Biological Oxygen Demand(BOD), laboratory analysis

When it comes to designing effluent treatment plants, one crucial factor stands out: Biological Oxygen Demand (BOD). This value is the linchpin for balancing equations and determining flow rates between equipment. So, how do we get this vital number? Essentially, we measure the dissolved oxygen levels in a sample over a five-day period. It's a tried-and-true method that's still widely used today, even with fancy modern instruments available. Why? Because it's cost-effective and gets the job done!

Biological Oxygen Demand (BOD) Laboratory Procedure

Biological Oxygen Demand (BOD) is a crucial parameter in water quality assessment. It measures the amount of oxygen consumed by microorganisms in breaking down organic matter in water. In this post, we'll outline the laboratory procedure for determining BOD and provide a handy calculator to simplify the calculation process.

Analytical procedure: 5 days method

Testing Apparatus:

1. Bottle with stopper (250ml)

2. Incubator 

 

Chemical Reagents for BOD Testing

To ensure accurate BOD results, you'll need the following chemical reagents:

1. NaOH Solution (1N)

2. HCl Solution (1N)

3. Sodium Sulphite Solution

Dissolve 1.5g of sodium sulphite in 1 liter of water. Important: Don't mix this solution with any previous test solutions.

4. Phosphate Buffer Solution

Dissolve the following in 500ml of water:

- 8.5g KH2PO4

- 21.75g K2HPO4

- 33.4g Na2HPO4.H2O

- 1.7g NH4Cl

Then, make up the solution to 1 liter. Remember: Maintain a pH of 7.2.

5. MgSO4.7H2O Solution

Dissolve 22.5g of MgSO4.7H2O in water and make up to 1 liter in a volumetric flask.

6. CaCl2 Solution

Dissolve 27.5g of CaCl2 in water and add to a 1-liter volumetric flask.

7. FeCl3.6H2O Solution

Dissolve 0.25g of FeCl3.6H2O in water and make up to 1 liter.

8. Seeding Material

Use effluent water from the sample point as your seeding material.

By having these chemical reagents ready, you'll be all set to conduct your BOD testing accurately and efficiently.

Sample Preparation for BOD Testing Procedure:

To get accurate BOD results, we need to prepare our sample carefully. Here's a step-by-step guide:

Step 1: pH Adjustment

• Adjust the pH of your sample to 7 using acid and base solutions. This ensures that the microorganisms can thrive.

Step 2: Remove Residual Chlorine

• Add sodium sulphite solution to remove any residual chlorine, which can harm the microorganisms.

Step 3: Prepare Dilution Water

• Store your dilution water at 20°C and use it at approximately the same temperature.

Step 4: Add Nutrients

• For every liter of water, add:

- 1ml phosphate buffer solution

- 1ml magnesium sulphate solution

- 1ml calcium chloride solution

- 1ml ferric chloride solution

Step 5: Add Seeding Material

• Add 0.1-1% seeding material to your dilution water. This helps microorganisms grow.

Step 6: Dilute the Sample

• Dilute your sample by 5%. For example, if you have 500ml of sample, add 500ml of dilution water.

Step 7: Prepare Bottles

• Pour the diluted sample into two glass-stoppered bottles. Repeat this process for lower-concentration samples.

Step 8: Measure Initial DO

• Test the initial DO concentration in one of the sample bottles and a blank one.

Step 9: Incubate

• Incubate the bottles at 20°C for 5 days.

Step 10: Measure Final DO

• After 5 days, measure the DO concentration in the diluted sample and the blank.

Calculate BOD

Now that you have your DO readings, you can calculate the BOD using the following formula:

BOD = (D₁-D₂)-(C₁-C₂) F/P

• D₁ initial DO sample.
• D₂ DO after incubation of sample.
• C₁ Seeded dilution water initial DO
• C₂ Seeded dilution water after incubation DO 
• F =ratio of the seed in the sample to that in the control, that is percent seed in D₁ divided by percent seed in C₁ and 
• P = decimal fraction of the sample used

By following these steps, you'll be able to accurately measure the BOD of your sample and gain valuable insights into its water quality.

BOD Calculator 

Use our handy calculator to simplify the BOD calculation:

 

Initial DO (mg/L):

Final DO (mg/L):

Dilution Ratio:

Chemical oxygen demand determination, COD analysis

Outline of the method – COD determined by the refluxing the sample with an excess of potassium dichromate in acid condition and estimated by titration to find the amount of dichromate consumed which directly proportion to COD.

