A method for improving the anaerobic digestion efficiency of molasses alcohol wastewater using Desmodesmus alba GXU-A4

Abstract

The present invention belongs to the technical field of sewage treatment. The present invention relates to a method for improving the anaerobic digestion efficiency of molasses alcohol wastewater by utilizing Desmodesmus algae GXU‑A4, wherein Desmodesmus algae GXU‑A4 is mixed with molasses alcohol wastewater and then inoculated with granular sludge for co-digestion. The addition of Desmodesmus algae GXU‑A4 during the anaerobic digestion of molasses alcohol wastewater of the present invention effectively alleviates the inhibitory effect caused by the high C / N ratio of molasses alcohol wastewater, significantly improves the digestion efficiency of molasses alcohol wastewater, promotes the hydrolysis and acidification efficiency of granular sludge on organic matter in wastewater, and can also improve the methane potential of organic matter, and also provides a new method for the full recycling of microalgae biomass.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a method for improving the anaerobic digestion efficiency of molasses alcohol wastewater by utilizing Desmodesmus algae GXU-A4. Background Art

[0002] Sugarcane molasses alcohol wastewater (Molasses vinasse, MV) is a byproduct produced in the process of producing alcohol using sugarcane molasses as raw materials. It has the characteristics of high chemical oxygen demand (COD) and sulfate concentration, which makes it difficult to treat and has poor treatment effects. Anaerobic digestion (AD) can rely on anaerobic microbial flora to convert organic metabolites in industrial wastewater into biogas, which is characterized by high efficiency, safety, low cost and high productivity. However, the high organic matter concentration in molasses alcohol wastewater leads to a high C / N ratio, which seriously inhibits the efficiency of anaerobic digestion. The efficiency of single-substrate anaerobic treatment of molasses alcohol wastewater has been unable to achieve a substantial breakthrough, so it is of great significance to explore the effect of additional addition of other organic matter on anaerobic fermentation.

[0003] Desmodium has great potential in wastewater treatment. It accumulates high value-added products such as oil and pigments during anaerobic wastewater treatment and has certain economic value. However, microalgae biomass after lipid extraction still has great methane potential. Moreover, in the current study, it was found that adding algae biomass to food wastewater can improve digestion stability, but it will reduce the specific biogas production. Commonly used microalgae are mainly Chlorella and Spirulina, mainly because of their high algae protein content and rapid growth. Spierling et al. found that when 50% algae, 40% sorted organic municipal waste and 10% wastewater sludge were used for co-digestion, the methane production reached 0.40 liters / gram volatile solids (VS) and the organic loading rate (OLR) was 2gVS / (L·day) (Spierling R.Anaerobic Co-digestion of Microalgae with Food Waste and Wastewater Sludge, California Polytechnic State University, 2011); Lee et al. used Chlorella and found that the methane production was the largest when COD / N was 24, and the methane production increased the most when COD / N was 15 (Lee K, Chantrasakdakul P, Kim D, et al.Anaerobic co-digestion of food waste leachatewith microalgae for improvement of methane production[J].2014,28,55e60). Each type of microalgae has different structures and components, which leads to different differences in the anaerobic digestion system. Studying the addition strategy of Desmodesmus in the anaerobic digestion system is of great significance for the wastewater resource treatment system. Summary of the invention

[0004] The object of the present invention is to provide a method for improving the anaerobic digestion efficiency of molasses alcohol wastewater by utilizing Desmodesmus umbelliferae GXU-A4. The present invention adds Desmodesmus umbelliferae GXU-A4 into molasses alcohol wastewater, effectively alleviates the inhibitory effect caused by the high C / N ratio of molasses alcohol wastewater, promotes the digestion efficiency of molasses alcohol wastewater, and can also improve the methane potential of organic matter, and also provides a new method for the full recycling of microalgae biomass, thereby effectively solving the problems of great difficulty in treating molasses alcohol wastewater, poor treatment effect and low methane potential of organic matter in the wastewater.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a method for improving the anaerobic digestion efficiency of molasses alcohol wastewater by utilizing Desmodesmus glabra GXU-A4. Granular sludge is inoculated into the molasses alcohol wastewater, and then Desmodesmus glabra GXU-A4 is added for co-digestion.

