COD or Chemical Oxygen Demand is the total measurement of all chemicals (organics & in-organics) in the water / waste water;
BOD is a measure of, the amount of oxygen that require for the bacteria to degrade the organic components present in water / waste water.
The ratio of BOD/COD is about; COD is higher than that of BOD; maximum of up to 4 times in medium scale industries; but it varies based on the industrial process and nature of the raw materials used;
Relationship between the COD and BOD is in a ratio that a man can not be understood without the other, and found as natural phenomena happened in the water and the activities of living things, to the man in the wastewater, and change, while maintaining an average ratio in environments where exist.
Where there is water and wastewater exist the COD and BOD, and is in a ratio with the variation mentioned above.
Dr. Kani's answer is correct. There are numerous terminologies applied in estimating parameters during biological waste water treatment. These usually depend on whether a substrate (C, N, P) for utilisation by wastewater microbial populations is soluble or insoluble and determines the structure of microbial communities (aerobic, anaerobic, chemotrophs, heterotrophs, etc). BOD was originally used in 19th Century Britian and is often reported as the BOD5. The '5' was used as no stream in Britian took more than 5 days to reach the ocean. It is a reliable indicator of the degree of purification wastewater has undergone. Nevertheless, BOD/COD and BOD measured over longer periods than 5 days provide a more accurate and precise measure of the succes of the treatment process.
Good Luck.
Dr Kani is correct. Attached is a page from a Masters thesis which shows the relationship of measured values of BOD and COD. Note that the BOD value is close to zero when the COD value is around 50 since the BOD reflects only the dissolved organics while COD includes total dissolved organic and inorganic compounds. The thesis is titled DYNAMIC PERFORMANCE OF A SUBMERGED PACKED BED BIOLOGICAL FILTER FOR WASTEWATER TREATMENT by V. Dhagumudi, SUNY-ESF, Syracuse, New York, 2008.
Almost all treatment plants are required to measure one of these three items as a measure of the pollution value in the water. COD should always measure higher than TOC and then BOD.
COD or Chemical Oxygen Demand is the total measurement of all chemicals in the water that can be oxidized. TOC or Total Organic Carbon is the measurement of organic carbons. BOD- Biochemical Oxygen Demand is supposed to measure the amount of food (or organic carbons) that bacteria can oxidize.
Preceding discussion on the BOD-COD relationships and the model anaiysis of the actual plant lead to the following conclusions.
- The BOD-COD relationships obtained in this work make it possible to calculate the value of BODs which needs 5 days fbr its determination,by using the value of COD, which can be measured in an hour. From the calculated value of BOD, the performance of the activated sludge process can be evaluated in an hour.
- The Monod model can be applied to the anaiysis of the activated sludge process with extended aeration fbr the treatment of the raw sewage in the University where the flow rate and the contaminants concentration make heavy change.
- The BOD-COD relationship for the treated sewage water, esttmated from the linearized equation for substrate balance with the Monod model, agrees weli with the measured relationship.
COD is the amount of oxygen required to chemically oxidize organic matter in your wastewater into inorganic matter. whereas BOD is the amount of oxygen required to biologically oxidize the organics in your sample, usually after 5 days or 21 days of incubation time, depending on the bioassay followed.
The ratio of BOD/COD of a waste water is a good indication of how much of the total organic load (or oxygen demand) is bioavailable for degradation.
If you want a concise answer the relationship between the COD and BOD values in urban wastewater is about 2.
Thanx for all your contribution for my question. And there is any standard values for BOD/COD ratio to identify the type of the waste water?
the ratio is important for wastewater containing mixture of domestic and industrial wastewater. HIgh BOD/COD ratio indicates that toxicity is less. Low ratio indicate that toxicity is more. BOD indicates that wastewater has biodegradable content and so difference means non-biodegradable or toxic components are more. Therefore for industrial wastewaters, both COD and BOD are measured
As an expatriate of SrI Lanka, I am very happy to read your interest in water anaylys. I agree with the previous comment. If the waste water is polluted with discharge metal waste, the COD will be high and the water is considered toxic to be discharged to natural water ways. To preserve the natural beauty of Sri Lanka, the country is need of reserach chemists like you.
Water requires treatment if the COD is high.
