A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry

Abstract

A continuous three-stage membrane separation-vacuum membrane distillation treatment process for separating carbon, nitrogen and phosphorus components in biogas slurry, comprising the following steps: 1) biogas slurry wastewater pretreatment: first centrifugation is performed using a tubular centrifuge, and then the biogas slurry is flocculated and pretreated using PAM, and then placed in a sedimentation column for sedimentation, and then further centrifuged using a high-speed centrifuge; 2) continuous three-stage membrane separation equipment: microfiltration membranes, ultrafiltration membranes and nanofiltration membranes with different membrane pore sizes are used to sequentially separate carbon, nitrogen and phosphorus components from the biogas slurry treated in step 1); 3) vacuum membrane distillation: the biogas slurry treated in step 2) is subjected to membrane distillation, and sulfuric acid or phosphoric acid is used as the draw liquid.

Description

Technical Field

[0001] The invention relates to the field of biogas slurry resource recycling, and in particular to a continuous three-stage membrane separation-vacuum membrane distillation treatment process for separating carbon, nitrogen and phosphorus components in biogas slurry. Background Art

[0002] The biomass resource utilization industry is expected to provide new solutions to the problems of fossil energy depletion and environmental pollution. This industry will inevitably produce a large amount of waste liquid and waste residue byproducts, so the effective utilization of waste liquid is a key problem that the industry must solve. By the end of 2016, China had built 113,000 biogas projects of various types, with an annual biogas production capacity of about 14.5 billion. Biogas projects not only reasonably dispose of waste and inferior biomass such as agricultural straw and livestock and poultry manure, but also can prepare renewable energy biogas, but they also produce a large amount of biogas liquid, which has a high content of salts such as nitrogen and phosphorus, and also contains a variety of metal ions such as copper and zinc, and the C / N ratio is seriously imbalanced, making it difficult to biochemically treat. Due to the large and concentrated amount of biogas liquid produced by large and medium-sized biogas projects, the surrounding farmland cannot be fully digested, and the lack of storage and transportation equipment means that it can only be discharged into the surrounding water bodies, which will not only pollute the environment, but also cause a large amount of nutrient loss. Therefore, achieving effective biogas liquid treatment is an urgent problem that biogas projects need to solve.

[0003] Biogas projects produce a large amount of biogas slurry. Due to the lack of perfect storage and transportation, it cannot be widely returned to the fields. If it is directly discharged, it will pollute the environment. The main traditional methods are: 1. Reuse part of the biogas slurry for anaerobic fermentation to reduce its emissions; 2. Degrade the pollutants in it to meet the emission standards; 3. Concentrate and recover the nutrients in the biogas slurry to reduce its emissions. At present, traditional biogas slurry treatment technologies mainly include natural biological treatment technology, biochemical treatment technology, agricultural resource comprehensive utilization technology, etc., but the comprehensive utilization of these technologies is limited by their low nutrient concentration and large-volume equipment. In order to treat biogas slurry efficiently and environmentally friendly, appropriate biogas slurry treatment technology should be explored.

[0004] At present, traditional research on biogas slurry treatment in China is mostly focused on solid-liquid separation and biogas slurry concentration. Pan Jianmin et al. used a raw liquid suction unit, a liquid-slag separation unit, a biogas slag extrusion unit and a biogas slurry storage unit to separate biogas slurry into solids and liquids, thereby improving the solid-liquid separation efficiency of biogas slurry. Wu Linsong et al. used extraction, mechanical centrifugation and conditioning agents to separate biogas slurry into solids and liquids. Chen Liang et al. invented a biogas slurry separation tank, which filtered out the waste residue in the biogas slurry through the solid-liquid separation filter plate on the top of the effluent bottom tank, and the waste liquid flowed into the effluent bottom tank. Zhao Nanjie et al. invented the ANAMMOX process to concentrate pig farm biogas slurry, and Zhang Cong et al. used NF technology to concentrate pig manure biogas slurry, and the concentrations of nitrogen, phosphorus and potassium increased by 2.06 times, 3.1 times and 3.7 times respectively. However, the process research on the recovery and reuse of nutrients in biogas slurry is relatively in-depth. Summary of the invention

