Microalgae efficient resource treatment method

Abstract

The application discloses a kind of microalgae efficient resource processing method, the method is in the wastewater required to be treated with the inoculation of microalgae concentrated liquid with dry weight greater than 30mg / L, then different physiological stages of microalgae are added with different concentrations of nano zero-valent iron suspension, after 14 days of culture, obtain microalgae culture solution, detect COD, NH4 + -N, PO4 3‑ -P index in microalgae culture solution, after 9h of microalgae culture solution, make microalgae self-flocculation settlement, centrifugal treatment is carried out to microalgae culture solution after self-flocculation settlement, after filtration, freeze-drying is carried out, obtain microalgae powder, then chloroform-methanol method is used to extract microalgae oil.The application adds different concentrations of nano zero-valent iron in different growth stages of microalgae, enhances the performance of microalgae to remove nutrients in wastewater, and promotes the flocculation ability of microalgae and the accumulation of oil content.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wastewater treatment and microalgae resource treatment, and particularly relates to a microalgae high-efficiency resource treatment method. BACKGROUND

[0002] In the face of the imminent water quality deterioration crisis and the realization of the double carbon target, microalgae biotechnology is widely used in wastewater treatment. Microalgae is a kind of oil-rich algae that can grow by photoautotrophy or heterotrophy, and has a high removal capacity for nutrients in wastewater. Through the resource treatment of microalgae on wastewater, many high-value biological products (such as lipids, proteins, and carbohydrates) are obtained while treating wastewater, which will greatly reduce the economic cost of environmental governance and promote sustainable development. The self-flocculation performance of microalgae is crucial to the efficiency of microalgae harvesting, and simply relying on flocculants for microalgae harvesting obviously does not meet the economic applicability and environmental friendliness of large-scale application of microalgae biological treatment of wastewater. And in view of the current research on microalgae biological treatment of wastewater, the biological activity of microalgae per unit cultivation time, the wastewater removal performance, and the self-flocculation effect after wastewater treatment still need to be improved, which to some extent leads to the reduction of the engineering application potential of microalgae biological treatment of wastewater.

[0003] In addition, there is a certain contradiction between wastewater treatment effect and microalgae lipid accumulation in the treatment of wastewater by microalgae biotechnology. When microalgae treat high-concentration ammonia-nitrogen wastewater, although the accumulation of lipids can be promoted, the removal capacity of nutrients in wastewater is poor; while microalgae treat low-concentration wastewater, it is often difficult to promote the accumulation of lipids. SUMMARY

[0004] In order to solve the problems of low efficiency, low flocculation and sedimentation efficiency, and low microalgae lipid content in the resource treatment of wastewater by microalgae, the present application provides a microalgae high-efficiency resource treatment method, which adds different concentrations of nano zero-valent iron at different growth stages of microalgae, enhances the performance of microalgae in removing nutrients in wastewater, and promotes the flocculation ability and lipid content accumulation of microalgae.

[0005] To achieve the above effects, the specific technical scheme adopted by the present application is as follows: a microalgae high-efficiency resource treatment method, comprising the following steps:

[0006] Step one, determination of different physiological stages of microalgae: inoculate microalgae concentrate with a dry weight greater than 30 mg / L in the wastewater to be treated, then add different concentrations of nano zero-valent iron suspension at different physiological stages of microalgae, and obtain microalgae culture solution after 14 days of cultivation;

[0007] Step two, determination of microalgae wastewater treatment efficiency: centrifuge a certain amount of microalgae culture solution, filter the filtrate and store it in a refrigerator at 4℃, and detect the COD, NH4+ -N, PO4 3- -P index

[0008] Step three, microalgae flocculation and sedimentation: after the microalgae culture solution is left for 9 hours, the microalgae are allowed to flocculate and sediment by themselves;

[0009] Step four, extraction of microalgae oil: after the microalgae culture solution that has flocculated and settled by itself is centrifuged, filtered and freeze-dried, microalgae powder is obtained, and then the microalgae oil is extracted by using the chloroform-methanol method.

