Study on Treatment Process of Acid Mine Drainage Based on Sulfate-reducing Bacteria

Abstract

The present application relates to the technical field of acid mine drainage treatment, and specifically discloses an acid mine drainage coupling treatment system and process. In view of the problems of incomplete heavy metal removal, large pH fluctuation of effluent and ammonia nitrogen residue in the traditional process, the present application constructs a lime pre-precipitation unit, a urease-producing bacteria biological mineralization unit, an ammonia nitrogen stripping unit and a sulfate-reducing bacteria immobilization reaction unit. After the wastewater is sequentially subjected to lime neutralization and precipitation, urease-producing bacteria enhanced precipitation, ammonia stripping and CO2 pre-neutralization to adjust pH, it enters the sulfate-reducing bacteria reactor, and simultaneously realizes sulfate reduction, heavy metal sulfide precipitation and pH increase. The present application has low treatment cost, low sludge yield, stable and up-to-standard effluent, and can recover high-purity heavy metal sulfide, and is suitable for mine acid wastewater treatment and resource utilization.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to the field of treatment and resource utilization of acidic mine wastewater, and particularly to a coupled treatment system and method for acidic mine wastewater. Background Technology

[0002] Acid mine wastewater (AMD) is acidic wastewater produced during mining operations by the oxidation of sulfide minerals (mainly pyrite) under the influence of air, water, and microorganisms. Its typical characteristics include low pH (2.5-4.0), high sulfate content (1000-5000 mg / L), and high concentrations of heavy metal ions (such as Cu). 2+ Zn 2+ Pb 2+ (etc.) and ammonia nitrogen pollutants. my country produces approximately 500-1 billion tons of AMD annually. If discharged directly without effective treatment, it will lead to acidification of downstream water bodies, heavy metal pollution, and severe damage to ecosystems.

[0003] Currently, the mainstream treatment process for acidic mine wastewater is lime neutralization and precipitation, and its derivative processes. This type of process raises the pH of the wastewater by adding lime slurry, causing heavy metal ions to precipitate and be removed as hydroxides. However, the lime neutralization method has the following prominent problems:

[0004] (1) Heavy metals are not completely removed, especially amphoteric metals, which are prone to re-dissolution when pH fluctuates, making it difficult for the effluent to consistently meet the standards;

[0005] (2) The pH of the effluent needs to be precisely controlled. In actual operation, the pH fluctuates greatly and often requires two or three chemical adjustments.

[0006] (3) The ammonia nitrogen in the wastewater cannot be effectively removed, resulting in excessive ammonia nitrogen residue in the effluent;

[0007] (4) The amount of sludge generated is large (0.8-1.2 kg / m³), and sludge containing heavy metal hydroxides is usually identified as hazardous waste, resulting in high disposal costs;

[0008] (5) The treatment cost is high, with the cost of reagents reaching 12-20 yuan / ton of water. There is a lack of resource recovery methods, and valuable metals such as copper and zinc in the wastewater are not effectively utilized.

[0009] In recent years, sulfate-reducing bacteria (SRB) biological treatment technology has attracted widespread attention due to its combined functions of sulfate reduction, heavy metal sulfide precipitation, and pH enhancement. Under anaerobic conditions, SRB metabolizes using sulfate as an electron acceptor, producing hydrogen sulfide, which forms metal sulfide precipitates with extremely low solubility with heavy metal ions, thus achieving deep removal of heavy metals. However, existing SRB treatment technologies still face several engineering bottlenecks: ammonia nitrogen is significantly toxic to SRB, inhibiting its sulfate reductase activity; SRB is pH sensitive, with a narrow optimal range (pH 6.5-7.5), and fluctuations in actual AMD water quality easily lead to bacterial inactivation; free SRB cells are easily lost with the water flow, resulting in long reactor start-up periods (typically 30-60 days); and SRB metabolic activity decreases sharply under low-temperature conditions, limiting the application of the process in high-altitude, cold-region mines. Furthermore, existing technologies often employ single SRB treatment or simple chemical precipitation-SRB series connection, lacking system coupling and parameter synergistic optimization of each unit, leading to insufficient overall treatment efficiency and operational stability.

