Pretreatment method for inhibiting escape of hydrogen sulfide in sludge dewatering process

Abstract

The invention provides a pretreatment method for inhibiting hydrogen sulfide escape in a sludge dewatering process. The pretreatment method comprises the following steps: S1, carrying out chemical pretreatment on sludge through an iron-based desulfurizer before dewatering. Before mechanical dehydration of sludge, specific iron salt is added for pretreatment, so that escape of hydrogen sulfide is inhibited from the source. And the specific problem of instantaneity and high-concentration H2S escape caused by physical extrusion in a mechanical dehydration link is solved in a targeted manner. And source control and process blocking are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sludge treatment, and particularly relates to a pretreatment method for inhibiting hydrogen sulfide emission in a sludge dewatering process. BACKGROUND

[0002] In the process of municipal and industrial sludge treatment, mechanical dewatering (such as using a screw press, a centrifuge, a plate-and-frame filter press, etc.) is a key link. However, under the high-intensity extrusion and shear disturbance of the dewatering machine, sulfides produced by metabolic activities of sulfate-reducing bacteria rich in sludge, and soluble sulfides wrapped inside the sludge floc, will be released in the form of hydrogen sulfide. Field measurements show that the instantaneous concentration of H2S in the dewatering machine room environment can reach 100-500 ppm, which not only seriously endangers the health of operating personnel and poses an explosion risk (the lower explosion limit is 4.3%), but also causes serious corrosion to the equipment and plant structure.

[0003] At present, the industry generally adopts end-of-pipe waste gas treatment technology, that is, the dewatering machine room is sealed, and the waste gas is transported to an alkali absorption tower, a biological filter or a chemical scrubbing tower for treatment through a gas collection system. This method has the following inherent defects: 1. Large equipment investment: a complete closed gas collection, transportation and end-of-pipe treatment system needs to be established, which occupies a large area and has high initial investment.

[0004] 2. High operating cost: the fan runs continuously with high energy consumption, and the absorbent such as alkali needs to be continuously added and supplemented, resulting in continuous reagent costs.

[0005] 3. Limited treatment efficiency: due to the dispersion of H2S emission points and the high instantaneous concentration, it is difficult for the collection system to be completely sealed, resulting in insufficient collection efficiency, and the overall removal rate is usually between 70%-85%.

[0006] 4. Secondary pollution: the sulfur-containing waste liquid generated after alkali absorption or the waste filter material of the biological filter needs to be treated as hazardous waste, increasing the disposal cost and environmental risk.

[0007] The prior art (such as CN112250132A - A process system for removing ammonia nitrogen by using a targeted adsorption material and a use method thereof) also discloses a method of adding iron salt to sludge to stabilize heavy metals, but it does not specifically solve the problem of instantaneous and high-concentration H2S emission caused by physical extrusion in the mechanical dewatering link.

[0008] Therefore, there is an urgent need and significant industrial value to develop a pretreatment method that can fix sulfides from the source, is economical and efficient, causes no secondary pollution, and can be seamlessly embedded into the existing dewatering process. SUMMARY

[0009] The technical problem solved by the present application is to provide a pretreatment method for inhibiting hydrogen sulfide emission in the sludge dewatering process.

[0010] The technical solution of the present application to solve the above technical problems is as follows: a pretreatment method for inhibiting hydrogen sulfide emission in the sludge dewatering process, comprising: S1, chemically pretreating the sludge by an iron-based desulfurizer before dewatering.

[0011] The beneficial effects of the technical solution of the present application are: before mechanical dewatering of the sludge, the sludge is pretreated by adding a specific iron salt to inhibit the emission of hydrogen sulfide from the source. The specific problem of instantaneous and high-concentration H2S emission caused by physical extrusion in the mechanical dewatering link is solved. Source control and process blocking are achieved.

[0012] Further, step S1 comprises: S11, adding an iron-based desulfurizer to the sludge before the sludge enters the mechanical dewatering equipment; S12, mixing and reacting to fix the sulfide before dewatering.

[0013] The beneficial effects of the above further technical solution are: by chemically pretreating the sludge before dewatering, the soluble sulfide in the liquid phase is converted into stable solid metal sulfide, eliminating the generation and emission potential of H2S from the source, and completely solving the H2S pollution and safety problems in the dewatering workshop. No absorption waste liquid needs to be treated subsequently, and the metal sulfide generated by the reaction has stable chemical properties. H2S is solidified in the pretreatment stage, and there is no significant emission in the dewatering link.

