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Water Treatment > Water Quality Parameters > Flashcards

Water Quality Parameters Flashcards

1
Q

Equation for Ultimate Oxygen Demand?

A

Lu = Co - Cu

Co - Initial C of DO
Cu - Final C of DO

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2
Q

Equation for BOD(t)?

A

BOD(t) = Co - Ct

Co - Initial C of DO
Ct - C of DO at t

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3
Q

What does biochemical oxygen demand measure?

A

BOD measures the oxygen used by microorganisms to decompose the organic waste (carbonaceous demand) in wastewater and environmental waters only.

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4
Q

What would the BOD be if there is large quantity of organic waste in water?

A
  • Lots of organic waste
  • High quantities of microorganisms to decompose waste
  • Higher demand of O2
  • High BOD
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5
Q

Equation for the BOD, considering the degree of dilution?

A

BOD 5 = (I – F) D

I - Initial DO
F - Final DO
D - Dilution as fraction (Eg. If 1:10, D = 10)

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6
Q

Describe the test for BOD.

A
  • Take two water samples.
  • Measure the initial DO of one sample immediately.
  • Seal the second sample and incubate in darkness at 20°C for 5 days to prevent photosynthesis and oxygen absorption.
  • Measure the final DO after 5 days.
  • Calculate BOD.
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7
Q

Give the equation for BOD (t) with ultimate oxygen demand.

A

BOD(t) = Lu [1- e(-kt) ]

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8
Q

What is k and what does it depend on?

A

k = BOD rate constant

Depends on type of effluent or waste quality

Rapid oxidation of effluent = high k

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9
Q

Give the equation relating to k and concentrations of DO.

A

e (-kt) = [ (Ct - Cu) / (Co - Cu) ]

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10
Q

Name five factors that affect BOD.

A

Light
Antibiotics
Type of organics
Toxic materials
Particle size

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11
Q

Name the typical BOD values for clean river water, treated and untreated sewage water.

A

Clean river water- < 5 mg/L
Treated sewage - 20 mg/L
Untreated sewage- 300 mg/L

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12
Q

Describe water quality using BOD levels.

A

1-2 = Very good (not much organic waste)

3-5 = Fairly clean

6-9 = Somewhat polluted (organic waste present)

100+ = Very polluted

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13
Q

Why is BOD not used as a water quality indicator for drinking water?

A
  • BOD measures the oxygen demand of microorganisms to decompose organic waste.
  • No organic matter is expected in potable water.
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14
Q

How does the pH of water affect aquatic life?

A

Eggs and larvae develop at specific pH levels.

Low pH in water causes invertebrates with Ca shells (alkaline) to solidfy, causing them to die, disrupting food chain.

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15
Q

Why is pH of water significant in surface waters?

A
  • Surface runoff from agriculture and industry may contain Fe, Al, NH3 etc
  • Toxic effects displayed depending on the water’s pH and concentration of elements.

E.g. 4 mg/l of Fe at pH 4.8 is safe but 0.9 mg/l of Fe at a pH 5.5 can cause fish to die.

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16
Q

Name three issues with high turbidity of water.

A
  1. In drinking water, turbidity linked to increased gastrointestinal
    diseases.
  2. Reduces water disinfection using chlorine and UV sterilisation as SS act as shields for the microorganisms.
  3. SS blocks the light from reaching lower depths of water bodies, affecting submerged aquatic vegetation and organisms.
17
Q

Why are nitrates in drinking water harmful?

A
  • Human body breaks down nitrates to nitrites
  • Reacts with red blood cells to produce methemoglobin which prevents oxygen transportation around body (baby blue disease).
  • Causes brown blood disease in fish.
18
Q

Name four sources of high nitrate levels.

A
  1. Nitrogen fertilisers (60%)
  2. Livestock farming
  3. Inadequate private septic tanks
  4. Municipal wastewater treatment discharges
19
Q

What are TDS?

A

A measure of the combined content of all inorganic and organic
substances contained in a liquid in: molecular, ionised or colloidal
suspended form. Refers to freshwater.

E.g salts, organic materials, nutrients, minerals.

20
Q

What is the difference between TDS and TSS?

A

TDS are smaller so can pass through a 2 µm sieve and remain dissolved.

TSS cannot pass through the sieve and remain suspended in water.

21
Q

What do TDS levels affect?

A

Extremely high or low TDS can limit growth or cause death in aquatic organisms.

22
Q

Do TDS levels affect humans?

A
  • Not harmful to human health.
  • Indicates aesthetic water quality and potential chemical pollution.
  • High TDS = hard water.
23
Q

How does total phosphate link to turbidity?

A

Phosphates can attach to SS, thus increasing water turbidity.

24
Q

Name two sources of phosphate levels in water.

A

Fertilisers and detergents.

25
Q

What is total phosphate?

A

Total Phosphate gives an estimate of the total amount of phosphate potentially available in a given water supply.

26
Q

What is the quality index if total phosphate > 10 ppm?

A

Quality index = 2 indicating poor water quality

27
Q

Name two problems with total phosphate.

A
  1. Eutrophication (overgrowth of algae).
  2. Decreases oxygen levels, harming aquatic life.
28
Q

Name the three main organisms to test for when determining presence of pathogens.

A
  1. Total Coliforms (TC) - General indicator.
  2. Faecal Coliforms (FC) - Linked to human feces like E. coli
  3. Faecal Streptococci (FS) - Linked to agriculture.
29
Q

Why is it important to test for pathogens?

A
  • High levels indicate failures in water treatment.
  • Increased risk of waterborne diseases.
30
Q

Name three natural sources of TOCs.

A
  1. Decaying vegetation
  2. Bacterial growth
  3. Metabolic activities
31
Q

Name four synthetic sources of TOCs.

A
  1. Pesticides
  2. Industrial chemicals
  3. Chlorinated organics
  4. Detergents
32
Q

Why is TOC important?

A
  • Critical for drinking water quality and disinfection processes.
  • High TOC promotes the growth of microorganisms (e.g. algae) depletes oxygen levels and harms aquatic life.
33
Q

What does chemical oxygen demand measure?

A

Measures the oxygen to decompose the organic materials and oxidise the inorganic materials
(ammonia, nitrate).

34
Q

Compare COD to BOD.

A

Both measure organic pollution.

COD is less specific—measures everything chemically oxidisable, not just biologically active organic matter.

COD levels are higher than BOD because more compounds are oxidised chemically than biologically.

35
Q

Describe the test of COD.

A
  • Incubate water sample with potassium dichromate (K₂Cr₂O₇) and sulfuric acid (H₂SO₄).
  • Boil under controlled temperature and time.
  • Measures oxygen consumed by organic and inorganic materials.
36
Q

List three benefits of COD testing.

A
  • Faster than BOD—completed in 3 hours.
  • Accurate and reproducible test for organic pollution.
  • Performed daily for monitoring water/wastewater quality.

Water Treatment (3 decks)

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