Biofilm-Membrane Photobioreactor and Method for Treating Municipal Sewage ROC

Abstract

Biofilm-membrane photobioreactor for treating municipal sewage ROC, including a reaction vessel, a membrane module and a light module. Fillers for forming a biofilm are added to the reaction vessel; the fillers for forming the biofilm are obtained by a film hanging operation of adding fillers and microalgae to a culture medium, and the microalgae are Scenedesmus sp, FACHB-1574. The present invention also provides a method for treating reverse osmosis concentrate water. An intermittent operation method is adopted, and the operation cycle is divided into a water inlet period, a first aeration period, a second aeration period and a water outlet period; in the water inlet period, municipal sewage ROC is introduced; in the first aeration period, CO2 is introduced, and the flow rate is controlled to keep the pH at 6.5-7.3; in the second aeration period, air is introduced, and the pH of the reaction system is increased by the growth of the microalgae itself to remove Ca 2+ , Mg 2+ ; in the water outlet period, the algal liquid is separated through the membrane module, the sewage is discharged, and the microalgae are retained inside the reaction vessel.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, relates to the treatment of reverse osmosis concentrate (ROC) of municipal sewage, and particularly relates to a biofilm-membrane photobioreactor and method for treating ROC of municipal sewage. Background Art

[0002] Reverse osmosis (RO) technology has the advantages of high pollutant removal efficiency, stable water quality, convenient operation, etc., and plays an increasingly important role in the resource utilization of municipal sewage. However, the ROC generated by the reverse osmosis process is one of the main difficulties hindering the wide application of this technology. With the continuous increase in the reuse amount of municipal sewage, the quantity of ROC of municipal sewage has risen rapidly, which has exerted great pressure on the environment. ROC accounts for about 25-50% of the input stream and almost contains all the high-concentration components in the input stream. Its water quality characteristics are high concentrations of nitrogen (TN: 23-62 mg / L), phosphorus (TP: 1-20 mg / L), poor biodegradability, high total dissolved solids (TDS) content (1129-5560 mg / L), and high concentrations of Ca 2+ (250-400 mg / L), Mg 2+ (70-250 mg / L) are prone to scale formation.

[0003] The mainstream treatment process for the existing ROC of municipal sewage is advanced oxidation technology, which mainly aims at the removal of organic matter and has low removal efficiency for nitrogen, phosphorus and hardness ions in ROC. Microalgae provide an effective way to simultaneously remove nitrogen, phosphorus, etc. in the ROC of municipal sewage: as photoautotrophic organisms, microalgae do not require organic matter to provide a carbon source and can effectively remove nitrogen and phosphorus. And during the growth process of algae, the pH value of the solution will increase, and Ca 2+ , Mg 2+ are removed by chemical precipitation. In addition, the nitrogen and phosphorus absorbed by microalgae can achieve the purpose of resource recovery by recycling microalgae, and the biomass produced can also be used for the production of bioenergy, food, animal feed and drugs, which is a promising wastewater treatment technology.

[0004] The membrane photobioreactor can effectively separate the algal liquid, accumulate a large amount of biomass inside the reactor, and thus has the advantages of shortening the reaction time and efficiently recycling microalgae. However, culturing microalgae in suspension will cause problems such as light shading, large gas transmission resistance and high water content of recycled microalgae under high-density conditions. Summary of the Invention

[0005] To overcome the above-mentioned drawbacks of the prior art, the object of the present invention is to provide a biofilm-membrane photobioreactor and method for treating urban sewage ROC. By adopting the method of immobilized microalgae culture, through fixing or adding microalgae attachment materials in the suspension culture system, microalgae form a biofilm on the moving packing, thereby constructing a biofilm-membrane photobioreactor, which can effectively treat nitrogen, phosphorus, Ca 2+ , Mg 2+ etc. in urban sewage ROC, and can efficiently accumulate microalgae biomass to achieve the treatment of urban sewage ROC and the recovery of microalgae.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A biofilm-membrane photobioreactor for treating urban sewage ROC, comprising a reaction vessel, a membrane module in the reaction vessel, and a light module outside the reaction vessel. Packing for forming a biofilm is added to the reaction vessel; the packing for forming a biofilm is obtained by performing a film hanging operation by adding packing and microalgae to a culture medium.

