A method for treating high-salt, recalcitrant oilfield wastewater

Abstract

This invention belongs to the field of wastewater treatment technology, specifically relating to a method for treating high-salinity, recalcitrant oilfield wastewater. The method involves first mixing the high-salinity, recalcitrant oilfield wastewater with domestic sewage, then adding anaerobic bacteria for acclimation; next, mixing the high-salinity, recalcitrant oilfield wastewater with domestic sewage, then adding aerobic bacteria for acclimation; finally, mixing the high-salinity, recalcitrant oilfield wastewater with domestic sewage, and then sequentially introducing the acclimated anaerobic bacteria container and aerobic bacteria container for hydrolysis acidification and aerobic treatment, ultimately discharging the wastewater after it meets discharge standards. The apparatus used in the treatment method includes an equalization tank, a hydrolysis acidification tank, and an aerobic tank connected in sequence. This invention reduces the salinity of wastewater while increasing the types, activity, and quantity of microorganisms, solving the technical problems of achieving compliant discharge and exceeding pollutant standards for high-salinity, recalcitrant oilfield wastewater using ordinary biochemical methods; furthermore, the wastewater treatment apparatus used has the advantages of wide application range, strong adaptability, and low cost.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for treating high-salt, recalcitrant oilfield wastewater. Background Technology

[0002] During oilfield production, the amount of produced wastewater containing high concentrations of inorganic salts, recalcitrant chemical agents, and high-molecular-weight organic pollutants is increasing. This wastewater is difficult to degrade and treat. If it is directly treated biologically before discharge, the high salinity can easily reduce the activity of microorganisms in the biological system. At the same time, the high concentration of recalcitrant organic pollutants will impact subsequent biological treatment processes, significantly increasing the biological load on these processes and greatly affecting their treatment effectiveness.

[0003] Chinese patent application CN112279461A discloses a modified biochemical-MBR process for treating high-salt wastewater in the hazardous waste industry, which allows for adjustments based on the characteristics of waste disposed of in physicochemical treatment workshops, thus improving its practicality. However, the overall process is complex and requires a large dosage of flocculants.

[0004] Another Chinese patent application, CN104250056B, provides a treatment scheme of "source control and separate enhanced treatment to achieve emission standards." This scheme employs a combination of advanced oxidation pretreatment and subsequent biological treatment. However, this method is only suitable for wastewater with small flow rates and high pollutant concentrations.

[0005] Chinese patent application CN201873595U also discloses a physicochemical treatment system for high-salinity wastewater. Their method requires ozone oxidation of recalcitrant organic matter, and the amount of dilution water added is usually more than 20 times the amount of water to be treated. This results in high consumption of dilution water and a significant increase in the volume of the biological tank, which is not conducive to saving resources and costs. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for treating high-salt, recalcitrant oilfield wastewater. This method can reduce the salt content of the wastewater while increasing the types, activities, and quantities of microorganisms, thus solving the technical problems of achieving standard discharge and exceeding pollutant limits for high-salt, recalcitrant oilfield wastewater using ordinary biochemical methods.

[0007] To achieve the objectives of this invention, the following technical solution is adopted:

[0008] A method for treating high-salt, recalcitrant oilfield wastewater includes the following steps:

[0009] (1) Anaerobic bacteria domestication: Mix high-salt, difficult-to-degrade oilfield wastewater and domestic sewage, and then add anaerobic bacteria for domestication;

[0010] (2) Aerobic bacteria domestication: Mix high-salt, difficult-to-degrade oilfield wastewater and domestic sewage, and then add aerobic bacteria for domestication;

[0011] (3) Wastewater treatment: High-salt, difficult-to-degrade oilfield wastewater and domestic sewage are mixed and then sequentially fed into acclimatized anaerobic bacteria containers and aerobic bacteria containers for hydrolysis acidification and aerobic treatment before the wastewater is discharged after meeting the standards.

[0012] Preferably, during the acclimatization process in steps (1)-(2), the volume ratio of the high-salt, recalcitrant oilfield wastewater to the domestic sewage is 1-1.5:1.

[0013] Preferably, when continuously treating wastewater, the volume ratio of the high-salt, recalcitrant oilfield wastewater to domestic sewage in step (3) is 1-5:1.

