A wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilms

Abstract

The present invention discloses a wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilms. This method detects the cadmium concentration in the influent wastewater and the cadmium concentration in the effluent wastewater after the wastewater is treated by an algal biofilm reactor supplemented with light. If the cadmium concentration in the influent wastewater is less than or equal to 2.5 mg / L, sulfate is added, and the algal biofilm reactor is used for treatment supplemented with light. If the cadmium concentration in the influent wastewater is higher than 2.5 mg / L, the amount of sulfate added is determined according to the cadmium concentration in the effluent wastewater, and the algal biofilm reactor is used for treatment supplemented with light. This method can achieve that the treated effluent concentration with an influent cadmium concentration less than 25 mg / L is stably lower than 0.1 mg / L, and at the same time, nitrogen, phosphorus, etc. meet the standards; this method is simple, easy to operate, has a low dosing cost, does not involve introducing new species and genes, has no biosafety hazards, does not produce secondary pollution, and is easy to realize automatic regulation in cooperation with an automatic monitoring and light control system, and has high potential for popularization and application.

Description

Technical Field

[0001] The present invention relates to a wastewater treatment method for enhancing cadmium tolerance and cadmium removal of algal biofilms, and particularly to a wastewater treatment method for synergistically controlling sulfate and light conditions to strengthen cadmium tolerance and cadmium removal of algal biofilms, belonging to the technical field of sewage biological treatment. Background Art

[0002] Cadmium-containing wastewater has a wide source and high toxicity, seriously threatening human health and ecological safety, and is a major problem in the field of water treatment. In recent years, the method of using microalgae to treat heavy metal-containing wastewater has received increasing attention. However, it is still limited to the idea of physical and chemical treatment. Existing methods focus on how to use algal biomass to prepare adsorbents, so more attention is paid to the screening of algal species and the development of biomass adsorption materials. In recent years, more and more studies have shown that an active algal biological community is more effective in removing heavy metals than simply using biomass as an adsorbent. Especially the algal biofilm system growing in the form of a biofilm has a high cadmium tolerance ability, can remove pollutants such as nitrogen and phosphorus in sewage and wastewater while removing cadmium, greatly reducing the pressure of subsequent treatment, and has a lower cost. However, the extremely high toxicity of cadmium may still lead to a decrease in the treatment efficiency of algal biofilms at higher cadmium concentrations, resulting in limited application scope. Therefore, enhancing the cadmium tolerance and cadmium removal efficiency of algal biofilms is the key to ensuring the application of this technology in the proper treatment of cadmium-containing wastewater and ultimately achieving the synchronous and efficient removal of cadmium and other pollutants.

[0003] Currently, there is no relevant technology for enhancing the cadmium tolerance and cadmium removal efficiency of algal biofilms. However, there are some technologies for enhancing the cadmium tolerance and cadmium removal efficiency of pure algae or other systems. Among them, one category is to obtain species with high cadmium tolerance and cadmium removal ability through screening and cultivation for adding to a specific system to improve the cadmium tolerance and cadmium removal ability of the system. For example, CN114907987A discloses a Curvularia strain that is cadmium-tolerant and can adsorb cadmium, which is used to adsorb cadmium in the environment. CN115895949A discloses a method for preparing a composite cadmium-reducing microbial agent, and the application of the agent to the soil enhances the cadmium tolerance of plants and alleviates the absorption and accumulation of cadmium by plants. Another category is to use gene mutation or gene editing technology to improve the cadmium tolerance and cadmium removal ability of a certain type of microorganism. For example, CN113549554A screened a Chlamydomonas mutant that tolerates high concentrations of cadmium, and fixed it in a gel solution for enriching cadmium in wastewater; CN115739977A discloses a Paenibacillus kribbensis mutant obtained by space mutagenesis, which has stronger cadmium tolerance than the wild-type strain; CN107760693A inserted the aphⅧ fragment into the LRR gene of Chlamydomonas reinhardtii to reduce the expression of the LRR gene or inactivate it, thereby improving the cadmium tolerance of Chlamydomonas reinhardtii.

