A method for treating cassava starch wastewater by using a microalgae-fungus symbiotic system

Abstract

The application discloses a method for treating cassava starch wastewater by using a microalgae-fungus symbiotic system, and belongs to the technical field of wastewater biological treatment. The method for treating cassava starch wastewater comprises the following steps: pre-culturing oil-rich neochloris oleoabundans to obtain oil-rich neochloris oleoabundans liquid; pre-culturing aspergillus fumigatus to obtain aspergillus fumigatus spores; mixing the oil-rich neochloris oleoabundans liquid, the aspergillus fumigatus spores and filtered and sterilized cassava starch wastewater, and carrying out shaking bed culture to obtain microalgae-fungus biological balls; carrying out sedimentation and sand filtration treatment on the cassava starch wastewater to obtain pretreated cassava starch wastewater; and adding the microalgae-fungus biological balls into the pretreated cassava starch wastewater, carrying out biological treatment in a photobioreactor, and killing algae bacteria to obtain treated cassava starch wastewater. The method has the advantages of good treatment effect, high economic benefit, low cost and low carbon emission, and aims to solve the problems and defects in the prior art.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater biological treatment, and in particular relates to a method for treating cassava starch wastewater by utilizing a microalgae-fungus symbiotic system. Background Art

[0002] Cassava starch wastewater is a high-concentration organic wastewater generated during the production of cassava starch. Its water-soluble organic matter is primarily composed of proteins and sugars, with small amounts of fine fibers and starch. High COD, BOD, ammonia nitrogen, and total phosphorus values ​​in cassava starch wastewater make it challenging to treat. Currently, the main treatment methods for high-concentration organic wastewater, such as starch wastewater, include sedimentation, flocculation, aeration, biological treatment, and membrane separation. Biological treatment is widely used in production due to its ease of operation, high treatment effectiveness, and low investment costs.

[0003] Biological treatment of cassava starch wastewater utilizes the metabolic capabilities of microorganisms to degrade dissolved and colloidal organic pollutants in the wastewater, converting them into harmless gases or retaining them in organisms. Because cassava starch wastewater is highly concentrated and biodegradable, it can be purified using traditional aerobic treatment processes. There are also cassava starch wastewater treatment processes based on anaerobic digestion, such as the "UASB+SBR" process, the "UASB-CASS" coagulation process, and the "upflow multi-stage anaerobic reactor."

[0004] Microalgae-fungus symbiotic systems can effectively remove pollutants from wastewater, demonstrating superior performance compared to monoculture systems. Microalgae are a general term for microorganisms that contain chlorophyll a and can photosynthesize, belonging to the class of protists. Fungi are spore-forming, chloroplast-free eukaryotic organisms with a typical filamentous, branching vegetative body. Both microalgae and fungi absorb pollutants such as inorganic and organic nitrogen sources and phosphates from wastewater, using them to synthesize essential biochemical components within their cells, thereby purifying the wastewater. In a microalgae-fungus symbiotic system, a synergistic effect exists between the two: the microalgae provide the fungi with oxygen, organic matter, and other nutrients through photosynthesis, while the fungi protect the microalgae from harmful light and provide CO2, minerals, growth factors, and other nutrients to promote their growth. Under suitable conditions, filamentous fungi can form clumps of mycelial pellets with excellent settling properties. In this symbiotic system, the mycelial pellets can adsorb the microalgae, enabling low-cost recovery of the microalgae. Microalgae are recognized as highly efficient carbon sequestering organisms and a key avenue for carbon reduction. Microalgae can fix CO2 through photosynthesis. After CO2 is introduced into the microalgae bioreactor, part of it enters the microalgae cells through free diffusion, and the other part dissolves in the solution to form HCO 3-, which is converted into CO2 within the cell by carbonic anhydrase and finally fixed through the Calvin cycle, achieving biological carbon fixation. Overall, the microalgae-fungus symbiotic system has the advantages of low cost, high efficiency, low carbon emissions, and high biomass value in the field of wastewater treatment, and is attracting increasing attention.

[0005] At present, the treatment of cassava starch wastewater in engineering is still mainly based on the traditional aerobic treatment process. This type of process is simple to operate and has strong adaptability, but it also has the disadvantages of poor economic benefits, large sludge production, and high carbon emissions. In addition, a composite cassava starch wastewater treatment process based on anaerobic digestion is also widely used. The treatment effect is better than that of a single traditional aerobic treatment process, the treatment cost is lower, and energy materials can be produced, but there are also problems such as complex process flow and low treatment efficiency. There is an urgent need to develop a new cassava starch wastewater treatment method to replace the existing aerobic and anaerobic biological treatment technologies and meet the biological treatment requirements of cassava starch wastewater with high efficiency, high economic benefits, low operating costs, and low carbon emissions. Therefore, the present invention discloses a method for treating cassava starch wastewater using a microalgae fungal symbiotic system to solve the problems existing in the prior art. Summary of the Invention

[0006] To solve the above technical problems, the present invention proposes a method for treating cassava starch wastewater using a microalgae-fungal symbiotic system. The method described in the present invention has the advantages of good treatment effect, high economic benefit, low cost, and low carbon emissions, and aims to solve the problems and shortcomings of existing biological treatment technologies.