[0008] In one embodiment, the packing material is polyethylene, cylindrical, and its density is less than that of water so that it can be suspended in water. The culture medium is BG-11 culture medium, and the culture medium can submerge the packing.

[0009] In one embodiment, the microalgae is Scenedesmus sp, and the number in the Freshwater Algae Species Bank of the Chinese Academy of Sciences is FACHB-1574.

[0010] In one embodiment, for the film hanging operation, the time is 20 to 40 days. During this period, CO2 is introduced to supplement the carbon source, the light intensity is set to 5000 to 15000 lux, the light-dark time ratio is 6h / 6h to 10h / 2h, the culture medium is replaced during this period, and microalgae are intercepted by the membrane module.

[0011] In one embodiment, the volume ratio of the packing for forming a biofilm in the reaction vessel is 20 to 50%, and the initial biomass is 1.50 to 2.00 g / L.

[0012] In one embodiment, before the microalgae are added to the culture medium containing packing, they are first cultured in another culture medium under weak light conditions of 1500 to 5000 lux until the logarithmic growth phase.

[0013] In one embodiment, the membrane module is made of PVDF hollow fiber membrane filaments, the membrane pore size is less than 0.22 μm, and the effective surface area of the membrane module adapts to the size of the reactor used.

[0014] The present invention also provides a method for treating ROC in urban sewage, which is realized based on the biofilm-membrane photobioreactor for treating ROC in urban sewage, and includes the following steps:

[0015] Step 1), adopt an intermittent operation method, set the operation cycle, and divide the operation cycle into a water inlet period, a first aeration period, a second aeration period, and a water outlet period;

[0016] Step 2), in the water inlet period, introduce ROC into the biofilm-membrane photobioreactor; in the first aeration period, stop water inlet, introduce CO2 into the biofilm-membrane photobioreactor, and control the flow rate to keep the pH of the reaction system at 6.5-7.3; in the second aeration period, stop introducing CO2, introduce air into the biofilm-membrane photobioreactor, and utilize the self-growth of microalgae to increase the pH of the reaction system, thereby removing Ca 2+ 、Mg 2+ ; in the water outlet period, separate the algal liquid through the membrane module, discharge the sewage, and retain the microalgae inside the reaction vessel to form concentrated algal liquid inside the reaction vessel.

[0017] In one embodiment, in the water inlet period, CO2 is introduced synchronously; in the water outlet period, air is continuously introduced.

[0018] In one embodiment, in the water outlet period, measure the dry weight of the microalgae in the concentrated algal liquid, and discharge part of the concentrated algal liquid by calculation so that the microalgae biomass inside the reaction vessel remains at 2.00-2.29 g / L during the next batch of test runs.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] The present invention uses microalgae, which can effectively remove nitrogen, phosphorus, Ca 2+ 、Mg 2+ in ROC. At the same time, microalgae can use CO2 for photosynthesis, which is a potential carbon fixation method.

[0021] The membrane module placed in the reactor of the present invention can filter and retain the microalgae in the reactor during water outlet, while discharging the treated sewage separately. Therefore, high-density microalgae can be accumulated inside the reactor to improve the treatment efficiency. At the same time, by selecting appropriate fillers, the phenomenon of light shading can be effectively avoided; the algal liquid can be effectively separated, and the moisture content in the recovered biomass can be reduced, which is beneficial to subsequent biomass recovery. Description of the Drawings

[0022] Figure 1 is a schematic structural diagram of the biofilm-membrane photobioreactor of the present invention. Detailed Embodiments

[0023] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples.

[0024] As Figure 1 shown, the present invention provides a biofilm-membrane photobioreactor for treating urban sewage ROC. A general membrane photobioreactor includes a reaction vessel 1, a membrane module 2 is arranged in the reaction vessel 1, and a light module 4 is arranged outside. On this basis, the present invention adds a filler for forming a biofilm. The filler for forming a biofilm is obtained by performing a film hanging operation by adding a filler and microalgae to a culture medium, and is added to the reaction vessel 1.

