Method and system for recycling sodium sulfide through anaerobic treatment of leather wastewater

Abstract

The invention discloses a method and a system for recovering sodium sulfide through anaerobic treatment of leather wastewater, and belongs to the technical field of tannery wastewater treatment and resource recovery. The method for recycling sodium sulfide through anaerobic treatment of leather wastewater comprises the following steps: sequentially carrying out pretreatment and water quality regulation on high-sulfur leather wastewater to obtain tempered wastewater; feeding the conditioned wastewater into an anaerobic reactor for anaerobic treatment, and separating to obtain H2S-containing biogas and desulfurized wastewater; introducing the obtained H2S-containing biogas into alkali liquor for neutralization reaction to obtain sodium sulfide and desulfurized biogas; the anaerobic reactor is an internal circulation anaerobic reactor or an up-flow anaerobic sludge blanket reactor. According to the method, H2S generated in the anaerobic process reacts with additional cheap alkali (NaOH) to generate Na2S, and the sulfur element traditionally serving as a pollutant is converted into commercial sodium sulfide with market value.

Description

Technical Field

[0001] This invention belongs to the field of leather wastewater treatment and resource recycling technology, and particularly relates to a method and system for anaerobic treatment of leather wastewater to recover sodium sulfide. Background Technology

[0002] In the leather manufacturing process, the ash-alkali dehairing section generates a large amount of high-concentration organic wastewater, characterized by high chemical oxygen demand (COD), high suspended solids, and high concentrations of sulfides (mainly in the form of sodium sulfide). Other sections also introduce sulfates. Traditional treatment methods often employ a "physicochemical pretreatment (such as catalytic oxidation) + aerobic biological treatment" process, which has the following drawbacks: 1) Resource waste: The sulfides (S...) in the wastewater... 2- 1) It is oxidized into elemental sulfur or sulfate, and the high-value sodium sulfide cannot be recovered; 2) High operating cost: The oxidation process requires the addition of a large amount of catalyst or oxidant (such as air, hydrogen peroxide, ferrous sulfate, etc.), and the cost of the reagents is high; 3) Risk of secondary pollution: Improper treatment can easily produce toxic hydrogen sulfide gas to escape, or form sulfur-containing sludge, causing secondary pollution; 4) Unutilized carbon source: The abundant organic matter in the wastewater is only oxidized and degraded, and no energy utilization is achieved.

[0003] Although existing technologies have proposed methods for recovering sulfur from wastewater, they mostly focus on recovering elemental sulfur or sulfuric acid, and suffer from drawbacks such as complex processes and poor economic efficiency. Therefore, developing a process that can simultaneously achieve efficient removal of pollutants, production of organic matter, and direct recovery of high-value chemical products such as sodium sulfide has significant environmental and economic benefits. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method and system for anaerobic treatment and recovery of sodium sulfide from leather wastewater.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for anaerobic treatment and recovery of sodium sulfide from leather wastewater, comprising the following steps: pretreating and conditioning high-sulfur leather wastewater sequentially to obtain conditioning wastewater; sending the conditioning wastewater into an anaerobic reactor for anaerobic treatment, and separating it to obtain biogas containing H2S and desulfurized wastewater; passing the H2S-containing biogas into an alkaline solution for neutralization reaction to obtain sodium sulfide and desulfurized biogas.

[0007] The anaerobic reactor is either an internal circulation anaerobic reactor or an upflow anaerobic sludge bed reactor.

[0008] Furthermore, the water quality conditioning includes: mixing pretreated high-sulfur leather wastewater and low-sulfur organic wastewater to obtain conditioning wastewater;

[0009] The concentration of sulfides in the high-sulfur leather wastewater is 800~2700 mg / L, and the concentration of sulfate is 3000~5000 mg / L;

[0010] The low-sulfur organic wastewater is leaching wastewater, acid leaching wastewater, or tanning wastewater; the concentration of sulfides in the low-sulfur organic wastewater is 10~30 mg / L;

[0011] The volume percentage of high-sulfur leather wastewater in the conditioning wastewater is 15-25%;

[0012] The conditioned wastewater has a sulfide concentration ≤300mg / L, a pH value of 6.5~7.5, and a temperature of 25±2℃~35±2℃.