Apparatus 

• COD digester
• Reaction vessels with condensers

Reagents

• 0.25 N Potassium dichromate:-Dissolve 49.036 gm of potassium dichromate in 1 litre distilled water for 1 N solution. Dissolved 12.259 gm of potassium dichromate in 1 litre distilled water for preparation of 0.25 N solution.
• Silver sulphate Sulphuric acid:-Dissolve 10gm of silver sulphate in 2.5 lit of con Sulphuric acid.
• STD ferrous ammonium Sulphates 0.1N:- Dissolve 40g of ferrous ammonium Sulphates in a previously cooled mixture of 40ml of Sulphuric acid & 200ml of water, dilute with water to1000 ml and mix it thoroughly.
• Ferro ion indicator:-Dissolve1.3485g of 1, 10-phenanthroline (monohydrate), together with 0.695g of ferrous sulphate in distilled water and dilute to 100ml.
• Potassium acid phthalates for STD:-Dissolve 425.1 gm of potassium acid phthalate (which is dried for 1 hr in the oven at 1500C ) in 1 lit distilled water. This solution corresponds to 500 ppm COD

Procedure
1. Take 10ml potassium dichromate (0.25N) + 20ml sample + 30ml silver sulphate Sulphuric acid solution + 1 g mercuric sulphate in reaction vessel. Add one or two glass bead in each reaction vessel.

2. Insert the reaction vessel in the holes of digestion block which has attained 1500C temperature. Put air condensers on the reaction vessels. Reflux the contents for 2 hr. cool the mixture content and transfer them to the 200ml conical flask.

3. Remove all the mixture contents by washing the reaction vessel with distilled water. Add 80ml distilled water in the same flask and titrate the excess potassium dichromate with the Standard ferrous ammonium sulphate (FAS) using 4 to 5 drops of ferrion indicator. The endpoint colour changes from yellow to reddish brown (in case of an auto-titration indicator is not required. The endpoint is detected by the electrode.

4. Do the blank same way.

Calculation of COD in ppm = (blanking reading – sampling reading) X N of FAS X 8000/ sample volume

Free Carbon Dioxide Determination in Waste Water

Uncovering Hidden CO2 in Industrial Wastewater: A Simple yet Powerful Titration Method

Industrial wastewater often harbors a stealthy pollutant: Dissolved carbon dioxide (CO2). But fear not! With a straightforward titration method, you can accurately quantify CO2 levels in wastewater samples.

The reaction involves the conversion of carbon dioxide to carbonate ions, which are then titrated with the standardized sodium carbonate solution. The endpoint of the titration is indicated by a color change from colorless to pink, signaling the complete neutralization of the carbon dioxide.

This reliable and accurate method is essential for monitoring and controlling wastewater treatment processes. By understanding CO2 levels, you can optimize treatment strategies, reduce environmental impacts, and ensure compliance with regulations.

Reagents:

1. Phenolphthalein Indicator Solution

Phenolphthalein is a pH indicator that changes color from colorless to pink at a pH range of 8.2-9.8.

Materials needed:

- Phenolphthalein powder (C20H14O4)

- Ethanol (95%)

- Distilled water

Instructions:

1. Weigh 1 gram of phenolphthalein powder.

2. Dissolve the powder in 100 ml of ethanol (95%) in a glass beaker.

3. Add 100 ml of distilled water to the beaker and stir well.

4. Transfer the solution to a glass bottle with a tight-fitting lid.

5. Label the bottle with the date, reagent name, and concentration (1% w/v).

2. Standard Sodium Carbonate Solution (0.1 N)

Sodium carbonate (Na2CO3) is a strong base used as a titrant in acid-base reactions.

Materials needed:

- Anhydrous sodium carbonate powder (Na2CO3)

- Distilled water

Instructions:

1. Weigh 5.3 grams of anhydrous sodium carbonate powder.

2. Dissolve the powder in 1000 ml of distilled water in a glass beaker.

3. Stir the solution until the powder is completely dissolved.

4. Transfer the solution to a glass bottle with a tight-fitting lid.

5. Label the bottle with the date, reagent name, and concentration (0.1 N).

Gadgets used for making both reagents:

- Glass beaker

- Glass bottle with lid

- Weighing balance

- Stirring rod

Note: The concentration of the sodium carbonate solution can be adjusted to suit the specific requirements of the titration reaction.