[0025] Through the "filler for forming a biofilm", when using the present invention to treat urban sewage ROC, on the one hand, microalgae will consume nutrients such as nitrogen and phosphorus in the water during growth and synthesize their own cell substances, thereby achieving the removal of nitrogen and phosphorus pollutants in the water. Therefore, the microalgae therein can be used to remove nitrogen and phosphorus in ROC; and by increasing the pH value, Ca 2+ and Mg 2+ in the water can be removed. On the other hand, microalgae can use CO2 for photosynthesis, thereby achieving effective carbon fixation. On the third hand, the extracellular polymer (EPS) secreted by microalgae adheres the microalgae to the surface-rough filler, that is, a biofilm is formed, so that a layer of microalgae adheres to the surface of the filler, achieving a high biomass. Due to the increase in pH value and the formation of Ca 2+ and Mg 2+ precipitates, the microalgae will self-flocculate to the bottom of the reactor, affecting the pollutant treatment effect. Therefore, adding a filler can prevent the microalgae on the filler from self-flocculating to the bottom of the reactor, increasing the stability of the pollutant removal efficiency.

[0026] At the same time, the membrane module 2 of the reaction vessel 1 can filter and intercept microalgae during water outlet, effectively separating the algal liquid, reducing the moisture content in the recovered biomass, achieving high-density accumulation of microalgae, and the biomass generated can also be used for biomass recycling.

[0027] In some embodiments of the present invention, the filler material is selected as polyethylene, the shape is selected as cylindrical, the diameter can generally be 20-30 mm, and 25 cm is further preferably selected. The height can generally be 5-15 mm, and 10 cm is further preferably selected. Its density is less than the density of water, that is, the density is 1.00 g / cm 3 Hereinafter, in order to make it capable of suspending in water, the density of 0.9720 g / cm is selected in this embodiment 3 .

[0028] In this example, the polyethylene filler is white and has a large pore structure, allowing light to penetrate effectively. It also refracts light to a certain extent, allowing it to better penetrate the reactor interior. The presence of the filler and aeration further enhance the movement of the algae liquid within the reactor, ensuring that microalgae at different locations receive effective light.

[0029] In some embodiments of the present invention, during the biofilm formation operation, the culture medium used is BG-11 culture medium, which should be sterilized by high pressure before use, and the culture medium should be able to submerge the filler.

[0030] In some embodiments of the present invention, the microalgae is Scenedesmus sp., which has the species number FACHB-1574 from the Freshwater Algae Library of the Chinese Academy of Sciences and can be purchased through public commercial channels.

[0031] The microalgae Scenedesmus sp. FACHB-1574 used in this example is a single-celled green lower plant, typically 2 to 20 μm in size. It grows rapidly, multiplying within a few hours. Currently, the application of this microalgae remains in the laboratory stage, and there are no public reports on its specific uses.

[0032] In some embodiments of the present invention, the biofilm formation operation can be completed in other containers and then transferred to the reaction vessel 1. This embodiment provides a specific process for the biofilm formation operation. After the filler is sterilized at high temperature, it is added to the second container, and the sterilized BG-11 culture medium is added thereto until the filler is just submerged. Microalgae are then added. The biofilm formation operation generally takes 20 to 40 days, and can be further preferably 30 days. During this period, CO2 is introduced to supplement the carbon source, the light intensity is set to 5000 to 15000 lux, and can be further preferably 10000 lux, and the light-dark time ratio is 6h / 6h to 10h / 2h, and can be further preferably 10h / 2h; during this period, the culture medium is replaced by a peristaltic pump, and the microalgae are retained by the membrane assembly.

[0033] For example, in this embodiment, the microalgae can be centrifuged at 6000 rpm for 10 minutes and washed twice with pure water before being added. The second container is cylindrical, with a diameter of 160 mm, a height of 318 mm, and an internal effective volume of 5 L. The membrane assembly used can be an ultrafiltration membrane assembly, with a CO2 concentration of 5% (volume concentration, the remainder being air) and a gas flow rate of 100 mL / min. A biofilm is formed on the surface of the filler through a biofilm formation operation.

