Water Microbiology Part II

Question 1

Theory behind water quality testing

Indicator types:

Answer 1

Cannot check for all pathogens especially those that come in small quantities

Check for organisms present in large quantities in feces such as E. coli - indicators of pollution and presence indicates higher change of pathogen presence

Coliforms: facultative aerobes, gram-neg, no spores, rod-shaped, lactose fermenting + gas within 48 hours at 35°C
- not all intestinal in origin

Fecal coliforms: coliforms from intestines of warm-blooded animals, thermotolerant and grow at 44.5°C
- presence indicates unsafe drinking water - absence does not guarantee safe drinking water (ex. cysts)

Question 2

Testing for coliforms

Answer 2

Membrane filtration: pass sample through filter, then place filter on agar plate to culture
- Tests 100 ml (large amount) of water
- faster and easier than MPN

MPN: samples added to lactose broth - dilution series of 1ml per tube
- Gas production tests positive color change
- use of statistical estimate to gauge number of coliforms and fecal coliforms in sample

Question 3

Goals of water treatment

Standard of quality control in Montreal water

Answer 3

remove pathogens, improve clarity, remove bad tasting or smelling compounds, soften the water

treatment intensity depends on water source

Montreal: <10 coliforms/100 ml and <1 fecal coliforms/100 ml

Question 4

Steps of water treatment

Answer 4

1) Sedimentation - large particles settle to bottom in resevoir

2) Flocculation treatment - chemical coagulation, flocs precipitate and trap fine particles (clay, bacteria, viruses and protists)
- 80% removal - should be clear looking

3) Filtration through sand - remove G. lamblia cysts and remaining bacteria
- 98-99.5% bacteria removal

4) Disinfection - chlorination to kill remaining microbes by oxidation and neutralizes remaining bad tasting compounds
- residual chlorine remains in water after treatment to protect distribution
- Ozone is more effective but shorter half-life

Question 5

Goal of wastewater (sewage) treatment

Answer 5

Reduce BOD

Destroy pathogens

Question 6

Steps of primary wastewater treatment

Answer 6

Primary:
1) Screening
2) Sedimentation - +flocculation sometimes, produces primary sludge
- reduces BOD to 25-40% and bacteria by 25-75%
- sludge is incinerated

Question 7

Steps of secondary wastewater treatment

Answer 7

Secondary: Not done for all wastewater
3a) Trickling filter - liquid sprayed over rocks/honeycomb to form biofilms coating surface and oxidizing organic matter in sewage
- BOD ↓ 80-95% and bacteria ↓ 90-95%

3b) Activated sludge - air blown through liquid and slime-forming bacteria grow and clump into flocs/activated sludge to oxidize organic matter –> settling tank and sludge removed
- BOD ↓ 85-95%, bacteria ↓ 90-98%

4) Sludge can be fermented in anaerobic sludge digester –> CH4 to power plant by methanogenesis
- remaining material can be buried or incinerated

Question 8

Steps of tertiary wastewater treatment

Answer 8

Further reduction of BOD, N, P and bacteria

Biological treatments - algae ponds
Flocculation
Filtration
Chlorination or ozonation

Final effluent liquid might be suitable for drinking if tertiary treatment is done

Question 9

Septic tanks

Answer 9

Involve minimal treatment of sewage

Sedimentation with minimal sludge digestion
- BOD reduction 60%

Requires periodic emptying - liquid goes to a leeching field
- still >10,000 coliforms/ml
- soil acts as filter and organisms decompose matter
- contamination of nearby groundwater is a concern (don’t use wells)