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Biochemical oxygen demand

biochemical oxygen demand, biochemical oxygen demand calculation
Biochemical oxygen demand BOD, also called biological oxygen demand is the amount of dissolved oxygen needed ie, demanded by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at 20 °C and is often used as a surrogate of the degree of organic pollution of water1

BOD can be used as a gauge of the effectiveness of wastewater treatment plants It is listed as a conventional pollutant in the US Clean Water Act

BOD is similar in function to chemical oxygen demand COD, in that both measure the amount of organic compounds in water However, COD is less specific, since it measures everything that can be chemically oxidized, rather than just levels of biodegradable organic matter

Contents

  • 1 Background
    • 11 Typical values
  • 2 Methods
    • 21 Dilution method
    • 22 Manometric method
  • 3 Alternative methods
    • 31 Biosensor
    • 32 Fluorescent RedOx Indicator
    • 33 Software sensor
  • 4 Dissolved oxygen probes: Membrane and luminescence
  • 5 Test limitations
    • 51 Toxicity
    • 52 Appropriate microbial population
  • 6 History
  • 7 See also
  • 8 Further References
  • 9 References
  • 10 External links

Backgroundedit

Most natural waters contain small quantities of organic compounds Aquatic microorganisms have evolved to use some of these compounds as food Microorganisms living in oxygenated waters use dissolved oxygen to oxidatively degrade the organic compounds, releasing energy which is used for growth and reproduction Populations of these microorganisms tend to increase in proportion to the amount of food available This microbial metabolism creates an oxygen demand proportional to the amount of organic compounds useful as food Under some circumstances, microbial metabolism can consume dissolved oxygen faster than atmospheric oxygen can dissolve into the water or the autotrophic community algae, cyanobacteria and macrophytes can produce Fish and aquatic insects may die when oxygen is depleted by microbial metabolism2

Biochemical oxygen demand is the amount of oxygen required for microbial metabolism of organic compounds in water This demand occurs over some variable period of time depending on temperature, nutrient concentrations, and the enzymes available to indigenous microbial populations The amount of oxygen required to completely oxidize the organic compounds to carbon dioxide and water through generations of microbial growth, death, decay, and cannibalism is total biochemical oxygen demand total BOD Total BOD is of more significance to food webs than to water quality Dissolved oxygen depletion is most likely to become evident during the initial aquatic microbial population explosion in response to a large amount of organic material If the microbial population deoxygenates the water, however, that lack of oxygen imposes a limit on population growth of aerobic aquatic microbial organisms resulting in a longer term food surplus and oxygen deficit3

A standard temperature at which BOD testing should be carried out was first proposed by the Royal Commission on Sewage Disposal in its eighth report in 1912:

" c An effluent in order to comply with the general standard must not contain as discharged more than 3 parts per 100,000 of suspended matter, and with its suspended matters included must not take up at 65°F more than 20 parts per 100,000 of dissolved oxygen in 5 days This general standard should be prescribed either by Statute or by order of the Central Authority, and should be subject to modifications by that Authority after an interval of not less than ten years

This was later standardised at 68 °F and then 20 °C This temperature may be significantly different from the temperature of the natural environment of the water being tested

Although the Royal Commission on Sewage Disposal proposed 5 days as an adequate test period for rivers of the United Kingdom of Great Britain and Ireland, longer periods were investigated for North American rivers Incubation periods of 1, 2, 5, 10 and 20 days were being used into the mid-20th century4 Keeping dissolved oxygen available at their chosen temperature, investigators found up to 99 percent of total BOD was exerted within 20 days, 90 percent within 10 days, and approximately 68 percent within 5 days5 Variable microbial population shifts to nitrifying bacteria limit test reproducibility for periods greater than 5 days The 5-day test protocol with acceptably reproducible results emphasizing carbonaceous BOD has been endorsed by the United States Environmental Protection Agency This 5-day BOD test result may be described as the amount of oxygen required for aquatic microorganisms to stabilize decomposable organic matter under aerobic conditions6 Stabilization, in this context, may be perceived in general terms as the conversion of food to living aquatic fauna Although these fauna will continue to exert biochemical oxygen demand as they die, that tends to occur within a more stable evolved ecosystem including higher trophic levels3

