Editing Biochemical oxygen demand (section)

== Alternative methods ==

=== Biosensor ===
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 bottlenecks.<ref>{{cite web |last1=Lei |first1=Yu |title=Microbial biosensors |url=http://www.cbs.umn.edu/sites/default/files/public/downloads/microbial%20sensor%2006.pdf |website=www.cbs.umn.edu |publisher=Analytica Chimica Acta 568 (2006) 200–210 |access-date=2014-09-16 |archive-url=https://web.archive.org/web/20150319212940/http://www.cbs.umn.edu/sites/default/files/public/downloads/microbial%20sensor%2006.pdf |archive-date=2015-03-19 |url-status=dead }}</ref>

Many micro organisms useful for BOD assessment are relatively easy to maintain in pure cultures, grow and harvest at low cost. Moreover, the use of microbes in the field of biosensors has opened up new possibilities and advantages such as ease of handling, preparation and low cost of device. A number of pure cultures, e.g. ''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 etc.<ref name="igib.res.in">{{cite web |last1=Kumar |first1=Rita |title=Immobilized Microbial Consortium Useful for Rapid and Reliable BOD Estimation |url=http://www.igib.res.in/pme/patents.htm |date=2004 |website=Patents |publisher=CSIR-Institute of Genomics & Integrative Biology (IGIB) |location=New Delhi, India |id=United Kingdom; GB2360788;(3-11-2004)}}</ref>

A defined microbial consortium can be formed by conducting a systematic study, i.e. 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, i.e. charged nylon membrane. Charged nylon membrane is suitable for microbial immobilization, due to 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, i.e. 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 pollutant strength, in a wide variety of industrial waste water within a very short time.<ref name="igib.res.in" />

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; e.g. 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 ===
A surrogate to BOD<sub>5</sub> has been developed using a [[resazurin]] derivative which reveals the extent of oxygen uptake by micro-organisms for organic matter mineralization.<ref>{{cite patent |country=US |number=2013130308 A |title=Process for directly measuring multiple biodegradabilities |pubdate=2013-05-23 |fdate=2012-11-21 |pridate=2011-11-23 |invent1=Nathalie Pautremat |invent2=Romy-Alice Goy |invent3=Zaynab El Amraoui |invent4=Yves Dudal |assign1= Envolure}}</ref> A cross-validation performed on 109 samples in Europe and the United-States showed a strict statistical equivalence between results from both methods.<ref>{{cite journal |last1=Muller |first1=Mathieu |last2=Bouguelia |first2=Sihem |last3=Goy |first3=Romy-Alice |last4=Yoris |first4=Alison |last5=Berlin|first5=Jeanne |last6=Meche |first6=Perrine |last7=Rocher |first7=Vincent |last8=Mertens |first8=Sharon |last9=Dudal |first9=Yves |title=International cross-validation of a BOD5 surrogate |journal=Environmental Science and Pollution Research |volume=21 |issue=23 |date=2014 |pages=13642–13645 |doi=10.1007/s11356-014-3202-3|pmid=24946712 |bibcode=2014ESPR...2113642M |s2cid=31998587 }}</ref>

An electrode has been 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:<ref>Garcia-Fresnadillo, D., M. D. Marazuela, et al. (1999). "Luminescent Nafion Membranes Dyed with Ruthenium(II) Complexes as Sensing Materials for Dissolved Oxygen." Langmuir 15(19): 6451-6459.</ref>

:<math chem>I_0/I~=~1~+~K_{SV}~[\ce{O2}]</math>

* <math>I</math>: Luminescence in the presence of oxygen
* <math>I_0</math>: Luminescence in the absence of oxygen
* <math>K_{SV}</math>: Stern-Volmer constant for oxygen quenching
* <chem>[O2]</chem>: 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 reproducibility.<ref>Titze, J., H. Walter, et al. (2008). "Evaluation of a new optical sensor for measuring dissolved oxygen by comparison with standard analytical methods." Monatsschr. Brauwiss.(Mar./Apr.): 66-80.</ref>

===Polargraphic method===
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 1950s.<ref>Kemula, W. and S. Siekierski (1950). "Polarometric determination of oxygen." Collect. Czech. Chem. Commun. 15: 1069-75.</ref> 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 down to levels of ± 0.1&nbsp;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]].