Thanx Chintha for ur appreciation and I had completed my BSC in water science and technology (first batch in Sri Lanka) and expect to join in job with water analysis field.
I was not aware of the Uva Wellassa university. I was in Sri Lanka in March and did travel through Badulla to Horton Plains. I had two friends from US with me and we hiked the World's End Trail In Horten Plains.
I am graduate of The Oil & Gas Refining Technology Universty in Moscow , Russia (formally USSR). I am a research chemist for a private company. You can check opur company website :Taylor Technologies, Sparks, Maryaland ,USA.
I was surprised to see so many grads & undergrads in the Uva Wellisa University who are in the Research Gate community: good luck to all of you.
Thanx Chintha, our university is newly established one and therefore i am a pioneer student in my degree programme. My research is also done in risk assessment in implement water safety plan. And I also wish you all the best for ur work.
That is great news. So proud to know that SL has given an oppertunity for intelligent young adults to advance in such a promissing field in technology. Which school did you go to? I went to Visakha Vidyalaya in Colombo.
I am sponsering 5 high school students from the Nikaweritiya Maha Vidyalaya for the last 5 years. I think two of the students are doing their A-Levels this time and hope they will be lucky as you to get into a university. I created a scholarship fund in the memory of my parents.
My nephew ownes Qualitron who does sales & service for Scentific Instrumentation such as HPLC, GC etc. Have you heard about them? His name is Roshan Perera and thier company is situated in Nawala, Rajagiriya.
By the way is the Uva university funded by any Foreign country?
No. It is also under controlled by UGC in Sri Lanka. I went to Taxila Central College, Horana. I am very happy to heard about ur great work in sponsoring for students. In future, I also expect to involve in this kind of great work. I heard about ur nephew's selling instruments and I learned about HPLC and GC under mu course module (Analytical Techniques and Instrumentation). Good luck.
I am glad that Analytical Instrumenttation is a part of your course module. If ever you get a chance to contact Qualitron, mention about me to Roshan.
At the moment our company has a contract with an Australian water testing company to make a "Camera Lab". What it does is read test trips and interpolate the tested parameters. Taylor makes test strips to check the quality of swimming pools and spa water supplys. The parameters we check out free Chlorine/ Bromine, total alkalinity, calcium hardness, Cyanuric acid and pH. The strip has reagent pads that test each parameter when dipped in the water supply. Tested strip is inserted into teh camera which is programmed to read the different colors and correlate into the levels of each parameter.
May be you could research this area for field testing the water sources in SL
I glad to know this method but i have a problem, if this parameters are checked in colorimetric method therefore it gives a certain value or range ?
I worked as a trainee in Kandana Water Treatment Laboratory, National Water Supply and Drainage Board (NWS&DB) and they follow standard methods for water and waste water book.
Yes these tests are based on the Standard Methods for water. The Pool / Spa industry does not fall under Enviorenmental standards but under Health Dept: so they can use dry chemistry test strips to maintain the water in pools/spas. The water treatment plants are under Enviorenmental policy and only tests acepted are the Standard methods (you are correct). The tests are based on "colorimetric standards". The resulting colors are matched against a standard color chart for each parameter to determine the levels.
In any effluent like that of distillery , tannery paper mill etc the COD/BOD will be very high. It all depends on the load of organics in the effluent. The organics may be either biodegradable or non-biodegradable . The effluent ought to be diluted and the organics degraded by specific microbial consortium. Mostly employing biological tools will be greatly appreciated. Or the resulting sludge in the solar evaporation pond can be used for bio -composting as it has been proven in the case of Distillery effluent
The answer is not easy; BOD is due to the degradation made from bacteria and change from one kind of bacteria to other vs a specific substrate; for COD it is a chemical reaction and it is bonded to the specific substrate too but the action of the chemical oxidation is more under control. So their ratio depends how it is done BOD (wich group of bacteria) and the COD of the analysis on the same substrate and this ratio is specific for each situation.
Regards
the standard ratio BOD:COD is as 0.6:1.0 (BOD is about 60%of COD) in standard raw communal wastewater in Europe. It seems, in Asia is the same ratio, the poeople have the same metabolismus. It is valid for standard sewage, without industrial or food industry waste water. In industrial water is wery diferrent ratio, in food industry is ratio higher, 80-90%.
