Method for preparing microalgae biological fertilizer from domestic sewage

Abstract

The invention relates to the technical field of sewage treatment, in particular to a method for preparing a microalgae biological fertilizer from domestic sewage. The method comprises the following steps: pretreating domestic sewage, removing suspended solids and large-particle impurities, converting organic nitrogen and phosphorus into inorganic nitrogen and phosphorus, and adding trace elements to obtain pretreated domestic sewage; mixing the pretreated domestic sewage with the activated sludge-microalgae mixture, and co-culturing to obtain a microalgae-microorganism culture solution; carrying out solid-liquid separation on the microalgae-microorganism culture solution to obtain a microalgae-microorganism mixture and water treated to reach the standard; the microalgae microorganisms and crop straw are mixed and fermented, and the microalgae biological fertilizer is obtained. According to the method, the microalgae and the activated sludge are co-cultured by taking the domestic sewage as a culture medium, the domestic sewage treatment is realized while water and nitrogen, phosphorus and potassium fertilizer resources are saved, and the microalgae biological fertilizer has the advantages of realizing resource recycling, improving the nutrient content of the biological fertilizer and the like.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and specifically to a method for preparing microalgae bio-fertilizer using domestic wastewater. Background Technology

[0002] Microalgae bio-fertilizer is a new type of green organic bio-fertilizer containing beneficial single-celled photosynthetic algae, beneficial microorganisms that promote the release of organic nutrients, small-molecule organic carbon, biomass, and trace elements. Due to its excellent effects in improving soil physicochemical properties and microbial community structure, promoting crop metabolism and growth, enhancing crop absorption and utilization of nutrients, improving crop stress resistance, and increasing crop yield and product quality, the application of microalgae bio-fertilizer in agricultural production has attracted much attention.

[0003] Microalgae bio-fertilizer is typically produced by inoculating industrially cultivated microalgae into agricultural organic waste such as livestock and poultry manure and crop straw, as well as municipal sludge, after the waste has been decomposed and rendered harmless. The industrial cultivation of microalgae requires significant water resources and also necessitates the provision of nutrients such as nitrogen, phosphorus, and potassium, resulting in high production costs. While microalgae can form a symbiotic relationship with the microorganisms in the decomposed agricultural organic waste and sludge to metabolize substances, this symbiotic relationship needs further strengthening to maximize its beneficial effects on agricultural production.

[0004] Domestic sewage contains abundant organic matter and essential nutrients such as nitrogen, phosphorus, and potassium, necessary for the growth and metabolism of microalgae and microorganisms, making it an excellent culture medium for microalgae and microorganisms. Using it to cultivate microalgae and microorganisms can significantly reduce the cost of water and fertilizer resources consumed in the industrial cultivation of microalgae, and can also treat domestic sewage, achieving resource recycling while protecting the environment. Furthermore, the resulting algae-sludge mixture exhibits a strong symbiotic relationship between microalgae and microorganisms, enhancing their beneficial effects on agricultural production upon application. However, the preparation of microalgae bio-fertilizer using domestic sewage treatment technology based on algae-microorganism symbiosis faces challenges, including the loss of organic matter and nutrients such as nitrogen through the conversion of these substances into CO2, N2, and NH3, which are emitted into the atmosphere, and the low fertilizer efficiency due to an improper ratio of microalgae to microorganisms. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for producing microalgae bio-fertilizer using domestic sewage. The method involves co-culturing microalgae and microorganisms using domestic sewage as a substrate, and using the cultured microalgae and activated sludge to produce microalgae bio-fertilizer. This method treats domestic sewage while producing microalgae bio-fertilizer, thereby achieving the goal of saving and recycling water, nitrogen, phosphorus, and potassium fertilizer resources.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] The first aspect of this invention provides a method for preparing microalgae biofertilizer using domestic sewage, comprising the following steps:

[0008] 1) Pre-treat domestic sewage to remove suspended solids and large particulate impurities, perform anaerobic treatment and add trace elements to obtain pre-treated domestic sewage;

[0009] 2) Pretreated domestic sewage is mixed with activated sludge-microalgae mixture and co-cultured to obtain microalgae-microorganism culture medium;

[0010] 3) Perform solid-liquid separation on the microalgae-microorganism culture medium to obtain microalgae-microorganism precipitate and water filtered out by solid-liquid separation;

[0011] 4) Mix the microalgae microbial precipitate with crop straw for fermentation to obtain microalgae bio-fertilizer.

