1. Treatment and analysis
Water
Treatment and analysis

2. Water Treatment Average household uses 300 litres per day Criteria
Colourless
Odourless
Safe to drink (no active bacteria)
Fluorinated
To ensure water is of an adequate standard for drinking, it must be treated

3. 7 Stages Water from Lakes and Rivers Screening Flocculation Settlement
Filtration
Chlorination
Fluoridation
pH Adjustment
Water to homes and industry

5. Flocculation * flocculating agent ( or
Screening * Wire mesh
1st stage * Removes large solids and
floating debris like twigs,
plastics etc
Flocculation * flocculating agent ( or
2nd stage flocculant) usually aluminium
sulphate (alum) is added.
* Makes smaller suspended
solids coagulate or stick
together in large clumps, so
they are easier to remove at the next stage

6. Settlement * Large tanks
3rd stage * Water goes in at the bottom and
rises slowly to the top, at < 2m/hr
* Particles settle to the bottom
* Over 90% of suspended solids
removed at this stage
Filtration * Large beds of sand
4th stage * Removes remaining susp solids
* Sand supported on a layer of gravel
* Sand cleaned regularly
* Water now clear but may contain
harmful bacteria

7. Chlorination * Cl2 gas is added
5th stage * Sterilises water
* Very small quantities 0.2 – 0.5 ppm
* Controlled carefully
* Monitored by bacteriological exam
of the water
Fluoridation * NaF or H2SiF6 added
6th stage (hexafluorosilicic acid)
* Added by law as helps to reduce
dental decay by strengthening the
enamel
* Small quantities ~ 1ppm

8. Water is now ready for consumption and use
pH Adjustment 7th stage
Optimum level is between 7 - 9
Too Acidic * may cause damage to pipes
* may be corrected by addition of Ca(OH)2 (lime)to raise the pH
* If very hard water, might be
softened by addition of NaCO3
which is a base
Too Basic * may be corrected by addition of dilute H2SO4 to lower the pH
Water is now ready for consumption and use

9. Oxygen Dissolves from air into water Low solubility in water
Temperature inversely affects solubility
Temp Solubility of O2
E.g oC
9.2 20oC

10. Water pollution
The release of substances into the environment that damage the environment is called pollution
3 main types
Eutrophication
Organic Waste
Heavy metals

11. Eutrophication
Enrichment with nutrients (fertilisers / nitrates / phosphates)
Due to run off from land (erosion from land) / due to pollution / dispersion in water / absorption by plants
Rapid growth of plants (algae) on surface / algal blooms formed
Light blocked from (photosynthesis reduced in) plants below surface
Decay by bacteria of algae, algal blooms / increase in bacteria /
Dissolved oxygen depleted (lowered, used up) / oxygen level falls
Fish levels reduced or killed off

12. Discharge of Organic Waste
Domestic sewage, slurry, silage effluent, effluent from food processing factories, milk, industrial waste, etc
Bacteria and other micro-organisms feed
Waste is broken down, O2 used up
Organic matter + O CO2 + H2O
O2 used up, reducing levels of fish and possibly killing off fish life.
O2 gone, anaerobic bacteria take over, river will smell due to presence of by product, Hydrogen Sulphide, H2S

13. Heavy Metals Lead Cadmium Mercury Pb2+ Cd2+ Hg2+ Cumulative poisons
Industrial effluents
Battery dumping
Regulations have brought about improvements
Removed by precipitation

14. BOD Test Biochemical Oxygen B.O.D. test Demand BOD is defined as
the amount of dissolved O2 consumed by biological action when a sample of water is kept in the dark at 200C for 5 days

15. The Winkler method is used to determine the amount of dissolved Oxygen in a water sample
2 bottles sampled
1st one tested straight away >> ppm of O2
2nd one tested after 5 days >> ppm of O2
Difference between the two readings is the BOD level, as this is the amount of O2 used up.

16. Winkler Method 1 cm3 Manganese (II) Sulphate
1cm3 alkaline potassium iodide solution (KI)
1cm3 H2SO4

17. Titrated against standard sodium thiosulphate
Mn2+ + OH- ions
react together
Mn(OH)2
reacts with O2
Mn(OH)3
acid added
I- + Mn(OH)3
iodine liberated I2
Titrated against standard sodium thiosulphate
1 O2 : 4 S2O32-
White precipitate
Brown precipitate

18. Sewage Treatment 3 main stages Primary treatment physical
Secondary Treatment biological
Tertiary Treatment chemical

20. Primary Treatment The physical stage
The incoming sewage is screened to remove debris and non-biodegradable material.
It passes into large deep sedimentation (settlement) tanks where about 50% of the suspended solids and about 33% of BOD are removed
Liquid on top is then passed onto to secondary treatment

21. Secondary Treatment The biological stage
The incoming sewage from first stage of treatment is passed into aeration tanks where mechanical stirrers aerate it.
This allows aerobic bacteria and other micro-organisms to decompose the solid matter into a harmless sludge called Activated Sludge.
Sewage then flows into settling tanks, sludge can be reused, or or recyled to make methane
About 95% of BOD removed

22. Tertiary Treatment The chemical stage
When the liquid passes out of the second round of settling, it is clean and inoffensive, but it may contain compounds of nitrates and phosphates
Phosphates from washing powders and washing up liquids, and nitrates from organic material in sewage
Must be removed before water discharged into river as could cause eutrophication.

23. Phosphate removal
aluminium sulphate added, aluminium phosphate precipitates out
Iron (III) chloride added, iron (III) phosphate precipitates out
Lime may also be used
Insoluble phosphate compounds allowed to settle out before discharge into waterway
Nitrate removal
difficult and expensive as nitrogen may be present in many forms, NH3, NO2- , NO3-, organic compounds containing N

24. Instrumental Methods of Analysis
pH meter
Atomic Absorption Spectrometry
Colorimetry – determining conc. of free chlorine in swimming pool water
DPD tablets added, reacts with chlorine in water
Compare colour with ones of known concentration
Comparator - disc of precalibrated solutions Or
Colorimeter – measure absorbance of known solutions and plot graph