What Are BOI and KOI Parameters? BOI and KOI parameters are two fundamental parameters in Environmental Engineering for determining the levels of pollution in water resources, identifying the pollution potential of wastewater, and designing and operating treatment facilities.
The two parameters that will be explained in detail below are fundamentally determined by the oxidation of organic matter in water, either through natural processes or at high temperatures, in the presence of various chemicals.
BOD, or Biochemical/Biological Oxygen Demand, can be defined as the amount of oxygen required for the decomposition and digestion of organic matter (chemical compounds containing carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur) by bacteria in aerobic conditions (in a water environment containing air).
The term BOD was first used in the 1800s to measure organic pollution in rivers in England. At that time, BOD was standardized at 18.3°C and 5 days. One of the reasons for choosing these figures was that there were no rivers in England with a flow duration exceeding 5 days and that the average temperature in the summer months was 18.3°C. Therefore, the worst conditions in terms of oxygen demand were taken into account in determining the standards. Later, the standard was set at 20°C and a 5-day incubation (microorganism growth) period.
Research conducted on organic matter and microorganisms has shown that under test conditions at 20°C, the metabolic activities of bacteria can continue for days. Under these conditions, theoretically, infinite time is required for the complete biological oxidation of organic matter. However, for practical purposes, it has been accepted that the reaction is completed in 20 days. Due to the long duration of the 20-day period, this time was limited to 5 days, and the analysis was named BOD5. Since the natural decomposition of organic matter takes more than 5 days, this analysis provides only a portion of the actual BOD value. Research on domestic and industrial wastewater has found that this 5-day BOD value constitutes about 70-80% of the total (final) BOD value, and this result has been deemed sufficient, leading to the acceptance of a 5-day waiting period for the test.
COD, or Chemical Oxygen Demand, refers to the oxidation of organic matter in water using strong oxidizing chemicals at high temperatures in an acidic environment.
is based on lending. During the test, carbon-containing organic substances are converted into CO2 and water, while nitrogenous organic substances are converted into NH3 (ammonia).The most significant advantage of the COD analysis is that it can be completed within a total of 3 hours. Due to the short duration of the analysis, it is preferred over BOD analysis in many cases.During the COD analysis, the oxidation of biologically non-oxidizable organic substances causes the COD parameter, except in some exceptional cases, to always be higher than the BOD parameter. In untreated raw domestic and industrial wastewater, there is a ratio of BOD5/COD = 0.4 – 0.8. This ratio can be considered as an average of 0.5 for domestic wastewater and 0.65 for industrial wastewater.In the COD test, due to the occurrence of chemical redox (oxidation-reduction) reactions instead of the biochemical reactions in the BOD test, the COD parameter should be evaluated together with the BOD parameter, especially during the design of treatment plants. For example, in one of two different industrial wastewater samples with equal COD values of 1000 mg/liter, the BOD value is 100 mg/liter, while in the other sample, the BOD value is 700 mg/liter. In such a case, if similar treatment processes are applied to these wastewaters solely because their COD values are equal, one of the wastewaters can be easily treated while the other cannot. Therefore, to prevent various engineering and design errors, these parameters need to be interpreted together.