[0013] Furthermore, the flow rate of the conditioning wastewater fed into the anaerobic reactor is 100 m / s. 3 / h.

[0014] Furthermore, the anaerobic reactor has an oxidation-reduction potential ≤300mV, a hydraulic retention time of 27h, and an upward flow velocity of 0.66m / h.

[0015] Furthermore, the anaerobic reactor contains sulfate-reducing bacteria and methanogenic bacteria.

[0016] Furthermore, the flow rate of the H2S-containing biogas is 80~110 m / h; the concentration of the sodium hydroxide solution is 2~10 mol / L.

[0017] The present invention provides a system for the method described in the above technical solution, comprising a pretreatment unit, an anaerobic reaction unit, a biogas desulfurization unit, a resource recovery unit, and a sodium sulfide recovery unit.

[0018] Furthermore, the pretreatment unit includes a screen, a sedimentation tank, an equalization tank, and a pH / temperature adjustment device.

[0019] Furthermore, the anaerobic reaction unit includes an anaerobic reactor and an online monitoring and control system for oxidation-reduction potential, pH, and temperature.

[0020] Furthermore, the biogas desulfurization unit includes a biogas desulfurization tower, an alkali storage tank, and an alkali circulation pump.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects:

[0022] The method for anaerobic treatment and recovery of sodium sulfide from leather wastewater provided by this invention has the following advantages: (1) High-efficiency resource recovery: The H2S generated by the anaerobic process reacts with the added inexpensive alkali (NaOH) to generate Na2S, converting sulfur, which is traditionally a pollutant, into commercial sodium sulfide with market value, creating significant economic benefits and offsetting part of the operating costs; (2) Environmentally friendly: The entire process realizes a closed-loop sulfur cycle, avoiding H2S air pollution and the generation of sulfur-containing sludge. The anaerobic process also removes a large amount of COD and produces clean energy methane; (3) High treatment efficiency: The improved high-efficiency anaerobic reactor is used, and the removal rates of sulfides and COD can reach more than 80%. The load on the subsequent aerobic treatment system is greatly reduced when the effluent enters the system. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1 This is a process flow diagram of the method for anaerobic treatment and recovery of sodium sulfide from leather wastewater in Example 1;

[0025] Figure 2 This is a schematic diagram of the system used in the anaerobic treatment and sodium sulfide recovery method for leather wastewater in Example 1; wherein, 1 is the pretreatment system, 1.1 is the bar screen, 1.2 is the sedimentation tank, 1.3 is the equalization tank, 1.4 is the pH / temperature adjustment device, 2 is the anaerobic reactor, 2.1 is the lift pump, 2.2 is the anaerobic reactor inlet, 2.3 is the return pipe, 2.4 is the anaerobic reactor outlet, 2.5 is the biogas inlet, 2.6 is the sulfur-containing biogas outlet, 2.7 is the biogas pipe, and 3 is the gas-liquid separator. 3.1 is the inlet of the gas-liquid separator, 3.2 is the biogas outlet of the gas-liquid separator, 3.3 is the reflux liquid outlet of the gas-liquid separator, 4 is the biogas desulfurization tower, 4.1 is the biogas inlet of the biogas desulfurization tower, 4.2 is the biogas outlet of the biogas desulfurization tower, 4.3 is the circulating liquid outlet of the biogas desulfurization tower, 4.4 is the circulating liquid inlet of the biogas desulfurization tower, 5 is the NaOH alkali solution storage tank, 6 is the alkali solution circulation pump, 7 is the biogas storage tank, 8 is the biogas blower, 9 is the water inlet of the pretreatment system, and 10 is the biogas utilization outlet. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] This invention provides a method for anaerobic treatment and recovery of sodium sulfide from leather wastewater, comprising the following steps: pretreating and conditioning high-sulfur leather wastewater sequentially to obtain conditioning wastewater; sending the conditioning wastewater into an anaerobic reactor for anaerobic treatment, and separating it to obtain biogas containing H2S and desulfurized wastewater; passing the H2S-containing biogas into a sodium hydroxide solution for neutralization reaction to obtain sodium sulfide and desulfurized biogas.

[0029] In a preferred embodiment, the pretreatment specifically involves removing large particulate impurities from the high-sulfur leather wastewater by passing it through a screen and sedimentation.

