CN113735266A

CN113735266A - Method for treating wastewater containing nitrate ions

Info

Publication number: CN113735266A
Application number: CN202010477264.1A
Authority: CN
Inventors: 李煦; 荣峻峰; 宗保宁; 郄凤翔; 孙春燕
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2020-05-29
Filing date: 2020-05-29
Publication date: 2021-12-03

Abstract

The invention relates to the field of wastewater treatment, and discloses a method for treating nitrate ion-containing wastewater. The method comprises the following steps: introducing microalgae and a culture solution containing the nitrate ion-containing wastewater into an open wastewater treatment device, and culturing the microalgae by using the culture solution; wherein the open wastewater treatment device comprises a culture tank (1) for accommodating the culture solution, and a light guide member and a ventilation member (3) which are arranged in the culture tank (1); the light guide component comprises more than one light guide plate (2), the light guide plate (2) is used for guiding light irradiated on the top of the light guide plate to the position below the liquid level of the culture solution, the top end of the light guide plate is arranged above the liquid level of the culture solution, and the bottom end of the light guide plate is arranged below the liquid level of the culture solution. The method has high treatment efficiency and stability, and obtains microalgae biomass in high yield while treating wastewater, thereby having good economic benefit, ecological benefit and social benefit.

Description

Method for treating wastewater containing nitrate ions

Technical Field

The invention relates to the field of wastewater treatment, in particular to a method for treating nitrate ion-containing wastewater.

Background

The rapid development of human society greatly increases the demand for water resources. And the acceleration of the industrialization process brings about serious water pollution while improving the life quality of people. The variety of water pollutants is various, wherein nitrogen-containing wastewater, particularly nitrate ion-containing wastewater, poses serious threats to human health and ecological environment. The nitrate in drinking water is out of limits all over the world. And the phenomena of eutrophication, water aging and the like caused by the over-high nitrogen content in the environmental water body also bring serious ecological disasters, and the recovery of the water environment is extremely difficult and long. Therefore, the treatment of wastewater containing nitrate ions has been a hot spot in the field of water treatment, and is also a difficult point and a key point.

At present, the methods for treating the wastewater containing nitrate ions mainly comprise a biological denitrification method, a neutralization method, a chemical reduction method and the like. The most widely used method is the biological denitrification method, which utilizes the denitrification of denitrifying bacteria to reduce nitrate nitrogen into nitrogen gas, which is released into the atmosphere. However, due to the limitations of slow growth speed of denitrifying bacteria, low denitrifying efficiency, narrow tolerance range of pH and the like, the method cannot treat high-concentration nitrate ion-containing wastewater, needs a large amount of water for dilution, occupies a large area, causes high wastewater treatment cost, and does not recycle nitrogen elements. The neutralization method is to neutralize nitric acid in wastewater by using an alkaline substance and then treat the nitric acid by concentration and the like. This process actually converts nitric acid to nitrate only and does not actually remove the contaminants. The chemical reduction method utilizes the oxidation of nitrate ions and reduces nitrate nitrogen to nitrogen or ammonia using a chemical reducing agent. The method needs to add a large amount of medicament and may bring new pollution, and the ammonia nitrogen generated by reduction is also a serious pollutant and needs to be further treated, so that secondary pollution is easily generated. It can be seen that there is a lack of technology for efficiently treating wastewater containing nitrate ions at a relatively high concentration.

Disclosure of Invention

The invention aims to solve the problems of low treatment efficiency, low resource utilization degree, secondary pollution and the like in the prior art, and provides a treatment method of nitrate ion-containing wastewater.

In order to achieve the above object, the present invention provides a method for treating nitrate ion-containing wastewater, comprising: introducing microalgae and a culture solution containing the nitrate ion-containing wastewater into an open wastewater treatment device, and culturing the microalgae by using the culture solution; wherein the open wastewater treatment device comprises a culture tank for accommodating the culture solution, and a light guide member and a ventilation member which are arranged in the culture tank; the light guide component comprises more than one light guide plate, the light guide plate is used for guiding light irradiated on the top of the light guide plate to the position below the liquid level of the culture solution, the top end of the light guide plate is arranged above the liquid level of the culture solution, and the bottom end of the light guide plate is arranged below the liquid level of the culture solution.

Preferably, the light guide plate is formed of a transparent material, and includes an upper light absorbing part and a lower light scattering part.

More preferably, the light absorbing portion has an inverted trapezoidal cross section, and the light scattering portion has a rectangular cross section.