Procedure for Determining Free Carbon Dioxide in Water and Wastewater

Steps:

1. Sample Preparation: Carefully take 100ml of the unfiltered sample in a measuring cylinder, avoiding any agitation that might disturb the sample.
2. Adding Indicator: Add 10 drops of phenolphthalein indicator to the sample. This indicator will help you detect the endpoint of the titration reaction.
3. Titration: Run in standardized sodium carbonate solution (0.5ml at a time) while gently stirring the sample with a glass rod. Make sure to raise and lower the rod thoroughly to mix the sample well.
4. Endpoint Detection: Continue adding the sodium carbonate solution until a definite pink color persists for 5 minutes. This indicates that the reaction has reached its endpoint.

Calculation of Free Carbon Dioxide

The amount of free carbon dioxide in the sample can be calculated using the following formula:

• Free carbon dioxide (CO2), mg/l = 4.4 V

Where:

V = volume in ml of standardized sodium carbonate solution consumed during the titration.

Explanation of the Formula

The formula is based on the reaction between carbon dioxide and sodium carbonate:

CO2 + Na2CO3 → 2NaHCO3

The standardized sodium carbonate solution is used to react with the free carbon dioxide in the sample. The volume of sodium carbonate solution consumed during the titration is directly proportional to the amount of free carbon dioxide present in the sample.

The factor 4.4 in the formula is a conversion factor that takes into account the molar mass of carbon dioxide and the volume of the sample. This factor allows you to express the result in milligrams per liter (mg/l) of free carbon dioxide.

Technical Tips and Variations

- Use a pH meter to monitor the reaction and ensure accurate endpoint detection.

- Consider using alternative indicators, such as methyl orange or bromothymol blue, for different pH ranges.

- For more precise results, use a standardized sodium carbonate solution with a known concentration.

By mastering this simple yet powerful titration method, you'll be well-equipped to tackle the challenges of CO2 quantification in industrial wastewater.

Relationship Between Rate of Reaction and Concentration of Free CO2

The rate of reaction (r) can be related to the concentration of free CO2 (C) using the following equation:

r = k * C^n

where:

- r is the rate of reaction

- k is the rate constant

- C is the concentration of free CO2

- n is the order of reaction (typically 1 or 2 for CO2 reactions)

Sample Data for Plotting a Graph

Here's some sample data to illustrate the relationship between the rate of reaction and concentration of free CO2:

 Graph with the concentration of free CO2 on the x-axis and the Rate of Reaction on the y-axis.

Graph with the concentration of free CO2 Vs the rate of reaction show a positive correlation. we observe a curve that increases as the concentration of free CO2 increases. 

Graphical Representation:

 Graph with the concentration of free CO2 on the x-axis and the Reaction time on the y-axis.

This is graphed with the concentration of free CO2 Vs reaction time projects a negative correlation. This curve decreases as the concentration of free CO2 increases. 

Note: This is a simplified example, and actual data may vary depending on the specific reaction and conditions. The shape of the curves in both graphs will depend on the order of reaction (n) and the rate constant (k).

Chlorides estimation by Mohrs Method

Two methods are prescribed for the determination of chloride. One of them is Mohr’s method,  it is suitable for use when 0.15 to 10mg of chlorine (Cl) is present in the portion of sample titrated.


Chloride is determined in neutral or slightly alkaline solution by titration with STD silver nitrate solution in the presence of potassium chromate indicator. Silver chloride is precipitated and at the end point, red silver chromate is formed.

Method:
The sample, after neutralization, is titrated against STD silver nitrate solution using potassium chromate indicator end colour is from yellow to bricks red.

Reagents:
1. Aluminium hydroxide suspension:
Dissolve 125g of potassium or ammonium alum in 1lt of distilled water. Precipitate the aluminium by adding ammonium hydroxide slowly along with stirring. Wash the precipitate by successive decantation with several portions of distilled water until free from Sulphates.
2. Hydrogen peroxide 30%
3. Calcium carbonate.
4. Dilute nitric acid 0.1N
5. Potassium dichromate:
Dissolve 5g of potassium chromate in distilled water and makeup to 100ml. Add silver nitrate solution to produce a slight red precipitate and filter.
6. Std silver nitrate solution:
Dissolve 4.791g of silver nitrate, dried at 105^oC in distilled water and makeup to 1 lit. The solution to stored at the dark place.

Producer:

100ml of the sample is pretreated with decolourization, adjusting pH, filtrations for removal of suspension. Decolourize by adding 3ml of aluminium hydroxide suspension. Stir thoroughly and after a few minutes filter and wash with 10 to 15ml of distilled water. If Sulphites are present, add 1ml of hydrogen peroxide with stirring.

