CN112624537A

CN112624537A - Method and system for decrement treatment of biochemical excess sludge

Info

Publication number: CN112624537A
Application number: CN201910907369.3A
Authority: CN
Inventors: 高峰; 杨宇宁; 桑军强; 赵锐
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2019-09-24
Filing date: 2019-09-24
Publication date: 2021-04-09
Anticipated expiration: 2039-09-24
Also published as: CN112624537B

Abstract

The invention relates to the field of sludge treatment, and discloses a method and a system for decrement treatment of biochemical excess sludge. The method comprises the following steps: (1) performing an alkali pretreatment reaction on the biochemical excess sludge and a first alkali source to obtain a material I, wherein the dosage of the first alkali source enables the pH value of a mixed material flow subjected to the alkali pretreatment reaction to be kept at 8-10; (2) carrying out a thermal hydrolysis reaction on the material I and a second alkali source to obtain a material II, wherein the second alkali source is used in an amount which keeps the pH value of a mixed material flow subjected to the thermal hydrolysis reaction at 9-11; (3) performing sludge-water separation on the material II to obtain supernatant and solid sludge; (4) and carrying out anaerobic reaction treatment on the supernatant. The method for reducing the amount of the biochemical excess sludge provided by the invention has the advantages of low treatment cost due to low medicament consumption, and good treatment effect.

Description

Method and system for decrement treatment of biochemical excess sludge

Technical Field

The invention relates to the field of sludge treatment, in particular to a method for reducing biochemical excess sludge and a system for reducing biochemical excess sludge.

Background

In recent years, the environmental protection industry in China is rapidly developed, the sewage treatment capacity and the treatment efficiency are rapidly improved, and the construction of a large number of sewage treatment plants undoubtedly plays an important role in protecting the water environment, but a large amount of biochemical excess sludge is generated. For the part of biochemical sludge, the sewage treatment plant usually adopts a 'mechanical dehydration + outsourcing' method for treatment, and only 10000m can be treated although the equipment investment is less³The sludge containing 98 percent of water is reduced to about 1200 tons in volume, the sludge is huge in volume, and the residual sludge contains a large amount of toxic and harmful substances, so that enterprises need to spend high expense and outsourcing treatment every year.

The biochemical excess sludge is an extremely complex heterogeneous body composed of organic debris, microorganisms, inorganic particles and the like, has strong pollution to the environment, is complex in components and difficult to treat, and has become a hot spot of people. In order to solve the problem of environmental pollution caused by biochemical excess sludge, people develop a great deal of research and development work on the aspect of sludge reduction technology, and develop a series of technologies, such as sludge drying and landfill technology, composting technology, incineration technology and the like. The technologies have certain effect on sludge reduction, but have obvious defects, such as the drying landfill technology not only occupies a large amount of land, but also forms pollution risk to underground water; the composting technology causes heavy metal pollution and biological pollution to soil in the using process; the incineration technology has high requirements on equipment and high treatment cost, and harmful gases such as dioxin and the like can be generated. These have forced the development of more cost effective technologies.

The sludge pyrohydrolysis technology can disintegrate microbial flocs, break cell structures, hydrolyze organic macromolecules such as proteins, polysaccharides and lipids, reduce solid content in sludge, reduce viscosity of sludge particles and change water distribution characteristics in sludge due to pyrohydrolysis, improve dehydration capacity of sludge, and achieve sludge reduction effect from two aspects of reducing total solid content and improving dehydration performance of sludge, so that the sludge pyrohydrolysis technology is widely researched. Such as:

CN102718384A discloses a sludge alkaline catalysis thermal hydrolysis treatment method, which comprises the following steps: a, injecting sludge and alkaline substances into a reaction kettle, and controlling the pH value of the sludge in the reaction kettle to be 10-14; and B, injecting saturated steam of 0.5MPa to 1.6MPa into the reaction kettle, and reacting for 15 to 60 minutes to obtain hydrolyzed sludge. The prior art adopts a method of adding alkaline substances into sludge to improve the hydrolysis efficiency of the sludge, and is beneficial to the rapid breaking of sludge cells and the rapid hydrolysis of organic matters under the conditions of alkaline environment and heating. As the alkaline substance is added into the sludge to improve the hydrolysis efficiency of the sludge, saturated steam of 0.5MPa to 1.6MPa can be injected into the reaction kettle, the design pressure of the reaction kettle is reduced due to the reduction of the saturated steam pressure, so that the investment cost is greatly reduced, the investment of matched equipment such as a boiler and the like is greatly reduced due to the reduction of the saturated steam pressure, and the energy consumption is reduced due to the reduction of the steam usage amount. However, the addition of large amounts of base results in higher costs for the work-up and also tends to cause fouling of the reactor, which affects long-term operation.

Therefore, there is a need to develop an economically feasible biochemical sludge reduction technology to greatly reduce the volume of excess sludge and reduce the environmental hazard.

Disclosure of Invention

The invention aims to overcome the problems in the prior art and provide a method for reducing biochemical excess sludge and a system for reducing biochemical excess sludge, which have stable operation and good treatment effect.

In order to achieve the above object, a first aspect of the present invention provides a method for the reduction treatment of biochemical excess sludge, the method comprising:

(1) performing an alkali pretreatment reaction on the biochemical excess sludge and a first alkali source to obtain a material I, wherein the dosage of the first alkali source enables the pH value of a mixed material flow subjected to the alkali pretreatment reaction to be kept at 8-10;

(2) carrying out a thermal hydrolysis reaction on the material I and a second alkali source to obtain a material II, wherein the second alkali source is used in an amount which keeps the pH value of a mixed material flow subjected to the thermal hydrolysis reaction at 9-11;

(3) performing sludge-water separation on the material II to obtain supernatant and solid sludge;

(4) and carrying out anaerobic reaction treatment on the supernatant.

The method for reducing the biochemical excess sludge has the advantage of good treatment effect (the treated sludge has a low VSS/SS ratio).

In a second aspect, the present invention provides a system for the abatement treatment of biochemical excess sludge, the system comprising: a sludge pretreatment tank, a thermal hydrolysis reactor, a settling tank and an anaerobic reactor which are sequentially communicated through pipelines; the system further comprises: a first alkali source supply unit and a second alkali source supply unit;

the sludge pretreatment tank is communicated with the first alkali source supply unit through a pipeline, so that biochemical excess sludge and a first alkali source provided by the first alkali source supply unit are subjected to alkali pretreatment reaction in the sludge pretreatment tank to obtain a material I;

the thermal hydrolysis reactor is communicated with the second alkali source supply unit through a pipeline, so that the material I and a second alkali source provided by the second alkali source supply unit are subjected to thermal hydrolysis reaction in the thermal hydrolysis reactor to obtain a material II;

the inlet of the anaerobic reactor is communicated with the supernatant outlet of the settling tank through a pipeline.

The method for reducing the amount of the biochemical excess sludge has the advantages of low treatment cost due to low medicament consumption. The method for reducing the biochemical excess sludge has the advantages of good treatment effect (high VSS removal rate of the treated sludge and high sludge reduction rate), and the embodiment of the invention shows that by adopting the method provided by the invention, the VSS removal rate of the treated sludge obtained by treating 72% of sludge with VSS/SS by the method provided by the invention can reach 65%, and the sludge reduction rate can reach 96.01%. That is, the method for reducing the amount of the biochemical excess sludge provided by the invention can realize excellent treatment effect on the premise of low cost.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

In the present invention, unless otherwise specified, "first" and "second" in the present invention do not represent a sequential order, but merely distinguish, for example, "first" and "second" in "first alkali source" and "second alkali source" in the present invention are merely to distinguish between alkali sources introduced in two different reactions, and those skilled in the art should not be construed as limiting the present invention.

The invention provides a method for reducing and treating biochemical excess sludge, which comprises the following steps:

(4) and carrying out anaerobic reaction treatment on the supernatant.

The biochemical excess sludge of the present invention may be a biochemical excess sludge from, for example, a concentration tank of a sewage treatment plant.