More preferably, the light scattering portion is subjected to a base material doping treatment and/or a laser etching treatment to reduce its light transmittance.

More preferably, in the light scattering portion, a lower portion has higher light transmittance than an upper portion.

Preferably, the aeration component comprises an aeration pipe and more than one aeration pipe, and aeration holes are distributed on the aeration pipe.

More preferably, the aeration tube is disposed at the bottom of the culture tank.

More preferably, the aeration pipe is disposed below the light guide plate.

More preferably, the aeration holes are disposed toward the light guide plate.

More preferably, the total nitrogen content of the wastewater containing nitrate ions is more than or equal to 200mg/L calculated by nitrogen element.

More preferably, the proportion of nitrogen element in the form of nitrate ions in the waste water containing nitrate ions is more than or equal to 1 percent of the total nitrogen element.

Preferably, the introduction of the nitrate ion-containing wastewater causes NO to be present in the culture solution₃ ^-The content of nitrate ions is 0.005-5 g/L.

Preferably, the pH of the culture solution is 8.0-11.0.

Preferably, the pH value of the culture solution is adjusted by adding a pH regulator; more preferably, the pH adjusting agent is nitric acid, sodium bicarbonate and CO₂One or more of (a).

Preferably, relative to 1m³The ventilation amount of the ventilation component is 0.02-2m³/min。

Preferably, the gas introduced into the ventilation part is one or more selected from the group consisting of air, carbon dioxide and nitrogen.

Preferably, the culture solution further contains other nutrients for microalgae growth.

Preferably, the other nutrient components include one or more of a carbon source, a phosphorus source, an iron source, a magnesium source, and trace elements.

Preferably, the method further comprises: at least part of the culture solution is taken out and the nitrate ion-containing wastewater is supplemented.

Preferably, the OD of the microalgae in the culture solution₅₆₀When the content is more than 1.5%, taking out the cultureCultivating liquid;

preferably, the culture solution is removed continuously or intermittently.

Preferably, the microalgae are separated from the withdrawn culture broth by a filtration process.

Preferably, the filtering treatment mode is one-stage filtering treatment or more than two stages of serial filtering treatment.

Preferably, the filtration treatment comprises at least ultrafiltration with a molecular weight cut-off of < 100 kDa.

Preferably, the clear solution resulting from the filtration process does not contain microalgal cells and molecules with a molecular weight >100 kDa.

Preferably, after separating microalgae from the culture solution taken out, returning the obtained clear solution to the open wastewater treatment device; more preferably, the OD of the microalgae in the culture broth is controlled while returning the clear solution₅₆₀Is 0.5-1.5.

Preferably, the microalgae are eukaryotic and/or prokaryotic algae, preferably prokaryotic algae, more preferably spirulina.

Through the technical scheme, the invention utilizes the microalgae to absorb the nitrate ions in the wastewater, realizes the purpose of treating (converting) the wastewater containing the nitrate ions by the microalgae, has higher treatment efficiency and stability, does not generate secondary pollutants, obtains microalgae biomass in high yield while treating the wastewater, and has good economic benefit, ecological benefit and social benefit. The microalgae biomass can be applied to the fields of feeds, health-care products, materials and the like through post-processing, and has higher economic value. Furthermore, the arrangement matching of the ventilation component and the light guide component, the ventilation amount and the optimization of the orientation of the aeration holes can reduce the adhesion of microalgae on the surface of the light guide component, improve the illumination effect and reduce the operation and cleaning cost of the treatment device.

Drawings

Fig. 1 is a front view of an open type wastewater treatment apparatus of the present invention.

FIG. 2 is a sectional view of the open type wastewater treatment apparatus of the present invention.

FIG. 3 shows NO in the treatment of examples and comparative examples₃ ^-The efficiency of the cleaning.

FIG. 4 shows NO in the course of treatment of examples and comparative examples₃ ^-The clearance rate.

Description of the reference numerals

1. Culture pond 2, light guide plate 3, ventilation member

201. Light absorbing part 202, light scattering part 301, and aeration tube

302. Aeration hole

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein. In the present invention, the terms "upper", "lower", "vertical", and the like are used in the corresponding directions in the drawings.

The method for treating the nitrate ion-containing wastewater comprises the following steps: introducing microalgae and a culture solution containing the nitrate ion-containing wastewater into an open wastewater treatment device, and culturing the microalgae by using the culture solution; as shown in fig. 1-2, the open wastewater treatment apparatus includes a culture tank 1 for containing the culture solution, and a light guide member and a ventilation member 3 provided in the culture tank; the light guide member includes one or more light guide plates 2, the light guide plates 2 are used for guiding light irradiated on the tops of the light guide plates to the lower part of the liquid level of the culture solution, the tops of the light guide plates are arranged above the liquid level of the culture solution, and the bottoms of the light guide plates are arranged below the liquid level of the culture solution.

