Wastewater sample collection is a fundamental step in water quality monitoring, pollution control and environmental assessment. Its standardization directly affects the accuracy and reliability of subsequent analysis results. The following key issues need to be noted during the collection process:
I. Preparations Before Sampling
Clarify the plan: Determine the monitoring points, frequency, water sample type (instantaneous sample/mixed sample, etc.) and testing items based on the monitoring purpose to ensure representativeness.
Container adaptation: Select the material according to the project (such as polyethylene bottles for heavy metals and brown glass bottles for organic substances), clean in advance and affix labels (point location, time, etc.).
Tools and Protection: Use inert material sampling tools (stainless steel, polytetrafluoroethylene), and provide protective equipment such as gloves and goggles for toxic sewage.
Ii. Key Points of the Sampling Process
Accurate location: Select areas with smooth water flow and uniform mixing (such as the middle of the pipeline, 10-30cm below the liquid surface), avoiding dead corners and sediment areas. Sampling at the sewage outlet should be conducted at 3 to 5 times the pipe diameter downstream.
Quantity and bottling: The sampling volume should meet the testing requirements and leave a margin of 10% to 20%. Special projects should pay attention to the filling degree (for example, VOCs need to be filled to the brim to prevent volatilization).
Method specification: For stable water quality, instantaneous samples should be taken; for large fluctuations, mixed samples should be collected based on the time/flow ratio. Avoid stirring the sediment at the bottom to prevent excessive impurities from being mixed in.
On-site treatment: Record water temperature, pH, appearance of sewage and working conditions; Water samples that need to be fixed should be treated on-site (such as adding nitric acid to heavy metals to adjust pH to less than 2), and direct sunlight should be avoided.
Iii. Post-sampling Management
Transportation and storage: Sealed and leak-proof, stand upright; Water samples that need to be refrigerated (such as BOD and microorganisms) should be transported in a 0-4℃ refrigerated container to prevent cracking due to freezing.
Time control: Control the storage time as required by the project (such as code testing within 24 hours), and send for inspection in a timely manner.
Handover record: Verify information with the laboratory, sign the handover form, and ensure traceability and traceability.
Iv. Special Circumstances
Containing a large amount of suspended solids: Filter through a 63μm screen and record.
Sudden pollution: Increase frequency, expand scope, and give priority to collecting original water samples.
Rain and snow weather: Indicate the impact to avoid dilution and interference by rainwater.