[0014] Preferably, the domestic sewage mentioned in steps (1)-(3) is fecal water.

[0015] Preferably, the anaerobic bacteria in step (1) are selected from at least one of anaerobic microorganisms, facultative anaerobic microorganisms, commercially available anaerobic engineered bacteria, and facultative anaerobic engineered bacteria that are cultured in the laboratory or in the biochemical treatment system of a petrochemical plant.

[0016] Preferably, the anaerobic bacteria in step (1) are selected from at least one of anaerobic microorganisms and facultative anaerobic microorganisms.

[0017] Preferably, the concentration of anaerobic bacteria in the system is 10-50%, and nutrients are added during the domestication process at a ratio of COD:N:P = 100:5:1.

[0018] Preferably, the anaerobic bacteria in step (1) are BZT hydrolytic acidifying bacteria.

[0019] Preferably, the aerobic bacteria in step (2) are selected from at least one of aerobic microorganisms, facultative anaerobic microorganisms, commercially available anaerobic engineered bacteria, and facultative anaerobic engineered bacteria from a petrochemical plant biochemical treatment system cultured in the laboratory.

[0020] Preferably, the aerobic bacteria in step (2) are selected from at least one of aerobic microorganisms and facultative anaerobic microorganisms;

[0021] Preferably, the concentration of aerobic bacteria is 10-50%, and nutrients are added during the domestication process at a ratio of COD:N:P = 100:5:1.

[0022] Preferably, the aerobic bacteria in step (2) are COD removal agents.

[0023] Preferably, microbial packing material is also added in steps (1)-(2).

[0024] Preferably, the microbial packing material is a glass ball packing material, which contains plastic filaments or sponge inside, and the packing material has a filling rate of more than 50%.

[0025] Preferably, the acclimatization time in steps (1)-(2) is 6-8 days.

[0026] Preferably, the hydrolysis acidification treatment or aerobic treatment in step (3) takes 2-24 hours and the treatment temperature is 5-40℃.

[0027] Another objective of this invention is to provide a treatment device for high-salt, recalcitrant oilfield wastewater, used to implement the above-mentioned treatment method. The device includes an equalization tank, a hydrolysis acidification tank, and an aerobic tank connected in sequence. The equalization tank is used to mix high-salt, recalcitrant oilfield wastewater and domestic sewage. The hydrolysis acidification tank is used to perform hydrolysis acidification treatment, and the aerobic tank is used to perform aerobic treatment.

[0028] Different proportions of high-salinity, recalcitrant oilfield wastewater and domestic sewage can be added to the equalization tank. Adding domestic sewage to the oilfield wastewater serves two purposes: firstly, its low salinity (generally not exceeding 1 g / L) helps reduce the overall salinity of the wastewater; secondly, domestic sewage, especially fecal matter, contains a large number of bacteria, fungi, algae, protozoa, and metazoa, which can increase the variety, activity, and quantity of microorganisms in the wastewater. The synergistic effect of these microorganisms increases the efficiency of activated sludge in treating organic matter.

[0029] The hydrolysis acidification tank utilizes acid-producing bacteria in activated sludge to break down the carbon-coated chains (CCs) of organic molecules, hydrolyzing long chains into short chains, branched chains, or ring structures into straight chains. This reduces the toxicity of wastewater and improves its biodegradability. In the aerobic tank, packing materials such as glass spheres are added. The large specific surface area of ​​the glass spheres provides strong adsorption capacity, allowing microorganisms to proliferate on their surface, forming a biofilm. This concentrates oxygen and organic matter in the surrounding area, increasing contact time and leading to the decomposition of adsorbed COD components. The addition of glass spheres also significantly improves the system's salt tolerance and resistance to shock loads.