According to the invention, the open type wastewater treatment device is used for providing conditions in the process of microalgae culture, so that the purpose of treating nitrate ion-containing wastewater is achieved, and the structure can be used for completing the efficient culture of microalgae. In the open wastewater treatment apparatus, the culture tank 1 is an open culture tank, and may be a columnar structure having no top wall.

In the open wastewater treatment device, the light guide component is used for guiding sunlight incident above the open wastewater treatment device into the culture solution, so that microalgae at a position where sunlight cannot transmit in a deeper part of the culture solution can be sufficiently illuminated, and the culture efficiency is improved; the ventilation component 3 is used for providing gases such as carbon dioxide and the like required by the growth of the microalgae and promoting the growth of the microalgae. By providing appropriate conditions, the microalgae cells utilize a plurality of photosensitive pigments which are contained in the microalgae cells and can absorb photons with specific wavelength ranges to convert light energy into chemical energy, and the chemical energy is provided for the microalgae cells for substance assimilation, thereby achieving the purpose of wastewater treatment.

According to the present invention, the structure and arrangement of the light guide plate 2 are not particularly limited. From the viewpoint of further facilitating the introduction of external light into the culture solution, it is preferable that the light guide plate 2 includes an upper light absorbing portion 201 and a lower light scattering portion 202. The light absorbing part 201 and the light scattering part 202 are integrally formed, at least part of the light absorbing part 201 is positioned above the liquid level so as to absorb light during use, and at least part of the light scattering part 202 is positioned below the liquid level so as to scatter the light absorbed by the light absorbing part 201, so that a good light guide effect is realized. The light guide plate 2 is preferably a plate-shaped structure. From the viewpoint of facilitating absorption and scattering of light, it is preferable that, as shown in fig. 2, the upper side of the cross section of the light absorbing portion 201 is longer than the lower side, and may be, for example, an inverted trapezoid, and the cross section of the light scattering portion 202 is rectangular. The cross section is a plane perpendicular to the plate-like plane of the light guide plate 2. The size of the light guide plate is matched with the size of the culture pond. Further, it is preferable that the light guide plates 2 are vertically arranged in the culture well 1, and the number of the light guide plates 2 is preferably 2 to 5/m at an interval of 10 to 50 cm.

According to the present invention, the material of the light guide plate 2 is not particularly limited, and the material constituting the light guide plate 2 is preferably a solid transparent material, and may be one or more of glass, surface-treated glass, polypropylene, polyvinyl chloride, polycarbonate, polystyrene, polymethyl methacrylate, and a composite organic material, for example.

According to a preferred embodiment of the present invention, in order to improve the scattering efficiency of the light scattering portion 202, it is preferable that the light absorbing portion 201 is a transparent substrate, and the light scattering portion 202 reduces its light transmittance by a substrate doping process and/or a laser etching process, thereby uniformly scattering incident light in a range of a certain angle from the vertical direction to the horizontal direction.

Further, the light transmittance of the light guide plate 2 may be uniform or non-uniform, and the light guide plate 2 having non-uniform light transmittance can achieve the effect of adjusting the light intensity at different depths of the culture solution. The light transmittance of the light guide plate 2 at different positions can be adjusted by adjusting the doping level and/or the laser etching level, for example, a material with a higher doping level or a higher laser etching level has a low light transmittance, and more light is scattered in the horizontal direction, so that the light irradiation intensity on the surface is higher. According to a preferred embodiment of the present invention, the light scattering portion 202 is subjected to a base material doping treatment and/or a laser etching treatment to reduce its light transmittance; more preferably, the light transmittance of the lower portion of the light scattering portion 202 is higher than that of the upper portion, and even more preferably, the light transmittance of the light scattering portion 202 is higher as it approaches the lower portion.