[0007] Preferably, the Desmodesmus GXU-A4 has been deposited in the China Type Culture Collection in Wuhan, China on December 17, 2021. The deposit address is Wuhan University, No. 299, Bayi Road, Wuchang District, Wuhan City, Hubei Province, and the deposit number is CCTCC NO:M 20211641.

[0008] Preferably, the addition amount of the Desmodesmus algae GXU-A4 is 1-8 g, and the pH value of the molasses alcohol wastewater is 6-8.

[0009] Preferably, the inoculation volume ratio of the granular sludge is molasses alcohol wastewater: granular sludge = (2-4):1.

[0010] Preferably, the temperature of the anaerobic fermentation is 35-38°C, and the time of the anaerobic fermentation is 38-50 days.

[0011] Preferably, the Desmodesmus algae GXU-A4 is added once every 5-20 days, and the amount added each time is 0.1-1.8 g.

[0012] Preferably, the granular sludge is the bottom sludge of molasses alcohol wastewater containing fermentation bacteria.

[0013] Preferably, the Desmodium GXU-A4 is fresh Desmodium or defatted Desmodium.

[0014] By adopting the above technical solution, the present invention has the following beneficial effects:

[0015] The technical solution of the present invention organically combines the microalgae treatment system with the anaerobic digestion system, adds Desmodesmus GXU-A4 to molasses alcohol wastewater for anaerobic digestion treatment, effectively alleviates the inhibitory effect caused by the high C / N ratio of molasses alcohol wastewater, significantly improves the anaerobic digestion efficiency, promotes the hydrolysis and acidification efficiency of granular sludge on organic matter in the wastewater, improves the methane production potential of organic matter, and provides a new method for the full recycling of microalgae biomass, thereby effectively solving the problems of difficulty in treating molasses alcohol wastewater, poor treatment effect and low methane potential of organic matter in the wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 SEM images of two kinds of microalgae, GXU-A4 and GXU-A9 (A is the GXU-A4 fresh algae mud group, scale bar = 5 μm; B is the GXU-A4 defatted algae residue group, scale bar = 5 μm, and C is the GXU-A9 group, scale bar = 100 μm);

[0017] Figure 2 is the SCOD removal rate of GXU-A4 in the AD process (where A is the fresh algae mud group and B is the defatted algae residue group);

[0018] Figure 3 is the SCOD removal rate of GXU-A9 during AD process;

[0019] Figure 4 The total VFA concentration of GXU-A4 during the AD process (A is the fresh algae mud group, and B is the defatted algae residue group);

[0020] Figure 5 The results of the determination of methane yield of GXU-A4 during the AD process (A is the fresh algae mud group, and B is the defatted algae residue group);

[0021] Figure 6 The pH value of GXU-A4 during the AD process (A is the fresh algae mud group, and B is the defatted algae residue group);

[0022] Figure 7 The ammonia nitrogen concentration of GXU-A4 during the AD process was measured (A is the fresh algae mud group and B is the defatted algae residue group).

[0023] Biological deposit information

[0024] Desmodesmus sp. GXU-A4 was deposited in the China Center for Type Culture Collection on December 17, 2021. The deposit address is Wuhan University, Wuhan, China, and the deposit number is CCTCC NO:M 20211641. DETAILED DESCRIPTION

[0025] The invention provides a method for improving the anaerobic digestion efficiency of molasses alcohol wastewater by utilizing Desmodesmus glabra GXU-A4. Granular sludge is inoculated into the molasses alcohol wastewater, and then Desmodesmus glabra GXU-A4 is added to perform co-digestion and anaerobic fermentation.

[0026] In the present invention, the Desmodesmus GXU-A4 was preserved in the China Type Culture Collection in Wuhan, China on December 17, 2021. The preservation address is Wuhan University, No. 299, Bayi Road, Wuchang District, Wuhan City, Hubei Province, and the preservation number is CCTCC NO:M 20211641.

[0027] In the present invention, the pH value of the molasses alcohol wastewater is preferably 6-8, further preferably 6.5-7.5, and further preferably 6.9-7.2. In the present invention, the addition amount of the Desmodium GXU-A4 is 1-8g, further preferably 1.1-7.5g, and further preferably 1.2-7.2g. In the present invention, the addition frequency of the Desmodium GXU-A4 is preferably once every 5-20d, further preferably once every 8-16d, and further preferably once every 8d or once every 16d; the addition amount each time is preferably 0.1-1.8g, further preferably 0.14-1.6g, and further preferably 0.2-1.2g. In the present invention, the Desmodium GXU-A4 is preferably fresh Desmodium GXU-A4 or defatted Desmodium GXU-A4.