[0030] In a preferred embodiment, the water quality conditioning includes: mixing pretreated high-sulfur leather wastewater and low-sulfur organic wastewater to obtain conditioned wastewater.

[0031] In a preferred embodiment, during the water quality conditioning process, the concentration of sulfides in the high-sulfur leather wastewater is 800~2700 mg / L, and the concentration of sulfate is 3000~5000 mg / L.

[0032] In a preferred embodiment, during the water quality conditioning process, the low-sulfur organic wastewater is leaching wastewater, acid leaching wastewater, or tanning wastewater; the concentration of sulfides in the low-sulfur organic wastewater is 10~30 mg / L.

[0033] In a preferred embodiment, during the water quality conditioning process, the volume percentage of high-sulfur leather wastewater in the conditioning wastewater is 15-25%.

[0034] In a preferred embodiment, the sulfide concentration of the conditioning wastewater is ≤300 mg / L, more preferably 200 mg / L; the sulfate concentration of the conditioning wastewater is ≤4000 mg / L, more preferably 3970 mg / L; the pH value of the conditioning wastewater is 6.5~7.5, more preferably 7.0; and the temperature of the conditioning wastewater is 25±2℃~35±2℃, more preferably 35±2℃.

[0035] In a preferred embodiment, the flow rate of the conditioning wastewater fed into the anaerobic reactor is 100 m / s. 3 / h.

[0036] In a preferred embodiment, the anaerobic reactor is an internal circulation anaerobic reactor (IC) or an upflow anaerobic sludge blanket reactor (UASB); the anaerobic reactor is equipped with a stripping gas collection hood and a stripping perforated pipe. This invention employs an anaerobic reactor equipped with a stripping gas collection hood and a stripping perforated pipe. The stripping perforated pipe is stripped and collected by the stripping gas collection hood, then lifted to a gas-liquid separator for gas-liquid separation and drying, and then desulfurized by a desulfurization tower. Starting a blower accelerates the biogas flow rate, allowing the biogas to re-enter the reactor, the stripping perforated pipe, and the stripping gas collection hood, thereby reducing the hydrogen sulfide content inside the reactor, reducing inhibition of anaerobic bacteria, and thus improving the anaerobic treatment efficiency of leather wastewater.

[0037] In a preferred embodiment, the anaerobic reactor contains sulfate-reducing bacteria (SRB) and methanogenic bacteria (MPA). Under strictly anaerobic conditions, sulfate / sulfite in the wastewater is reduced to sulfides (S) by sulfate-reducing bacteria (SRB). 2- / HS - Meanwhile, the complex organic matter in the wastewater is degraded into methane and carbon dioxide by methanogenic bacteria (MPA).

[0038] In a preferred embodiment, the anaerobic reactor has an oxidation-reduction potential (ORP) ≤ 300 mV, a hydraulic retention time (HRT) of 27 h, and an upflow velocity of 0.66 m / h. This invention optimizes the metabolic balance between sulfate-reducing bacteria and methanogenic bacteria by controlling the ORP, hydraulic retention time, and upflow velocity of the anaerobic reactor, thereby achieving efficient sulfate reduction and stable methanogenesis from organic matter.

[0039] In a preferred embodiment, the volume percentage of H2S in the H2S-containing biogas is 5-20%, and the flow rate of the H2S-containing biogas is 80-110 m / h; the concentration of the sodium hydroxide solution is 2-10 mol / L. The biogas produced by the anaerobic reactor is rich in H2S and CH4. After the sodium hydroxide solution is introduced, it can absorb the H2S in the biogas. The H2S reacts with NaOH to form sodium sulfide (Na2S) solution, which is efficiently absorbed. The reaction formula is: H2S + 2NaOH → Na2S + 2H2O. The purified methane gas (H2S content <50 ppm) can be recovered as an energy source.

[0040] In a preferred embodiment, the sulfur-rich (Na2S) solution produced by the neutralization reaction can be used directly in leather production, or it can be further processed to precipitate sodium sulfide nonahydrate (Na2S·9H2O) crystals or anhydrous sodium sulfide through evaporation crystallization, thereby obtaining a finished product that meets industrial standards (such as "HG / T 6079-2022" industrial sodium sulfide).