[0014] Further, in step S11, the iron-based desulfurizer is added to the sludge through a dosing point before the sludge enters the mechanical dewatering equipment; the mechanical dewatering equipment is a stacked screw dewatering machine, a centrifugal dewatering machine or a plate-and-frame filter press; and the mechanical dewatering equipment is provided with a mechanical dewatering equipment feed pump.

[0015] The beneficial effects of the above further technical solution are: the reacted sludge is transported to the mechanical dewatering equipment, such as a stacked screw machine, a centrifugal machine or a plate-and-frame filter press, for dewatering.

[0016] Further, in step S11, the dosing point is located in a sludge conditioning tank, a mixing tank or a buffer pool before the mechanical dewatering equipment feed pump.

[0017] The beneficial effects of the above further technical solution are: after the sludge is sequentially concentrated, it enters the pretreatment unit, such as a conditioning tank or a mixing tank, where the iron-based desulfurizer is added and mixed. No expensive waste gas collection and end treatment system needs to be added, and the existing sludge treatment facilities, such as a sludge conditioning tank, a mixing tank or a buffer pool, can be directly used. By adding a low-cost reagent, the problem can be solved, and the comprehensive operating cost is lower than that of the traditional end treatment method.

[0018] Further, in step S12, the mixing reaction is performed for a time ranging from 0.5 minute to 5 minutes.

[0019] The beneficial effect of the above further technical solution is to ensure that the medicament and the sludge are fully contacted and reacted, so that H2S is solidified in the pretreatment stage, and there is no significant escape in the dehydration link.

[0020] Further, in step S12, when the mixing reaction is performed, the mechanical stirrer is stirred at a preset speed or the turbulent flow in the pipeline is utilized to fully mix the iron-based desulfurizer and the sludge, so that the sulfide is fixed to form sulfur-containing substances before dehydration, wherein the sulfide is H2S, and the sulfur-containing substances are FeS or elemental S.

[0021] The beneficial effect of the above further technical solution is that the iron-based desulfurizer is added to the sludge before the sludge enters the mechanical dehydration equipment, the mechanical stirrer is stirred at a preset speed or the turbulent flow in the pipeline is utilized to fully mix the iron-based desulfurizer and the sludge, and a full mixing reaction is performed, so that the sulfide is fixed before dehydration. By chemically pretreating the sludge before dehydration, the soluble sulfide in the liquid phase is converted into stable solid metal sulfide, the generation and escape potential of H2S is eliminated from the source, and the H2S pollution and safety problems in the dehydration workshop are completely solved. No absorption waste liquid needs to be treated subsequently, the metal sulfide generated in the reaction has stable chemical properties, H2S is solidified in the pretreatment stage, and there is no significant escape in the dehydration link.

[0022] Further, the iron-based desulfurizer is at least one of ferrous chloride, ferric chloride, and polyferric sulfate.

[0023] The beneficial effect of the above further technical solution is that the iron-based desulfurizer is at least one of ferrous chloride, ferric chloride, and polyferric sulfate, which facilitates the selection of the type of iron-based desulfurizer according to actual needs and reduces costs.

[0024] Further, the molar ratio of metal ions in the iron-based desulfurizer to sulfides in the sludge is 1.2:1-2.0:1, wherein the concentration of sulfides in the sludge is obtained by an online monitoring device.

[0025] The beneficial effect of the above further technical solution is that the molar ratio of metal ions in the iron-based desulfurizer to sulfides in the sludge is 1.2:1-2.0:1, which facilitates the full reaction of the iron-based desulfurizer and the sulfides in the sludge, so that H2S is solidified in the pretreatment stage, and there is no significant escape in the dehydration link. The soluble sulfide in the liquid phase is converted into stable solid metal sulfide, the generation and escape potential of H2S is eliminated from the source, and the H2S pollution and safety problems in the dehydration workshop are completely solved.

[0026] Further, the pH value of the sludge ranges from 5.0 to 8.5.