Preferably, the water content of the biochemical excess sludge is 95 to 99.9 wt%, more preferably 96 to 99.5 wt%, for example 97 to 99 wt%; the volatile content ratio f is 50 to 80%, and more preferably 65 to 72%, where f is VSS/SS.

In the invention, VSS refers to volatile suspended matter, SS refers to total solid suspended matter, and VSS/SS is used for representing the content of volatile substances in the sludge.

In the invention, SS and VSS in the sludge are obtained by a weight method (CJ/T221-2005).

In the method provided by the invention, the sludge is treated in the steps (1) and (2) under the specific pH value, so that organic matters in the sludge can be removed under the condition of low consumption of alkali sources. The usage amount of the alkali source is small, so that the reactor is not easy to scale and can stably run for a long period.

According to a preferred embodiment of the invention, the pH of the mixture flow subjected to the thermal hydrolysis reaction is higher than the pH of the mixture flow subjected to the alkaline pretreatment reaction. By adopting the preferred embodiment, the method is more beneficial to improving the result of the biochemical excess sludge reduction treatment and is more beneficial to preventing the reactor used in the alkaline pretreatment reaction in the step (1) from scaling.

Further preferably, the first alkali source is used in an amount such that the pH of the mixture stream subjected to the alkali pretreatment reaction is maintained at 8 to 9.

Further preferably, the second source of alkalinity is used in an amount such that the pH of the mixture stream subjected to the thermal hydrolysis reaction is maintained between 9 and 10.

For the purpose of further optimizing sludge reduction, the time of the alkaline pretreatment reaction is preferably 0.1 to 16 hours, preferably 0.5 to 4 hours, and further preferably 1 to 4 hours; further preferably, the temperature of the alkali pretreatment reaction is 20 to 120 ℃, preferably 20 to 70 ℃, and further preferably 30 to 60 ℃. By adopting the preferred embodiment of the invention, the temperature of the alkali pretreatment reaction is not higher than 120 ℃, which is more favorable for realizing the release of organic matters, and little or no hydrolysis reaction occurs, which is more favorable for further improving the treatment effect of the biochemical excess sludge reduction.

The alkaline pretreatment reaction may be performed in a sludge pretreatment tank.

For the purpose of further optimizing the sludge reduction, the time of the thermal hydrolysis reaction is preferably 0.1 to 16 hours, preferably 0.5 to 4 hours, and further preferably 1 to 4 hours; further preferably, the temperature of the thermal hydrolysis reaction is 120-230 ℃, preferably 140-200 ℃. The optimal thermal hydrolysis reaction condition is adopted, so that the release of organic matters in the biochemical excess sludge is facilitated, and the organic matter removal effect is improved.

The thermal hydrolysis reaction may be carried out in a thermal hydrolysis reactor.

The alkali source of the present invention may be any substance capable of maintaining the pH of the mixture stream of the alkali pretreatment reaction and the thermal hydrolysis reaction at a defined value or range, but, in order to obtain a better treatment effect, it is preferable that the first alkali source and the second alkali source each be independently selected from at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium oxide, sodium peroxide, potassium oxide, potassium peroxide, calcium oxide, calcium peroxide, calcium carbonate, potassium bicarbonate, and sodium bicarbonate; more preferably, each of the first and second alkali sources is independently sodium hydroxide and/or potassium hydroxide.

In the present invention, the manner of introducing the first alkali source and the second alkali source is not particularly limited. In the present invention, the first alkali source and the second alkali source may be introduced in a solid form or may be introduced in a solution form, and preferably, the first alkali source and the second alkali source are used in a solution form (e.g., an aqueous solution).

Particularly preferably, the first alkali source and the second alkali source in the present invention are aqueous sodium hydroxide solutions having a concentration of 10 to 50 wt%.

According to the present invention, after the alkali pretreatment and the thermal hydrolysis reaction, sludge needs to be subjected to sludge-water separation to obtain supernatant and solid sludge, so that the released organic matter can be more easily separated from the sludge. Specifically, in step (3), the sludge-water separation is performed under such conditions that the water content of the obtained solid sludge is not more than 99% by weight, and more preferably not more than 98% by weight. The sludge-water separation method may be any conventional method known to those skilled in the art, such as centrifugation or sedimentation, preferably sedimentation, and the separation results in a solid sludge and a supernatant.