[0028] In the present invention, the preparation method of the defatted GXU-A4 algae is as follows: the obtained GXU-A4 fresh algae mud is extracted with a fat extractor, and the extraction solvent is preferably anhydrous ethanol; the extraction temperature is preferably 50-70°C, further preferably 55-65°C, and further preferably 60°C; the extraction cycle is preferably 5-10h, further preferably 7-9h, and further preferably 8h. After the extraction, the algae residue is filtered through filter paper to obtain the algae residue, and then the obtained algae residue is dried, and the drying temperature is preferably 50-70°C, further preferably 55-65°C, and further preferably 60°C; the algae residue is dried to constant weight to obtain defatted algae residue.

[0029] In the present invention, the inoculation volume ratio of the granular sludge is preferably molasses alcohol wastewater: granular sludge = (2-4): 1, further preferably (2.5-3.5): 1, and further preferably 3: 1. The granular sludge of the present invention is the bottom mud of molasses alcohol wastewater containing fermentation bacteria, and the granular sludge comes from the IC anaerobic reactor with a working volume of 22L in this laboratory (the IC anaerobic reactor is described in the Chinese patent record with publication number CN217535593U). After the granular sludge is domesticated with long-term high-concentration molasses alcohol wastewater, the granular sludge flora can withstand high organic load shock. In the present invention, the fermentation bacteria preferably include Ercella succinigenes, Fermentimonas caenicola, Porphyromonadaceaebacterium, Rikenellaceae bacteriu, Methanothrix soehngenii and Methanosarcinabarkeri.

[0030] In the present invention, the temperature of the anaerobic fermentation is preferably 35-38°C, further preferably 36-37.7°C, and further preferably 36.5-37.5°C; the time of the anaerobic fermentation is preferably 38-50d, further preferably 40-46d, and further preferably 44d.

[0031] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0032] Example 1

[0033] (I) Obtaining fermentation substrate and seed sludge

[0034] 1. Desmodesmus GXU-A4 and Chlorophytum corymbiferum GXU-A9

[0035] a. Fresh Desmodium GXU-A4 and Yellow Silk Algae GXU-A9

[0036] The GXU-A9 is a small yellow filament algae purchased from the freshwater algae species bank of the Chinese Academy of Sciences, numbered FACHB-2215, and its Latin species name is Tribonema minus; GXU-A9 is the number name of the inventor's laboratory.

[0037] The preserved GXU-A4 (Desmodesmus sp. GXU-A4) and GXU-A9 (Tribonema minus GXU-A9) algae were placed in The columnar microalgae photobioreactor is then filled with 1-2% CO 2 The culture was carried out in BG11 medium (4.5mmol sodium nitrate as nitrogen source) with compressed air at 25±1℃ and 150μmol / (m 2 ·s) light intensity continued illumination. After culturing for 5 days and entering the exponential phase, the culture supernatant was removed by centrifugation at 3500 rpm for 7 min, and the residual culture medium nutrients on the surface of the algae were washed off with sterile water. Then, the initial concentration OD 750 The molasses alcohol wastewater (COD after dilution was within the range of 8000±100) was inoculated with 0.5±0.1, and 1% of the modified nitrogen-free BG-11 medium was added. The culture was carried out in a columnar photobioreactor and a stream rich in 1-2% CO 2 The culture was carried out with compressed air at a temperature of 25±1°C and a light intensity of 300μmol / (m 2 ·s) continuous illumination, the culture period is 8 days, the culture solution is centrifuged at a speed of 3500 rpm for 7 minutes, the supernatant is removed, and the precipitate is fresh algae mud.

