1Module 4

Water Chemistry & MicrobiologyOn completion of this module you should be able to:

• Have some knowledge of the chemical and physical properties of water

• Have an understanding of water microbiology

• Be aware of some disease causing microorganisms

• Be able to describe the microbiological standards of drinking water

2Module 4

Typical Raw Water

Good Poor Reject

Average BOD5 mg/L 1.5 - 2.5 2.5 – 4 > 4

Max BOD5 mg/L 3 – 4 4 – 6 > 6

Average coliform (MPN) 100 – 5000 5000 – 20000 > 20000

Max coliform <20% > 5000 <5% > 20000

pH 5 – 9 3.8 – 10.3 < 3.8

Chlorides mg/L 50 – 250 250 – 600 > 600

Fluorides mg/L 1.5 – 3.0 > 3

3Module 4

Drinking Water Quality

• Water for human consumption must be free from pathogenic organisms and from chemicals hazardous to health

• Water must be aesthetically acceptable (odour, colour, taste), and also non-corrosive or scale forming

• Water should conform to some acceptable guidelines e.g. WHO, NHMRC

4Module 4

Water Quality CharacterisationWe can characterise water quality in terms of the following

• Chemical

• Physical

• Radiological

• Bacteriological

5Module 4

Chemical Properties of Water

• Dependent on the composition of solutes present

• Solutes are natural or introduced anions and cations in water, which may contribute to taste, odour and hardness

• Concentrations of solutes that are injurious to to health

• Solutes are largely inorganic but some may be organic

6Module 4

Maximum acceptable values in drinking water

Characteristic WHO guidelinemg/L

Australianguideline mg/L

Arsenic 0.01 0.007

Aluminium 0.2 0.2

Barium 0.7 0.7

Cadmium 0.003 0.002

Chromium 0.05 0.05

Cyanide - 0.08

Fluoride 1.5 1.5

Lead 0.01 0.01

Mercury 0.001 0.001

Nitrate (as N) 50 as NO3- 50

Some Health related Chemical Characteristics

7Module 4

pH of water

• pH = -log10 [H3O]

• Buffering – ionic forms of CO2 that offer resistance to pH change

• Diurnal changes in raw water may affect pH values

1 M HCl Pure water 1 M NaOH

0 7 14

Gastric juice

seawater

Householdammonia

Module 4 8

Effects of buffering in water

Pure water Carbonate in water

Carbonic acid Well water

9Module 4

Physical Properties of Water

• Colour

• Turbidity or total suspended solids (TSS)

• Total dissolved solids (TDS) which may be related to hardness

• Odour and taste

• Temperature

10Module 4

RadiologicalRadioactivity is the energy released from the breakdown of radionuclides

• Naturally occurring radioactive species in drinking water sources

• Contamination from concentration of natural levels such as mining and processing of minerals

• Artificial radionuclides which may enter drinking water supplies from medical and industrial use of radioactive materials

11Module 4

Water MicrobiologyOf living organisms (apart from animals and plants) there is a third kingdom of Protisa

• Eucaryotic cells (2 - 200 micron)

• Procaryotic cells (0.5 - 2 micron)

• Viruses (20 - 100 nm)

12Module 4

Procaryotic CellsBacteria, blue green algae (cyano-bacteria)

• Small size with simple organisation

• Nuclear region - single DNA molecule not separated from cytoplasm by any defined structure

• Cytoplasm - a site of protein synthesis (RNA), a colloidal suspension of proteins, carbohydrates and complex organic compounds

• Cytoplasm membrane with enzymes for transport of food into cells and removal of wastes

• Cell wall to maintain rigidity and shape of cell

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A Bacterium Cell

Module 4 14

Bacteria Cells

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BacteriaSome are pathogenic. Majority assist in breaking down matter. The bacterial cell is a chemical machine that transforms energy through metabolism

• Catabolism where larger molecules are broken down with the release of energy

• Anabolism a biosynthesis of new molecules from simple nutrients

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Bacteria may be classified as

