Application of microalgae in killing escherichia coli in wastewater

Abstract

The application belongs to the technical field of water disinfection, and particularly relates to application of microalgae in killing Escherichia coli in wastewater, wherein the microalgae are one or more of Chlorella vulgaris Pediastrum ) and Chlorella pyrenoidosa Chlorella ). The application discloses for the first time that the pH and dissolved oxygen of the metabolism of the microalgae can synergistically inactivate the Escherichia coli, and play a disinfection role. In practical application, the removal rate of the Escherichia coli can reach 100%, the removal of pollutants such as TP and TN meets the discharge standard, the microalgae can independently treat the contaminated water, the removal of the pollutants does not need to be performed in advance through the conventional activated sludge method, and additional structures are not needed to kill the microorganisms in the water, so that the construction cost and operation cost are saved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of water disinfection, and particularly relates to application of microalgae in killing Escherichia coli in wastewater. BACKGROUND

[0002] The existence of Escherichia coli in water can cause serious public health risks, ecological safety threats and social and economic losses. This kind of bacteria is not only a clear indicator of fecal pollution, but also can directly carry pathogenic Escherichia coli, causing diseases such as diarrhea and uremic syndrome. Ecologically, its proliferation can exacerbate water eutrophication, consume dissolved oxygen to cause anaerobic environment, cause fish suffocation and release of toxins such as hydrogen sulfide, and at the same time, it can destroy the balance of microbial communities, interfere with nitrogen cycle and primary productivity. Pollution mainly comes from sewage treatment plant overflow, livestock and poultry breeding wastewater and urban runoff, therefore, it is of great significance to human health and production and life to treat sewage and kill Escherichia coli in sewage.

[0003] At present, methods such as chlorine disinfection, ultraviolet disinfection and ozone disinfection are mainly used to kill Escherichia coli in sewage. Chlorine disinfection is widely used in water treatment due to its low cost and continuous disinfection capacity. However, this technology inevitably produces harmful by-products such as trihalomethane during disinfection, which has potential risks of carcinogenesis and gene mutation, and may cause secondary pollution to the environment and water sources. Ultraviolet disinfection, as a non-chemical disinfection technology, has the core advantage of efficient, fast and no by-product production. However, ultraviolet disinfection has high requirements for water quality transmittance, and is greatly affected by suspended solids, organic matter and other factors in water body, and the technology does not have continuous disinfection capacity, and photoreactivation phenomenon is easy to occur after disinfection. Ozone disinfection has the characteristics of high efficiency and rapidness, and can not only effectively kill various pathogens, but also degrade organic pollutants in sewage. However, its equipment is complex, the operation cost is high, and the stability of ozone is poor, which needs to be prepared and used on site.

[0004] It can be seen that although the traditional methods for killing Escherichia coli in sewage have good effects, there are problems of secondary pollution and high maintenance cost, and an economic and environmentally friendly solution is urgently needed. Secondly, with the enhancement of social environmental awareness and the continuous expansion of urban development, the total amount of sewage treatment also shows a trend of increasing year by year, and the sewage treatment and disinfection capacity also needs to be continuously strengthened, and therefore there may be a contradiction between the shortage of urban land resources and the expansion of sewage treatment sites. Therefore, it is urgent to develop a new strategy for killing Escherichia coli in sewage. SUMMARY

[0005] To solve the above problems, the application provides application of microalgae in killing Escherichia coli in wastewater.

[0006] The application is realized by the following technical scheme:

[0007] The application relates to the application of microalgae in killing Escherichia coli in wastewater, wherein the microalgae are one or more of Chlorella vulgaris Pediastrum ) and Chlorella pyrenoidosa Chlorella ) and Chlorella pyrenoidosa

[0008] Preferably, the wastewater is municipal sewage, aquaculture wastewater or medical wastewater.

[0009] Preferably, the initial biomass of the microalgae in the wastewater is 0.1g / L-0.5g / L.

[0010] Preferably, the Escherichia coli in the wastewater is killed by forming an environment with high alkaline pH and high dissolved oxygen, wherein the high alkaline pH refers to a pH value greater than 10, and the high dissolved oxygen refers to a DO value greater than 5mg / L.

[0011] Preferably, the microalgae and the municipal sewage are reacted for 44h-96h.

[0012] Preferably, the microalgae and the aquaculture wastewater are reacted for 2d-10d.

[0013] A method for killing Escherichia coli in wastewater by using microalgae, wherein the microalgae are used in the wastewater with an initial biomass of 0.1g / L-0.5g / L.

[0014] Preferably, the light intensity for killing the Escherichia coli in the wastewater is 8000lux-15000lux, and the temperature is 20℃-30℃.