[0007] To achieve the above object, the present invention provides a method for treating cassava starch wastewater using a microalgae-fungus symbiotic system, comprising the following steps:

[0008] Microalgae pre-culture of Neochloris oleoabundans to obtain Neochloris oleoabundans liquid;

[0009] Aspergillus fumigatus Fresenius is pre-cultured to obtain Aspergillus fumigatus spores;

[0010] The oil-rich new green algae liquid, the Aspergillus fumigatus spores and the cassava starch wastewater that has been filtered and sterilized are mixed, and cultured on a shaking table to obtain microalgae fungal bio-balls;

[0011] The cassava starch wastewater is precipitated and sand filtered to obtain pretreated cassava starch wastewater;

[0012] The microalgae fungus bio-ball is added to the pretreated cassava starch wastewater, and biological treatment is carried out in a photobioreactor to kill algae and obtain treated cassava starch wastewater.

[0013] Preferably, the microalgae pre-culture comprises the following steps:

[0014] The oil-rich new green algae is inoculated into a mixture of cassava starch wastewater and culture solution in a volume ratio of 20:80, and is shaken and cultured to obtain a first-generation oil-rich new green algae; the first-generation oil-rich new green algae is transferred to a mixture of cassava starch wastewater and culture solution in a volume ratio of 40:60 for secondary culture to obtain a second-generation oil-rich new green algae; the second-generation oil-rich new green algae is transferred to a mixture of cassava starch wastewater and culture solution in a volume ratio of 60:40 for three culture to obtain a third-generation oil-rich new green algae; the third-generation oil-rich new green algae is transferred to a mixture of cassava starch wastewater and culture solution in a volume ratio of 80:20 for four culture to obtain a fourth-generation oil-rich new green algae; the fourth-generation oil-rich new green algae is transferred to cassava starch wastewater for five culture to obtain a fifth-generation oil-rich new green algae; the fifth-generation oil-rich new green algae is centrifuged to obtain an oil-rich new green algae liquid.

[0015] Preferably, the culture medium is BG-11 culture medium.

[0016] Preferably, the culture conditions for the shaking culture, secondary culture, tertiary culture, quadruple culture and quintuple culture are the same, namely, the culture conditions are: temperature 25°C, light intensity 200 μmol / m 2 / s, light-dark ratio 12h light / 12h dark, rotation speed 120r / min, culture time 7d.

[0017] Preferably, the fungus pre-culture comprises the following steps:

[0018] Aspergillus fumigatus was inoculated into an agar medium prepared with cassava starch wastewater as a solvent. After spores emerged, the spores were transferred to an agar medium prepared with cassava starch wastewater as a solvent. This was repeated three times, and the Aspergillus fumigatus spores were collected using a 0.1% Tween 80 solution.

[0019] Preferably, the filtration and sterilization treatment uses a 0.22 μm water filter membrane.

[0020] Preferably, the mixing ratio of the oil-rich new green algae liquid, Aspergillus fumigatus spores and filtered and sterilized cassava starch wastewater is 1.2×10 9 cells:1.2×10 4 cells:1L.

[0021] Preferably, the culture conditions of the shaking culture are: temperature 25-28°C, light intensity 200 μmol / m 2 / s, light-dark ratio 12h light / 12h dark, rotation speed 150-190r / min, and culture time 3-4d.

[0022] Preferably, the amount of microalgae fungus bio-balls added is determined by the volume of the pretreated cassava starch wastewater, and the addition amount is 200-400 gDW / m 3 .

[0023] Preferably, the biological treatment conditions are: under sunlight, temperature of 25-28° C., operating flow rate of 0.3-0.4 m / s, and operating time of 8-10 days.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] 1. The microalgae-fungus symbiotic system constructed by the present invention utilizes the extracellular enzymes produced by fungi to efficiently decompose macromolecular organic matter in wastewater, thereby strengthening the system interaction between microalgae and fungi, improving the growth efficiency of microalgae, and achieving better denitrification effect.

[0026] 2. The method for constructing the microalgae fungal bioball of the present invention is simple to operate, highly feasible, and has strong environmental adaptability and biological activity. Through the recycling of the bioball, the operating cost of wastewater treatment is lower.