[0004] There is no publicly reported technology specifically for enhancing the cadmium tolerance and cadmium removal efficiency of algal biofilms. The existing technologies for enhancing the cadmium tolerance and cadmium removal efficiency of pure-cultured microorganisms mainly focus on screening species with high cadmium tolerance and cadmium removal efficiency, or enhancing the cadmium tolerance and cadmium removal efficiency of a certain species through gene mutation or editing. Essentially, the ideas of these methods are to optimize from the stage of community construction, but there is still a lack of effective methods for enhancing the formed algal biofilms during actual operation. Secondly, species screening and gene editing often take a long time, and the screened pure-cultured species may be difficult to adapt to the mixed cadmium-containing wastewater conditions and are easily lost in the competition with other indigenous microorganisms. Moreover, the application of gene-edited species to actual wastewater treatment poses biosafety risks and is still highly controversial. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilms, which promotes the production of thiol substances in algal biofilms by controlling the sulfate concentration and light intensity, and uses the strong specific binding of thiol substances to cadmium to achieve efficient removal of cadmium in wastewater while masking the cadmium toxicity.

[0006] Technical Solution: A wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilms according to the present invention includes the following steps:

[0007] (1) Detect the cadmium concentration in the influent wastewater, subject the wastewater to treatment with an algal biofilm reactor supplemented with light, and detect the cadmium concentration in the effluent of the treated wastewater.

[0008] (2) If the cadmium concentration in the influent wastewater is less than or equal to 2.5 mg / L, add sulfate to the wastewater, pass the wastewater containing sulfate through an algal biofilm reactor supplemented with light, or after the wastewater enters the algal biofilm reactor, add sulfate to the wastewater in the algal biofilm reactor and supplement with light treatment, and the addition amount of the sulfate does not exceed 40 mg / L of water.

[0009] (3) If the cadmium concentration in the influent wastewater is higher than 2.5 mg / L, determine the amount of sulfate to be added according to the cadmium concentration in the effluent of the wastewater in step (1), add sulfate to the wastewater, pass the wastewater containing sulfate through an algal biofilm reactor supplemented with light, or after the wastewater enters the algal biofilm reactor, add sulfate to the wastewater in the algal biofilm reactor and supplement with light treatment.

[0010] Further, in step (1), the cadmium concentration in the influent wastewater is less than 25 mg / L.

[0011] Further, in step (1), the algal biofilm reactor is a rotary algal biofilm reactor, an algal biofilm biological disk, or an algal-bacterial particle fluidized bed reactor.

[0012] Further, in steps (2) and (3), the sulfate is potassium sulfate, sodium sulfate, zinc sulfate or magnesium sulfate.

[0013] Further, in steps (1)-(3), the light intensity is 50-1000 μmol / s·m 2 , and the light intensity is increased or decreased according to the effluent situation of the wastewater.

[0014] Further, in steps (1)-(3), the light:dark cycle in the algal biofilm reactor is 12h:12h, and the residence time of the wastewater in the algal biofilm reactor is more than 24h.

[0015] Further, in steps (1)-(3), the intensity of the light needs to be relatively stable within a 12h light cycle.

[0016] Further, in step (1), the light intensity supplemented with light treatment is 50-130 μmol / s·m 2 .

[0017] Further, in step (2), when the concentration of cadmium in the wastewater is less than or equal to 2.5 mg / L, at a light intensity of 50-130 μmol / s·m 2 , the dosage of sulfate is increased in a gradient of 10 mg / L of water until the treated wastewater meets the standard.

[0018] Further, in step (3), when the cadmium concentration in the wastewater is greater than 2.5 mg / L, if 50 mg / L of water of sulfate is added for every 1 mg / L of cadmium remaining in the effluent of step (1) wastewater, the light intensity is increased in a gradient of 100 μmol / s·m 2 until the wastewater meets the discharge standard.