[0027] The beneficial effect of the further technical solution is that the pH value of the sludge ranges from 5.0 to 8.5, without additional adjustment, easy to promote in large-scale engineering application.

[0028] Further, the sludge in step S1 is concentrated sludge; and after step S1, the method comprises: S2, dehydrating the sludge by a mechanical dehydration device to generate a sludge cake and a filtrate.

[0029] The beneficial effect of the further technical solution is that the iron salt itself is also a good flocculant, especially ferric chloride and polymeric ferric sulfate, which can significantly improve the floc structure of the sludge, form large and dense alum flowers, thereby synergistically improving the dehydration efficiency, and further reducing the water content of the sludge cake after dehydration.

[0030] The advantages of the additional aspects of the application will be partially given in the following description, partially become obvious from the following description, or be understood by the practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0032] Figure 1 One of the schematic flow block diagrams of the pretreatment method for inhibiting hydrogen sulfide emission in the sludge dewatering process provided by the embodiments of the application.

[0033] Figure 2 One of the schematic flow block diagrams of the pretreatment method for inhibiting hydrogen sulfide emission in the sludge dewatering process provided by the embodiments of the application. DETAILED DESCRIPTION

[0034] The principles and characteristics of the application are described below in conjunction with the drawings, and the embodiments are only used to explain the application and not to limit the scope of the application.

[0035] In order to make the purpose, technical scheme and advantages of the embodiments of the application more clear, the technical scheme in the embodiments of the application will be described clearly and completely below in conjunction with the drawings of the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, not all the embodiments. The components of the embodiments of the application described and shown in the drawings here can be arranged and designed in various different configurations.

[0036] Therefore, the following detailed description of embodiments of the application provided in the accompanying drawings is not intended to limit the scope of the application claimed, but merely represents selected embodiments of the application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the application without creative labor fall within the scope of the application.

[0037] It should be noted that similar reference numbers and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0038] In the description of the embodiments of the application, it should be noted that the orientation or position relationship indicated by the terms "upper", "lower", "horizontal", "inner" and the like is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship when the product of the application is usually placed, and is only for the convenience of describing the application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the application.

[0039] In the description of the embodiments of the application, it should also be noted that unless otherwise explicitly specified and limited, the terms "arranged", "mounted", "connected", "linked" should be understood broadly, for example, can be fixedly connected, can be detachably connected, or integrally connected, can be mechanically connected, or electrically connected, can be directly connected, or indirectly connected through an intermediate medium, or can be connected inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0040] As shown in Figure 1 The embodiment of the application provides a pretreatment method for inhibiting hydrogen sulfide emission in a sludge dewatering process, which comprises the following steps: S1, chemically pretreating the sludge by using an iron-based desulfurizer before dewatering.

[0041] The beneficial effects of the technical scheme of the application are as follows: the specific iron salt is added for pretreatment before mechanical dewatering of the sludge, so that the emission of hydrogen sulfide is inhibited from the source. The specific problem of instantaneous and high-concentration H2S emission caused by physical extrusion in the mechanical dewatering link is solved. Source control and process blocking are achieved.

[0042] The application relates to the technical field of environmental protection, in particular to sludge treatment and malodorous gas control technology, and particularly relates to a method for inhibiting hydrogen sulfide emission from the source by adding a specific iron salt for pretreatment before mechanical dewatering of sludge.

[0043] The iron salt addition point and purpose of the prior art are essentially different from the "source control-process blocking" of the application.

[0044] In view of the deficiencies of the existing end exhaust gas treatment technology, the purpose of the present application is to provide a pretreatment method for inhibiting hydrogen sulfide emission in the sludge dewatering process. The method converts the soluble sulfide in the liquid phase into stable solid metal sulfide by chemical pretreatment of the sludge before dewatering, thereby eliminating the generation and emission potential of H2S from the source and completely solving the H2S pollution and safety problems in the dewatering workshop.

[0045] Further, step S1 comprises: S11, adding an iron-based desulfurizer to the sludge before the sludge enters the mechanical dewatering equipment; and S12, performing a mixing reaction to fix the sulfide before dewatering.