[0010] In the method, the nano zero-valent iron suspension is obtained by uniformly suspending the nano zero-valent iron in deionized water and ultrasonically oscillating for 0.5 hours, and the concentration is not more than 1000 mg / L.

[0011] In the method, the particle size of the nano zero-valent iron is 50 nm.

[0012] In the method, the physiological stages of the microalgae include an adaptation period, a growth period, a stable period and a decline period; the adaptation period is 0-4 days from the inoculation day, the nano zero-valent iron suspension with a dosing concentration of 0.05-0.10 mg / L is added, the growth period is 4-8 days, the nano zero-valent iron suspension with a dosing concentration of 0.05-0.10 mg / L is added, and the stable period is after 8 days, the nano zero-valent iron suspension with a dosing concentration of 0.05-0.10 mg / L is added.

[0013] In the method, the culture conditions are as follows: the temperature is 25℃±2℃, the light intensity is 200 μmol·m-2·s-1, the light / dark ratio is 12 hours / 12 hours, and the humidity is 45%. -2 ·S -1

[0014] Due to the adoption of the technical solutions, the present application has the beneficial effects that the present application adds nano zero-valent iron with different concentrations at different growth stages of microalgae, enhances the performance of microalgae in removing nutrients in wastewater, promotes the flocculation ability of microalgae and the accumulation of oil content, improves the production of microalgae biofuel, greatly reduces the economic cost, and achieves the win-win purpose with the maximum benefit. In addition, the present application can also enhance the self-flocculation performance of microalgae, and can reduce the economic cost in the microalgae harvesting process. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The figure is a growth curve of microalgae at different physiological stages in Example 1 of the present application;

[0016] Figure 2 a is a COD recovery efficiency diagram when the dosing concentration of nano zero-valent iron is 0.05 mg / L in Example 2 of the present application;

[0017] ​Figure 2 b is a schematic diagram of COD recovery efficiency when the concentration of nano-zero valent iron added in Example 2 of the present invention is 0.10 mg / L;

[0018] Figure 2 c represents the concentration of nano-zero valent iron added in Example 2 of this invention when the concentration of NH4 is 0.05 mg / L. + -N recovery efficiency diagram;

[0019] Figure 2 d represents the concentration of nano-zero valent iron added in Example 2 of this invention when the concentration of NH4 is 0.10 mg / L. + -N recovery efficiency diagram;

[0020] Figure 2 e represents the concentration of nano-zero valent iron added in Example 2 of this invention when PO4 is 0.05 mg / L. 3- -P recovery efficiency diagram;

[0021] Figure 2 f represents the concentration of nano-zero valent iron added in Example 2 of this invention when the concentration of PO4 is 0.10 mg / L. 3- -P recovery efficiency diagram;

[0022] Figure 3 This is a schematic diagram illustrating the enhancement of microalgae self-flocculation performance in Embodiment 3 of the present invention;

[0023] Figure 4 This is a schematic diagram illustrating the process of increasing the lipid content of microalgae in Embodiment 4 of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] Example 1

[0026] Determination of different physiological stages of microalgae growth: Microalgae concentrate with a dry weight greater than 30 mg / L was inoculated into the wastewater to be treated, and the growth curve of the microalgae was monitored to determine the different physiological stages of microalgae growth.

[0027] The wastewater formulation used in this embodiment is as follows:

[0028] 0.02 g / L K2HPO4·3H2O, 0.075 g / L MgSO4·7H2O, 0.036 g / L CaCl2·2H2O, 0.02 g / L Na2CO3, 2.86 mg / L H3BO3, 0.049 mg / L Co(NO3)2·6H2O, 0.39 mg / L Na2MoO4·2H2O, 1.81 mg / L MnCl2·H2O, 0.079 mg / L CuSO4·5H2O, 0.222 mg / L ZnSO4·7H2O. The pH of the wastewater was 7.1±0.2, the initial COD was 257 mg / L, NH4 + -N was 32 mg / L, PO4 3- -P was 8 mg / L.

