Water Quality and Treatment Flashcards
Why is drinking water quality important
- To protect the consumers health
- To be sure that the water is acceptable
- To protect the distribution system
Water quality characteristics
- Physical- may affect acceptability, treatment or indicate possible contamination
- Chemical- may affect health, acceptability, aquatic life, treatment or distribution
- Biological- usually applies to flora or fauna in natural water and used for assessing pollution
- Microbiological- organism too small to be seen by the naked eye, many will be harmless but some may be pathogens
Quality issues which may need treatment
- Physical- suspended solids in surface water
- Chemical- arsenic in groundwater
- Microbiological- removal of pathogens
- Aesthetic- unacceptable taste, odour, colour
What do many countries base their water quality standards off
WHO drinking water guidelines- most recent 4th edition in 2011. They are only guidelines but many countries base their standards off these
What do the WHO guidelines provide detail on
- Microbial aspects
- Chemical Aspects
- Radiological Aspects
- Acceptability aspects
Transmission categories for water related diseases
- Water Borne
o Diseases where pathogens are ingested in water
o E.g., Cholera and Typhoid
o Transmission relates to the quality of water drunk - Water-Washed/Water-Scarce- a number of possible pathogen routes
o Ingested because of poor hygiene- faecal-oral route
o Will affect the skin, e.g. scabies or the eyes e.g. trachoma because people can’t wash themselves regularly
o Infections carried by lice, e.g. typhus - Water-Based
o Pathogen spends part of its life in an aquatic animal
o All are caused by parasitic worms
o E.g. Bilharzia and Guinea Worm - Insect-Vector Route
o Diseases carried by insects that breed in or bite near to water
o E.g. Malaria, River blindness
What does the F diagram show
Faecal Oral transmission routes
Primary chemical water quality concerns
- Arsenic
- Fluoride
- Nitrate/Nitrite
- Mercury, Lead, Selenium, Uranium (Heavy Metals)
- Pesticides
- Salinity
- pH and Hardness
- Iron and Manganese
Diseases caused by chemicals in drinking water
- Geogenic (naturally occurring)
o Arsenic- Arsenicosis
o Fluoride- Fluorosis - Anthropogenic
o Nitrate (main source agriculture and wastewater)- methemoglobinemia
o Lead-plumbism (lead poisoning)
o Pesticides – poisoning
How should water samples be stored and for how long before testing
- Within 2 hours if samples are kept in a cool dark place without refrigeration
- Within 6 hours if samples are chilled rapidly to 4 degrees
Cold temperatures prevent reproduction, and dark places prevent bacteria being killed by UV light. Any sample which has been kept for more than 24 hours after collection should be discarded.
Why do we use indicator organisms rather than testing for specific pathogens
When testing water we don’t test for specific pathogens, as there are so many different types of pathogens which could be present in water, and doing so would be lengthy and expensive. Also testing for specific pathogens would fail to show the presence of other pathogens. Instead we use indicator organisms.
Characteristics of an indicator organism
- Indicate that faecal contamination has occurred
- Relatively easy to culture and detect
- Present in faeces in large numbers
- Not particularly harmful, but indicate that far more dangerous organisms may be present
- Principal bacteria used as indicators of faecal pollution: the coliform family
- Total coliforms can be cultured at 37 C but not all are of faecal origin
- Some coliforms can grow at 44 C and ferment lactose to produce acid, these are thermotolerant coliforms
What is turbidity
- Most visible aspect of contamination
- Optical property
- Suspended solids and colloids
- Also includes pathogens and algae
How do you test turbidity
- Testing for turbidity involves filling a tube with the sample until you can no longer see that pattern at the bottom of the tube
Issues with turbidity
Pathogens can adhere to solid particles, which inhibits disinfection
Limitations of water quality testing
- Analysis only gives a snapshot of the current situation
- Small discrete samples- what about the wider area
- Limited information on the causes of contamination
- Also need to consider transport and storage- need to consider behaviour not just hardware