[0027] 3. The present invention realizes the proliferation of microalgae in the process of treating cassava starch wastewater. The microalgae fixes carbon dioxide through photosynthesis during the proliferation process, which significantly reduces the carbon emission intensity of the treatment process.

[0028] 4. The fatty acid content of the oil-rich new green algae of the present invention can reach 30%, of which the triacylglyceride content accounts for about 80% of the total lipids. It is a good raw material for producing biodiesel and has high economic benefits.

[0029] 5. The Aspergillus fumigatus described in the present invention is a filamentous fungus that has good pelleting effect under mechanical stirring, can provide conditions for the attachment and growth of microalgae, achieve mutually beneficial symbiosis with the microalgae, and has good sedimentation properties, thereby reducing biomass recovery costs. DETAILED DESCRIPTION

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0031] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0032] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0033] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0034] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0035] The cassava starch wastewater in the examples of the present invention and the comparative examples was prepared by the following method: fresh cassava was prepared into a cassava starch suspension (the mass ratio of cassava to water was 1:4) using a crushing-slurry separator, and the suspension was allowed to stand until the starch was completely precipitated, and the supernatant was taken to obtain the cassava starch wastewater.

[0036] The standards used for measuring the concentrations of water pollutants in the Examples and Comparative Examples of the present invention are: pH value according to GBT6920-1986, suspended solids according to GBT11901-1989, five-day biochemical oxygen demand according to HJ505-2009, chemical oxygen demand according to HJ / T399-2007, ammonia nitrogen according to HJ535-2009, total nitrogen according to GB / T11894-1989, total phosphorus according to GB / T11893-1989, and total cyanide according to HJ484-2009.

[0037] The initial physical and chemical indicators of the cassava starch wastewater in the examples of the present invention and the comparative example are as follows: pH 4.4, suspended solids 6430 mg / L, five-day biochemical oxygen demand 4850 mg / L, chemical oxygen demand 8960 mg / L, ammonia nitrogen 94.8 mg / L, total nitrogen 186 mg / L, total phosphorus 58.6 mg / L, and total cyanide 12.4 mg / L.

[0038] The oil-rich neochloris (Neochloris oleoabundans) in the examples and comparative examples of the present invention was from the UTEX algae collection in the United States (number UTEX-1185), and the Aspergillus fumigatus Fresenius was from the Henan Industrial Microbial Strain Engineering Technology Research Center (number BNCC-338385).

[0039] The BG-11 culture medium and the mixture of cassava starch wastewater and culture medium (C-BG-11 culture medium) in the examples of the present invention and the comparative examples need to be filtered and sterilized with a 0.22 μm water filter membrane before use, and the Czapek agar medium (CDA medium) and the Czapek agar medium with cassava starch wastewater as a solvent (C-CDA medium) need to be autoclaved at 121° C. for 15 min before use.

[0040] The open raceway pond photobioreactors in the embodiments of the present invention and the comparative examples have an effective volume of 200 L and dimensions of 1600 mm*500 mm*300 mm.

[0041] The technical solution of the present invention is further illustrated by the following examples.

[0042] Example 1

[0043] The oil-rich new green algae (Neochloris oleoabundans) was inoculated in BG-11 culture medium and cultured to the logarithmic phase. Then, the logarithmic phase oil-rich new green algae was inoculated into a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 20:80, and cultured with shaking to obtain the primary generation of oil-rich new green algae; the primary generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 40:60 for secondary culture to obtain the second generation of oil-rich new green algae; the second generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG- The third generation of oil-rich new green algae was cultured three times in a mixture of cassava starch wastewater and BG-11 culture medium in a volume ratio of 60:40 to obtain the third generation of oil-rich new green algae; the third generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium in a volume ratio of 80:20 and cultured four times to obtain the fourth generation of oil-rich new green algae; the fourth generation of oil-rich new green algae was transferred to cassava starch wastewater and cultured five times to the logarithmic phase to obtain the fifth generation of oil-rich new green algae; the fifth generation of oil-rich new green algae was centrifuged at a speed of 4000r / min for 4 minutes, the supernatant was removed, and the oil-rich new green algae liquid was obtained.

[0044] The culture conditions for shaking culture, secondary culture, tertiary culture, quadruple culture and quintuple culture were the same, namely, temperature 25°C, light intensity 200 μmol / m 2 / s, light-dark ratio 12h light / 12h dark, rotation speed 120r / min, culture time 7d.