[0034] In some embodiments of the present invention, before the microalgae are added to the culture medium containing fillers, they can be first expanded in other containers, that is, expanded in another culture medium under low light conditions of 1500 to 5000 lux until the logarithmic growth phase. Generally, it is preferred to expand at 3000 lux for 6 - 8 days to reach the logarithmic growth phase.

[0035] In some embodiments of the present invention, the volume ratio of the filler for forming the biofilm in the reaction vessel 1 is 20 - 50%, preferably 30%, and the initial biomass is 1.50 - 2.00 g / L, preferably 2.00 g / L.

[0036] In some embodiments of the present invention, the membrane module 2 is made of PVDF hollow fiber membrane filaments, and can be selected as a microfiltration membrane module, that is, the membrane pore size is less than 0.22 μm, and more preferably 0.17 μm. The effective surface area of the membrane module adapts to the size of the reactor used. In this embodiment, it is set to 0.2 m 2 。

[0037] The membrane module 2 of this embodiment can effectively filter and retain the microalgae, while discharging the treated sewage separately, accumulating high-density microalgae inside the reactor.

[0038] Using the above biofilm-membrane photobioreactor to treat urban sewage ROC, first build a complete framework according to the above biofilm-membrane photobioreactor, refer to Figure 1 as shown, that is, the sewage tank 7 is directly connected to the reaction vessel 1 through the peristaltic pump 5, and the effluent tank 8 is connected to the membrane module 2 through the peristaltic pump 6. The aeration head at the bottom of the reaction vessel 1 is connected to the external gas cylinder 9 and the air aerator 10. The gas cylinder 9 contains CO2, and the outlet of the air aerator 10 can be mixed with the outlet of the gas cylinder 9.

[0039] The treatment process mainly includes the following steps:

[0040] Step 1), adopt an intermittent operation method, set the operation cycle, and divide the operation cycle into an inlet water period, a first aeration period, a second aeration period, and an outlet water period in sequence.

[0041] In the embodiment of the present invention, taking 36 h as an operation cycle, the gas flow rate is 400 mL / min, where the inlet water period is 10 min, the first aeration period is 12 h, the second aeration period is 23 h, and the outlet water period is 50 min.

[0042] In this step, during the water inlet period, CO2 can be introduced synchronously in advance; while during the water outlet period, the introduction of air can be continued. That is to say, the first aeration period covers the water inlet period, and the second aeration period covers the water outlet period. At this time, the first aeration period extends forward by 10 minutes, and the aeration is synchronized with the water inlet. The second aeration period extends backward by 50 minutes, and the aeration is synchronized with the water outlet. Introducing carbon dioxide synchronously during water inlet can save time, allowing carbon dioxide to start entering the solution during water inlet, enabling microalgae to quickly carry out photosynthesis to remove pollutants. Continuing to introduce air during water outlet is because during water outlet, microalgae will be adsorbed onto the surface of the membrane module, and the introduction of air causes the bubbles to scour the membrane surface.

[0043] Step 2), during the water inlet period, ROC is introduced into the biofilm-membrane photobioreactor.

[0044] In the embodiment of the present invention, for a membrane photobioreactor with an effective volume of 5 L, 3.5 L of ROC can be added, 220 fillers with biofilms formed on the surface are added, so that the volume ratio of the fillers is 30%, and the initial biomass is about 2.00 g / L. The fillers forming biofilms in the reaction vessel 1 have two forms, one is a suspended state, suspended in the liquid, and the other is an attached state, with a biofilm formed on the surface of the fillers. The filler 3 attached with microalgae is shown in the figure.

[0045] During the first aeration period, the water inlet is stopped, and CO2 is introduced into the biofilm-membrane photobioreactor, and the flow rate is controlled to keep the pH of the reaction system at 6.5 - 7.3.

[0046] During the second aeration period, the introduction of CO2 is stopped, and air is introduced into the biofilm-membrane photobioreactor, and the pH of the reaction system is increased by the growth of microalgae itself to remove Ca 2+ 、Mg 2+ .