Place the treated sample in a porcelain basin. If the pH of the sample is less than 6.8, add a small amount of calcium carbonate to the sample in the basin so as to neutralize the acidity. If the pH is above 10, determine the amount of dilute nitric acid required to neutralized 100ml of the sample, and this amount of the acid to the portion used for the chloride determination, and then add a trace of calcium carbonate. Add 1ml of Potassium dichromate and titrated with std silver nitrate solution with constant stirring until there is perceptible reddish colouration. Substrate 0.2 ml from the titration figures to allow for the excess of reagents required to from silver chromate.

Calculation
Chloride (as Cl), mg/l = 10 V
Where V= volume in ml of std silver nitrate sol consumed in terms of CaCO₃
Cl- (mg/l) = (S-B) ×N×Eq Wt of Cl-×1000 / vol of sample
S = sample value
B = blank sample value

Volumetric methods of testing water

Advanced Water Quality Assessment: Bridging the Gap between Simple Testing Procedures and Sophisticated Analytical Techniques

While simple, small-scale laboratory testing procedures can provide a preliminary estimate of water quality, they are limited in their accuracy and comprehensiveness. For instance, the 12-analysis approach, although suitable for describing contaminated water sources, falls short in providing a detailed and quantitative assessment of water quality. In contrast, advanced analytical instruments such as UV spectrophotometers and High-Performance Liquid Chromatography (HPLC) systems, coupled with computerized data processing and electronic processing systems, offer unparalleled precision and sensitivity in detecting and quantifying a wide range of water pollutants.

These sophisticated analytical techniques enable the detection of trace levels of contaminants, including heavy metals, pesticides, and industrial pollutants, which may not be detectable through simple testing procedures. Furthermore, advanced analytical instruments can provide detailed information on the chemical composition and physical properties of water, allowing for a more comprehensive understanding of water quality. By bridging the gap between simple testing procedures and advanced analytical techniques, water quality professionals can ensure more accurate and reliable assessments of water quality, ultimately informing effective management and treatment strategies to protect public health and the environment.

The list of the tests is used as a way to find out the results on a general basis and requires the concepts of concentration calculation and standard solutions preparation.

List of tests:

1. Total residual chlorine
2. Chlorides
3. Total Hardness
4. Calcium
5. Magnesium
6. Alkalinity
7. Free Carbon dioxide
8. Sulphites
9. Sulphates
10. Dissolved Oxygen
11. Chemical Oxygen Demand
12. Biochemical Oxygen Demand

Testing procedures

Total Residual Chlorine Determination: A Critical Analysis of Sampling and Analytical Methodologies

The accurate determination of total residual chlorine (TRC) in effluent samples is a crucial aspect of water quality monitoring. However, the residual chlorine content is prone to decrease after sample collection, particularly in hot weather conditions, highlighting the importance of on-site testing. When dealing with samples containing suspended matter, it is essential to allow a portion to settle for 15 minutes and test the supernatant to ensure accurate results.

The iodometric method is a widely employed technique for TRC determination, based on the principle that chlorine liberates iodine from potassium iodide, which is subsequently titrated against a standardized sodium thiosulphate solution. This method is suitable for detecting residual chlorine concentrations between 1 and 10 mg/L. However, it is susceptible to interferences from nitrites, ferric, and manganic compounds, which can lead to inaccurate results. To mitigate these interferences, titration should be performed within a pH range of 4.5 to 8.0, and the results should be reported with a clear indication of whether the titration was conducted in acid solution or not. By acknowledging the limitations and nuances of the iodometric method, water quality professionals can ensure more accurate and reliable TRC determinations.

Reagents

• Dil Sulphuric acid - 4N
• Potassium iodide solution – 10 percent w/v
• Acetic acid – glacial.
• Std potassium hydrogen iodate sol – 0.005N dissolve 0.1625g of potassium hydrogen iodate dried at 105^oC in water and make it to 1 lit.
• Std sodium thiosulphate sol – 0.005N dissolve 1.241g of sodium thiosulphate in freshly boiled and cooled water and makeup to 1 lit add 5 ml of chloroform or 0.4g sodium hydroxide per liter as a preservative.
• Starch indicator – triturate 5g of starch and 0.01g of mercuric iodide with 30ml of cold water and slowly pour it with stirring into 1 lit of boiling water. Boil for 3 min allow the solution to cool and decant the supernatant clear liquid.

