Question

Biological Oxygen Demand (BOD) can be defined as, (a) the amount of oxygen required by bacteria to break down the organic matter of a sample of water (b) the amount of chemicals required to break (c) the amount of phosphate required to oxidise the organic matter of a sample of water (d) the amount of organic matter present in the given sample of water.

Short answer

The correct answer is (a) the amount of oxygen required by bacteria to break down the organic matter of a sample of water.

Step-by-step solution

Understanding the concept of Biological Oxygen Demand (BOD)

BOD is a measure of the quantity of oxygen used by microorganisms (e.g., aerobic bacteria) in the oxidation of organic matter. Thus, it is necessary to associate the definition of BOD with the oxygen demand required to break down organic matter by bacteria.

Eliminating incorrect options

Options (b), (c), and (d) do not correctly define BOD. Option (b) mentions 'chemicals' which is not specific to oxygen or microbial action. Option (c) incorrectly constrains BOD to the use of phosphate, which is not a measure of oxygen demand. Option (d) describes the amount of organic matter, not the demand for oxygen.

Identifying the correct option

By understanding the true definition of BOD and eliminating the incorrect options, it is clear that option (a) 'the amount of oxygen required by bacteria to break down the organic matter of a sample of water' accurately defines BOD.

Key concepts

Oxidation of Organic Matter

The process of oxidation of organic matter in water is a crucial element of understanding Biological Oxygen Demand (BOD). Essentially, oxidation refers to the biochemical reaction where organisms, specifically aerobic bacteria, utilize oxygen to break down organic substances, releasing energy in the process. This reaction is a key part of the natural cycle in aquatic ecosystems, helping to decompose dead plants, animals, and waste products.

For instance, when an apple core is discarded into a stream, aerobic bacteria set to work, using atmospheric or dissolved oxygen to convert the organic matter within the core to inorganic substances like carbon dioxide, water, and mineral salts. These end products are less harmful and more stable than the original organic matter.

An understanding of this process is vital for students, as it helps explain why high levels of organic pollution can deplete the oxygen in water bodies, posing a threat to aquatic life. In the context of BOD, the rate of oxidation reflects the amount of organic pollution present. Therefore, higher BOD values indicate a greater quantity of readily decomposable organic matter, implying poorer water quality.

Aerobic Bacteria

Aerobic bacteria play a star role in determining BOD levels in water, as they are the primary agents of organic matter decomposition. These microorganisms require oxygen to survive and are thus found in environments where oxygen is present, such as the upper layers of water bodies.

The role of aerobic bacteria is multifaceted: they not only break down waste but also maintain a healthy ecosystem by recycling nutrients. For example, when these bacteria decompose organic matter, they convert nitrogen within the waste into nitrates, which can then be used by plants to grow.

Bacteria Efficiency and BOD

The efficiency of bacteria at breaking down organic pollutants is directly related to the BOD measurement. High BOD values suggest that a significant amount of oxygen is consumed by bacteria in the water, illustrating that there is an abundance of organic waste for them to decompose. Conversely, low BOD values indicate an environment with less organic material, which typically means better water quality.

Water Quality Monitoring

Monitoring water quality is a critical aspect of environmental management, and BOD is a key indicator used to assess the impact of wastewater and pollutants on aquatic environments. By measuring BOD, scientists and engineers can estimate the potential harm that effluents might pose to a body of water.

Regular BOD assessments inform authorities about the levels of organic pollution and the ecological balance of water bodies. For example, a sudden spike in BOD levels could indicate a recent pollution event, such as a sewage overflow or industrial discharge.

Implications of High BOD

High BOD levels typically mean that the water's natural cleansing process is overwhelmed, potentially leading to conditions like hypoxia, where there is not enough oxygen for aquatic life to survive. This information can prompt immediate remedial action, such as investigating and addressing the source of pollution.