Regards,
very high variability of BOD/COD ratio is typical for landfill leachates. The ratio of BOD/COD, from 0.70 to 0.04, decreases rapidly with the aging of the landfills. Try: http://www.aseanenvironment.info/scripts/count_article.asp?Article_code=41016793. You will find also the review of treatment methods including enhancement of biodegradability .
Thanx so much for all your contribution. I follow these statements.
COD is greater than BOD, and COD can find with in 3hour but for BOD 5 days
why BOD taking so much days to find out? any simple method to find out the same?
COD = Quantification of oxidizable amount of carbon
BOD = Quantification of biodegradable carbon (through biological oxidation)
Only one relation of COD to BOD is COD > BOD always.
There is no any thumb rule for BOD/COD ratio
Some average sewage BOD/COD ratio may be 0.6 and for Industrial waste it varies and depends on type of effluent.
The only relation between COD & BOD is - COD > BOD.
For most industrial process waste water, community sewage, drains and even some hetrogeneous sources, COD/BOD ratio has been found to be in a defined range and hence, COD result gives more or less BOD value range for such identifiable waste water.
COD is required to be done before BOD is most cases where the waste/water sample is from unknown source as fixing dilution is critical for BOD.
BOD(5 d, 20C) can be replaced by BOD (3 d, 27 C) as the values are more or less similar and yield faster result.
Dear Iresha! Is your Q answered sufficiently? If not, please give us a more specific Q! I can suppose that you are trying to degrade the organic contents in wastewater. For this task the cheapest way is to let microorganisms do the work. BOD is jus this - a measure of how much O2 use microorganisms to oxidize the organic C. Lower the BOD compared to COD - less efficient are the microorganisms, thus more problematic (toxic) is the wastewater ... Does this answer better your Q?
More the BOD/COD ratio of wastewater more will be the biodegradability.
This ratio is not fix, it may vary according to the wastewater characteristics
Bod 5 relates to the 5 days it took for sewage effluent to move from London to the mouth of the Thames River it is a purely arbitrary time of 5 days, it should be considered a qualitative result as it is difficult to get reproducible results due to variations in seed cultures and the natural variations in biological systems
The topic is very interesting. I strongly suggest the following book: "Third century of biochemical oxygen demand" by Rodger Baird, and Roy Keith Smith.
COD or Chemical Oxygen Demand is the total measurement of all chemicals in the water that can be oxidized. BOD- Biochemical Oxygen Demand is supposed to measure the amount of food (or organic carbons) that bacteria can oxidize.
Natural organic detritus and organic waste from waste water treatment plants, failing septic systems, and agricultural and urban runoff, acts as a food source for water-borne bacteria. Bacteria decompose these organic materials using dissolved oxygen, thus reducing the DO present for fish. Biochemical oxygen demand (BOD) is a measure of the amount of oxygen that bacteria will consume while decomposing organic matter under aerobic conditions.
Chemical oxygen demand (COD) does not differentiate between biologically available and inert organic matter, and it is a measure of the total quantity of oxygen required to
oxidize all organic material into carbon dioxide and water. COD values are always
greater than BOD values.
COD-chemical oxygen demand measures the total oxygen including inorganic and organic oxygen content.But BOD represents only the amount of oxygen required to degrade to degrade the organic matters present in waste water by the micro organism.If the content of organic matter is more more the value of BOD.In general COD is always more than BOD.
BOD: Biochemical Oxygen demand in waste water : The amount of oxygen required to stabilize organic matter at room temperature and 5 days , biochemically.
COD: Chemical Oxygen demand: The amount of oxygen required to stabilize organic matter by chemically.
I´ve read all the conversation here and it brings to my mind a discussion I´ve had with my boss. Her main experience comes from wastewater treatment plants and she insists that since hi BOD consumes oxygen very fast, there is no way you could have a sample of waste water with hi DO and hi BOD. While I think that, as long as the source of oxygen stays constant (aeration, intense photosynthesis, etc.), the DO level will stay hi, maybe not saturated, but not anoxic. I´m I wrong or my logic is correct?
Dear Ferrand! You MAY be correct, but not necessary! Play with microbial and chemical kinetics to see when is valid the first and when the second fact. Microbial and chemical kinetics are well depicted in any good wastewater treatment book, e.g. in the States: Metcalf and Eddy.
