View source for Chemistry:Theoretical oxygen demand

'''Theoretical oxygen demand''' ('''ThOD''') is the calculated amount of [[Chemistry:Oxygen|oxygen]] required to oxidize a compound to its final oxidation products.<ref name="Penn">{{cite encyclopedia |encyclopedia=Environmental and Ecological Chemistry |volume=II |title=Biochemical Oxygen Demand |first=Michael R. |last=Penn |author2=James J. Pauer |author3=James R. Mihelcic |editor=Aleksandar Sabljic |year=2009 |publisher=EOLSS}}</ref> However, there are  some differences between standard methods that can influence the results obtained: for example, some calculations assume that [[Chemistry:Nitrogen|nitrogen]] released from [[Chemistry:Organic compound|organic compound]]s is generated as [[Chemistry:Ammonia|ammonia]], whereas others allow for ammonia oxidation to [[Chemistry:Nitrate|nitrate]]. Therefore, in expressing results, the calculation assumptions should always be stated.

In order to determine the  '''ThOD''' for [[Chemistry:Glycine|glycine]] (CH<sub>2</sub>(NH<sub>2</sub>)COOH) using the following assumptions:

#In the first step, the organic carbon and [[Chemistry:Nitrogen|nitrogen]] are  converted to [[Chemistry:Carbon dioxide|carbon dioxide]] (CO<sub>2</sub>) and [[Chemistry:Ammonia|ammonia]]  (NH<sub>3</sub>), respectively.
#In the second and third steps, the ammonia is  oxidized sequentially to [[Chemistry:Nitrite|nitrite]] and [[Chemistry:Nitrate|nitrate]]. 
#The ThOD is the sum of the [[Chemistry:Oxygen|oxygen]] required for all three steps.

We can calculate by following steps:
#Write balanced reaction for the [[Biology:Carbonaceous biochemical oxygen demand|carbonaceous oxygen demand]].<br>CH<sub>2</sub>(NH<sub>2</sub>)COOH + 1.5O<sub>2</sub> → NH<sub>3</sub> + 2CO<sub>2</sub> + H<sub>2</sub>O
#Write balanced reactions for the nitrogenous oxygen demand.<br>NH<sub>3</sub> + 1.5O<sub>2</sub> → HNO<sub>2</sub> + H<sub>2</sub>O<br> HNO<sub>2</sub> + 0.5O<sub>2</sub> → HNO<sub>3</sub><br>NH<sub>3</sub> + 2O<sub>2</sub> → HNO<sub>3</sub> + H<sub>2</sub>O
#Determine the ThOD.<br>ThOD = (1.5 + 2) mol O<sub>2</sub>/mol glycine<br>= 3.5&nbsp;mol O<sub>2</sub>/mol glycine × 32 g/mol O<sub>2</sub> / 75 g/mol glycine<br>= 1.49 g O<sub>2</sub>/g glycine

The theoretical oxygen demand represents the worst-case scenario. The actual oxygen demand of any [[Chemistry:Chemical compound|compound]] depends on the biodegradability of the compound and the specific organism metabolizing the compound. The actual [[Chemistry:Oxygen|oxygen]] demand can be measured experimentally and is called the [[Chemistry:Biochemical oxygen demand|biochemical oxygen demand]] (BOD).

==See also==
* Biological oxygen demand
* [[Biology:Chemical oxygen demand|Chemical oxygen demand]]
* [[Biology:Carbonaceous biochemical oxygen demand|Carbonaceous biochemical oxygen demand]]

==References==
{{reflist}}

[[Category:Environmental chemistry]]

{{Sourceattribution|Theoretical oxygen demand}}