Biochemical Oxygen Request ( BOD , also called Biological Oxygen Request ) is the amount of dissolved oxygen required (eg demanded) by aerobic biological organisms to break down the bottom organic material is present in the water sample which is given at a certain temperature over a period of time. The BOD value is most often expressed in milligrams of oxygen consumed per liter of sample for 5 days incubation at 20 ° C and is often used instead of the level of organic water contamination.
BOD can be used as a measure of 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), both of which measure the amount of organic compounds in water. However, COD is less specific, because it measures everything that can be chemically oxidized, rather than just the level of decomposable organic material.
Video Biochemical oxygen demand
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Most natural waters contain small amounts of organic compounds. Water microorganisms have evolved to use some of these compounds as food. Microorganisms that live in oxygenated waters use dissolved oxygen to oxidatively degrade organic compounds, releasing the energy used for growth and reproduction. The population of these microorganisms tends to increase in proportion to the amount of food available. This microbial metabolism creates the demand for oxygen in proportion to the amount of organic compounds useful as food. In some circumstances, microbial metabolism can consume dissolved oxygen faster than water soluble oxygen or autotropic communities (algae, cyanobacteria and macrophytes) can be produced. Fish and water insects can die when the oxygen is consumed by microbial metabolism.
Biochemical oxygen demand is the amount of oxygen required for microbial metabolism of organic compounds in water. This demand occurs over several periods of time depending on the temperature, concentration of nutrients, and enzymes available to native microbial populations. The amount of oxygen required to fully oxidize organic compounds into carbon dioxide and water through the generation of microbial growth, death, decay, and cannibalism is the total biochemical oxygen demand (total BOD). The amount of BOD is more important for the food web than the water quality. The dissolved oxygen depletion is most likely to be evident during the initial aquatic microbial population explosion in response to large amounts of organic matter. If microbial populations dehydrogenate water, however, that lack of oxygen imposes a limit on the growth of aquatic microbial populations that produce long-term food surpluses and oxygen deficits.
The standard temperature at which the BOD test must be performed was first proposed by the Royal Wastewater Commission in its eighth report in 1912:
(c) An effluent to comply with general standards shall not contain more than 3 parts per 100,000 suspended substances, and with suspended items including shall not take at 65 ° F more than 2.0 parts per 100,000 of dissolved oxygen within 5 days of this Standard shall be determined either by the Statute or by order of the Central Authority, and shall be subject to modification by the Authority after an interval of not less than ten years.
These are then standardized at temperatures of 68 ° F, and then 20 ° C. This temperature may differ significantly from the natural environmental temperature of the water under test.
Although the Royal Commission on Waste Disposal proposes 5 days as an adequate test period for rivers in Great Britain and Ireland, longer periods are investigated for North American rivers. Incubation periods 1, 2, 5, 10, and 20 days were used in the mid-20th century. Keeping dissolved oxygen available at their chosen temperature, researchers found up to 99 percent of total BOD administered in 20 days, 90 percent in 10 days, and about 68 percent in 5 days. Variable microbial populations shifted to bacterial nitrification test of reproducibility limits for periods longer than 5 days. A 5-day test protocol with well-reproducible results that emphasize carbon-containing BOD has been endorsed by the United States Environmental Protection Agency. The 5 day BOD test result can be described as the amount of oxygen needed for water microorganisms to stabilize decomposed organic matter under aerobic conditions. Stabilization, in this context, can be considered generally as the conversion of food into aquatic living fauna. Although these fauna will continue to exert biochemical oxygen demand as they die, which tends to occur in more stable and growing ecosystems including higher trophic levels.
Typical values ​​
Most pure rivers will have a 5-day carbonate BOD below 1 mg/L. Heavily polluted streams may have BOD values ​​in the range of 2 to 8 mg/L. River can be considered highly polluted when the BOD value exceeds 8 mg/L. which are efficiently handled by a three-stage process will have a value of about 20 mg/L or less. Unprocessed waste varies, but averages around 600Ã,Â-mg/L in Europe and as low as 200 mg/L in the US, or where there is severe groundwater or surface water infiltration. The generally lower value in the US comes from the use of water per capita that is much larger than in other parts of the world.
Maps Biochemical oxygen demand
Method
There are two commonly known methods for measuring BOD.
Dilution method
This standard method is recognized by the US EPA, labeled Method 5210B in the Standard Method for Water and Wastewater Inspection To obtain BOD 5 , the dissolved oxygen concentration (DO) in the sample should be measured before and after the incubation period, and adjusted appropriately with samples of suitable dilution factors. This analysis was carried out using 300 ml of incubation bottle in which the water of the buffer diluent was fed the seed microorganism and stored for 5 days in the dark room at 20 ° C to prevent the production of DO through photosynthesis. In addition to various dilution of BOD samples, this procedure requires dilution of empty water, glucose glutamic acid (GGA) control, and seed control. Empty dilution water is used to confirm the quality of dilution water used to liquefy other samples. This is necessary because the impurities in water dilution can cause significant changes in yield. GGA control is a standard solution for determining seed quality, where the recommended BOD 5 concentration is 198 mg/l  ± 30.5 mg/l. For the measurement of carbon BOD (cBOD), the nitrification inhibitor was added after dilution water was added to the sample. Inhibitors inhibit the oxidation of ammonia nitrogen, which supplies nitrogen (nBOD) BOD. When performing the BOD 5 test, it is a conventional practice to measure only cBOD because nitrogen demand does not reflect the oxygen demand of organic matter. This is because nBOD is produced by protein breakdown, whereas cBOD is produced by breaking organic molecules.
