Sewage sampling

- Aug 13, 2020-

1. Sewage sampling point of sewage treatment plant

   (1) The sampling points of the first type of sewage specified in the national comprehensive sewage discharge standard are all set at the discharge outlet of the workshop or workshop treatment facility or the discharge outlet of the facility for the treatment of such pollutants.

   (2) Sampling points for the second type of pollutants are all located at the outlet of the pollutant discharge unit.

   (3) When monitoring the efficiency of the entire sewage treatment facility, set up sampling points at the inlets of various sewage treatment facilities and the total discharge outlets of the sewage treatment facilities.

   (4) When monitoring the efficiency of each sewage treatment unit, set up sampling points at the inlets of various sewage treatment facilities and the total discharge outlets of sewage treatment facilities.

  (5) Set up water monitoring points at the sewage discharge outlets and the inlets and outlets of sewage treatment facilities.

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2. Sewage sampling frequency of sewage treatment plant

   The sampling frequency of the urban sewage treatment plant is at least once every two hours, and the 24h mixed sample is taken and calculated on a daily basis. Industrial wastewater monitoring frequency, production cycle <8h, sampling once every 2h, production cycle>8h, sampling once every 4h. For other sewage samples, no less than 2 times within 24 hours. The maximum allowable emission concentration is calculated based on the daily average value.

   

3. Sewage sampling equipment of sewage treatment plant

  Sampling can be used colorless hard glass bottle with stopper or polyethylene bottle with stopper or bucket.

   (1) Shallow water sampling

When wastewater is discharged into public waters in the form of canals, appropriate weirs should be set up. Containers or long-handled water scoops can be used to directly sample from the overflow of the weir. When sampling in sewage pipes or channels, water samples should be collected at parts with liquid flow.

   (2) Deep water sampling

It is suitable for the collection of water samples in wastewater or sewage treatment tanks, and can be collected with a dedicated deep sampler.

   (3) Automatic sampling

Use automatic sampler or continuous automatic timing sampler to collect. In a production cycle, a certain amount of water samples can be collected in different containers according to a time program; during automatic mixing sampling, the sampler can periodically and continuously collect a certain amount of water samples or water samples collected according to the flow ratio. In a container.

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4. Sewage sampling volume of sewage treatment plant

In principle, calculate the required amount of water samples based on the number of monitoring items, and collect water samples based on 1.1 to 1.3 times the required amount. The sampling volume of a single monitoring item should be between 50 ~ 500ml, and 2L of water sample for general physical and chemical analysis.

  

5. Sampling methods and precautions for sewage treatment plants

  1) Sampling method

The basic requirement for collecting water samples in sewage treatment plants is that the water samples taken are representative. Attention should be paid when sampling: fixed time, fixed starting point, fixed quantity, and fixed method. At the same time make a record.

   2) Matters needing attention

   When sampling, carefully collect water samples according to the sampling plan, and make the water samples do not deteriorate or become contaminated before analysis.

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6. Storage of water samples

   

1. Factors affecting water quality changes

   Physical effects: the volatilization and loss of volatile components; the absorption of the components on the side of the container wall and suspended solids in the water; the dissolution of the components to be tested from the walls and suspended solids, etc.

  Chemical action: biological action such as the occurrence of redox: the activities of bacteria and other microorganisms and algae change the components to be tested; in addition, the death of microorganisms and algae releases certain components into the water.

  

2. Water sample storage container

  The commonly used container materials for storing water samples are borosilicate glass, quartz, polyethylene and polytetrachloroethylene.

  A. The container cannot be a new source of pollution. For example, borosilicate glass bottles cannot be used when measuring silicon and boron.

   B. The container wall should not absorb or adsorb certain components to be tested. For example, when measuring organic matter, polyethylene bottles cannot be used.

  C. The container cannot react with certain components to be tested. For example, when measuring oxygen, water samples should not be stored in glass bottles.

  D. For the determination of light-sensitive components, the water sample should be stored in a brown reagent bottle. Preservation of sewage water samples of sewage treatment plants

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3. How to preserve water samples

  A: refrigerate or freeze

It can inhibit the activities of microorganisms and slow down the speed of physical effects and chemical reactions. If the water sample is stored under freezing conditions of -18~-22°C, the stability of monitoring items such as phosphorus, nitrogen, silicon compounds and biochemical oxygen demand in the water sample will be significantly improved, and it will not affect the subsequent analysis and determination.

  B: Add preservation medicine

Adding appropriate preservation reagents to the water sample can inhibit the activity of microorganisms and slow down the occurrence of redox reactions. The method of adding can be added immediately after sampling; it can also be added in separate bottles as needed when the water sample is divided.

  C: filtration and centrifugal separation

Turbidity of the water sample will also affect the analysis results. The filter with proper pore size can effectively remove algae and bacteria, and the stability of the filtered sample is improved. Generally speaking, clarification, centrifugation, filtration and other measures can be used to separate suspended solids in water samples.

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4, the storage conditions of water samples

   The allowable storage time of the water sample is related to many factors such as the nature of the water sample, the analysis index, the acidity of the solution, the storage container and the storage temperature. The allowable storage time for different water samples is also different. It is generally believed that the maximum storage time of water samples is: 72 hours for clean water samples, 48 hours for lightly polluted water samples, and 12 hours for heavily polluted water samples.