[0041] The present invention provides a system for the method described in the above technical solution, comprising a pretreatment unit, an anaerobic reaction unit, a biogas desulfurization unit, a resource recovery unit, and a sodium sulfide recovery unit.

[0042] In a preferred embodiment, the pretreatment unit includes a screen, a sedimentation tank, an equalization tank, and a pH / temperature adjustment device.

[0043] In a preferred embodiment, the anaerobic reaction unit includes an anaerobic reactor and an online monitoring and control system for oxidation-reduction potential, pH, and temperature.

[0044] In a preferred embodiment, the biogas desulfurization unit includes a biogas desulfurization tower, an alkali storage tank, and an alkali circulation pump.

[0045] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0046] Example 1

[0047] A method for anaerobic treatment and recovery of sodium sulfide from leather wastewater, process flow diagram is shown below. Figure 1 The structural diagram of the system used is shown in [reference needed]. Figure 2 The specific steps are as follows:

[0048] (1) High-sulfur leather wastewater with a sulfide concentration of 850 mg / L and a sulfate concentration of 4500 mg / L is sent to pretreatment system 1 through pretreatment system inlet 9. Large particulate impurities are removed by screen 1.1 and sedimentation tank 1.2 to obtain pretreated high-sulfur leather wastewater. Then, it enters equalization tank 1.3 and is mixed with low-sulfur wastewater with a sulfide concentration of 25 mg / L. The pH value of the mixed solution is adjusted to 7.0 and the temperature is 35℃ by pH / temperature adjustment device 1.4 to obtain conditioned wastewater with a sulfide concentration of 200 mg / L, a sulfate concentration of 3970 mg / L and a COD of 8000 mg / L. Among them, the volume ratio of high-sulfur leather wastewater in conditioned wastewater is 21.2%.

[0049] (2) The conditioning wastewater obtained in step (1) is treated with 100m³ of water. 3 The flow rate of / h is pumped from the anaerobic reactor inlet 2.2 into an effective volume of 2700m³ via booster pump 2.1. 3In anaerobic reactor 2, which is an internal circulation anaerobic reactor, sulfate-reducing bacteria and methanogenic bacteria are contained. The oxidation-reduction potential of the anaerobic reactor is 300 mV, the HRT is 27 h, and the water flow rate is 0.66 m / h for anaerobic treatment, yielding desulfurization wastewater and sulfur-containing biogas carrying sludge. The desulfurization wastewater is then discharged from the anaerobic reactor outlet 2.4. The discharged desulfurization wastewater shows a reduction in sulfide concentration to below 50 mg / L, sulfate concentration to below 600 mg / L, and COD removal rate to [missing value]. 87.5%; Sulfur-containing biogas carrying mud and water enters gas-liquid separator 3 from sulfur-containing biogas outlet 2.6 via biogas pipe 2.7 through gas inlet 3.1 for separation, yielding biogas containing H2S (H2S volume content of 13.57%) and mud and water; the mud and water flow back to anaerobic reactor 2 through gas-liquid separator return liquid outlet 3.3 into return pipe 2.3 installed inside anaerobic reactor 2; H2S-containing biogas is discharged through gas-liquid separator biogas outlet 3.2 and then enters biogas desulfurization tower biogas inlet 4.1 for biogas desulfurization. In tower 4, a 10 mol / L NaOH solution from the NaOH alkali storage tank 5 is simultaneously introduced into the biogas desulfurization tower 4 via the alkali circulation pump 6 from the circulating liquid inlet 4.4 for neutralization and desulfurization. The reaction endpoint is controlled so that the mass concentration of the NaOH solution is not less than 1%, and the H2S absorption rate is >98%, yielding desulfurized biogas and sodium sulfide solution. The sodium sulfide solution and NaOH solution flow out from the circulating liquid outlet 4.3 of the biogas desulfurization tower and then enter the NaOH alkali storage tank 5 for circulating spray absorption of H2S. When the mass concentration of the OH solution is 1%, it is discharged from the desulfurization system, and a new 10 mol / L NaOH solution is prepared for desulfurization. The desulfurized biogas escapes from the biogas outlet 4.2 of the biogas desulfurization tower and enters the biogas storage tank 7. Then, it enters the anaerobic reactor 2 through the biogas blower 8 from the biogas inlet 2.5 for stripping to remove H2S dissolved in the mud water. It then enters the gas-liquid separator 3 through the sulfur-containing biogas outlet 2.6 and biogas pipe 2.7. Finally, it is discharged from the biogas outlet 3.2 of the gas-liquid separator and enters the biogas desulfurization tower 4 to achieve circulation.