THX for your response Boris, I understand that the two options are correct under certain circumstances and conditions, the thing is that we are getting a bunch of data from samples taken from industrial discharges and treatment plants showing hi BOD and medium to hi levels of DO. She, claiming that such behavior is impossible, is sending back those results to the lab and or just deleting them!!!
i think i will side with your boss. it is difficult for me too to imagine a system with hi DO and hi BOD at the same time. if there is hi BOD then your DO should have been low since BOD is a demand for oxygen. or is the measurement of the DO and BOD done at different points or with different samples? try checking your DO measuring devices or ur method for BOD determination.
In my case, the DO is mesured on the field in natural water bodies usually presenting natural agitation and aireation, then a sample is taken and BOD (5 days) is messured at the lab. My point is that at the field the oxigen is constantly entering the system maintaining a hi DO level, the demand of it is hi too since there is organic matter to be decomposed.
Dear Ferrand your results may be correct because in case of natural water bodies as you observed the DO will be more, i appreciate your observation of natural agitation. In the same way natural water bodies will have an ability to purify water and acts as a sink for pollutants. That is why natural water bodies will have very low BOD values on the other hand BOD and COD are used to measure the degree of pollution in polluted water not for clean water. I think you got the answer
COD includes both biodegradbale and non-biodegradable substances whereas BOD contains only bio-degradable. Hence COD is always greater than BOD
BOD means Biochemical oxygen demand. The microorganisms use organic matter as a food source through oxidation which oxygen is consumed. COD, Chemical Oxygen Demand, is a measure of the total quantity of oxygen required to oxidize all organic material into carbon dioxide and water. COD values are always greater than BOD values, but COD measurements can be made in a few hours while BOD measurements take five days.
What is the ration of bod/cod for sewage and waste water how wil find cod based on bod value please help me .
There are not ratio between COD and BOD which correspond with all type of wastewater. The quality of wastewater is different from a source of discharge to another and from a region to another. However, for exemple in France, one usually assumes that, for domestic wastewater, 2 < COD/BOD5 < 3; for wastewater from food-industries, 1,5
Usually in wastewaters the BOD values are around 30 to 70% of the COD 70%. It depends on the type of waste water as well as thw treatmnet used.
I agree with the Tadjouwa answer and the COD value is always greater than BOD. commonly most of the researchers are deal with the COD when they analyze the waste water and BOD is generally focused on the drinking water samples because of the cost factor.
Both COD and BOD has same purpose, different approaches and meanings. Measuring Oxygen Demanding Wastes, by chemical method is carried out by COD and using biological species as seed, it is carried out by BOD.
As already known both are measure of Dissolved Oxygen (DO) required to oxidize dissolved organic pollutant in waste-water sample.
Although BOD is perfect test if carried out as per standard methods, it takes 5 days of time to know the results. which can quickly be carried out in 3 hours by COD (chemical method).
BOD is always lower than COD.
COD is based on chromic acid oxidation because it is strongest oxidizing agent. Assuming all Organic matter gets converted to CO2 and H2O.
BOD is based on the real demand for DO in sample under natural conditions.
Hence both are most important parameters while assessing water quality.
Please go through Encyclopedias on air, water, soil by some publishers ( i dont remember right now)
We can use this BOD/COD relationship for assessing toxicity. If BOD is too lower compared to COD then the sample can be visualized as toxic, although its not confirmation. In general BOD to COD ration is 0.6+. The lower the ration higher is toxicity. If the sample is highly toxic then BOD can never be more than 0.2 at any cost.
We use COD/BOD5 is more than 2.5 for the indication of industrial wastewaters. For municipal wastewaters BOD5/COD is generally 0.5 (in our cases).
As a general rule: this ratio is 0.5 in a domestic sewer.
It depends on the own characteristics of the specific wastewater.
As this ratio is above this value means that the residual water is more biodegradable, and if smaller, that have a higher content of refractory or poorly biodegradable compounds.
COD values are generally higher than BOD, however, there is no real ratio. It depends on the treatment process i.e if the same process is used all the time under the same conditions. Other factors can affect both factors such as composition of the waste being treated.
The ratio BOD: COD is a characteristic of a particular wastewater and is a simple and direct measure related to its biodegradability. That is, there is no absolute value for any residual water, but will directly depend on its composition.