Determination of Total Chlorine in Water Samples

Procedure:

1. Sample Preparation: Take 500ml of the water sample.
2. Alkalinity Adjustment: If the total alkalinity of the sample exceeds 400mg/L, add sufficient dilute Sulphuric acid (H2SO4) to reduce the alkalinity to 400mg/L.
3. Addition of Reagents: Add 5 ml of potassium iodide (KI) solution and 5 ml of acetic acid (CH3COOH) to the sample. Mix well.
4. Titration: Immediately titrate the sample with standardized sodium thiosulphate (Na2S2O3) solution until the color of iodine is nearly discharged.
5. Addition of Starch Indicator: Add 2 ml of starch indicator solution to the sample.
6. Final Titration: Continue the titration with sodium thiosulphate solution until the blue color disappears for at least 30 seconds.
7. Calculation: Calculate the total chlorine content of the sample using the volume of sodium thiosulphate solution used.

Total residual chlorine, mg/l = 0.1773×1000×v/500

Where v = volume in ml of std sodium thiosulphate sol required for the titration.

Total Residual Chlorine Calculator

Volume of Sodium Thiosulphate (v) in ml:

Total Residual Chlorine (mg/L):

This calculator allows the user to input the volume of sodium thiosulphate solution (v) in milliliters and return the Total Residual Chlorine (TRC) in milligrams per liter (mg/L).

Note:

- The starch indicator solution should be prepared fresh daily.

- The sodium thiosulphate solution should be standardized before use.

- The titration should be performed in a well-ventilated area, away from direct sunlight.

- The result should be expressed in mg/L (milligrams per liter) of total chlorine.

Analysis of particle size of suspended solids:

The particle size of suspended solids is determined by wet screening of the freshly drawn sample through the specified sieve. Since the suspended solids in the sample are likely to coalesce keeping, the test should be carried out on the spot. Leaves, twigs and other wind-blown debris, which are extraneous to the sample, should be removed.

Apparatus :

• Sieve: 850micron sieve
• Enameled pail: of a diameter slightly bigger than that of the sieve

Procedure: 

Hold the sieve in one hand and with the other pour gently on the mesh surface of the sieve one litre of well-mixed sample. Pour the sample so that it covers the entire mesh surface. If necessary create a vibration while sieving the sample by a gentle rocking motion of the hand holding the sieve. Fill the enameled pail with fresh water. Then having the screen on opposite sides with the two hands brings it to the surface of the water in the enameled pail and wet screen by jigging(up and down motion). Take care to see that while jigging the sieve is dipped in the water only to half its depth and there is no overflow from the mesh through the sides as suspended solids would be washed out without passing through the screen. If necessary wash the material on the screen with a fine jet of water from a wash bottle until all lodged particles are loosened.

The suspended matter shall be considered passing through the sieve only if no residue is left on it.

Precautions

- Conduct the test on the spot to prevent coalescence of suspended solids.

- Ensure the sieves are clean and free of contaminants before use.

- Handle the sample and suspended solids carefully to avoid loss or contamination.

Estimation and determination of Phenolic compounds:

General: The phenols are first isolated by distillation under acidic conditions and then determined either by the amino antipyrine method or bromination method depending upon the quantity of phenol present
Isolation of Phenols:

Apparatus :

• Distillation apparatus: all glass assembly with 1-litre distillation flask and preferably, Graham condenser.
• Separating funnel: with ground glass stoppers

Reagents

• Copper sulphate solution= 10 percent w/v
• Phosphoric acid= 1:10 v/v
• Methyl orange indicator= dissolve 0.01 g of methyl orange in 100 ml of water
• Sodium chloride
• Chloroform
• Sodium hydroxide solution= approximately 1N

Procedure:

To 500 ml of the sample add 5.0ml of copper sulfate solution and acidify to pH less than 4.0 with phosphoric acid, using methyl orange as an indicator. Omit this treatment in the case of samples preserved by the addition of copper sulfate and phosphoric acid. Transfer to the distillation apparatus and distill until about 450ml of the distillate is collected. Stop distillation and when boiling ceases add 50 ml of water to the distillation flask. Continue the distillation operation until a total of 500 ml has been collected.

Acidify the distillate with 1 ml of phosphoric acid and add 5 ml of copper sulfate solution. Transfer to a separating funnel and add 150 grams of sodium chloride. Extract thrice with chloroform, using 50ml of chloroform for each extraction. Take care that all the sodium chloride goes into the solution during the first extraction. Combine the chloroform extracts and discard the aqueous layer. Extract the phenols from the chloroform portion with two successive 75 ml quantities of sodium hydroxide solution. Dilute the combined alkaline extracts to 250 ml with water. Heat in a water bath until the chloroform is driven off completely and dilute with water to 500ml.

Note: when phenol concentration in the sample is known to be high, distill a smaller volume, but collect about 450 ml of distillate by adding water to the sample in the distillation flask towards the end and continuing the distillation as above, preferably using a smaller capacity flask for distillation when the volume taken is small.