[0012] A second aspect of the present invention provides a microalgae bio-fertilizer prepared by the above method.

[0013] A third aspect of the present invention provides an application of the above-mentioned microalgae bio-fertilizer in soil improvement.

[0014] Compared with the prior art, the beneficial effects of the present invention include:

[0015] (1) Water conservation: Through the wastewater treatment technology of activated sludge and microalgae symbiosis, nutrients in domestic sewage can be effectively utilized, reducing the demand for fresh water resources and realizing the recycling of water resources.

[0016] (2) Save nitrogen, phosphorus and potassium fertilizer resources: Domestic sewage contains abundant nutrients such as nitrogen and phosphorus. These nutrients are absorbed and utilized by microalgae and transformed into microalgae bio-fertilizer, reducing dependence on external nitrogen and phosphorus fertilizers and lowering fertilizer costs.

[0017] (3) Achieving domestic sewage treatment: This method effectively treats domestic sewage while producing microalgae bio-fertilizer, making it meet discharge standards and reducing environmental pollution.

[0018] (4) Realize the recycling of domestic sewage resources: Nitrogen and phosphorus pollutants in domestic sewage are converted into valuable fertilizer resources and water is converted into water resources, thus realizing the recycling of resources.

[0019] (5) Improve the nutrient content of microalgae bio-fertilizer: The prepared microalgae bio-fertilizer is rich in organic matter and nutrients, which can improve the nutrient content. Detailed Implementation

[0020] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0021] This invention utilizes domestic sewage as a substrate for the co-cultivation of microalgae and microorganisms. The cultivated microalgae and activated sludge are then used to produce microalgae bio-fertilizer. Simultaneously, domestic sewage is treated during the production of microalgae bio-fertilizer, achieving the goals of water conservation and recycling of nitrogen, phosphorus, and potassium fertilizer resources. Furthermore, by improving production process conditions, the production efficiency of microalgae bio-fertilizer, the secretion of active substances from microalgae, and fertilizer efficacy are enhanced.

[0022] This invention provides a method for producing microalgae biofertilizer using domestic sewage, comprising the following steps:

[0023] 1) Pre-treat domestic sewage to remove suspended solids and large particulate impurities, perform anaerobic treatment and add trace elements to obtain pre-treated domestic sewage;

[0024] 2) Pretreated domestic sewage is mixed with activated sludge-microalgae mixture and co-cultured to obtain microalgae-microorganism culture medium;

[0025] 3) Perform solid-liquid separation on the microalgae-microorganism culture medium to obtain microalgae-microorganism precipitate and water filtered out by solid-liquid separation;

[0026] 4) Mix microalgae-microorganism precipitate with crop straw for fermentation to obtain microalgae bio-fertilizer.

[0027] In this invention, step 1) of the pretreatment further includes adjusting the pH value to 7.8–8.2 and adjusting the ratio of carbon, nitrogen, and phosphorus sources in the domestic sewage to maintain the C:N:P molar ratio at 100:10:1–120:12:1. For example, when the influent COD is <150 mg / L, glucose or sodium acetate at a concentration of 50–100 mg / L is added as a carbon source to maintain the C:N:P molar ratio in the domestic sewage at 100:10:1–120:12:1. Preferably, the buffer solution for adjusting the pH value is selected from a carbonate-bicarbonate buffer system to ensure that the pH fluctuation of the domestic sewage is ≤0.3 units / day. More preferably, the concentration of the carbonate-bicarbonate buffer system used is 0.05–0.1 mol / L.

[0028] According to embodiments of this application, large floating objects and suspended solids, such as branches, plastic bags, bottles, and other large particulate matter that may interfere with subsequent treatment, are removed from wastewater by interception.

[0029] According to embodiments of this application, the trace elements include any one or more of Fe, Mg, Cu, Zn, and Mo; further, based on domestic sewage, the concentration of Fe is 1.0-1.5 mg / L, the concentration of Mg is 0.5-0.8 mg / L, the concentration of Cu is 0.02-0.05 mg / L, the concentration of Zn is 0.05-0.1 mg / L, and the concentration of Mo is 0.01-0.02 mg / L.

[0030] According to embodiments of this application, the microalgae are selected from one or more of Chlorella, diatoms, and Scenedesmus.

