Sewage treatment device and method

Abstract

The present invention belongs to the field of sewage treatment, and specifically relates to a sewage treatment device and method. The technical scheme is: inoculating denitrifying microorganisms in sewage, adding biochar, and inoculating algae. The sewage treatment system includes an algae purification system and a denitrification system, and the algae purification system and the denitrification system are connected through a filtering structure; the algae purification system includes an algae growth box, and the algae growth box is made of transparent materials. The denitrification system includes a denitrification box, and the denitrification box is inoculated with denitrifying microorganisms and is filled with nutrients for the survival of the denitrifying microorganisms. A carbon replenishing column that can slowly release a carbon source into the denitrification box is arranged in the denitrification box. The present invention provides a new sewage treatment device and method, which can control the slow release degree of biochar, promote algae growth, strengthen microbial denitrification, promote the purification of agricultural non-point source pollution and the conversion of nutrients such as nitrogen and phosphorus into high value-added components of algae, and reduce greenhouse gas emissions.

Description

Technical Field

[0001] The invention belongs to the field of sewage treatment, and in particular relates to a sewage treatment device and method. Background Art

[0002] In recent years, agricultural non-point source pollution has become an important factor affecting water quality in the basin. Agricultural non-point source pollution is usually rich in nitrogen and phosphorus nutrients, low C / N, and high nitrate ratio. Direct discharge will not only cause a large amount of nutrient loss, but also cause serious water quality and environmental pollution. Therefore, how to achieve ecological treatment and resource treatment of agricultural non-point source pollution is the current research focus.

[0003] In my country, a large amount of waste biomass such as crop straw and wetland aquatic plants are left idle or burned on site due to the lack of effective treatment methods, which not only pollutes the environment but also causes great waste. Carbonization of plants into biochar is an important resource utilization direction for this type of waste. As a highly stable carbon-rich substance, biochar can lock the carbon fixed in biomass to prevent it from entering the atmosphere through direct incineration and microbial decomposition, and can effectively play the role of carbon sink. In sewage treatment, biochar has the characteristics of providing carbon source, enhancing pollutant adsorption and promoting biofilm formation, which can help achieve biological denitrification of sewage.

[0004] Microalgae are common single-cell organisms in agricultural and other water bodies. They not only have the characteristics of high photosynthesis efficiency, fast growth rate and strong environmental adaptability, but also are rich in high value-added ingredients such as protein, oil, polysaccharide and pigment. Using microalgae for sewage treatment can simultaneously achieve nitrogen and phosphorus recovery, sewage purification, CO 2 Multiple effects such as emission reduction and algae accumulation. However, the slow autotrophic growth rate of microalgae and the low biomass concentration limit their application in sewage treatment. Heterotrophic and mixed growth of microalgae are usually faster than photoautotrophic growth.

[0005] In summary, if a device and method can be provided for combining microalgae and microorganisms to treat low-C / N wastewater such as initial agricultural non-point source wastewater, combining microalgae cultivation with denitrification, and utilizing the enhancing effect of low-temperature biochar on denitrification performance and microalgae growth, thereby promoting the purification of polluted water bodies such as farmland runoff and the growth of microalgae and reducing greenhouse gas emissions, it is expected to deeply denitrify and treat resource-based agricultural non-point source polluted water bodies and other low-C / N wastewater, meet the green development concept under the background of "carbon neutrality", and effectively promote the transformation of agricultural non-point source pollution treatment from "removal" to "resource utilization". Summary of the invention

[0006] The object of the present invention is to provide a sewage treatment device and method.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a sewage treatment system, the sewage treatment system includes an algae purification system and a denitrification system, the algae purification system and the denitrification system are connected through a water-permeable filtering structure;

[0008] The algae purification system comprises an algae growth box made of transparent material, the denitrification system comprises a denitrification box, the denitrification box contains denitrifying microorganisms and nutrients for the survival of the denitrifying microorganisms, and the denitrification box is provided with a carbon replenishing column which can slowly release carbon source into the denitrification box.

[0009] Preferably, the carbon replenishing column is filled with a slow-release carbon source, and a plurality of carbon source release holes are provided on the surface of the column located inside the denitrification box.

