Mathematical relationship between bod and cod

some relationship or correlation between contents and compare the data of both the plants. Keywords: BOD, ammonium nitrogen, nitrogen, phosphorus, suspended solids, wastewater .. Chemical Oxygen demand (COD). The objective of this paper is to correlate BOD (Biochemical Oxygen Demand) with COD (Chemical Oxygen Demand) and TOC (Total Organic Carbon). So that . mathematical models can generate equations to estimate BOD as a results showed that BOD could be estimated mathematically through its relationship The chemical oxygen demand (COD) stood out among the selected.

If the lab's average is considerable LOWER thanjust the opposite is true, and the regulatory agency should be on the lab's case. In the table of suggested dilutions for various BOD samples, at the bottom of the table where the suggested volumes to be diluted are 1.

Caution the analyst to remember to multiply the BOD result by that additional dilution factor. Source water is the single most common cause of bad blanks, and it deserves a discussion. All of these have a bad impact on BOD tests, and must be avoided in the source water. Sometimes it is best to buy distilled water NOT distilled drinking water The purpose of the biochemical oxygen demand BOD5 test is to measure the potential of wastewater and other waters to deplete the oxygen level of receiving waters.

Wastewater treatment plant operators also use the BOD5 test to determine the efficiency of their plant by measuring the BOD5 of the influent, and of the effluent, and then calculating the percent removal. The BOD5 test may also be used to test waters other than wastewaters to determine their oxygen-depleting potential.

Oxygen is required used up, depleted, consumed by microorganisms as they assimilate various organic and inorganic materials transported by the water. Some of those materials contain reduced forms of nitrogen. Collectively, these materials are called nitrogenous materials, and they are consumed by nitrifying bacteria. If those nitrifying bacteria are inhibited, usually by using a pyridine compound, the test measures only the carbonaceous organic material, and is referred to as carbonaceous BOD5, or CBOD5.

Carbonaceous material is that consumable material which does not contain nitrogen. While the Term "BOD" technically refers to the oxygen uptake demand of contaminated water, the term is commonly used to refer to the organic and inorganic materials consumed by bacteria, as if "BOD" is a contaminant in the water. For example, wastewater treatment plants report "percent removal of "BOD" as an indication of how well the plant is performing.

Many biological treatment plant effluents contain enough nitrifying bacteria that their consumption of nitrogenous material material containing nitrogen is significant. Because nitrogenous demand has historically been considered an interference i. It would take the bacteria in a wastewater sample 20 - plus days to assimilate all the consumable material in a water sample. Because it is impractical to spend 20 days waiting for the test to finalize, a 5-day test has been established as the standard hence, BOD5.

The BOD5 test is widely used to determine the degree to which a waste stream will contribute to pollution of receiving waters by depriving organisms in those waters fish of their source of oxygen.

The BOD5 test is of prime importance in regulatory programs and in determining the overall health of receiving waters. It is Standard Methods B or its derivative that is most commonly used in environmental laboratories. To be a valid test, at least 2. If necessary, samples must be pretreated to assure proper pH, temperature, and absence of toxic materials e. Sampling, Sample Preservation, Holding times a. Discharge permits or other regulatory documents usually specify sampling locations.

Care must be taken to make sure the sample is representative of the water body from which the sample was taken. Samples should be taken in a clean plastic or glass container of sufficient size to provide enough sample for all of the tests and the quantity of BOD bottles that will be incubated for that sampling site. Another consideration in determining sample size, is that the sample must be representative of the waste stream, and the smaller the sample, the more difficult it is to make sure that it is representative.

Preservation and Holding Times 1 In most environmental samples, bacteria naturally present in a waste stream are consuming oxygen before, during and after the sample is taken. Therefore, starting the analysis as soon after taking the sample is very important. Discharge permits specify whether samples should be grab or composite. A variance is allowed by 40 CFR if the permittee has data showing specific types of samples under study are stable for a longer time unlikely to add more than 24 hours [72 hours total].