[0031] The activated sludge is obtained by inoculating and cultivating sludge from the aerobic tank or secondary sedimentation tank of a wastewater treatment plant.

[0032] According to embodiments of this application, the activated sludge-microalgae mixture needs to undergo pre-acclimation before being mixed with pretreated domestic sewage to obtain a symbiotically stable activated sludge-microalgae mixture. Preferably, the pre-acclimation time is 3-5 days. More preferably, the symbiotic stability period of the activated sludge-microalgae mixture is greater than 30 days, and the removal rate of organic matter is greater than 70%.

[0033] In a preferred embodiment, the mass ratio of microalgae to activated sludge in the activated sludge-microalgae mixture is (0.1-0.9):(1-3).

[0034] In a preferred embodiment, the activated sludge contains active microorganisms. The Shannon-Wiener diversity index of the activated sludge is 3.5–4.5, the abundance of dominant species is 40–50%, and the synergy index is ≥1.2.

[0035] In some embodiments of the present invention, the microalgae, acting as photosynthetic bacteria, fix carbon dioxide through photosynthesis while releasing oxygen as a metabolic byproduct, thereby reducing carbon emissions from domestic sewage and providing a dissolved oxygen environment. Furthermore, during their growth, the microalgae synthesize and secrete various organic carbon sources (such as polysaccharides, organic acids, extracellular polymers, etc.) and carbon-containing biomass. These organic carbon sources and biomass produced by the microalgae provide a nutrient substrate for the aforementioned active microorganisms, which utilize these organic substances for heterotrophic growth and metabolic activities. During this process, the microorganisms decompose and mineralize these organic carbon sources and large organic molecules such as organic nitrogen and phosphorus, converting them into bioavailable soluble inorganic nutrients, including ammonia nitrogen (NH4+). 4+ / NH3), nitrates (NO 3- ), nitrite (NO 2- ) and phosphate (PO4) 3-These soluble inorganic nutrients are released back into the culture environment and efficiently absorbed and utilized by microalgae, thereby closing the cycle of key nutrients such as nitrogen and phosphorus and reducing dependence on external nutrient additions.

[0036] During the process of metabolizing organic carbon, the active microorganisms release carbon dioxide, which is captured by microalgae and used for photosynthetic carbon fixation, forming an internal carbon cycle.

[0037] According to an embodiment of this application, based on a microalgae-microorganism mixture, the concentration of the activated sludge is 3000-4000 mg / L, and the concentration of the microalgae is 300-1000 mg / L.

[0038] For example, the concentration of activated sludge can be 3000 mg / L, 3100 mg / L, 3200 mg / L, 3300 mg / L, 3400 mg / L, 3500 mg / L, 3600 mg / L, 3700 mg / L, 3800 mg / L, 3900 mg / L, 4000 mg / L, or any value between 3000 and 4000 mg / L, and the concentration of microalgae can be 300 mg / L, 500 mg / L, 1000 mg / L, 2000 mg / L, 3000 mg / L, or any value between 300 and 3000 mg / L.

[0039] According to the embodiments of this application, by precisely controlling the ratio of microalgae and activated sludge, the conversion efficiency of organic carbon sources is improved, and the nutrients such as nitrogen and phosphorus contained in domestic sewage are fully converted while ensuring the fertilizer effect of the final product.

[0040] In some embodiments of this application, in step 2), the co-cultivation is carried out under alternating dark and light conditions, wherein the light source is an LED light source with an intensity of 4500–8000 lux. By employing alternating light and dark conditions, alternating aerobic and anaerobic environments can be provided for microorganisms, creating favorable conditions for the growth of various functional microorganisms.

[0041] For example, the illuminance of an LED light source can be any value between 4500 lux, 5000 lux, 6000 lux, 7000 lux, 8000 lux, or 4500 to 8000 lux.

[0042] Furthermore, the photosynthetically active radiation of the LED light source is 100-250 μmol·m⁻¹. -2 ·s -1 The LED light source is configured with a light quality ratio of red, blue, and green light of 4:2:1 to control the spectral composition.

[0043] According to an embodiment of this application, the ratio of light to darkness time is (12-16)h:(8-12)h.