[0015] Preferably, the ratio of nitrogen to phosphorus in the wastewater is 16-32:1.

[0016] Compared with the prior art, the application has the following beneficial effects:

[0017] The application relates to the application of microalgae in killing Escherichia coli in wastewater, wherein the microalgae are one or more of Chlorella vulgaris Pediastrum ) and Chlorella pyrenoidosa Chlorellaone or more of the following: a pH of 10.0 to 12.0, a dissolved oxygen of 5.0 to 10.0 mg / L, a temperature of 20 to 40 DEG C, and a light intensity of 5000 to 10000 lux. The present application discloses for the first time that the elevated pH and dissolved oxygen of microalgae metabolism can synergistically inactivate fecal coliform, playing a role in disinfection. The present application can achieve a removal rate of 100% for fecal coliform in practical application, and the removal of pollutants such as TP and TN meets the discharge standard. Microalgae can independently treat contaminated water, without the need for prior removal of pollutants by conventional activated sludge method, and without the need for additional structures for microbial killing, saving construction and operation costs. Microalgae can absorb ammonia nitrogen and phosphorus by using its own assimilation function, while increasing the pH and dissolved oxygen in water, which creates conditions for killing fecal coliform. The main mechanism is as follows: the main component of the cell wall of fecal coliform is peptidoglycan, and the high alkaline environment will deprotonate the acidic groups (such as carboxyl) in peptidoglycan, change the charge properties and structural integrity of the cell, and then increase the permeability of the cell wall, disturb and destroy the arrangement of lipid molecules in the cell membrane, cause abnormal fluidity of the cell membrane, break the osmotic pressure balance in the cell, and finally cause the cell to be damaged or even die; secondly, dissolved oxygen can generate more reactive oxygen species (ROS), which can oxidize amino acid residues in protein molecules, change the structure of proteins and cause loss of their functionality; in addition, microalgae have a large specific surface area that can adsorb and fix microorganisms in water, and the combination of the above three factors makes the inactivation effect of microalgae on fecal coliform significant.

[0018] In addition, during the process of disinfecting fecal coliform by microalgae, the simultaneous removal of pollutants and disinfection is achieved, saving equipment investment and increasing space utilization; the equipment for biological disinfection of microalgae is simple, economical and environmentally friendly. Microalgae not only can fix carbon dioxide in the air through photosynthesis, but also will not generate toxic by-products, avoiding secondary pollution to the environment; the harvested microalgae can be reused as biological feed, fertilizer, etc. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0020] Figure 1 Figure 4 is a graph showing the change in the number of fecal coliform colonies in municipal sewage treated by the four groups of comparative experiments of the present application over time.

[0021] Figure 2 Figure 4 is a graph showing the change in the number of fecal coliform colonies in municipal sewage treated by the four groups of comparative experiments of the present application over time.

[0022] Figure 3 Figure 4 is a graph showing the change in DO over time for the four groups of comparative experiments of the present application treating municipal wastewater.

[0023] Figure 4 Figure 5 is a graph showing the change in NH4 + concentration over time for the four groups of comparative experiments of the present application treating municipal wastewater.

[0024] Figure 5 Figure 6 is a graph showing the change in TN concentration over time for the four groups of comparative experiments of the present application treating municipal wastewater.

[0025] Figure 6 Figure 7 is a graph showing the change in TP concentration over time for the four groups of comparative experiments of the present application treating municipal wastewater.

[0026] Figure 7 Figure 8 is a SEM image of wastewater treated by Chlorella vulgaris according to the present application.

[0027] Figure 8 Figure 9 is a SEM image of wastewater treated by Chlorella vulgaris according to the present application.

[0028] Figure 9 Figure 10 is a graph showing the change in E. coli colonies for municipal wastewater treated by Chlorella vulgaris according to the present application.

[0029] Figure 10 Figure 11 is a graph showing the change in E. coli colonies for municipal wastewater treated by Chlorella vulgaris according to the present application.

[0030] Figure 11 Figure 12 is a graph showing the sterilization effect of Chlorella vulgaris on cow urine wastewater according to the present application.

[0031] Figure 12 Figure 13 is a graph showing the pollutant removal effect of Chlorella vulgaris on cow urine wastewater according to the present application.

[0032] Figure 13 Figure 14 is a graph showing the change in E. coli colonies for cow urine wastewater treated by Chlorella vulgaris according to the present application. DETAILED DESCRIPTION

[0033] In order to facilitate the understanding of the present application, a more comprehensive description of the present application will be provided below, and a preferred embodiment of the present application will be provided. However, the present application can be implemented in many different forms, and is not limited to the embodiments described in the present application. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0035] The beneficial effects of the present invention will be illustrated below through specific embodiments.