[0046] The beneficial effects of the above further technical solution are: the soluble sulfide in the liquid phase is converted into stable solid metal sulfide by chemical pretreatment of the sludge before dewatering, thereby eliminating the generation and emission potential of H2S from the source and completely solving the H2S pollution and safety problems in the dewatering workshop. No absorption waste liquid that needs subsequent treatment is generated, and the metal sulfide generated by the reaction has stable chemical properties. H2S is solidified in the pretreatment stage, and there is no significant emission in the dewatering link.

[0047] Further, in step S11, the iron-based desulfurizer is added to the sludge through a dosing point before the sludge enters the mechanical dewatering equipment; the mechanical dewatering equipment is a stacked screw dewatering machine, a centrifugal dewatering machine or a plate and frame filter press; and the mechanical dewatering equipment is provided with a mechanical dewatering equipment feed pump.

[0048] The beneficial effects of the above further technical solution are: the sludge after the reaction is conveyed to the mechanical dewatering equipment, such as a stacked screw machine / centrifugal machine / plate and frame filter press, for dewatering.

[0049] Further, in step S11, the dosing point is located in a sludge conditioning tank, a mixing tank or a buffer pool before the mechanical dewatering equipment feed pump.

[0050] The beneficial effects of the above further technical solution are: after the sludge is sequentially concentrated, it enters the pretreatment unit, such as a conditioning tank / mixing tank, where the iron-based desulfurizer is added and mixed. No expensive exhaust gas collection and end treatment system needs to be added, and the existing sludge treatment facilities, such as a sludge conditioning tank, a mixing tank or a buffer pool, can be directly used. The problem can be solved by only adding low-cost reagents, and the comprehensive operating cost is lower than that of the traditional end treatment method.

[0051] Further, in step S12, the mixing reaction time ranges from 0.5 minutes to 5 minutes.

[0052] The beneficial effect of the further technical scheme is that the medicament and the sludge are fully contacted and reacted, so that H2S is solidified in the pretreatment stage, and no significant H2S is emitted in the dehydration stage.

[0053] In the mixing reaction, a normal pressure container (pressure can also be applied) is adopted, and the temperature is set according to the temperature of the sludge raw material (generally normal temperature-85℃).

[0054] Further, in the step S12, when the mixing reaction is performed, the iron-based desulfurizer and the sludge are fully mixed by a mechanical stirrer at a preset speed or by using the turbulence in the pipeline, so that the sulfide is fixed to form a sulfur-containing substance before dehydration, wherein the sulfide is H2S, and the sulfur-containing substance is FeS or elemental S.

[0055] The beneficial effect of the further technical scheme is that the iron-based desulfurizer is added to the sludge before the sludge enters the mechanical dehydration equipment, the iron-based desulfurizer and the sludge are fully mixed by a mechanical stirrer at a preset speed or by using the turbulence in the pipeline, and a full mixing reaction is performed, so that the sulfide is fixed before dehydration. By performing chemical pretreatment on the sludge before dehydration, the soluble sulfide in the liquid phase is converted into stable solid metal sulfide, the generation and emission potential of H2S is eliminated from the source, and the H2S pollution and safety problem in the dehydration workshop are completely solved. No absorption waste liquid needs to be treated subsequently, the metal sulfide generated in the reaction has stable chemical properties, H2S is solidified in the pretreatment stage, and no significant H2S is emitted in the dehydration stage.

[0056] Further, the iron-based desulfurizer is at least one of ferrous chloride, ferric chloride, and polyferric sulfate.

[0057] The beneficial effect of the further technical scheme is that the iron-based desulfurizer is at least one of ferrous chloride, ferric chloride, and polyferric sulfate, so that the type of the iron-based desulfurizer can be selected according to actual needs, and the cost is reduced.

[0058] Further, the molar ratio of metal ions in the iron-based desulfurizer to sulfides in the sludge is 1.2:1-2.0:1, and the concentration of the sulfides in the sludge is obtained by an online monitoring device.

[0059] The beneficial effect of the further technical scheme is that the molar ratio of metal ions in the iron-based desulfurizer to sulfides in the sludge is 1.2:1-2.0:1. The iron-based desulfurizer and the sulfides in the sludge are fully reacted, H2S is solidified in the pretreatment stage, and no significant H2S is emitted in the dehydration stage. The soluble sulfide in the liquid phase is converted into stable solid metal sulfide, the generation and emission potential of H2S is eliminated from the source, and the H2S pollution and safety problem in the dehydration workshop are completely solved.