[0038] The preparation process of the improved nitrogen-free BG-11 medium is as follows: MgSO 4 7H 2 O 75 mg, CaCl 2 ·2H 2 O 36mg, Na 2 CO 3 20mg, K 2 HPO 4 40mg, FeCl 3 ·2H 2 O 3.15mg, Na 2 EDTA·2H 2 O 4.36mg and Citric acid (citric acid) 6.0mg and A5 mix 1mL add water to 1L and sterilize. The preparation of A5 mix is ​​to add H 3 BO 3 2.86g, MnCl 2 ·4H 2 O 1.81g, ZnSO 4 7H 2 O 0.222g, CuSO 4 ·5H 2 O 0.079g, NaMoO 4 ·2H 2 O0.39g, Co(NO 3 ) 2 6H 2 O 49.4mg and concentrated H 2 SO 4 1 mL, then add water to 1 L and sterilize.

[0039] b. Defatted Desmodium GXU-A4

[0040] The GXU-A4 fresh algae mud in the above operation 1 was used to extract oil using a fat extractor, the extraction solvent was anhydrous ethanol, the extraction temperature was 60°C, and the extraction cycle was 8 hours. Then, the algae residue obtained by filtering with filter paper was dried at 60°C to constant weight to obtain defatted algae residue.

[0041] 2. Molasses alcohol wastewater and granular sludge

[0042] The molasses alcohol wastewater used in this embodiment comes from an alcohol factory in Guangxi. The liquid is dark brown and relatively clear, with a pH of 3-4, and is stored in plastic barrels at room temperature.

[0043] The granular activated sludge came from the IC anaerobic reactor in operation in the laboratory.

[0044] (II) Anaerobic fermentation system

[0045] 1. Experimental setup and design

[0046] The AMPTS Ⅱ fully automatic methane potential test system (Bioprocess Control AB, Sweden) was used to study the anaerobic co-digestion of molasses alcohol wastewater with Alpinia fasciatus. The second-generation AMPTS fully automatic methane potential test system (AMPTS II) mainly consists of three units, namely the digestion unit, the gas absorption device unit and the gas meter unit. The setting of experimental parameters and the statistics and reading of real-time methane production are controlled by the connected computer terminal, as follows:

[0047] Digestion unit: The digestion unit consists of multiple glass digestion bottles (digesters), with mechanical stirring devices on the top of the glass bottles and a constant temperature water bath pot that can adjust the temperature. The speed and frequency of mechanical stirring can be controlled and adjusted on the computer terminal.

[0048] Gas absorption device unit: The absorption unit consists of several 100mL glass bottles, which are connected to the digestion unit through silicone tubes. When working, a 3mol / L NaOH solution containing an indicator is added to the glass bottle to absorb acidic impurity gases such as carbon dioxide and hydrogen sulfide produced by the digestion unit.

[0049] Gas meter unit: The gas meter unit is connected to the gas absorption device unit through a silicone tube, and uses a built-in sensor to record the gas flow in real time and transmit the data to the computer terminal. Each anaerobic digestion unit corresponds to an independent gas metering device.

[0050] 2. Experimental Design and Operation of Anaerobic System

[0051] This experiment consists of 39 250mL glass digestion bottles with an effective working volume of 200mL. Granular sludge was inoculated into molasses alcohol wastewater, and anaerobic fermentation was carried out at a volume ratio of molasses alcohol wastewater to granular sludge of 3:1. Then, the algae mud or defatted algae residue obtained above was added for co-digestion, and the fermentation temperature was mesophilic anaerobic digestion (37±0.5℃). 20 treatment groups were set up, namely SC_Blank, SF2_8, SF2_16, SF4_8, SF4_16, SF6_8, SF6_16, SP2_8, SP2_16, SP4_8, SP4_16, SP6_8, SP6_16, TC_Blank, TF2_8, TF2_16, TF4_8, TF4_16, TF6_8 and TF6_16, with three parallels in each group (see Table 1 for specific settings). The experiment adopted a semi-continuous sampling method, the pH value of the sampled wastewater was adjusted in the range of 6.9-7.2, 50 mL of sample was injected and discharged by syringe every day, and manual homogenization was performed twice a day. The experiment was run for a total of 44 days, and the SCOD and VFAs of the inlet and outlet water were measured regularly, and the daily methane production was recorded.

[0052] Table 1 Treatment group settings

[0053]

[0054] (III) Determination methods of various indicators

[0055] 1. Observation of the morphological structure of microalgae GXU-A4 and GXU-A9

[0056] (1) Sampling: Collect algae mud or algae residue samples from the sampling port of each photobioreactor, centrifuge at 4°C and 10,000 rpm for 3 min, and discard the supernatant.