[0047] During the water outlet period, the algal liquid is separated through the membrane module 2, the sewage is discharged, and the microalgae are retained inside the reaction vessel 1, forming a concentrated algal liquid inside the reaction vessel 1. Discharging algae each time during water outlet can ensure that the microalgae biomass in the reactor remains basically stable.

[0048] During the process, the effective light intensity on the surface of the reactor is 30000 lux, the light-dark time ratio is 10 h / 2 h, the water temperature is maintained at 24.5 - 25.5 °C, and the microalgae biomass in the reactor is maintained at 2.00 - 2.29 g / L (where the microalgae content in the suspension is 1.00 - 1.22 g / L).

[0049] In this step, during the water discharge period, the dry weight of microalgae in the concentrated algae solution is measured, and a part of the concentrated algae solution is discharged by calculation so that the microalgae biomass inside the reaction vessel (1) during the next batch of tests runs is maintained at 2.00 - 2.29 g / L (where the suspended microalgae biomass is 1.00 - 1.22 g / L).

[0050] During the process of the treatment method of the present invention, a rotameter and a peristaltic pump can be used to control the CO2 concentration, aeration intensity, influent and effluent of the reactor respectively.

[0051] The following are specific embodiments of the present invention.

[0052] Example 1

[0053] In this example, the effective volume of the biofilm-membrane photobioreactor is 5 L, and the municipal sewage ROC is taken from a certain reclaimed water plant in Beijing. The influent COD value is 38 mg / L, the influent TN is 28 mg / L, and the influent TP is 0.44 mg / L. The temperature inside the reactor is 24.5 - 25.5 °C, and the pH is 6.5 - 7.8. Since too high nitrogen-phosphorus ratio in the raw water will affect the removal effect of TN, the nitrogen-phosphorus mass ratio in the raw water is adjusted to 14:1 (the dosage of K2HPO4·3H2O is 14.72 mg / L).

[0054] In this example, the optimization process of the microalgae biomass inside the biofilm-membrane photobioreactor is as follows:

[0055] 1) The initial microalgae biomass in the reactor is 1.08 g / L (where the packing volume ratio is 30%, the microalgae biomass on the packing surface is 0.82 g / L, and the suspended microalgae biomass is 0.26 g / L). The reactor uses peristaltic pump 1 to feed water, and the influent volume is 3.5 L.

[0056] 2) Turn on the gas flowmeter, aerate the reactor, and introduce a gas flow of 400 mL / min and a CO2 with a volume concentration of 5% (the balance is air), maintain the solution pH at 6.5 - 7.3, the temperature at 24.5 - 25.5 °C, the light intensity at 30000 lux, and the light-dark time ratio at 10 h / 2 h.

[0057] 3) Each operation cycle of the reactor is 48 h, the influent period is 10 min, continuous aeration is 48 h, and the drainage period is 50 min. Sampling is carried out at intervals of 12 h. A total of 6 cycles are run.

[0058] 4) The peristaltic pump device is connected to the membrane module for drainage, and the microalgae are retained inside the reactor.

[0059] 5) After the operation is completed, the removal of TN and TP in the effluent is measured, and the microalgae biomass is monitored in a timely manner to find the appropriate range of microalgae biomass inside the reactor.

[0060] 6) In this embodiment, as the microalgae biomass in the reactor increases, the TN removal rate also increases. However, when the biomass concentration reaches 2.29 g / L (the suspended microalgae biomass is 1.22 g / L), the TN removal rate in the system no longer increases significantly. Therefore, the optimized reactor biomass range selected is 2.00 - 2.29 g / L (the suspended microalgae is 1.00 - 1.22 g / L). The specific information is shown in Table 1 below.

