What is closed reflux method?

In the closed reflux method, ampules and culture tubes with premeasured reagents are used and then samples is placed in the tube and COD is determined. Reaction with dichromate solution of sample: Potassium dichromate is a strong oxidizing agent and it can be used to prepare solution of exact normality.

Why do we use reflux method for determining COD?

The chemical oxygen demand (COD) determines the amount of oxygen required for chemical oxidation of organic matter using a strong chemical oxidant, such as, potassium dichromate under reflux conditions. The amount of dichromate consumed is proportional to the oxygen required to oxidize the oxidizable organic matter.

What is COD method?

1.1 The Chemical Oxygen Demand (COD) method determines the quantity of oxygen required to oxidize the organic matter in a waste sample, under specific conditions of oxidizing agent, temperature, and time. For lower concentrations of carbon such as in surface water samples, the Low Level Modification should be used.

What is the purpose of using HgSO4 and Ag2SO4 in the COD test?

The most general COD determination uses potassium dichromate (K2Cr2O7) in excess in an acidic medium with the aid of silver sulfate (Ag2SO4) as a catalyst, and mercuric sulfate (HgSO4) added to remove interference of chlorides.

Why is COD higher than BOD?

COD stands for ‘Chemical Oxygen Demand’ where BOD stands for Biochemical Oxygen Demand. COD is normally higher than BOD because more organic compounds can be chemically oxidised than biologically oxidised.

What causes high COD in wastewater?

COD increases as the concentration of organic material increases. It also increases if inorganic compounds susceptible to oxidation by the oxidant (typically dichromate) are present. Water with high COD typically contains high levels of decaying plant matter, human waste, or industrial effluent.

Is high COD good or bad?

1.1 Chemical Oxygen Demand. COD is an indicative measurement of the amount of oxygen that can be consumed by reactions in a measured solution. COD detection can be used to easily quantify the amount of organics in water. The higher the COD value, the more serious the pollution of organic matter by water.

What is BOD COD ratio?

BOD (Biochemical oxygen demand) is the pollution index of any water sample. BOD : COD (Chemical oxygen demand) ratio using the formulated seed comes in the range of 0.7-0.8 whereas that using BODSEED comes in the ratio of 0.5-0.6. The ultimate BOD (UBOD) was also performed by exceeding the 3-day dilution BOD test.

How do you treat high COD?

One way to reduce COD in water is to use coagulants and flocculants to bind sludge together. Once they are bound into big enough masses that they can be easily filtered out and deposited into a sedimentation tank for removal. This method does however rely on the use of chemicals, and requires high reoccurring cost.

What causes COD in wastewater?

Background: Chemical oxygen demand (COD) is often used to measure organic matter in wastewater, treated effluent, and receiving waters. Residual food waste from bottles and cans, antifreeze, emulsified oils are all high in COD and are common sources of COD for industrial stormwater.

What happens if COD is high?

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.

Why is high COD bad?

How does the Cod Open reflux method work?

Join ResearchGate to ask questions, get input, and advance your work. The closed reflux method we use magnetic stirrer to stir the samples for 10 minutes, then pipiette 2 ml of the sample and add into the reagent vials. Heated for 2 hours at 150 degree celcius, and read the COD reading using the colorimeter.

How does the closed reflux method ( Nemi ) work?

The closed reflux method (5220 C) is economical in the use of metallic salt reagents, but requires homogenization of samples containing suspended solids to obtain reproducible results. The most common interferent is the chloride ion. Chloride reacts with silver ion to precipitate silver chloride, and thus inhibits the catalytic activity of silver.

Which is a parameter of the closed reflux method?

This parameter is generally of interest in wastewaters and natural waters. The closed reflux method (5220 C) is economical in the use of metallic salt reagents, but requires homogenization of samples containing suspended solids to obtain reproducible results. The most common interferent is the chloride ion.

How do you cool a reflux round bottomed flask?

After a few minutes of air cooling, the round bottomed flask can be immersed in a tap water bath to accelerate the cooling process (Figure 1.65b). Pour liquid into the flask along with a stir bar or boiling stones. Use an extension clamp on the round bottomed flask to connect to the ring stand or latticework.