: the difference value between the front and the back of COD is 1069mg/L, and the volume of the UASB reactor is 12m31g of COD produced 0.35L of methane, and the yield of methane per cubic meter of dehydrated water was 374.15L.
Drawings
FIG. 1 is a flow chart of the method for treating excess sludge by the combined process of thermokalysis, magnesium ammonium phosphate fixation of phosphorus and nitrogen, and dehydration utilization.
Detailed Description
The invention provides a method for treating excess sludge by a combined process of thermoalcalinization-magnesium ammonium phosphate fixation phosphorus nitrogen-dehydration utilization, which comprises the following steps:
(1) concentrating the residual sludge to obtain concentrated sludge;
(2) mixing the concentrated sludge obtained in the step (1) with alkali, and carrying out thermokalysis reaction to obtain thermokalysis mixture;
(3) mixing the thermal alkaline hydrolysis mixture obtained in the step (2) with magnesium salt, and carrying out magnesium ammonium phosphate precipitation reaction to obtain a mixture containing MAP;
(4) dehydrating the mixture containing MAP obtained in the step (3) to obtain dehydrated water and a mud cake containing MAP;
(5) refluxing the dehydrated water obtained in the step (4) to a denitrification unit for sewage treatment for carbon supplement;
or, carrying out anaerobic digestion on the dehydrated water obtained in the step (4) to produce methane, then using the obtained methane in a methane steam boiler to produce steam, and using the steam as a heat source of the thermoalkaline hydrolysis reaction in the step (2).
The invention carries out concentration treatment on the excess sludge to obtain the concentrated sludge. In the invention, the concentration treatment can remove water in part of the excess sludge and improve the solid content of the sludge.
In the present invention, the concentration treatment preferably includes gravity concentration, air flotation concentration or centrifugal concentration. The device for the concentration treatment of the present invention is not particularly limited, and a device of a sludge concentration unit known to those skilled in the art may be used. In the present invention, the sludge concentration unit preferably includes a gravity concentration tank, an air flotation concentration tank, or a centrifugal concentrator.
In the present invention, the solid content of the concentrated sludge is preferably 2.0% to 5.0%, more preferably 2.5% to 3.0%. The invention has no special limit on the concentration of COD, orthophosphate and ammonia nitrogen of the concentrated sludge, and the concentration of COD, orthophosphate and ammonia nitrogen of the concentrated sludge can be recorded when the solid content of the concentrated sludge can reach 2.0-5.0%. In the invention, when the solid content of the concentrated sludge can reach 2.0-5.0%, the COD of the concentrated sludge is preferably 178-295.6 mg/L, and more preferably 200-258 mg/L; the orthophosphate of the concentrated sludge is preferably 15.1-28.5 mg/L, and more preferably 20-25 mg/L; the ammonia nitrogen of the concentrated sludge is preferably 13.8-39.8 mg/L, and more preferably 20-30 mg/L. In the invention, after the concentration treatment, the parameters of the concentrated sludge are in the range, and the influence of the subsequent treatment process on each parameter can be monitored by recording the parameters of the concentrated sludge.
After the obtained concentrated sludge is obtained, the concentrated sludge is mixed with alkali for thermokalysis reaction to obtain thermokalysis mixture.
In the present invention, the alkali preferably includes sodium hydroxide or calcium hydroxide. In the invention, the alkali can provide the required alkaline condition for the thermal alkaline hydrolysis reaction, so that the pre-concentrated sludge is fully broken. The amount of the alkali used in the present invention is not particularly limited, and the pH of the initial reaction of the thermal alkaline hydrolysis reaction may be adjusted as desired.
In the invention, the initial pH value of the thermal alkaline hydrolysis reaction is preferably 10.0-11.0. In the invention, when the initial pH value of the thermal alkaline hydrolysis reaction is in the range, the cell breaking rate is favorably improved, so that the concentrated sludge can be fully broken.
In the invention, the temperature of the thermal alkaline hydrolysis reaction is preferably 70.0-90.0 ℃, and more preferably 75.0-80.0 ℃; the time of the thermal alkaline hydrolysis reaction is preferably 30.0-90.0 min, and more preferably 40.0-50.0 min. In the invention, when the temperature and the time of the thermal alkaline hydrolysis reaction are in the range, the cells of the concentrated sludge can be fully broken, the cell wall rupture of microorganisms in the residual sludge and the release of substances in the cells are promoted, and orthophosphate, ammonia nitrogen and organic matters in the residual sludge are dissolved out.