[0030] Because high-salinity oilfield wastewater often lacks petroleum-degrading bacteria, inoculation is necessary. This invention uses a bio-enhancing method to add bacteria effective in degrading recalcitrant organic matter, such as petroleum and petrochemical degrading bacteria and chemical product degrading bacteria from a certain company, to increase the targeted treatment of recalcitrant organic matter by activated sludge. During this process, the ratio of high-salinity, recalcitrant oilfield wastewater to domestic sewage should be changed in the equalization tank, and the activated sludge in the hydrolysis acidification tank and aerobic tank should be acclimated to allow the acid-producing bacteria to adapt to the high-salinity wastewater environment and maintain their activity. During acclimation, nutrients are added to the water at a ratio of COD:N:P = 100:5:1.

[0031] In winter, the water temperature is low, which will inhibit the growth of activated sludge and the treatment efficiency. Heating and insulation devices should be installed on the hydrolysis acidification tank and the aerobic tank.

[0032] Preferably, the device is used by first adding high-salt, difficult-to-degrade oilfield wastewater and domestic sewage into an equalization tank through a pipeline, mixing them evenly, and then entering a hydrolysis acidification tank. Effective degrading microorganisms are added to the hydrolysis acidification tank, and then the wastewater flows into an aerobic tank. Aerobic bacteria are added to the aerobic tank, and after acclimatization, the wastewater is degraded. Finally, the water in the aerobic tank is discharged after meeting the standards.

[0033] Another object of the present invention is to provide the application of the above-mentioned treatment method or treatment device in the treatment of wastewater.

[0034] Preferably, the wastewater is high-salt, recalcitrant oilfield wastewater.

[0035] Preferably, the high-salt, recalcitrant oilfield wastewater has a salt content of 8000-40000 mg / L, a COD content of 1000-20000 mg / L, and a high molecular weight water-soluble polyether content of 1000-10000 mg / L.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] (1) It solves the problem of poor treatment effect of existing technologies: In the traditional activated sludge process, the salt concentration must be kept below 1wt%. If the concentration is too high, the activity of microorganisms will be reduced, which will inhibit the growth of microorganisms and reduce the organic matter removal rate. However, this invention can treat high-salt and difficult-to-degrade wastewater. After the wastewater is treated by physicochemical methods, the organic matter concentration is reduced, the subsequent biochemical load is reduced, and the effluent meets the standards.

[0038] (2) It solves the problem of high operational difficulty in existing technologies: During operation, sudden changes in salt and organic matter concentrations have a great impact on microorganisms, which can directly disrupt their normal operation, causing bacterial flocs to disintegrate, sludge to float, and COD of effluent to increase. However, the process used in the biochemical part of this invention has significantly improved salt tolerance, toxicity resistance, and shock load resistance, and the salt concentration can reach 8.5wt%.

[0039] (3) This invention solves the problem of high treatment costs in existing technologies: While ion exchange, membrane separation, or heating evaporation methods can produce better effluent quality, they involve issues such as ion exchange resin regeneration, membrane pore blockage, or extremely high electricity consumption, leading to high treatment costs. This invention eliminates the need for water treatment agents, resulting in a simple process and low operating costs. Furthermore, it incorporates bacteria that effectively degrade recalcitrant organic matter, eliminating the need for ozone oxidation. Simultaneously, the volume ratio of domestic sewage to high-salt, recalcitrant oilfield wastewater does not exceed 1:1, saving on domestic sewage, reducing the volume of the biological tank, and decreasing investment. This makes it particularly suitable for use in areas lacking freshwater resources, such as deserts, remote areas, and well sites. The wastewater treatment device of this invention features wide application range, strong adaptability, and low cost. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a process for treating high-salt, recalcitrant oilfield wastewater. Detailed Implementation

[0041] The following detailed and complete description of a method for treating high-salt, recalcitrant oilfield wastewater provided by the present invention is provided in conjunction with embodiments. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0042] Device Example: A schematic diagram of the high-salt, recalcitrant oilfield wastewater treatment device of the present invention is shown below. Figure 1 As shown, it includes an equalization tank, a hydrolysis acidification tank, and an aerobic tank connected in sequence by pipelines.

