Anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials

Abstract

This invention provides an anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials, comprising: S1, firstly, removing suspended solids and fibrous impurities from the palm oil wastewater through a filter; S2, sending the filtered wastewater into an equalization tank and adding an alkaline regulator to the equalization tank, the alkaline regulator comprising calcium hydroxide and synergistic alkaline mineral materials, the synergistic alkaline mineral materials comprising one or more of magnesium hydroxide, calcium carbonate, red mud powder, or dolomite powder; S3, passing the uniformly mixed palm oil wastewater in the equalization tank into an anaerobic reactor for anaerobic fermentation. This invention, by adding an alkaline regulator composed of calcium hydroxide and synergistic alkaline mineral materials, introduces multiple alkaline minerals, establishes a stable multi-component buffer system, regulates the pH of the wastewater, inhibits VFA accumulation, promotes sludge granulation, and improves the efficiency and system stability of anaerobic fermentation.

Description

Technical Field

[0001] This invention relates to the field of anaerobic fermentation technology, and in particular to an anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials. Background Technology

[0002] Palm oil wastewater is a high-concentration organic wastewater generated during palm oil production. Its complex characteristics and challenging treatment make it a typical type of industrial wastewater. Palm oil wastewater is characterized by high COD, high suspended solids, high oil content, and low pH. Direct discharge without treatment will cause serious environmental pollution. Currently, anaerobic fermentation technology has become one of the main methods for treating high-concentration organic wastewater due to its advantages such as high energy recovery efficiency and low sludge production.

[0003] However, existing anaerobic fermentation processes still have the following problems when treating palm oil wastewater:

[0004] 1. Traditional processes often use sodium hydroxide or calcium hydroxide as a single alkaline substance to adjust the pH. However, the decomposition of oil in palm oil wastewater produces a large amount of volatile fatty acids (VFA), which can easily lead to pH fluctuations and affect system stability.

[0005] 2. Existing pH adjustment methods often react quickly but have a short duration, which cannot cope with the acidic substances continuously generated during anaerobic processes, resulting in the need to frequently add alkaline substances and increase operating costs.

[0006] 3. Palm oil wastewater contains a variety of substances that may inhibit the activity of anaerobic microorganisms, and existing single alkaline regulators are difficult to effectively adsorb and remove these inhibitors.

[0007] 4. The high oil content in palm oil wastewater can affect the settling performance and granulation process of anaerobic sludge, and existing technologies lack effective measures to promote sludge particle formation.

[0008] 5. The addition of alkaline regulators is not precise or automated enough, and manual operation leads to large pH fluctuations, which affects the treatment effect.

[0009] Therefore, there is an urgent need to develop an anaerobic fermentation treatment process for palm oil wastewater that can synergistically regulate pH, promote sludge particle formation, and improve system stability, so as to improve treatment efficiency and biogas production. Summary of the Invention

[0010] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials, in order to solve the problems in the existing technology of anaerobic treatment of palm oil wastewater such as acidic pH, rapid accumulation of volatile fatty acids, lack of stable buffer system, difficulty in the formation of anaerobic sludge particles, and limited pH adjustment ability of Ca(OH)2 alone.

[0011] To achieve the above and other related objectives, this invention provides an anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials, comprising the following steps:

[0012] S1. First, pass the palm oil wastewater through a filter to remove suspended solids and fibrous impurities;

[0013] S2. The filtered wastewater is sent into the equalization tank, and an alkaline regulator is added to the equalization tank. The alkaline regulator includes calcium hydroxide and synergistic alkaline mineral materials. The synergistic alkaline mineral materials include one or more of magnesium hydroxide, calcium carbonate, red mud powder or dolomite powder.

[0014] S3. The palm oil wastewater that is mixed evenly in the equalization tank is fed into the anaerobic reactor for anaerobic fermentation.

[0015] Furthermore, in step S2, the mass ratio of calcium hydroxide to the synergistic alkaline mineral material is 1:(0.2-1.0).

