Sewage treatment method based on microalgae thin-layer fountain photobioreactor

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to a sewage treatment method based on a microalgae thin-layer fountain photobioreactor, which comprises the following steps: S1, inoculating microalgae cells into the thin-layer fountain photobioreactor, and culturing to a logarithmic phase to obtain a high-activity microalgae seed solution; s2, sewage to be treated is introduced into the thin-layer fountain photobioreactor containing the high-activity microalgae seed solution in the step S1, and the concentration of microalgae cells is maintained at 0.01-5.0 g / L; s3, according to the sewage turbidity and the treatment stage, dynamically adjusting the thickness of a transparent material and a liquid layer of the surface sealing degree (namely the sealing film ratio) of the thin-layer fountain photobioreactor, and supplementing water in real time according to the evaporation condition so as to maintain the stable operation of the system; and S4, cooperatively regulating and controlling parameters such as the flow of a water pump, the pH value of a culture solution and the thickness of a liquid layer of the thin-layer fountain photobioreactor, and continuously operating until the effluent reaches the discharge standard. According to the method disclosed by the invention, gas-liquid mass transfer and light energy utilization of the microalgae culture solution are remarkably enhanced through a thin-layer fountain structure, and the light limiting effect in high-turbidity sewage is effectively overcome; according to the method, the temperature, evaporation and light receiving conditions are cooperatively controlled in combination with dynamic adjustment of the sealing film ratio, the COD removal rate is larger than or equal to 90%, the ammonia nitrogen removal rate is larger than or equal to 95%, the total phosphorus removal rate is larger than 99% under the condition that an exogenous carbon source and complex pretreatment are not needed, and microalgae high-density culture and biomass resource recycling are synchronously completed. The system has the characteristics of low operation cost, easiness in amplification and wide applicability, and provides a technical scheme with industrial potential for efficient and low-carbon treatment of aquaculture sewage and the like.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a wastewater treatment method based on a microalgae thin-layer fountain photobioreactor. Background Technology

[0002] With the continuous growth of the global population and changes in dietary structure, the increased demand for livestock and poultry products has driven the large-scale development of the livestock industry, while the discharge of industrial and domestic wastewater has continued to rise. Various types of wastewater (including livestock and poultry farming wastewater and aquaculture effluent) are typically rich in nutrients such as nitrogen and phosphorus, heavy metals, and high concentrations of suspended solids (turbidity often exceeding 500 NTU). Direct discharge can easily lead to eutrophication and ecological imbalance in water bodies. Current wastewater treatment technologies are mainly divided into three categories: physical methods, chemical methods, and biological methods. While physical methods such as screening, sedimentation, and filtration can effectively remove suspended solids and some colloids, their effectiveness in removing dissolved pollutants (especially nutrients such as nitrogen and phosphorus) is limited. Chemical methods, through the addition of coagulants and flocculants, can effectively precipitate phosphorus and remove some colloids and heavy metals, but they suffer from high reagent costs, the generation of chemical sludge, and secondary pollution.

[0003] Given the limitations of physical and chemical treatment processes in efficiently removing dissolved nutrients and their associated costs and secondary pollution, traditional biotechnology methods, such as activated sludge and biofilm processes, also face significant challenges. These processes typically rely on abundant and stable available carbon sources in wastewater for removing nutrients like nitrogen and phosphorus, as well as organic pollutants. However, actual aquaculture wastewater often exhibits a carbon-to-nitrogen ratio imbalance (C:N ratio frequently below 5:1), leading to decreased pollutant removal efficiency. This often necessitates the addition of exogenous carbon to maintain treatment effectiveness, further increasing operating costs and introducing potential secondary pollution risks. Simultaneously, the large amounts of colloidal particles, recalcitrant organic matter, and microbial aggregates present in aquaculture wastewater result in persistently high turbidity (often exceeding 500 NTU). This not only weakens mass transfer and metabolic efficiency in traditional biological treatment processes but also significantly reduces the effective utilization of light energy by light-dependent treatment processes, limiting the application of various bioaugmentation and resource recovery technologies in practical engineering.

[0004] Microalgae technology has attracted much attention due to its combined potential for efficient pollutant removal and biomass resource utilization. It can absorb CO2 and synthesize organic matter through photosynthesis, providing an in-situ inorganic carbon source for wastewater denitrification and alleviating the carbon-to-nitrogen imbalance. However, the large-scale application of this technology still faces multiple constraints: traditional photobioreactors are often costly due to their complex structure and large footprint; their thick culture medium layer (>5.0 cm) causes severe light attenuation when treating high-turbidity wastewater, resulting in photolimited microalgae and generally low microalgae density; simultaneously, insufficient mixing and mass transfer efficiency further limits microalgae growth and the utilization of atmospheric CO2; in addition, the low biomass density necessitates the treatment of large volumes of water in subsequent harvesting processes, requiring reliance on energy-intensive technologies such as high-speed centrifugation, leading to high overall costs. These combined problems severely restrict the overall economic viability and engineering potential of this technology.