Measurement of Dissolved Oxygen DO. Applicable methods are EPA Method An oxygen-sensitive membrane electrode, polarographic or galvanic, with appropriate meter meets EPA-approved method requirements. The YSI series, and Orion series instruments are examples of commercial meters meeting those requirements for measuring DO. The method calls for calibrating the meter using oxygen-saturated water, water-saturated air, or a Winkler titration before each use.

If DO is routinely measured using an electrode and meter, checking calibration of the meter periodically with a Winkler titration will help make sure the meter is functioning properly.

Burettes capable of measuring accurately to 0. If using an air incubator, the thermometer should be immersed to the immersion line in a suitable container e. If using a water bath, simply immerse the thermometer to the immersion line. Calibrate a less expensive thermometer for general use.

Incubator or Water Bath. Either an air incubator or water bath may be used to incubate BOD bottles. It must be of sufficient size to hold all BOD bottles for a given batch i.

For reasons explained later, it is also advantageous for an air incubator to be large enough to hold the dilution water container used for the BOD5 determination. A household refrigerator can be modified to meet BOD5 test needs. One required modification is installation of a small fan to create an airflow and ensure an even temperature throughout the refrigerator. The thermometer used to monitor temperature in the incubator should be placed in the vicinity of the majority of the BOD bottles.

A glass or plastic container of laboratory grade e. Although not required, a convenient way to introduce dilution water into BOD bottles without creating air bubbles is to siphon the water from the dilution water container.

If this technique is used, the siphon hose should terminate with a 6-inch length of glass tube for filling the BOD bottle from the bottom without submerging the hose. The dilution water container and all associated equipment must be kept clean washing with detergent and rinsing with distilled water should be sufficient. They can be either, or mL mL is the most widely used.

Just like the dilution water container, BOD bottles must be kept clean. Wash after each use with detergent, rinse with distilled water, drain, and store such that the bottles are not exposed to dust or other contaminants in the lab. If blanks unexpectedly test higher than normal, it may mean the BOD bottles need acid washing. This can be done by first washing, rinsing, and draining as above, and then rinsing with 1: Rinsing is accomplished by carefully swirling 10 to 20 mL of the dilute acid until all inner surfaces of the bottle are wetted.

Allow the bottle to sit for a few minutes before properly discarding the acid. Then rinse the bottle with distilled water and drain. Acid rinsing is not necessary every time the BOD bottles are used and might never be required as long as blanks test less than 0.

BOD bottles used for blanks should be chosen randomly to avoid checking only the "cleanest" bottle. To provide the optimum environment for survival of bacteria in the incubated sample, it is necessary to buffer the sample such that it maintains a pH of 6.

The buffer can be prepared with various phosphate compounds, or it can be purchased ready-made. It must be discarded if such growth appears because the growth has an oxygen demand which would introduce a positive bias into all BOD5 measurements. The pH of the buffer solution should be 7. In addition to the nutrient value of the phosphate buffer, nutrients in the form of ammonium chloride, and trace metals in the form of ferric chloride, magnesium sulfate, and calcium chloride are added to the dilution water.

These solutions can be purchased ready made all combined in one packetor they can be prepared individually. Hach Company, North Central Labs, and perhaps others sell packets pillows containing both buffers and nutrients. To provide a check on efficiency of the seed and effectiveness of dilution water, Standard Methods B implies that a standard solution should be analyzed with each batch of BOD5 samples.

This solution can be prepared as described in Appendix A, or purchased as a solution from a commercial vendor such as Hach Company or North Central Labs. If a lab's average is considerably less thata stronger seed should be tried A single lab should be able to achieve a standard deviation much lower than A typical single lab standard deviation would be in the mid- to low- teens.

Mathematical Relationship between COD & BOD levels in Effluent?

A standard deviation approaching or exceeding Pretreatment of Samples a. After removing any items that are obviously not representative of the sampled water e.

This can be done with a food blender on a slow speed, an aggressive stirring bar, or other device that provides thorough mixing without being overly disruptive to microorganisms in the sample as might occur if, for example, a high-speed blender is used.