[0045] Aspergillus fumigatus Fresenius was cultured in Czapek agar medium (CDA medium), and then inoculated into Czapek agar medium prepared with cassava starch wastewater as a solvent, i.e., C-CDA medium. After sporulation, the spores were transferred to Czapek agar medium prepared with cassava starch wastewater as a solvent. This was repeated three times, and the Aspergillus fumigatus spores were collected using a 0.1% Tween 80 solution.

[0046] The oil-rich new green algae liquid, Aspergillus fumigatus spores and cassava starch wastewater sterilized by 0.22 μm water filter membrane were mixed in a ratio of 1.2×10 9 cells:1.2×10 4 cells: 1L mixed, temperature 25°C, light intensity 200 μmol / m 2 / s, a light-dark ratio of 12h light / 12h dark, and a rotation speed of 170r / min for 4 days to obtain a large number of microalgae fungal bio-balls with a diameter of 3-7mm, which were harvested using a filter (pore size 3mm).

[0047] The cassava starch wastewater was subjected to sedimentation treatment for 48 hours and then sand filtration treatment to remove suspended pollutants in the wastewater to obtain pretreated cassava starch wastewater.

[0048] 40 g (measured by dry weight) of microalgae fungal bioballs were added to 200 L of pretreated cassava starch wastewater and biologically treated in an open runway pool photobioreactor. The reactor was placed in the open air, the light source was sunlight, the temperature was controlled at 25-28 ° C, and the biological treatment was carried out under the operating conditions of a flow rate of 0.3 m / s. The treatment cycle was 10 days. After the treatment, it was emptied into the sedimentation tank with a hydraulic retention time of 4 h. The particle size of the microalgae fungal bioballs in the sediment was 3-14 mm. Two sets of filter screens (pore size 3 mm and pore size 7 mm) were used to sieve the sediment to separate the fungal microalgae balls with a particle size of 3-7 mm. 40 g (measured by dry weight) was taken and refluxed to the photobioreactor, and new pretreated cassava starch wastewater was injected to start a new round of circulation. The supernatant overflowed through the effluent weir and then entered the disinfection tank to sterilize the algae with sodium hypochlorite, thus completing the biological treatment of cassava starch wastewater.

[0049] Example 2

[0050] The oil-rich new green algae was inoculated into BG-11 culture medium and cultured to the logarithmic phase. Then, the logarithmic phase oil-rich new green algae was inoculated into a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 20:80, and cultured with shaking to obtain the primary generation of oil-rich new green algae; the primary generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 40:60 for secondary culture to obtain the second generation of oil-rich new green algae; the second generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 40:60 for secondary culture to obtain the second generation of oil-rich new green algae. The third generation of oil-rich new green algae was cultured three times in a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 60:40 to obtain the third generation of oil-rich new green algae; the third generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 80:20 and cultured four times to obtain the fourth generation of oil-rich new green algae; the fourth generation of oil-rich new green algae was transferred to cassava starch wastewater and cultured five times to the logarithmic phase to obtain the fifth generation of oil-rich new green algae; the fifth generation of oil-rich new green algae was centrifuged at a speed of 4000r / min for 4 minutes, and the supernatant was removed to obtain the oil-rich new green algae liquid.

[0051] The culture conditions for shaking culture, secondary culture, tertiary culture, quadruple culture and quintuple culture were the same, namely, temperature 25°C, light intensity 200 μmol / m 2 / s, light-dark ratio 12h light / 12h dark, rotation speed 120r / min, culture time 7d.

[0052] Aspergillus fumigatus is cultured in Czapek agar medium (CDA medium), and then inoculated into Czapek agar medium prepared with cassava starch wastewater as a solvent, namely C-CDA medium. After sporulation, the spores are transferred to Czapek agar medium prepared with cassava starch wastewater as a solvent. This is repeated three times, and the Aspergillus fumigatus spores are collected with 0.1% Tween 80 solution.

[0053] The oil-rich new green algae liquid, Aspergillus fumigatus spores and cassava starch wastewater sterilized by 0.22 μm water filter membrane were mixed in a ratio of 1.2×10 9 cells:1.2×10 4 cells: 1L mixed, temperature 25°C, light intensity 200 μmol / m 2 / s, a light-dark ratio of 12h light / 12h dark, and a rotation speed of 170r / min for 4 days to obtain a large number of microalgae fungal bio-balls with a diameter of 3-7mm. Two sets of filter screens (pore size 3mm, pore size 5mm) were used to harvest the microalgae fungal bio-balls with a diameter of 3-5mm.

[0054] The cassava starch wastewater was subjected to sedimentation treatment for 48 hours and then sand filtration treatment to remove suspended pollutants in the wastewater to obtain pretreated cassava starch wastewater.

