Table 10-7. - Procedures for Manual Wastewater Sample Collection
samples are also used when a batch dump or sludge discharge is seen.
A composite sample yields data about the wastewater over a longer span of time. A series of grab samples may be taken over a certain amount of time and combined to form a composite sample. These samples should show the time and frequency of the sample; for example, an 8-hour composite of 30-minute grab samples. The composite sample is used to find BOD, COD, suspended solids, and nutrients.
The composite may be flow proportional. For this type of sample, the volume of the sample changes in proportion to the flow. The flow- proportional composite sample is most often run for 24 hours with a 2-hour interval between each collection. To collect this kind of sample, the volume needed for the tests and the average daily flow for the plant must be known. Table 10-8 shows the volumes required for some tests. The following formula may be used to find the volume of sample to be taken at each interval.
For example, to collect an 8-hour composite sample with a 2-hour interval, five samples would be needed. If a total sample of 2 liters was needed, the average daily flow was 60,000 gallons (227 cubic meters), and the flow at the first sample time was 45,000 gallons per day (170 cubic meters),Continue Reading