[0005] It is worth noting that single microalgae systems are susceptible to substrate inhibition and toxin accumulation in complex wastewater environments, often resulting in limited metabolic activity. In recent years, by introducing bacteria and microalgae to construct synergistic systems, the complementary functions of different microorganisms in carbon, nitrogen, and organic matter metabolic pathways have enabled the synergistic enhancement of pollutant conversion and energy utilization. Among these, photosynthetic bacteria (such as *Rhodopseudomonas* and *Chromobacterium*) are often used as important functional groups in microbial systems due to their combined ability to utilize light energy and convert organic matter, promoting carbon cycling and nitrogen conversion processes, and are considered to have significant application potential. However, traditional reactors, due to uneven flow field distribution and slow gas-liquid interface renewal, struggle to maintain long-term stable coexistence of microbial systems; simultaneously, light attenuation caused by high-turbidity wastewater further weakens the synergistic effect of photosynthesis. Therefore, there is an urgent need to develop a novel wastewater treatment technology that can adapt to the characteristics of high-turbidity wastewater, effectively alleviate light limitations, and promote efficient synergistic effects between bacteria and algae, thereby improving system stability and pollutant removal efficiency while reducing overall treatment costs. Summary of the Invention The purpose of this invention is to provide a wastewater treatment method based on a microalgae thin-layer fountain photobioreactor. This method uses the applicant's developed thin-layer fountain photobioreactor (see patent document CN 219409682 U) as its core device. Leveraging its extremely thin liquid layer, efficient gas-liquid mass transfer, strong mixing, and light utilization characteristics, it can efficiently remove organic pollutants, ammonia nitrogen, and total phosphorus from wastewater while achieving high-density microalgae cultivation. Furthermore, it boasts advantages such as low construction and operating costs, controllable water evaporation and temperature, and ease of scale-up, providing a practical and feasible industrial solution for the resource-based treatment of wastewater.

[0006] This photobioreactor effectively reduces light attenuation in turbid media by directly introducing microalgae seed solution and aquaculture wastewater into the thin-layer culture area, thus ensuring the light absorption efficiency of microalgae in wastewater. The system regulates the flow rate of the fountain pump to promote uniform suspension of microalgae cells and continuous surface renewal, improving light energy utilization efficiency and enhancing mass exchange at the gas-liquid interface, particularly increasing the absorption of CO2 from the air. Furthermore, it utilizes the naturally occurring high pH environment (typically maintained at 9.0-12.0) generated by the efficient photosynthesis of microalgae, combined with the turbulence and surface renewal effect produced by the fountain mixing, to accelerate the mass transfer and dissipation of free ammonia (NH3) from the liquid phase to the gas phase (based on the reaction: NH4+). + OH - → NH3↑ + H2O), which synergistically achieves efficient removal of ammonia nitrogen from wastewater, high-density growth of microalgae, and deep purification of pollutants.

[0007] Furthermore, by adjusting the area ratio of the transparent covering material on the reactor surface, the internal temperature and water evaporation rate of the reactor can be effectively controlled, making it suitable for wastewater of different turbidities, different stages of microalgae growth, and changes in the external environment. While maximizing the efficiency of water evaporation and microalgae growth, it significantly reduces operating costs and improves the overall wastewater treatment efficiency, demonstrating promising prospects for engineering applications.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: 1. A wastewater treatment method based on a microalgae thin-layer fountain photobioreactor, comprising the following steps: S1. Microalgal cells are inoculated into a thin-layer fountain photobioreactor and cultured to the logarithmic growth phase to obtain a highly active microalgal seed solution. The thin-layer fountain photobioreactor includes a reactor body, inside which a microalgal culture chamber is formed. The reactor body is equipped with a culture solution circulation device for conveying the culture solution in the microalgal culture chamber upwards and scattering the culture solution at a high altitude before it falls back down. A transparent material covering the surface of the thin-layer fountain photobioreactor and capable of adjusting the sealing degree (i.e., sealing ratio) is also included. The culture solution circulation device includes a water pump, a delivery pipe, and a water outlet. The delivery pipe is connected to the outlet of the water pump, and the water outlet is connected to the upper end of the delivery pipe. S2. The wastewater to be treated is introduced into the thin-layer fountain photobioreactor containing the highly active microalgae seed liquid from step S1, so that the microalgae cell concentration is maintained at 0.01-5.0 g / L; S3. Based on the turbidity of the wastewater and the treatment stage, dynamically adjust the sealing ratio and liquid layer thickness of the thin-layer fountain photobioreactor, and replenish water in real time according to the evaporation situation to maintain stable system operation; S4. Coordinate and regulate the water pump flow rate, culture medium pH value, and liquid layer thickness parameters of the thin-layer fountain photobioreactor, and continue to operate until the effluent meets the discharge standards.