Taking samples from the influent raw wastewater stream for BOD measurements at a wastewater treatment plant in Haran-Al-Awamied near Damascus in Syria

Typical valuesedit

Most pristine rivers will have a 5-day carbonaceous BOD below 1 mg/L Moderately polluted rivers may have a BOD value in the range of 2 to 8 mg/L Rivers may be considered severely polluted when BOD values exceed 8 mg/L7 Municipal sewage that is efficiently treated by a three-stage process would have a value of about 20 mg/L or less Untreated sewage varies, but averages around 600 mg/L in Europe and as low as 200 mg/L in the US, or where there is severe groundwater or surface water Infiltration/Inflow The generally lower values in the US derive from the much greater water use per capita than in other parts of the world1

Methodsedit

There are two commonly recognized methods for the measurement of BOD

Dilution methodedit

This standard method is recognized by US EPA, which is labeled Method 5210B in the Standard Methods for the Examination of Water and Wastewater8 In order to obtain BOD5, 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 ml incubation bottles in which buffered dilution water is dosed with seed microorganisms and stored for 5 days in the dark room at 20 °C to prevent DO production via photosynthesis 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 BOD5 concentration is 198 mg/l ± 305 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 BOD5 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

BOD5 is calculated by:

  • Unseeded: B O D 5 = D 0 − D 5 P _=-D_
  • Seeded: B O D 5 = D 0 − D 5 − B 0 − B 5 f P _=-D_-B_-B_f

where:

D 0 is the dissolved oxygen DO of the diluted solution after preparation mg/l D 5 is the DO of the diluted solution after 5 day incubation mg/l P is the decimal dilution factor B 0 is the DO of diluted seed sample after preparation mg/l B 5 is the DO of diluted seed sample after 5 day incubation mg/l f is the ratio of seed volume in dilution solution to seed volume in BOD test on seed

Manometric methodedit

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

Alternative methodsedit

Biosensoredit

An alternative to measure BOD is the development of biosensors, which are devices for the detection of an analyte that combines a biological component with a physicochemical detector component Enzymes are the most widely used biological sensing elements in the fabrication of biosensors Their application in biosensor construction is limited by the tedious, time consuming and costly enzyme purification methods Microorganisms provide an ideal alternative to these bottlenecks9

The vast variety of micro organisms are relatively easy to maintain in pure cultures, grow and harvest at low cost Moreover, the use of microbes in biosensor field has opened up new possibilities and advantages such as ease of handling, preparation and low cost of device A number of pure cultures, eg Trichosporon cutaneum, Bacillus cereus, Klebsiella oxytoca, Pseudomonas sp etc individually, have been used by many workers for the construction of BOD biosensor On the other hand, many workers have immobilized activated sludge, or a mixture of two or three bacterial species and on various membranes for the construction of BOD biosensor The most commonly used membranes were polyvinyl alcohol, porous hydrophilic membranes etc10

A defined microbial consortium can be formed by conducting a systematic study, ie pre-testing of selected micro-organisms for use as a seeding material in BOD analysis of a wide variety of industrial effluents Such a formulated consortium can be immobilized on suitable membrane, ie charged nylon membrane useful for BOD estimation Suitability of charges nylon membrane lies in the specific binding between negatively charged bacterial cell and positively charged nylon membrane So the advantages of the nylon membrane over the other membranes are : The dual binding, ie Adsorption as well as entrapment, thus resulting in a more stable immobilized membrane Such specific Microbial consortium based BOD analytical devices, may find great application in monitoring of the degree of pollutional strength, in a wide variety of Industrial waste water within a very short time10

