Editing Biochemical oxygen demand (section)

== Methods ==
Winkler published  the methodology of a simple, accurate and direct dissolved oxygen analytical procedure in 1888.<ref>Winkler, L. W. (1888). "Die zur Bestimmung des in Wasser gelösten Sauerstoffes " Berichte der Deutschen Chemischen Gesellschaft 21(2): 2843-2854.</ref> Since that time, the analysis of dissolved oxygen levels for water has been key to the determination of surface water. The Winkler method is still one of only two analytical techniques used to calibrate oxygen electrode meters; the other procedure is based on oxygen solubility at saturation as per [[Henry's law]].

There are two recognized  methods for the measurement of dissolved oxygen for  BOD and a number of other methods not currently internationally recognised as standard methods

=== Dilution method ===
[[File:Disposable BOD Bottles.jpg|thumb|Disposable BOD bottle]]
[[File:BOD Bottle.jpg|thumb|Glass BOD bottle]]
This standard method is recognized by EPA, which is labeled Method 5210B in the ''Standard Methods for the Examination of Water and Wastewater.''<ref>{{cite book |title=Standard Methods For the Examination of Water and Wastewater |edition=21 |editor-last1=Eaton |editor-first1=Andrew D. |editor-last2=Greenberg |editor-first2=Arnold E. |editor-last3=Rice |editor-first3=Eugene W. |editor-last4=Clesceri |editor-first4=Lenore S. |editor-last5=Franson |editor-first5=Mary Ann H. |year=2005 |publisher=American Public Health Association |isbn=978-0-87553-047-5 |id=Also available on CD-ROM and [http://www.standardmethods.org/ online] by subscription}}</ref> In order to obtain BOD<sub>5</sub>, dissolved oxygen (DO) concentrations in a sample must be measured before and after the incubation period, and appropriately adjusted by the sample corresponding dilution factor. This analysis is performed using 300&nbsp;mL incubation bottles in which [[buffered dilution water]] is dosed with seed microorganisms and stored for 5 days in the dark room at 20&nbsp;°C to prevent DO production via photosynthesis. The bottles have traditionally been made of glass, which required cleaning and rinsing between samples. A SM 5210B approved, disposable, plastic [[BOD bottle]] is available which eliminates this step. In addition to the various dilutions of BOD samples, this procedure requires dilution water blanks, [[glucose glutamic acid]] (GGA) controls, and seed controls. The dilution water blank is used to confirm the quality of the dilution water that is used to dilute the other samples. This is necessary because impurities in the dilution water may cause significant alterations in the results. The GGA control is a standardized solution to determine the quality of the seed, where its recommended BOD<sub>5</sub> concentration is 198&nbsp;mg/L ± 30.5&nbsp;mg/L. For measurement of '''carbonaceous BOD''' (cBOD), a nitrification inhibitor is added after the dilution water has been added to the sample. The inhibitor hinders the [[oxidation]] of ammonia nitrogen, which supplies the nitrogenous BOD (nBOD). When performing the BOD<sub>5</sub> test, it is conventional practice to measure only cBOD because nitrogenous demand does not reflect the oxygen demand from organic matter.  This is because nBOD is generated by the breakdown of proteins, whereas cBOD is produced by the breakdown of organic molecules.

BOD<sub>5</sub> is calculated by:
*Unseeded :<math>\mathrm{BOD}_5 = \frac{(D_0 - D_5)}{P}</math>
*Seeded: <math>\mathrm{BOD}_5 = \frac{(D_0 - D_5) - (B_0 - B_5)f}{P}</math>

where:
:<math> D_0</math> is the dissolved oxygen (DO) of the diluted solution after preparation (mg/L)
:<math> D_5</math> is the DO of the diluted solution after 5 day incubation (mg/L)
:<math> P</math> is the decimal dilution factor
:<math> B_0</math> is the DO of diluted seed sample after preparation (mg/L)
:<math> B_5</math> is the DO of diluted seed sample after 5 day incubation (mg/L)
:<math> f</math> is the ratio of seed volume in dilution solution to seed volume in BOD test on seed

=== Manometric method ===
This method is limited to the measurement of the oxygen consumption due only to carbonaceous oxidation. [[Ammonia]] oxidation is inhibited.

The sample is kept in a sealed container fitted with a [[pressure sensor]]. A substance that absorbs [[carbon dioxide]] (typically [[lithium hydroxide]]) is added in the container above the sample level. The sample is stored in conditions identical to the dilution method. Oxygen is consumed and, as ammonia oxidation is inhibited, carbon dioxide is released. The total amount of gas, and thus the pressure, decreases because carbon dioxide is absorbed. From the drop of pressure, the sensor electronics computes and displays the consumed quantity of oxygen.

The main advantages of this method compared to the dilution method are:
* simplicity: no dilution of sample required, no seeding, no blank sample.
* direct reading of BOD value.
* continuous display of BOD value at the current incubation time.