[0029] The culture conditions in this example were temperature 25℃±2℃, light intensity 200 μmol·m -2 ·s -1 , light / dark ratio 12 hours / 12 hours, and humidity 45%.

[0030] The microalgae used in this example were Chlorella vulgaris.

[0031] Biomass determination: 5 mL of microalgae culture solution was taken, and the absorbance was determined at a wavelength of 680 nm using an ultraviolet spectrometer. The dry weight standard curve was used for conversion. The standard curve used in Example 1 was:

[0032] DW(mg / L)=19.6559×OD680-1.5504, R 2 =0.99292, and DW was the dry weight.

[0033] Referring to Figure 1 , the different physiological stages of the microalgae determined in this example were adaptation period 0-4 days, growth period 4-8 days, and stable period after 8 days. It is explained here that different microalgae have different time periods of physiological stages, which should be determined according to actual experiments.

[0034] Example 2

[0035] Microalgae wastewater treatment efficiency determination: a certain amount of microalgae culture solution was taken in a 10 mL centrifuge tube, centrifuged at 4000 rpm for 10 minutes, then filtered with a 0.45 μm filter, stored in a refrigerator at 4℃, and determined as soon as possible.

[0036] The indicators of wastewater determined in this example were COD, NH4 + -N, PO4 3-P. The wastewater index was determined by using the Hash reagent and Hash instrument.

[0037] In this embodiment, the 0.05CVO group represents the addition of 0.05 mg / L of nano zero-valent iron on day 0, the 0.10CV4 group represents the addition of 0.10 mg / L of nano zero-valent iron on day 4, and the rest is similar.

[0038] 1. See Figure 2 a and Figure 2 b. In this embodiment, the COD concentration of the control group measured after 14 days of culture was 103 mg / L, and the recovery rate was 59.92%. The best COD concentration recovered by microalgae was 75.33 mg / L, which was measured in the 0.10CV4 group with the addition of 0.10 mg / L of nano zero-valent iron on day 4, and the recovery rate was 70.69%.

[0039] 2. See Figure 2 c and Figure 2 d. In this embodiment, nano zero-valent iron was added at different physiological stages, and the recovery rate of NH4 + -N was almost 100%.

[0040] 3. See Figure 2 e and Figure 2 f. In this embodiment, nano zero-valent iron was added at different physiological stages, and the concentration of PO4 3- -P in the control group was 1.05 mg / L, and the recovery rate was 86.88%. The best experimental group was the 0.05CV0 group, with a PO4 3- -P concentration of 0.4 mg / L and a recovery rate of 95%. The second best was the 0.05CV4 group and the 0.10CV4 group, both with a PO4 3- -P concentration of 0.47 mg / L and a recovery rate of 94.13%. Compared with the control group, the recovery efficiency of PO4 3- -P was increased by 8.12% and 7.25%, respectively.

[0041] Example 3

[0042] Microalgae flocculation and sedimentation, and calculation of self-flocculation efficiency.

[0043] Microalgae flocculation and sedimentation method: Since the addition of nano zero-valent iron suspension at different physiological stages of microalgae in this embodiment promotes the self-flocculation performance of microalgae, the microalgae liquid was allowed to stand for 9 h to achieve good flocculation and sedimentation.

[0044] In this embodiment, the flocculation efficiency was calculated after 9 h. The addition of 0.05 mg / L or 0.10 mg / L of nano zero-valent iron suspension at any different physiological stage of microalgae promoted the self-flocculation performance of microalgae. For details, see Figure 3 .

[0045] Microalgae self-flocculation efficiency determination method: take 10 mL of microalgae culture solution in a centrifuge tube, measure the OD680 of microalgae, and record it as Am. Then let the centrifuge tube stand for a certain period of time, and then take the supernatant to measure the OD680, and record it as An.

[0046] Self-flocculation efficiency = ((Am-An) / Am) x 100%.