It is usual to consider a wastewater that has a BOD ratio: COD with a value greater than 0.4 indicates that you can apply a biological treatment if necessary.
However, as this relationship will depend on the data quality of BOD and COD, analytical quality assurance should be applied, so that the data are sufficiently reliable.
In the case of the BOD, as this method is made applying an inoculum of microorganisms, among other things, you must ensure that toxic compounds are not present, in order to guarantee the correct grow of such microorganisms.
Is there any possibility for getting higher COD value than BOD value..?? whether it depends on the source of samples??
Thanks Munavar Iqbal and friends here...
I have a lot of unpublished work carried out in this area. However this para is intended for a better understanding of the concept.
BOD is based on activity of microbes. COD is based on chemical reaction (oxidation). If microbial seed we use for BOD is not active then it results in lower BOD. It is as good as no microbe is added.
Even if the same microbial seed is more active or more in volume, then also it results in lower BOD. It takes a lot of time and expertize to carry out BOD for 100% accuracy. Hence I believe in standardized BOD namely using a seed of uniform composition tested with glucose as standard alone provides good accuracy.
To avoid all confusions Take it granted that COD of filtered samples free from inorganic compounds (mostly anions) alone is reliable.
Regarding using BOD5:CODCr ratio as an indicator of Toxicity, We need a lot of work to be carried out with different standard solutions, standardized microbes, toxicity tests etc.
Unfortunately I never had an oppurtunity to work on this demanding topic after my PhD days.
The relation between COD and BOD depends on the characteristics of water sample and the ratio between them is changeable with regard to treatment time
One of the answer mentioned the toxicity based on the ratio of BOD to COD, why if the ratio is too low, it indicates that that the sample is toxic?
Hi Iresha
I think is not necessary to explain about BOD or COD you know this. Here the important thing is that you must obtain your ratio by your own. Then, the most important thing is that you have to standardize your method for your own samples to obtain the values of COD and BOD after your repeated many times your analysis. When you do so, then you will have a better knowledge of your samples then you can apply the necessary treatment if required. The only true thing is that you have to follow the international standards for the methods. Then, in the description of your methods you have to explain how you did, especially if you did some modifications. As many colleagues already wrote here, there is not an accurate ratio, because the wastes are different and how you treat your samples.
what is the usual BOD range for pond waters ?? I am getting 12 -132 ppm. Is this ok or I should get below 10?
All in all, i should understand that there is not formula to obtain BOD from COD which I think is the main issue of the initial question.
In generally, for municipal waste water is relation BOD as 60% of COD (Cr - dichroman method) or ?80% of manganistan method. If in waste water is relevant part of industrial water, is valid for resistant contamination lower ratio and for best degradable contamination (food industry, conservation, sugar mill and othesrs) is ratio highest, to 80% od Cr-CVOD.
In generally, for municipal waste water is relation BOD as 60% of COD (Cr - dichroman method) or ?80% of manganistan method. If in waste water is relevant part of industrial water, is valid for resistant contamination lower ratio and for best degradable contamination (food industry, conservation, sugar mill and othesrs) is ratio highest, to 80% od Cr-COD.
COD includes both Organic and inorganic. Whereas BOD includes Organic alone. COD is the measure of amount of substance that can be chemically oxidized by strong oxidizing agent.BOD is the measure of substance that can biologically oxidized by Microorganism. Sometimes a substance can be oxidized by chemically and Biologically. so they are represented by ratios and not by percentage.
The findings from my research chemical analysis if tannery effluent treatment shows a slight variations from your opinion above. However, I cannot make a valid conclusion yet until I am done with the research work.
You'll certainly hear from me.
BOD (Biochemical oxyen demand) - The amount of oxygen required by bacteria to degrade the organic matter ( biodegradable).
While , COD (Chemical oxygen demnad) - is ti degrade both the organic as well as inorganic matter (biodegradable and non biodegradable ) present in the wastewater samples by using strong chemical agent (such as K2CR2O7).
The ratio of COD/BOD, COD values are tending to be always higher than the BOD values and also depend in the type of water or waste waters.
BOD is the acronym for Biochemical oxygen demand. It is the amount of oxygen required by bacteria to degrade the biodegradable organic matter in the process of biodegradation.