[0043] The principle of treating high-salinity, recalcitrant oilfield wastewater is as follows:

[0044] The equalization tank has two inlets, one for high-salinity, recalcitrant oilfield wastewater and the other for domestic sewage. The ratio of these two types of water is adjustable to meet the salinity requirements of the activated sludge in the subsequent hydrolysis-acidification and aerobic tanks. After thorough mixing in the equalization tank, the two types of water enter the hydrolysis-acidification tank through the outlet pipe. Suitable effective degradation microorganisms are added to the hydrolysis-acidification tank, and the activated sludge is then acclimated. After a certain period of acclimation, the activated sludge adapts to the salinity of the mixed water, breaking down long-chain recalcitrant organic matter in the water into short chains, branched chains, or ring structures into straight chains, reducing the toxicity of the wastewater and improving its biodegradability. The effluent from the hydrolysis-acidification tank then enters the aerobic tank, where suitable effective degradation microorganisms are added again for activated sludge acclimation. Fluidized balls are added to the aerobic tank to adsorb and multiply microorganisms, forming a biofilm that concentrates oxygen and organic matter in the surrounding area, increasing contact time, decomposing COD, and significantly improving the system's salt tolerance and resistance to shock loads. Finally, the water from the aerobic tank meets discharge standards.

[0045] The high-salt, recalcitrant oilfield wastewater in the following examples and comparative examples is the bottom wastewater of an oil depot tank. It contains 4200 mg / L of chloride ions, 10000 mg / L of salt, and is classified as high-salt wastewater. It also contains 5000 mg / L of COD and approximately 3000 mg / L of high-molecular-weight water-soluble polyethers, which are recalcitrant organic compounds.

[0046] The following are examples of wastewater treatment. In these examples, the supplier of BZT hydrolysis acidifying bacteria agent is Foshan Biwofeng Biotechnology Co., Ltd.; the supplier of aerobic bacteria is Foshan Biwofeng Biotechnology Co., Ltd., and the product name is COD removal bacteria agent (chemical wastewater).

[0047] Example 1

[0048] Wastewater treatment flow chart as follows Figure 1 As shown.

[0049] (1) Acclimation: Wastewater from the bottom of the oil depot tanks and domestic sewage were mixed at a volume ratio of 1:1 to obtain a mixed solution. Then, BZT hydrolytic acidifying bacteria and COD removal bacteria (chemical wastewater) were mixed with the above mixed solution at a volume ratio of 1:9 and added to the hydrolysis acidification tank and aerobic tank respectively. Microbial packing materials were also added to the hydrolysis acidification tank and aerobic tank respectively. Acclimation was then carried out. During acclimation, nutrients (urea and potassium dihydrogen phosphate or potassium hydrogen phosphate) were added at a COD:N:P = 100:5:1. Wastewater from the bottom of the oil depot tanks and domestic sewage were mixed at a volume ratio of 1:1 in the equalization tank. The water was changed in batches every day. The water change volume of each tank was 1 / 2 for the first 3 days of acclimation. In the next 4 days, the proportion of wastewater from the bottom of the tanks was gradually increased, and finally the volume ratio of wastewater from the bottom of the tanks and domestic sewage was 4:1. Acclimation was carried out for a total of 7 days to complete the biofilm formation and microbial acclimation of the packing materials. The microbial packing materials were glass ball packing materials containing plastic filaments, with a filling rate of 60%.

[0050] (2) After the acclimatization step is completed, the wastewater from the bottom of the oil depot tank and the domestic sewage are mixed in the equalization tank at a volume ratio of 4:1, and then successively enter the hydrolysis acidification tank and the aerobic tank. The hydraulic retention time of the sewage is 6 hours, and the COD of the effluent can be reduced to 480 mg / L, of which the content of water-soluble polyether substances is 300 mg / L, which meets the Class III standard of the "Integrated Wastewater Discharge Standard". Then it enters a certain industrial wastewater treatment plant for further treatment.