[0016] Furthermore, in step S2, the amount of alkaline regulator added to the wastewater is 0.5%~1%, that is, 5-10 kg of alkaline regulator is added to 1 ton of wastewater, so that the pH value of the wastewater in the equalization tank is stabilized between 6.8 and 7.2.

[0017] Furthermore, all the alkaline regulators are powders with an average particle size of less than 100 μm.

[0018] Specifically, the average particle size of calcium hydroxide is 10–30 μm, the average particle size of magnesium hydroxide is 5–20 μm, the average particle size of calcium carbonate or dolomite powder is 20–50 μm, and the average particle size of red mud powder is 100 μm.

[0019] Magnesium hydroxide provides Mg 2+ Ca2 + Mg 2+The combined action of these components with extracellular polymeric substances (EPS) and fatty acids forms a bridging structure, enhancing the strength, density, and settling properties of anaerobic granular sludge. It also forms insoluble salts with volatile fatty acids, reducing their toxicity and slowing acid accumulation. Meanwhile, the slow-release components in calcium carbonate, dolomite, or red mud gradually dissolve, providing delayed regulation of VFA bursts and load fluctuations, and inhibiting drastic pH drops. Compared to the rapid regulation and drop of Ca(OH)2, this is more conducive to maintaining the long-term stable operation of the anaerobic system. Red mud has a porous structure, enabling it to adsorb oils, heavy metals, phosphorus, phenolic substances, etc., and can also serve as a support carrier for microbial attachment, improving start-up speed and strain stability. Specifically, the red mud powder is a dried and pulverized powder with a particle size of less than 100 μm. Smaller particle size results in a larger specific surface area and better adsorption effect; and its pH value is greater than 9.

[0020] Furthermore, both the equalization tank and the anaerobic reactor are equipped with stirring and mixing devices. The stirring and mixing device in the equalization tank is preferably a low-speed plug-flow agitator with a rotation speed of 30-60 rpm, ensuring thorough mixing of the alkaline regulator and wastewater while avoiding increased energy consumption due to excessive stirring. The stirring and mixing device in the anaerobic reactor operates at a speed controlled at 20-40 rpm, running intermittently for 10-20 minutes per hour. The stirring and mixing device preferably uses frequency conversion control, which can automatically adjust the stirring intensity according to the wastewater volume in the tank.

[0021] Furthermore, the anaerobic reactor is also equipped with a level gauge, a temperature sensor, a pressure sensor, a biogas flow meter, a biogas gas analyzer, and a pH meter. The level gauge is an ultrasonic level gauge to monitor changes in the liquid level within the reactor in real time; the temperature sensor is a PT100 resistance thermometer to monitor the temperature within the reactor and is linked to the heating system; the pressure sensor monitors the gas phase pressure within the reactor to prevent overpressure; the biogas flow meter is a thermal gas mass flow meter to accurately measure the biogas production; the biogas gas analyzer monitors the content of gases such as methane, carbon dioxide, and hydrogen sulfide in the biogas online; and the pH meter uses an industrial online pH electrode to monitor changes in the pH value within the reactor in real time.

[0022] In one embodiment of the present invention, a dual-path automatic powder metering and dosing device is provided above the equalization tank, which is used to add calcium hydroxide and synergistic alkaline mineral materials respectively, directly adding solid powder into the equalization tank. This dosing method is more precise and automated. The control system automatically adjusts the dosage of calcium hydroxide and synergistic alkaline mineral materials according to the real-time monitoring results of the wastewater pH value, ensuring that the wastewater pH value is maintained within the target range.

[0023] In another embodiment of the present invention, a pneumatic conveying system is provided above the regulating tank to realize the dust-free transfer of the alkaline regulator, which is then mixed with water to form a homogeneous mixture for addition.