[0005] The object of the present invention is to solve the above-mentioned problems in the prior art and to provide a fast, low-consumption and high-efficiency continuous three-stage membrane separation-vacuum membrane distillation treatment process for separating carbon, nitrogen and phosphorus components in biogas slurry, wherein the carbon component and the P component are concentrated in the three-stage membrane separation process, and the N component is concentrated in the vacuum membrane distillation process, thereby simultaneously obtaining independent high-purity carbon, nitrogen and phosphorus three components.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry, comprising the following steps:

[0008] 1) Pretreatment of biogas slurry wastewater: First, centrifuge the biogas slurry with a tubular centrifuge, then use PAM to flocculate the biogas slurry, then place it in a sedimentation column for sedimentation, and then use a high-speed centrifuge for further centrifugation;

[0009] 2) Three-stage membrane separation: using microfiltration membrane, ultrafiltration membrane and nanofiltration membrane with different membrane pore sizes to successively separate the carbon, nitrogen and phosphorus components of the biogas slurry treated in step 1);

[0010] 3) Vacuum membrane distillation: The biogas slurry treated in step 2) is subjected to membrane distillation, using sulfuric acid or phosphoric acid as the draw liquid.

[0011] In step 1), the sedimentation time is 24 to 36 hours.

[0012] In step 1), the concentration of PAM is 20-25 g / L.

[0013] In step 2), the pore size of the microfiltration membrane is 0.22 μm or 0.45 μm, the pore size of the ultrafiltration membrane is 1000 to 50000 Da, and the pore size of the nanofiltration membrane is 100 to 200 Da.

[0014] In step 2), the membrane material used is polyamide, polyethersulfone or polytetrafluoroethylene.

[0015] In step 2), the transmembrane pressure difference is 0.3-0.5 MPa, and the biogas slurry flow rate is 5-10 m / s.

[0016] In step 2), the filtering method is cross-flow filtration.

[0017] In step 3), the temperature is 60-90° C. and the volume flow rate through the liquid inlet is 5-6 L / h.

[0018] In step 3), the pH of the biogas slurry is 5-12.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] The present invention uses a technical route combining a three-stage membrane separation process and a vacuum membrane distillation process. The pretreated biogas slurry is first subjected to a three-stage membrane separation process to separate the carbon and phosphorus components, and then a vacuum membrane distillation route is used to separate the nitrogen component, so as to achieve the purpose of separating and purifying the carbon, nitrogen and phosphorus components in the biogas slurry, thereby obtaining a high-concentration organic matter concentrate and a high-concentration nitrogen and phosphorus solution, while having a higher recovery rate and separation efficiency of the carbon, nitrogen and phosphorus components.

[0021] Aiming at the main technical bottleneck of waste liquid utilization in the biomass industry, the purpose of highly selective separation and recovery of carbon, nitrogen and phosphorus in biogas slurry and high-value utilization is achieved. The present invention combines the process routes of membrane separation and vacuum membrane distillation to achieve a completely continuous biogas slurry treatment process operation, which can simultaneously meet the requirements of separating three independent carbon, nitrogen and phosphorus components with high purity, successfully construct a new way to utilize new biogas slurry, and solve the scientific and engineering basic problems involved in the new technology established based on this method, providing necessary scientific support for the development of biogas slurry treatment technology.

[0022] In step 3) of the present invention, the membrane assembly of the vacuum membrane distillation process increases the spatial depth of the permeation side, ensuring the effective area of ​​the membrane. The biogas slurry treated in step 3) is directly obtained from step 2), ensuring the continuity of the preparation method.

