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Biological oxygen demand : 

Biological oxygen demand

Introduction : 

Introduction BOD -measure of the quantity of oxygen consumed by microorganisms during the decomposition of organic matter. BOD is the most commonly used parameter for determining the oxygen demand on the receiving water of a municipal or industrial discharge. BOD can also be used to evaluate the efficiency of treatment processes, and is an indirect measure of biodegradable organic compounds in water.

Classification : 

Classification divided into two parts- carbonaceous oxygen demand nitrogenous oxygen demand. carbonaceous oxygen demand: result of the breakdown of organic molecules such a cellulose and sugars into carbon dioxide and water

Slide 5: 

Nitrogenous oxygen demand: result of the breakdown of proteins. Proteins contain sugars linked to nitrogen After the nitrogen is "broken off" a sugar molecule, it is usually in the form of ammonia, which is readily converted to nitrate in the environment. The conversion of ammonia to nitrate requires more than four times the amount of oxygen as the conversion of an equal amount of sugar to carbon dioxide and water

Significance : 

Significance Basic means for determining degree of H2O pollution Important measurement in operation of sewage treatment plant Comparing BOD of incoming sewage & effulent- efficiency, effectiveness of treatment is judged

Slide 7: 

For example, in a typical residential city raw sewage has a BOD value of around 300 mg/L. If the effluent from the sewage treatment plant has a BOD of about 30 mg/L, the plant has removed 90 percent of the BOD. If water of a high BOD value flows into a river, the bacteria in the river will oxidize the organic matter,consuming oxygen from the river faster than it dissolves back in from the air. If this happens, fish will die from lack of oxygen, a consequence known as a fish kill.

Slide 8: 

BOD Level(in ppm) 1 – 2 3 – 5 6 – 9 100 or greater Water Quality Very GoodThere will not be much organic waste present in the water supply Fair: Moderately Clean Poor: Somewhat PollutedUsually indicates organic matter is present and bacteria are decomposing this waste. Very Poor: Very PollutedContains organic waste

Methods for BOD measurement : 

Methods for BOD measurement Measure rate of O2 uptake by microbes in sample at 20ºC and over a period of 5 days in dark Two methods are widely used dilution method manometric method

Dilution method : 

Dilution method standard method conducted by placing portions of the sample into bottles and filling the bottles with dilution water ↓ contains a known amount of dissolved oxygen completely filled, freed of air bubbles, sealed and allowed to stand for five days at a controlled temperature of 20 °C (68 °F) in the dark. end of the five-day period, the remaining dissolved oxygen is measured.

Manometric method : 

Manometric method Measurement of BOD is easier oxygen consumed is measured directly rather than with chemical analysis sample is kept in a sealed container fitted with a pressure sensor A substance that absorbs CO2 (typically lithium hydroxide) is added in the container above the sample level. stored in conditions identical to the dilution method

Slide 12: 

total amount of gas, and thus the pressure, decreases because carbon dioxide is absorbed. From the drop of pressure, the sensor electronics computes and displays the consumed quantity of oxygen. Advantages: Simplicity direct reading of BOD value continuous display of BOD value at the current incubation time.



Introduction : 

Introduction In environmental chemistry, COD test is commonly used to indirectly measure the amount of organic compounds in water. COD test predicts the oxygen requirement of the effluent and is used for monitoring and control of discharges, and for assessing treatment plant performance.

Using potassium dichromate : 

Using potassium dichromate a strong oxidizing agent under acidic conditions Acidity is usually achieved by the addition of sulfuric acid In the process of oxidizing the organic substances found in the water sample, potassium dichromate is reduced, forming Cr3+.

Slide 16: 

The amount of Cr3+ is determined after oxidization is complete, and is used as an indirect measure of the organic contents of the water sample. BLANK: it is important that no outside organic material be accidentally added to the sample to be measured To control for this, blank sample is used created by adding all reagents (e.g. acid and oxidizing agent) to a volume of distilled water COD is measured for both and the two are compared COD of blank - COD of sample

Slide 17: 

an excess amount of potassium dichromate (or any oxidizing agent) must be present Once oxidation is complete, the amount of excess potassium dichromate must be measured to ensure that the amount of Cr3+ can be determined with accuracy To do so, the excess potassium dichromate is titratedwith ferrous ammonium sulfate (FAS) until all of the excess oxidizing agent has been reduced to Cr3+.

Slide 18: 

the oxidation-reduction indicator Ferroin is added during this titration step the Ferroin indicator changes from blue-green to reddish-brown, once dichromate is reduced Calculations where b is the volume of FAS used in the blank sample, s is the volume of FAS in the original sample, and n is the normality of FAS

Slide 19: 

COD = (C/FW)(RMO)(32) Where C = Concentration of oxidizable compound in the sample, FW = Formula weight of the oxidizable compound in the sample, RMO = Ratio of the # of moles of oxygen to # of moles of oxidizable compound in their reaction to CO2, water, and ammonia




INTRODUCTION term organic is used to describe materials relating to or derived from living organisms. The amount of organic matter in a soil is often used as an indicator of the potential sustainability of a system Carbon makes up approximately 50% and nitrogen 0.5 to 10% (dependent on residue type) of the molecules in organic matter; some of which turns over rapidly and is available to plants, whilst other more recalcitrant forms contribute to the stable organic pools

Slide 22: 

Organic carbon influences many soil characteristics including colour, nutrient holding capacity Total carbon is the sum of three carbon forms; organic, elemental and inorganic total organic carbon refers specifically to the organic carbon fraction amount of carbon bound in an organic compound and is often used as a non-specific indicator of water quality or cleanliness of pharmaceutical manufacturing equipment.

Measurement : 

Measurement Since all TOC analyzers only actually measure total carbon, TOC analysis always requires some accounting for the inorganic carbon that is always present. One analysis technique involves a two-stage process commonly referred to as TC-IC measures the amount of inorganic carbon (IC) evolved from sample and amount of total carbon (TC) present in the sample. TOC =IC value - TC

Slide 24: 

Whether the analysis of TOC is by TC-IC or NPOC methods, it may be broken into three main stages: Acidification: removal of IC and POC gases from the liquid sample by acidification Oxidation: oxidation of the carbon in the remaining sample in the form of carbon dioxide (CO2) and other gases Detection and Quantification: most vital components

Application : 

Application first chemical analysis to be carried out on potential petroleum source rock in oil exploration. It is very important in detecting contaminants in drinking water, cooling water, water used in semiconductor manufacturing, and water for pharmaceutical use

Thank u : 

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