[0055] 40 g (measured by dry weight) of microalgae fungal bio-balls were added to 200 L of pretreated cassava starch wastewater and biologically treated in an open runway pool photobioreactor. The reactor was placed in the open air, the light source was sunlight, the temperature was controlled at 25-28 ° C, and the biological treatment was carried out under the operating conditions of a flow rate of 0.3 m / s. The treatment cycle was 10 days. After the treatment, the pellet was emptied into the sedimentation tank with a hydraulic retention time of 4 h. The particle size of the microalgae fungal bio-balls in the sediment was 3-13 mm. Two sets of filter screens (pore size 3 mm and pore size 5 mm) were used to sieve the sediment to separate the fungal microalgae balls with a particle size of 3-5 mm. 40 g (measured by dry weight) was taken and refluxed into the photobioreactor, and new pretreated cassava starch wastewater was injected to start a new round of circulation. The supernatant overflowed through the effluent weir and then entered the disinfection tank to sterilize the cassava starch wastewater with sodium hypochlorite, thus completing the biological treatment of the cassava starch wastewater.

[0056] Example 3

[0057] The oil-rich new green algae was inoculated into BG-11 culture medium and cultured to the logarithmic phase. Then, the logarithmic phase oil-rich new green algae was inoculated into a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 20:80, and cultured with shaking to obtain the primary generation of oil-rich new green algae; the primary generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 40:60 for secondary culture to obtain the second generation of oil-rich new green algae; the second generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 40:60 for secondary culture to obtain the second generation of oil-rich new green algae. The third generation of oil-rich new green algae was cultured three times in a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 60:40 to obtain the third generation of oil-rich new green algae; the third generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 80:20 and cultured four times to obtain the fourth generation of oil-rich new green algae; the fourth generation of oil-rich new green algae was transferred to cassava starch wastewater and cultured five times to the logarithmic phase to obtain the fifth generation of oil-rich new green algae; the fifth generation of oil-rich new green algae was centrifuged at a speed of 4000r / min for 4 minutes, and the supernatant was removed to obtain the oil-rich new green algae liquid.

[0058] The culture conditions for shaking culture, secondary culture, tertiary culture, quadruple culture and quintuple culture were the same, namely, temperature 25°C, light intensity 200 μmol / m 2 / s, light-dark ratio 12h light / 12h dark, rotation speed 120r / min, culture time 7d.

[0059] Aspergillus fumigatus is cultured in Czapek agar medium (CDA medium), and then inoculated into Czapek agar medium prepared with cassava starch wastewater as a solvent, namely C-CDA medium. After sporulation, the spores are transferred to Czapek agar medium prepared with cassava starch wastewater as a solvent. This is repeated three times, and the Aspergillus fumigatus spores are collected with 0.1% Tween 80 solution.

[0060] The oil-rich new green algae liquid, Aspergillus fumigatus spores and cassava starch wastewater sterilized by 0.22 μm water filter membrane were mixed in a ratio of 1.2×10 9 cells:1.2×10 4 cells: 1L mixed, temperature 25°C, light intensity 200 μmol / m 2 / s, a light-dark ratio of 12h light / 12h dark, and a rotation speed of 170r / min for 4 days to obtain a large number of microalgae fungal bio-balls with a diameter of 3-7mm, which were harvested using a filter (pore size 3mm).

[0061] The cassava starch wastewater was subjected to sedimentation treatment for 60 hours and then sand filtration treatment to remove suspended pollutants in the wastewater to obtain pretreated cassava starch wastewater.

[0062] 60 g (measured by dry weight) of microalgae fungal bioballs were added to 200 L of pretreated cassava starch wastewater and biologically treated in an open runway pool photobioreactor. The reactor was placed in the open air, the light source was sunlight, the temperature was controlled at 25-28 ° C, and the biological treatment was carried out under the operating conditions of a flow rate of 0.4 m / s. The treatment cycle was 8 days. After the treatment, the microalgae fungal bioballs were emptied into the sedimentation tank with a hydraulic retention time of 4 h. The particle size of the microalgae fungal bioballs in the sediment was 3-12 mm. Two sets of filter screens (pore size 3 mm and pore size 7 mm) were used to sieve the sediment to separate the fungal microalgae balls with a particle size of 3-7 mm. 60 g (measured by dry weight) was taken and refluxed to the photobioreactor, and new pretreated cassava starch wastewater was injected to start a new round of circulation. The supernatant overflowed through the effluent weir and then entered the disinfection tank to sterilize the algae with sodium hypochlorite, thus completing the biological treatment of cassava starch wastewater.