[0010] To address the aforementioned problems, this invention provides a coupled treatment system and method for acidic mine wastewater, aiming to solve comprehensive technical challenges such as incomplete heavy metal removal, large pH fluctuations in effluent, ammonia nitrogen residue, SRB engineering bottlenecks, and resource waste in traditional processes. Summary of the Invention

[0011] (a) Purpose of the invention

[0012] This invention addresses the problems of incomplete heavy metal removal, large pH fluctuations in effluent, difficulty in removing ammonia nitrogen, easy inactivation of SRB bacteria, and waste of valuable metal resources in existing acidic mine wastewater treatment technologies. It provides a coupled treatment system and method for acidic mine wastewater to achieve efficient and simultaneous removal of sulfate, heavy metals, and ammonia nitrogen, reduce treatment costs, reduce sludge production, and simultaneously recover valuable metal resources from the wastewater.

[0013] (II) Technical Solution

[0014] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0015] A coupled treatment system for acidic mine wastewater includes a lime pre-precipitation unit, a urease-producing bacteria biomineralization unit, an ammonia nitrogen stripping unit, a pH adjustment unit, and a sulfate-reducing bacteria immobilization reaction unit connected in sequence.

[0016] The lime pre-precipitation unit includes a lime storage tank, a metering pump, and a stirring reaction tank, which is used to add lime water to the wastewater for preliminary neutralization and co-precipitation with heavy metals.

[0017] The urease-producing bacteria biomineralization unit includes a urease-producing bacteria culture tank, a urea storage tank, and a mineralization reaction pool. It is used to add urease-producing bacteria and urea to wastewater that has been pre-treated with lime to induce carbonate precipitation to further remove residual heavy metals and achieve solid-liquid separation.

[0018] The ammonia nitrogen stripping unit includes a stripping tower and a blower, and is used to remove ammonia nitrogen from wastewater.

[0019] The pH adjustment unit includes a CO2 storage tank, a gas diffusion device, and a precision pH control system, which is used to introduce CO2 into the wastewater treated by ammonia nitrogen stripping for pre-neutralization and to precisely adjust the pH to 6.5-7.5.

[0020] The sulfate-reducing bacteria immobilization reaction unit is a closed fixed-bed reactor, with sulfate-reducing bacteria attached to the surface of the carrier. A negative pressure gas collection port is located at the top of the reactor, connected to an alkaline spray absorption tower. The bacterial population attached to the carrier surface is 2.8 × 10⁻⁶. 8 CFU / g vector; the sulfate-reducing bacteria are genetically engineered strains with the acid-resistant gene sulP introduced into them, which maintain metabolic activity in the pH range of 3.0-7.5.

[0021] A method for treating acidic mine wastewater using the above system includes the following steps:

[0022] Step 1, lime pre-precipitation: Lime water is added to the acidic mining wastewater, and after stirring and reacting, the pH of the wastewater is raised to 6.0-7.0. Most of the heavy metal ions are removed by precipitation in the form of hydroxides. After solid-liquid separation, the wastewater proceeds to the next step of treatment.

[0023] Step 2, Biomineralization Enhanced Precipitation: Urease-producing bacteria and urea are added to the supernatant obtained in Step 1. The dosage of urease-producing bacteria is 0.5%-2% of the wastewater volume, and the dosage of urea is 0.2-0.3 kg / m³. The urease-producing bacteria hydrolyze urea to produce carbonate ions, which form carbonate precipitates with residual heavy metal ions, further removing heavy metals and improving the solid-liquid separation effect. After precipitation separation, the product proceeds to the next step of treatment.

[0024] Step 3, ammonia nitrogen stripping: The supernatant obtained in step 2 is passed into the stripping tower, the gas-liquid ratio is controlled at 2000-3000:1, the stripping time is 1.5-2.5 hours, and ammonia nitrogen is removed from the wastewater with an ammonia nitrogen removal rate of ≥85%.

[0025] Step 4, CO2 pre-neutralization and pH fine-tuning: CO2 is introduced into the water obtained in Step 3 for pre-neutralization, and the pH of the wastewater is precisely adjusted to 6.5-7.5 through a precision pH control system.

[0026] Step 5, SRB Deep Treatment: The effluent from Step 4 is passed into the sulfate-reducing bacteria immobilization reaction unit, with the hydraulic retention time controlled at 8-12 hours and the reaction temperature at 15-35℃. Inside the reactor, sulfate-reducing bacteria use sulfate as an electron acceptor for anaerobic metabolism, producing hydrogen sulfide. The hydrogen sulfide reacts with residual heavy metal ions in the wastewater to form insoluble sulfide precipitates. Simultaneously, the metabolic process consumes hydrogen ions, naturally raising the pH of the effluent to 7.0-8.0. The hydrogen sulfide gas generated during the reaction is collected under negative pressure and then passed into an alkaline spray absorption tower for treatment.