[0010] Preferably, the carbon replenishment column is a split structure, including a first carbon replenishment column located in the algae growth box and a second carbon replenishment column located in the denitrification box. The first carbon replenishment column can rotate relative to the second carbon replenishment column. The inner side wall of the first carbon replenishment column is fixedly connected to a first baffle plate, and the inner side wall of the second carbon replenishment column is correspondingly provided with a second baffle plate adapted to the first baffle plate. When the first carbon replenishment column rotates relative to the second carbon replenishment column, the first baffle plate and the second baffle plate cooperate with each other, and the first carbon replenishment column and the second carbon replenishment column switch between being spatially connected and forming two independent spatial states.

[0011] Preferably, a stirring rod is provided on the outer surface of the first carbon replenishing column.

[0012] Preferably, a rotating shaft is provided on the outer surface of the first carbon replenishing column, and the rotating shaft extends to the outer surface of the algae growth box and is fixedly connected to a rotating handle.

[0013] Preferably, the algae purification system and the denitrification system are arranged left and right, and a push plate connected to an elastic component is arranged in the first carbon-feeding column. When the first carbon-feeding column rotates relative to the second carbon-feeding column until the spaces of the first carbon-feeding column and the second carbon-feeding column are independent of each other, the elastic component is in a compressed state, and the slow-release carbon source in the first carbon-feeding column squeezes the push plate; when the first carbon-feeding column rotates relative to the second carbon-feeding column until the spaces of the first carbon-feeding column and the second carbon-feeding column are connected, the elastic component is in a stretched state, and the push plate squeezes the slow-release carbon source in the first carbon-feeding column.

[0014] Correspondingly, the method for treating sewage using the sewage treatment system is to inoculate denitrifying microorganisms in the sewage to be treated, add biochar, and inoculate algae to form a microalgae-denitrification combined treatment system.

[0015] Preferably, the biochar is loaded into a carbon replenishing column, and the carbon replenishing column is placed into the sewage to be treated.

[0016] Preferably, the biochar comes from agricultural crop waste.

[0017] Preferably, the method for preparing the biochar is: cutting the waste biomass into segments, washing it, drying it at 50-60° C., and then carbonizing and pyrolyzing it at 100° C.-300° C. for 1-3 hours to obtain the biochar.

[0018] The present invention has the following beneficial effects:

[0019] The present invention provides a new sewage treatment device and method, which can artificially control the slow release degree of biochar to a certain extent, promote the growth of microalgae, strengthen the denitrification of microorganisms, promote the purification of agricultural non-point source pollution such as farmland runoff and the conversion of nutrients such as nitrogen and phosphorus into high value-added components of microalgae, and reduce greenhouse gas emissions. Biochar can also release organic matter, help achieve the enrichment of denitrifying and denitrifying microorganisms, promote denitrification, and reduce N 2 O and CO 2 The porous structure of biochar itself can also absorb and filter impurities, further purifying water.

[0020] The present invention selects waste biomass such as corn cobs and foxtail algae as the source of biochar raw materials, which can stably release carbon sources and release less nitrogen and phosphorus pollutants; elements such as nitrogen and phosphorus in the microalgae culture medium can also be provided by waste, which reduces the cultivation cost of microalgae, realizes the resource utilization of waste, and improves the growth efficiency of microalgae and the accumulation of nutrients. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the principle of the present invention;

[0022] Figure 2 It is a schematic structural diagram of a sewage treatment system in one embodiment of the present invention when the standby slow-release carbon source is not released;

[0023] Figure 3 for Figure 2 A magnified image of point A;

[0024] Figure 4 It is a schematic structural diagram of a sewage treatment system according to one embodiment of the present invention when releasing a standby slow-release carbon source;

[0025] Figure 5 It is a schematic structural diagram of another embodiment of the sewage treatment system of the present invention when the standby slow-release carbon source is not released;

[0026] Figure 6 It is a schematic structural diagram of another embodiment of the sewage treatment system of the present invention when releasing a standby slow-release carbon source;

[0027] Figure 7 Schematic diagram of COD release curves of different biochars;

[0028] Figure 8 Schematic diagram of TN release curves of different biochars;

[0029] Fig. 9 Schematic diagram of TP release curves of different biochars;

[0030] Fig.10 Schematic diagram of TN changes of sewage under combined treatment;

[0031] Fig.11 Schematic diagram of the accumulation of photosynthetic pigments, lipids, proteins and polysaccharides in microalgae. DETAILED DESCRIPTION

[0032] The present invention provides a sewage treatment method, such as Figure 1 As shown, waste biomass such as corn cobs can be used as carbon sources and culture substrates, and algae, especially microalgae, and denitrifying microorganisms can be used in sewage treatment, which can not only reduce the COD and nitrogen and phosphorus content in sewage, but also help the growth of microalgae to obtain high added value. The method specifically includes the following steps:

[0033] 1. Prepare slow-release biochar. Cut the discarded biomass of aquatic plants such as foxtail algae into small pieces of 1 to 3 cm, wash them with tap water, then wash them with pure water three times, place them in a 55°C oven for 24 hours, and take them out after drying. Put the dried product in a ceramic crucible, compact it, cover it with a lid, wrap it tightly with tin foil, and put it in an artificial intelligence box-type resistance furnace for pyrolysis and carbonization. The pyrolysis temperature is 100°C to 300°C, and the pyrolysis time is 2 hours to obtain low-temperature biochar.

[0034] 2. Inoculate denitrifying microorganisms in the sewage to be treated, and add corresponding low-temperature biochar. At the same time, inoculate algae, preferably microalgae. Form a microalgae-denitrification combined treatment system. The preferred solution is: the biochar is loaded into a carbon replenishment column, the carbon replenishment column is put into the sewage to be treated, and the biochar is slowly and gradually released into the sewage through the carbon replenishment column.

[0035] The present invention also provides a sewage treatment device, including an algae purification system and a denitrification system, wherein the algae purification system and the denitrification system are connected through a water-permeable filter structure 40. The algae purification system includes an algae growth box 10, which is made of a transparent material, and the denitrification system includes a denitrification box 20, in which denitrification microorganisms are inoculated and nutrients for the survival of the denitrification microorganisms are installed, and a carbon supplement column that can slowly release a carbon source into the denitrification box 20 is arranged in the denitrification box 20.

[0036] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. The data obtained are all average values ​​obtained after at least 3 repetitions, and all the data obtained in each repetition are valid data.

[0037] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0038] Example 1: Preparation of sewage treatment device

[0039] like Figures 2 to 6 As shown, a sewage treatment system includes an algae purification system and a denitrification system, and the algae purification system and the denitrification system are connected through a breathable and water-permeable filter structure 40. The filter structure 40 is breathable and water-permeable, and can prevent algae from entering the denitrification system, prevent biochar from entering the algae purification system, or at least prevent algae from entering the denitrification system in large quantities, and prevent biochar from entering the algae purification system in large quantities. The filter structure 40 can directly use one or more layers of breathable and water-permeable filter membranes, such as a hydrophilic PTFE microporous filter membrane with a pore size of 1.2μm. The preferred solution is: a multi-layer structure combining a filter membrane and a porous baffle, that is, one or more layers of porous baffles made of plastic or the like are respectively arranged above and below the filter membrane, so as to facilitate the installation of a carbon supplement column on the filter structure 40.

[0040] The algae purification system includes an algae growth box 10, which is made of transparent materials, such as transparent glass, transparent plastic, etc., to facilitate the entry of sunlight and ultraviolet rays to promote algae growth. The algae growth box 10 is provided with algae input and removal windows, which are not shown in the figure.

[0041] The denitrification system includes a denitrification box 20, in which denitrification microorganisms and nutrients for the survival of the denitrification microorganisms are installed. The nutrients are preferably waste biomass of crops to save energy and waste treatment. A preferred solution is that a matrix is ​​also installed inside the denitrification box 20 for the attachment and growth of microorganisms to facilitate faster and better formation of biofilms. The matrix is ​​preferably waste biomass.

[0042] A carbon replenishing column that can slowly release the carbon source into the denitrification box 20 is arranged in the denitrification box 20. The carbon replenishing column is filled with a slow-release carbon source, and a plurality of carbon source release holes 31 are arranged on the surface of the column located in the inner part of the denitrification box 20, through which the slow-release carbon source can gradually enter the denitrification box 20. The preferred scheme is: the pore size of the carbon source release hole 31 is smaller than the minimum particle size of the slow-release carbon source in the carbon replenishing column, so as to avoid the slow-release carbon source from leaking out directly as soon as it is loaded. During the treatment process, the slow-release carbon source near the carbon source release hole 31 gradually contacts with the microorganisms, becomes smaller, and gradually leaks out from the carbon source release hole 31.