The microalgae cells undergo photosynthesis during the autotrophic growth process, and assimilate carbon dioxide into organic matter as part of the biomass accumulated by the microalgae. Therefore, it is necessary to supply a carbon source to the microalgae cells by contacting with a carbon dioxide-containing gas by means of stirring, aeration, flow, or the like. In the open wastewater treatment apparatus of the present invention, the aeration means 3 is used to supply a gas such as carbon dioxide required for the growth of microalgae. The mode of installing the aeration member 3 is not particularly limited, and it is preferable that the aeration member 3 includes an aeration pipe and one or more aeration pipes 301, and aeration holes 302 are arranged at regular intervals on the aeration pipes 301. The aeration pipe is used for introducing gas into the aeration pipe 301, and the aeration holes 302 are used for discharging the introduced gas. The number of the aeration tubes 301 is preferably the same as the number of the light guide plates. The gas introduced into the ventilation part 3 may be one or more selected from air, carbon dioxide and nitrogen, and is preferably air or carbon dioxide; the ventilation amount of the ventilation member 3 can be appropriately adjusted as needed, and may be 1m, for example³The culture solution has ventilation amount of 0.02-2m³Min, preferably 0.5-2m³And/min. From the viewpoint of increasing the concentration of gas such as carbon dioxide at various places in the culture solution, it is preferable that the aeration tubes 301 are provided near the bottom of the culture tank 1 and are uniformly distributed.

In addition, a stirring member may be further provided inside the culture pond 1, the stirring member is used to promote the absorption and utilization of nutrients in the culture solution by the microalgae, prevent the inhibition effect of the accumulation of oxygen around the microalgae on the photosynthesis of the microalgae, and prevent cell death and anaerobic decomposition due to the sinking of the microalgae, and the stirring member may be a stirring paddle or the like. In contrast, the present inventors have found that aeration into the wastewater treatment system through the aeration holes 302 provides carbon dioxide required for wastewater treatment to the microalgae, and that the culture solution is stirred by the mutual movement of the bubbles and the liquid to prevent the algal bodies from sinking, i.e., the aeration member has the effect of the stirring member. According to a preferred embodiment of the present invention, the aeration tube 301 is disposed below (more preferably, at a lower midpoint position) the light guide plate 2, and more preferably, the aeration hole 302 is disposed toward the light guide plate 2. That is, it is preferable that the position and length of the aeration tube 301 are selected in accordance with the position and size of the light guide plate 2. By arranging the aeration pipe 301 as above, not only can the carbon dioxide concentration of the part with higher illumination intensity around the light guide component be increased so as to promote the growth of microalgae, but also the introduced wastewater containing nitrate ions can be fully mixed with other additional components so as to avoid the flocculation and sedimentation of the microalgae, and meanwhile, the gas introduced from the aeration holes 302 is used for purging the light guide component, so that the aims of preventing the microalgae from being gathered on the light guide component to shield light, reducing the oxygen concentration around the microalgae and reducing the operation and cleaning cost of the treatment device are fulfilled. Therefore, in the open wastewater treatment apparatus according to the preferred embodiment of the present invention, in which the aeration member 3 is appropriately provided, a good wastewater treatment effect can be achieved similarly without providing the stirring member.

In the present invention, the "nitrate ion-containing wastewater" refers to wastewater containing nitrate ions, wherein the nitrate ions may be present in the form of nitric acid, nitrate, or the like depending on the pH, and the wastewater containing the above-mentioned nitrate ions may be wastewater to be treated by the method of the present invention, specifically, wastewater containing nitrate ions discharged from various industries, and the method of the present invention is particularly advantageous for treating wastewater containing a high content of nitrate ions. By utilizing the method, the nitrate ions can be used as a nitrogen source required by the growth of the microalgae, so that the nitrate ions in the wastewater containing the nitrate ions can be consumed by the culture of the microalgae, and the aim of treating the wastewater is fulfilled.

In the nitrate ion-containing wastewater, the total nitrogen content in terms of nitrogen is preferably not less than 50mg/L, more preferably not less than 200mg/L, such as 1000-5000 mg/L. And, preferably, the proportion of nitrogen element present therein in the form of nitrate ions to the total nitrogen element is not less than 1%, more preferably not less than 50%. The method for measuring the total nitrogen content (TN) refers to the flowing injection-naphthyl ethylenediamine hydrochloride spectrophotometry for measuring the total nitrogen of the HJ 668-2013 water quality. The method for measuring nitrate ions refers to a phenol disulfonic acid spectrophotometry method for measuring nitrate nitrogen in water of GB 7480-87. According to a preferred embodiment of the invention, the introduction of said nitrate ion-containing waste water is such that NO is present in the culture broth₃ ^-The nitrate ion content is 0.005-5g/L, preferably 0.5-2 g/L. When the concentration of the nitrate ions is higher than that required by microalgae culture, water can be properly added for dilution.