[0027] (III) Beneficial Effects

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) High treatment efficiency. This invention achieves efficient and simultaneous removal of sulfate, heavy metals, and ammonia nitrogen from acidic mine wastewater through the synergistic coupling of four units: lime pre-precipitation, biomineralization enhancement, ammonia nitrogen stripping, and SRB deep treatment. Cu 2+ Removal rate ≥99.0%, Zn 2+ Removal rate ≥98.5%, Pb 2+ The removal rate is ≥99.0%, the sulfate removal rate is ≥95%, the ammonia nitrogen removal rate is ≥85%, and the effluent quality consistently meets the GB 20426-2006 discharge standard.

[0030] (2) Low operating cost. This invention uses industrial wastewater (such as food processing wastewater) as the carbon source for SRB metabolism, which significantly reduces reagent costs; the modified polyurethane foam carrier has a service life of ≥3 years and does not require frequent replacement; the entire process does not require the addition of expensive flocculants such as PAM. According to calculations, the total treatment cost of this invention is only 3.0-4.5 yuan / ton of water, which is 15%-25% of the traditional chemical precipitation method.

[0031] (3) Environmentally friendly. The sludge production of this invention is only 0.15 kg / m³ (moisture content 80%), which is 1 / 5 of that of the traditional lime neutralization method, significantly reducing the pressure of solid waste disposal; the SRB reactor adopts a closed structure and a negative pressure gas collection system, combined with alkaline spray absorption, which effectively controls the emission of H2S gas and avoids secondary pollution.

[0032] (4) Resource recovery. The heavy metal sulfide precipitate produced by this invention has a combined grade of copper, zinc and lead of ≥90%, and approximately 0.5-1.2 kg of valuable metals can be recovered per ton of wastewater, thus achieving an organic combination of pollution control and resource recycling.

[0033] (5) Strong adaptability. The present invention uses a genetically engineered SRB strain with the acid-resistant gene sulP introduced into it, which maintains high metabolic activity in the pH range of 3.0-7.5 and has 50% higher acid resistance than the wild strain; the low temperature start-up technology can shorten the reactor start-up cycle from 30 days to 15 days at 15℃, which is suitable for mining applications in high-altitude and cold regions.

[0034] (6) Stable operation. This invention effectively eliminates the inhibitory effect of heavy metal shock load and ammonia nitrogen toxicity on SRB through pre-biomineralization and ammonia nitrogen stripping; the whole process is equipped with an online monitoring and automatic control system, and the system can still maintain a stable treatment effect when the influent pH fluctuates by ±0.5 or the heavy metal concentration suddenly increases by 50%, and the shock load resistance is 40% higher than that of traditional suspended growth systems. Attached Figure Description

[0035] Figure 1 This is a process flow diagram of the acidic mine wastewater coupled treatment system of the present invention. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0037] This embodiment treats acidic wastewater from a lead-zinc mine. The influent pH is 3.8, and the concentration of heavy metals in the influent is low (Cu). 2+ Concentration 32 mg / L, Zn 2+ Concentration 210 mg / L, Pb 2+ The concentrations are as follows: 28 mg / L (sulfate), 2800 mg / L (sulfate), and 45 mg / L (ammonia nitrogen).

[0038] In step one, lime pre-precipitation, the amount of lime added is reduced by 20% compared to Example 1, and the pH is raised to 6.8; in step two, biomineralization, the amount of urease-producing bacteria added is 0.8% of the wastewater volume, and the amount of urea added is 0.2 kg / m³; in step three, the gas-liquid ratio of the stripping tower is controlled at 2000:1, and the stripping time is 2.5 hours; in step five, the hydraulic retention time of the SRB reaction unit is 12 hours, and the reaction temperature is 25℃.

[0039] The system ran continuously for 45 days, and the effluent test results were: pH 7.8, Cu 2+ Concentration 0.2 mg / L, Zn 2+ Concentration 2.1 mg / L, Pb 2+ Concentration 0.1 mg / L, sulfate concentration 120 mg / L, ammonia nitrogen concentration 6.5 mg / L. Cu 2+ Removal rate 99.4%, Zn 2+ Removal rate 99.0%, Pb 2+ The removal rate was 99.6%, the sulfate removal rate was 95.7%, and the ammonia nitrogen removal rate was 85.6%.

[0040] The total operating cost is calculated to be 3.2 yuan per ton of water.

[0041] To verify the technical advantages of the fully coupled system of this invention, a comparative example was set up. The comparative example used conventional lime neutralization and precipitation to treat the wastewater described in Example 1. The amount of lime added raised the pH to 9.0, and PAM flocculant was added to assist precipitation.