The heating mode of the thermokalysis reaction is not particularly limited, and the thermokalysis reaction can be carried out at the temperature of 70.0-90.0 ℃ by adopting the heating mode known by the technical personnel in the field. In the present invention, the heating manner of the thermal alkaline hydrolysis reaction preferably includes electric heating, steam heating or heat conducting oil heating, and more preferably steam heating. In the present invention, the heating mode is the above type, which can ensure the thermal alkaline hydrolysis reaction at the required temperature.
The device for the thermal alkaline hydrolysis reaction is not particularly limited, and a thermal alkaline hydrolysis reaction kettle known to those skilled in the art can be adopted. In the invention, the thermal insulation material is preferably arranged outside the thermal alkaline hydrolysis reaction kettle, so that the reaction temperature in the thermal alkaline hydrolysis reaction kettle is ensured to be 70.0-90.0 ℃. In the present invention, the heat insulating material preferably includes glass wool, rock wool, extruded polystyrene foam, or polyurethane rigid foam.
In the invention, the thermokalysis reaction device is preferably that more than 2 thermokalysis reaction kettles are connected in parallel to realize the continuous operation of the system. The number of the thermal alkaline hydrolysis reaction kettles is not particularly limited, and the number of the thermal alkaline hydrolysis reaction kettles can be adjusted according to the amount of the excess sludge to be treated. In the present invention, the number of the thermal alkaline hydrolysis reaction vessels is preferably 2 or more, and more preferably 2 to 3.
In the invention, the COD of the thermal alkaline hydrolysis mixture is preferably 2589-4508 mg/L, and more preferably 3000-4000 mg/L; the orthophosphate of the thermal alkaline hydrolysis mixture is preferably 52.5-68.6 mg/L, and more preferably 60-65 mg/L; the ammonia nitrogen content of the thermal alkaline hydrolysis mixture is preferably 64.6-136.3 mg/L, and more preferably 80-120 mg/L. In the invention, the thermokalysis reaction can fully promote cell breakage in the excess sludge, release intracellular substances in the excess sludge and dissolve orthophosphate, ammonia nitrogen and organic matters in the excess sludge.
After a thermal alkaline hydrolysis mixture is obtained, the thermal alkaline hydrolysis mixture is mixed with magnesium salt, and ammonium magnesium phosphate precipitation reaction is carried out to obtain a mixture containing MAP.
In the present invention, the ratio of the amount of the magnesium salt to the amount of the phosphorus in the hot alkaline hydrolysis mixture is preferably (1.5 to 1.8):1, and more preferably (1.6 to 1.7): 1. In the invention, the magnesium ammonium phosphate precipitation reaction is a heterogeneous reaction system, the added magnesium salt can form various precipitates, the resource utilization rate of phosphorus is reduced due to insufficient magnesium when the magnesium-phosphorus molar ratio is less than 1.5, but the magnesium salt is wasted due to the large surplus of magnesium when the magnesium-phosphorus molar ratio is more than 1.8. In the present invention, when the ratio of the magnesium salt to the amount of phosphorus in the thermal alkaline hydrolysis mixture is in the above range, it is advantageous to increase the efficiency of the struvite precipitation reaction and to increase the recovery rate of phosphorus.
The kind of the magnesium salt is not particularly limited in the present invention, and a commercially available magnesium salt known to those skilled in the art may be used. In the present invention, the magnesium salt preferably includes one or more of magnesium chloride, magnesium sulfate and magnesium carbonate. In the present invention, when the kind of the magnesium salt is the above-mentioned kind, it is more advantageous to complete the precipitation reaction of struvite sufficiently.
In the invention, the initial pH value of the magnesium ammonium phosphate precipitation reaction is preferably 9.4-9.9, and more preferably 9.5-9.8. In the invention, the magnesium ammonium phosphate precipitation reaction is a complex heterogeneous reaction system, and due to the existence of other buffer salts, the MAP formation rate is very low when the pH is less than 9.4; however, when the pH is more than 9.9, the cost of the preparation is increased and the subsequent dehydration is adversely affected. In the present invention, the magnesium ammonium phosphate precipitation reaction is sufficiently completed when the initial pH of the magnesium ammonium phosphate precipitation reaction is within the above range.
