Sewage Treatment Knowledge articles: Analysis of common problems in COD determination and solutions

As an essential project for water quality monitoring, COD determination often encounter a variety of problems, the treatment of these problems is directly related to the accuracy of wastewater treatment, today Xiaobian summary for everyone in the COD measurement common Problems and solutions.

1, no reagent or water sample alarm

(1) Blocking of the sampling tube Unable to mention reagent, check the blockage, clean or replace the blocked tube.

(2) If the 9-way valve is clogged, the 9-way valve can be disassembled for cleaning if the plug can not be removed externally.

(3) sampling tube leakage, check the sampling tube and the nine-way valve connected to each screw, whether the compression, with or without leakage, if any, please re-connect the pipeline and compressed.

(4) High and low signal is not identified, check the light signal of the signal board and high and low signal If the signal board is no problem, please replace the light source (usually emitting and receiving light damage).

(5) No corresponding reagent, check and make up the appropriate reagent.

(6) Peristaltic pump tube damaged or not compressed caused by insufficient negative pressure pumping liquid, check the peristaltic pump tube to see if there is damage, such as damaged, please replace the new pump tube, and compressed.

2, the temperature anomalies?

(1) Actual temperature greater than 500 ° C Check temperature transmitter or A / D module is damaged

(2) The actual temperature is less than 200 thermocouple or A / D damage

3, COD in the normal silver sulfate, pumping silver sulfate added to the digestion tank inside. When the valve switches to silver sulfate again, the liquid in the reagent tubes of potassium dichromate and mercury sulfate is quickly returned to the corresponding reagent bottle.

Analysis: First of all, we will consider the nine-way valve caused by the valve, the nine-way valve removed to repair or replace a new nine-way valve to try again, or the situation. After the inspection found to be digestion tank inside the white with a fixed black soft leather pad plug off, resulting in the switch valve position, digestion pool pull is not solid, causing the above mentioned situation!

4, manually switch the nine-way valve to the location of digestion pool, did not hear the corresponding sound of the solenoid valve?

Analysis: There may be caused by the digestion tank seal is not good, it may be caused by the coil of the solenoid valve burned. Two cases of the scene have been ruled out by inspection, not the reasons for the above two places, after inspection found that from the PLC to control the solenoid valve relay control line caused by poor contact. Replace a new control line, the equipment is operating normally.

5, COD equipment in the case of standby can not be converted from the manual state to the measurement state?

Analysis of the reasons: check the password 1111 → calibration cycle → valid → no modification of the date of use, the normal should be changed December 12, 12. If you still can not check the settings of the parameters right. If not enough to re-PLC and touch screen from the new program.

6, COD equipment no problem in the calibration, but when the water was heated just prompt photoelectric abnormalities?

Analysis: First check the measured optical signals, look at the number of optical signals, is less than 100. The digestion tank outside the open lid found digestion tank glass tube liquid is relatively cloudy, but also with a white precipitate. The final confirmation is the reagent 3 (silver sulfate) problem, replace a bottle of new silver sulfate, the device measured water samples normal.

7, COD alarm and prompted into the drainage error?

Cause Analysis:

1, first check the level of the optical signal value is normal, if the level of the optical signal value difference of more than 300, the system will alarm and prompt into the drain error or peristaltic pump has been reversed;

2, if the level of optical signal is normal, then it is necessary to check whether the connecting shaft of the stepper motor driven by the nine-way valve is loose (the connecting shaft of the motor that drives the nine-way valve has a hexagon socket to fasten it. If Loosening will cause the connecting shaft loose, driven by nine-way valve to valve in place caused by the intake and exhaust errors);

3, if the above two points are no problem and nine-way valve is normal, then you need to change the program.

8, the measurement data fluctuations

Analysis: First check the indoor temperature is normal, to see whether the normal operation of air conditioning. Check the signal fluctuation to see if the equipment is connected to ground. Check the heating temperature is normal (heating wire without break, temperature transmitter is normal)

9, when the water sample COD value is less than 30, the instrument may be 0, how to avoid 0?

The solution: confirm the water sample signal is lower than the distilled water signal under the premise of the calibration cycle interface, the original calibration immediately defaults to 1, to 2. Then re-calibration, water samples will not COD 0.

10, COD digester burst several possible reasons, how to avoid digestion burst?

(1) digestion solenoid valve is not closed, there is leakage phenomenon.

Phenomenon: observe the heating digestion process, there are bubbles, the liquid boiling phenomenon, serious, the digester liquid from the tube out. Attention to safety, once found a bubble, to immediately stop digestion. Find the reason, then test. (Note: The reagent tube connecting the digestion tank and the 9-way valve must be fixed so as to avoid the detachment under strong pressure.)

(2) reagent problem. Reagents with the wrong, or other reasons lead to mention the reagent.

(3) The digester inlet is clogged, unable to join the potion, or the liquid can not be discharged from the digester to the metering tube.

(4) The digester glass itself has flaws, or in the maintenance, maintenance, disassemble the digester, the installation screwed too tight, resulting in damage to the glass.

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