[0043] The carbon replenishment column is preferably a split structure, including a first carbon replenishment column 32 located in the algae growth box 10 and a second carbon replenishment column 30 located in the denitrification box 20. Figure 2 , 3 As shown, the split structure can set the docking part of the first carbon supplement column 32 and the second carbon supplement column 30 as a mortise and tenon structure, and the first carbon supplement column 32 and the second carbon supplement column 30 can be formed into a whole by splicing. After the two are spliced, the first carbon supplement column 32 can rotate relative to the second carbon supplement column 30. The second carbon supplement column 30 is fixed on the filter structure 40, or fixed inside the algae growth box 10 and / or the denitrification box 20, forming a whole with the sewage treatment system; the fixation can be a detachable connection such as snap-on, splicing, or a non-detachable connection such as bonding, welding, etc., which can be selected according to actual conditions. After the second carbon supplement column 30 is fixed, the first carbon supplement column 32 rotates relative to the second carbon supplement column 30, that is, it is rotated inside the sewage treatment system.

[0044] In order to facilitate the rotation of the first carbon replenishing column 32, a more preferred solution is: a rotating shaft is provided on the outer surface of the first carbon replenishing column 32, and the rotating shaft extends to the outer surface of the algae growth box 10 and is fixedly connected to the rotating handle 35. A more preferred solution is: a scale is provided at a corresponding position on the outer surface of the algae growth box 10 to indicate the rotation direction and rotation position. Figure 2 , 4 As shown, when the algae growth box 10 is arranged above the denitrification box 20 and the two are arranged in an upper and lower manner, it is only necessary to set a rotating handle 35 to conveniently realize rotation. Figure 5 , 6 As shown, when the algae growth box 10 and the denitrification box 20 are arranged on the left and right, a transmission structure 38 such as a belt or chain can be sleeved on the rotating handle 35, and the other end of the transmission structure 38 extends upward to the sewage surface. A rotating shaft or other rotating structure (not shown in the figure, which is a conventional technology in the art) can be sleeved according to actual conditions to drive the transmission structure 38 to rotate when necessary, thereby driving the rotating handle 35 to rotate. In this case, the scale indicating the rotation direction and position can be set on the rotating structure on the sewage surface.

[0045] The inner side wall of the first carbon replenishing column 32 is fixedly connected to the first baffle plate 34, and the inner side wall of the second carbon replenishing column 30 is correspondingly provided with a second baffle plate 33 adapted to the first baffle plate 34. When the first carbon replenishing column 32 rotates relative to the second carbon replenishing column 30, the first baffle plate 34 and the second baffle plate 33 cooperate with each other, and the first carbon replenishing column 32 and the second carbon replenishing column 30 switch between being spatially connected and forming two independent spatial states. A slow-release carbon source for initial treatment is placed inside the second carbon replenishing column 30, and a spare slow-release carbon source is placed inside the first carbon replenishing column 32. In the initial stage of treatment, the first carbon replenishing column 32 rotates until the first baffle plate 34 and the second baffle plate 34 cooperate, and the first carbon replenishing column 32 forms an independent space relative to the second carbon replenishing column 30 (such as Figure 2 , 3 After a certain period of time, most or all of the slow-release carbon source in the second carbon replenishment column 30 is consumed or lost. At this time, the first carbon replenishment column 32 can be rotated until the entire internal space of the carbon replenishment column is connected (as shown in FIG. Figure 4 , 6 As shown in FIG. 1 , the standby slow-release carbon source located inside the first carbon replenishing column 32 enters the second carbon replenishing column 30. According to actual conditions, the first carbon replenishing column 32 can also be rotated to a partially open state to gradually replenish the slow-release carbon source.

[0046] When the algae growth box 10 is arranged above the denitrification box 20, the standby slow-release carbon source will naturally fall under the action of gravity. When the algae growth box 10 and the denitrification box 20 are arranged side by side, after the internal space of the carbon replenishment column is connected, some of the standby slow-release carbon source is difficult to automatically fall into the second carbon replenishment column 30. It is necessary to wait for the denitrifying microorganisms in the denitrification box 20 to gradually enter the first carbon replenishment column 32 through the carbon source release hole 31 before being consumed. The process takes a long time. If it is necessary to release the standby slow-release carbon source more quickly, the preferred solution is as follows: Figure 5 , 6 As shown, a push plate 39 connected to an elastic component is provided in the first carbon replenishing column 32, and the elastic component can be selected as a spring or the like. When the first carbon replenishing column 32 rotates relative to the second carbon replenishing column 30 until the spaces of the first carbon replenishing column 32 and the second carbon replenishing column 30 are independent of each other, the elastic component is in a compressed state, and the slow-release carbon source in the first carbon replenishing column 32 squeezes the push plate 39; when the first carbon replenishing column 32 rotates relative to the second carbon replenishing column 30 until the spaces of the first carbon replenishing column 32 and the second carbon replenishing column 30 are connected, the elastic component is in a stretched state, and the push plate 39 squeezes the slow-release carbon source in the first carbon replenishing column 32. A more preferred solution is: the elastic component is wrapped with a waterproof, elastic plastic film (not shown in the figure) on the outside. The elasticity of the plastic film needs to ensure that the plastic film is not damaged when stretched to the maximum stroke of the elastic component. The plastic film can prevent the slow-release carbon source from entering the internal gap of the elastic component, reducing the difficulty of use, cleaning and replacement.