[0019] Mechanism for treating wastewater: In the method of the present invention, adding sulfate provides a substrate for the algal biofilm to produce thiol substances. The thiol substances form a strong specific binding with cadmium, masking the toxicity of ionic cadmium while promoting the adsorption and absorption removal of cadmium. Since the process of absorbing sulfate and assimilating it into thiol substances requires a large amount of energy from microorganisms, when the cadmium concentration is relatively high, it is difficult to produce enough thiol substances only relying on the original metabolism of microorganisms. Therefore, the purpose of increasing the light intensity while adding sulfate is to provide sufficient energy for photosynthetic microorganisms (mainly algae) to assimilate sulfate.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0021] (1) The method of the present invention can achieve a stable effluent concentration of less than 0.1 mg / L with an influent cadmium concentration of less than 25 mg / L, and key indicators such as nitrogen and phosphorus meet the standards simultaneously; for extreme conditions with a concentration higher than 25 mg / L, it can also effectively improve the cadmium tolerance and cadmium removal efficiency of the algal biofilm, enhance the ability to withstand shock loads, and relieve the pressure of pre-treatment in the front section or advanced treatment in the back section.

[0022] (2) The dosing cost of this method is low, and the algal biofilm has extremely high utilization efficiency of sulfate ions. On the premise of reasonable use of this method, the risk of secondary pollution is very low.

[0023] (3) The control method of this method is simple and easy to operate. It is easy to achieve automatic regulation in cooperation with an automatic monitoring and light control system, and has high potential for popularization and application.

[0024] (4) This method does not involve introducing new species and genes, has no biosafety hazards, has higher feasibility, and does not generate biological risks. Description of the Drawings

[0025] Figure 1 It is a flow chart of the wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of the algal biofilm of the present invention;

[0026] Figure 2 It is a graph showing the changes in the content and composition of sulfhydryl substances in the algal biofilm before and after strengthening in Example 4;

[0027] Figure 3 It is a graph showing the changes in the coordination groups of cadmium in the algal biofilm before and after strengthening analyzed by X-ray near-edge absorption spectroscopy in Example 4. Detailed Embodiments

[0028] The technical solutions of the present invention will be further described below with reference to the drawings.

[0029] Example 1

[0030] Simulated cadmium-containing wastewater with cadmium concentrations of 0.5, 2.5, 10, and 25 mg / L was prepared in the laboratory. Other main indicators of the simulated cadmium-containing wastewater were: chemical oxygen demand 180 mg / L, total nitrogen 40 mg / L, and total phosphorus 3.5 mg / L. The above 4 groups of wastewater were passed through an algal biofilm reactor, supplemented with a light intensity of 130 μmol / s·m 2 treatment, the hydraulic retention time in the algal biofilm reactor was 24 h, and the light:dark cycle was 12 h:12 h.

[0031] The results of wastewater treatment are shown in Table 1.

[0032] Table 1 Concentrations of cadmium, total nitrogen, and total phosphorus in the effluent treated by 4 algal biofilm reactors

[0033]

[0034] It can be found from Table 1 that except for the reactor with an influent cadmium concentration of 0.5 mg / L, the effluent of all other reactors did not meet the standards, indicating that it is difficult to achieve standard discharge by using only algae biofilm to treat cadmium-containing wastewater in many cases, and it is necessary to enhance its cadmium resistance and cadmium removal efficiency.

[0035] Example 2

[0036] The experimental process was the same as in Example 1, wherein the cadmium concentration in the wastewater was 2.5 mg / L. When the wastewater passed through the algae biofilm reactor, 0 mg / L, 10 mg / L, and 20 mg / L of industrial-grade potassium sulfate were added to the algae biofilm reactor, respectively, and the light intensity was 130 μmol / s·m 2 Treatment was performed for 24 h with a light:dark cycle of 12 h:12 h. Figure 1 The process shown was optimized for cadmium-resistant cadmium removal, and three groups of wastewater treatment results were obtained, as shown in Table 2.

[0037] Table 2 Cadmium, total nitrogen and total phosphorus concentrations in effluent after treatment with different potassium sulfate dosages

[0038]

[0039] It can be seen from Table 2 that when the cadmium concentration in the wastewater is 2.5 mg / L, the addition of 20 mg / L industrial-grade potassium sulfate can achieve standard discharge of effluent cadmium, total nitrogen and total phosphorus.