[0044] In this invention, by precisely controlling the light intensity and duration, the photosynthetic carbon fixation efficiency, biomass accumulation, and organic carbon secretion of microalgae are optimized in a targeted manner, thereby influencing the metabolic activity and nitrogen and phosphorus regeneration capacity of microorganisms in a cascade manner.

[0045] In some embodiments of the present invention, the water filtered out by the solid-liquid separation is treated by filtration and disinfection so that the effluent meets the sewage treatment standards, reducing environmental pollution and realizing the recycling of water resources.

[0046] In a preferred embodiment, in step 4), the mass ratio of the microalgae-microorganism precipitate to the crop straw is 4:1 to 5:1; preferably, the crop straw is selected from one or more of rice straw, wheat straw, and corn straw, and is preferably corn straw.

[0047] In a preferred embodiment, the mixed fermentation further requires the addition of a fermentation aid, which is selected from one or two of cellulase and Armillaria mellea. Preferably, the fermentation aid is selected from 0.5-1.0% w / w cellulase and 0.8-1.2% w / w Armillaria mellea.

[0048] In a preferred embodiment, the fermentation includes a mesophilic stage, a hyperthermic stage, and a post-ripening stage. The mesophilic stage has a temperature of 33–38°C, a moisture content of 60–65% w / w, an oxygen concentration of 15–18% v / v, and a duration of 8–10 days. The hyperthermic stage has a temperature of 48–53°C, a moisture content of 50–55% w / w, an oxygen concentration of 10–15% v / v, and a duration of 4–6 days. The post-ripening stage has a temperature of 28–33°C, a moisture content of 40–45% w / w, an oxygen concentration of 5–10% v / v, and a duration of 13–19 days. Microalgae bio-fertilizer rich in organic matter and nutrients is obtained through fermentation.

[0049] The present invention also provides a microalgae bio-fertilizer prepared by the above method.

[0050] The present invention also provides an application of the above-mentioned microalgae bio-fertilizer in soil improvement.

[0051] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention; in the specification and claims of the present invention, unless otherwise expressly stated in the text, the singular forms "a", "an" and "this" include the plural forms.

[0052] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0053] Unless otherwise stated, the experimental methods, detection methods, and preparation methods disclosed in this invention all employ conventional techniques in molecular biology, biochemistry, chromatin structure and analysis, analytical chemistry, cell culture, recombinant DNA technology, and related fields.

[0054] Example 1

[0055] Secondary effluent from a municipal wastewater treatment plant (COD 238 mg / L, total nitrogen 46 mg / L, total phosphorus 4.3 mg / L) was treated according to the following parameters: the pH was adjusted to 7.8–8.2 using a 0.05–0.1 mol / L carbonate-bicarbonate buffer solution, and the carbon, nitrogen, and phosphorus sources were adjusted accordingly. Anaerobic treatment was performed for 5 hours. An activated sludge-microalgae mixture was added to the wastewater, with a sludge concentration of 4500 mg / L. The microalgae species was *Chlorella vulgaris*, and the activated sludge was from the local wastewater treatment plant, with a mass ratio of 1:5. The mixture was cultured at room temperature in autumn, supplemented with trace elements at concentrations of 1.2 mg / L Fe, 0.6 mg / L Mg, 0.03 mg / L Cu, 0.08 mg / L Zn, and 0.01 mg / L Mo. The activated sludge-microalgae mixture was obtained by pre-acclimation of the activated sludge and microalgae for 3–5 days. During fermentation, it is mixed with corn stalks at a mass ratio of 4:1 and fermented for 30 days. The fermentation process includes: a mesophilic stage at 38℃, 60% moisture content, and 15% v / v oxygen concentration, lasting for 8 days; a hyperthermic stage at 50℃, 53% moisture content, and 18% v / v oxygen concentration, lasting for 6 days; and a post-ripening stage at 28℃, 40% moisture content, and 10% v / v oxygen concentration, lasting for 16 days.

[0056] After the above treatment, during stable operation, the wastewater COD removal rate was 92%, the total nitrogen removal rate was 86%, and the total phosphorus removal rate was 94%; the wastewater microalgae-microorganism mixture yield reached 0.18 gDS / L; and the final microalgae bio-fertilizer contained 5.3% total nitrogen, 2.8% total phosphorus, and 56% organic matter.

[0057] The basic concepts have been described above. Obviously, for those skilled in the art, the detailed disclosure above is merely illustrative and does not constitute a limitation of this specification. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this specification. Such modifications, improvements, and corrections are suggested in this specification and therefore remain within the spirit and scope of the exemplary embodiments described herein.