While , COD is chemical oxygen demand. It considers both the organic as well as inorganic matter (biodegradable and non biodegradable ) present in the water or wastewater by using strong oxidizing agents like potassium dichromate or potassium permanganate.
BOD is the oxygen demand of microbes for degradation of organic matter. COD is oxygen demand consumed in chemical reaction (oxidation).
COD is always higher than BOD and the ratio may even exceed 2.5 depending upon the type of water or wastewater.
COD for both (biodegradable and non biodegradable) using chemical oxidizing agent, while BOD is only for (biodegradable) using bacteria.
For that reason COD is always higher than BOD.
What I have not read here yet (I admit I have not read every entry) is that the use of "Standard Methods..." is pivotal for many to communicating BOD5 or COD. This means that many of us think in terms of the Standard Method. Therefore, BOD is the result of the difference between two DO measurements: one at the beginning of the 5 day incubation period and the other after the 5 day incubation period.
Additionally, according to some sources, after 7 days (instead of 5) the process will complete with a maximum of 80% of the total DO depleted. There is also a case to be made for 21 days and another for 60 to 90 days for ultimate oxygen depletion or for absolute depletion but still no more than 80% which apparently is an asymptotic effect. But for all practical purposes the 5-day will suffice for most process control efforts.
Confusing? Yes. But we have nothing better to measure with. The COD is a similar test but instead of letting the bugs do the work we add chemicals and we don't need 5 days: a few hours will work. This means the COD test has more utility and value in a hectic production environment. In my opinion the COD is more consistent and not subject to as many opportunities for error or anomalous variables (humans) to skew the data, as is the BOD test.
The principal objective of wastewater treatment is generally to allow human and industrial effluents to be disposed of without danger to human health or unacceptable damage to the natural environment. Irrigation with wastewater is both disposal and utilization and indeed is an effective form of wastewater disposal (as in slow-rate land treatment). However, some degree of treatment must normally be provided to raw municipal wastewater before it can be used for agricultural or landscape irrigation or for aquaculture. The quality of treated effluent used in agriculture has a great influence on the operation and performance of the wastewater-soil-plant or aquaculture system. In the case of irrigation, the required quality of effluent will depend on the crop or crops to be irrigated, the soil conditions and the system of effluent distribution adopted. Through crop restriction and selection of irrigation systems which minimize health risk, the degree of pre-application wastewater treatment can be reduced. A similar approach is not feasible in aquaculture systems and more reliance will have to be placed on control through wastewater treatment.
The most appropriate wastewater treatment to be applied before effluent use in agriculture is that which will produce an effluent meeting the recommended microbiological and chemical quality guidelines both at low cost and with minimal operational and maintenance requirements (Arar 1988). Adopting as low a level of treatment as possible is especially desirable in developing countries, not only from the point of view of cost but also in acknowledgement of the difficulty of operating complex systems reliably. In many locations it will be better to design the reuse system to accept a low-grade of effluent rather than to rely on advanced treatment processes producing a reclaimed effluent which continuously meets a stringent quality standard.
Nevertheless, there are locations where a higher-grade effluent will be necessary and it is essential that information on the performance of a wide range of wastewater treatment technology should be available. The design of wastewater treatment plants is usually based on the need to reduce organic and suspended solids loads to limit pollution of the environment. Pathogen removal has very rarely been considered an objective but, for reuse of effluents in agriculture, this must now be of primary concern and processes should be selected and designed accordingly (Hillman 1988). Treatment to remove wastewater constituents that may be toxic or harmful to crops, aquatic plants (macrophytes) and fish is technically possible but is not normally economically feasible. Unfortunately, few performance data on wastewater treatment plants in developing countries are available and even then they do not normally include effluent quality parameters of importance in agricultural use.