In the invention, the temperature of the magnesium ammonium phosphate precipitation reaction is preferably 45-55 ℃, and more preferably 48-50 ℃; the time of the magnesium ammonium phosphate precipitation reaction is preferably 30.0-45.0 min, and more preferably 35.0-40.0 min. In the present invention, when the temperature and time of the magnesium ammonium phosphate precipitation reaction are within the above ranges, the magnesium ammonium phosphate precipitation reaction can be promoted to be sufficiently completed, and phosphorus in the thermal alkaline hydrolysis mixture can be sufficiently reacted to form magnesium ammonium phosphate.
The device for magnesium ammonium phosphate precipitation reaction is not particularly limited in the present invention, and a precipitation reaction device known to those skilled in the art may be used. In the present invention, the precipitation reaction apparatus is preferably a jacket-cooled reaction vessel.
In the invention, the device for magnesium ammonium phosphate precipitation reaction is preferably that more than 2 reaction kettles are connected in parallel to realize continuous operation of the combined process. The number of the reaction kettles is not particularly limited, and the number of the reaction kettles can be adjusted according to the amount of the thermal alkaline hydrolysis mixture to be treated. In the present invention, the number of the reaction vessels is preferably 2 or more, and more preferably 2 to 3.
After obtaining the mixture containing MAP, the invention dehydrates the mixture containing MAP to obtain dehydrated water and mud cakes containing MAP.
In the present invention, the dehydration preferably comprises pressure filtration or centrifugation. The apparatus used in the dehydration in the present invention is not particularly limited, and an apparatus of a dehydration unit known to those skilled in the art may be used. In the present invention, the sludge dewatering unit preferably comprises a plate and frame filter press, a belt filter press or a centrifuge. In the present invention, when the sludge dewatering unit is of the above type, solid-liquid separation of the MAP-containing mixture can be sufficiently achieved.
In the present invention, the dehydration is preferably a conditioning dehydration. In the present invention, the agent for conditioning dehydration preferably includes ferric chloride, calcium chloride or cationic polyacrylamide. The operation method of the conditioning dehydration is not particularly limited in the present invention, and a method of conditioning dehydration known to those skilled in the art may be used. In the present invention, the conditioned dehydration can increase the dehydration rate of the MAP-containing mixture.
In the invention, the mud cake containing MAP is preferably directly applied as a slow release fertilizer. In the invention, the mud cake obtained by dehydrating the MAP-containing mixture is alkaline and comprises a large amount of magnesium ammonium phosphate, and can be used as an alkaline slow release fertilizer for improving acid soil. The method for directly applying the mud cake containing the MAP as the slow release fertilizer is not particularly limited, and the application method known by the technicians in the field is adopted.
The invention preferably applies the MAP-containing mud cake after drying. In the invention, the drying temperature is preferably 55-70 ℃, and more preferably 60-65 ℃; the drying time is preferably 2.0-4.0 h, and more preferably 2.5-3.0 h. In the present invention, when the temperature and time of the drying are within the above ranges, the moisture in the solid obtained by dehydration can be sufficiently removed.
After the dehydrated water is obtained, the dehydrated water is refluxed to a denitrification unit for sewage treatment to supplement carbon. In the invention, the dehydrated water contains organic matters, which can provide carbon sources for the denitrification unit and realize resource utilization of the organic matters in the dehydrated water.
The device and operation of the denitrification unit are not particularly limited in the present invention, and those known to those skilled in the art can be used.
Or, the dehydrated water is subjected to anaerobic digestion reaction to generate methane, the obtained methane is used for generating steam by a methane steam boiler, and the steam is used as a heat source of thermal alkaline hydrolysis reaction.
The apparatus for anaerobic digestion reaction according to the present invention is not particularly limited, and an apparatus for anaerobic digestion reaction known to those skilled in the art may be used. In the present invention, the apparatus for anaerobic digestion reaction preferably includes a UASB reactor, an IC reactor, or an anaerobic fluidized bed, and more preferably a UASB reactor. The operation method and parameters of the anaerobic digestion reaction are not particularly limited, and the operation method and parameters of the anaerobic digestion reaction well known to those skilled in the art can be adopted and adjusted according to the experimental needs.