[0009] Preferably, the surface of the thin-layer fountain photobioreactor is provided with a device for adjusting the sealing ratio, which is used to control one or more of the following: the gas exchange rate inside and outside the reactor, the water evaporation rate, and the temperature.

[0010] Preferably, the target thickness of the culture medium in step S3 is dynamically set according to the initial turbidity of the introduced wastewater: when the initial turbidity of the wastewater is ≥200 NTU, the thickness of the liquid layer is controlled to be 0.1-2.0 cm; when the initial turbidity of the wastewater is <200 NTU, the thickness of the liquid layer is controlled to be ≥2.0 cm.

[0011] Preferably, the flow rate of the fountain pump in step S4 is in the range of 0.1-100 L / min.

[0012] Preferably, the temperature of the culture medium in steps S1 to S4 is controlled between 20°C and 45°C.

[0013] Preferably, the pH value of the culture medium in step S4 is 9.0-12.0.

[0014] Preferably, by synergistically controlling multiple technical parameters such as sealing ratio, liquid layer thickness, water pump flow rate, pH and temperature, efficient wastewater purification and microalgae resource utilization can be achieved.

[0015] Preferably, the microalgae mentioned in step S1 are one or more of Chlorella, Microspirilla, and Spirulina, which have the characteristics of being resistant to high ammonia nitrogen.

[0016] Preferably, in step S2, 0.01-5.0 g / L of photosynthetic bacteria are added to the reactor after the sewage is introduced.

[0017] Preferably, the sealing ratio in step S1 is 60%.

[0018] Implementing this invention has the following beneficial effects: 1) High-efficiency mass transfer and light utilization: This invention employs a thin-layer fountain photobioreactor. Through a design combining an extremely thin liquid layer (0.1-30 cm) with a circulating fountain, it significantly improves gas-liquid mass transfer efficiency, achieving a mass transfer coefficient more than 100 times that of traditional reactors. This effectively enhances the absorption of CO2 from the air, providing a carbon source for microalgae growth. The thin-layer structure also significantly reduces light attenuation, making it particularly suitable for high-turbidity wastewater. It can significantly increase the average light intensity received by microalgae, thereby promoting their growth and pollutant degradation. This system can directly treat high-turbidity, high-ammonia-nitrogen aquaculture wastewater without complex pretreatment. COD removal rate ≥90%, ammonia-nitrogen removal rate ≥95%, and total phosphorus removal rate up to >99%. While achieving highly efficient water purification, it significantly reduces energy consumption and operating costs, and simultaneously enables high-density microalgae cultivation and biomass recovery.

[0019] 2) Synergistic Regulation of Temperature and Evaporation via Membrane Sealing: An adjustable transparent covering layer is applied to the reactor surface. By changing the sealing ratio (0%-100%, preferably 20%-80%), the temperature and evaporation intensity within the reactor can be synergistically regulated without additional energy consumption. This method can stably control the temperature within the optimal growth range of microalgae (20-45℃, preferably 25-40℃). Furthermore, by adjusting the evaporation rate (0.05-5 mm / h), it effectively promotes water evaporation and pollutant concentration, significantly increasing the treatment load and purification efficiency per unit volume of wastewater while continuously expanding the gas-liquid contact interface. This synergistic regulation mechanism jointly constructs a stable and efficient reaction environment, achieving triple optimization of temperature management, evaporation enhancement, and wastewater treatment capacity improvement.

[0020] 3) Multi-dimensional operating parameter coordinated control system Light utilization optimization and high-density cultivation: The liquid layer thickness is adjusted in real time according to the initial turbidity: when the turbidity is ≥200 NTU, it is controlled at 0.1-2.0 cm, which significantly reduces light attenuation and enables high-turbidity wastewater to be treated efficiently; when the turbidity is <200 NTU, it is expanded to 2.0-30 cm, which increases the treatment throughput while ensuring sufficient light exposure, thereby achieving high-density cultivation of microalgae.