In order to meet the requirement of microalgae culture, the culture solution also contains other nutrient components for providing microalgae growth. The other nutrient components comprise a carbon source, a phosphorus source, an iron source, a magnesium source, trace elements and the like. Specific compositions of the other nutrients can be selected according to the selected microalgae, and for example, the other nutrients can be selected with reference to at least one of BG-11 medium, SE medium, Pr medium, f/2 medium, and Zarrouk medium (preferably Zarrouk medium).

According to the present invention, in order to provide conditions for microalgae growth, the pH of the culture solution is preferably 8.0-11.0, preferably 8.5-10.5. By adjusting the pH of the culture solution to the above range, the growth of microalgae can be promoted. When the pH of the culture solution is not within the above range, the pH of the culture solution can be adjusted by adding a pH adjusting agent, preferably nitric acid, sodium bicarbonate and CO₂One or more of (a).

In certain processing devices, there is an upper limit to the cell density at which microalgae can grow, and as this upper limit is approached, the rate of uptake of foreign matter by the microalgae decreases significantly. In order to maintain the processing efficiency of the processing apparatus at a high level, the method of the present invention may further comprise: at least part of the culture solution is taken out and the nitrate ion-containing wastewater is supplemented. Preferably the OD of the microalgae in the culture solution₅₆₀When the concentration is 1.5 or more, the culture medium is taken out. The culture solution may be continuously or intermittently withdrawn in a specific manner, and it is more preferable that the culture solution withdrawn continuously or intermittently is 5 to 80% by weight, preferably 30 to 70% by weight, based on the total amount of the culture solution. The microalgae can be separated from the culture broth taken out, for example, by filtration treatment; the filtering treatment mode is one-stage filtering treatment or more than two-stage series filtering treatment.

In addition, the inventor of the present invention found in the research process that microalgae secrete a plurality of bioactive substances to the surrounding environment during the growth process, and when the concentration of the bioactive substances is accumulated to a certain level, the growth of the microalgae may be inhibited, so that the nitrate nitrogen removal efficiency of the device is affected. Therefore, when separating microalgae from the culture medium taken out, it is preferable to remove these active substances together to prevent the reuse of the filtered clear solution from affecting the growth of microalgae in the treatment system. Specifically, the inventors of the present invention found that, when the culture solution is filtered by using an ultrafiltration apparatus having a cut-off molecular weight of 100kDa or less, the resulting filtered clear solution does not contain substances that inhibit the growth of microalgae, and the reuse of the filtered clear solution does not adversely affect the growth efficiency of microalgae and the removal efficiency of nitrate nitrogen. Thus, the filtration treatment according to the invention comprises at least an ultrafiltration with a primary molecular weight cut-off of < 100 kDa. Through the ultrafiltration, the clear liquid obtained by the filtration treatment does not contain microalgae cells and molecules with molecular weight of more than 100 kDa. Particularly, the invention preferably adopts two-stage series filtration by comprehensively considering the factors of filtration efficiency, energy consumption, equipment maintenance cost and the like, wherein the two-stage series filtration comprises ultrafiltration with the primary cut-off molecular weight less than or equal to 100 kDa.

In addition, microalgae are aspirated from the culture brothNitrate nitrogen is collected and fixed as a part of the biomass itself by assimilation. Therefore, the efficiency of microalgae in scavenging nitrate nitrogen from wastewater depends to a large extent on the rate of accumulation of microalgae biomass. The microalgae biomass in the treatment system is maintained at a higher level, which is beneficial to improving the accumulation rate of the microalgae biomass, thereby improving the treatment capacity of the treatment device. On the other hand, when the microalgae biomass reaches a higher level, the accumulation rate of the microalgae biomass may decrease due to the limitation of environmental conditions. Therefore, the microalgae biomass in the treatment system is not suitable to be too high. Combining the above two factors, and combining the control conditions of the wastewater treatment process, the inventors of the present invention found in the research process that the cell density (OD at optical density of 560nm) of the microalgae in the treatment device was properly controlled₅₆₀Measured) is advantageous in maintaining a high treatment efficiency of the wastewater treatment plant. For spirulina, it is preferable to control the OD of microalgae in the culture solution₅₆₀Is 0.5-1.5, particularly, OD₅₆₀Control in the range of 0.8 to 1.2 enables the highest nitrate treatment capacity to be achieved. The cell density of the microalgae can be adjusted by adjusting the adding amount of the nitrate ion-containing wastewater, the amount of the returned clear liquid, the added water amount and the like. The clear liquid obtained after separating the microalgae can be returned to the treatment device, so that the cell density of the microalgae in the culture solution is far away from the upper limit, and the treatment efficiency of the treatment device is prevented from being reduced.