[0024] Furthermore, the pneumatic conveying system includes a powder storage tank, a pneumatic conveying pipeline, a water supply pipeline, and a Venturi mixer. The lower end of the powder storage tank is connected to the pneumatic conveying pipeline, which uses compressed air to convey the powder to the Venturi mixer. The pneumatic-water supply pipeline conveys water to the Venturi mixer. The alkaline regulator and water are mixed in the Venturi mixer to form an alkaline slurry, which is then added to the equalization tank. This addition method avoids dust pollution and improves the quality of the operating environment and the uniformity of addition.

[0025] Furthermore, the lower end of the powder storage tank is connected to a pneumatic conveying pipeline via a rotary feeder to control the amount of powder entering and exiting, ensuring sealing and quantitative conveying.

[0026] Alkaline powders such as calcium hydroxide and red mud are prone to absorbing moisture and clumping. Direct dry application will generate a large amount of alkaline dust, which is irritating to the eyes and nose and highly corrosive. The pneumatic conveying system is a fully enclosed conveying system, which greatly reduces the risk of occupational hazards on site. Combined with a Venturi mixer, "dry conveying and wet mixing" is achieved, where the powder is instantly dispersed in high-speed water flow to form a stable slurry, resulting in a more thorough reaction. Under load shocks (such as VFA accumulation), the alkali source can be quickly added to enhance the buffer capacity and ensure that the anaerobic system does not collapse. Furthermore, wet dispersion reduces the problem of Ca(OH)2 clumping and deposition, extending the service life of pipelines, pumps, and valves.

[0027] As described above, the anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials of the present invention has the following beneficial effects:

[0028] 1. This invention introduces a variety of alkaline minerals by adding an alkaline regulator composed of calcium hydroxide and synergistic alkaline mineral materials, establishing a stable multi-component buffer system to regulate wastewater pH, inhibit VFA accumulation, promote sludge granulation, and improve the efficiency and system stability of anaerobic fermentation. Compared with traditional single-alkali source regulation methods, this invention significantly improves COD removal rate and biogas yield, and reduces H2S concentration, making it suitable for the resource utilization of high-concentration organic wastewater such as palm oil wastewater.

[0029] 2. Magnesium hydroxide provides Mg 2+ Ca2 + Mg 2+ Together, they form bridging structures with extracellular polymers and fatty acids, enhancing the strength, density, and settling properties of anaerobic granular sludge. They also form insoluble salts with volatile fatty acids, reducing their toxicity and slowing down acid accumulation. Meanwhile, the slow-release components in calcium carbonate, dolomite, or red mud gradually dissolve, providing delayed regulation of VFA bursts and load fluctuations, and inhibiting drastic pH drops. Compared to the "rapid regulation and rapid drop" of Ca(OH)2, this is more conducive to maintaining the long-term stable operation of the anaerobic system.

[0030] 3. The red mud in the synergistic alkaline mineral material has a porous structure, which can adsorb oils, heavy metals, phosphorus, phenols and other substances; it can also serve as a support carrier for microbial attachment, promote the formation of anaerobic sludge particles, and improve the settling properties and reaction efficiency of sludge.

[0031] 4. Alkaline materials are automatically added through a pneumatic conveying system, achieving contactless and closed conveying, which can avoid the dust hazards caused by dry feeding; combined with a Venturi mixer jet to achieve "dry feeding and wet mixing", the powder is instantly dispersed in high-speed water flow to form a stable slurry, and the reaction is more thorough. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the anaerobic fermentation treatment device for palm oil wastewater based on the synergistic regulation of multiple alkaline materials disclosed in Embodiment 1 of the present invention.

[0033] Figure 2 This is a schematic diagram of the pneumatic conveying system disclosed in Embodiment 5 of the present invention.

[0034] Component designation explanation:

[0035] 1. Filter; 2. Equalization tank; 21. Dual-path automatic powder metering and dosing device; 22. Mixing device; 3. Anaerobic reactor; 31. Temperature sensor; 32. Level gauge; 33. Pressure sensor; 34. Biogas flow meter; 35. Biogas analyzer; 36. pH meter; 4. Pneumatic conveying system; 41. Powder storage tank; 42. Rotary feeder; 43. Pneumatic conveying pipeline; 44. Water supply pipeline; 45. Compressor; 46. Venturi mixer injector. Detailed Implementation

[0036] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0037] Example 1

[0038] This embodiment provides an anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials. The structure of the device used in the anaerobic fermentation process is referenced. Figure 1 The processing technology includes the following steps:

[0039] S1. First, pass the palm oil wastewater through filter 1 to remove suspended solids and fibrous impurities.