[0021] High pH promotes ammonia nitrogen volatilization and removal: Based on algal photosynthesis, especially the efficient growth of microalgae, the pH of the culture medium can be naturally raised and maintained at a relatively high level of 9.0-12.0 (preferably 10.0-11.0). This alkaline environment, while meeting the growth requirements of microalgae, can effectively promote NH4+ evaporation and removal. + Conversion of NH3 to NH4 + + OH - → NH3↑), and ammonia nitrogen removal is enhanced by volatilization. When the pH is higher than 12.0 (preferably >11.0), waste gas containing CO2 can be introduced to prevent excessive alkalization.

[0022] Enhanced mixing and mass transfer: By adjusting the water pump flow rate (0.1-100 L / min, preferably 5-50 L / min), turbulence is created within the system, enhancing liquid mixing and surface renewal. This mechanism promotes the gas-phase escape of NH3 (ammonia nitrogen removal rate >95%) and improves microalgal cell suspension and light distribution, thereby directly promoting algal growth; simultaneously, it indirectly enhances evaporation and gas-liquid exchange processes by accelerating surface renewal.

[0023] 4) Comprehensive Resource Utilization Capacity: This invention constructs an integrated continuous operation system for wastewater treatment, microalgae cultivation, and biomass recovery, achieving simultaneous and efficient pollutant removal and biomass production. By adjusting the reactor sealing ratio, evaporation intensity, operating temperature, and light conditions can be synergistically controlled, ensuring stable system operation under natural light conditions and effectively avoiding the inhibition of microalgae activity by strong light or high temperatures, thus guaranteeing continuous wastewater treatment and efficient microalgae growth. The microalgae biomass harvested during the treatment process can be used as a resource-based raw material for the production of biodiesel, high-protein feed, or organic fertilizer, realizing the transformation from pollution control to resource utilization and significantly improving overall technical and economic benefits.

[0024] In summary, this invention, through the synergistic design of a thin-layer fountain photobioreactor and an adjustable sealing ratio, significantly enhances the gas-liquid mass transfer process under extremely thin liquid layer conditions (0.1-30 cm), effectively improving the absorption efficiency of CO2 from the air, while simultaneously enhancing the light energy utilization and photosynthetic activity of microalgae in high-turbidity wastewater. The system can directly treat high-turbidity, high-ammonia-nitrogen aquaculture wastewater without complex pretreatment, achieving COD removal rates ≥90%, ammonia-nitrogen removal rates ≥95%, and total phosphorus removal rates up to >99%. By dynamically controlling the liquid layer thickness, sealing ratio, pH, temperature, and fluid conditions, the system can simultaneously optimize evaporation, gas exchange, and thermal management, achieving continuous and stable wastewater treatment. This technology is particularly suitable for large-scale aquaculture farms, with a single system capable of treating 50-200 m³ per day. 3 While efficiently purifying water, it produces microalgae biomass that can be utilized as a resource, forming a circular economy model of "sewage-microalgae-resources", which has outstanding environmental and economic benefits. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the thin-layer fountain photobioreactor structure of the present invention.

[0026] Figure 2 This is a diagram showing the mass transfer effect of different types of photobioreactors in Embodiment 1 of the present invention.

[0027] Figure 3 This is a graph showing the changes in water quality indicators of wastewater treatment group 1 in Embodiment 2 of the present invention.

[0028] Figure 4This is a graph showing the changes in dry weight of microalgae and pH value in wastewater treatment group 1 of Example 2 of the present invention.

[0029] Figure 5 This is a graph showing the changes in water quality indicators of wastewater treatment group 2 in Embodiment 2 of the present invention.

[0030] Figure 6 This is a graph showing the changes in dry weight of microalgae and pH value in wastewater treatment group 2 of Example 2 of the present invention.

[0031] Figure 7 This is a design diagram of the reactor with different sealing ratios in Embodiment 3 of the present invention. In the diagram, the black area represents the sealing area.

[0032] Figure 8 This is a graph showing the daily evaporation rate in the reactor under different sealing ratios in Example 3 of the present invention.

[0033] Figure 9 This is a graph showing the daily temperature variation in the reactor under different sealing ratios in Example 3 of the present invention. Detailed Implementation

[0034] To better understand the present invention, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. However, those skilled in the art will understand that the following embodiments are not intended to limit the scope of protection of the present invention, and any changes and variations made on the basis of the present invention are within the scope of protection of the present invention.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0036] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0037] The specific structure of the thin-layer fountain photobioreactor described in this invention is disclosed in the published patent document CN219409682 U. All seven modes disclosed in that document can be applied to this invention. In this embodiment, the mushroom-shaped water splash mode is used.