[0061] Table 1 Pollutant removal efficiency and microalgae biomass during the optimization process of microalgae biomass in the reactor:

[0062]

[0063]

[0064] Example 2

[0065] In this embodiment, the effective volume of the biofilm - membrane photobioreactor is 5 L, and the urban sewage ROC is taken from a certain reclaimed water plant in Beijing. The influent COD value is 38 mg / L, the influent TN is 28 mg / L, and the influent TP is 0.44 mg / L. The temperature in the reactor is 24.5 - 25.5 °C, and the pH is 6.5 - 7.8. Since too high nitrogen - phosphorus ratio in the raw water will affect the TN removal effect, the nitrogen - phosphorus mass ratio in the raw water is adjusted to 14:1 (the dosage of K2HPO4·3H2O is 14.72 mg / L).

[0066] In this embodiment, the optimization process of the hydraulic retention time of the biofilm - membrane photobioreactor is as follows:

[0067] 1) The initial microalgae biomass in the reactor is 1.94 g / L, and the microalgae biomass in the reactor is maintained at 2.00 - 2.29 g / L in subsequent experiments. The reactor is fed with water by peristaltic pump - 5, and the influent volume is 3.5 L.

[0068] 2) Turn on the gas flowmeter, aerate the reactor, the gas flow rate is 400 ml / min, the temperature is 24.5 - 25.5 °C, the light intensity is 30000 lux, and the light - dark time ratio is 10 h / 2 h. Since the formation of Ca 2+ , Mg 2+ precipitates requires an increase in pH, the aeration method in the reactor is changed. 5% CO2 (the balance is air) is introduced for the first 12 h, and then air aeration is changed for the next 36 h to increase the pH value in the reactor to remove Ca 2+ , Mg 2+ .

[0069] 3) The operation cycle of the reactor is 48 h, with the water inlet period being the first 10 min and the drainage period being the last 50 min. Samples are taken every 12 h. A total of 5 cycles are run.

[0070] 4) The peristaltic pump device is connected to the membrane module for drainage, and the microalgae are retained inside the reactor. The microalgae and Ca 2+ , Mg 2+ precipitates deposited in the reactor are discharged every 2 d to ensure the stability of the reactor.

[0071] 5) After the operation is completed, the removal of TN, TP, Ca 2+ , Mg 2+ by the microalgae is mainly investigated, and the biomass of suspended microalgae and the change of pH value in the reactor are monitored to find the optimal hydraulic retention time.

[0072] 6) In this example, the removal rates of Ca 2+ , Mg 2+ are relatively low in the first 12 h and the highest from 12 to 24 h. And the increase of pH and the Ca 2+ , Mg 2+ precipitates will cause microalgae self-flocculation, resulting in changes in the content of suspended microalgae. If the time of pH increase is too long, it will affect the treatment effect of the next batch of influent. Therefore, the hydraulic retention time is selected as 36 h. The specific information is shown in Table 2.

[0073] Table 2 Removal efficiency of pollutants and microalgae biomass during the optimization of hydraulic retention time

[0074]

[0075] Example 3

[0076] In this example, the effective volume of the biofilm-membrane photobioreactor is 5 L, and the urban sewage ROC is taken from a certain reclaimed water plant in Beijing. The influent COD value is 38 mg / L, the influent TN is 28 mg / L, and the influent TP is 0.44 mg / L. The temperature in the reactor is 24.5 - 25.5 °C, and the pH is 6.5 - 7.8. Since too high nitrogen-phosphorus ratio in the raw water will affect the removal effect of TN, the nitrogen-phosphorus mass ratio in the raw water is adjusted to 14:1 (the dosage of K2HPO4·3H2O is 14.72 mg / L).

[0077] In this example, the stable operation process of the biofilm-membrane photobioreactor is as follows:

[0078] 1) The microalgae biomass in the reactor is maintained at 2.00 - 2.29 g / L, and the reactor is fed with water by peristaltic pump -5, with the influent volume being 3.5 L.

[0079] 2) Turn on the gas flowmeter, aerate the reactor, and introduce a gas flow rate of 400 mL / min. Among them, the first 12 h is the first aeration period, and a CO2 gas with a concentration of 5% (the balance is air) is introduced to maintain the solution pH at 6.5 - 7.3. The subsequent 24 h is the second aeration period, with air aeration, a temperature of 24.5 - 25.5 °C, a light intensity of 30000 lux, and a light - dark time ratio of 10 h / 2 h.