[0040] Specifically, palm oil wastewater contains a large amount of suspended solids and fibrous impurities, which can affect the stability and efficiency of subsequent anaerobic fermentation processes. Therefore, an automatic filter with a pore size of 0.5-2 mm is first used to pretreat the raw palm oil wastewater to remove suspended solids and fibrous impurities. The filter is installed at an angle, allowing the trapped solids to slide down the filter screen surface into the collection tank, preventing filter clogging. The suspended solids content in the filtered wastewater is reduced by more than 80%, creating favorable conditions for subsequent treatment.

[0041] S2. The filtered wastewater is sent into the equalization tank 2, and an alkaline regulator is added to the equalization tank. The alkaline regulator includes calcium hydroxide and a synergistic alkaline mineral material, wherein the synergistic alkaline mineral material is magnesium hydroxide. 3 kg of calcium hydroxide and 2 kg of magnesium hydroxide are added per ton of wastewater to stabilize the pH at 6.9–7.1. The average particle size of calcium hydroxide is 20 μm, and the average particle size of magnesium hydroxide is 10 μm. This particle size distribution can maintain a good slow-release effect and sedimentation balance.

[0042] A dual-path automatic powder metering and dosing device 21 is installed above the equalization tank, used for adding calcium hydroxide and magnesium hydroxide respectively. This device includes two independent storage silos, a metering screw feeder, and a control system. The control system automatically adjusts the dosage of the two alkaline materials based on real-time monitoring of the wastewater pH value, ensuring that the wastewater pH value is maintained within the target range. A stirring and mixing device 22 is also installed inside the equalization tank.

[0043] S3. The palm oil wastewater that is mixed evenly in the equalization tank is fed into anaerobic reactor 3 for anaerobic fermentation.

[0044] Palm oil wastewater, with its pH adjusted to a suitable range and thoroughly mixed in the equalization tank, is then transported to the anaerobic reactor via a lift pump and pipeline system. The anaerobic reactor employs an upflow anaerobic sludge blanket (UASB) structure, with an effective volume three times the daily wastewater treatment capacity and a hydraulic retention time of 3 days. The reactor temperature is controlled within a mesophilic range of 35±2℃, which is conducive to the growth and metabolic activities of anaerobic microorganisms.

[0045] The anaerobic reactor is equipped with a mixing device 22, which combines low-speed mechanical stirring with biogas recirculation stirring to ensure uniform mixing of materials within the reactor and prevent the formation of dead zones. The mechanical stirrer operates at a speed controlled between 20-40 rpm, intermittently for 15 minutes per hour. The anaerobic reactor 3 is also equipped with monitoring devices such as a level gauge 32, a temperature sensor 31, a pressure sensor 33, a biogas flow meter 34, a biogas gas analyzer 35, and a pH meter 36.

[0046] During anaerobic fermentation, organic matter in palm oil wastewater is decomposed into gaseous products such as methane and carbon dioxide, as well as simple organic matter, by anaerobic microorganisms. Calcium hydroxide, an alkaline regulator added in the early stages, can rapidly neutralize the organic acids produced during the acid-producing phase, while magnesium hydroxide can continuously and slowly release alkalinity, maintaining a stable pH level in the system, effectively preventing acidification of the anaerobic system, and improving the system's resistance to shock loads.

[0047] During anaerobic fermentation, the biogas yield is stable at 385 L / kg COD, with a methane content of 70% and a COD removal rate of 82%. The biogas produced, after desulfurization and dehydration, can be used for boiler combustion or power generation, achieving energy recovery and utilization. The COD concentration of the effluent after anaerobic treatment is reduced to 10,000-15,000 mg / L, allowing for further aerobic treatment or reuse in farmland irrigation.