• Heterotrophic requiring an external organic source for energy and carbon

• Autotrophic that utilises inorganic compounds for energy and uses CO2 as a carbon source

• Aerobic, anaerobic and facultative in relation with O2

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Eucaryotic CellsExamples are algae, fungi, protozoa

• More complex than procaryotic cells

• Well defined nucleus with a nucleus membrane

• Membrane bound organelles that perform various tasks

• Unicellular or multicellular

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Algae

• Resembles plants but without roots, stems, leaves

• Photosynthetic, autotrophic microorganism

• Important role of recycling nutrients in the aquatic food chain

• Contributes to clogging of filters, odour & taste in water, and eutrophication

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Fungi (yeast, mould, mushroom)The ability of fungi to survive under low pH and nitrogen limiting conditions, and distinctive degradative ability makes them important in wastewater treatment

• Non-photosynthetic

• Multi/or unicelluar and immotile

• Reproduce sexually or asexually

• Yeasts are unicellular, capable of aerobic and anaerobic growth

• Moulds are strict aerobes

20Module 4

Protozoa

• Non-photosynthetic

• Single cell eucaryote that obtain energy from metabolising organic matter by feeding on bacteria, fungi and algae

• Important role in the secondary settling of the wastewater treatment process

• Some are a concern in drinking water e.g. cryptosporidium, giardia

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ProtozoaThe discovery of the cryptosporidium parasite in water supplies in Glasgow (Aug 2002) comes a matter of months after an outbreak struck the north east of Scotland. The latest alert has affected about 140,000 people in Glasgow after the infection, which can cause severe diarrhoea, was detected in the Mugdock Reservoir in Milngavie. Those in the affected areas have been urged to boil water before drinking it.

Cryptosporidium is commonly spread by animals

However, Scottish Water said it was safe to use for washing clothes and dishes and for bathing - although not for bathing babies.

22Module 4

VirusesDo not have the ability to reproduce themselves but replicated only within a host cell

• Small structures of non-living compounds

• Composed of 2 kinds of macromolecules i.e protein and DNA or RNA

• Acellular

• Obligate intracellular parasites

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Waterborne Diseases and AgentsDependent on the causal agent

• Bacterial e.g. cholera, typhoid fever

• Viral e.g. hepatitis A, diarrhoea

• Protozoal e.g. amoebic dysentry, giardiasis

• Helminths e.g. schistosomiasis

24Module 4

Indicator Microorganisms for Drinking WaterColiform group of microorganisms is present in large numbers in animal and human excreta. Why is there a need for such indicators?

• Pathogenic microorganisms are small in numbers

• Routine testing is not practicable and expensive

• Involves skilled labour and specialist equipment

• Specific tests may not be available

25Module 4

Indicator Microorganisms PropertiesMicrobial indicators are E.coli and the coliform group

• Always present when pathogens of like origin are present

• Present in large numbers, >> pathogens

• Easy and quick to detect

• Equal or greater survival time than pathogens

• Absent from unpolluted waters

• Similar sensitivity to disinfection as pathogens

26Module 4

Bacterial Standards of Drinking Water

• 98% of samples in any one year should not have any E.coli in 100 mL

• 95% of samples in any one year should not have any coliform organisms in 100 mL

• Max 10 coliform organisms per 100 mL in any one sample

• No coliform organism in 100 mL of any two consecutive samples

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Objectives of Water Sampling

• Ensure aesthetic qualities, adequate residual chlorine and free from harmful chemicals

• Bacterial qualities of raw and treated water are acceptable

• Sources of pollution or potential contamination are known

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Types of SamplingRelated to population size

• Residual chlorine concentration

• Simple bacteriological test

• Simple chemical analysis

• Full chemical and bacteriological analysis

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Frequency of SamplingRelated to population size

Population served Minimum number of samples

Above 100 0006 samples per week, plus 1 additional sample per month for each 10 000 above 100 000

5 000 – 100 0001 sample per week, plus 1 additional sample per month for each 5 000 above 5 000

1 000 - 5 000 1 sample per week

Under 1 000 Minimum samples for small water supplies

30Module 4

END OF MODULE 4