[0047] A more preferred solution is that a stirring rod 36 is disposed on the outer surface of the first carbon supplementation column 32. The shape of the stirring rod 36 can be set according to actual conditions. The stirring rod 36 can provide a growth carrier for algae, and on the other hand, when the first carbon supplementation column 32 rotates, the stirring rod 36 can be driven to rotate in the algae growth box 10 at the same time, so as to break up and remix the algae that grow together, so that the algae growing at the bottom and inside can also be fully exposed to sewage, substrate, and sunlight.

[0048] The sewage treatment system is provided with a sewage inlet 21 and a sewage outlet 22, so that the sewage to be treated can flow through the algae growth box 10 and the denitrification box 20 for treatment and then flow out. If the sewage inlet 21 is higher than the sewage outlet 22, there is no need to set up a pump body or other pumping and drainage device, and the water body can flow naturally through the sewage treatment system according to gravity and other effects. The preferred scheme is: the sewage outlet 22 is higher than the sewage inlet 21, and a pumping pump, a peristaltic pump, etc. are set at the sewage inlet 21 to pump the sewage into the sewage treatment system. After the sewage treatment is completed inside the system, the water body slowly overflows from the sewage outlet 22. This method can extend the hydraulic retention time, thereby improving the single treatment effect. The sewage inlet 21 and the sewage outlet 22 are correspondingly provided with an openable and closable door (not shown in the figure). It should be noted that the sewage inlet 21 and the sewage outlet 22 in the figure are only names and examples, and do not limit the corresponding openings to be used only as inlets or outlets. In practice, the inlet can be used as an outlet or vice versa as needed, and the inlet or outlet can also be used as a sampling port.

[0049] The preferred solution is: a water-permeable and air-permeable filter membrane is arranged at the sewage inlet 21 and / or the sewage outlet 22. When the door at the sewage inlet 21 and the sewage outlet 22 is opened, the filter membrane can prevent the internal algae (when the sewage inlet 21 or the sewage outlet 22 is arranged on the algae growth box 10) or the biofilm and the culture matrix (when the sewage inlet 21 or the sewage outlet 22 is arranged on the denitrification box 20) from seeping out. The filter membrane can be detachably installed on the sewage outlet for easy replacement and sampling.

[0050] Example 2: Effect of biochar on sewage treatment

[0051] This example mainly shows the three indicators of TN (total nitrogen), TP (total phosphorus), and COD (chemical oxygen demand) before and after sewage treatment, and confirms the following two issues: (1) confirm whether the addition of different biochars to the water body will cause the above three indicators to increase, that is, whether pollutants will be introduced, or even if pollutants are introduced, whether the system can handle the pollutants introduced by itself when it is finally discharged; (2) confirm the change of COD of the water body over time after adding biochar, so as to screen out biochar that is more suitable for microbial growth.

[0052] 1. Preparation of biochar: Pick fresh foxtail algae (Myriophyllum verticillatum), clean it and cut it into small pieces of about 1 cm, wash it with an equal volume of pure water for more than 3 times, and place it in a 70℃ electric blast drying oven (WGL-45B) for 24 hours. Take 15g of dried foxtail algae and put it in a 50mL ceramic crucible, compact it, cover it, wrap it tightly with tin foil, and put it in an artificial intelligence box-type resistance furnace for pyrolysis and carbonization. The pyrolysis temperature was set to 100℃, 200℃, and 300℃, the pyrolysis time was 2h, the sample repetition number was 3, and 3 groups of biochar were obtained: 100℃-2h, 200℃-2h, 300℃-2h (B100, B200, B300), and the raw materials that were dried and not carbonized were used as the control group B.