The mud-water separation may be carried out in a settling tank.

According to a preferred embodiment of the present invention, the material II is cooled to obtain a material III, and then the material III is subjected to the mud-water separation. Preferably, the mud-water separation comprises: and (3) contacting the material III with acid for settling separation. In the research process, the inventor of the invention finds that the addition of acid to the material III in the sedimentation separation process is more beneficial to separating the released organic matters from the sludge.

The amount of acid added is selected within a wide range according to the invention, preferably such that the pH of the mixture stream subjected to the settling separation is in the range of 6 to 9, more preferably 6.5 to 8.5. The acid according to the invention may be any substance which is capable of maintaining the pH of the mixed stream subjected to the settling separation at a defined value or range. The acid may be used in the form of a solution. Preferably, the acid is selected from at least one of hydrochloric acid, sulfuric acid, and nitric acid, and more preferably concentrated sulfuric acid having a mass concentration of 75 to 98 wt%.

In order to effectively utilize the heat of the material II and reduce the energy consumption, the material II and the material I are preferably subjected to heat exchange to realize the cooling of the material II. The heat exchange can be carried out by adopting a heat exchanger.

According to the present invention, preferably, the method further comprises dehydrating the solid sludge obtained in step (3); further preferably, the dewatering is such that the water content of the dewatered sludge is not higher than 60% by weight. The dehydration method can refer to the conventional method in the field, and is not described herein again. In fact, the solid sludge with the water content not higher than 60 wt% can be obtained by the method of the present invention, which is also one of the beneficial effects of the present invention. The dewatering can be carried out in a dewatering device, such as a dehydrator.

According to an embodiment of the invention, the dewatered solid sludge may be sent for disposal, e.g. for incineration and/or landfill.

The method provided by the invention preferably further comprises the step of carrying out anaerobic reaction treatment on the supernatant obtained by dewatering the solid sludge. Specifically, the supernatant of step (4) and the supernatant obtained by dewatering the solid sludge may be mixed and then subjected to the anaerobic reaction treatment. The anaerobic reaction may be carried out according to methods and conditions conventional in the art, and the present invention is not particularly limited thereto, and preferably, the conditions of the anaerobic reaction treatment include: the temperature is 25-50 ℃, and the preferable temperature is 30-40 ℃; the pH is 6 to 8, more preferably 6.5 to 8.5; the residence time is from 2 to 128h, more preferably from 12 to 72 h. The anaerobic reaction may be carried out in an anaerobic reactor. And if the COD value of the wastewater after the anaerobic reaction treatment reaches the discharge or recycling standard, the wastewater is directly discharged or recycled, and if the COD value does not reach the discharge or recycling standard, the wastewater can be returned to a sewage treatment plant for further treatment.

The first alkali source supply unit and the second alkali source supply unit may be two independent alkali source supply units, or may be the same alkali source supply unit.

According to a preferred embodiment of the present invention, the system further comprises an acid supply unit in line communication with the settling tank for supplying acid to the settling tank. In the sedimentation process of the sedimentation tank, the addition of acid is more beneficial to separating the released organic matters from the sludge.

According to a preferred embodiment of the invention, the system further comprises a heat exchanger arranged on a pipeline for communicating the pyrohydrolysis reactor with the settling tank, wherein the heat exchanger is used for exchanging heat between the material II at the outlet of the pyrohydrolysis reactor and the material I obtained at the outlet of the sludge pretreatment tank so as to cool the material II, and the cooled material is sent to the settling tank. By adopting the preferred embodiment, the heat of the material II at the outlet of the thermal hydrolysis reactor can be effectively utilized, and the energy consumption is reduced.

According to a preferred embodiment of the present invention, the system further comprises a dewatering device in pipeline communication with the settling tank for dewatering the solid sludge obtained at the outlet of the settling tank. The dehydration device may be a dehydrator.