[0063] Comparative Example 1

[0064] The oil-rich new green algae was inoculated into BG-11 culture medium and cultured to the logarithmic phase. Then, the logarithmic phase oil-rich new green algae was inoculated into a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 20:80, and cultured with shaking to obtain the primary generation of oil-rich new green algae; the primary generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 40:60 for secondary culture to obtain the second generation of oil-rich new green algae; the second generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 40:60 for secondary culture to obtain the second generation of oil-rich new green algae. The third generation of oil-rich new green algae was cultured three times in a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 60:40 to obtain the third generation of oil-rich new green algae; the third generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 80:20 and cultured four times to obtain the fourth generation of oil-rich new green algae; the fourth generation of oil-rich new green algae was transferred to cassava starch wastewater and cultured five times to the logarithmic phase to obtain the fifth generation of oil-rich new green algae; the fifth generation of oil-rich new green algae was centrifuged at a speed of 4000r / min for 4 minutes, and the supernatant was removed to obtain the oil-rich new green algae liquid.

[0065] The culture conditions for shaking culture, secondary culture, tertiary culture, quadruple culture and quintuple culture were the same, namely, temperature 25°C, light intensity 200 μmol / m 2 / s, light-dark ratio 12h light / 12h dark, rotation speed 120r / min, culture time 7d.

[0066] The oil-rich new green algae liquid and the cassava starch wastewater sterilized by filtration with a 0.22 μm water filter membrane were mixed in a ratio of 1.2×10 9 cells: 1L mixed, temperature 25°C, light intensity 200 μmol / m 2 / s, a light-dark ratio of 12h light / 12h dark, and a rotation speed of 170r / min were used for light cultivation for 4 days to obtain the expanded oil-rich new green algae liquid.

[0067] The cassava starch wastewater was subjected to sedimentation treatment for 48 hours and then sand filtration treatment to remove suspended pollutants in the wastewater to obtain pretreated cassava starch wastewater.

[0068] 40g (measured by dry weight) of oil-rich new green algae was added to 200L of pretreated cassava starch wastewater and biological treatment was carried out in an open raceway pool photobioreactor. The reactor was placed in the open air, the light source was sunlight, the temperature was controlled at 25-28°C, and the biological treatment was carried out under the operating conditions of a flow rate of 0.3m / s. The treatment cycle was 10 days. After the treatment, it was emptied into the sedimentation tank with a hydraulic retention time of 4h. The precipitate was mainly oil-rich new green algae. 40g (measured by dry weight) was taken and refluxed into the photobioreactor, and new pretreated cassava starch wastewater was injected to start a new round of circulation. The supernatant overflowed through the effluent weir and then entered the disinfection tank to sterilize the algae with sodium hypochlorite, thus completing the biological treatment of cassava starch wastewater.

[0069] Comparative Example 2

[0070] The oil-rich new green algae was inoculated into BG-11 culture medium for amplification and culture, and the mixture was centrifuged at a speed of 4000 r / min for 4 minutes. The supernatant was removed to obtain the oil-rich new green algae liquid.

[0071] The culture conditions were: temperature 25°C, light intensity 200 μmol / m 2 / s, light-dark ratio 12h light / 12h dark, rotation speed 120r / min, culture time 7d.

[0072] Aspergillus fumigatus was cultured in Czapek agar medium (CDA medium), and after sporulation, Aspergillus fumigatus spores were collected using 0.1% Tween 80 solution.

[0073] The oil-rich new green algae liquid, Aspergillus fumigatus spores and cassava starch wastewater sterilized by 0.22 μm water filter membrane were mixed in a ratio of 1.2×10 9 cells:1.2×10 4cells: 1L mixed, temperature 25°C, light intensity 200 μmol / m 2 / s, a light-dark ratio of 12h light / 12h dark, and a rotation speed of 170r / min for 4 days to obtain a large number of microalgae fungal bio-balls with a diameter of 3-5mm, which were harvested using a filter (pore size 3mm).

[0074] The cassava starch wastewater was subjected to sedimentation treatment for 48 hours and then sand filtration treatment to remove suspended pollutants in the wastewater to obtain pretreated cassava starch wastewater.

[0075] 40 g (measured by dry weight) of microalgae fungal bioballs were added to 200 L of pretreated cassava starch wastewater and biologically treated in an open runway pool photobioreactor. The reactor was placed in the open air, the light source was sunlight, the temperature was controlled at 25-28 ° C, and the biological treatment was carried out under the operating conditions of a flow rate of 0.3 m / s. The treatment cycle was 10 days. After the treatment, the microalgae fungal bioballs were emptied into the sedimentation tank with a hydraulic retention time of 4 h. The particle size of the microalgae fungal bioballs in the sediment was 3-10 mm. Two sets of filter screens (pore size 3 mm and pore size 5 mm) were used to sieve the sediment to separate the fungal microalgae balls with a particle size of 3-5 mm. 40 g (measured by dry weight) was taken and refluxed to the photobioreactor, and new pretreated cassava starch wastewater was injected to start a new round of circulation. The supernatant overflowed through the effluent weir and then entered the disinfection tank to sterilize the algae with sodium hypochlorite, thus completing the biological treatment of cassava starch wastewater.

