BOD (Biological Oxygen Demand) means the amount of oxygen (in mg/l) microorganisms like bacteria need to 'consume' the organic pollutants. The main focus of wastewater treatment plants is to reduce the BOD in the effluent Chemical oxygen demand (COD) does not differentiate between biologically available . These chemicals are often found in association with each other. It is essential to obtain a correlation between BOD5 and COD for various BOD under certain conditions and by determining the COD, the information about the.
The temporal variations in BOD and COD showed a regular pattern for urban areas whereas they were relatively irregular for non-urban areas. Irrespective of the sewer pipes and the types of the areas, two distinct peaks were identified from the synchronous fluorescence spectra, which correspond to protein-like fluorescence PLF and humic-like fluorescence HLFrespectively.
HLF in sewer samples appears to be associated with fluorescent whitening agents. Five fluorescence characteristics were selected from the synchronous spectra and the first-derivatives. Among the selected fluorescence indices, a peak in the PLF region i. A multiple regression approach based on suspended solid SS and Index I used to compensate for the contribution of SS to BOD and COD revealed an improvement in the estimation capability, showing good correlation coefficients of 0.
Introduction The water quality of combined sewer systems is affected by the lifestyle of the inhabitants as well as the temporal flow pattern e. It may also be significantly changed by other factors such as the infiltration of groundwater, the leakage of pipes, the distance, and the hydraulic gradient [ 2 ]. Such a pre-evaluation step can help to avoid excessive loadings to other sewer lines and other undesirable environmental impact during the project.
Obtaining the high time resolution about water quality data for combined sewer overflows is also important for the proper evaluation of the influence of storm water flows on wastewater treatment plants as well as for the assessment of its impact on receiving waters.
In addition, it provides the basis for the construction of mathematical modeling for the simulation of the two above-mentioned behaviors and the influences [ 3 ].
Variations in waste water quality are relatively large and abrupt changes may take place due to infiltration, leakage and storm events. Biochemical oxygen demand BOD and chemical oxygen demand CODindirect indicators of organic matters, are representative parameters for sewer water quality.
However, it is very difficult to obtain continuous water quality data because of the scarcity of accessible space within the sewer systems and the necessity of separate laboratory experiments. Moreover, at least five days are required to acquire BOD data from the experiment and BOD itself may be biased by the presence of toxic substances that might cause the inhibition of the oxidizing bacteria.
Recently, optical techniques such as UV-visible spectroscopy and fluorescence measurements were suggested as fast and versatile monitoring tools for BOD and COD in water samples [ 4 ]. It is well known that UV absorbance at — nm is correlated with the concentrations of organic matters in sewage samples [ 5 ]. The other parameters are based on oxygen, which is required to reduce or to oxidise the samples' substances.
Formation of sum parameters The BOD biological or biochemical oxygen demand can be considered as the 'mother' of the sum parameters. It had been already found and defined in the 19th century , apparently as a consequence of the canalisation of the big cities. The canalisation had provided definitive advantages for hygiene.
Waste water and refuse had started to be taken underground by channels. However, these waste water had a high oxygen demand and led to an oxygen deficiency in water bodies, into which the waste water was discharged. Hence, the oxygen content of these water decreased to zero.
A higher fish mortality was the consequence. Since then the engagement with biological and biochemical oxygen demand has intensified. In the following years, further parameters have been defined.
BOD, biochemical oxygen demand The BOD indicates the content of oxygen needed to decompose organic compounds in waste water by bacteria. In most cases the special factor BOD5 is perceived as the BOD, which requires a detailed definition 5 represents the 5 days analysis time . For the determination of BOD5 there are nitrification inhibitors added to the samples, which suppress the degradation of nitrogen compounds.
Due to this limitation, an essential process of sewage treatment is not considered: In the real sense, BOD measurements are respiration measurements. Due to their rapidity, respiration measurements are preferred for online analysis.
Due to the 5 day analysis time and the measurement of the carbonaceous BOD instead of total BOD, the BOD5 is not suitable to assess the current capacity of the waste waters' degradation by bacteria. The BOD5 is only a time-delayed information about the pollution of waste water and cannot be used for optimization or control of a WWTP. Alternatively, BOD analysers or respiration analysers can be used, which enable measurements within 5 to 60 minutes. Thus, estimations can be made promptly for the biodegradability of the waste water and its behavior in the plants.
The market is dominated by short-time respiration measurements by O2 electrodes. Due to the low oxygen solubility of the waste water, the small respirations are extrapolated to the final result by using factors. Essentially, only the easy biodegradable substances are detected this way. Alternatively, LAR AG provides an online respirometer that operates like a miniature waste water treatment plant: This BOD analyser degrades nitrogen and carbon compounds in special waste water cascades, so that the significant total BOD is determined.
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.
Chemical oxygen demand
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.BOD and COD in hindi biochemical oxygen demand and chemical oxygen demand
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.
Mathematical Relationship between COD & BOD levels in Effluent?
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.
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.
BOD, COD, TOC and TOD – sum parameters in environmental analysis -
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.