After the methane is obtained, the methane is used for steam generated by the methane steam boiler, and then the steam is used as a heat source for thermal alkaline hydrolysis reaction.
In the invention, the methane can be used as fuel, and the methane can be used for a methane steam boiler to produce steam. The biogas steam boiler is not particularly limited, and the biogas steam boiler known to those skilled in the art can be adopted.
In the invention, the steam generated by the methane steam boiler has higher heat, can provide heat for the thermal alkaline hydrolysis reaction, and can be used as a heat source for the thermal alkaline hydrolysis to realize the resource utilization of organic matters in the dehydrated water.
In the present invention, the flow chart of the process of the method for treating excess sludge by the combined process of thermal alkaline hydrolysis-magnesium ammonium phosphate fixation phosphorus nitrogen-dehydration utilization is preferably as shown in fig. 1. As can be seen from fig. 1, the excess sludge is concentrated in a sludge concentration unit, the obtained concentrated sludge is subjected to alkali addition and heating in a thermokalysis reaction kettle to break cells, then magnesium salts are added into the obtained thermokalysis mixture in the reaction kettle to perform ammonium magnesium phosphate precipitation reaction, and then the obtained ammonium magnesium phosphate mixture is dehydrated in a dehydration unit to obtain dehydrated water and a sludge cake containing MAP; refluxing the dehydrated water to a denitrification unit for sewage treatment for carbon supplement; or the dehydrated water enters a methane production device, methane is produced through anaerobic digestion reaction, the methane obtained through the anaerobic digestion reaction is used for a methane steam boiler to produce steam, and the steam is used as a heat source of thermokalysis reaction, so that the resource utilization of orthophosphate, ammonia nitrogen and organic matters in the residual sludge is realized.
The invention provides a method for treating excess sludge by a combined process of thermokalysis-magnesium ammonium phosphate fixation of phosphorus and nitrogen-dehydration utilization, which is characterized in that the excess sludge is concentrated, the solid content of the excess sludge is improved, and then the excess sludge is mixed with alkali and subjected to thermokalysis reaction to break cells, so that microbial cell wall breaking and intracellular substance release in the sludge are promoted; dissolving out orthophosphate, ammonia nitrogen and organic matters in the residual sludge, carrying out magnesium ammonium phosphate precipitation reaction on the orthophosphate, the ammonia nitrogen and an additional magnesium salt to obtain a mixture containing MAP, and using the dewatered mud cake containing MAP as a slow release fertilizer to realize resource utilization of nitrogen, phosphorus and organic matters released in the sludge; the dehydrated water generated by sludge dehydration can generate methane through anaerobic digestion reaction, the generated methane can be used for steam generated by a methane steam boiler, the obtained steam is used as a heat source for thermokalysis reaction, or the steam can directly flow back to a denitrification unit for sewage treatment to supplement carbon, so that the reduction, harmlessness and recycling of the residual sludge are realized.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Suppliers of the thermokalite hydrolysis reaction kettle, the magnesium ammonium phosphate reaction kettle (MAP reaction kettle), the plate-and-frame filter press (sludge dewatering unit) and the UASB reactor in the embodiment are all Guangxi environmental protection technology Co., Ltd, Guangzhou, and the gravity concentration tank (sludge concentration unit) is an existing facility of Tiger door Green Source Water utilities Ltd, Dongguan.