[0076] Comparative Example 3

[0077] The oil-rich new green algae was inoculated into BG-11 culture medium and cultured to the logarithmic phase. Then, the logarithmic phase oil-rich new green algae was inoculated into a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 20:80, and cultured with shaking to obtain the primary generation of oil-rich new green algae; the primary generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 40:60 for secondary culture to obtain the second generation of oil-rich new green algae; the second generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 40:60 for secondary culture to obtain the second generation of oil-rich new green algae. The third generation of oil-rich new green algae was cultured three times in a mixture of culture medium with a volume ratio of 60:40 to obtain the third generation of oil-rich new green algae; the third generation of oil-rich new green algae was transferred to a mixture of cassava starch wastewater and BG-11 culture medium with a volume ratio of 80:20 and cultured four times to obtain the fourth generation of oil-rich new green algae; the fourth generation of oil-rich new green algae was transferred to cassava starch wastewater and cultured five times to the logarithmic phase to obtain the fifth generation of oil-rich new green algae; the fifth generation of oil-rich new green algae was centrifuged at a speed of 4000r / min for 4min to remove the supernatant to obtain the oil-rich new green algae liquid.

[0078] The culture conditions for shaking culture, secondary culture, tertiary culture, quadruple culture and quintuple culture were the same, namely, temperature 25°C, light intensity 200 μmol / m 2 / s, light-dark ratio 12h light / 12h dark, rotation speed 120r / min, culture time 7d.

[0079] Aspergillus fumigatus is cultured in Czapek agar medium (CDA medium), and then inoculated into Czapek agar medium prepared with cassava starch wastewater as a solvent, namely C-CDA medium. After spore production, the spores are transferred to Czapek agar medium prepared with cassava starch wastewater as a solvent. This is repeated three times, and the Aspergillus fumigatus spores are collected with 0.1% Tween 80 solution.

[0080] Aspergillus fumigatus spores were mixed with cassava starch wastewater sterilized by 0.22 μm water filter membrane at a ratio of 1.2×10 4 cells: 1L mixed, temperature 25°C, light intensity 200 μmol / m 2 / s, a light-dark ratio of 12h light / 12h dark, and a rotation speed of 170r / min for 4 days to obtain a large number of mycelial balls with a diameter of 5-8mm, which were harvested using a filter (pore size 3mm).

[0081] The cassava starch wastewater was subjected to sedimentation treatment for 48 hours and then sand filtration treatment to remove suspended pollutants in the wastewater to obtain pretreated cassava starch wastewater.

[0082] 30g (measured by dry weight) of oil-rich new green algae and 10g (measured by dry weight) of Aspergillus fumigatus mycelium pellets were added to 200L of pretreated cassava starch wastewater and biological treatment was carried out in an open runway pool photobioreactor. The reactor was placed in the open air, the light source was sunlight, the temperature was controlled at 25-28°C, and the biological treatment was carried out under the operating conditions of a flow rate of 0.3m / s. The treatment cycle was 10 days. After the treatment, it was emptied into the sedimentation tank with a hydraulic retention time of 4h. The sediment was mainly microalgae fungal bioballs. The supernatant overflowed through the effluent weir and then entered the disinfection tank to kill algae and bacteria with sodium hypochlorite, thus completing the biological treatment of cassava starch wastewater.

[0083] Experimental Example 1

[0084] The results of cassava starch wastewater treatment are shown in Tables 1 and 2 below.

[0085] Table 1 Test results of cassava starch wastewater in Examples 1 to 3

[0086]

[0087]

[0088] Table 2 Comparative Examples 1 to 3 Cassava Starch Wastewater Test Results

[0089]

[0090] According to the records in Table 1 above, after the cassava starch wastewater is treated by the methods of Examples 1 to 3 of the present invention, the pH, suspended solids, five-day biochemical oxygen demand, chemical oxygen demand, ammonia nitrogen, total nitrogen, total phosphorus, total cyanide and other indicators meet the direct emission limits in the "Starch Industry Water Pollutant Discharge Standard" (GB25461-2010). It has the advantages of good treatment effect, low operating cost, convenient bioball precipitation and recovery, and high by-product value. It can replace the current existing biological treatment technology and avoid the use of chemical flocculants.

