Rapid measurement method for BOD (Biochemical Oxygen Demand) in sewage treatment

Abstract

The invention relates to the technical field of sewage treatment, in particular to a method for rapidly measuring BOD (Biochemical Oxygen Demand) in sewage treatment. According to the method, under the anaerobic condition, facultative anaerobic microorganisms are subjected to denitrification reaction by utilizing organic matters and nitrate nitrogen in a water sample to be detected, in the process, the organic matters are oxidized into carbon dioxide and water by utilizing atomic oxygen in the nitrate nitrogen, and the nitrate nitrogen is reduced into nitrite nitrogen or nitrogen; in the process, the reduction amount of the oxygen element in the reaction system before and after the reaction is the BOD of the water sample to be detected. Compared with traditional BOD5, the method disclosed by the invention is shorter in time consumption and greatly improves the detection efficiency, and meanwhile, compared with an aerobic method during BOD5 measurement, the method disclosed by the invention effectively avoids the oxygen consumption of aerobic proliferation of microorganisms in the process, so that the detection accuracy is improved, and the method is convenient to popularize and use.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a method for quickly measuring BOD in sewage treatment. Background Art

[0002] BOD is the biochemical oxygen demand of sewage. There are many organic pollutants in sewage. Some organic matter can be metabolized into carbon dioxide and water by microorganisms, while others cannot. We express the amount of organic matter that can be directly degraded by microorganisms by the amount of oxygen required by microorganisms in degrading the organic matter. The more oxygen is used, the more biodegradable organic matter is in the sewage, and the more serious the pollution is. The unit is mg / L.

[0003] The existing method is to reduce the dissolved oxygen due to respiration through the natural proliferation and degradation of organic matter by aerobic microorganisms in the presence of dissolved oxygen. Since the process is slow, the laboratory usually cultures for five days, which is called the five-day biochemical oxygen demand (BOD5). However, in the process of microbial proliferation, both the degradation of organic matter and self-proliferation require oxygen. Since the proliferation rate of aerobic microorganisms is considerable, combining the two as the BOD value of sewage is not accurate. At the same time, the test preparation is cumbersome, the time span is as long as 5 days, the culture preparation is complicated, the experimental conditions are strict, the calculation formula is complicated, and it is not easy to use. In addition, the existing method only focuses on the BOD value under aerobic conditions. However, most of the organic matter in sewage assists microorganisms in denitrification and phosphorus removal under anaerobic conditions, and is also oxidized into carbon dioxide and water. This is not paid attention to in the existing methods.

[0004] Therefore, developing a simpler and faster BOD measurement method is of great significance for the accurate and rapid detection of sewage indicators, and also plays a positive and beneficial role in sewage treatment. Summary of the invention

[0005] The purpose of the present invention is to provide a rapid measurement method for BOD in sewage treatment to solve the problem that the existing measurement method is time-consuming, is affected by the proliferation of aerobic microorganisms themselves, and is not accurate.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for rapid measurement of BOD in sewage treatment, comprising the following steps:

[0007] S1. Take the effluent from the aerobic tank of the sewage treatment plant, let it settle, discard the supernatant and take the activated sludge;

[0008] S2, add a certain amount of water sample to be tested and excess nitrate nitrogen solution to the activated sludge in S1, add water to make up the volume and stir to homogenize;

[0009] S3, avoiding full reaction under aeration conditions, and after the reaction is complete, measuring the contents of nitrate nitrogen and nitrite nitrogen in the reaction solution;

[0010] S4. Calculate the BOD of the water sample to be tested based on the data in S2-S3.

[0011] Furthermore, in the S1, the static sedimentation time is 20 to 30 minutes, and the mud-water interface is clear.

[0012] Furthermore, in S2, the COD of the water sample to be tested is measured; after adding water to make the volume, the concentration ratio of COD to nitrate nitrogen in the mixed system is 3 to 5:1.

[0013] Furthermore, in the above-mentioned S2-S3, a magnetic stirrer is used, the magnetic rotation speed is 60-100 rpm, and there is no splash on the liquid surface.

[0014] Furthermore, in the S3, samples are collected at regular intervals during the reaction, and when the nitrate nitrogen concentration no longer decreases, the sampling is stopped, at which point the reaction is complete.

[0015] Furthermore, in the S4, the difference between the oxygen content in the nitrate nitrogen before the reaction and the oxygen content in the remaining nitrate nitrogen and the generated nitrite nitrogen after the reaction is the BOD of the water sample to be tested.

[0016] Beneficial effects of the present invention:

[0017] 1. The method of using high-concentration activated sludge in the present invention is faster and more efficient. Compared with the traditional BOD5, the method of the present invention only takes half a day to complete, which effectively improves the efficiency of detection.

[0018] 2. The method of the present invention has higher accuracy. Compared with the traditional BOD5, the method of the present invention is carried out under anaerobic conditions. Under anaerobic conditions, the proliferation of facultative anaerobic microorganisms is only 5% of that of aerobic microorganisms, which effectively improves the accuracy of the detection and is convenient for promotion and use. DETAILED DESCRIPTION

[0019] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0020] Example 1

[0021] A water sample to be tested was taken, and its COD (chemical oxygen demand) was measured. The dichromate method (HJ 828-2017) was adopted in the process. After measurement, the COD in the water sample to be tested was 425 mg / L.

[0022] Take the effluent from the end of the aerobic tank of the sewage treatment plant and let it stand for 20 to 30 minutes until a clear mud-water interface appears. After the standing is completed, carefully pour out the supernatant and take the remaining activated sludge.