[0036] Example 1: Screening of microalgae

[0037] 1. *Panstarella* ( Pediastrum ) Filtering

[0038] Algal samples were collected from natural water bodies and aseptically cultured in BG11 medium at 25°C and 8000 lux in a light incubator. Dominant algal populations were screened by microscopic observation. Subsequently, a gradient acclimation process was implemented, gradually increasing the proportion of municipal wastewater in the culture medium in 10% increments until it reached 100%, while simultaneously monitoring algal cell density and nutrient removal rate. A semi-continuous culture mode was used, with centrifugation at 8000×g for 3 min, periodically removing 50% of the culture medium and replenishing with fresh wastewater. After 6 cycles, an acclimated algal strain exhibiting stable and efficient removal efficiency for nitrogen, phosphorus, and fecal coliforms was obtained, yielding *Platycerium chinense* (also known as *Platycerium chinense*). Pediastrum ).

[0039] 2. Chlorella ( Chlorella ) Filtering:

[0040] Algal samples were collected from natural water bodies and aseptically cultured in BG11 medium at 20°C and 10,000 lux in a light incubator. Dominant algal populations were screened by microscopic observation. Subsequently, a gradient acclimatization process was implemented, gradually increasing the proportion of municipal wastewater in the culture medium in 10% increments until it reached 100%, while simultaneously monitoring algal cell density and nutrient removal rate. A semi-continuous culture mode was used, with 50% of the culture medium periodically removed and fresh wastewater added by centrifugation at 8000×g for 3 min. After 6 cycles, acclimatized algal strains exhibiting stable and high removal efficiency for nitrogen, phosphorus, and fecal coliforms were obtained, yielding *Chlorella vulgaris* (*Chlorella*). Chlorella ).

[0041] The *Plasmodium* obtained by screening in this invention ( Pediastrum ) was published in Park, JBK, Craggs, RJ, & Shilton, AN (2015). Algal recycling enhances algal productivity and settleability in Pediastrum boryanum pure cultures. Water Research, 87, 97–104.”

[0042] The Chlorella obtained by screening in this invention ( Chlorella) was disclosed in "[1] Church, J., Hwang, J.-H., Kim, K.-T., McLean, R., Oh, Y.-K., Nam, B., Joo, J.C., Lee, W.H., 2017. Effect of salt type and concentration on the growth and lipid content of Chlorella vulgaris in synthetic saline wastewater for biofuel production. Bioresour. Technol. 243 (Supplement C), 147-153."

[0043] Example 2, Practical application of microalgae in inactivation of fecal coliform in inactivated municipal wastewater

[0044] The municipal wastewater was obtained from the fine grid effluent of a wastewater treatment plant in Nanchang City, Jiangxi Province. The suspended solids in the water were removed using 0.45 μm qualitative filter paper. The water quality indicators after filtration are shown in Tables 1 and 2.

[0045] Table 1 Water quality indicators after filtration of the wastewater treatment plant in Nanchang City

[0046]

[0047] Note: The number of fecal coliform colonies is in units of CFU / L.

[0048] Table 2 Water quality indicators after microalgae treatment

[0049]

[0050] Note: The number of fecal coliform colonies is in units of CFU / L.

[0051] To investigate the disinfection effect of microalgae on municipal wastewater, four groups of comparative experiments were designed, namely the Scenedesmus discolor treatment group, the Chlorella pyrenoidosa treatment group, the NaOH treatment group, and the raw water control group. The initial biomass was 0.1 g / L, and the sodium hydroxide group was used as a drug control group. The pH was adjusted according to the change of microalgae, and the frequency was adjusted once every 2 h. The effect on the number of fecal coliform bacteria and various water quality indicators in wastewater was investigated. The entire experiment was carried out in a constant temperature shaking incubator with light intensity of 15000 lux, temperature setting of 30℃, and shaking frequency of 120 rpm / min. The ratio of nitrogen to phosphorus in the municipal wastewater was 32:1.

[0052] Different microalgae have varying effects on killing fecal coliforms in municipal sewage, such as... Figure 1 As shown in the figure. *Plasmodium spp.* showed the best removal effect on fecal coliforms, achieving a 100% removal rate at 44 hours; while *Chlorella vulgaris* was slower, reaching the target at 72 hours, but also achieving a 100% removal rate at 96 hours. The pH and DO change trends of *Plasmodium spp.* and *Chlorella vulgaris* were similar, as shown in the figure. Figure 2 and Figure 3 As shown, over time, the assimilation of microalgae intensifies, the pH in the environment increases, and the pH of both types of microalgae can reach above 10.5 within 48 hours, while the dissolved oxygen concentration is eventually maintained at around 5.5 mg / L.