[0038] Example 1: Comparative Experiment on Mass Transfer Effect of Different Types of Photobioreactors like Figure 1As shown, the thin-layer fountain photobioreactor of the present invention mainly includes a reactor body (1), the interior of which forms a microalgae culture chamber. To enhance mixing and mass transfer, the reactor is equipped with a culture medium circulation device (2), which consists of a water pump (21), a delivery pipe (22), and an outlet (23). The water pump (21) transports the culture medium to a high position through the delivery pipe (22), and after being scattered by the outlet (23), it falls back to the liquid surface, forming a continuous fountain-like circulation. The surface of the reactor body (1) is covered with a transparent material (3) with a light transmittance of 95%. In this embodiment, the coverage area accounts for 80% of the reactor surface area, that is, the sealing ratio is 80%. To further optimize the operating conditions, the reactor is also equipped with a sealing ratio adjustment device (4), which can be used to manually or automatically adjust the coverage ratio of the transparent material. In addition, the reactor can be equipped with a temperature control device (not shown in the figure), which can be driven by solar energy or electricity and works in conjunction with the sealing ratio adjustment device (4) to achieve precise control of the culture medium temperature.

[0039] To verify the gas-liquid mass transfer efficiency advantage of the thin-layer fountain photobioreactor compared to traditional photobioreactors, the oxygen transfer coefficient k was tested using the aforementioned thin-layer fountain photobioreactor. La (O2) was measured. Specifically, liquid layer thickness gradients of 1.0 cm, 2.0 cm, 3.0 cm, and 5.0 cm were set, and a flat-plate photobioreactor (60 cm long, 5 cm wide, and 50 cm high) and a column-type photobioreactor (5 cm in diameter and 45 cm in height) were used as controls. The results are as follows: Figure 2 As shown, the thin-layer fountain reactor achieves mixing by driving the liquid flow with a water pump (flow rate 20 L / min); the flat plate and column reactors use compressed air introduced from the bottom for mixing, with air flow rates of 1.5 L / min and 1.0 L / min, respectively.

[0040] Before the experiment, different volumes of pure water corresponding to different liquid layers (1.0 cm-2.20 L, 2.0 cm-4.15 L, 3.0 cm-6.10 L, 5.0 cm-10.00 L) were added to the thin-layer fountain photobioreactor, while 80% of the volume of pure water was added to the column (700 ml) and flat-plate photobioreactor (12 L). Then, pure oxygen was continuously introduced into each reactor to raise the dissolved oxygen concentration to above 20 mg / L. After the reactors were started up, the dynamic changes in dissolved oxygen content in the pure water were continuously monitored using a dissolved oxygen meter, and the corresponding oxygen transfer coefficient k was calculated accordingly. La (O2).

[0041] The experimental results are as follows: according to Figure 2 The measured results shown indicate that the k value of the thin-layer fountain photobioreactor... La(O2) increases significantly with decreasing culture medium thickness. When the medium thickness is 1.0 cm, k La (O2) reached its highest value of 167.555 ± 5.791 h. -1 This indicates that the liquid layer depth is a key factor affecting the mass transfer performance of the reactor. It is noteworthy that even when the liquid layer thickness increases to 5.0 cm, its k... La (O2)(42.883 ± 4.549 h -1 The efficiency is still much higher than that of a flat-plate photobioreactor (8.780 ± 0.395 h). -1 ), and compared with a column reactor (42.715 ± 1.095 h) -1 )quite.

[0042] This superior mass transfer performance is primarily due to the significantly increased gas-liquid contact area provided by the thin-layer fountain structure. Calculations show that the total gas-liquid contact area of ​​the thin-layer fountain reactor is approximately 0.973 m². 2 The fountain area contributed approximately 0.785 m. 2 In contrast, the gas-liquid contact area of ​​plate-type and column-type reactors is only 0.030 m². 2 and 0.002 m 2 The gas-liquid contact area is 1 / 26.17 and 1 / 292.50 of that of the thin-layer fountain reactor, respectively. This demonstrates that the larger gas-liquid contact area is a key reason why the thin-layer fountain photobioreactor outperforms the traditional photobioreactor in mass transfer.

[0043] Example 2: Thin-layer fountain photoreactor reactor for culturing microalgae in pig wastewater This embodiment uses the anaerobic digestion wastewater from a large-scale pig farm in Zhangzhou City, Fujian Province as the treatment target. Relevant water quality indicators are shown in Table 1: Table 1. Wastewater and its indicators referenced in this embodiment.

[0044] This study used the thin-layer fountain photobioreactor from Example 1 to verify its effectiveness in treating pig wastewater. The specific experimental steps are as follows: S1. Chlorella ( Chlorella sp . Cells were seeded into the self-designed 50 cm diameter thin-layer fountain photobioreactor and cultured to the logarithmic growth phase to obtain highly active microalgae seed solution.