[0051] Example 2

[0052] Adopting such Figure 1 The processing device shown below performs the following processing:

[0053] (1) Acclimation: Wastewater from the bottom of the oil depot tanks and domestic sewage were mixed at a volume ratio of 1.5:1 to obtain a mixed solution. Then, BZT hydrolytic acidifying bacteria and COD removal bacteria (chemical wastewater) were mixed with the above mixed solution at a volume ratio of 1:4 and added to the hydrolysis acidification tank and aerobic tank respectively. Microbial packing materials were also added to the hydrolysis acidification tank and aerobic tank respectively. Acclimation was then carried out. During acclimation, nutrients (urea and potassium dihydrogen phosphate) were added at a COD:N:P = 100:5:1. Wastewater from the bottom of the oil depot tanks and domestic sewage were mixed at a volume ratio of 1.5:1 in the equalization tank. The water was changed in batches every day. The water change volume of each tank was 1 / 2 for the first 3 days of acclimation. In the next 4 days, the proportion of wastewater from the bottom of the tanks was gradually increased, and finally the volume ratio of wastewater from the bottom of the tanks and domestic sewage was 4:1. Acclimation was carried out for a total of 7 days to complete the biofilm formation and microbial acclimation of the packing materials. The microbial packing materials were glass ball packing materials containing sponges, with a filling rate of 65%.

[0054] (2) After acclimatization, high-salt, difficult-to-degrade oilfield wastewater and domestic sewage were added to the equalization tank through pipelines at a volume ratio of 3:1 and mixed evenly. They were then sequentially introduced into the hydrolysis acidification tank and the aerobic tank. The hydraulic retention time of the sewage was 12 hours, and the COD of the effluent could be reduced to 240 mg / L, with a removal rate of 95.2%. The content of water-soluble polyether substances was about 100 mg / L, which met the Class III standard of the "Integrated Wastewater Discharge Standard". The effluent was then sent to an industrial wastewater treatment plant for further treatment.

[0055] Example 3

[0056] Adopting such Figure 1 The processing device shown below performs the following processing:

[0057] (1) Acclimation: Wastewater from the bottom of the oil depot tanks and domestic sewage were mixed at a volume ratio of 1:1 to obtain a mixed solution. Then, BZT hydrolytic acidifying bacteria and COD removal bacteria (chemical wastewater) were mixed with the above mixed solution at a volume ratio of 1:1 and added to the hydrolysis acidification tank and aerobic tank respectively. Microbial packing materials were also added to the hydrolysis acidification tank and aerobic tank respectively. Acclimation was then carried out. During acclimation, nutrients (urea and potassium dihydrogen phosphate or potassium hydrogen phosphate) were added at a COD:N:P = 100:5:1. Wastewater from the bottom of the oil depot tanks and domestic sewage were mixed at a volume ratio of 1:1 in the equalization tank. The water was changed in batches every day. The water change volume of each tank was 1 / 2 for the first 3 days of acclimation. In the next 4 days, the proportion of wastewater from the bottom of the tanks was gradually increased, and finally the volume ratio of wastewater from the bottom of the tanks and domestic sewage was 4:1. Acclimation was carried out for a total of 7 days to complete the biofilm formation and microbial acclimation of the packing materials. The microbial packing materials were glass ball packing materials containing plastic filaments, with a filling rate of 60%.

[0058] (2) After acclimatization, high-salt, difficult-to-degrade oilfield wastewater and domestic sewage are added to the equalization tank through pipelines at a volume ratio of 1:1 and mixed evenly. They are then sequentially introduced into the hydrolysis acidification tank and the aerobic tank. The hydraulic retention time of the sewage is 12 hours, and the COD of the effluent can be reduced to 120 mg / L, with a removal rate of 97.6%. The content of water-soluble polyether substances is 90 mg / L, which meets the Class II standard of the "Integrated Wastewater Discharge Standard" and is discharged in compliance with the standard.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that the wastewater treatment methods used in this example are advanced oxidation, ozone, air flotation, and conventional activated sludge process in sequence. The rest is the same as in Example 1. The final test result is that the COD content is reduced to 2000 mg / L, which does not meet the discharge standard.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 3 is that the volume ratio of wastewater to domestic sewage is 1:0.7. The effluent COD can be reduced to 550 mg / L, with a removal rate of 89%, and the content of water-soluble polyether substances is 450 mg / L.

[0063] Comparative Example 3

[0064] The difference between this comparative example and Example 3 lies in the aerobic bacteria added to the aerobic tank; specifically, it uses Baojinqing No. 1 special bacteria, commercially available from Shanghai Dongqin Environmental Protection Biotechnology Co., Ltd. Its effluent COD can be reduced to 600 mg / L, with a removal rate of 88%, and the water-soluble polyether content is 430 mg / L. The supplier of Baojinqing No. 1 special bacteria is Shanghai Dongqin Environmental Protection Biotechnology Co., Ltd.