[0023] In this embodiment, 300 mL of activated sludge was taken, 5 mL of sodium nitrate solution with a nitrogen content of 5 g / L and 200 mL of the water sample to be tested were added thereto, and water was added to make the volume to 1000 mL. Aeration was avoided (air holes were provided), and a magnetic stirrer was used to stir and mix at 60-100 rpm. The reaction was started when there was no splash on the liquid surface.

[0024] At the beginning of the reaction, the dissolved oxygen content in the mixed solution was measured by the DO electrode to be 0.43 mg / L; at the same time, sampling was immediately taken after the reaction started to measure the initial nitrate nitrogen concentration in the reaction solution (nitrate nitrogen will remain in the activated sludge, and the residual nitrite nitrogen and COD can be ignored), and then sampling was taken every 0.5 h to measure the nitrate nitrogen and nitrite nitrogen contents in the reaction solution (HG 634-2012) until the reaction was complete; it was measured that at the beginning of the reaction, the nitrate nitrogen content in the reaction solution was 25.7 mg / L.

[0025] After the reaction is complete (when the nitrate nitrogen concentration no longer decreases and the nitrite nitrogen no longer increases, which generally takes 2.5 to 4 hours), it is measured that the remaining nitrate nitrogen content in the reaction solution is 13.3 mg / L, the nitrite nitrogen content is 0.015 mg / L, and the dissolved oxygen content is 0.12 mg / L.

[0026] Therefore, initially, the content of oxygen in the reaction solution is:

[0027] Q1=25.7÷14×16×3+0.43=88.54mg / L

[0028] After the reaction is complete, the content of oxygen in the reaction solution is:

[0029] Q2=13.3÷14×16×3+0.015÷14×16×2+0.12=45.75mg / L

[0030] Therefore, the amount of oxygen consumed in the reaction process is 42.79 mg / L. Since the water sample to be tested is diluted 5 times, the BOD of the water sample to be tested in this embodiment is about 214 mg / L.

[0031] During the implementation of the method of the present invention, it is necessary to measure the dissolved oxygen content in the reaction solution before and after the reaction. A DO electrode is used in the process. However, in actual operation, when the dissolved oxygen content is low, the measurement of the DO electrode is not accurate and is prone to large errors. Therefore, during the specific implementation of the method of the present invention, the measurement process of the dissolved oxygen content can be omitted. After omitting this step, on the one hand, the operation is simpler, and on the other hand, it will not cause a great impact on the measurement result. For example, after removing the dissolved oxygen measurement step as mentioned above, the final calculated BOD is about 212 mg / L, which is almost the same as the measured dissolved oxygen and has no impact on the actual project.

[0032] In addition, it should be noted that in this embodiment, the content of nitrite nitrogen generated is relatively small, but in actual engineering, due to the variety of sewage types, such as industrial wastewater, more nitrite nitrogen will be produced. Therefore, nitrite nitrogen must be considered and cannot be omitted. However, the principle is the same and will not be repeated.

[0033] In actual measurement, a blank reference may also be set, such as replacing the water sample to be tested with tap water or purified water, to illustrate the accuracy of the measurement of the method of the present invention.

[0034] In practical engineering applications, the method of the present invention can also directly estimate the COD value of the effluent. For the COD and BOD changes of the inlet and outlet water, the following relationship is satisfied:

[0035] COD 进水 -BOD 进水 =COD 出水 +BOD 出水

[0036] In the above formula, BOD is measured by the method of the present invention. The BOD measured by the method of the present invention is an absolute value (the traditional BOD5 is a relative value), where BOD 出水 Can be ignored, that is:

[0037] COD 进水 -BOD 进水 =COD 出水

[0038] In other words, knowing the influent COD and BOD values ​​can estimate the effluent COD value, which is of great significance for the judgment of microbial treatment of industrial wastewater.

[0039] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for rapid measurement of BOD in sewage treatment, characterized in that: The following steps are involved: S1. Take the effluent from the aerobic tank of the sewage treatment plant, let it settle, discard the supernatant and take the activated sludge; S2, add a certain amount of water sample to be tested and excess nitrate nitrogen solution to the activated sludge in S1, add water to make up the volume and stir to homogenize; S3, avoiding full reaction under aeration conditions, and after the reaction is complete, measuring the contents of nitrate nitrogen and nitrite nitrogen in the reaction solution; S4. Calculate the BOD of the water sample to be tested based on the data in S2-S3.

2. The method for rapid measurement of BOD in sewage treatment according to claim 1, characterized in that: In the S1, the static sedimentation time is 20 to 30 minutes, and the mud-water interface is clear.

3. The method for rapid measurement of BOD in sewage treatment according to claim 1, characterized in that: In the S2, the COD of the water sample to be tested is measured; after adding water to make up the volume, the concentration ratio of COD to nitrate nitrogen in the mixed system is 3 to 5:

1.

4. The method for rapid measurement of BOD in sewage treatment according to claim 1, characterized in that: In the above-mentioned S2-S3, a magnetic stirrer is used, the magnetic spindle speed is 60-100 rpm, and there is no splash on the liquid surface.

5. The method for rapid measurement of BOD in sewage treatment according to claim 1, characterized in that: In the above-mentioned S3, samples are collected at regular intervals during the reaction, and when the nitrate nitrogen concentration no longer decreases, the sampling is stopped, indicating that the reaction is complete.

6. The method for rapid measurement of BOD in sewage treatment according to claim 1, characterized in that: In the above-mentioned S4, the difference between the oxygen content in the nitrate nitrogen before the reaction and the oxygen content in the remaining nitrate nitrogen and the generated nitrite nitrogen after the reaction is the BOD of the water sample to be tested.