[0053] 2. Add each group of biochar to pure water, according to the mass ratio, biochar: pure water = 1:250. Then take samples from each group and measure COD, TN, and TP respectively. Among them, COD is determined by potassium dichromate method (GB11914-89), TN is determined by alkaline potassium persulfate digestion ultraviolet spectrophotometry (HJ 636-2012), and TP is determined by ammonium molybdate spectrophotometry (GB11893-89). The measurement is continued for 24 hours to obtain the COD, TN, and TP release curves of each group of biochar in water.

[0054] COD release curve Figure 7 As shown, the results show that within 24 hours, B and B100 release COD rapidly within the first 10 hours, and the COD concentration no longer has a significant upward trend after 10 hours, indicating that there is almost no COD release, and the 24-hour COD release reaches about 350mg / L. The COD release of B300 is small, and the release time is short, and the 24-hour COD release reaches about 90mg / L. Although B200 also releases COD in a rapid process, it has been showing an upward trend, indicating that COD has been released, and the 24-hour COD release reaches about 235mg / L.

[0055] The release curves of TN and TP are shown in Figure 8 , 9 As shown in the figure, the results show that within 24 hours, the TN and TP release of B and B100 are the highest. The TN and TP release of B300 is small and can be ignored. The TN release of B200 is small and almost negligible; the TP release of B200 is much smaller than that of B and B100.

[0056] Example 3: Demonstration of the effect of combined treatment of sewage by microalgae, biochar and denitrifying bacteria

[0057] 1. Prepare a sewage treatment system according to Example 1 (according to Figure 2), prepare 3 groups of biochar according to Example 2. Configure sewage to simulate farmland drainage. The nitrate content in farmland drainage is high and the C / N is very low, which affects the normal biological denitrification and makes it impossible to further remove nitrate. Water quality of distribution sewage: TN 42mg / L, TP 4.2mg / L, C / N=0.1. Weigh each group of biochar and put it into the test device at a ratio of 3g / L. Microalgae (Chlorella) and denitrifying bacteria (E. acetylbacterium, CGMCC No.14620) are added at a ratio of 10% and 5% of the volume of the treatment system, respectively. The initial OD of the microalgae is 680 ≈0.1, initial OD of denitrifying bacteria 600 ≈0.02. At the same time, the experimental sewage without biochar was set as the control group Z, the experimental groups with B, B100, B200, B300 and microalgae were marked as ZB, ZB100, ZB200, ZB300, and the experimental group with only B200 and no microalgae was marked as B200. The hydraulic retention time of each group was set to 3 days and 6 days respectively (after the corresponding substances and sewage were added, the sewage outlet 22 was blocked for a specific time, and the sewage outlet 22 was opened for sampling during the measurement), and the total nitrogen and total phosphorus of the water quality were measured and the pollutant removal rate was calculated.

[0058] Changes in nitrate nitrogen, total nitrogen and total phosphorus Fig.10 As shown. For nitrate nitrogen and total nitrogen, the removal effects of nitrate nitrogen and total nitrogen in groups B200 and ZB200 were the most significant. The removal rates of total nitrogen reached 85% under the conditions of hydraulic retention time of 3 days and 6 days, which was more than 65% higher than that of the control group Z. This shows that the combined treatment of microalgae and denitrification can improve the treatment effect of total nitrogen.

[0059] For total phosphorus, the addition of biochar caused an increase in total phosphorus in the sewage. Taking the hydraulic retention time of 3 days as an example, the total phosphorus of B and B100 increased the most, followed by B200, and then ZB200. The increase in total phosphorus of ZB300 was small. Since microalgae can effectively remove total phosphorus, the increase in total phosphorus of ZB200 combined with microalgae is less than that of B200, and the difference is particularly obvious when the hydraulic retention time is 6 days. This shows that the combined treatment of microalgae and denitrification can make up for the difficulty in removing total phosphorus during denitrification, and increasing the retention time can improve the total phosphorus treatment efficiency. Although the addition of biochar leads to the release of a certain amount of total phosphorus, B200 has the best denitrification effect in comparison. During the treatment, most of the released TP can be effectively removed by microalgae, and the impact on total phosphorus is relatively small.

