Wastewater New York State Practice Exam

Using only a single aliquot from a bacteriological sample, how likely is it to accurately estimate the coliform density?

1. High - because of a concentrated sample

2. Moderate - based on sample size

3. Low - because of the distribution of bacteria in the sample

4. Very High - due to consistent bacteria distribution

The correct answer is: Low - because of the distribution of bacteria in the sample

The estimate of coliform density from a single aliquot of a bacteriological sample is considered low in accuracy primarily due to the uneven distribution of bacteria within the sample. In environmental samples, bacterial populations are often heterogeneous, meaning they are not uniformly distributed throughout the sample. Factors such as sedimentation, water currents, and organism interactions can cause significant variation in bacterial concentration from one part of the sample to another. When only one aliquot is taken, it may not represent the entire bacterial population accurately. If that aliquot happens to be taken from a region of the sample with a high or low concentration of coliforms, it can lead to misleading results. Therefore, multiple aliquots or replicates are often recommended to achieve a more reliable and representative estimation of bacterial density, ultimately emphasizing the inherent variability of biological samples in environmental assessments. In this context, high accuracy cannot be guaranteed solely based on the characteristics of the sample, as the random nature of bacterial distribution plays a critical role.