(1) Concentrating the residual sludge in a gravity concentration tank to obtain concentrated sludge, wherein the solid content (TS) of the concentrated sludge is 3.2%, the ammonia nitrogen content (N/N) is 26.5mg/L, and the orthophosphate content (N/N) is 27.0mg/L, COD is 278.8 mg/L;
(2) mixing the concentrated sludge obtained in the step (1) with sodium hydroxide in a jacket heating reaction kettle, and breaking cells to obtain a thermoalclysis mixture;
wherein the heating mode of the thermokalysis reaction is heating by a heat conducting oil jacket, the thermokalysis reaction temperature is 80.0 ℃, the pH value of the thermokalysis reaction initial reaction is 10.0, the thermokalysis reaction time is 45.0min, and the heat insulation material is glass wool; the ammonia nitrogen in the supernatant of the thermal alkaline hydrolysis mixture is 138.5mg/L, and the orthophosphate is 52.5mg/L, COD is 2948.2 mg/L;
(3) cooling the thermal alkaline hydrolysis mixture obtained in the step (2) to 50 ℃ in a jacket cooling reaction kettle, adding magnesium chloride, and carrying out magnesium ammonium phosphate precipitation reaction to obtain a mixture containing MAP;
wherein the ratio of the amount of magnesium salt to the amount of phosphorus in the hot alkaline hydrolysis mixture is 1.8: 1, the initial reaction pH value of the precipitation reaction is 9.9, and the precipitation reaction time is 30.0 min; after the precipitation reaction, the ammonia nitrogen of the supernatant is 107.6mg/L, and the orthophosphate is 24.5mg/L, COD mg/2652.3 mg/L;
(4) adding cationic polyacrylamide into the mixture containing MAP obtained in the step (3), conditioning, and then dehydrating in a plate-and-frame filter press to obtain dehydrated water and a mud cake containing MAP;
wherein the ammonia nitrogen in the dehydrated water is 63.7mg/L, and the orthophosphate is 3.6mg/L, COD to 1865.8 mg/L;
(5) enabling the dehydrated water obtained in the step (4) to enter a UASB reaction, carrying out anaerobic digestion to produce methane, using the methane obtained by the anaerobic digestion in a methane steam boiler to produce steam, and providing heat source for the thermal-alkaline hydrolysis reaction kettle in the step (2) by using the steam;
wherein, the ammonia nitrogen in the effluent after the anaerobic digestion reaction is 41.2mg/L, and the orthophosphate is 2.2mg/L, COD is 796.8 mg/L.
From example 1, it can be seen that after the thermal alkaline hydrolysis reaction: the ammonia nitrogen release rate is 422.6 percent, the orthophosphate release rate is 94.4 percent, and the COD release rate is 957.5 percent; after the precipitation reaction of magnesium ammonium phosphate: the ammonia-nitrogen conversion rate is 22.3 percent, and the orthophosphate conversion rate is 53.3 percent; after dehydration treatment of the MAP-containing mixture: the recovery rate of ammonia nitrogen is 54.0 percent, and the recovery rate of orthophosphate is 93.1 percent; producing methane by UASB: the difference value between the front and the back of COD is 1069mg/L, and the volume of the UASB reactor is 12m31g of COD produced 0.35L of methane, and the yield of methane per cubic meter of dehydrated water was 374.15L.
Example 2
(1) Concentrating the residual sludge in a gravity concentration tank to obtain concentrated sludge, wherein the solid content (TS) of the concentrated sludge is 3.0%, the ammonia nitrogen content (NH) is 36.8mg/L, and the orthophosphate content (NH) is 28.5mg/L, COD is 295.6 mg/L;
(2) mixing the concentrated sludge obtained in the step (1) with sodium hydroxide in a jacket heating reaction kettle, and breaking cells to obtain a thermoalclysis mixture;
wherein the heating mode of the thermokalysis reaction is heating by a heat conducting oil jacket, the thermokalysis reaction temperature is 80.0 ℃, the initial reaction pH value of the thermokalysis reaction is 10.0, the thermokalysis reaction time is 45.0min, and the heat-insulating material is glass wool; the ammonia nitrogen of the supernatant of the thermal alkaline hydrolysis mixture is 117.8mg/L, and the orthophosphate is 63.0mg/L, COD is 3067.8 mg/L;
(3) cooling the thermal alkaline hydrolysis mixture obtained in the step (2) to 50 ℃ in a jacket cooling reaction kettle, and then adding magnesium chloride to perform magnesium ammonium phosphate precipitation reaction to obtain a mixture containing MAP;
wherein the ratio of the amount of magnesium salt to the amount of phosphorus in the hot alkaline hydrolysis mixture is 1.8: 1, the initial reaction pH value of the precipitate is 9.9, and the precipitation reaction time is 30.0 min; after the precipitation reaction, the ammonia nitrogen of the supernatant is 80.6mg/L, and the orthophosphate is 23.5mg/L, COD mg/2865.8 mg/L;
(4) adding cationic polyacrylamide into the mixture containing MAP obtained in the step (3), conditioning, and then dehydrating in a plate-and-frame filter press to obtain dehydrated water and a mud cake containing MAP;
wherein the ammonia nitrogen in the dehydrated water is 45.6mg/L, and the orthophosphate is 2.8mg/L, COD and 1713.2 mg/L;
(5) enabling the dehydrated water obtained in the step (4) to enter a UASB reaction, carrying out anaerobic digestion to produce methane, using the methane produced in the anaerobic digestion reaction in a methane steam boiler to produce steam, and providing a heat source for the thermal-alkaline hydrolysis reaction kettle in the step (2) by using the steam;
wherein, the ammonia nitrogen in the effluent water of the anaerobic digestion reaction is 28.6mg/L, and the orthophosphate is 1.5mg/L, COD is 697.6 mg/L.