[0023] The invention has simple process, convenient operation, environmental friendliness, low energy consumption, can realize continuous production, can appropriately expand the scale of the device, and is easy to carry out industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the sedimentation column of the present invention;

[0025] Figure 2 It is a schematic diagram of the cross-sectional structure of the membrane module device of the membrane distillation of the present invention;

[0026] Figure 3 It is a schematic diagram of the structure of the upper cover of the membrane assembly when viewed from above;

[0027] Figure 4 It is a schematic diagram of the top cover structure of the membrane assembly from above;

[0028] Figure 5 This is a schematic diagram of the structure of the lower cover of the membrane assembly when viewed from above. DETAILED DESCRIPTION

[0029] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0030] A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry, comprising the following steps:

[0031] 1) Pretreatment of biogas slurry wastewater: First, use a tubular centrifuge for centrifugation at a speed of 5000r for 15min, then use PAM with a concentration of 20-25g / L to flocculate the biogas slurry and place it in a sedimentation column for sedimentation for 24-36h; then use a high-speed centrifuge at a speed of 5000r for centrifugation for 5min.

[0032] 2) Three-stage membrane separation: using microfiltration membrane, ultrafiltration membrane and nanofiltration membrane with different membrane pore sizes to successively separate the carbon, nitrogen and phosphorus components of the biogas slurry treated in step 1), the pore size of the microfiltration membrane is 0.22μm or 0.45μm, the pore size of the ultrafiltration membrane is 1000-50000Da, and the pore size of the nanofiltration membrane is 100-200Da; the membrane material used is polyamide or polyethersulfone; and the filtration method adopts cross-flow filtration.

[0033] 3) Vacuum membrane distillation: the biogas slurry treated in step 2) is subjected to membrane distillation, using sulfuric acid or phosphoric acid as the draw liquid; the heating temperature is 60-90° C., the volume flow rate through the liquid inlet is 5-6 L / h; the pH of the biogas slurry is 5-12.

[0034] like Figure 1 As shown, in step 1), the volume of the sedimentation column is 5 to 8 L, and the sedimentation column is divided into 4 parts from top to bottom according to the position of the water outlet, namely L1, L2, L3, and L4, so as to facilitate the removal of the lower layer of biogas without affecting the upper biogas, wherein L1 and L4 are 0.1 m long, L2 and L3 are 0.4 m long, respectively; in addition, a water outlet with a large flow rate is set at the bottom of the sedimentation column to facilitate the cleaning of the bottom sediment, and a replaceable simple glass orifice plate is placed above the water outlet for separating the sediment produced after flocculation, and the biogas slurry is placed in the sedimentation column, PAM is weighed and added to the sedimentation column, the column is covered, and the column is left to stand, and the changes in the biogas slurry in the sedimentation column are observed. After obvious stratification is observed, the water outlets on the sedimentation column are opened from top to bottom in turn, and the biogas slurry is taken out, and the pretreated biogas slurry is frozen and stored at 4° C. for use in the next experiment.

[0035] In this embodiment, step 2) uses a continuous three-stage membrane separation device to perform separation operation. The continuous three-stage membrane separation device is respectively provided with a primary membrane separation device, a secondary membrane separation device and a tertiary membrane separation device according to the microfiltration membrane, ultrafiltration membrane and nanofiltration membrane used. The above devices are connected in sequence to continuously separate the treated biogas slurry.

[0036] Before the experiment, the membrane material and the continuous three-stage membrane separation equipment were simply cleaned with clean water, and then the pressure and flow rate were adjusted to keep the pressure at 0.5MPa and the flow rate at 20m / s. The power was turned off after the water output was observed to be stable.

[0037] First, use a microfiltration membrane to remove large molecular suspended particles. Specifically, take out the pretreated biogas slurry and put it into the feed side of the first-level membrane separation equipment. Turn on the power to adjust the instrument parameters and wait for the biogas slurry to enter the continuous three-stage membrane separation equipment. When the biogas slurry flow rate is observed to be stable, keep the pressure flow rate unchanged and continue to operate the continuous three-stage membrane separation equipment, wherein the transmembrane pressure difference is 0.3-0.5MPa and the biogas slurry flow rate is 5-10m / s. When it is observed that the volume of the feed liquid side of the first-level membrane separation equipment is less than 100ml, turn off the power of the first-level membrane separation equipment.