[0058] Furthermore, this specification uses specific terms to describe embodiments thereof. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of this specification. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Moreover, certain features, structures, or characteristics in one or more embodiments of this specification can be appropriately combined.

[0059] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be illustrative rather than limiting, and should be considered consistent with the teachings of this specification. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.

Claims

1. A method for preparing microalgae bio-fertilizer using domestic sewage, comprising the following steps: 1) Pre-treat domestic sewage to remove suspended solids and large particulate impurities, perform anaerobic treatment and add trace elements to obtain pre-treated domestic sewage; 2) Pretreated domestic sewage is mixed with activated sludge-microalgae mixture and co-cultured to obtain microalgae-microorganism culture medium; 3) Perform solid-liquid separation on the microalgae-microorganism culture medium to obtain microalgae-microorganism precipitate and water filtered out by solid-liquid separation; 4) Mix the microalgae microbial precipitate with crop straw for fermentation to obtain microalgae bio-fertilizer.

2. The method as described in claim 1, characterized in that, In step 1), the pretreatment further includes adjusting the pH value to 7.8-8.2, adjusting the ratio of carbon source, nitrogen source and phosphorus source of domestic sewage to maintain the C:N:P ratio at 100:10:1-120:12:1; and / or, the trace elements include one or more of Fe, Mg, Cu, Zn and Mo.

3. The method as described in claim 2, characterized in that, Based on domestic sewage, the concentration of Fe is 1.0-1.5 mg / L, the concentration of Mg is 0.5-0.8 mg / L, the concentration of Cu is 0.02-0.05 mg / L, the concentration of Zn is 0.05-0.1 mg / L, and the concentration of Mo is 0.01-0.02 mg / L.

4. The method as described in claim 1, characterized in that, In step 2), the activated sludge-microalgae mixture needs to be pre-acclimated before being mixed with pretreated domestic sewage to obtain a symbiotically stable activated sludge-microalgae mixture; and / or, the activated sludge is obtained by inoculating and culturing sludge from the aerobic tank sludge or the secondary sedimentation tank sludge of a sewage treatment plant, preferably, the Shannon-Wiener index of the microbial diversity index in the activated sludge is 3.5 to 4.5; and / or, the microalgae are selected from one or more of Chlorella, diatoms, and Scenedesmus; and / or, in the activated sludge-microalgae mixture, the mass ratio of microalgae to activated sludge is (0.1 to 0.9):(1 to 3).

5. The method as described in claim 1, characterized in that, In step 2), based on the microalgae-microbial culture medium, the concentration of the activated sludge is 3000-4000 mg / L, and the concentration of the microalgae is 300-3000 mg / L.

6. The method as described in claim 1, characterized in that, In step 2), the co-cultivation is carried out under alternating dark and light conditions. The light source is an LED light source with an intensity of 4500-8000 lux and a photosynthetically active radiation of 100-250 μmol·m-2·s-1. The spectral composition of the LED light source is controlled by a light quality ratio of red, blue, and green light of 4:2:

1.

7. The method as described in claim 1, characterized in that, In step 4), the mass ratio of the microalgae-microorganism precipitate to crop straw is 4:1 to 5:1, and the crop straw is selected from one or more of rice straw, wheat straw, and corn straw; and / or, the mixed fermentation also requires the addition of a fermentation aid, which is selected from one or two of cellulase and Armillaria mellea.

8. The method as described in claim 1, characterized in that, In step 4), the fermentation includes a mesophilic stage, a hyperthermic stage, and a post-ripening stage. The mesophilic stage has a temperature of 33–38°C, a moisture content of 60–65% w / w, an oxygen concentration of 15–18% v / v, and a duration of 8–10 days. The hyperthermic stage has a temperature of 48–53°C, a moisture content of 50–55% w / w, an oxygen concentration of 10–15% v / v, and a duration of 4–6 days. The post-ripening stage has a temperature of 28–33°C, a moisture content of 40–45% w / w, an oxygen concentration of 5–10% v / v, and a duration of 13–19 days.

9. A microalgae bio-fertilizer prepared by the method according to any one of claims 1 to 8.

10. The application of the microalgae bio-fertilizer as described in claim 9 in soil improvement.