MC8: Waste water treatment, water purification, and waterborne microbial diseases Flashcards Preview

BS1040: Microbiology and Cell Biology > MC8: Waste water treatment, water purification, and waterborne microbial diseases > Flashcards

Flashcards in MC8: Waste water treatment, water purification, and waterborne microbial diseases Deck (25)
Loading flashcards...

What is the water cycle?

The cyclic exchange of water between the atmosphere and biosphere


Desribe the water (hydrological) cycle.

Water precipitates as rain and falls to Earth

It is returned by evaporation to the air

Human communities interact with the hydrological cycle by drawing water for drinking and other purposes, and by returning waterwater


Define 'wastewater'

Liquid derived from domestic sewage or industry that cannot be discharged into lakes/streams due to health, economic, environmental, or aesthetic reasons


What is the most important single measure available to ensure public health?

Water purification


How are microbes used in water purification?

They are used to identify, remove, and degrade


Name two pathogens associated with water

Vibrio choleraeSalmonella


Where does Vibrio cholerae occur?

Naturally in the plankton of fresh, brackish, and salt water


What symptoms does cholera cause?

Exhaustive diarrhoea, vomiting


How many Vibrio cholerae must be injected to cause cholera in a normal healthy adult?

100 million


What disease does Salmonella enterica cause?



How is water tested for the contamination of human sewage?

Coliform test


What is the current statutory test for human faeces in water?

The presumptive coliform test


Describe the MPN method of coliform test


  • 15 Durham tubes innoculated with samples of the water:
    • 5 with 10 mL
    • 5 with 1 mL
    • 5 with 0.1 mL
  • They are placed upside down in tubes of MacConkey agar solution and incubated at 35°C for 24 hours
  • After 24 hours, the tubes are both examined for gas production
  • Gas production = positive presumptive result
  • All positive presumptive cultures are used to innoculate tubes of brilliant freen lactose bile broth, which are then incubated for 48 hours at 35°C
  • A positive test result is gas production which is used to determine MPN 


Describe the MF method of coliform test

  • A membrane filter is placed on a filter support
  • The water sample is filtered through the membrane
  • Membrane filter removed and placed in plate containing the appropriate medium
  • Incubated for 24 hours
  • Typical coliform colonies


What bacteria are used for coliform tests in the USA?

Enterococcus faecalis (90-95%)

Enterococcus faecium (5-10%)


What is BOD?

Biochemical oxygen demand

  • Water passing through the ground picks up nutrients
  • Carbon run-off accelerates microbial respiration
    • O2 becomes depleted
  • Microbial oxygen consumption creates a biochemical oxygen demand
    • High BOD accelerates heterotrophic respiration which can cause a massive die-off of fish and other aquatic animals


How is BOD used to test for microbial load?

  • The O2 content of the water under test is measured (reading 1)
  • It is measured again five days later after being stored in a sealed bottle (reading 2)
  • BOD5 = reading 1 – reading 2 (mg/L = ppm)
  • This is an indirect measure of organic material
  • The maximum concentration permitted in sewage works discarded into rivers is 20 ppm BOD5


What are the four stages of wastewater treatment?

  1. Preliminary treatment: removes solid debris
  2. Primary treatment: fine screens and sedimentation tanks remove insoluble particles
  3. Secondary treatment: microbial decomposition of organic content
  4. Tertiary (advanced) treatment: chlorination or other chemical applications to remove pathogens


What are the goals of wastewater treatment?

  • Kill pathogens
    • Many die outside the human body anyway as this is their niche and outside it they are less competitive
    • Chlorination (hypochlorite: OCl) or irradiation with UV to produce ozone and kill remaining pathogens
  • Removing organic material
    • Oxidation of organic compounds is a microbial process


List the processes and microbes associated with primary wastewater treatment

Wastewater → grates and screens → settled

Processed water still has a high BOD so most plants have secondary treatment


List the processes and microbes associated with secondary wastewater treatment

  1. Complex polymers (polysaccharides, lipids, proteins) are hydrolysed by microbial enzymes (anarobic bacteria)
  2. Monomers (sugars, fatty acids, amino acids) are fermented by fermentative acetogenic bacteria
  3. Acetatehydrogen gas, and carbon dioxide gas undergo methanogenesis by menthanogenic archaea


How do trickle filters work?

  • Bed of stones or plastic
  • Trickle wastewater through
  • Develop film of attached organisms
  • Bacteria/fungi/protozoa/worms (grazers)
  • Ratio of 8:1:1:2
  • Mainly Gram negative bacteria
    • Pseudomonas
    • Zoogloea
    • Sphaerotilus


How does activated sludge work?

  • Aerate settled sewage to get 'activated floc'
  • Selects for organisms that flocculate and sediment
    • e.g. Gram negative bacteria
      • Pseudomonas
      • Zoogloea
      • Archromobacter
    • e.g. ciliates
      • Vorticella
  • Complex engineering, sensitive to shock, economical with space


What is water purification?

The process of removing undesirable chemical and biological contaminants from raw waiter, with the aim to produce water fit for a specific purpose – usually for human consumption


What are the three main methods of water purification?

  • Physical
    • Filtration
    • Sedimentation
  • Biological
    • Slow sand filters
    • Activated sludge
  • Chemical
    • Flocculation
    • Chlorination
    • UV