As can be seen from example 2: after the thermal alkaline hydrolysis reaction: the ammonia nitrogen release rate is 220.1 percent, the orthophosphate release rate is 121.1 percent, and the COD release rate is 937.8 percent; after the precipitation reaction: the ammonia-nitrogen conversion rate is 37.1 percent, and the orthophosphate conversion rate is 62.7 percent; after dehydration treatment of the MAP-containing mixture: the recovery rate of ammonia nitrogen is 31.6 percent, and the recovery rate of orthophosphate is 95.6 percent; producing methane by UASB: the difference value before and after COD is 1015.6mg/L, and the volume of the UASB reactor is 12m31g of COD produced 0.35L of methane, and the yield of methane per cubic meter of dehydrated water was 355.46L.
Example 3
(1) Concentrating the residual sludge in a gravity concentration tank to obtain concentrated sludge, wherein the solid content (TS) of the concentrated sludge is 2.9%, the ammonia nitrogen content (ammonian) is 39.8mg/L, and the orthophosphate content (orthophosphate content) is 26.5mg/L, COD is 278.6 mg/L;
(2) mixing the concentrated sludge obtained in the step (1) with sodium hydroxide in a jacket heating reaction kettle, and breaking cells to obtain a thermoalclysis mixture;
wherein the heating mode of the thermokalysis reaction is heating by a heat conducting oil jacket, the thermokalysis reaction temperature is 80.0 ℃, the initial reaction pH value of the thermokalysis reaction is 10.0, the thermokalysis reaction time is 45.0min, and the heat-insulating material is glass wool; the ammonia nitrogen of the supernatant of the thermal alkaline hydrolysis mixture is 158.6mg/L, and the orthophosphate is 56.0mg/L, COD is 2587.8 mg/L;
(3) cooling the thermal alkaline hydrolysis mixture obtained in the step (2) to 50 ℃ in a jacket cooling reaction kettle, and then adding magnesium chloride to perform magnesium ammonium phosphate precipitation reaction to obtain a mixture containing MAP;
wherein the ratio of the amount of magnesium salt to the amount of phosphorus in the hot alkaline hydrolysis mixture is 1.8: 1, the initial reaction pH value of the precipitation reaction is 9.9, and the precipitation reaction time is 30.0 min; after the precipitation reaction, the ammonia nitrogen of the supernatant is 108.6mg/L, and the orthophosphate is 30.0mg/L, COD to 2265.8 mg/L;
(4) adding cationic polyacrylamide into the mixture containing MAP obtained in the step (3), conditioning, and then dehydrating in a plate-and-frame filter press to obtain dehydrated water and a mud cake containing MAP;
wherein the ammonia nitrogen in the dehydrated water is 56.7mg/L, and the orthophosphate is 2.0mg/L, COD and 1513.2 mg/L;
(5) enabling the dehydrated water obtained in the step (4) to enter a UASB reaction, performing a digestion reaction to generate methane, using the methane generated in the anaerobic digestion reaction in a methane steam boiler to generate steam, and providing a heat source for the thermal-alkaline hydrolysis reaction kettle in the step (2) by using the steam;
wherein, the ammonia nitrogen in the effluent water of the anaerobic digestion reaction is 38.5mg/L, and the orthophosphate is 1.2mg/L, COD is 630.5 mg/L.