[0045] S2. The two types of wastewater were separately introduced into a thin-layer fountain photobioreactor containing highly active microalgae seed solution. Wastewater 1 had a turbidity <200 NTU, and its culture medium layer was set at 2.5 cm (corresponding to an effective volume of 5.12 L); Wastewater 2 had a turbidity >200 NTU, and its culture medium layer was set at 1.0 cm (corresponding to an effective volume of 2.18 L). The initial inoculation density of Chlorella was 0.3 g / L (dry weight). No pretreatment was performed on the wastewater during cultivation; only static settling was used to remove large suspended particles. The experiment relied entirely on natural light (daily average light intensity 800-1200 μmol / m²). 2 / s).

[0046] S3. In this embodiment, the sealing ratio is 80%, and the moisture evaporation rate is 1.0-6.0 L / m. 2 / day, the temperature is in the range of 20℃-45℃, and water is replenished in real time according to the evaporation during the experiment to maintain the set culture medium thickness (2.5 cm in wastewater 1 and 1.0 cm in wastewater 2 in this example); S4. During the experiment, the water pump flow rate, culture medium pH value and culture medium thickness parameters of the thin-layer fountain photobioreactor were adjusted in real time within the range of 9.0-12.0 until the treated wastewater met the discharge standards.

[0047] Three 20 mL aliquots of algal solution were collected daily for dry weight determination: First, the pH of the algal solution was adjusted to 5-6 with hydrochloric acid, and the supernatant was discarded after centrifugation at 9000 rpm for 5 minutes; the precipitated algal cells were resuspended in 40 mL of distilled water and washed, and the centrifugation and washing steps were repeated 3 times; then the algal cells were transferred to plexiglass culture dishes and dried in an oven at 105 ℃ until constant weight, and finally weighed and calculated using a precision analytical balance.

[0048] The removal process of major pollutants in wastewater 1 is as follows: Figure 3 As shown in the figure, the initial concentrations of COD, ammonia nitrogen, and total phosphorus were 701.75 mg / L, 43.85 mg / L, and 44.00 mg / L, respectively. On day 1 of incubation, these concentrations decreased to 86.478 mg / L, 17 mg / L, and 12 mg / L, respectively. By the end of incubation (day 8), COD further decreased to 48.433 mg / L, achieving a removal rate of 93.1%; ammonia nitrogen decreased to 0.425 mg / L, achieving a removal rate of 99.03%; and total phosphorus was completely removed by day 5 (100% removal rate). Furthermore, turbidity decreased continuously from the initial 73.26 NTU to 17.41 NTU, reflecting an improvement in water transparency.

[0049] like Figure 4As shown, after culturing *Chlorella vulgaris* in wastewater 1 for 8 days, its biomass increased from the initial 0.3 g / L to 3.01 g / L, indicating that the microalgae can effectively utilize the nutrients in the wastewater for growth and support high-density cultivation. During the cultivation process, the pH dynamically changed with the growth and metabolism of the microalgae: in the first 6 days, due to the consumption of dissolved inorganic carbon by photosynthesis, the pH steadily increased to 10.09; after entering the stable growth period, the pH gradually decreased, reflecting the phased changes in metabolic activity.

[0050] The treatment effect of wastewater 2 is as follows Figure 5 As shown in the figure, the concentrations of COD, ammonia nitrogen, and total phosphorus all showed a continuous decreasing trend during the cultivation process: the initial values ​​were 830.96 mg / L, 60.82 mg / L, and 37.44 mg / L, respectively; on day 1, they decreased to 455.70 mg / L, 24.71 mg / L, and 24.82 mg / L, respectively; by day 8, COD further decreased to 56.88 mg / L, with a removal rate of 93.16%, ammonia nitrogen decreased to 0.21 mg / L, with a removal rate of 99.65%, and total phosphorus was completely removed by day 7 (removal rate of 100%). In addition, the turbidity decreased continuously from the initial 350.43 NTU to 79.51 NTU, indicating that the water transparency improved significantly with the treatment process.

[0051] like Figure 6 As shown, the growth trend of Chlorella in wastewater 2 was basically the same as that in wastewater 1: after 8 days of cultivation, the biomass increased from the initial 0.3 g / L to 2.69 g / L; the pH also showed a pattern of first rising and then falling. These results indicate that although high-turbidity wastewater can limit the photosynthesis of Chlorella to some extent, efficient growth of microalgae can still be ensured by adjusting the liquid layer thickness and optimizing the light distribution.