[0048] Example 2

[0049] This embodiment provides an anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials. The only difference between this process and Embodiment 1 is that:

[0050] In step S2, the alkaline regulator includes calcium hydroxide and synergistic alkaline mineral materials. The synergistic alkaline mineral materials are selected from magnesium hydroxide and calcium carbonate, that is, 3 kg of calcium hydroxide, 0.65 kg of magnesium hydroxide, and 1.35 kg of calcium carbonate are added per ton of wastewater to stabilize the pH at around 7.2. The average particle size of calcium hydroxide is 20 μm, the average particle size of magnesium hydroxide is 10 μm, and the average particle size of calcium carbonate is 25 μm.

[0051] During the anaerobic fermentation process, the biogas yield is stable at 410 L / kg COD, the methane content reaches 71%, the COD removal rate reaches 85%, and the COD concentration of the effluent after anaerobic treatment is reduced to 8000-12000 mg / L.

[0052] Example 3

[0053] This embodiment provides an anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials. The only difference between this process and Embodiment 1 is that:

[0054] In step S2, the alkaline regulator includes calcium hydroxide and synergistic alkaline mineral materials. The synergistic alkaline mineral materials are selected from magnesium hydroxide and red mud powder, that is, 3 kg of calcium hydroxide, 0.65 kg of magnesium hydroxide, and 1.35 kg of red mud powder are added per ton of wastewater to stabilize the pH at 6.9~7.2. The average particle size of calcium hydroxide is 20 μm, the average particle size of magnesium hydroxide is 10 μm, and the average particle size of red mud powder is 90 μm.

[0055] During the anaerobic fermentation process, the biogas yield remained stable at 430 L / kg COD, the methane content reached 70%, the COD removal rate reached 87%, the COD concentration of the effluent after anaerobic treatment decreased to 8000-12000 mg / L, and the H2S concentration in the biogas decreased from 1800 ppm to 820 ppm.

[0056] Example 4

[0057] This embodiment provides an anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials. The only difference between this process and Embodiment 1 is that:

[0058] In step S2, the alkaline regulator includes calcium hydroxide and synergistic alkaline mineral materials. The synergistic alkaline mineral materials are selected from magnesium hydroxide, calcium carbonate, red mud powder, and dolomite powder. Specifically, 3 kg of calcium hydroxide, 0.5 kg of magnesium hydroxide, 0.5 kg of calcium carbonate, 0.5 kg of red mud powder, and 0.5 kg of dolomite powder are added per ton of wastewater to stabilize the pH at 6.9~7.2. The average particle size of calcium hydroxide is 20 μm, the average particle size of magnesium hydroxide is 10 μm, the average particle size of calcium carbonate is 25 μm, the average particle size of red mud powder is 90 μm, and the average particle size of dolomite powder is 40 μm.

[0059] During anaerobic fermentation, the biogas yield remained stable at 445 L / kg COD, the methane content reached 73%, the COD removal rate reached 88%, the COD concentration of the effluent after anaerobic treatment decreased to 5000-10000 mg / L, and the H2S concentration in the biogas decreased to 900 ppm.

[0060] Example 5

[0061] This embodiment provides an anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials. The only difference between this process and Embodiment 1 is that:

[0062] A pneumatic conveying system 4 is installed above the equalization tank to mix the alkaline regulator with water to form a homogeneous mixture before adding it, thereby achieving dust-free transport of the alkaline regulator.

[0063] refer to Figure 2The pneumatic conveying system 4 includes a powder storage tank 41, a pneumatic conveying pipeline 43, a water supply pipeline 44, and a Venturi mixer jetter 46. The lower end of the powder storage tank is connected to the pneumatic conveying pipeline 43 via a rotary feeder 42, which precisely controls the powder feed rate, ensuring sealed and quantitative conveying. The pneumatic conveying pipeline 43 uses the positive pressure provided by the compressor 45 to convey the powder to the Venturi mixer jetter 46, and the water supply pipeline conveys water to the Venturi mixer jetter. After the alkaline regulator and water are mixed in the Venturi mixer jetter, an alkaline slurry is formed and added to the regulating tank. Venturi mixing improves powder dispersion efficiency and reaction rate, while avoiding dust dispersion, thus improving the quality of the operating environment and the uniformity of addition.