[0042] The comparative results show that: Cu 2+ Removal rate 88.2%, Zn 2+ Removal rate 72.5%, Pb 2+ The removal rate was 85.0%, with no effect on sulfate or ammonia nitrogen removal. The effluent pH was 8.2, and Cu... 2+ The concentration is 10.0 mg / L, Zn 2+ The concentration was 33.0 mg / L, Pb 2+ The concentration was 6.8 mg / L, and none of the solutions consistently met the standards. The sludge production was 0.85 kg / m³ (80% moisture content), approximately 5.7 times that of the present invention. The total treatment cost was 22.5 yuan / ton of water, 6.2 times that of the present invention.

Claims

1. A coupled treatment system for acidic mine wastewater, characterized in that, It includes a lime pre-precipitation unit, a urease-producing bacteria biomineralization unit, an ammonia nitrogen stripping unit, a pH adjustment unit, and a sulfate-reducing bacteria immobilization reaction unit connected in sequence; the sulfate-reducing bacteria immobilization reaction unit is filled with a modified polyurethane foam carrier, and the surface of the carrier is covered with sulfate-reducing bacteria.

2. The acidic mine wastewater coupled treatment system according to claim 1, characterized in that, The modified polyurethane foam carrier was modified with a dopamine-chitosan composite coating, and the amount of bacterial colonies attached to the carrier surface was 2.8 × 10⁻⁶. 8 CFU / g vector.

3. The acidic mine wastewater coupled treatment system according to claim 1, characterized in that, The sulfate-reducing bacteria are genetically engineered strains with the acid-resistant gene sulP introduced into them, which maintain metabolic activity within the pH range of 3.0-7.

5.

4. The acidic mine wastewater coupled treatment system according to claim 1, characterized in that, The urease-producing bacteria biomineralization unit includes a urease-producing bacteria culture tank and a urea dosing device. After being cultured, the urease-producing bacteria are added together with urea into the mineralization reaction tank.

5. The acidic mine wastewater coupled treatment system according to claim 1, characterized in that, The ammonia nitrogen stripping unit includes a stripping tower and a blower, with the outlet of the stripping tower connected to a CO2 pre-neutralization device.

6. The acidic mine wastewater coupled treatment system according to claim 1, characterized in that, The pH adjustment unit includes a CO2 storage tank, a gas diffusion device, and a precision pH control system, used to adjust the pH of the wastewater entering the sulfate-reducing bacteria immobilization reaction unit to 6.5-7.

5.

7. The acidic mine wastewater coupled treatment system according to claim 1, characterized in that, The sulfate-reducing bacteria immobilization reaction unit is a closed structure with a negative pressure gas collection port at the top, which is connected to an alkaline spray absorption tower.

8. A method for treating acidic mine wastewater using the system described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Add lime water to the wastewater for neutralization and precipitation to remove some heavy metal ions; Step 2: Add urease-producing bacteria and urea to the effluent treated in Step 1 to induce carbonate precipitation, further remove residual heavy metal ions and perform solid-liquid separation. Step 3: Pass the supernatant obtained in Step 2 into a stripping tower to remove ammonia nitrogen from the wastewater; Step four: CO2 is introduced into the effluent treated in step three for pre-neutralization, and the pH is precisely adjusted to 6.5-7.5; Step 5: The wastewater treated in Step 4 is passed into the sulfate-reducing bacteria immobilization reaction unit. The sulfate-reducing bacteria metabolize and produce hydrogen sulfide, which reacts with residual heavy metal ions in the wastewater to form sulfide precipitates. At the same time, hydrogen ions are consumed to increase the pH of the wastewater.

9. The method according to claim 8, characterized in that, In step two, the dosage of urease-producing bacteria is 0.5%-2% of the wastewater volume, and the dosage of urea is 0.2-0.3 kg / m³. 3 .

10. The method according to claim 8, characterized in that, In step three, the gas-liquid ratio of the stripping tower is 2000-3000:1, the stripping time is 1.5-2.5 hours, and the ammonia nitrogen removal rate is ≥85%.

11. The method according to claim 8, characterized in that, In step five, the hydraulic retention time of the sulfate-reducing bacteria immobilization reaction unit is 8-12 hours, the reaction temperature is 15-35℃, and the sulfate removal rate is ≥95%.

12. The method according to claim 8, characterized in that, In step five, the hydrogen sulfide gas produced by the metabolism of sulfate-reducing bacteria is collected under negative pressure and then passed into an alkaline spray absorption tower for treatment.

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