Biosensors can be used to indirectly measure BOD via a fast usually <30 min to be determined BOD substitute and a corresponding calibration curve method pioneered by Karube et al, 1977 Consequently, biosensors are now commercially available, but they do have several limitations such as their high maintenance costs, limited run lengths due to the need for reactivation, and the inability to respond to changing quality characteristics as would normally occur in wastewater treatment streams; eg diffusion processes of the biodegradable organic matter into the membrane and different responses by different microbial species which lead to problems with the reproducibility of result Praet et al, 1995 Another important limitation is the uncertainty associated with the calibration function for translating the BOD substitute into the real BOD Rustum et al, 2008

Fluorescent RedOx Indicatoredit

A surrogate to BOD5 has been developed using a resazurin derivative which reveals the extent of oxygen uptake by micro-organisms for organic matter mineralization11 A cross-validation performed on 109 samples in Europe and the United-States showed a strict statistical equivalence between results from both methods12 The French start-up Envolure Montpellier, France offers the kit ENVERDI which enables the users to perform up to 40 BOD5 simultaneously in 48 hours in a single 96-wells microplate

Software sensoredit

Rustum et al 2008 proposed the use of the KSOM to develop intelligent models for making rapid inferences about BOD using other easy to measure water quality parameters, which, unlike BOD, can be obtained directly and reliably using on-line hardware sensors This will make the use of BOD for on-line process monitoring and control a more plausible proposition In comparison to other data-driven modeling paradigms such as multi-layer perceptrons artificial neural networks MLP ANN and classical multi-variate regression analysis, the KSOM is not negatively affected by missing data Moreover, time sequencing of data is not a problem when compared to classical time series analysis

Dissolved oxygen probes: Membrane and luminescenceedit

Since the publication of a simple, accurate and direct dissolved oxygen analytical procedure by Winkler,13 the analysis of dissolved oxygen levels for water has been key to the determination of surface water purity and ecological wellness 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 Though many researchers have refined the Winkler analysis to dissolved oxygen levels in the low PPB range, the method does not lend itself to automation

The development of an analytical instrument that utilizes the reduction-oxidation redox chemistry of oxygen in the presence of dissimilar metal electrodes was introduced during the 1950s14 This redox electrode utilized an oxygen-permeable membrane to allow the diffusion of the gas into an electrochemical cell and its concentration determined by polarographic or galvanic electrodes This analytical method is sensitive and accurate to down to levels of ± 01 mg/l dissolved oxygen Calibration of the redox electrode of this membrane electrode still requires the use of the Henry's law table or the Winkler test for dissolved oxygen

During the last two decades, a new form of electrode was developed based on the luminescence emission of a photo active chemical compound and the quenching of that emission by oxygen This quenching photophysics mechanism is described by the Stern–Volmer equation for dissolved oxygen in a solution:15

I 0 / I   =   1   +   K S V   O 2 /I~=~1~+~K_~
  • I : Luminescence in the presence of oxygen
  • I 0 : Luminescence in the absence of oxygen
  • K S V : Stern-Volmer constant for oxygen quenching
  • O 2 : Dissolved oxygen concentration

The determination of oxygen concentration by luminescence quenching has a linear response over a broad range of oxygen concentrations and has excellent accuracy and reproducibility16 There are several recognized EPA methods for the measurement of dissolved oxygen for BOD, including the following methods:

  • Standard Methods for the Examination of Water and Wastewater, Method 4500 O17
  • In-Situ Inc Method 1003-8-2009 Biochemical Oxygen Demand BOD Measurement by Optical Probe18

Test limitationsedit

The test method involves variables limiting reproducibility Tests normally show observations varying plus or minus ten to twenty percent around the mean19:82

