Explanation:

Wastewater is the water that has been used and discarded from various sources such as domestic, industrial, and agricultural activities. The quality of wastewater is determined by measuring various parameters, including the biochemical oxygen demand (BOD).

BOD (Biochemical Oxygen Demand):
BOD is a measure of the amount of dissolved oxygen required by microorganisms to decompose the organic matter present in wastewater under aerobic conditions. It provides an indication of the organic pollution level of water. The higher the BOD value, the greater the organic pollution.

Measurement of BOD:
BOD is measured by determining the oxygen consumption of microorganisms during the decomposition of organic matter in wastewater. The measurement is typically carried out by determining the difference in dissolved oxygen (DO) concentration before and after incubating a wastewater sample for a specific period, usually 5 days, at a specified temperature, typically 20°C.

Significance of BOD measurement:
BOD measurement is important in assessing the impact of wastewater discharge on the receiving water bodies. High BOD levels indicate a higher concentration of biodegradable organic matter in the water, which when discharged into natural water bodies, can lead to oxygen depletion due to microbial decomposition. This oxygen depletion can have detrimental effects on aquatic life, leading to the death of fish and other organisms.

Options:
a) Total organic matter: While total organic matter is an important parameter to assess the pollution level of water, it does not specifically measure the oxygen consumption by microorganisms and, therefore, cannot estimate the BOD accurately.

b) Biodegradable organic matter: Biodegradable organic matter is a component of total organic matter that can be decomposed by microorganisms. While it is related to BOD, directly measuring biodegradable organic matter does not provide a direct estimation of BOD.

c) Oxygen evolution: Oxygen evolution refers to the production of oxygen through a chemical or biological process. It is not directly related to BOD measurement.

d) Oxygen consumption: Oxygen consumption measurement is the most accurate method to estimate BOD. It directly measures the amount of oxygen consumed during the decomposition of organic matter, providing a reliable estimation of the organic pollution level in wastewater.

Therefore, the correct answer is option D, i.e., Oxygen consumption.