Which of the following best defines 'biochemical oxygen demand'?

Biochemical oxygen demand (BOD) is best defined as the amount of oxygen consumed by microorganisms in water over a specific period, typically five days at a controlled temperature. This measurement reflects the degree of organic pollution in a water body, as it indicates how much organic matter is present that can be biologically degraded by bacteria.

When organic material is present in water, microorganisms break it down, and doing so consumes dissolved oxygen. The more organic material in the water, the higher the oxygen demand will be, signifying poorer water quality. BOD is a critical parameter in assessing the impact of wastewater and other discharges on aquatic environments, as high BOD levels can lead to oxygen depletion, adversely affecting aquatic life.

The other options provided refer to different water quality measurements. For instance, measuring suspended solids relates more to turbidity and particulate matter in water rather than organic decomposition. The total amount of organic material in water can be indirectly inferred from BOD but does not capture the actual consumption of oxygen. Lastly, the level of dissolved oxygen available is crucial for supporting aquatic organisms but is not what BOD directly measures; instead, BOD is indicative of how much dissolved oxygen is likely to be consumed due to the presence of organic pollutants.