===Software sensor===
There have been proposals for automation to make rapid prediction of BOD so it could be used for on-line process monitoring and control. For example, the use of a computerised [[Self-organizing map|machine learning]] method to make rapid inferences about BOD using easy to measure water quality parameters. Ones such as flow rate, chemical oxygen demand, ammonia, nitrogen, pH and suspended solids can be obtained directly and reliably using on-line hardware sensors. In a test of this idea, measurements of these values along with BOD which had been made over three years was used to train and test a model for prediction. The technique could allow for some missing data.  It indicated that this approach was possible but needed sufficient historic data to be available.<ref name="Rustum-etal2008">{{cite journal |last1=Rustum |first1=Rabee |last2=Adeloye |first2=Adebayo J. |last3=Scholz |first3=Miklas |title=Applying Kohonen Self-Organizing Map as a Software Sensor to Predict Biochemical Oxygen Demand |journal=Water Environment Research |date=2008 |volume=80 |issue=1 |pages=32–40 |doi=10.2175/106143007X184500 |jstor=23804289 |pmid=18254396 |bibcode=2008WaEnR..80...32R |s2cid=24738186 |url=https://www.jstor.org/stable/23804289 |access-date=3 September 2021|url-access=subscription }}</ref>

=== Real-time BOD monitoring ===
Until recently, real-time monitoring of BOD was unattainable owing to its complex nature. Recent research by a leading UK university has discovered the link between multiple water quality parameters including electrical conductivity, turbidity, TLF and CDOM.<ref>{{Cite journal|last1=Khamis|first1=K.|last2=Bradley|first2=C.|last3=Hannah|first3=D. M.|date=2018|title=Understanding dissolved organic matter dynamics in urban catchments: insights from in situ fluorescence sensor technology|journal=Wiley Interdisciplinary Reviews: Water|volume=5|issue=1|pages=e1259|doi=10.1002/wat2.1259|issn=2049-1948|doi-access=free|bibcode=2018WIRWa...5E1259K }}</ref><ref name=":0">{{Cite journal|last1=Khamis|first1=K.|last2=R. Sorensen|first2=J. P.|last3=Bradley|first3=C.|last4=M. Hannah|first4=D.|last5=J. Lapworth|first5=D.|last6=Stevens|first6=R.|date=2015|title=In situ tryptophan-like fluorometers: assessing turbidity and temperature effects for freshwater applications|journal=Environmental Science: Processes & Impacts|volume=17|issue=4|pages=740–752|doi=10.1039/C5EM00030K|pmid=25756677|doi-access=free}}</ref> These parameters are all capable of being monitored in real-time through a combination of traditional methods (electrical conductivity via electrodes) and newer methods such as fluorescence. The monitoring of tryptophan-like fluorescence (TLF) has been successfully utilised as a proxy for biological activity and enumeration, particularly with a focus on ''Escherichia coli'' (E. Coli).<ref>{{Cite journal|last1=Reynolds|first1=D. M.|last2=Ahmad|first2=S. R.|date=1997-08-01|title=Rapid and direct determination of wastewater BOD values using a fluorescence technique|journal=Water Research|volume=31|issue=8|pages=2012–2018|doi=10.1016/S0043-1354(97)00015-8|bibcode=1997WatRe..31.2012R |issn=0043-1354}}</ref><ref name=":0" /><ref>{{Cite book|last1=Okache|first1=J.|last2=Haggett|first2=B.|last3=Maytum|first3=R.|last4=Mead|first4=A.|last5=Rawson|first5=D.|last6=Ajmal|first6=T.|title=2015 IEEE Sensors |chapter=Sensing fresh water contamination using fluorescence methods |date=November 2015|pages=1–4|doi=10.1109/ICSENS.2015.7370462|isbn=978-1-4799-8203-5|s2cid=22531690}}</ref><ref>{{Cite journal|last1=Fox|first1=B. G.|last2=Thorn|first2=R. M. S.|last3=Anesio|first3=A. M.|last4=Reynolds|first4=D. M.|date=2017-11-15|title=The in situ bacterial production of fluorescent organic matter; an investigation at a species level|journal=Water Research|volume=125|pages=350–359|doi=10.1016/j.watres.2017.08.040|pmid=28881211|bibcode=2017WatRe.125..350F |issn=0043-1354|doi-access=free|hdl=1983/a6b8b5fc-6ced-4901-9bb8-75ab3c05dd02|hdl-access=free}}</ref> TLF based monitoring is applicable across a wide range of environments, including but by no means limited to sewage treatment works and freshwaters. Therefore, there has been a significant movement towards combined sensor systems that can monitor parameters and use them, in real-time, to provide a reading of BOD that is of laboratory quality.