[0060] 2. Prepare a sewage treatment system according to Example 1 (according to Figure 2 The biochar was prepared according to step 1 of this embodiment. Each group of biochar was put into the test device at a ratio of 3 g / L, and microalgae and denitrifying bacteria were added at a ratio of 10% and 5% of the volume of the treatment system, respectively. The initial OD of the microalgae was 680≈0.1, initial OD of denitrifying bacteria 600 ≈0.02. After the experiment, after 6 days of hydraulic retention time (after adding the corresponding substances and sewage, the sewage outlet 22 was blocked for 6 days), samples were taken to measure the total photosynthetic pigments, oils, proteins and polysaccharides of the microalgae. Because some microalgae will adhere to the device, in order to improve the accuracy of the results, the device was ultrasonically treated after the experiment, and various indicators before and after ultrasound were tested respectively. At the same time, a control group was set up: the setting method is the same as step 1.

[0061] (1) Photosynthetic pigments. The chlorophyll a (C a ), chlorophyll b(C b ) and carotenoids (C x+c ), through C a +C b +C x+c Calculate photosynthetic pigments. Take 1mL of uniform algae solution in a 1.5mL centrifuge tube and centrifuge at 10000rpm for 5min. Carefully remove the supernatant and collect the algae precipitated at the bottom. Add 1mL of anhydrous ethanol and shake to mix. Keep warm in a 78℃ metal bath for 5min. Then place in a completely dark environment overnight. After overnight, centrifuge at 4500rpm for 20min. Take 200μL of the supernatant and detect the absorbance values ​​(OD) of λ=470, 649, and 665nm on a 96-well plate respectively. Use the following formula to calculate the pigment content:

[0062] C a (mg / L)=13.36OD 665 -5.91OD 649 ; C b (mg / L)=27.43OD 649 -5.91OD 665 ;

[0063] C x+c (mg / L)=(1000OD 470 -2.13C a -97.64C b ) / 209.

[0064] (2) Oil. The lipid content in biomass was determined by Nile red fluorescence colorimetry. Take 1 mL of uniform algae solution in a 1.5 mL centrifuge tube and centrifuge at 10,000 rpm for 5 min. Carefully remove the supernatant and collect the algae precipitated at the bottom. Add 1 mL of anhydrous ethanol and oscillate to mix. Keep warm in a 78°C metal bath for 5 min and place for 10 min to achieve the purpose of decolorization and reduce the interference of photosynthetic pigments on oil determination. Then centrifuge at 4,500 rpm for 20 min. Carefully remove the supernatant and collect the algae precipitated at the bottom. Repeat twice and add 1 mL of ultrapure water. Disrupt in an ultrasonic disruptor for 20 min (4°C, power 180w, work 2s and stop 2s). After the disruption is completed, the Chlorella cell tissue is fully disrupted, and then 20 μL of Nile red dye is added. After waiting for 10 min in the dark, take 200 μL of the supernatant and measure its fluorescence intensity on a 96-well plate at Ex=530 and Em=580 respectively.

[0065] (3) Protein. Take 5 mL of uniform algae solution in a 10 mL centrifuge tube and centrifuge at 10,000 rpm for 5 min. Carefully remove the supernatant and collect the algae precipitated at the bottom. Add 5 mL of 2 mol / L NaOH solution, shake well to dissolve it completely, boil in a boiling water bath for 10 min, take it out and cool it to room temperature, add 2 mol / L HCl to each group to neutralize it, shake well and centrifuge, take the supernatant, and use the BCA protein concentration assay kit to determine the protein concentration.

[0066] (4) Polysaccharides. Take 5 mL of uniform algae solution and place it in a 10 mL centrifuge tube. Centrifuge at 10,000 rpm for 5 min. Carefully remove the supernatant and collect the algae precipitated at the bottom. Add 5 mL of 2 mol / L NaOH solution, shake well to dissolve it completely, boil in a boiling water bath for 10 min, take it out and cool it to room temperature, add 2 mol / L HCl to each group to neutralize it, shake well and centrifuge, and take the supernatant for later use. The polysaccharide concentration was determined by the sulfuric acid-phenol method.