As can be seen from example 3: thermal alkaline hydrolysis reactionAnd (3) after: the ammonia nitrogen release rate is 298.5%, the orthophosphate release rate is 111.3%, and the COD release rate is 828.8%; after the precipitation reaction: the ammonia-nitrogen conversion rate is 31.5 percent, and the orthophosphate conversion rate is 46.4 percent; after dehydration treatment of the MAP-containing mixture: the recovery rate of ammonia nitrogen is 64.2 percent, and the recovery rate of orthophosphate is 96.4 percent; producing methane by UASB: the difference value before and after COD is 882.7mg/L, and the volume of the UASB reactor is 12m31g of COD produced 0.35L of methane, and the yield of methane per cubic meter of dehydrated water was 308.95L.
From the data, N, P and organic matters and the like in the excess sludge can be fully dissolved out by treating the excess sludge through a combined process of thermal alkaline hydrolysis, ammonium magnesium phosphate phosphorus nitrogen fixation and dehydrated water utilization, N, P reacts with magnesium salts to generate ammonium magnesium phosphate sludge which can be used as a slow release fertilizer, the organic matters can be used for generating methane through anaerobic digestion reaction, the methane is used for a methane steam boiler to generate steam, and the steam is used for providing heat source steam for a thermal alkaline hydrolysis reaction kettle. Or can directly flow back to the denitrification unit for sewage treatment to supplement carbon.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A method for treating excess sludge by a combined process of thermokalysis, magnesium ammonium phosphate fixation of phosphorus and nitrogen, dehydration and utilization comprises the following steps:
(1) concentrating the residual sludge to obtain concentrated sludge;
(2) mixing the concentrated sludge obtained in the step (1) with alkali, and carrying out thermokalysis reaction to obtain thermokalysis mixture;
(3) mixing the thermal alkaline hydrolysis mixture obtained in the step (2) with magnesium salt, and carrying out magnesium ammonium phosphate precipitation reaction to obtain a mixture containing MAP;
(4) dehydrating the mixture containing MAP obtained in the step (3) to obtain dehydrated water and a mud cake containing MAP;
(5) refluxing the dehydrated water obtained in the step (4) to a denitrification unit for sewage treatment for carbon supplement;
or, carrying out anaerobic digestion on the dehydrated water obtained in the step (4) to produce methane, then using the obtained methane in a methane steam boiler to produce steam, and using the steam as a heat source of the thermoalkaline hydrolysis reaction in the step (2).
2. The method for treating surplus sludge according to claim 1, wherein said concentration treatment in the step (1) comprises gravity concentration, air flotation concentration or centrifugal concentration.
3. The method for treating excess sludge according to claim 1, wherein the solid content of the concentrated sludge in the step (1) is 2.0% to 5.0%.
4. The method for treating surplus sludge according to claim 1, wherein said alkali in the step (2) comprises sodium hydroxide or calcium hydroxide.
5. The method for treating excess sludge according to claim 1, wherein the temperature of the thermoalkaline hydrolysis reaction in the step (2) is 70.0 to 90.0 ℃, and the time of the thermoalkaline hydrolysis reaction is 30.0 to 90.0 min.
6. The method for treating excess sludge according to claim 1, wherein the initial pH of the thermoalkaline hydrolysis reaction in the step (2) is 10.0 to 11.0.
7. The method for treating surplus sludge according to claim 1, wherein the magnesium salt in the step (3) comprises magnesium chloride, magnesium sulfate or magnesium carbonate.
8. The method for treating excess sludge according to claim 1, wherein the ratio of the amount of magnesium salt to the amount of phosphorus in the thermal alkaline hydrolysis mixture in the step (3) is (1.5-1.8): 1.
9. The method for treating surplus sludge according to claim 1, wherein the initial pH value of the magnesium ammonium phosphate precipitation reaction in the step (3) is 9.4 to 9.9, and the time for the magnesium ammonium phosphate precipitation reaction is 30.0 to 60.0 min.
10. The method for treating surplus sludge according to claim 1, wherein said dewatering in said step (4) comprises filter pressing or centrifugation.
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| CN113860703A (en) * | 2021-09-17 | 2021-12-31 | 华南理工大学 | Method for reducing and recycling excess sludge through persulfate pretreatment by thermal activation |
| CN114735911A (en) * | 2022-03-23 | 2022-07-12 | 东华工程科技股份有限公司 | Method for in-situ resource utilization of excess sludge in chemical industrial park |
| CN114772886A (en) * | 2022-03-23 | 2022-07-22 | 东华工程科技股份有限公司 | Method for full-scale denitrification and denitrification of excess sludge |
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