If BOD5 is expected to be so high that a very small aliquot must be taken, the entire sample can be diluted such that a larger, more readily measured, aliquot may be taken. If a pipette is used to measure the sample aliquot, use of a wide-tip variety is beneficial i. This can be done by placing sample containers in cold water in a sink if they are too warm, or in warm water if they are too cold. Sample pH must be in the range of 6. Add sulfuric acid H2SO4 or sodium hydroxide NaOH of sufficient concentration so that the quantity of acid or base added does not dilute the sample by more than 0.

For example, if the sample is one liter 1, mLthe acid or base should be strong enough that no more than 5 mL would be added to the sample to bring it into the range of 6.

If allowed by the discharge permit and if possible given the design of the treatment plant, BOD5 samples taken at wastewater treatment plants using chlorine to disinfect the final effluent should be taken ahead of the chlorination point.

If this is not possible, dechlorination is required, and following dechlorination, samples must be seeded because the chlorination process kills the bacteria that otherwise would consume the BOD in the waste sample. Samples taken from waste streams where the final effluent is dechlorinated usually do not need further dechlorination in the lab.

Determining how much sodium sulfite is required to dechlorinate a given amount of sample requires acidification of the sample, addition of potassium iodide, and titration with standard sodium sulfite. Since this entire procedure cannot be done on the samples that are later incubated, it must be done on a sample dedicated to that purpose.

Some wastes, particularly industrial wastes, contain metals which are toxic to the organisms responsible for oxygen depletion during the BOD5 incubation. Such toxic materials would result in a negative bias i. The presence of toxic substances can be confirmed by testing a set of serial dilutions. If the measured BOD5 for a given sample increases significantly as the sample is increasingly diluted, a toxic substance in the sample i. If that toxic substance cannot be avoided, its presence should be reported with results submitted by the lab.

Commercial labs may know nothing about possible toxicity of samples received from most clients. In such cases, the lab might consider doing a set of serial dilutions. Although it will be too late to do anything about toxicity at the end of the five-day incubation period, the presence of a matrix interference can at least be reported to the lab client. If initial dissolved oxygen DO readings with a properly calibrated DO meter or as measured with a Winkler titration indicate the sample contains more DO than it should for the barometric pressure and sample temperature at the time, the sample is supersaturated with DO.

Supersaturation might result when the sample has been vigorously agitated just prior to the DO reading without giving air bubbles in the sample a chance to escape, or when the sample is undergoing photosynthesis. Supersaturation at the time of initial DO reading would result in a positive bias. A problem with supersaturation is usually indicated by high blank results e.

Most waste streams contain bacteria that consume nitrogen-containing organic and inorganic materials. Ammonia is an example of an inorganic material consumed by nitrifying bacteria i. The materials they consume are called nitrogenous materials, or nitrogenous BOD5.

This is done by adding 2-chloro trichloro methyl pyridine TCMP. If the lab is using the bottle method, 3 milligrams of TCMP should be added to each bottle. If the lab is using the graduated cylinder method, sufficient TCMP should be added to make the final concentration in the dilution water 10 milligrams TCMP per liter of dilution water.

Pure TCMP dissolves very slowly in water. It may be advantageous to use commercially prepared reagent. Preparation of Dilution Water 1 Source Water.

Water used for preparing reagent solutions and dilution water, hereafter referred to as source water, must be of the highest quality. It must contain less than 0. Distilled water prepared using a glass still in the lab is sometimes suitable, although water from some stills might contain trace metals, chlorine, ammonia, or volatile organic materials making it unsuitable. Distilled water coming from a copper still is seldom suitable. Deionized DI water sometimes contains organic materials leached from the resin bed.

Some purchased distilled waters are suitable, and some are not. If water is purchased, many labs have found steam distilled water to provide the best results.

Distilled drinking water is not suitable as it generally contains chemicals e. If unseeded BOD5 blanks always run high i. Some labs have had success using tap water, others spring water If it does not, try another source of water.