[0050] The results showed that after treating the high-sulfur leather wastewater using the method in Example 1, approximately 18725 Nm³ of biogas containing H₂S was produced per day. 3 Approximately 57.8 tons of 15% Na₂S solution can be obtained daily. This Na₂S solution can be directly reused in leather processing, or it can be evaporated and concentrated to 28%, cooled to 10°C for crystallization, and then centrifuged and dried to obtain flake sodium sulfide with a purity ≥95%, with a daily output of approximately 9.13 tons. Methane production is approximately 3668 Nm³. 3 / d; The purified desulfurized biogas contains less than 100 ppm H2S and can be used as boiler fuel.

[0051] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for anaerobic treatment and recovery of sodium sulfide from leather wastewater, characterized in that, Includes the following steps: High-sulfur leather wastewater is pretreated and conditioned sequentially to obtain conditioned wastewater; the conditioned wastewater is sent to an anaerobic reactor for anaerobic treatment, and separated to obtain biogas containing H2S and desulfurized wastewater; the H2S-containing biogas is passed into a sodium hydroxide solution for neutralization reaction to obtain sodium sulfide and desulfurized biogas. The anaerobic reactor is either an internal circulation anaerobic reactor or an upflow anaerobic sludge bed reactor.

2. The method for anaerobic treatment and recovery of sodium sulfide from leather wastewater according to claim 1, characterized in that, The water quality conditioning includes: mixing pretreated high-sulfur leather wastewater and low-sulfur organic wastewater to obtain conditioning wastewater; The concentration of sulfides in the high-sulfur leather wastewater is 800~2700 mg / L, and the concentration of sulfate is 3000~5000 mg / L; The low-sulfur organic wastewater is leaching wastewater, acid leaching wastewater, or tanning wastewater; the concentration of sulfides in the low-sulfur organic wastewater is 10~30 mg / L; The volume percentage of high-sulfur leather wastewater in the conditioning wastewater is 15-25%; The conditioned wastewater has a sulfide concentration ≤300mg / L, a pH value of 6.5~7.5, and a temperature of 25±2℃~35±2℃.

3. The method for anaerobic treatment and recovery of sodium sulfide from leather wastewater according to claim 1, characterized in that, The flow rate of the conditioning wastewater fed into the anaerobic reactor is 100 m / s. 3 / h.

4. The method for anaerobic treatment and recovery of sodium sulfide from leather wastewater according to claim 1, characterized in that, The anaerobic reactor has an oxidation-reduction potential of ≤300mV, a hydraulic retention time of 27h, and an upward flow velocity of 0.66m / h.

5. The method for anaerobic treatment and recovery of sodium sulfide from leather wastewater according to claim 1, characterized in that, The anaerobic reactor contains sulfate-reducing bacteria and methanogenic bacteria.

6. The method for anaerobic treatment and recovery of sodium sulfide from leather wastewater according to claim 1, characterized in that, The flow rate of the H2S-containing biogas is 80~110 m / h; the concentration of the sodium hydroxide solution is 2~10 mol / L.

7. A system for use in the method according to any one of claims 1 to 6, characterized in that, It includes a pretreatment unit, an anaerobic reaction unit, a biogas desulfurization unit, a resource recovery unit, and a sodium sulfide recovery unit.

8. The system according to claim 7, characterized in that, The pretreatment unit includes a screen, a sedimentation tank, an equalization tank, and a pH / temperature adjustment device.

9. The system according to claim 7, characterized in that, The anaerobic reaction unit includes an anaerobic reactor and an online monitoring and control system for oxidation-reduction potential, pH, and temperature.

10. The system according to claim 7, characterized in that, The biogas desulfurization unit includes a biogas desulfurization tower, an alkali storage tank, and an alkali circulation pump.

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