Separating the microalgae from the culture solution taken out in order to further process nitrate ions in the culture solution from which the microalgae are separated, and returning the obtained clear solution to the open wastewater treatment device; more preferably, the OD of the microalgae in the culture medium is controlled while returning the clear solution₅₆₀Is 0.5-1.5. By taking out a part of the culture solution and separating the microalgae therein, the downstream high-value application can be provided.

In addition, because the culture pond 1 is an open culture pond, the culture solution is continuously evaporated in the whole treatment process, and the nitrate ion-containing wastewater can be properly supplemented into the culture solution according to the needs, thereby achieving the effect of continuously treating the wastewater. Also, the OD of microalgae in the culture solution is controlled by using the method of the present invention₅₆₀The microalgae may beContinuously maintains higher activity, and does not need to supplement algae seeds in the whole treatment process.

In the present invention, the microalgae used may be various microalgae capable of using nitrate ions in wastewater as a nitrogen source, including eukaryotic algae and/or prokaryotic algae, preferably, the microalgae is Chlorella (e.g., Chlorella vulgaris, Chlorella ellipsoidea, or Chlorella pyrenoidosa), monoraphe (e.g., monochoria tenella (monoraphywski)), scenedesmus (e.g., scenedesmus obliquus), scenedesmus (s.acutus), scenedesmus curvatus, scenedesmus turbinatus, or scenedesmus tetrandra (s.crispatus), or Spirulina (e.g., Spirulina platensis (Spirulina platensis) or Spirulina maxima (Spirulina maxima)), wherein Spirulina is preferably Spirulina.

The present invention will be described in detail below by way of examples. In the following examples, the composition of the nitrate ion-containing wastewater was: NO₃ ^-18.7g/L、SO₄ ^2-34mg/L、PO₄ ^3-16.5mg/L、Na⁺553mg/L、K⁺13.1mg/L、Ca²⁺36.8mg/L, toluene 0.01mg/L and caprolactam 1mg/L, and is from the nitric acid cleaning section of the caprolactam production process.

Measurement of absorbance (OD value) of culture solution: measuring with spectrophotometer with distilled water as reference, and measuring absorbance of the culture solution at maximum absorption peak wavelength (560nm) as microalgae concentration index.

The method for measuring nitrate ions refers to a phenol disulfonic acid spectrophotometry method for measuring nitrate nitrogen in water of GB 7480-87.

NO₃ ^-Efficiency of scavenging (initial NO of culture broth)₃ ^-concentration-NO of the culture broth after the end of the treatment₃ ^-Concentration + reduced NO by adding wastewater₃ ^-Concentration) x depth of culture broth/treatment day.

NO₃ ^-Clearance rate (initial NO of culture broth)₃ ^-concentration-NO of the culture broth after the end of the treatment₃ ^-Concentration + reduced NO by adding wastewater₃ ^-Concentration)/added wastewater reduced NO₃ ^-Concentration X100%.

Wherein the added wastewater is converted into NO₃ ^-The concentration was 18.7g/L × 0.3L × number of treatment days/1000L.

In the following examples, the microalgae were Spirulina platensis assigned as FACHB-314 from freshwater algae seed pool of Chinese academy of sciences.

Example 1

An open wastewater treatment apparatus shown in FIGS. 1-2, which comprises a culture tank 1 for containing a culture solution, and a light guide member and an aeration member 3 provided in the culture tank 1, was used to perform nitrate ion-containing wastewater treatment. The length of the culture pond 1 is 1m, the width thereof is 1m, the liquid depth thereof is 30cm, and the culture pond can hold the total volume of the culture solution to be 0.3m³。

The light guide member includes a light guide plate 2 formed of 5 pieces of polymethyl methacrylate, which is integrally formed of an upper light absorbing portion 201 and a lower light scattering portion 202, the light absorbing portion 201 having an inverted trapezoidal cross section (a top width of 5cm, a height of 5.6cm, a lower width of 1cm), the light scattering portion 202 having a rectangular cross section (a width of 1cm, a height of 22cm), the light guide plate 2 having a width of 0.9m and a pitch of 15 cm. The top end of the light guide plate 2 is arranged above the liquid level of the culture solution, and the bottom end of the light guide plate 2 is arranged below the liquid level of the culture solution (the bottom edge is 7cm away from the bottom of the culture tank 1). The side of the light guide plate 2 is laser etched to guide the light incident from the top to the side. The light scattering portion 202 of the light guide plate 2 is etched to a large extent, thereby increasing the light intensity of the light scattering portion 202.