BOD 5 dihitung oleh:
- Tidak dibutuhkan:
- Seeded:
dimana:
- adalah oksigen terlarut (DO) dari larutan encer setelah persiapan (mg/l)
- adalah DO larutan yang diencerkan setelah inkubasi 5 hari (mg/l)
- adalah faktor pengenceran desimal
- adalah DO sampel biji yang diencerkan setelah persiapan (mg/l)
- adalah DO sampel benih diencerkan setelah 5 hari inkubasi (mg/l)
- adalah rasio volume benih dalam larutan pengenceran terhadap volume benih dalam tes BOD pada biji
Metode manometrik
This method is limited to measuring oxygen consumption only because of carbon oxidation. Ammonia oxidation is inhibited.
Samples are stored in sealed containers equipped with pressure sensors. A substance absorbing carbon dioxide (usually lithium hydroxide) is added in a container above the sample level. Samples are stored in conditions identical to dilution methods. Oxygen is consumed and, because the oxidation of ammonia is inhibited, carbon dioxide is released. The total amount of gas, and thus the pressure, decreases as carbon dioxide is absorbed. From a drop of pressure, the electronic sensors calculate and display the amount of oxygen consumed.
The main advantages of this method compared with the dilution method are:
- Simplicity: no sample dilution required, no seeding, no empty sample.
- Direct reading of BOD value.
- Continuous display of BOD values ​​at current incubation time.
Alternate method
Biosensor
An alternative to measuring BOD is the development of biosensors, which are devices for detecting analyte combining biological components with physicochemical detector components. Enzymes are the most widely used biological sensing element in the manufacture of biosensors. Their application in biosensor construction is limited by enzyme purification methods that are time-consuming and expensive. Microorganisms provide an ideal alternative to this bottleneck.
A wide variety of micro organisms are relatively easy to maintain in pure culture, growing and harvesting at low cost. In addition, 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 the device. A number of pure cultures, eg. Trichosporon cutaneum, Bacillus cereus, Klebsiella oxytoca, Pseudomonas sp. etc. individually, has been used by many workers for the construction of BOD biosensors. On the other hand, many workers have immobilized active sludge, or mixed two or three species of bacteria and on various membranes for the construction of BOD biosensors. The most commonly used membranes are polyvinyl alcohol, porous hydrophilic membrane, etc.
A defined microbial consortium can be established by conducting a systematic study, ie pre-testing of selected micro-organisms for use as a seeding material in the BOD analysis of various industrial wastes. Such a formulated consortium can be immobilized on an appropriate membrane, ie a loaded nylon membrane useful for BOD estimation. The conformity of the nylon membrane charge lies in the specific binding between the negatively charged bacterial cell and the positively charged nylon membrane. So the advantages of the nylon membrane over the other membranes are: Double binding, ie Adsorption as well as traps, resulting in a more stable immobilized membrane. Such a specific microbial consortium BOD analysis tool, can find a good application in monitoring the level of pollution power, in a wide range of industrial wastewater in a very short period of time.
Biosensors can be used to indirectly measure BOD via fast (usually & lt; 30 min) to be determined alternate BOD and appropriate calibration curve method (pioneered by Karube et al., 1977). As a result, biosensors are now commercially available, but they have some limitations such as high maintenance costs, limited running lengths due to the need for reactivation, and inability to respond to changes in quality characteristics as they usually occur in wastewater treatment streams; eg the process of diffusion of biodegradable organic matter into membranes and different responses by different microbial species that cause problems with reproducibility of results (Praet et al., 1995). Another important limitation is the uncertainty associated with the calibration function to translate BOD substitutes into the actual BOD (Rustum et al. , 2008).
RedOx Fluorescent Indicator
A substitute for BOD 5 has been developed using a resazurin derivative that expresses the rate of oxygen uptake by micro-organisms for mineralizing organic matter. A cross-validation conducted on 109 samples in Europe and the United States demonstrates the strict statistical equivalence between the results of both methods. The Beginning of France Envolure (Montpellier, France) offers an ENVERDI kit that allows users to perform up to 40 BOD 5 simultaneously within 48 hours in a 96-well microplate.
Software sensor
Rustum et al. (2008) proposes the use of KSOM to develop intelligent models to make quick conclusions 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 controlling more sensible propositions. Compared to other data-driven modeling paradigms such as multi-layer artificial neural network perceptrons (MLP ANN) and classical multi-variation regression analysis, KSOM is not negatively affected by missing data. In addition, data sorting time is not a problem when compared to classical timetable analysis.