Per liter of source water, add 1. Use a plastic or glass carboy or other container of sufficient volume that will provide sufficient water for an entire batch, but small enough that it can be easily shaken if shaking is used to aerate. To allow free movement of oxygen to and from the container during storage, the top of the container should be loosely fitted, or replaced with a loosely-packed wad of cotton. Check stored dilution water to determine if sufficient ammonia remains after storage.

Add ammonium chloride solution if necessary to bring the ammonia level to approximately 0. Dilution Water for BOD5. It is advantageous to do this no later than the day before the BOD5 test. Approximately one hour before the BOD bottles are to be set up, add the buffer and nutrient reagents to the dilution water. Do this so as to minimize introduction of air bubbles into the dilution water container. For the CBOD5 test, the nitrifying bacteria are inhibited and therefore not a problem see par.

Regardless of how it is made, it is necessary to check dilution water with every batch of BOD5 samples to make sure it is not causing error in the test. Although not mentioned in Standard Methods B, the dilution water can be checked after buffers and nutrients have been added to determine if the buffers have stabilized the pH to approximately the pH of the dilution water 6.

If not, the source water is suspect and alternate sources of water should be tried. DO depletion should not exceed 0. If DO depletion of the blank consistently exceeds 0. If DO depletion for the blank is excessive only periodically, suspect lab procedures.

Contamination, calibration, equipment failure or lapse in procedure may be the cause. Being able to confidently predict the BOD5 value is especially useful for commercial labs which might have no idea of the approximate BOD5 of incoming samples. Samples which do not already contain enough of the proper bacteria can be analyzed for BOD5 only after addition of "seed.

Mathematical Relationship between COD & BOD levels in Effluent? | India Water Portal

Influent to a domestic wastewater treatment plant generally contains sufficient bacteria and usually does not need to be seeded. The BOD levels were computed using the initial and final concentration of dissolved oxygen? The conversion factor for BODS. Separate analysis of linear regressions for. Potassium hydrogen phthalate could be degraded by heterogenous microbial populations in the BOD3 experiments.

Significant biodegradation with rapid acclimatization of microbes is possible even if it has an aromatic'ring. Pure synthetic compounds require an addition of a suitable source of micro-organisms seeding for their degradation by biochemical means.


The purecompounds become mixtures of solutions when 'seed material' is added. As the rates of biochemical oxidation increase with temperature, oxygen demand is also increased. The effect of higher temperatures room temperature is thus seen to compared with lower duration of the incubation period.

LO3 obtained by Chaudri6 The regression equations under the conditions studied could be of immense use for the verification of analytical results; either for BOD or COD under similar experimental conditions maintained in the study. It is also desirable to determine whether the correlation of BOD3 and COD exists for a wide variety of seed materials and substrates.

The composition of food processing waste is determined by the products and manufacturing processes involved. They differ from domestic sewage in general characteristics in particular by their higher concentration of organic matter.

It is evident that none of the COD and BOD3 values of the three industries satisfies the waste water quality requirements for such industrial effluents to be discharged into inland surface waters. Separate analyses of COD and BOD3 for different food industries indicated that it is possible to develop linear regression equations if the waste waters are of constant compositions and contain no toxic materiaIs. An operator of an effluent treatment plant will have to wait for minimum of 3 days to obtain the BOD value for the effluent.

The above correlation deduced by us will assist him to obtain BOD3 value through the determination of COD which can be done within a short period of time. If there is an extensive data base for each of industrial waste waters covering a large range of BOD3 and COD values regression equations under the conditions studied could be of immense use to obtain maximum information in shorter time with less costs incurred either for chemicals and manpower. Acknowledgement We thank Dr R.

Alwis, of the Labour Department, Dr L. Sally, and Mr K. Surface waterpollution and its control. Water quality and its control - Waste water engineering treatment; disposal; muse. In Water pollution micro- biology, Ed R. BOD test for tropical countries.

Walski Environmental Engineering 2: Analytical aspects 'of environmental chemistry. Inhibition of nitrogenous BOD and treatment plant performance evaluation. WaterPollution Control Federation 53 World health organization WHO report