[0038] After turning off the power of the primary membrane separation equipment, continue to operate the secondary and tertiary membrane separation equipment. When it is observed that the volume of the feed liquid side of the secondary separation equipment is less than 100 ml, turn off the power of the secondary membrane separation equipment.

[0039] After turning off the power of the secondary membrane separation equipment, continue to operate the tertiary membrane separation equipment. When the volume of the feed liquid side of the tertiary membrane separation equipment is observed to be less than 100 ml, turn off the power of the tertiary membrane separation equipment. Collect the permeate and concentrate obtained from the continuous tertiary membrane separation equipment and store them in a refrigerator at 4°C.

[0040] like Figures 2 to 5 The figure shows a schematic diagram of a membrane assembly of a membrane distillation device of the present invention, wherein the membrane assembly comprises an upper cover, a lower cover and a hydrophobic membrane, and the upper cover and the lower cover are made of polytetrafluoroethylene. The upper cover is provided with a central cavity, two discharge ports and four bolt interfaces, and a first sealing groove and a second sealing groove are provided around the central cavity; the lower cover is provided with a central cavity, two feed ports and four bolt interfaces; the feed port and the discharge port adopt a ball valve interface. When in use, the hydrophobic membrane is clamped in the cavity formed by the upper cover and the lower cover, the sealing ring is installed in the first sealing groove and the second sealing groove, and then the upper cover and the lower cover are compacted and sealed through four bolt interfaces. The cavity of the upper cover constitutes the permeation side, and a vacuum pump is externally connected to the ball valve; the cavity of the lower cover constitutes the raw material side, and a raw material tank is externally connected to the ball valve. Specifically, in this embodiment, the hydrophobic membrane adopts a hydrophobic membrane made of polytetrafluoroethylene with a pore size of 0.45μm. During heating, the biogas slurry in the raw material tank can be heated through a water bath, and then circulated back to the feed biogas slurry through a peristaltic pump. After heating, the volatile components are only ammonia nitrogen and water vapor. Due to the effect of the hydrophobic membrane, only ammonia passes through the hydrophobic membrane and is recovered from the outlet of the upper cover.

[0041] In addition, on the permeation side of the traditional membrane pool, the membrane will be deformed by the vacuum suction and adsorbed on the upper wall of the upper cover, so that the effective area of ​​the membrane is only the area corresponding to the two discharge ports, and the effective area of ​​the membrane is greatly wasted. Compared with the traditional membrane pool, the membrane distillation component of the present invention increases the depth of the permeation side space, so that the membrane still maintains a certain distance from the upper wall of the upper cover when it is deformed, ensuring the effective area of ​​the membrane. Experiments have shown that the high-depth permeation side space of the membrane distillation component of the present invention is conducive to the recovery of ammonia nitrogen.

[0042] The separation principle of the present invention is as follows:

[0043] 1. According to the molecular size of carbon, nitrogen and phosphorus components in biogas slurry. N component is less than 100Da, P component is between 100 and 200Da, and C component is above 1000Da. Therefore, separation is carried out according to the different molecular weights combined with the characteristics of cross-flow filtration.

[0044] 2. Since the N component in the biogas slurry mainly exists in the form of ammonia nitrogen, the N in ammonia nitrogen is negatively charged, and the P component in the biogas slurry mainly exists in the form of phosphate, the P in phosphate is positively charged, and the membrane material used is positively charged, it can achieve both the retention of the P component and the permeation of the N component.

