lecture 2 Flashcards
What is turbidity
A measure of suspended matter.
How is turbidity measured?
It is measured using a turbimeter and the answer is displayed in nephelometric turbidity units (NTU’s). The light is shone through the water sample, and the amount scatted is measured and displayed in NTU’s.
What would be considered a
- normal
-DRINKNG WATER
- v high
turbidity reading ?
- 10NTU’s
- 5
-250
What are secchi disks for
can also measure turbidity
disk divided into black & white quarters used to gauge water clarity by measuring depth at which it is no longer visible from the surface
sources of turbidity?
Runoff from drainage basins
Waste discharges – sewage or industrial
Algae/aquatic weeds & their breakdown
products
High iron concentrations - give waters a
rust-red coloration
Air bubbles & particles from water
treatment process
What is TS? how is it calculated?
The total solids. This is measured by evaporating a sample (A) and then - B (which is the total sample pre evaporation at 103). Divided by the sample in litres
What is the relationship between TSS and turbidity
1TSS ~ 1-1.5 NTU’s
They both measure the suspended matter in sample but turbidity measures how many particles and what size
What is TSS?
The total suspended solids. To get the sample it is passed through a 0.45μm filter, whatever is left on the filter is the suspended matter. This is A and this is - B (which is the pre filter). All divided by sample in litres.
What is the impact of a high TSS?
High TSS can block light from the water, this means plants cannot photosynthesize and thus the oxygen concentration declines. If it is so bad the plants die then bacteria will use oxygen to decompose these which will lower the oxygen even more.
It also gets into fish kills, smoothers eggs, can change river courses causing flooding
What is TDS?
Total dissolved solids. The sample is passed through a 0.45μm filter to remove suspended material so only dissolved is left and is evaporated (A). This is A- B (original water that was passed through filter
What is electrical conductivity?
measure of the ions in water (low EC=low ions)
How is EC and TDS related?
TDS=ECxK
What is K?
a constant that depends on the dissolved ions. it is between 0.54-0.96 and typically 0.67 is used when value is unknown
What impacts EC?
- local geology (limestone (calcium carbonate) dissolves giving higher EC in drainage
basin ) - catchment area (larger has more likely had contact with soil and thus increased dissolved substances and EC)
- pollution (agriculture and wastewater treatment can inc)
-Evaporation of water from the surface of a lake concentrates dissolved
substances in the remaining water giving a higher EC - Microbial metabolism can alter EC – within thermally stratified lakes,
released CO2
rapidly dissolves in water to form carbonic acid (H2CO3),bicarbonate ions (HCO3-) & carbonate ions (CO32-) depending on water pH – these ions increase EC
What is the difference between an acid and a base?
Acid has more hydrogen ions (lower pH)
Base has more hydroxide (higher pH)
how do we measure pH?
Indicator paper (cheap and inaccurate)
liquid colorimetric indicator (slightly more accurate but interference due to colour changes in water)
electronic pH meter (accurate)
Why is pH important?
organisms need specific pH
wastewater treatment and well as many biological and chemical parameters too.
What range should pH be kept in?
5-9
What controls the pH of surface water?
carbonate buffering
pH between 6.5-8.5
What is alkalinity?
measures the ability of water to neutralise acid and resist a pH change (the capacity of carbonate buffering)
What happens when water is too basic?
carbonate dissociates into bicarbonate and hydrogen so that the hydroxide can be bound up and pH lowered
what happen when water is too acidic?
bicarbonate joins with the hydrogen ions to raise pH
What is water hardness
this is the mineral content is water
What is the value for soft water? what type of geology has influenced this?
0-75 (Concentration CaCO3mg/l)
from impermeable rocks like granite
What is the value for hard water? what type of geology has influenced this?
100-300
from porous rocks like chalk and limestone
what are the issues?
anecdotal evidence has linked to heart disease
limescale
lowers efficiency of detergents
what is total hardness
sum of Ca2+ & Mg2+
what is carbonate hardness?
this is called temporary hardness, when the Ca2+ & Mg2+ bind to carbonate or bicarbonate
what is non-carbonate?
this is permanent hardness. this occurs when Ca2+ & Mg2+ bind to anything but bicarb or carbonate
how to soften water?
we can remove the hardness from carbonate hardness via chemical precipitation or ion exchange.
Chemical precipitation
– lime (Ca(OH)2
) or soda ash (Na2CO3
) added which
raise pH & causes precipitation of calcium & magnesium as calcium carbonate
or magnesium hydroxide
what is ion exchange?
Ion exchange – synthetic resins
exchanging an ion in their structure
for one in solution
– usually Na+
are exchanged for
Ca2+ & Mg2