[0040] Example 3

[0041] The experimental process was the same as in Example 2, wherein the cadmium concentration in the wastewater was 10 mg / L and 25 mg / L, and the algae biofilm reactor was supplemented with a light intensity of 130 μmol / s·m 2 , treated for 24 hours with a light: dark cycle of 12h:12h (without potassium sulfate), the residual cadmium concentrations in the water were detected to be 2.65mg / L and 5.23mg / L, respectively. Based on the addition of 50mg / L sulfate for every 1mg / L of residual cadmium, 130mg / L and 260mg / L of industrial grade potassium sulfate were added, respectively. 2 The light intensity was increased gradually, the cadmium concentration of the wastewater was 10 mg / L, 130 mg / L potassium sulfate was added, and the light intensity was adjusted to 230 μmol / s·m 2 and 330 μmol / s·m 2 The treatment was carried out for 24 hours with a light: dark cycle of 12h:12h. The cadmium concentration of the wastewater was 25mg / L, 260mg / L potassium sulfate was added, and the light intensity was adjusted to 230μmol / s·m 2 、330μmol / s·m 2 、430μmol / s·m2 , 530 μmol / s·m 2 , 630 μmol / s·m 2 , with a light:dark cycle of 12 h:12 h for treatment for 24 h. As shown in Figure 1 the process shown, the cadmium tolerance and cadmium removal were optimized, and a total of 7 sets of wastewater treatment results were obtained, as shown in Table 3-4.

[0042] Table 3 Cadmium concentration 10 mg / L, adding 130 mg / L potassium sulfate, adjusting light intensity, cadmium, total nitrogen, and total phosphorus concentrations in the effluent

[0043]

[0044] As can be seen from Table 3, for the algal biofilm reactor with a cadmium concentration of 10 mg / L in the wastewater, after adding 130 mg / L potassium sulfate, when the light intensity reached 330 μmol / s·m 2 , the discharge standards were achieved.

[0045] Table 4 Cadmium concentration 25 mg / L, adding 260 mg / L potassium sulfate, adjusting light intensity, cadmium, total nitrogen, and total phosphorus concentrations in the effluent

[0046]

[0047] As can be seen from Table 4, for the algal biofilm reactor with a cadmium concentration of 25 mg / L in the wastewater, after adding 260 mg / L potassium sulfate, when the light intensity reached 630 μmol / s·m 2 , the discharge standards were achieved.

[0048] Comparative Example 1

[0049] The experimental procedure was the same as in Example 3, with a cadmium concentration of 10 mg / L in the influent wastewater. The difference was that only potassium sulfate was added and the light intensity was maintained at 130 μmol / s·m 2 unchanged. The input amount of industrial potassium sulfate was 130 mg / L, and the experimental results are shown in Table 5.

[0050] Comparative Example 2

[0051] The experimental procedure was the same as in Example 3, with a cadmium concentration of 10 mg / L in the influent wastewater. The difference was that no potassium sulfate was added and only the light was increased. The initial light intensity was 130 μmol / s·m 2 , and the light intensity was increased to 330 μmol / s·m 2 at a gradient of 100 μmol / s·m 2 . The experimental results are shown in Table 5.

[0052] Table 5 Cadmium, total nitrogen, and total phosphorus concentrations in the effluent after treatment by the algal biofilm reactor under different experimental conditions

[0053]

[0054] As can be seen from Table 5, the strengthening effect of only adding potassium sulfate in Comparative Example 1 and only increasing the light intensity in Control Ratio 2 on the cadmium tolerance and cadmium removal efficiency of algal biofilms is very limited. This result shows that when the cadmium concentration is relatively high, the method of simultaneously controlling the sulfate concentration and light intensity in the present invention can effectively enhance the cadmium tolerance and cadmium removal efficiency of algal biofilms.