The short-term variations in wastewater flows observed at municipal wastewater treatment plants follow a diurnal pattern. Flow is typically low during the early morning hours, when water consumption is lowest and when the base flow consists of infiltration-inflow and small quantities of sanitary wastewater. A first peak of flow generally occurs in the late morning, when wastewater from the peak morning water use reaches the treatment plant, and a second peak flow usually occurs in the evening. The relative magnitude of the peaks and the times at which they occur vary from country to country and with the size of the community and the length of the sewers. Small communities with small sewer systems have a much higher ratio of peak flow to average flow than do large communities. Although the magnitude of peaks is attenuated as wastewater passes through a treatment plant, the daily variations in flow from a municipal treatment plant make it impracticable, in most cases, to irrigate with effluent directly from the treatment plant. Some form of flow equalization or short-term storage of treated effluent is necessary to provide a relatively constant supply of reclaimed water for efficient irrigation, although additional benefits result from storage.
I agree with MS JAK Full answer.
COD= organic+ inorganic pollutants ( chemical oxidation), oxidizing agent K2Cr2O7
For that COD is always higher than BOD about 5 times more.
BOD= Organic pollutants only ( Biological degradation) microorganisms using oxygen
Kind regards
I agree with the above answers. Also would like to add the following.. BOD is mostly considered when analyzing drinking water compared to COD.
COD is a measure of total organic molecules dissolved in waste water. After the treatment, COD should come to zero or to a reasonable limit of 10 ppm, if it is to be let into river.If it is to be let onto healthy living soil, then COD is food for such soil. Soil can carry out the treatment and reduce COD through its utilization. COD becomes organic food for the a living soil.
BOD5 has been named so,because most of the British rivers meet the sea within 5 days, they decided to bother only about 5-days BOD, which will be less than the ultimate BOD that will be somewhat closer to COD. They also selected test temperature of 250C that they have. They also agreed that BOD should be brought down to 30 ppm because after 5 times dilution, the river still can have BOD less than 6 ppm and this can be safe for the aquatic life.
BOD/COD ratio is a measure of food value. If the ratio is higher, it has higher food and less toxicity. Sewage, for example, may have BOD/COD ratio of 0.5 before treatment.
Chemical Oxygen Demand is an important water quality parameter because, similar to BOD, it provides an index to assess the effect discharged wastewater will have on the receiving environment. Higher COD levels mean a greater amount of oxidizable organic material in the sample, which will reduce dissolved oxygen (DO) levels. A reduction in DO can lead to anaerobic conditions, which is deleterious to higher aquatic life forms. The COD test is often used as an alternate to BOD due to shorter length of testing time.
The following link will be useful,
https://cgi.tu-harburg.de/~awwweb/wbt/emwater/lessons/lesson_a1/lm_pg_1068.html
Typical values for the ratio of BOD/COD for untreated municipal wastewater are in the range from 0.3 to 0.8.
If the BOD/COD ratio for untreated wastewater is 0.5 or greater, the waste is considered to be easily treatable by biological means. If the ratio is below about 0.3, either the waste may have some toxic components or acclimated microoorganisms may be required in its stabilization. The corresponding BOD/TOC ratio for untreated wastewater varies from 1.2 to 2.0. In using these ratios it important to remember that they will change significantly with the degree of treatment the waste has undergone.
Alternately the ratio of COD to BOD is often 2:1. I have hundreds of data points for samples from a cattle slaughterhouse which show that the ratio is 2:1 almost exactly.
I agree with the above answers, given to us!hHave a nice weekend!
Natural organic detritus and organic waste from waste water treatment plants, failing septic systems, and agricultural and urban runoff, acts as a food source for water-borne bacteria. Bacteria decompose these organic materials using dissolved oxygen, thus reducing the DO present for fish. Biochemical oxygen demand (BOD) is a measure of the amount of oxygen that bacteria will consume while decomposing organic matter under aerobic conditions. Biochemical oxygen demand is determined by incubating a sealed sample of water for five days and measuring the loss of oxygen from the beginning to the end of the test. Samples often must be diluted prior to incubation or the bacteria will deplete all of the oxygen in the bottle before the test is complete. The main focus of wastewater treatment plants is to reduce the BOD in the effluent discharged to natural waters. Wastewater treatment plants are designed to function as bacteria farms, where bacteria are fed oxygen and organic waste. The excess bacteria grown in the system are removed as sludge, and this “solid” waste is then disposed of on land. Chemical oxygen demand (COD) does not differentiate between biologically available and inert organic matter, and it is a measure of the total quantity of oxygen required to oxidize all organic material into carbon dioxide and water. COD values are always greater than BOD values, but COD measurements can be made in a few hours while BOD measurements take five days.
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