The aeration component 3 comprises an aeration pipe 301 arranged at the bottom of the culture tank 1, aeration holes 302 with the diameter of 2.5mm are arranged on the aeration pipe 301 at intervals of 5cm, and the aeration holes 302 are positioned at the middle lower part of the bottom of the light guide plate 2 and are 5cm away from the bottom of the light guide plate 2.

Introducing Zarrouk culture medium (without adding nitrate) into culture pond 1, inoculating Spirulina species, introducing the nitrate ion-containing wastewater to be treated to obtain culture solution, and making NO of the culture solution₃ ^-The concentration was 1g/L (total volume of the culture solution was 0.3 m)³). OD of post-inoculation culture solution₅₆₀About 0.3, passing through an aeration pipe301 introducing air into the culture pond 1, and irradiating at 28 deg.C under natural light with ventilation amount of 0.2m³Min (relative to 1 m)³Culture broth).

When OD of culture solution₅₆₀After reaching 0.5, culture fluid samples were collected every day and OD was measured₅₆₀And nitrate concentration, and 0.3L of nitrate ion-containing wastewater was added to the culture solution. OD of the culture solution₅₆₀When the concentration reached 1.5, a part (200L) of the culture solution was taken out from the culture tank 1, and subjected to primary filtration using a 320 mesh nylon filter, and then the primary filtrate was fed to an ultrafiltration apparatus for secondary ultrafiltration. The inlet pressure of the ultrafiltration device is 0.12MPa, the outlet pressure is 0.06MPa, and the molecular weight cut-off of the membrane component is 100 kDa. Mixing the secondary ultrafiltration concentrated solution with the primary filtered algae mud, drying, and storing at low temperature. Returning the second-stage ultrafiltration clear liquid to the culture tank 1, and controlling OD of the culture liquid in the tank₅₆₀And (5) continuing to process and sampling for detection, and circulating in the range of 0.5-1.5.

Example 2

Wastewater treatment was carried out in the same manner as in example 1 except that OD of the culture solution to be cultured was changed₅₆₀When 1.2 is reached, a part of the culture solution is taken out of the culture tank 1, and the OD of the culture solution in the tank is controlled when the secondary ultrafiltrate is returned to the culture tank 1₅₆₀Between 0.8 and 1.2.

Comparative example 1

Wastewater treatment was carried out in the same manner as in example 2, except that the light guide plate 2 was not installed in the culture tank.

Comparative example 2

Wastewater treatment was carried out in the same manner as in example 2, except that the aeration tube 301 was not disposed in the culture tank, and a mechanical agitation mixing apparatus was installed to circulate the liquid in an amount of 2m³/h。

Example 3

Wastewater treatment was carried out in the same manner as in example 2, except that the aeration tube 301 was disposed just below the gap between the two light guide plates 2 at a vertical distance of 5cm from the bottom of the light source.

Example 4

Wastewater treatment was carried out in the same manner as in example 2 except that nitrate-containing ions were added to the culture tankWaste water to make NO₃ ^-The concentration was 5 mg/L.

Example 5

Wastewater treatment was carried out in the same manner as in example 2 except that nitrate ion-containing wastewater was added to the culture tank to make NO₃ ^-The concentration was 0.5 g/L.

Example 6

Wastewater treatment was carried out in the same manner as in example 2 except that nitrate ion-containing wastewater was added to the culture tank to make NO₃ ^-The concentration was 2 g/L.

Example 7

Wastewater treatment was carried out in the same manner as in example 2 except that nitrate ion-containing wastewater was added to the culture tank to make NO₃ ^-The concentration was 10 g/L.

Example 8

Wastewater treatment was carried out in the same manner as in example 2 except that the OD of the culture solution was changed₅₆₀When the concentration reaches 0.5, filtering to control OD of culture solution in the tank₅₆₀Between 0.2 and 0.5.

Example 9

Wastewater treatment was carried out in the same manner as in example 2 except that OD of the culture solution to be cultured was changed₅₆₀When the concentration reaches 2.0, filtering to control OD of culture solution in the tank₅₆₀Between 1.5 and 2.0.

Example 10

Wastewater treatment was carried out in the same manner as in example 2, except that the culture broth taken out of the culture tank was filtered using a 320 mesh nylon filter, and the filtrate was directly returned to the culture tank without ultrafiltration.

Example 11

Wastewater treatment was carried out as in example 2, except that the ultrafiltration membrane module had a molecular weight cut-off of 300 kDa.