[0055] Example 4

[0056] The experimental process was the same as that in Example 3. The cadmium concentration in the influent wastewater was 10 mg / L. It passed through the algal biofilm reactor with a light intensity of 130 μmol / s·m 2 , and was treated for 24 h with a light:dark cycle of 12 h:12 h (without adding potassium sulfate). The residual cadmium concentration in the effluent water was detected to be 2.65 mg / L. Then the input amount of industrial potassium sulfate was 130 mg / L, and the initial light intensity was 130 μmol / s·m 2 , and the light intensity was increased stepwise to 330 μmol / s·m 2 at a gradient of 100 μmol / s·m 2 for 24 h, and the optimization of cadmium tolerance and cadmium removal was carried out according to the process shown in Figure 1 .

[0057] The content of sulfhydryl substances in the algal biofilm reactor of this example before and after the strengthening treatment was measured. Among them, the total amount of sulfhydryl groups was measured by the Ellman reagent (5,5'-dithiobis-(nitrobenzoic acid), DTNB) colorimetric method, and the small molecule sulfhydryl substances were measured by high performance liquid chromatography equipped with a fluorescence detector. The content of protein sulfhydryl substances was the total amount of sulfhydryl groups minus the content of small molecule sulfhydryl substances.

[0058] The content of sulfhydryl substances in the algal biofilm reactor before and after the strengthening is shown in Figure 2 . It can be observed from Figure 2 that after the strengthening, the total content of sulfhydryl substances in the algal biofilm increased by 8.7 times, and the proportion of the content of protein sulfhydryl substances increased. Since protein sulfhydryl substances are mainly distributed in extracellular polymeric substances, it is more conducive to the adsorption and removal of cadmium.

[0059] Furthermore, synchrotron radiation X-ray near-edge absorption spectroscopy was used to test the coordination chemical state of the algal biofilm sample after strengthening. The results are shown in Figure 3 . It was found from Figure 3 that the proportion of cadmium bound to sulfhydryl groups after strengthening increased from 51% to 92%.

[0060] The above phenomena confirm that the principle of the regulation strategy of the method of the present invention is to enhance the generation of sulfhydryl substances, improve the complexation of sulfhydryl substances with cadmium, and thus improve the cadmium tolerance and cadmium removal efficiency of algal biofilms.

[0061] Example 5

[0062] (1) In this example, cadmium-containing wastewater from an electroplating plant with a cadmium concentration of 7.39±2.54 mg / L was taken and passed through an algae biofilm reactor with the aid of a light intensity of 130 μmol / s·m 2 , treated with a light: dark cycle of 12h:12h for 24h (without adding potassium sulfate). It was determined that the effluent still contained 1.82±0.52mg / L of cadmium residue after treatment, and the effluent total nitrogen and total phosphorus were 16.21±3.37mg / L and 1.24±0.48mg / L, respectively, both of which were below the standard.

[0063] (2) The method of the present invention is used for treatment. Since the cadmium concentration in the effluent in step (1) is 1.82±0.52 mg / L, the excess cadmium content in the effluent is 2 mg / L, and 50×2=100 mg / L of industrial grade potassium sulfate is added. 2 The light intensity was increased gradually to 430 μmol / s·m 2 Afterwards, it was measured that the concentrations of cadmium, total nitrogen and total phosphorus in the water had steadily dropped to 0.04±0.02mg / L, 2.45±0.91mg / L and 0.18±0.07mg / L, which were in line with the first-level standard limits stipulated in the "Comprehensive Sewage Discharge Standard".

[0064] This example demonstrates the feasibility of using this method to enhance algal biofilm treatment of actual cadmium-containing wastewater.

[0065] Comparative Example 3

[0066] (1) The treatment object is the cadmium-containing wastewater from the electroplating plant in Example 5, and the cadmium concentration in the wastewater inlet is 7.39±2.54 mg / L. The difference is that the activated sludge with a sludge concentration of 3000 mg / L (consistent with the bioload in the algae biofilm reactor) is used for treatment, and the hydraulic retention time and lighting conditions are consistent with step (1) in Example 5. After measurement, the cadmium residue in the effluent after treatment is 1.56±0.84 mg / L cadmium residue, and the total nitrogen and total phosphorus in the effluent are 21.07±4.11 mg / L and 2.19±0.53 mg / L, respectively, both of which are not up to standard.