[0060] Further, the pH value of the sludge ranges from 5.0 to 8.5.

[0061] The beneficial effect of the further technical solution is that the pH value of the sludge ranges from 5.0 to 8.5, without additional adjustment, easy to promote in large-scale engineering applications.

[0062] The pH value of the sludge ranges from 5.0 to 8.5, and the pH interval is not a problem (the lower the pH, the higher the hydrogen sulfide content, and vice versa); the pH adjusting agent can be selected from low-cost industrial raw materials, such as hydrochloric acid, sodium hydroxide, or sodium carbonate.

[0063] Further, the sludge in step S1 is concentrated sludge; and after step S1, the method further comprises: S2, dehydrating the sludge by a mechanical dehydration device to generate a sludge cake and a filtrate.

[0064] The beneficial effect of the further technical solution is that the iron salt itself is also a good flocculant, especially ferric chloride and polymeric ferric sulfate, which can significantly improve the floc structure of the sludge, form large and dense alum flowers, thereby synergistically improving the dewatering efficiency, and further reducing the water content of the dewatered sludge cake.

[0065] The pretreatment method provided by the embodiment of the present application can inhibit the escape of hydrogen sulfide in the sludge dewatering process. Before the sludge enters the mechanical dehydration device, an iron-based desulfurizer is added to the sludge and fully mixed to fix the sulfides before dewatering. The iron-based desulfurizer is at least one of ferrous chloride, ferric chloride, and polymeric ferric sulfate.

[0066] Preferably, the mechanical dehydration device is a stacked screw dewatering machine, a centrifugal dewatering machine, or a plate and frame filter press.

[0067] Preferably, the addition point is located in a sludge conditioning tank, a mixing tank, or a buffer pool before a feed pump of the mechanical dehydration device.

[0068] Preferably, the molar ratio of metal ions in the iron-based desulfurizer to sulfides in the sludge is 1.2:1 to 2.0:1.

[0069] Preferably, the mixing reaction time after addition is 0.5 minutes to 5 minutes.

[0070] Preferably, the pH value of the sludge ranges from 5.0 to 8.5, without additional adjustment.

[0071] 1. Source control, efficient and thorough: from the root cause, the easily escaping H2S is fixed into a metal sulfide (such as FeS, elemental S, etc.) with extremely stable chemical properties, achieving “both treatment and prevention”. The H2S concentration in the dewatering workshop can be reduced from >100 ppm to <10 ppm, with a removal rate of more than 95%, which is much higher than the end treatment method, and fully meets the occupational health and safety standards.

[0072] 2. Significant cost-effectiveness: There is no need to add expensive waste gas collection and end-of-pipe treatment systems. Existing sludge treatment facilities (such as conditioning tanks) can be used directly, and the problem can be solved simply by adding low-cost agents. The overall operating cost can be reduced by about 40% compared with traditional end-of-pipe treatment methods.

[0073] 3. Environmentally friendly and free from secondary pollution: It does not produce absorption waste liquid that requires subsequent treatment. The metal sulfides generated in the reaction are chemically stable and have leaching toxicity lower than the limit of the "Identification Standard for Hazardous Waste - Leaching Toxicity Identification" (GB 5085.3-2007), posing no environmental risk.

[0074] 4. Synergistic improvement of dewatering performance: Iron salts are also good flocculants, especially ferric chloride and polyferric sulfate, which can significantly improve the floc structure of sludge and form large and dense flocs, thereby synergistically improving dewatering efficiency and further reducing the moisture content of the dewatered sludge cake by 2-3%.

[0075] 5. Simple operation and strong adaptability: This method can be directly embedded into the existing sludge treatment process without changing the main process. It has a wide adaptability range to the original pH of sludge (5.0-8.5), and engineers do not need to carry out complicated debugging. It is easy to promote and apply on a large scale in engineering projects.