[0067] Under different experimental conditions, the accumulation of photosynthetic pigments, lipids, proteins and polysaccharides in microalgae Fig.11 shown. Fig.11The figure in the lower right corner is a photosynthetic pigment diagram. Photosynthetic pigments include chlorophyll a, chlorophyll b and carotene. The total amount of photosynthetic pigments in each bar is the total amount of photosynthetic pigments in this group after the superposition of multiple pigment columns. The results show that the total photosynthetic pigments, polysaccharides, oils and proteins after ultrasound are higher than those before ultrasound, indicating that part of the microalgae grows on the device. The attached growth part of ZB200 accounts for the largest proportion, and the photosynthetic pigments of its attached growth part account for 22.79% of the total. The addition of biochar increases the total photosynthetic pigments, polysaccharides, oils and proteins of microalgae, and enhances the ability of attached growth. Among them, the improvement effect of each biomass component of microalgae in B, ZB100 and ZB200 is equivalent, and the promotion effect is significantly higher than that of ZB300. The total photosynthetic pigments, polysaccharides, oils and proteins of microalgae in the biochar addition group can be increased by up to 3.47 times, 6.67 times, 1.92 times and 7.21 times compared with the experimental group Z, and carotene was only measured in the ZB200 group. This shows that low-temperature biochar can not only improve the denitrification effect by releasing organic matter, but also the nutrients in the biochar and the CO generated during the denitrification process. 2 It promotes the synthesis of microalgae biomass, increases the accumulation of various microalgae components, and transforms nitrogen, phosphorus, etc. into high value-added microalgae components.

[0068] The embodiments described above are only descriptions of the preferred modes of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations, modifications, and substitutions made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A sewage treatment system, characterized in that: The sewage treatment system comprises an algae purification system and a denitrification system, wherein the algae purification system and the denitrification system are connected via a water-permeable filtering structure (40); The algae purification system comprises an algae growth box (10), the algae growth box (10) is made of a transparent material, the denitrification system comprises a denitrification box (20), the denitrification box (20) contains denitrifying microorganisms and nutrients for the survival of the denitrifying microorganisms, a carbon replenishing column which can slowly release a carbon source into the denitrification box (20) is arranged in the denitrification box (20); the carbon replenishing column contains a slow-release carbon source, and a column surface of the carbon replenishing column located inside the denitrification box (20) is provided with a plurality of carbon source release holes (31); the carbon replenishing column is a split structure, comprising a first carbon replenishing column located in the algae growth box (10); The first carbon replenishing column (32) and the second carbon replenishing column (30) are located in the denitrification box (20); the first carbon replenishing column (32) can rotate relative to the second carbon replenishing column (30); the first material baffle plate (34) is fixedly connected to the inner wall of the first carbon replenishing column (32); the second material baffle plate (33) adapted to the first material baffle plate (34) is correspondingly arranged on the inner wall of the second carbon replenishing column (30); when the first carbon replenishing column (32) rotates relative to the second carbon replenishing column (30), the first material baffle plate (34) and the second material baffle plate (33) cooperate with each other, and the first carbon replenishing column (32) and the second carbon replenishing column (30) switch between the internal space of the carbon replenishing column being connected and forming two independent spatial states.

2. The sewage treatment system according to claim 1, characterized in that: A stirring rod (36) is arranged on the outer surface of the first carbon replenishing column (32).

3. The sewage treatment system according to claim 1, characterized in that: A rotating shaft is arranged on the outer surface of the first carbon replenishing column (32), and the rotating shaft extends to the outer surface of the algae growth box (10) and is fixedly connected to a rotating handle (35).

4. The sewage treatment system according to any one of claims 1 to 3, characterized in that: The algae purification system and the denitrification system are arranged on the left and right, and a push plate (39) connected with an elastic component is arranged in the first carbon replenishing column (32). When the first carbon replenishing column (32) rotates relative to the second carbon replenishing column (30) until the spaces of the first carbon replenishing column (32) and the second carbon replenishing column (30) are independent of each other, the elastic component is in a compressed state, and the slow-release carbon source in the first carbon replenishing column (32) squeezes the push plate (39); when the first carbon replenishing column (32) rotates relative to the second carbon replenishing column (30) until the spaces of the first carbon replenishing column (32) and the second carbon replenishing column (30) are connected, the elastic component is in a stretched state, and the push plate (39) squeezes the slow-release carbon source in the first carbon replenishing column (32).

5. A method for treating sewage using the sewage treatment system according to any one of claims 1 to 4, characterized in that: Denitrifying microorganisms are inoculated into the sewage to be treated, and biochar is added and algae are inoculated to form a microalgae-denitrification combined treatment system; the biochar is loaded into a carbon replenishing column, and the carbon replenishing column is put into the sewage to be treated.

6. The method according to claim 5, characterized in that: The biochar is derived from waste biomass.

7. The method according to claim 5, characterized in that: The method for preparing the biochar comprises cutting the waste biomass into sections, washing it, drying it at 50-60° C., and then carbonizing and pyrolyzing it at 100-300° C. for 1-3 hours to obtain the biochar.

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