[0064] Comparative Example 1

[0065] This comparative example provides an anaerobic fermentation treatment process for palm oil wastewater. Compared with Example 1, the only difference is that in step S2, only calcium hydroxide is used as the alkaline regulator, that is, 5 kg of calcium hydroxide is added per ton of wastewater to stabilize the pH at 7.0; wherein the average particle size of calcium hydroxide is 20 μm.

[0066] During anaerobic fermentation, the biogas yield is approximately 310 L / kg COD, the methane content is approximately 60%, the COD removal rate is approximately 74%, and the COD concentration of the effluent after anaerobic treatment is reduced to 16,000-18,000 mg / L.

[0067] In summary, this invention, by adding an alkaline regulator composed of calcium hydroxide and synergistic alkaline mineral materials, introduces multiple alkaline minerals to establish a stable multi-component buffer system, thereby regulating wastewater pH, inhibiting VFA accumulation, promoting sludge granulation, and improving the efficiency and stability of anaerobic fermentation. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial application value.

[0068] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An anaerobic fermentation treatment process for palm oil wastewater based on the synergistic regulation of multiple alkaline materials, characterized in that, Includes the following steps: S1. First, remove suspended solids and fibrous impurities from the palm oil wastewater through a filter; S2. The filtered wastewater is sent into the equalization tank, and an alkaline regulator is added to the equalization tank. The dosage of the alkaline regulator is 0.5%~1%, so that the pH value of the wastewater in the equalization tank is stabilized between 6.8 and 7.

2. The alkaline regulator comprises calcium hydroxide and synergistic alkaline mineral materials, which include magnesium hydroxide, calcium carbonate, red mud powder, and dolomite powder. The mass ratio of calcium hydroxide to synergistic alkaline mineral materials is 1:(0.2–1.0). The average particle size of calcium hydroxide is 10–30 μm, the average particle size of magnesium hydroxide is 5–20 μm, and the average particle size of calcium carbonate and dolomite powder is 20–50 μm, maintaining a balance between slow-release effect and sedimentation. The average particle size of red mud powder is less than 100 μm. S3. The uniformly mixed palm oil wastewater in the equalization tank is fed into an anaerobic reactor for anaerobic fermentation. A dual-path automatic powder metering and dosing device is installed above the equalization tank, used for adding calcium hydroxide and synergistic alkaline mineral materials respectively. A pneumatic conveying system is also installed above the equalization tank to achieve dust-free transfer of the alkaline regulator, which is then mixed with water to form a homogeneous mixture for addition. The pneumatic conveying system includes a powder storage tank, a pneumatic conveying pipeline, a water supply pipeline, and a Venturi mixer. The lower end of the powder storage tank is connected to the pneumatic conveying pipeline. The pneumatic conveying pipeline uses compressed air to transport the powder to the Venturi mixer, and the water supply pipeline transports water to the Venturi mixer. The alkaline regulator and water are mixed in the Venturi mixer to form an alkaline slurry, which is then added to the equalization tank.

2. The anaerobic fermentation treatment process for palm oil wastewater according to claim 1, characterized in that, The lower end of the powder storage tank is connected to the pneumatic conveying pipeline via a rotary feeder, which is used to control the amount of powder entering and exiting.

3. The anaerobic fermentation treatment process for palm oil wastewater according to claim 1, characterized in that, The regulating tank and the anaerobic reactor are equipped with stirring and mixing devices; the anaerobic reactor is also equipped with a level gauge, a temperature sensor, a pressure sensor, a biogas flow meter, a biogas analyzer, and a pH meter.

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