[0045] Embodiment 1:

[0046] The biogas slurry used was fermented pig manure from Jiangsu Province, with a total volume of 10L. It was stored in a refrigerator at 4°C to ensure that the biogas slurry components were relatively stable. The COD concentration was 22000mg / L and the NH 3 -N concentration is 4000mg / L, PO 4 3- The concentration is 200 mg / L. The biogas slurry was pretreated by centrifugation, flocculation, sedimentation and centrifugation, and the components of the treated biogas slurry were tested. At the same time, the membrane flux and transmembrane pressure difference in the three-stage membrane separation process were tested. The temperature and flow rate were controlled in the vacuum membrane distillation process to ensure that the ammonia nitrogen was recovered in the form of ammonium sulfate. First, 80 g of polyacrylamide was accurately weighed with a concentration of 20 g / L and used as a flocculant. The first centrifugation used a tubular centrifuge with a speed of 5000 r / s, and the second centrifugation used an ultrafiltration centrifuge with a speed of 5000 r / s. The molecular weights of the continuous three-stage membrane separation membranes used were 0.22 μm, 1000 Da, and 100 Da, respectively. The microfiltration membrane was made of polyamide, the ultrafiltration membrane was made of polytetrafluoroethylene, and the nanofiltration was made of polyethersulfone. The membrane area was 0.1 m 2 , the transmembrane pressure difference of the three-stage separation is stable at 0.5MPa, and the flow rate is 10m / s. The three-stage separation permeate obtained by the three-stage membrane separation process is further subjected to vacuum membrane distillation operation to ensure that the volume flow rate is 12L / h and the pH is 9-12. The results show that under the premise of ensuring the stability of the transmembrane pressure difference, the secondary separation membrane flux can reach up to 31L / m 2 h, the three-stage separation membrane flux can reach up to 24L / m 2 h, and at the same time, the organic component, i.e., the C component, can be concentrated by more than 5 times, with a P separation efficiency of more than 95%, and a concentrated phosphorus solution (400 mg / L) and a phosphorus-free solution (1.37 g / L) can be obtained at the same time. The vacuum membrane distillation process can separate more than 90% of ammonia nitrogen to obtain an ammonium sulfate solution as a N component recovery product.

[0047] Embodiment 2:

[0048] The biogas slurry used was fermented duck manure in Beijing, with a total volume of 40L, which was stored in a refrigerator at 4℃. The COD concentration was 11000mg / L and the NH 3 -N concentration is 1500mg / L, PO 4 3- The concentration is 80 mg / L. The biogas slurry was pretreated by centrifugation, flocculation, sedimentation and centrifugation, and the components of the treated biogas slurry were tested. At the same time, the membrane flux and transmembrane pressure difference of the three-stage membrane separation process were tested. In the vacuum membrane distillation process, the temperature and flow rate were controlled to ensure that the ammonia nitrogen was recovered in the form of ammonium sulfate. First, 80 g of polyacrylamide was accurately weighed with a concentration of 20 g / L and used as a flocculant. The first centrifugation used a tubular centrifuge with a speed of 5000 r / s, and the second centrifugation used an ultrafiltration centrifuge with a speed of 5000 r / s. The continuous three-stage membrane separation membrane molecular weights were 0.22 μm, 1000 Da, and 100 Da, respectively. The microfiltration membrane was made of polyamide, the ultrafiltration membrane was made of polytetrafluoroethylene, and the nanofiltration was made of polyethersulfone. The membrane area was 0.1 m 2 , the transmembrane pressure difference of the three-stage separation is stable at 0.5MPa, and the flow rate is 10m / s. The three-stage separation permeate obtained by the three-stage membrane separation process is further subjected to vacuum membrane distillation operation to ensure that the volume flow rate is 12L / h and the pH is 9-12. The results show that under the premise of ensuring the stability of the transmembrane pressure difference, the secondary separation membrane flux can reach up to 25L / m 2 h, the three-stage separation membrane flux can reach up to 31L / m 2 h, and at the same time, the organic component, i.e., the C component, can be concentrated by more than 3.8 times, with a P separation efficiency of more than 90%, and a concentrated phosphorus solution (185 mg / L) and a phosphorus-free solution (2.33 g / L) can be obtained at the same time. The vacuum membrane distillation process can separate more than 98% of ammonia nitrogen to obtain an ammonium sulfate solution as a N component recovery product.