According to the present invention, preferably, the inlet of the anaerobic reactor is communicated with the supernatant outlet of the dewatering device through a pipeline. In this preferred embodiment, the supernatant obtained by separating the sludge and water and the supernatant obtained by dehydrating may be subjected to the anaerobic reaction treatment together.

The treatment system provided by the invention has the advantages of simple equipment, no need of additionally adding new equipment, low treatment cost and good sludge dewatering effect after treatment.

The present invention will be described in detail below by way of examples. In the following examples, various raw materials used are commercially available ones unless otherwise specified.

In the following examples, the biochemical excess sludge is derived from a secondary sedimentation tank of a sewage treatment plant.

SS, VSS and sludge moisture content in the sludge are obtained through CJ/T221-2005.

The sludge reduction rate is (1-mass of sludge after reaction/mass of sludge before reaction) × 100%.

Examples 1 to 4

This example is provided to illustrate the method of the present invention for the abatement treatment of excess biochemical sludge.

(1) Biochemical excess sludge (water content and VSS/SS are listed in table 1 below) and a 30 wt% aqueous sodium hydroxide solution supplied from an alkali source supply unit were introduced into a sludge pretreatment tank, and an alkali pretreatment reaction was performed to obtain a material I, and the reaction conditions of the alkali pretreatment reaction are listed in table 1.

(2) The material I and a 30 wt% aqueous solution of sodium hydroxide supplied from an alkali source supply unit were introduced into a thermal hydrolysis reactor, and a thermal hydrolysis reaction was performed to obtain a material II, the reaction conditions of which are shown in table 1.

(3) And (3) carrying out heat exchange on the material II and the material I through a heat exchanger to cool the material II to obtain a material III, and sending the material III and 98 wt% of concentrated sulfuric acid provided by an acid supply unit into a settling tank (the pH value in the settling tank is shown in table 1) for settling so as to realize mud-water separation and obtain a supernatant and solid sludge.

(4) And (3) introducing the solid sludge into a dehydrator for dehydration and filter pressing to obtain a mud cake, wherein the water content, the VSS removal rate and the sludge reduction rate of the mud cake are listed in Table 1.

(5) And (3) feeding the supernatant obtained by settling in the step (3) and the supernatant obtained by dewatering in the step (4) into an anaerobic reactor for anaerobic reaction, wherein the conditions of the anaerobic reaction and the removal rate of COD (chemical oxygen demand) by the anaerobic reaction are shown in Table 1.

Comparative example 1

The procedure of example 4 was followed except that no alkali source was added in step 1, and the results are shown in Table 1.

Comparative example 2

The procedure of example 1 was followed except that no alkali source was added in step 1, and the results are shown in Table 1.

TABLE 1

Comparative example 3

Following the procedure of example 1, except that in this comparative example, the second alkali source was not added but only the first alkali source was added, and the first alkali source was added in such an amount that the pH of the material in the thermal hydrolysis reactor was maintained at 9.2, step (2) specifically included: and introducing the material I into a thermal hydrolysis reactor, and staying in the thermal hydrolysis reactor for 1h at 140 ℃ to obtain a material II. The water content of the obtained mud cake is 64 percent. The comparative example showed a VSS removal rate of 62% and a sludge reduction rate of 95.39%.

Example 5

The procedure of example 1 was followed except that the aqueous sodium hydroxide solution in step (1) and step (2) was added in such amounts that the pH in the sludge pretreatment tank and the pH of the material in the thermal hydrolysis reactor were each maintained at 10, respectively. The water content of the obtained mud cake is 63%. In this example, the VSS removal rate was 63% and the sludge reduction rate was 95.57%.

Example 6

The procedure of example 1 was followed except that the reaction temperature of the thermal hydrolysis reaction in step (2) was 100 ℃. The obtained mud cake had a water content of 75%. In this example, the VSS removal rate was 45% and the sludge reduction rate was 91.89%.

Example 7

The process of example 1 was followed except that concentrated sulfuric acid was not introduced during the settling in step (3). The obtained mud cake had a water content of 70%. In this example, the VSS removal rate was 65% and the sludge reduction rate was 94.68%.