[0080] 3) The operation cycle of the reactor is 36 h, with the first 10 min being the water inlet period and the subsequent 50 min being the drainage period. It operates for a total of 30 d.

[0081] 4) The peristaltic pump device is connected to the membrane module for drainage, and the microalgae are retained inside the reactor.

[0082] 5) After the experiment, the removal of TN, TP, Ca 2+ , Mg 2+ is measured, and the suspended microalgae biomass and the effluent pH are monitored in a timely manner to facilitate maintaining the microalgae biomass in the reactor within a reasonable range.

[0083] 6) In this embodiment, under the conditions of reasonable microalgae biomass and hydraulic retention time, the reactor shows good removal effects on pollutants. Some effluent data are shown in Table 3.

[0084] Table 3: Pollutant removal efficiency and effluent pH value during the stable operation of the reactor under optimized conditions

[0085]

[0086]

[0087] Thus, it can be seen that the present invention has the characteristics of high removal efficiency and simple operation. The selected microalgae (Scenedesmus sp. FAHB - 1574) can effectively adapt to the ROC of urban sewage, have a high removal efficiency for nitrogen and phosphorus, and can remove a certain amount of hardness ions. The presence of the filler can reduce the light shielding phenomenon and enhance the stability of the reactor during the removal of Ca 2+ , Mg 2+ . The presence of the membrane module can separate the microalgae retention time and the hydraulic retention time, effectively intercept the microalgae, enabling a relatively high - concentration accumulation of microalgae in the reactor, which is convenient for subsequent utilization of biomass resources.

[0088] The above - mentioned is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A method for treating reverse osmosis concentrate, which is realized based on a biofilm-membrane photobioreactor for treating municipal sewage ROC. The reactor includes a reaction vessel (1), a membrane module (2) in the reaction vessel (1), and a light module (4) outside the reaction vessel (1). A filler for forming a biofilm is added to the reaction vessel (1); the filler for forming a biofilm is obtained by a film hanging operation of adding a filler and microalgae to a culture medium. It is characterized in that It includes the following steps: Step 1), adopt an intermittent operation method, set an operation cycle, and divide the operation cycle into a water inlet period, a first aeration period, a second aeration period, and a water outlet period; Step 2), during the influent period, feed urban sewage ROC into the biofilm-membrane photobioreactor; during the first aeration period, stop influent, feed CO2 into the biofilm-membrane photobioreactor, and control the flow rate to keep the pH of the reaction system at 6.5 - 7.3; during the second aeration period, stop feeding CO2, feed air into the biofilm-membrane photobioreactor, and utilize the self-growth of microalgae to increase the pH of the reaction system, thereby removing Ca 2+ , Mg 2+ ; during the effluent period, carry out algal liquid separation through the membrane module (2), discharge the sewage, and retain the microalgae inside the reaction vessel (1) to form concentrated algal liquid inside the reaction vessel (1).

2. The method for treating reverse osmosis concentrate according to claim 1, characterized in that, During the water inlet period, CO2 is synchronously introduced; during the water outlet period, air is continuously introduced.

3. The method for treating reverse osmosis concentrated water according to claim 1, wherein During the water outlet period, measure the dry weight of microalgae in the concentrated algal solution, and discharge part of the concentrated algal solution by calculation so that the microalgae biomass inside the reaction vessel (1) remains at 2.00 - 2.29 g / L during the next batch of test runs.

4. The method for treating reverse osmosis concentrate according to claim 1 or 2 or 3, characterized in that, One operation cycle is 36 h, where the water inlet period is 10 min, the first aeration period is 5. The method for treating reverse osmosis concentrated water according to claim 1, characterized in that, ​ 6. The method for treating reverse osmosis concentrated water according to claim 1, wherein ​ 7. The method for treating reverse osmosis concentrate according to claim 1, wherein ​ 8. The method for treating reverse osmosis concentrate according to claim 1, characterized in that, ​ 9. The method for treating reverse osmosis concentrate according to claim 1, wherein ​

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