Biochemical Oxygen Demand Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the oxidation product of dissolved iron when exposed to oxygen in groundwater?

Fe2O3

Fe(OH)2

Fe(OH)3 (correct)

Fe(HCO3)2

Which method is used to determine the concentration of manganese in water samples?

Direct measurement without any reagents

Spectrophotometry at 480 nm

Using a Nessler cylinder without any dilution

Heating and boiling the sample with ammonium persulfate (correct)

What is the maximum permissible value of iron in drinking water?

50 μg/L

200 μg/L (correct)

100 μg/L

250 mg/L

Which step is NOT part of the iron concentration measurement method using a Nessler cylinder?

Heat the sample to boiling Signup and view all the answers

What is the wavelength used to check the concentration of sulphates in a water sample?

430 nm Signup and view all the answers

What does the biochemical oxygen demand (BOD) measure?

The amount of dissolved oxygen needed by microorganisms Signup and view all the answers

During which stage does nitrification occur in the BOD method?

After 6-10 days of incubation Signup and view all the answers

What is the purpose of the Winkler method in the BOD process?

To determine the dissolved oxygen concentration Signup and view all the answers

How many Winkler bottles are filled during the preparation of dilutions?

Two bottles for each dilution prepared Signup and view all the answers

What organic compounds are oxidized in Stage I of the BOD method?

Both simple and complex organic compounds Signup and view all the answers

To achieve a 1:5 dilution, how much dilution water is needed for a total sample volume of 500 mL?

100 mL of water and 400 mL of dilution water Signup and view all the answers

What is the chemical equation representing the oxidation of organic compounds in the BOD method?

organic compounds + O2 → CO2 + H2O + bacteria Signup and view all the answers

Which compound is NOT involved in the nitrification process during BOD testing?

CO2 (carbon dioxide) Signup and view all the answers

What is the correct dilution ratio for the second dilution in Set 1?

1:10 Signup and view all the answers

Which of the following compounds is NOT listed as a component of the dilution water?

Sodium bicarbonate Signup and view all the answers

What is the adjusted pH value of the dilution water?

7.2 Signup and view all the answers

If the BOD7 is calculated to be 80% of BODtotal, what percentage is BOD5 based on BODtotal?

68% Signup and view all the answers

In the BOD calculation formula, what does the variable 'a' represent?

Oxygen concentration before incubation Signup and view all the answers

What does the variable 'M' represent in the BOD calculation formula?

Amount of dilution water contained in 1 L of the sample Signup and view all the answers

What is the purpose of incubating the sample for 7 days?

To allow microorganisms to deplete the oxygen Signup and view all the answers

During the BOD5 calculation, which of the following values is subtracted?

Oxygen concentration in the sample after incubation Signup and view all the answers

At what dissolved oxygen levels does iron typically occur as Fe3+?

Greater than 1-2 mg/L Signup and view all the answers

What is the impact of elevated concentrations of iron and manganese in water?

Clogging of pipelines Signup and view all the answers

Which of the following statements is true regarding the solubility of metals in groundwater?

The solubility of metals is influenced by the amount of oxygen present. Signup and view all the answers

What concentration of dissolved oxygen is likely to keep iron present in the more soluble Fe2+ form?

Below 1 mg/L Signup and view all the answers

What health concern is likely associated with elevated aluminum levels in drinking water?

Alzheimer's disease Signup and view all the answers

During which stage is sodium thiosulphate used for titration?

Before and after incubation Signup and view all the answers

What is one of the most noticeable effects of high concentrations of iron in water?

An unpleasant metallic taste Signup and view all the answers

How does groundwater interact with metals found in soils and rocks?

It can dissolve metals and release them. Signup and view all the answers

Study Notes

Biochemical Oxygen Demand (BOD)

BOD is the amount of dissolved oxygen needed by aerobic microorganisms to mineralize organic compounds in a water sample.
The process can be represented by the equation: organic compounds + O₂ → CO₂ + H₂O + bacteria.

BOD Stages

Stage I: Oxidation of simple organic compounds like proteins, sugars, and starches. Also oxidation of complex organic compounds like fats, cellulose, and pectins.
Stage II (after 6-10 days): Nitrification - oxidation of nitrogen compounds (NH₄⁺ → NO₂⁻ → NO₃⁻) in aerobic conditions by autotrophic bacteria.

BOD Method

Fill Winkler bottles: Fill them with samples according to a specific procedure.
Determine initial dissolved oxygen: Measure dissolved oxygen in the samples using the Winkler method.
Incubation: Leave a set of samples for 7 days, sealed properly.
Determine final dissolved oxygen: Measure dissolved oxygen after incubation.
Dilution: Use a graduated cylinder to prepare dilutions for analysis (e.g., 1:5 to 1:10). These dilutions take total sample volume and divide it into the desired ratio of sample (water) & dilution water.
Calculations: Use the formula BOD = [(a-b) - (c-d)M] / 1000 to calculate BOD, where (a), (b), (c), and (d) are oxygen concentrations (in mg O₂/L) before and after incubation (for sample and dilution water respectively). M is the amount of dilution water mL contained in 1 L of sample and m is the mL amount of water in 1L of sample. The BOD₅ is typically calculated – the value at 5 days into the process.

Dilution Water (DW) Composition

Phosphate buffer, magnesium sulphate, calcium chloride, and magnesium chloride.
Saturated with oxygen (≈ 8 mg/L).
Adjusted pH value of 7.2.

Iron (Fe) and Manganese (Mn)

The solubility of Fe and Mn in groundwater is dependent on the oxygen concentration (more oxygen means less Fe, Mn, and thus less damage to pipes).
Iron exists as Fe²⁺ (reduced) or Fe³⁺ (oxidized) depending on the oxygen level. At higher oxygen levels, iron becomes Fe³⁺ which can cause rusty color deposits.
Manganese has similar oxidation states.
These metal levels need to be kept at safe concentrations.

Methods for Metals

Iron: Use a Nessler cylinder, hydroxylamine hydrochloride, acetate buffer, 1.10 phenanthroline, then use a spectrophotometer at 510 nm.
Manganese: Use 100 mL of water sample, specific reagent mixture, ammonium persulfate, heat for a minute, then a spectrophotometer at 525 nm.
Sulfates: Use 5.0 mL water sample, a "reagent", and a spectrophotometer at 430 nm.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on Biochemical Oxygen Demand (BOD), its stages, and the methodology used to measure it. This quiz covers the oxidation processes of organic compounds and the critical steps involved in the Winkler method. Challenge yourself and learn how BOD impacts water quality.