[0057] (2) Fixation: Take 0.1 mL of algal mud or algal residue sample after centrifugation and place it in a 2 mL centrifuge tube, add 1 mL of 2.5% glutaraldehyde, and place the sample in a 4°C refrigerator overnight.

[0058] (3) Rinse: Rinse the fixed samples three times with 0.1 M phosphate buffer (pH 6.8), each time for 10 min.

[0059] (4) Dehydration: Use 50%, 70%, 80%, 90%, and 100% alcohol for dehydration, each time for 15 minutes.

[0060] (5) Replacement: The dehydrated sample was replaced with a mixture of isoamyl acetate and anhydrous ethanol (v / v = 1) and pure isoamyl acetate, respectively, for 15 min each time.

[0061] (6) Drying: Place the replaced sample in a small box made of tin foil and dry it in a desiccator overnight.

[0062] (7) Sample preparation and loading: The dried sample is pasted and spread flat on a sample carrier covered with tape, and a metal film is sprayed on the sample surface using an ion sputtering coating device. The morphological structure of the anaerobic active algal mud or algal residue is then observed under a scanning electron microscope.

[0063] 2. Determination of lipid content of microalgae GXU-A4 and GXU-A9

[0064] Weigh 50-80 mg of algae mud or defatted algae residue and put it into a 15 mL glass centrifuge tube, and add a magnetic stirrer; first add 2 mL of dimethyl sulfoxide-methanol mixed solution (V:V=1:9) to the centrifuge tube, water bath at 50°C for 1.5 hours, centrifuge at 3000 rpm for 5 minutes, and collect the supernatant in a 15 mL glass vial; then add 4 mL of ether-n-hexane mixed solution (V:V=1:1) to the centrifuge tube, ice bath for 1.5 hours, centrifuge at 3000 rpm for 5 minutes, collect the supernatant into the same glass vial; repeat the above extraction process once. Then add 4 mL of distilled water to the vial collecting the supernatant, shake and mix, and then stand to separate; after separation, transfer the upper organic phase to a weighed 5 mL centrifuge tube, blow dry with nitrogen, and weigh it. The weight of the extracted lipids is calculated using the difference before and after the centrifuge tube, thereby obtaining the lipid content in the algae mud or algae residue.

[0065] 3. SCOD determination and SCOD removal rate calculation

[0066] Material description: COD special test reagent was purchased from Zhejiang Dites Technology Co., Ltd.

[0067] (1) Take 2 mL of the influent sample before anaerobic treatment and the effluent sample after anaerobic treatment, centrifuge at 10,000 r / min for 10 min, filter with a 0.45 μm microporous filter membrane to remove impurities, and keep the filtrate sample for testing.

[0068] (2) Take 2 ml of filtered water sample and add it to COD special test reagent, digest it with Hach DRB200 digester at 165℃ for 20 minutes, and after the digestion solution cools to room temperature, use Hach water quality detector DR900 to measure the COD value and record it. Calculate the SCOD removal rate. The calculation formula of SCOD removal rate is as follows:

[0069] SCOD removal rate = (SCOD 进 -SCOD 出 )×100 / SCOD 进

[0070] Among them: SCOD 进 Represents the SCOD of wastewater before treatment; SCOD 出 It represents the SCOD of the treated wastewater.

[0071] 4. Determination of total VFAs content

[0072] (1) The gas chromatograph measurement procedure is as follows:

[0073] ①Instrument: Fuli gas chromatograph GC9720Plus; detector: FID; chromatographic column: Agilent DB-FFAP, 30m×0.25mm×0.25mm.

[0074] ②Detector temperature: 250℃; column box temperature: 70℃; injection volume: 3μL; split ratio: 5:1.

[0075] ③ Heating program: maintain at 70℃ for 1 min; increase the temperature to 180℃ at 12℃ / min and maintain for 3 min; then increase the temperature to 200℃ at 20℃ / min and maintain for 3 min.

[0076] (2) Sample pretreatment: The water samples collected from each digester were centrifuged at 12000 rpm at 4°C for 5 min, and the supernatant was filtered through a 0.22 μm filter membrane. 1 mL of the filtrate was acidified to pH 2.0 with 3% formic acid solution.

[0077] (3) Prepare seven mixed standard solutions (acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid and valeric acid) with concentration gradients of 0 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, 300 mg / L, 400 mg / L and 500 mg / L respectively, and draw a mixed standard curve.

