Questions 14- 20

Question 1

What are the steps in sewage purification plants?

Answer 1

Mechanical step
- Mechanical grill: rough solids
- Grit removal: sand
- Separator of lightweight substances: fat and oil
- Primary sedimentation tank (after neutralisation): mechanical, sedimentation of settleable particles by low flow velocity
- Sludge goes to digestion tower
- Elimination of parasites (proglottides, eggs, larvae)

Biological step
- Imitates natural purification process of surface waters
- MO metabolise organic substrates (especially aerobic)
- Activated sludge tank: chemoorganotrophic MO, sometimes adding of oxygen to accelerate
- Secondary sedimentation tank: sedimentation of settleable particles, sludge goes to digestion tower
- Partial elimination of bacterial pathogens, viruses, protozoans

Abiotic chemical step
- Neutralization of sewage by addition of calcium carbonate or sodium hydroxide
- Elimination of phosphate, filtration, removing of toxins, disinfection

Finished goods
- Rubbish (plastic, metal, wood, sand) → garbage disposal
- Sludge → Digestion tower: closed, anaerobic stabilization of sludge, degradation of organic substances → inactivation of pathogens??
- Treatment with thickener, hydraulic press and dehumidifier → agriculture or burning
- Clean water → rivers

Question 2

Which factors are mainly influencing the number and kind of bacteria in surface water?

Answer 2

• Availability of nutrients
• Temperature
• Anorganic chemicals (oxygen)
• Other biota (MO, flora)

In environment
- Nutrient availability (e.g. fertilizers)
- Temperature
- Water (mobility)
- Host availability
…

Question 3

What are the main waterborne viral, bacterial, and parasitic infections?

Answer 3

• Bacteria: Campylobacter, Escherichia coli, Legionella, Pseudomonas, Salmonella typhi, Shigella, Vibrio cholerae (7, CELPSSV)
• Virus: infectious hepatitis A + B, Norovirus, Poliomyelitis, Rotavirus (4, HNPR)
• Parasitic: Cryptosporidium sp., Entomoeba histolytica, Giardia lamblia (3, CEG)

Question 4

What is done in order to control microorganisms in drinking water?

Answer 4

Control strategies of waterborne diseases
- Destroying pathogens in drinking water is easily achieved
- Drinking water treatment and distribution
- Wastewater treatment management
- Source water protection
- Vaccination (animals, humans, or both)
- Risk communication to susceptible populations

Question 5

What are some methods for the detection of antibiotic resistance in vitro?

Answer 5

Antibiotics susceptibility assays
→ which antibiotics work and which amount is needed?, specific antibiosis

Purification of cultures: diluted inoculation (3-loop-strike)

Agar diffusion assay (diameter of inhibition zones?)
- Standardized bacteria suspension/agar plate/workflow
- Apply defined concentration of AB – incubation – measure diameter in inhibition zones
- Classification of results: susceptible/intermediate/resistant
- + easy to perform, well-priced

Dilution assays (minimal inhibition concentration MiC?)
- Stepwise dilution of AB in liquid medium, each dilution step is inoculated with standardized suspension of bacteria (macro- or microdilution = small or big tubes)
- + easier standardisation, exact results - labour-intensive

E (Epsilometer) test: combination of agar diffusion and MIC assay
- Paper strips soaked with a gradient of AB concentration on agar plate
- + simple, high informational value

Question 6

What are the sources of water contamination?

Answer 6

• Humans (e.g. antibiotics)
• Birds
• Animal husbandry
• Ships
• Ice melting (e.g. glaziers)
• Wastewater
• Dumping of chemicals, industrial waste
• Traffic, emissions, households
• Landfills, underground storage tanks …

Question 7

What are some possibilities of inactivating microorganisms – physical, chemical, biological?

Answer 7

Conservation/Preservation
Treatment of organic substances to prolong storability → delays decomposition

Disinfection
Targeted inactivation of pathogens, reduction > 4 log10 steps → antisepsis

Sterilization
General elimination of all MO (including permanent stages) in a certain environment → sterility

Physical
* Temperature: refrigerate or freeze, pasteurize or sterilize (autoclaving in vacuum or dry heat for thermostable materials)
* 1 h: 50°C parasites, 70°C vegetative bacteria/viruses, 90°C thermoresistant viruses, 100°C spores
* Irradiation: UV-light best 256nm (damages genetic material, induces peroxides), beta or gamma
* High pressure, Sterile filtration

Chemical
* C: bacteriostatic chemicals, vacuum, fumigation
* D: chemical inactivation
* S: gas or cold sterilization (toxic gas denatures proteins)
* Biocides (D+S): damages cell structure
- cross-linking and denaturation of proteins in membrane/cell wall/genetic material (formaldehyde)
- lipolytic effect on membranes (alcohols)
- oxidative destruction of proteins (chlorine, ozone, iodine)
- hydrolytic destruction of cell wall/envelope/capsid (acids, alkaline solutions)

Biological/ biotechnological
- C: acidogenic bacteria
- D: thermophilic MO, exothermic decomposition, natural antibiosis, competition fur nutrients, change of environment, natural die-off effect
- S: not possible