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Theoretical oxygen demand
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<p>Theoretical oxygen demand (ThOD) is the calculated amount of <a href="/facts/Oxygen/acyn6o8r">oxygen</a> required to <a href="/facts/Oxidize/Pyd5RVcj">oxidize</a> a compound to its final <a href="/facts/Oxidation/Pyd5RVcj">oxidation</a> products. However, there are some differences between standard methods that can influence the results obtained: for example, some calculations assume that <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a> released from <a href="/facts/Organic_compound/gqCNaN45">organic compounds</a> is generated as <a href="/facts/Ammonia/MtLtJFtz">ammonia</a>, whereas others allow for ammonia <a href="/facts/Oxidation/Pyd5RVcj">oxidation</a> to <a href="/facts/Nitrate/5AnVlYnL">nitrate</a>. Therefore, in expressing results, the calculation assumptions should always be stated. </p><p>In order to determine the ThOD for <a href="/facts/Glycine/3nXI1hqW">glycine</a> (CH2(NH2)COOH) using the following assumptions: </p> <ol><li>In the first step, the <a href="/facts/Organic_carbon/noBXADsJ">organic carbon</a> and <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a> are converted to <a href="/facts/Carbon_dioxide/xGzpppEp">carbon dioxide</a> (CO2) and <a href="/facts/Ammonia/MtLtJFtz">ammonia</a> (NH3), respectively.</li> <li>In the second and third steps, the ammonia is oxidized sequentially to <a href="/facts/Nitrite/qkz2XScK">nitrite</a> and <a href="/facts/Nitrate/5AnVlYnL">nitrate</a>.</li> <li>The ThOD is the sum of the <a href="/facts/Oxygen/acyn6o8r">oxygen</a> required for all three steps.</li></ol> <p>We can calculate by following steps: </p> <ol><li>Write balanced reaction for the <a href="/facts/Carbonaceous_biochemical_oxygen_demand/8vDcugIo">carbonaceous oxygen demand</a>.CH2(NH2)COOH + 1.5O2 → NH3 + 2CO2 + H2O</li> <li>Write balanced reactions for the nitrogenous oxygen demand.NH3 + 1.5O2 → HNO2 + H2O HNO2 + 0.5O2 → HNO3NH3 + 2O2 → HNO3 + H2O</li> <li>Determine the ThOD.ThOD = (1.5 + 2) mol O2/mol glycine= 3.5 mol O2/mol glycine × 32 g/mol O2 / 75 g/mol glycine= 1.49 g O2/g glycine</li></ol> <p>The theoretical oxygen demand represents the worst-case scenario. The actual oxygen demand of any <a href="/facts/Chemical_compound/37FXqqtv">compound</a> depends on the <a href="/facts/Biodegradability/d1UW4dfR">biodegradability</a> of the compound and the specific organism <a href="/facts/Metabolizing/WxDrm8k5">metabolizing</a> the compound. The actual <a href="/facts/Oxygen/acyn6o8r">oxygen</a> demand can be measured experimentally and is called the <a href="/facts/Biochemical_oxygen_demand/8vDcugIo">biochemical oxygen demand</a> (BOD). </p>