Toxicityedit

Some wastes contain chemicals capable of suppressing microbiological growth or activity Potential sources include industrial wastes, antibiotics in pharmaceutical or medical wastes, sanitizers in food processing or commercial cleaning facilities, chlorination disinfection used following conventional sewage treatment, and odor-control formulations used in sanitary waste holding tanks in passenger vehicles or portable toilets Suppression of the microbial community oxidizing the waste will lower the test result19:85

Appropriate microbial populationedit

The test relies upon a microbial ecosystem with enzymes capable of oxidizing the available organic material Some waste waters, such as those from biological secondary sewage treatment, will already contain a large population of microorganisms acclimated to the water being tested An appreciable portion of the waste may be utilized during the holding period prior to commencement of the test procedure On the other hand, organic wastes from industrial sources may require specialized enzymes Microbial populations from standard seed sources may take some time to produce those enzymes A specialized seed culture may be appropriate to reflect conditions of an evolved ecosystem in the receiving waters19:85–87

Historyedit

The Royal Commission on River Pollution, which was established in 1865 and the formation of the Royal Commission on Sewage Disposal in 1898 led to the selection in 1908 of BOD5 as the definitive test for organic pollution of rivers Five days was chosen as an appropriate test period because this is supposedly the longest time that river water takes to travel from source to estuary in the UK In its sixth report the Royal Commission recommended that the standard set should be 15 parts by weight per million of water20 However, in the Ninth report the commission had revised the recommended standard :

" An effluent taking up 2–0 parts dissolved oxygen per 100,000 would be found by a simple calculation to require dilution with at least 8 volumes of river water taking up 02 part if the resulting mixture was not to take up more than 04 part Our experience indicated that in a large majority of cases the volume of river water would exceed 8 times the volume of effluent, and that the figure of 2–0 parts dissolved oxygen per 100,000, which had been shown to be practicable, would be a safe figure to adopt for the purposes of a general standard, taken in conjunction with the condition that the effluent should not contain more than 3–0 parts per 100,000 of suspended solids"20

This was the cornerstone 20:30 BOD:Suspended Solids + full nitrification standard which was used as a yardstick in the UK up to the 1970s for sewage works effluent quality

The United States includes BOD effluent limitations in its secondary treatment regulations Secondary sewage treatment is generally expected to remove 85 percent of the BOD measured in sewage and produce effluent BOD concentrations with a 30-day average of less than 30 mg/L and a 7-day average of less than 45 mg/L The regulations also describe "treatment equivalent to secondary treatment" as removing 65 percent of the BOD and producing effluent BOD concentrations with a 30-day average less than 45 mg/L and a 7-day average less than 65 mg/L21

See alsoedit

  • Theoretical oxygen demand
  • Carbonaceous biochemical oxygen demand
  • Wastewater quality indicators discusses both BOD and COD as indicators of wastewater quality

Further Referencesedit

  • Lenore S Clescerl; Arnold E Greenberg; Andrew D Eaton 1999 Standard Methods for Examination of Water & Wastewater 20th ed Washington, DC: American Public Health Association ISBN 0-87553-235-7  Also available by online subscription at wwwstandardmethodsorg
  • Rustum R, A J Adeloye, and M Scholz 2008 Applying Kohonen Self-organizing Map as a Software Sensor to Predict the Biochemical Oxygen Demand, Water Environment Research, 80 1, 32 – 40