[0091] According to the records in Table 2 above, it can be seen that when the oil-rich new green algae liquid (Comparative Example 1) is used alone for wastewater treatment, the concentrations of suspended solids, five-day biochemical oxygen demand, chemical oxygen demand, ammonia nitrogen, total nitrogen, total phosphorus, total cyanide, etc. in the treated wastewater are significantly higher than those in Examples 1 to 3; the pre-culture method of microalgae and fungi is adjusted, and the oil-rich new green algae and Aspergillus fumigatus are not adaptively cultured (Comparative Example 2), and the obtained microalgae fungus balls are used to treat cassava starch wastewater. The concentrations of pollutants in the treated wastewater are significantly higher than those in Examples 1 to 3; the preparation process of microalgae fungus bioballs is skipped, and the pretreated microalgae and fungi are directly used for wastewater treatment (Comparative Example 3). The concentrations of ammonia nitrogen and total phosphorus after treatment are significantly higher than those in Examples 1 to 3, and the total phosphorus concentration has exceeded the direct emission limit.

[0092] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for treating cassava starch wastewater using a microalgae-fungus symbiotic system, characterized in that: The following steps are involved: Microalgae pre-culture of Neochloris oleoabundans to obtain Neochloris oleoabundans liquid; Aspergillus fumigatus Fresenius is pre-cultured to obtain Aspergillus fumigatus spores; The oil-rich new green algae liquid, the Aspergillus fumigatus spores and the cassava starch wastewater that has been filtered and sterilized are mixed, and cultured on a shaking table to obtain microalgae fungal bio-balls; The cassava starch wastewater is precipitated and sand filtered to obtain pretreated cassava starch wastewater; adding the microalgae fungus bio-balls to the pretreated cassava starch wastewater, performing biological treatment in a photobioreactor to sterilize the algae, and obtaining treated cassava starch wastewater; The mixing ratio of the oil-rich new green algae liquid, Aspergillus fumigatus spores and filtered and sterilized cassava starch wastewater is 1.2×10 9 cells:1.2×10 4 cells:1L; The amount of microalgae fungus bio-balls added is determined by the volume of the pre-treated cassava starch wastewater, and the addition amount is 200-400gDW / m 3 .

2. The method according to claim 1, wherein: The microalgae pre-cultivation comprises the following steps: The oil-rich new green algae is inoculated into a mixture of cassava starch wastewater and culture solution in a volume ratio of 20:80, and is shaken and cultured to obtain a first-generation oil-rich new green algae; the first-generation oil-rich new green algae is transferred to a mixture of cassava starch wastewater and culture solution in a volume ratio of 40:60 for secondary culture to obtain a second-generation oil-rich new green algae; the second-generation oil-rich new green algae is transferred to a mixture of cassava starch wastewater and culture solution in a volume ratio of 60:40 for three culture to obtain a third-generation oil-rich new green algae; the third-generation oil-rich new green algae is transferred to a mixture of cassava starch wastewater and culture solution in a volume ratio of 80:20 for four culture to obtain a fourth-generation oil-rich new green algae; the fourth-generation oil-rich new green algae is transferred to cassava starch wastewater for five culture to obtain a fifth-generation oil-rich new green algae; the fifth-generation oil-rich new green algae is centrifuged to obtain an oil-rich new green algae liquid.

3. The method according to claim 2, wherein: The culture medium is BG-11 culture medium.

4. The method according to claim 2, wherein: The culture conditions for the shaking culture, secondary culture, tertiary culture, quadruple culture and quintuple culture were the same, and the culture conditions were: temperature 25°C, light intensity 200 μmol / m 2 / s, light-dark ratio 12h light / 12h dark, rotation speed 120r / min, culture time 7d.

5. The method according to claim 1, wherein: The fungus pre-culture comprises the following steps: Aspergillus fumigatus was inoculated into an agar medium prepared with cassava starch wastewater as a solvent. After spores emerged, the spores were transferred to an agar medium prepared with cassava starch wastewater as a solvent. This was repeated three times, and the Aspergillus fumigatus spores were collected using a 0.1% Tween 80 solution.

6. The method according to claim 1, wherein: The filtration sterilization process uses a 0.22 μm water filter membrane.

7. The method according to claim 1, wherein: The culture conditions of the shaking culture were: temperature 25-28°C, light intensity 200 μmol / m 2 / s, light-dark ratio 12h light / 12h dark, rotation speed 150-190r / min, and culture time 3-4d.

8. The method according to claim 1, wherein: The biological treatment conditions are: under sunlight, temperature of 25-28° C., operating flow rate of 0.3-0.4 m / s, and operating time of 8-10 days.

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