[0065] Comparative Example 4

[0066] The difference between this comparative example and Example 3 is that tap water was added instead of domestic sewage. The effluent COD was reduced to 500 mg / L, with a removal rate of 90%, and the water-soluble polyether content was 400 mg / L.

[0067] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A method for treating high-salt, recalcitrant oilfield wastewater, characterized in that, Includes the following steps: (1) Anaerobic bacteria domestication: Mix high-salt, difficult-to-degrade oilfield wastewater and domestic sewage, and then add anaerobic bacteria for domestication; (2) Aerobic bacteria domestication: Mix high-salt, difficult-to-degrade oilfield wastewater and domestic sewage, and then add aerobic bacteria for domestication; (3) Wastewater treatment: High-salt, difficult-to-degrade oilfield wastewater and domestic sewage are mixed and then sequentially fed into acclimatized anaerobic bacteria containers and aerobic bacteria containers. After hydrolysis and acidification treatment and aerobic treatment, the wastewater is discharged after meeting the standards. The aerobic bacteria mentioned in step (2) are COD removal agents; The anaerobic bacteria mentioned in step (1) are BZT hydrolytic acidifying bacteria; The high-salt, recalcitrant oilfield wastewater has a salt content of 8,000-40,000 mg / L, a COD content of 1,000-20,000 mg / L, and a high molecular weight water-soluble polyether content of 1,000-10,000 mg / L.

2. The processing method according to claim 1, characterized in that, During the acclimatization process in steps (1)-(2), the volume ratio of the high-salt, difficult-to-degrade oilfield wastewater to domestic sewage is 1-1.5:

1.

3. The processing method according to claim 1, characterized in that, The volume ratio of the high-salt, recalcitrant oilfield wastewater and domestic sewage mentioned in step (3) is 1-5:

1.

4. The processing method according to claim 1, characterized in that, The domestic sewage mentioned in steps (1)-(3) is fecal water.

5. The processing method according to claim 1, characterized in that, The concentration of anaerobic bacteria in the system in step (1) is 10-50%, and nutrients are added during the domestication process at a ratio of COD:N:P = 100:5:

1.

6. The processing method according to claim 1, characterized in that, In step (2), the concentration of aerobic bacteria in the system is 10-50%, and nutrients are added during the acclimatization process at a ratio of COD:N:P = 100:5:

1.

7. The processing method according to claim 1, characterized in that, In steps (1)-(2), microbial packing material is also added.

8. The processing method according to claim 7, characterized in that, The microbial packing material is a glass ball packing material, which contains plastic filaments or sponge inside, and the packing material has a filling rate of more than 50%.

9. The processing method according to claim 1, characterized in that, The acclimatization time for steps (1)-(2) is 6-8 days.

10. The processing method according to claim 1, characterized in that, The hydrolysis acidification treatment or aerobic treatment in step (3) takes 2-24 hours and the treatment temperature is 5-40℃.

11. A device for treating high-salt, recalcitrant oilfield wastewater, characterized in that, For implementing the treatment method according to any one of claims 1-10, the apparatus comprises an equalization tank, a hydrolysis acidification tank, and an aerobic tank connected in sequence; the equalization tank is used to mix high-salt, recalcitrant oilfield wastewater and domestic sewage, the hydrolysis acidification tank is used for hydrolysis acidification treatment, and the aerobic tank is used for aerobic treatment.

12. The processing apparatus according to claim 11, characterized in that, The device is used to first add high-salt, difficult-to-degrade oilfield wastewater and domestic sewage into the equalization tank through pipelines, mix them evenly, and then sequentially enter the hydrolysis acidification tank and the aerobic tank. Finally, the water in the aerobic tank is discharged after meeting the standards.

13. The application of the treatment method according to any one of claims 1-10 or the treatment apparatus according to any one of claims 11-12 in the treatment of wastewater.

14. The application according to claim 13, characterized in that, The wastewater is high-salt, recalcitrant oilfield wastewater.

Images