Sampling Industrial Effluent Discharged to Municipal Sewer Systems

Many Quebec municipalities have by-laws governing discharges to the sewer system. Among other things, these by-laws set maximum allowable concentrations for various contaminants. To ensure that your industrial or commercial business complies with these by-laws, you need to have your effluents characterized.

In this article, we discuss the reasons for having your industrial effluents sampled and the two types of effluent sampling (grab sampling and composite sampling), and we conclude with the three composite sampling methods.

Why characterize your industrial effluents?

Effluent characterization may be required to determine the pollutant load generated by an industrial process, to size treatment equipment, or to ensure that discharges to the sanitary sewer system comply with a municipal by-law such as Montréal’s CMM 2008-47 or Québec City’s RAVQ 1124.

Industrial effluent characterization is also often required when submitting an authorization application to Quebec’s Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs (MELCCFP).

What is grab sampling of industrial effluent?

Grab sampling is the simplest type of sampling. It consists of taking a single sample over a short period, usually less than 15 minutes. The sample is generally collected manually. A minimum of one litre of the effluent to be characterized is usually required.

Grab sampling is used when the effluent’s quality and flow are very stable, or when a profile of how the effluent changes over time is needed.

Grab sampling may also be necessary when the contaminants in the effluent are likely to be altered by a sampling method that involves long holding times, as is the case with composite sampling.

Special precautions must be taken when certain contaminants, such as volatile organic compounds, are suspected, or when certain specific analyses are required:

• Microbiological analyses
• Aquatic toxicity analyses
• Chemical analyses of sulphides and cyanides

What is composite sampling of industrial effluent?

Composite sampling involves taking several samples that are then combined. Samples can be collected manually, but using an automatic sampler is preferable. The sampling period is generally 24 hours.

A large number of 50 mL samples are generally collected and mixed together to form the composite sample. The total volume collected must be more than 1.5 times the minimum volume required for laboratory analyses.

How to split a composite sample of industrial effluent

If the composite sample must be split to meet the specific needs of the analyses, splitting at the collection site is preferred. Proceed as follows:

1. Stir the composite sample until the mixture is homogeneous
2. Remove the caps from the containers supplied by the laboratory
3. Transfer the sample:
   1. Add less than one third of the required volume to each container
   2. Keep stirring the composite sample during the transfer
   3. Repeat until all the containers supplied by the laboratory are full
4. Put the correct caps back on the correct containers
5. Label the containers

It is important to keep the containers at a temperature below 4 °C during the transfer and during transport to the laboratory.

Sample conditioning

Some analyses may require the sample to be filtered. If so, 0.45 µm filters should be used. Other analyses may require preservatives, which are generally supplied by the analytical laboratory.

What is time-proportional sampling of industrial effluent?

Time-proportional sampling is a type of composite sampling. A fixed volume is collected at regular intervals, with at least 6 samples taken per hour.

For a typical 24-hour industrial effluent characterization, for example, 24 samples of 50 mL would be taken, one every hour.

What is flow-proportional sampling of industrial effluent?

Flow-proportional sampling is a type of composite sampling. Samples are collected according to the effluent flow. Over a 24-hour period, more samples are taken when the effluent flow is high and fewer when it is low. This provides a more representative picture of the contaminant load discharged to the sewer.

What is hybrid composite sampling of industrial effluent?

In some cases, it may be advisable to divide the 24-hour period into three 8-hour periods to form three separate composite samples. This is known as hybrid composite sampling.

Consult water quality measurement and monitoring specialists

Each of the sampling methods presented in this article has its advantages and disadvantages. Each is suited to specific uses, and some are required by regulation. Consult Avizo Experts-Conseils’ water quality measurement and monitoring specialists to determine which method applies to your situation.

References

• https://www.ceaeq.gouv.qc.ca/documents/publications/echantillonnage/rejets_liquidesC2.pdf
• https://www.ceaeq.gouv.qc.ca/documents/publications/echantillonnage/Cahier2Addenda_section4.pdf