[0053] Within 72 hours of treating the municipal wastewater with microalgae, both types of algae achieved the discharge standards for the removal of fecal coliform bacteria, with the fecal coliform count ≤10. 3 CFU / L, NH4 + The removal of -N, TN, and TP all met the requirements of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002), demonstrating that this microalgae process achieves integrated pollutant removal and disinfection. The pollutant concentration changes in the four comparative experiments are shown below. Figure 4 , Figure 5 and Figure 6 As shown. The morphology of municipal wastewater after treatment is as follows. Figure 7 and Figure 8 As shown. The colony changes of *Plasmodium styracifolium* in killing *Escherichia coli* are as follows. Figure 9 As shown, the colony changes of Chlorella killing Escherichia coli are as follows: Figure 10 As shown.

[0054] Example 3: Practical application of microalgae in inactivating fecal coliforms in aquaculture wastewater

[0055] To investigate the disinfection effect of microalgae on aquaculture wastewater, cow urine wastewater was selected as the sample water quality. The cow urine wastewater sample came from a beef cattle farm in Shenyang. Cow urine is affected by the cattle's diet, health, and physiological cycle, and is typically yellow with a small amount of suspended solids. Its water quality characteristics include high salinity, high organic matter, and high ammonia nitrogen, and it contains a rich variety of microbial communities, such as Escherichia coli, Staphylococcus aureus, and yeast. The original cow urine wastewater water quality is shown in Table 3.

[0056] Table 3 Water quality indicators of cow urine wastewater

[0057]

[0058] This invention uses Chlorella ( Chlorella sp.) For experimental algae, a 2L simulated actual process condition photoreactor is constructed, and an electromagnetic stirring device and a peristaltic pump circulation system are provided to maintain the uniform suspension state of microalgae, optimize the microalgae growth and metabolism environment, so that the light intensity reaches 8000lux, and the temperature is 20 DEG C. Based on the analysis results of the water quality characteristics of the cattle urine wastewater, the nitrogen content is significantly high and significantly higher than the suitable threshold value of microalgae cultivation, and the total phosphorus content is relatively insufficient, and there is a phenomenon of nitrogen and phosphorus ratio imbalance. Therefore, gradient dilution and exogenous phosphorus addition methods are used for pretreatment of the raw water, the nitrogen and phosphorus ratio of the influent is adjusted to 16:1, and the nutrient medium system suitable for the growth of microalgae is constructed. The chlorella is used to treat the cattle urine wastewater, the initial biomass is 0.5g / L, and the water quality indexes after treatment are shown in Table 4. Figure 11 、 Figure 12 、 Figure 13 .

[0059] Table 4 Water quality indexes after chlorella treatment

[0060]

[0061] Note: " / " means no such item.

[0062] It should be noted that when the light intensity is 8000lux~15000lux, the temperature is 20 DEG C~30 DEG C, and the initial biomass of chlorella and chlorella is 0.1g / L~0.5g / L, the fecal coliform bacteria in the wastewater can be effectively killed, and the present application does not list the experiments.

[0063] The technical features of the above-described embodiments can be combined arbitrarily, and to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictory, it should be considered that it is within the scope of the present application.

[0064] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. For ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A method for killing fecal coliforms in wastewater using microalgae, characterized in that, The microalgae is *Planstarium* ( Pediastrum ) and Chlorella ( Chlorella One or more of the following; By creating a highly alkaline and highly dissolved oxygen environment, fecal coliform bacteria in wastewater are killed; the highly alkaline environment refers to a pH value greater than 10; the highly dissolved oxygen environment refers to a DO value greater than 5 mg / L. The microalgae were introduced into the wastewater at an initial biomass of 0.1 g / L to 0.5 g / L; The light intensity for killing fecal coliforms in wastewater is 8000 lux to 15000 lux, and the temperature is 20℃ to 30℃.

2. The method as described in claim 1, characterized in that, The wastewater is municipal sewage, aquaculture wastewater, or medical wastewater.

3. The method as described in claim 2, characterized in that, The interaction time between the microalgae and municipal sewage is 44h to 96h.

4. The method as described in claim 2, characterized in that, The interaction time between the microalgae and the aquaculture wastewater is 2 to 10 days.

5. The method as described in claim 1, characterized in that, The nitrogen-to-phosphorus ratio in the wastewater is 16-32:1.

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