[0076] like Figure 2 As shown, after initial concentration, the sludge enters the pretreatment unit (conditioning tank / mixing tank), where an iron-based desulfurizing agent is added and mixed. The reacted sludge is then pumped to mechanical dewatering equipment (screw press / centrifuge / plate and frame filter press) for dewatering. Throughout the process, H2S is solidified during the pretreatment stage, with no significant escape during dewatering. Specifically, the process is as follows: concentrated sludge → pretreatment unit (conditioning tank / mixing tank) → addition of iron-based desulfurizing agent (FeCl2 / FeCl3 / PFS) → mixing and reaction (0.5-5 minutes) → reacted sludge (sulfides fixed) → mechanical dewatering equipment → sludge cake (low H2S escape) and filtrate.

[0077] All reagents used are commercially available industrial-grade products.

[0078] Example 1: Treatment of oily wastewater sludge using ferrous chloride Scenario: In the sludge dewatering workshop of a certain oilfield joint treatment station, a centrifugal dewatering machine is used. During the dewatering process, the peak concentration of H2S reaches 238ppm.

[0079] step: 1. Add freshly prepared 10% ferrous chloride solution to the sludge conditioning tank before the centrifuge feed pump.

[0080] 2. The dosage is controlled based on the concentration of sulfides in the sludge monitored online. 2+With S 2- a molar ratio of 1.5:1.

[0081] 3. After dosing, turn on the mechanical stirrer in the conditioning tank and stir at medium speed (about 80 rpm) for 3 minutes to ensure that the reagent and sludge are in full contact and reaction.

[0082] 4. The reacted sludge enters the centrifugal dewatering machine for regular dewatering.

[0083] Effect detection: The peak concentration of H2S in the dewatering room environment air is reduced to 7 ppm. The produced mud cake is detected, and the sulfide fixation rate is greater than 99%, and the moisture content of the mud cake is reduced by 2.5% compared with that without dosing.

[0084] Example 2: Using ferric chloride to treat high-sulfur hydrogen sulfide sludge in high-sulfur oilfields Scenario: The sulfur-containing sludge in a certain oilfield joint treatment station has extremely serious H2S emission during plate and frame filter dewatering, with a concentration exceeding 500 ppm.

[0085] Steps: 1. In the conditioning tank before the plate and frame filter machine feed pump, add 10% concentration ferric chloride solution.

[0086] 2. Control the molar ratio of Fe 3+ to S 2- to be 1.8:1.

[0087] 3. After dosing, first stir quickly (120 rpm) for 1.5 minutes, and then slow stirring (40 rpm) for 3 minutes to facilitate floc growth.

[0088] 4. The reacted sludge enters the plate and frame filter.

[0089] Effect detection: The H2S concentration in the dewatering room is reduced to below 5 ppm. The moisture content of the mud cake is reduced from 85% to 80%, and the floc is dense and has better peelability.

[0090] Example 3: Using polymeric ferric sulfate to treat dilute oil sludge Scenario: There is a persistent odor and H2S problem in the sludge dewatering workshop of a certain oilfield joint treatment station, and the dewatering effect is unstable.

[0091] Steps: 1. In the pipe mixer before the decanter dewatering machine, continuously add diluted polymeric ferric sulfate solution (5% concentration).

[0092] 2. Control the molar ratio of total iron to S 2- to be 1.4:1.

[0093] 3. Use the turbulence in the pipe to achieve instantaneous mixing and reaction of the reagent.

[0094] 4. Sludge then enters the decanter dewaterer.

[0095] Effect detection: Environmental odor and H2S are fundamentally controlled (concentration <8 ppm). The sludge discharged from the decanter is more uniform and continuous, and the moisture content of the sludge cake is stable and about 3% lower than before.

[0096] Comparative Example 1 In the same municipal sewage treatment plant (same as Example 1 scenario), without adding iron-based desulfurizer, only using traditional alkali liquid spray tower to treat the exhaust gas after ventilation and gas exchange of the dewatering room.

[0097] Effect detection: Although the exhaust gas treatment system is put into operation, due to the problem of collection efficiency, the average concentration of H2S in the dewatering room still maintains about 50 ppm, and the peak value can reach 80 ppm. At the same time, about 0.5 tons of sulfur-containing waste liquid generated by absorbing H2S need to be treated daily, increasing the subsequent disposal cost.

[0098] Through the comparison of the example and the comparative example, it can be seen that the method (pre-treatment method for inhibiting hydrogen sulfide emission in sludge dewatering process) has overwhelming advantages in environmental improvement effect, operation cost, energy consumption and secondary pollution control.