[0078] (4) The pretreated samples were placed in a gas chromatograph in order for determination, and the concentrations of the various VFA components and the total VFA concentration were determined based on the standard curve analysis.

[0079] 5. Determination of methane production

[0080] Methane production is measured in real time using the AMPTS fully automatic methane potential test system, which can display the cumulative gas production per hour and the cumulative gas production per day.

[0081] (III) Measurement results

[0082] 1. SEM images and lipid content of microalgae GXU-A4 and GXU-A9

[0083] Table 2 Oil content of GXU-A4 and GXU-A9

[0084]

[0085]

[0086] from Figure 1It can be seen that the two microalgae have significant differences in structure; as can be seen from Table 2, the morphology of Desmodium GXU-A4 did not show obvious changes after ethanol degreasing treatment, but the oil content in the microalgae decreased from 19.53% to 0.37% after degreasing treatment, which indicates that the degreasing treatment did not cause obvious damage to the surface of the microalgae, but effectively removed the oil of the microalgae.

[0087] 2.SCOD removal rate

[0088] SCOD is an important indicator to measure the degree of wastewater pollution. Figure 2 As shown in the figure, the SCOD removal rate of the group with fresh algae mud was significantly higher than that of the control group in the mid-digestion period. SP2_8 obtained the highest SCOD removal rate on the 32nd day (SP2_8: 82.97%; SC_Blank: 69.37%), while the difference between the group with defatted algae residue and the control group was small. This indicates that the addition of fresh algae mud can effectively improve the removal of SCOD during anaerobic digestion in the mid- and late-stage fermentation.

[0089] like Figure 3 As shown in the figure, the addition amount and frequency of GXU-A9 had different effects on the AD process. The lower addition amount and longer addition frequency promoted the AD efficiency to a certain extent (TF2_8, TF2_16 and TF4_16), while the COD removal rate decreased significantly in the higher addition amount group.

[0090] 3. TVFA concentration

[0091] The VFA concentration reflects the hydrolysis efficiency in the digestive system. At the same time, acetic acid in VFA can directly participate in the methanogenesis pathway, but high concentrations of VFA inhibit anaerobic digestion and lead to system acidification. Figure 4 As shown in the figure, different addition amounts and addition frequencies of Desmodesmus GXU-A4 promoted the VFA content in the digestive system to varying degrees, but the VFA concentration remained stable and had no obvious inhibitory effect on the digester. In the middle of digestion, the VFA concentration of SF2_8 increased significantly after the 24th day, indicating that under this group of conditions, the sludge's ability to hydrolyze organic matter was significantly improved, and it could effectively degrade the macromolecular organic matter in the microalgae into volatile fatty acids, promoting the methane production efficiency of the sludge.

[0092] 4. Methane yield

[0093] Figure 5It can reflect the methane yield per unit of organic matter in the digester. Methane yield represents the ability of unit organic matter to be converted into methane. The addition of Desmodium GXU-A4 can significantly increase the methane potential of organic matter in the digester. The addition of fresh algae residue groups showed different degrees of promotion. The highest methane yield (107.3 ml CH 4 / g vs ), followed by SF2_16 with a methane yield of 101.56 ml CH 4 / g vs The third is that the methane yield of SF6_16 is 100.75ml CH 4 / g vs , and the organic methane yields were increased by 27%, 21% and 20% respectively compared with SC_Blank. However, the addition of high amounts of defatted algae residue (SF6_8 and SF6_16) inhibited the methane yield in the middle of digestion. SP2_8 obtained the highest methane yield (101mlCH 4 / g vs ), followed by SP2_8 with a methane yield of 97.59 ml CH 4 / g vs The results showed that adding fresh Desmodesmus algae GXU-A4 could improve the methane yield of organic matter in the anaerobic digestion system, the optimum addition amount was 2 g, and the addition frequency was 8 days.