Referencesedit

  1. ^ a b Clair N Sawyer; Perry L McCarty; Gene F Parkin 2003 Chemistry for Environmental Engineering and Science 5th ed New York: McGraw-Hill ISBN 0-07-248066-1 
  2. ^ Goldman, Charles R & Horne, Alexander J Limnology 1983 McGraw-Hill ISBN 0-07-023651-8 pp88&267
  3. ^ a b Reid, George K Ecology of Inland Waters and Estuaries 1961 Van Nostrand Reinhold pp 317–320
  4. ^ Norton, John F Standard Methods for the Examination of Water and Sewage 9th Ed 1946 American Public Health Association p139
  5. ^ Urquhart, Leonard Church Civil Engineering Handbook 4th Ed 1959 McGraw-Hill p 9–40
  6. ^ Sawyer, Clair N & McCarty, Perry L Chemistry for Sanitary Engineers 2nd Ed 1967 McGraw-Hill pp 394–399
  7. ^ Connor, Richard 2016 The United Nations World Water Development Report 2016: Water and Jobs, chapter 2: The Global Perspective on Water Paris: UNESCO p 26 ISBN 978-92-3-100155-0 
  8. ^ Lenore S Clesceri, Andrew D Eaton, Eugene W Rice 2005 Standard Methods for Examination of Water & Wastewater Method 5210B Washington, DC: American Public Health Association, American Water Works Association, and the Water Environment Association http://wwwstandardmethodsorg
  9. ^ Lei, Yu "Microbial biosensors" PDF http://wwwcbsumnedu Analytica Chimica Acta 568 2006 200–210  External link in |website= help
  10. ^ a b Kumar, Rita "IMMOBILIZED MICROBIAL CONSORTIUM USEFUL FOR RAPID AND RELIABLE BOD ESTIMATION" http://wwwigibresin CSIR-Institute of Genomics & Integrative Biology IGIB  External link in |website= help
  11. ^ A US 2013130308 A, Nathalie Pautremat; Romy-Alice Goy & Zaynab El Amraoui et al, "Process for directly measuring multiple biodegradabilities", published 2013-05-23, assigned to Envolure 
  12. ^ Muller, Mathieu; Bouguelia, Sihem; Goy, Romy-Alice; Yoris, Alison; Berlin, Jeanne; Meche, Perrine; Rocher, Vincent; Mertens, Sharon; Dudal, Yves 2014 "International cross-validation of a BOD5 surrogate" Environmental Science and Pollution Research: 1–4 doi:101007/s11356-014-3202-3 
  13. ^ Winkler, L W 1888 "Die zur Bestimmung des in Wasser gelösten Sauerstoffes " Berichte der Deutschen Chemischen Gesellschaft 212: 2843–2854
  14. ^ Kemula, W and S Siekierski 1950 "Polarometric determination of oxygen" Collect Czech Chem Commun 15: 1069–75
  15. ^ Garcia-Fresnadillo, D, M D Marazuela, et al 1999 "Luminescent Nafion Membranes Dyed with RutheniumII Complexes as Sensing Materials for Dissolved Oxygen" Langmuir 1519: 6451–6459
  16. ^ Titze, J, H Walter, et al 2008 "Evaluation of a new optical sensor for measuring dissolved oxygen by comparison with standard analytical methods" Monatsschr BrauwissMar/Apr: 66-80
  17. ^ Lenore S Clescerl, Andrew D Eaton, Eugene W Rice 2005 Standard Methods for Examination of Water & Wastewater 21st ed Washington, DC: American Public Health Association, American Water Works Association, and the Water Environment Association ISBN 0-87553-047-8 Also available by online subscription at http://wwwstandardmethodsorg
  18. ^ In-Situ Inc Method 1002-8-2009 Dissolved Oxygen Measurement by Optical Probe, In-Situ Inc, 221 E Lincoln Ave, Ft Collins, CO 80524 "Archived copy" Archived from the original on 2010-01-22 Retrieved 2010-01-12 
  19. ^ a b c Hammer, Mark J 1975 Water and Waste-Water Technology John Wiley & Sons ISBN 0-471-34726-4 
  20. ^ a b Final Report of the Commissioners Appointed to Inquire and Report What Methods of Treating and Disposing of Sewage 1912
  21. ^ US Environmental Protection Agency EPA Washington, DC "Secondary Treatment Regulation" Code of Federal Regulations, 40 CFR Part 133

External linksedit

  • BOD Doctor - a troubleshooting wiki for this problematic test

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