Simel Grace P. Condino BSChE – 4 CHE 151 OXYGEN SAG When the concentration of dissolved oxygen (DO) in a river into which sewage or another pollution has been released is graphed versus the distance downstream from the wastewater outlet, an oxygen sag curve is obtained. Water samples are collected in areas above and downstream of the sewage discharge (Hine, 2019). The biological oxygen demand (BOD), or the total amount of oxygen needed by all the people in a given location, is represented by the different levels on the oxygen sag curve. The oxygen sag curve is created when pollutants (waste or too much fertilizer) enter the water and affect the levels of BOD and DO. Around a point source of pollution, DO and BOD levels form distinct zones in a stream called the clean zone, decomposition zone, septic zone, and recovery zone. Figure 1. Characteristics of The River Oxygen Sag Curve (Ramal, 2012) An example of oxygen sag curve is the above figure, from research by Ramal (2019) about his evaluation of the wastewater effluents and its effects upon Al-Warar Canal, a canal in Iraq. Oxygen sag is an important measure of water quality and pollution consequences. The Environmental Protection Agency (EPA) publishes recommendations for determining water quality, including field measuring techniques. Low levels of dissolved oxygen have an impact on aquatic life and signal the presence of eutrophication, a situation in which certain organisms overgrow, resulting in poor oxygenation due to the consequent ecological imbalance (Safeopedia, 2015). REFERENCES Hine, R. (2019). A Dictionary of Biology (8th ed.). https://www.oxfordreference.com/display/10.1093/acref/9780198821489.001. 0001/acref-9780198821489-e3181;jsessionid=CB7BE9EA9E7DB674E46441026E824023#:~:text=The%20curve% 20obtained%20when%20the,downstream%20from%20the%20sewage%20outle t. Ramal, M. M. (2012). Evaluation the wastewater effluents and It’s Effects upon ALWARAR Canal. ResearchGate. https://www.researchgate.net/publication/320456583_Evaluation_the_waste water_effluents_and_It%27s_Effects_upon_AL-WARAR_Canal/figures?lo=1 Safeopedia, W. I. O. S.-. D. F. (2015). Oxygen Sag. safeopedia.com. https://www.safeopedia.com/definition/2842/oxygensag#:~:text=Oxygen%20sag%20is%20a%20key,procedures%20for%20field%20 measuring%20techniques.