[0067] (2) Since the cadmium concentration in the effluent in step (1) is 1.56±0.84 mg / L, the excess cadmium content in the effluent is 1.5 mg / L, and 50×1.5=75 mg / L of industrial grade potassium sulfate is added. 2 Gradual increase in light intensity, even when light intensity was increased to 630 μmol / s·m 2 There was no significant change in the concentrations of cadmium and total nitrogen in the effluent, but the total phosphorus increased to 2.73±0.40 mg / L, and about 70% of sulfate still remained in the effluent.

[0068] The above results show that for the sewage treatment technology based on other microbial communities, due to the lack of microbial groups that produce thiol substances, even if a large amount of sulfate substrate and light are provided, they cannot be effectively converted into thiol substances. This comparative example confirms that the method described in the present invention mainly specifically enhances the cadmium tolerance and cadmium removal ability of the algal biofilm community.

Claims

1. A wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilms, characterized in that, It includes the following steps: (1) Detect the concentration of cadmium in the influent wastewater, treat the wastewater through an algal biofilm reactor supplemented with light, and detect the concentration of cadmium in the effluent of the treated wastewater; (2) If the cadmium concentration in the influent wastewater is less than or equal to 2.5 mg / L, add sulfate to the wastewater, and pass the wastewater containing sulfate through an algal biofilm reactor with light treatment, or after the wastewater enters the algal biofilm reactor, add sulfate to the wastewater in the algal biofilm reactor and perform light treatment. The dosage of the sulfate is increased in a gradient of 10 mg / L of water until the wastewater treatment reaches the standard, and the addition amount of the sulfate does not exceed 40 mg / L of water, and the light intensity is 50 - 130 μmol / s·m 2 ; (3)If the cadmium concentration in the influent wastewater is higher than 2.5 mg / L, the amount of sulfate added is determined according to the cadmium concentration in the effluent wastewater of step (1). Sulfate is added to the wastewater, and the wastewater containing sulfate is treated by an algal biofilm reactor supplemented with light. Or after the wastewater enters the algal biofilm reactor, sulfate is added to the wastewater in the algal biofilm reactor and supplemented with light treatment. For every 1 mg / L of cadmium remaining in the effluent wastewater of step (1), 50 mg / L of water sulfate is added, with a light intensity increased at a gradient of 100 μmol / s·m 2 until the wastewater meets the discharge standards.

2. The wastewater treatment method for enhancing the cadmium resistance and cadmium removal of algal biofilms according to claim 1, wherein, In step (1), the concentration of cadmium in the influent wastewater is lower than 25 mg / L.

3. The wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilm according to claim 1, wherein In step (1), the algal biofilm reactor is a rotary algal biofilm reactor, an algal biofilm biological rotating disk, or an algal-bacterial particle fluidized bed reactor.

4. The wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilms according to claim 1, wherein, In steps (2) and (3), the sulfate is potassium sulfate, sodium sulfate, zinc sulfate, or magnesium sulfate.

5. The wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilms according to claim 1, characterized in that, In steps (1)-(3), the light intensity is 50-1000 μmol / s·m 2 , and the light intensity is increased or decreased according to the effluent situation of the wastewater.

6. The wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilms according to claim 1, characterized in that, In steps (1)-(3), the light:dark cycle in the algal biofilm reactor is 12 h:12 h, and the residence time of the wastewater in the algal biofilm reactor is more than 24 h.

7. The wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilms according to claim 6, wherein The intensity of the light needs to remain relatively stable during the 12-h light cycle.

8. The wastewater treatment method for enhancing the cadmium tolerance and cadmium removal of algal biofilms according to claim 1, characterized in that, In step (1), the light intensity supplemented by light treatment is 50 - 130 μmol / s·m 2 .

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