What are the requirements for sampling with a COD analyzer?

The sampling requirements for water quality samples of cod analyzers are the knowledge that needs to be known for monitoring the environment. cod is an important indicator of environmental pollution. Let me tell you that in the process of sewage treatment, the turbidity of the monitored water samples is obvious. Therefore, in order to obtain accurate COD monitoring results, it is necessary to obtain representative samples. In order to achieve this purpose, the following requirements are required. Several factors are fully understood: Sampling requirements of the cod analyzer 1. Fully shake the water sample. For COD determination of wastewater with high concentration and treated wastewater with medium concentration, it is necessary to plug the sample bottle tightly before sampling. Shake it fully to disperse all kinds of particles and lumps in the water sample as much as possible, so that some more uniform and representative water samples can be pipetted. In addition, for the basically qualified wastewater that becomes clear after treatment and has a low concentration, it is also necessary to fully shake the water sample before taking a sample for measurement. In the process of measuring COD in a large amount of sewage, it is known that the water samples measured after fully shaking are not prone to deviation, so it can be concluded that this sampling method is typical and representative. Sampling requirements of the cod analyzer 2. After the water sample is shaken, it needs to be sampled as soon as possible because there are a lot of various inhomogeneous suspended solids in the sewage. If the sample cannot be sampled quickly after shaking well, the suspended solids will sink quickly. Sampling The concentration of the water sample obtained by the distribution of the suction port of the pipette at the upper, middle and lower positions of the sample bottle is also different, especially the composition of the suspended solids is quite different, which cannot be used to determine the actual situation of the sewage. For a true and accurate response, the measured results are not representative. Therefore, samples need to be taken immediately after the water sample is shaken. This makes the absolute quantity form an error phenomenon, but the error caused by the absolute quantity and the error caused by the sample representativeness can not be taken into consideration. After fully shaking it, put the relatively Compared with the water samples taken for a long time and the shaken water samples measured immediately, the difference between the results of the former measurement and the actual water quality is obvious. Sampling requirements of the cod tester 3. Adjust the calibration standard Because the particle size of the suspended particulate matter in the water sample is usually larger than the diameter of the outlet nozzle of the pipette, when using a standard pipette to pipette domestic sewage samples, the The suspended matter in the sample cannot always be taken smoothly. Therefore, in this case, the measured result is only a small amount of sewage COD value that has removed suspended solids. Secondly, even if it is successfully pipetted onto a small portion of fine suspended matter, due to the influence of the pipette nozzle, the time to select the full scale is longer than the actual time, and the suspended matter that has been fully shaken in the sewage will Slowly settling, resulting in insufficient uniformity of the water samples taken, which cannot truly represent the actual water quality, and the results of the measured water samples vary greatly. Therefore, if a pipette with a fine suction port is used to draw a domestic sewage sample, the COD measurement results cannot be guaranteed to be correct. Therefore, in the process of pipetting domestic sewage water samples, especially water samples with a large number of suspended particles, it is necessary to properly modify the pipetting, enlarge the pore diameter, so that the suspended matter can be sucked as soon as possible, and then adjust the scale line to ensure a smoother measurement process. . Sampling requirements of cod analyzer 4. Sampling volume should be appropriate. If the sampling volume is too small, some kind of sewage can cause particles with high oxygen consumption to be taken out due to uneven effect, then the COD result measured in this way is the same as the actual situation. The difference between the oxygen demand of the sewage will be relatively obvious. For the same sample, use the same conditions such as 2.00, 10.00, 20.00 and 50.00mL of sampling volume to do the measurement experiment. There is a large gap in the water quality, and the regularity of the statistical data is not very obvious. When the water samples are 10.00 and 20.00mL, the regularity of the measurement results is relatively improved, and the 50.00mL water sample is taken. The COD results obtained have good regularity. Therefore, for sewage with a high COD concentration, it is necessary to use several methods for measurement to ensure that the sample has sufficient sampling volume. In highly representative cases, the addition of potassium bicatalyte should be adjusted to meet the water quality requirements of special samples. Requirements, the accuracy of the measured data results in this way is more obvious.
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