Why Biochemical Oxygen Demand (BOD) Measurement is Important to River Water Quality

This legislation specifies five key water quality parameters to be measured: pH, turbidity, ammonia, dissolved oxygen and temperature. However, there is an important caveat in this section of the legislation that states that the number of parameters to be measured may be increased to include “anything else specified in regulations made by the Secretary of State.”

Biochemical Oxygen Demand (BOD) measurement is widely used to assess wastewater treatment works’ efficacy. As a measurement in environmental monitoring of rivers, it is not only useful as an assessment of the water quality (as defined in the Water Framework Directive), but also for identifying point sources of pollution. It is a key parameter in understanding the impact of wastewater discharge on the receiving water body: where BOD is above typical levels, point sources of pollution should be identified and investigated.

Understanding BOD Measurement

BOD refers to the amount of oxygen required by microorganisms to break down organic matter present in water. This process is crucial for maintaining the balance of aquatic ecosystems. However, high BOD levels are indicative of pollution sources, as they reflect the degradation of organic substances by bacteria, leading to oxygen depletion in water bodies. BOD measurement quantifies this oxygen demand, providing crucial insight into the extent of pollution and its potential impact on aquatic life.

The traditional method of measuring BOD involves sample collection and an incubation period in a controlled environment for five days (BOD5). Using DO measurement over this period measures the amount of oxygen required by microorganisms to break down the organic material in water and therefore correlates to the number of microorganisms in the water.

However online surrogate measurements of BOD are available and have been used extensively in pollution monitoring in surface water bodies across the globe with a high degree of success. Measuring BOD with online surrogate measurements of organics would overcome some of the issues with the traditional BOD5 test:

• It is instantaneous
• Not reliant on sampling conditions and the challenges of storage and transport of that sample
• As reflective of BOD changes as the BOD5 test (considering that the BOD5 test is carried out in standardised conditions that do not necessarily reflect the conditions that are found in the actual water body from which the sample was taken)

Online BOD Measurement Using UV-Vis Spectroscopy

s::can have been pioneering the use of online BOD measurement using UV-Vis spectroscopy for 25 years and s::can online BOD measurement can be found across the globe in surface water monitoring, as well as right through wastewater treatment processes.

Absorbance at certain wavelengths within the UV region can be directly correlated to BOD. Selecting accurate wavelength identification is what s::can have specialised in over the last 25 years. Spectral sensors that measure across the UV and visible spectrum enable accurate measurement, even in flashy rivers with variable turbidity.

The Benefits of Online BOD measurement for EA21 Compliance

One of the key aspects of the Environment Act is environmental protection of UK rivers to prevent pollution. Online BOD measurement aligns seamlessly with these objectives by serving as a direct indicator of pollution levels in water bodies. The Act’s provisions to control and mitigate pollution sources can be greatly enhanced through incorporating online BOD data, enabling regulators and utilities to identify pollution trends, and devise remediation strategies.

For wastewater compliance monitoring, such as final effluent monitoring, it is typical to produce a site-specific calibration for BOD ensuring accurate readings for each site—however for river water monitoring this may not be necessary. Using online BOD measurements as a trending parameter may demonstrate when a pollution event has occurred and will be more likely to demonstrate the effect the pollution event has had on the water body, in comparison to the likes of pH and turbidity. With pollution events that cause elevated levels of BOD, the effect on dissolved oxygen levels may not be very large in the short term, but the pollution still exists. Online BOD measurement is arguably the best measurement to make when seeking to identify potential sources of pollution that may have long term effects on water quality in UK rivers.

Final Thoughts

BOD measurement is a crucial parameter in the pursuit of environmental preservation. By quantifying the oxygen demand required to break down organic matter, online BOD measurement offers insights into pollution levels and facilitates early detection of pollution incidents. By recognising the indispensable role of online BOD measurement; pollution prevention activities are strengthened and all industry stakeholders benefit from this additional data.

Learn more about our response to EA21 here.