[0049] Embodiment 3:

[0050] The biogas slurry used was fermented fruit pomace slurry from Xiamen, Beijing and Jiangsu. The three biogas slurries were mixed in equal amounts to obtain a total volume of 20 L of mixed biogas slurry, which was stored in a 4°C refrigerator in advance. The COD concentration was 17000 mg / L and the NH 3 -N concentration is 1200mg / L, PO 4 3-The concentration is 80 mg / L. The biogas slurry was pretreated by centrifugation, flocculation, sedimentation and centrifugation, and the components of the treated biogas slurry were tested. The membrane flux and transmembrane pressure difference in the three-stage membrane separation process were also tested. The temperature and flow rate were controlled in the vacuum membrane distillation process to ensure that the ammonia nitrogen was recovered in the form of ammonium sulfate. First, accurately weigh 80g of polyacrylamide with a concentration of 20g / L, and use it as a flocculant. The first centrifugation uses a tubular centrifuge with a speed of 5000r / s, and the second centrifugation uses an ultrafiltration centrifuge with a speed of 5000r / s. Six groups of continuous three-stage membrane separation membrane combination processes are set up, namely, the first group is 0.22μm, 50000Da, 100Da, the second group is 0.22μm, 50000Da, 200Da, the third group is 0.22μm, 10000Da, 100Da, the fourth group is 0.22μm, 10000Da, 200Da, the fifth group is 0.22μm, 1000Da, 200Da, and the sixth group is 0.22μm, 1000Da, 100Da. The microfiltration membrane is made of polyamide, the ultrafiltration membrane is made of polytetrafluoroethylene, and the nanofiltration is made of polyethersulfone. The membrane area is 0.1m 2 , the transmembrane pressure difference of the three-stage separation is stable at 0.5MPa, and the flow rate is 10m / s. The three-stage separation permeate obtained by the three-stage membrane separation process is further subjected to vacuum membrane distillation operation to ensure that the volume flow rate is 12L / h and pH=9-12. The results show that for the separation of P molecules, when the size of other molecules is much larger than the membrane pore size (100Da, 200Da), that is, the first, second, third, and fourth groups, the membrane pore size plays a major role, and the charge effect is smaller; when the size of other molecules is slightly larger than the membrane pore size (100Da, 200Da), that is, the fifth and sixth groups, the membrane pore size and charge effect work together. For N molecules, the size of ammonia nitrogen molecules is slightly smaller than the membrane pore size, and the charge effect plays a major role at this time. By setting a membrane combination process with different membrane pore sizes, the separation mechanism of carbon, nitrogen, and phosphorus components in biogas slurry is analyzed to achieve the optimal membrane separation method for biogas slurry from different sources.

[0051] Embodiment 4:

[0052] The biogas slurry used was fermented pig manure from Jiangsu Province, with a total volume of 10L, which was stored in a refrigerator at 4℃. The COD concentration was 22000mg / L and the NH 3 -N concentration is 4000mg / L, PO 4 3-The concentration is 200 mg / L. The biogas slurry was pretreated by centrifugation, flocculation, sedimentation and centrifugation, and the components of the treated biogas slurry were tested. At the same time, the membrane flux and transmembrane pressure difference in the three-stage membrane separation process were tested. The temperature and flow rate were controlled in the vacuum membrane distillation process to ensure that the ammonia nitrogen was recovered in the form of ammonium sulfate. First, 80 g of polyacrylamide was accurately weighed with a concentration of 20 g / L and used as a flocculant. The first centrifugation used a tubular centrifuge with a speed of 5000 r / s, and the second centrifugation used an ultrafiltration centrifuge with a speed of 5000 r / s. The molecular weights of the continuous three-stage membrane separation membranes used were 0.22 μm, 1000 Da, and 100 Da, respectively. The microfiltration membrane was made of polyamide, the ultrafiltration membrane was made of polytetrafluoroethylene, and the nanofiltration was made of polyethersulfone. The membrane area was 0.1 m 2 , the transmembrane pressure difference of the three-stage separation is stable at 0.5MPa, and the flow rate is 10m / s. The three-stage separation permeate obtained by the three-stage membrane separation process is further subjected to vacuum membrane distillation operation to ensure that the volume flow rate is 12L / h and pH is 9-12. When using a sedimentation column for a pretreatment operation method combining gravity sedimentation and flocculation sedimentation, the biogas slurry at the outlets of L1, L2, L3, and L4 is separated using a continuous three-stage membrane separation process, and the C, N, and P recovery rates of L1, L2, L3, and L4 are calculated. The results show that when using a sedimentation column for separation, the C, N, and P recovery rates of the L2 part are the highest, among which the C component recovery rate is 70%, the N component recovery rate is 90%, and the P component recovery rate is 95%.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 1 is that membrane distillation operation is not adopted, and as a result, a pure ammonia nitrogen solution cannot be obtained, and the separation of carbon, nitrogen and phosphorus components cannot be completely achieved.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1 is that the pretreatment method of centrifugation-flocculation-sedimentation-centrifugation is not adopted, so the membrane flux is low and the separation of carbon, nitrogen and phosphorus components cannot be achieved.

[0057] The present invention uses a technical route combining a three-stage membrane separation process and a vacuum membrane distillation process. The pretreated biogas slurry is first subjected to a three-stage membrane separation process to separate the carbon and phosphorus components, and then a vacuum membrane distillation route is used to separate the nitrogen component, so as to achieve the purpose of separating and purifying the carbon, nitrogen and phosphorus components in the biogas slurry, thereby obtaining a high-concentration organic matter concentrate and a high-concentration nitrogen and phosphorus solution, while having a higher recovery rate and separation efficiency of the carbon, nitrogen and phosphorus components.

Claims

1. A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry, characterized in that The following steps are involved: 1) Pretreatment of biogas slurry wastewater: First, centrifuge the biogas slurry with a tubular centrifuge, then use PAM to flocculate the biogas slurry, then place it in a sedimentation column for sedimentation, and then use a high-speed centrifuge for further centrifugation; 2) Three-stage membrane separation: using microfiltration membranes, ultrafiltration membranes and nanofiltration membranes with different pore sizes to successively separate the carbon, nitrogen and phosphorus components of the biogas slurry treated in step 1; 3) Vacuum membrane distillation: The biogas slurry treated in step 2) is subjected to membrane distillation, using sulfuric acid or phosphoric acid as the draw liquid; In step 2), the pore size of the microfiltration membrane is 0.22 μm or 0.45 μm, the pore size of the ultrafiltration membrane is 1000-50000 Da, and the pore size of the nanofiltration membrane is 100-200 Da.

2. A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry according to claim 1, characterized in that: In step 1), the sedimentation time is 24~36h.

3. A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry according to claim 1, characterized in that: In step 1), the concentration of PAM is 20-25 g / L.

4. A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry according to claim 1, characterized in that: In step 2), the membrane material used is polyamide, polyethersulfone or polytetrafluoroethylene.

5. A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry according to claim 1, characterized in that: In step 2), the transmembrane pressure difference is 0.3~0.5 MPa, and the biogas slurry flow rate is 5~10m / s.

6. A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry according to claim 1, characterized in that: In step 2), the filtering method is cross-flow filtration.

7. A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry according to claim 1, characterized in that: In step 3), the temperature is 60-90°C and the volume flow rate through the liquid inlet is 5-6 L / h.

8. A continuous three-stage membrane separation-vacuum membrane distillation process for separating carbon, nitrogen and phosphorus components in biogas slurry according to claim 1, characterized in that: In step 3), the pH of the biogas slurry is 5-12.

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