[0099] Comparative Example 2 In the same municipal sewage treatment plant (same as Example 1 scenario), a dosing point is directly set in the middle section of the feed pipe of the centrifugal dewaterer, and the same kind (10% ferrous chloride solution) and the same molar ratio (Fe 2+ :S 2- =1.5:1) of iron-based desulfurizer are added.

[0100] Mixing method: rely on natural turbulence during the dewaterer feeding process for mixing, without additional stirring or reserved reaction time.

[0101] Reaction time: from dosing to sludge discharge, the total residence time in the dewaterer is about 10-30 seconds, which is much shorter than 3 minutes in Example 1.

[0102] Dewatering process: sludge simultaneously undergoes desulfurization reaction and mechanical dewatering in the dewaterer.

[0103] Effect detection: Although the same kind (10% ferrous chloride solution) and the same molar ratio (Fe 2+ :S 2- =1.5:1) of iron-based desulfurizer are added in the middle section of the feed pipe of the centrifugal dewaterer, due to the problem of instantaneous and high-concentration H2S emission caused by physical extrusion in the mechanical dewatering process, the H2S removal rate in Comparative Example 2 is 60%-75%. At the same time, the subsequent disposal cost is increased.

[0104] By comparing the examples with the comparative examples, it can be seen that the method (pretreatment method for inhibiting hydrogen sulfide emission in sludge dewatering process) of the present application has overwhelming advantages in environmental improvement effect, operation cost, energy consumption and secondary pollution control. The specific problem of "instantaneous and high-concentration H2S emission in mechanical dewatering link" is solved.

[0105] 1) The preposition of the addition position (pretreatment unit before dewatering) is the key to the high efficiency and stability of the present application. Only by adding here can the iron-based desulfurizer provide sufficient reaction time and mixing conditions to achieve complete fixation of sulfides before dewatering, thereby truly realizing "source control".

[0106] 2) Technical advantage: Compared with in-machine addition, pretreatment before dewatering not only has higher H2S removal rate (H2S removal rate > 99% in the present application vs. H2S removal rate 60%-75% in Comparative Example 2), but also can synergistically improve dewatering efficiency, and is more stable and easier to integrate into existing processes.

[0107] 3) Industrial application significance: The present comparative example further proves that simply using the same medicament but with incorrect addition position cannot solve the specific problem of "instantaneous and high-concentration H2S emission in mechanical dewatering link". Thus highlighting the innovation and practicality of the present application in process design.

[0108] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A pretreatment method for inhibiting hydrogen sulfide emission in a sludge dewatering process, characterized by, The method comprises the following steps: S1, chemically pretreating the sludge by an iron-based desulfurizer before dehydration; step S1 comprises: S11, adding the iron-based desulfurizer into the sludge before the sludge enters a mechanical dehydration device; S12, performing a mixing reaction to fix sulfides before dehydration; in step S11, the iron-based desulfurizer is added into the sludge through a dosing point before the sludge enters the mechanical dehydration device; the mechanical dehydration device is a stacked screw dewaterer, a centrifugal dewaterer or a plate-and-frame filter press; the mechanical dehydration device is provided with a mechanical dehydration device feed pump; in step S11, the dosing point is located in a sludge conditioning tank, a mixing tank or a buffer tank before the mechanical dehydration device feed pump; in step S12, the time range of the mixing reaction is 0.5 minutes to 5 minutes; in step S12, the iron-based desulfurizer and the sludge are fully mixed by stirring at a preset speed through a mechanical stirrer or utilizing turbulent flow in a pipeline to fix the sulfides to form sulfur-containing substances before dehydration, wherein the sulfides are H2S, and the sulfur-containing substances are FeS or elemental S; the iron-based desulfurizer is at least one of ferrous chloride, ferric chloride and polyferric sulfate; the molar ratio of metal ions in the iron-based desulfurizer to sulfides in the sludge is 1.2:1 to 2.0:1, wherein the sulfide concentration in the sludge is obtained by an online monitoring device.

2. The pretreatment method of claim 1, wherein the method is characterized by, The pH value of the sludge ranges from 5.0 to 8.

5.

3. The pretreatment method of claim 1, wherein the method is characterized by, The sludge in step S1 is concentrated sludge.

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