Dissolved oxygen probes: Membrane and luminescence
Since the publication of Winkler's simple, accurate and direct oxygen dissolution procedures, the analysis of dissolved oxygen levels for water has been key to the determination of surface water purity and ecological health. The Winkler method is still one of two analytical techniques used to calibrate the oxygen electrode meter; another procedure is based on oxygen solubility in saturation according to Henry's law. Although many researchers have perfected Winkler's analysis to dissolve oxygen levels in the low-PPH range, this method does not allow automation.
The development of an analytical instrument utilizing the reduction chemistry-reduction (redox) of oxygen in the presence of different metal electrodes was introduced during the 1950s. These redox electrodes (also known as dissolved oxygen sensors) utilize oxygen-permeable membranes to allow gas diffusion into electrochemical cells and their concentration is determined by polarographic or galvanic electrodes. This analytical method is sensitive and accurate to descend to a level of 0.1 mg/l dissolved oxygen. The calibration of the redox electrode from the membrane electrode still requires the use of Henry's legal table or Winkler test for dissolved oxygen.
Over the past two decades, new electrode forms were developed based on luminescence emissions from photo-active chemical compounds and refrigeration from emissions by oxygen. It is also called optical dissolved oxygen sensor. This quenching photofisika mechanism is described by the Stern-Volmer equation for dissolved oxygen in solution:
- : Luminescence in front of oxygen
- : Luminescence without oxygen
- : Stern-Volmer is constant for cooling oxygen
-
] Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â{\ displaystyle {\ ce {[O2]}}} Â Â : Concentration of dissolved oxygen
The determination of oxygen concentration by luminescence cooling has a linear response to various oxygen concentrations and has excellent accuracy and reproducibility. There are several recognized EPA methods for the measurement of dissolved oxygen for BOD, including the following methods:
- Standard Method for Wastewater and Water Inspection, Method 4500 O
- In-Situ Inc. Method 1003-8-2009 Measurement of Biochemical Oxygen (BOD) Measurement with Optical Probe.
Test limitations
Test methods involve variables that limit reproducibility. Tests usually show observations varying plus or minus ten to twenty percent around the mean.
Toxicity
Some waste contain chemicals capable of suppressing growth or microbiological activity. Potential sources include industrial waste, antibiotics in pharmaceutical or medical waste, food processing cleansers or commercial cleaning facilities, chlorine disinfection used after conventional wastewater treatment, and odor control formulations used in sanitary waste storage tanks in passenger vehicles or portable toilets. The emphasis of microbial communities that oxidize waste will decrease test results.
Matched microbial population
Tests depend on microbial ecosystems with enzymes capable of oxidizing available organic materials. Some wastewater, such as those from secondary biological waste processing, already contain a large population of microorganisms acclimatized to tested water. A large portion of waste may be used during the storage period prior to the commencement of the test procedure. On the other hand, organic waste from industrial sources may require special enzymes. A microbial population from a standard seed source may take some time to produce the enzyme. Specific seed culture may be appropriate to reflect the evolving ecosystem conditions in the receiving water.
History
The Royal Commission on River Pollution , established in 1865 and the establishment of the Royal Commission on Waste Disposal in 1898 led to the election in 1908 from BOD 5 as the definitive test for organic river pollution. Five days were chosen as the right test period because this is the longest time river water takes to travel from source to estuary in England. In its sixth report, the Royal Commission recommends that the established standard be 15 parts by weight per million waters. However, in the Ninth report, the commission has revised the recommended standard:
"Wastes that take 2-0 parts of dissolved oxygen per 100,000 will be found with simple calculations to require dilution with at least 8 volumes of river water taking 0.2 parts if the resulting mixture does not take more than 0.4 parts Our Experience shows that in part large cases of river water volume will exceed 8 times the volume of waste, and that the 2-0 portion of dissolved oxygen per 100,000, which has been proven to be practicable, would be a safe number to adopt for general-purpose standards, taken along with conditions that waste does may contain more than 3-0 parts per 100,000 suspended solids. "
This is the foundation of 20:30 (BOD: Suspended Solids) a full nitrification standard used as a benchmark in the UK through the 1970s for waste that functions with waste quality.
The United States includes limitation of BOD waste in its secondary care regulation. Secondary waste treatment is generally expected to remove 85 percent of the BOD measured in the waste and produce BOD concentrations of waste with an average of 30 days less than 30 mg/L and an average of 7 days less than 45 mg/L. The regulation also explains " treatment equivalent to secondary treatment "because it removes 65 percent of BOD and produces BOD waste concentrations with an average of 30 days less than 45 mg/L and an average of 7 days less than 65 mg/L.
See also
- Biochemical oxygen demand containing carbon
- Theoretical oxygen request
- Wastewater quality indicators discuss both BOD and COD as indicators of wastewater quality.
References
Further reading
External links
- BOD Doctor - a troubleshooting wiki for this problem test
Source of the article : Wikipedia
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