[0052] This embodiment demonstrates a wastewater treatment method based on a microalgae thin-layer fountain photobioreactor. This method employs a strategy combining "thin-layer short optical path" and "turbulent mixing," adaptively adjusting the thickness of the culture medium layer according to the wastewater turbidity, thereby significantly reducing light attenuation and effectively overcoming the light limitation problem commonly encountered in traditional microalgae cultivation in high-turbidity wastewater. Without relying on additional wastewater pretreatment, this method can achieve efficient removal of wastewater pollutants and simultaneous co-production of microalgae biomass. The system also boasts advantages such as low operating costs and ease of scale-up, providing a promising industrial-scale technological path for the resource-based treatment of pig farm wastewater.

[0053] Example 3: Effect of different sealing film ratios on the wastewater treatment effect of thin-layer fountain photoreactor This embodiment uses the thin-layer fountain photobioreactor from Example 1. Wastewater 1 (from the same source as in Example 2) was introduced into six reactors, and the liquid layer thickness was adjusted to 2.5 cm. Different sealing area ratios were set by adding a transparent film with 95% light transmittance to the top of the reactor. The experiment included six treatment groups, with the sealing area as a percentage of the reactor's surface area to the external environment being 0% (i.e., completely open, no film coverage), 20%, 40%, 60%, 80%, and 100% (i.e., the top is almost completely covered, with only a few ventilation holes). Specific settings are as follows: Figure 7 As shown. On a sunny day, a thermometer was used to monitor the temperature change inside the reactor, and the daily evaporation rate was calculated by measuring the volume of residual wastewater at the end of the reaction.

[0054] Before the experiment began, Chlorella was inoculated into each reactor. Chlorella The initial inoculation density was set at 0.3 g / L (dry weight). During the cultivation process, wastewater was only allowed to settle to remove large suspended solids; no other pretreatment was performed. Natural light was used throughout the experiment, with an average daily light intensity of 800-1200 μmol / m². 2 The water temperature fluctuates naturally with the indoor environment, remaining at 26-30℃. The dry weight measurement method is the same as in Example 2.

[0055] The experimental results are as follows: The changes in evaporation rate and temperature within the reactor under different sealing ratios are as follows: Figure 8 and Figure 9 As shown, the evaporation rate first increases and then decreases with increasing sealing ratio: the evaporation rate is highest at a sealing ratio of 40%, reaching 6.33 L / m³. 2 / day; the evaporation rate is minimal at a sealing ratio of 100%, at only 0.31 L / m 2 / day. This indicates that water evaporation can be effectively controlled by adjusting the sealing ratio. Meanwhile, the water temperature inside the reactor increases significantly with increasing sealing area. The highest water temperature reached 41.3℃ in the completely closed group (100% sealing ratio), significantly higher than the 28.0℃ in the completely open group (0% sealing ratio). These results demonstrate that the sealing ratio can serve as an important means of regulating the reactor temperature, helping to maintain the water temperature within a suitable range for microalgae growth.

[0056] Table 2 shows the removal efficiency of the reactor for major pollutants in wastewater under different membrane sealing ratios. The 60% membrane sealing ratio group showed the most significant treatment effect: COD decreased from an initial 701.75 mg / L to 59.76 mg / L, with a removal rate of 91.48%; ammonia nitrogen decreased from 43.85 mg / L to 1.26 mg / L, with a removal rate of 97.24%; and total phosphorus was completely removed at the end of the experiment. This group treated a total of 38.4 L of wastewater, second only to the 40% membrane sealing ratio group (40.64 L). Figure 8 Data shows that maintaining the water temperature within the reactor at a suitable range of 30-35 ℃ is beneficial for microalgae to maintain high photosynthetic and metabolic activity, thus achieving efficient pollutant degradation. In comparison, the COD removal rate of the 40% sealing ratio experimental group was 76.4% (final concentration 165.32 mg / L), the ammonia nitrogen removal rate was 80.6% (final concentration 8.52 mg / L), and total phosphorus was completely removed, with a treatment effect slightly lower than the 60% group. In the other experimental groups, the 0% and 100% sealing ratios significantly inhibited microalgae metabolic activity due to excessively low or high temperatures, resulting in poor pollutant removal efficiency and cumulative treatment volume. Although the 20% and 80% sealing ratios showed some potential for wastewater treatment, the relatively slow growth rate of microalgae meant that the water purification effect was still not ideal.

[0057] Significant differences in microalgal biomass concentrations were observed among the groups under different sealing ratios (Table 2). The group with a sealing ratio of 60% achieved the highest biomass accumulation at 2.46 g / L, followed by the 80% group (2.14 g / L). This higher biomass yield was primarily attributed to maintaining the water temperature within the reactors at a suitable range of 30-35℃, which avoided both the decrease in photosynthetic efficiency caused by low temperatures and the potential inhibition of microalgal activity caused by high temperatures. Furthermore, after the experiment, the pH in each reactor increased to varying degrees, with a greater increase in pH at higher microalgal concentrations, reflecting the alkalization trend of the system due to the consumption of dissolved inorganic carbon by algal photosynthesis.