From the above results, it can be seen that the method for the reduction treatment of biochemical excess sludge according to the present invention can obtain a filter cake having a low water content, and has a high VSS removal rate and a high sludge reduction rate.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. A method for the abatement treatment of biochemical excess sludge, the method comprising:

(4) and carrying out anaerobic reaction treatment on the supernatant.

2. The method according to claim 1, wherein the pH of the mixture stream subjected to the thermal hydrolysis reaction is higher than the pH of the mixture stream subjected to the alkaline pretreatment reaction.

3. The method of claim 1, wherein the first alkali source is used in an amount such that the pH of the mixture stream subjected to the alkali pretreatment reaction is maintained at 8-9;

preferably, the time of the alkali pretreatment reaction is 0.1 to 16 hours, preferably 0.5 to 4 hours;

preferably, the temperature of the alkali pretreatment reaction is 20 to 120 ℃, preferably 20 to 70 ℃.

4. The method according to claim 1, wherein the second alkali source is used in an amount such that the pH of the mixture stream subjected to the thermal hydrolysis reaction is maintained between 9 and 10;

preferably, the time of the thermal hydrolysis reaction is 0.1-16h, preferably 0.5-4 h;

preferably, the temperature of the thermal hydrolysis reaction is 120-230 ℃, preferably 140-200 ℃.

5. The process of any one of claims 1-4, wherein the first and second base sources are each independently selected from at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium oxide, sodium peroxide, potassium oxide, potassium peroxide, calcium oxide, calcium peroxide, calcium carbonate, potassium bicarbonate, and sodium bicarbonate;

preferably, the first and second alkali sources are used in the form of solutions;

preferably, the first and second alkali sources are aqueous sodium hydroxide solutions having a concentration of 10 to 50 wt%.

6. The method according to any one of claims 1 to 5, wherein the material II is cooled to obtain a material III, and then the material III is subjected to the mud-water separation;

preferably, the mud-water separation comprises: contacting the material III with acid for settling separation;

preferably, the acid is used in an amount such that the pH of the mixture stream subjected to the settling separation is in the range of from 6 to 9, preferably from 6.5 to 8.5.

7. The method of claim 6, wherein the feed II is heat exchanged against the feed I to effect cooling of feed II.

8. The process according to any one of claims 1 to 7, further comprising dehydrating the solid sludge obtained in step (3);

preferably, the dewatering is such that the water content of the dewatered sludge is not higher than 60 wt%;

preferably, the method further comprises subjecting the supernatant obtained by dewatering the solid sludge to anaerobic reaction treatment.

9. The treatment method according to any one of claims 1 to 8, wherein the conditions of the anaerobic reaction treatment include: the temperature is 25-50 ℃, preferably 30-40 ℃; the pH is 6-8, preferably 6.5-8.5; the residence time is from 2 to 128 hours, preferably from 12 to 72 hours.

10. The method according to any one of claims 1 to 9, wherein the biochemical excess sludge has a water content of 95 to 99.9 wt.%, preferably 96 to 99.5 wt.%; the volatile content ratio f is 50-80%, wherein f is VSS/SS.

11. A system for the abatement treatment of biochemical excess sludge, the system comprising: a sludge pretreatment tank, a thermal hydrolysis reactor, a settling tank and an anaerobic reactor which are sequentially communicated through pipelines; the system further comprises: a first alkali source supply unit and a second alkali source supply unit;

12. The system of claim 11, further comprising an acid supply unit in line communication with the settling tank for providing acid to the settling tank.

13. The system of claim 11, further comprising a heat exchanger arranged on a pipeline for communicating the pyrohydrolysis reactor with the settling tank, wherein the heat exchanger is used for exchanging heat between the material II at the outlet of the pyrohydrolysis reactor and the material I obtained at the outlet of the sludge pretreatment tank so as to cool the material II, and the cooled material is sent to the settling tank.

14. The system according to any one of claims 11-13, further comprising a dewatering device in line communication with the settling tank for dewatering solid sludge obtained at the outlet of the settling tank;

preferably, the inlet of the anaerobic reactor is communicated with the supernatant outlet of the dewatering device through a pipeline.