[0094] Table 3 Methane potential of GXU-A4, GXU-A9 and other algae

[0095]

[0096]

[0097] As can be seen from Table 3, the methane potential of the two microalgae and other algae recorded in the existing literature, SF2_16 and SP2_16 obtained the highest methane potential (1272mL / g VS and 1210mL / g VS), which had a significant effect on the methane yield during the co-fermentation process. Gonzalez-Gonzalez et al. and Mussgnug et al. obtained the methane potential of two microalgae in the genus Scenedemus through batch experiments, which were 312mL / g VS and 287mL / g VS, respectively; while other genera of algae such as Chlorella, Lake blue algae and Alum flocculated alga were also lower than this experiment. It shows that GXU-A4 and MV co-fermentation have a synergistic effect with granular sludge during the AD process, which effectively improves the conversion efficiency of organic matter in the digester.

[0098] 5. pH

[0099] In the anaerobic digestion process, pH value is an important parameter to evaluate whether the reactor operation is stable (such as Figure 6 ). The optimum pH range for mesophilic methanogenic bacteria is 7.2-7.5. A lower pH will lead to acidification of the digestive system and cause the digestive system to collapse. All reactors were kept in the range of 7.2-8.0 throughout the fermentation process, and there was no acidification collapse. In the early stage of fermentation, it was stably maintained in the range of 7.2-7.5, but there was a rapid increase in pH during the last hydraulic retention time. It may be that semi-continuous sampling caused the accumulation of alkali in the fermentation system. The addition of fresh algal mud and defatted algal residue had no significant effect compared with the control group, indicating that the addition of Desmodium GXU-A4 would not affect the pH stability in the fermentation system.

[0100] 6. Ammonia nitrogen concentration

[0101] Molasses alcohol wastewater contains a large amount of organic nitrogen, which is converted into inorganic ammonia nitrogen by sludge bacteria under anaerobic conditions. High concentrations of ammonia nitrogen (1500 mg / L) will have a toxic effect on methanogenic bacteria. During the entire fermentation process, the ammonia nitrogen concentration of each group fluctuated within the range of 300-800 mg / L, and did not cause an inhibitory effect on the digestive system (such as Figure 7 The addition of Desmodesmus algae GXU-A4 did not significantly affect the ammonia nitrogen concentration.

[0102] It can be seen from the above embodiments that the present invention promotes the anaerobic digestion efficiency of molasses alcohol wastewater by adding Desmodium GXU-A4. The microalgae biomass accumulated after treating the wastewater is co-digested with the molasses alcohol wastewater, and the effluent SCOD, TVFA and methane yield are regularly monitored. The addition of GXU-A4 significantly improves the anaerobic digestion efficiency, promotes the efficiency of sludge hydrolysis and acidification of organic matter in wastewater, and improves the methane production potential of organic matter, and its methane potential is significantly higher than that of GXU-A9 and other microalgae. This method can organically combine the microalgae treatment system with the anaerobic digestion system, use Desmodium GXU-A4 to treat the effluent in the anaerobic digestion system, and accumulate microalgae biomass. Then, high-value products such as oils and fats in the microalgae biomass are extracted, and the defatted algae residue after extraction is co-fermented with molasses alcohol wastewater to form a closed loop, which greatly improves the recycling of organic matter in the wastewater.

[0103] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for improving the anaerobic digestion efficiency of molasses alcohol wastewater using Desmodesmus alba GXU-A4, It is characterized in that Molasses alcohol wastewater was inoculated with granular sludge, and then Desmodesmus algae GXU-A4 was added for co-digestion; The Desmodesmus GXU-A4 was deposited in the China Type Culture Collection in Wuhan, China on December 17, 2021. The deposit address is Wuhan University, No. 299, Bayi Road, Wuchang District, Wuhan City, Hubei Province, and the deposit number is CCTCC NO: M20211641; The inoculation volume ratio of the granular sludge is molasses alcohol wastewater: granular sludge = (2-4): 1; The temperature of the anaerobic fermentation is 35-38°C, and the time of the anaerobic fermentation is 38-50 days; The frequency of adding the Desmodesmus algae GXU-A4 is once every 5-20 days, and the amount added each time is 0.1-1.8 g.

2. The method according to claim 1, It is characterized in that The addition amount of the Desmodesmus algae GXU-A4 is 1-8 g, and the pH value of the molasses alcohol wastewater is 6-8.

3. The method according to claim 1, It is characterized in that The granular sludge is the bottom sludge of molasses alcohol wastewater containing fermentation bacteria.

4. The method according to claim 1, It is characterized in that The Desmodesmus salsa GXU-A4 is fresh Desmodesmus salsa or defatted Desmodesmus salsa.

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