[0058] Table 2. Changes in microalgae growth and water quality indicators under different film-sealing ratios.

[0059] The comparison of different membrane sealing methods in this embodiment reveals that the 60% membrane sealing group effectively maintained the water temperature within a suitable range, creating favorable conditions for microalgae growth. This group exhibited the highest microalgae biomass accumulation, the largest cumulative wastewater treatment capacity, and the most significant removal effects on pollutants such as COD, ammonia nitrogen, and total phosphorus. Overall, it demonstrated the best wastewater treatment performance and possesses significant application advantages.

[0060] In summary, this invention provides a wastewater treatment method based on a thin-layer fountain photobioreactor. This method achieves coordinated control of water evaporation, temperature, and light conditions within the reactor by adjusting the film coverage ratio. This maintains a suitable growth environment for microalgae, avoids photoinhibition and thermal inactivation, and ensures the efficiency and stability of the wastewater treatment process. The system supports continuous wastewater replenishment and treatment, increasing both pollutant treatment efficiency and throughput while also increasing microalgae biomass production. Furthermore, this invention can operate under natural light conditions, significantly reducing system energy consumption and operation and maintenance costs.

[0061] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A wastewater treatment method based on a microalgae thin-layer fountain photobioreactor, characterized in that, Includes the following steps: S1. Microalgal cells are inoculated into a thin-layer fountain photobioreactor and cultured to the logarithmic growth phase to obtain a highly active microalgal seed solution. The thin-layer fountain photobioreactor includes a reactor body, inside which a microalgal culture chamber is formed. The reactor body is equipped with a culture solution circulation device for conveying the culture solution in the microalgal culture chamber upwards and scattering the culture solution at a high altitude before it falls back down. A transparent material covering the surface of the thin-layer fountain photobioreactor and capable of adjusting the sealing degree (i.e., sealing ratio) is also included. The culture solution circulation device includes a water pump, a delivery pipe, and a water outlet. The delivery pipe is connected to the outlet of the water pump, and the water outlet is connected to the upper end of the delivery pipe. S2. The wastewater to be treated is introduced into the thin-layer fountain photobioreactor containing the highly active microalgae seed liquid from step S1, so that the microalgae cell concentration is maintained at 0.01-5.0 g / L; S3. Based on the turbidity of the wastewater and the treatment stage, dynamically adjust the sealing ratio and liquid layer thickness of the thin-layer fountain photobioreactor, and replenish water in real time according to the evaporation situation to maintain stable system operation; S4. Coordinate and regulate the water pump flow rate, culture medium pH value, and liquid layer thickness parameters of the thin-layer fountain photobioreactor, and continue to operate until the effluent meets the discharge standards.

2. The wastewater treatment method according to claim 1, characterized in that, The surface of the thin-layer fountain photobioreactor is equipped with a device for adjusting the sealing ratio, which is used to control one or more of the following: the gas exchange rate inside and outside the reactor, the water evaporation rate, and the temperature.

3. The wastewater treatment method according to claim 1, characterized in that, The target thickness of the culture medium in step S3 is dynamically set according to the initial turbidity of the introduced wastewater: when the initial turbidity of the wastewater is ≥200 NTU, the thickness of the liquid layer is controlled to be 0.1-2.0 cm; when the initial turbidity of the wastewater is <200 NTU, the thickness of the liquid layer is controlled to be ≥2.0 cm.

4. The wastewater treatment method according to claim 1, characterized in that, The flow rate of the fountain pump mentioned in step S4 is in the range of 0.1-100 L / min.

5. The wastewater treatment method according to claim 1, characterized in that, The temperature of the culture medium in steps S1 to S4 is controlled between 20℃ and 45℃.

6. The wastewater treatment method according to claim 1, characterized in that, The pH value of the culture medium in step S4 is 9.0-12.

0.

7. The wastewater treatment method according to any one of claims 1-6, characterized in that, By synergistically controlling multiple technical parameters such as sealing ratio, liquid layer thickness, water pump flow rate, pH and temperature, efficient wastewater purification and microalgae resource utilization can be achieved.

8. The wastewater treatment method according to claim 1, characterized in that, The microalgae mentioned in step S1 are one or more of Chlorella, Microspirilla, and Spirulina, which have the characteristics of being resistant to high ammonia nitrogen.

9. The wastewater treatment method according to claim 1, characterized in that, In step S2, 0.01-5.0 g / L of photosynthetic bacteria are added to the reactor after the wastewater is introduced.

10. The wastewater treatment method according to claim 1, characterized in that, The sealing ratio in step S1 is 60%.

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