Example 12

Wastewater treatment was carried out in the same manner as in example 2 except that chlorella was used as the algal species.

NO of the above examples and comparative examples₃ ^-Cleaning efficiency and cleaning rateAs shown in Table 1 below, the NO of FIG. 3 was obtained according to the above results₃ ^-Scavenging efficiency and NO of figure 4₃ ^-The clearance rate.

TABLE 1

As can be seen from Table 1, good NO can be achieved by treating the wastewater containing nitrate ions by the treatment method of the present application₃ ^-Scavenging efficiency and NO₃ ^-The clearance rate. Further, by appropriately selecting OD to be cultured₅₆₀Value range, NO in culture solution₃ ^-The concentration of the nitrogen-containing gas, the manner of installing the light source and the ventilation member, the conditions of filtration, the algal species to be blended, and the like, can be further improved₃ ^-Scavenging efficiency and NO₃ ^-The clearance rate.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. A method for treating wastewater containing nitrate ions, which is characterized by comprising the following steps: introducing microalgae and a culture solution containing the nitrate ion-containing wastewater into an open wastewater treatment device, and culturing the microalgae by using the culture solution;

wherein the open wastewater treatment device comprises a culture tank (1) for accommodating the culture solution, and a light guide member and a ventilation member (3) which are arranged in the culture tank (1);

the light guide component comprises more than one light guide plate (2), the light guide plate (2) is used for guiding light irradiated on the top of the light guide plate to the position below the liquid level of the culture solution, the top end of the light guide plate is arranged above the liquid level of the culture solution, and the bottom end of the light guide plate is arranged below the liquid level of the culture solution.

2. The process according to claim 1, wherein the light guide plate is made of a transparent material, the light guide plate comprising an upper light absorbing part (201) and a lower light scattering part (202);

preferably, the light absorbing part (201) has an inverted trapezoidal cross section, and the light scattering part (202) has a rectangular cross section;

preferably, the light scattering part (202) is subjected to base material doping treatment and/or laser etching treatment to reduce the light transmittance;

preferably, in the light scattering portion (202), the light transmittance of the lower portion is higher than that of the upper portion.

3. The treatment method according to claim 1, wherein the aeration means (3) comprises an aeration pipe and more than one aeration pipe (301), and aeration holes (302) are distributed on the aeration pipe (301);

preferably, the aeration pipe (301) is arranged at the bottom of the culture tank (1);

preferably, the aeration pipe (301) is arranged below the light guide plate (2);

preferably, the aeration holes (302) are disposed toward the light guide plate (2).

4. The treatment method according to any one of claims 1 to 3, wherein the total nitrogen content in the nitrate ion-containing wastewater in terms of nitrogen is not less than 50 mg/L;

preferably, the proportion of nitrogen element in the form of nitrate ions in the waste water containing nitrate ions in the total nitrogen element is more than or equal to 1 percent;

5. The treatment method according to any one of claims 1 to 3, wherein the pH of the culture solution is 8.0 to 11.0;

preferably, the pH value of the culture solution is adjusted by adding a pH regulator;

more preferably, the pH adjusting agent is nitric acid, sodium bicarbonate and CO₂One or more of (a).

6. The processing method according to any one of claims 1 to 3, wherein the processing method is performed with respect to 1m³The aeration amount of the aeration member (3) is 0.02 to 2m³/min；

Preferably, the gas introduced into the ventilation part (3) is one or more selected from air, carbon dioxide and nitrogen.

7. The process of any one of claims 1 to 3, wherein the culture medium further comprises other nutrients that provide for the growth of microalgae;

8. The processing method according to any one of claims 1 to 3, wherein the method further comprises: taking out at least part of the culture solution, and supplementing the nitrate ion-containing wastewater;

preferably, the OD of the microalgae in the culture solution₅₆₀When the concentration is 1.5 or more, taking out the culture solution;

preferably, the culture solution is removed continuously or intermittently.

9. The process of claim 8, wherein microalgae are separated from the withdrawn culture broth by a filtration process;

preferably, the filtering treatment mode is one-stage filtering treatment or more than two-stage series filtering treatment;

preferably, the filtration treatment comprises at least ultrafiltration with a molecular weight cut-off of < 100 kDa;

preferably, the clear solution obtained by the filtration treatment does not contain microalgae cells and molecules with molecular weight of more than 100 kDa;

10. The process of any one of claims 1 to 9, wherein the microalgae are eukaryotic and/or prokaryotic algae, preferably prokaryotic algae, more preferably spirulina.