Which sample type is best for determining settable solids?

The time integrated composite sample is the best choice for determining settable solids because it collects water over a defined period and integrates all variations in water quality and flow. This approach ensures that a representative volume of liquid is analyzed, capturing a broader picture of the solids present in the wastewater.

Settable solids, such as those that would settle in a clarifier, can vary significantly over time due to fluctuations in flow rates, thus making a grab sample potentially unrepresentative of the overall characteristics of the wastewater. A composite sample, on the other hand, accounts for these variations, leading to more accurate results for assessing the amount of solids that will settle out over time.

Furthermore, a sediment sample typically involves analyzing just the solids that have already settled out, which does not provide information about the solids in suspension that are and would remain in the wastewater. A surface water sample is generally taken from the upper layer of a water body, which may not accurately reflect the conditions and composition necessary for determining settable solids in wastewater. Overall, the time integrated composite method provides a comprehensive dataset that is crucial for effective analysis.