[0047] The addition of nano zero-valent iron at any stage on the 14th day can enhance the self-flocculation ability of microalgae. Among them, the flocculation performance of the control group is 84.84%, and the best flocculation performance is the 0.10CV4 group, and the flocculation performance is 93.84%, which is 9% higher than that of the control group.

[0048] The self-flocculation performance of microalgae is crucial in the microalgae harvesting process. The methods currently used for microalgae harvesting include physical methods such as filters, plate and frame filter presses, etc.; chemical methods such as inorganic flocculants such as ferric chloride or composite flocculants such as chitosan.

[0049] The essence of microalgae harvesting is the separation of microalgae and culture solution. Regardless of the method used for microalgae harvesting, the enhancement of microalgae self-flocculation performance is helpful for the microalgae harvesting process, and provides a solid foundation for the production of microalgae biofuels in the downstream process of the microalgae biological wastewater treatment process.

[0050] Example 4

[0051] Microalgae oil content determination: centrifuge part of the algal liquid at 4000 rpm for 20 minutes, and then freeze-dry. Take 100 mg of microalgae powder sample for oil determination, and use chloroform-methanol method.

[0052] In this embodiment, two concentrations of nano zero-valent iron suspension are added at different physiological stages of microalgae, which are 0.05 mg / L and 0.10 mg / L.

[0053] The schematic diagram of adding nano zero-valent iron at different physiological stages of microalgae to promote the increase of microalgae lipid content is shown in Figure 4 .

[0054] In this embodiment, different concentrations of nano zero-valent iron are added at different physiological stages of microalgae to significantly promote the increase of microalgae lipid content, so as to facilitate the production of microalgae biofuels. The oil content of the control group is 24.4%, the addition of 0.05 mg / L nano zero-valent iron promotes the trend of oil, and the influence range is 40.1-46.95%. The promotion effect of adding 0.10 mg / L nano zero-valent iron on lipid synthesis is lower than that of adding 0.05 mg / L, and the influence range is 34.59-41.70%.

Claims

1. A method for efficient resource utilization of microalgae, characterized in that... Includes the following steps: Step 1: Determination of different physiological stages of microalgae: Inoculate the wastewater to be treated with microalgae concentrate with a dry weight greater than 30 mg / L, and then add nano zero-valent iron suspension of different concentrations at different physiological stages of microalgae. After 14 days of cultivation, obtain microalgae culture medium. Step 2: Determination of microalgae wastewater treatment efficiency: A certain amount of microalgae culture medium was centrifuged, filtered, and the filtrate was stored in a refrigerator at 4°C. The COD and NH4 in the filtrate were then measured. + -N,PO4 3- -P index; Step 3: Microalgae flocculation and sedimentation: After the microalgae culture medium is left to stand for 9 hours, the microalgae will flocculate and settle. Step 4: Extraction of microalgal oil: The microalgal culture medium after self-flocculation and sedimentation is centrifuged, filtered, and then freeze-dried to obtain microalgal powder. Then, the microalgal oil is extracted using the chloroform-methanol method. The nano-zero valent iron suspension is obtained by uniformly suspending nano-zero valent iron in deionized water and ultrasonically vibrating for 0.5 h, and its concentration is not greater than 1000 mg / L. The physiological stages of the microalgae include the adaptation period, growth period, stationary period, and death period. Calculated from the inoculation date, the adaptation period is 0-4 days, during which a nano-zero ferric iron suspension with a concentration of 0.05-0.10 mg / L is added; the growth period is 4-8 days, during which a nano-zero ferric iron suspension with a concentration of 0.05-0.10 mg / L is added; and the stationary period is after 8 days, during which a nano-zero ferric iron suspension with a concentration of 0.05-0.10 mg / L is added.

2. The method for efficient resource utilization of microalgae according to claim 1, characterized in that: The particle size of the nano-zero valent iron is 50 nm.

3. The method for efficient resource utilization of microalgae according to claim 1, characterized in that: The culture conditions were: temperature 25℃±2℃, light intensity 200 μmol·m⁻². -2 ·S -1 The light-dark ratio is 12 hours / 12 hours, and the humidity is 45%.

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