Analyses of water

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Analyses of water Expt. 5 Water quality
parameters
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Marine water quality in HK 60 of HK is
sea. Antipollution strategies of
govt. Declaration of WCZ 1987-1996. Improvement
of WPCO cap. 358 Govt can declare area to
be WCZ, devise WQO, licenses for effluent
discharge Development of livestock waste control
scheme SMP and SSDS Dumping at sea
ordinance Chemical waste disposal 1993.
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Note 1 To study the oceanographic conditions
of marine water 2 To study the transparency and
light penetration of marine water which
relates to the appearance and aesthetic value of
a waterbody 3 To study the organic pollution of
marine water 4 To study the bacterial condition
of marine water and to indicate faecal
pollution 5 To study the eutrophic condition
of marine water as a consequence of
pollution by sewage livestock wastes, industrial
wastes, rural and urban runoff S 1m
below water surface M mid-depth of water
column B 1m above seabed
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To assess success of these strategies long-term
water quality monitoring program. 1. Marine water
quality determinands 2. Bottom sediment
determinands we look at some measurements in 1.
are values in compliance with WQO? Measurement
of pH seawater pH ranges from 7.6-8.5 photosynthe
sis pH?, CO2 reduced in water. organic
decomposition, pH?. Deep Bay polluted by organic
waste, lowest pH
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pH -log a(H) Glass electrode measures
potential across a membrane caused by
ion-exchange and migration of charge
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Operational definition of pH pH(X) pH(S) -
(Ex-Es)/S ?Ej/S pH(S) - (Ex-Es)/0.0592 compar
e the potential of the unknown solution (Ex) with
that of known pH value (pH(S)). S RTln10/F
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Errors in pH measurements

• 1. Alkaline error at pH gt11.
• 2. Acid error, pH lt 0.5.
• 3. Dehydration of electrode unstable performance
  and errors.
• 4. Variations in junction potentials
• 5. Activities of buffer solutions differ from
  those of low ionic strength solutions.
• 6. Error in pH of standard buffer
• 7. Temperature error

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Dissolved oxygen For a gas in equilibrium with a
solvent, the amount of gas which dissolves
depends on the pressure KH Xsolv/p(X,gas).
Larger KH, greater solubility. For O2, KH
1.3x10-3 mol dm-3 atm-1 at 25C. The atmosphere
contains 0.21 atm O2, so O2,aq KH x
p(O2,gas) 1.3x10-3x 0.21
2.7x10-4 mol dm-3 2.7x10-4 mol dm-3 x 32 g
mol-1 x 1000 mg g-1 8.7 mg dm-3 8.7ppm
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Most fish require 5-6ppm for survival. thermal
pollution, biomass decomposition oxidizable
substances (sewage, agricultural runoff,
effluents) deplete O2 in water.
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Measurement of DO Electrochemically (Makareth
oxygen electrode). In the electrochemical oxygen
sensor, oxygen diffuses into the cell through a
thin, disposable polyethylene membrane. The
electrode reactions are
cathode (made of silver) O2(g) 2H2O(l) 4e-
? 4OH-(aq) anode (made of lead) 4OH-(aq)
2Pb(s) ? 2Pb(OH)2(s) 4e- overall O2(g)
2H2O(l) 2Pb(s) ? 2Pb(OH)2(s)
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Dissolved gases in natural waters
Ammeter
Pb(s) ? Pb 2e-
Pb 2OH- ? Pb(OH)2(s)
4e- O2 2H2O ? 4OH-
Oxygen-permeable membrane
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From the Nernst equation, we can see that the
potential across this cell depends only upon
p(O2) Ecell E - RT / nF ln
1 / p(O2) In actual operation of the oxygen
electrode, which is a voltammetric device, a
constant potential is applied across the cell,
the current flow -- directly proportional to
O2,aq -- is measured. Use of a small battery as
the power source makes the device lightweight
portable, thus ideally suited to measurements
in the field.
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Nephelometry turbidimetry Nephelometry
determines amount of undissolved particles in a
suspension, based on measurement of amount of
light scattered. Turbidimetric methods based on
transmitted light measurement. For small,
uniform size/shape particles, Is ? conc.
Intensity of scattered light depends on number,
concentration, size, shape, RI of particles,
angle of scatter, intensity, wavelength of
incident radiation... also on bubbles,
scratches...
absorbing dissolved substances... (measure Is/It)
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Principle of measurement Ratio
turbidimeter (nephelometer) light path diagram
for measuring turbidities in both cloudy natural
waters and treated clear waters with turbidities
less than 1 NTU.
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• NTUnephelometric turbidity units. Use formazin
  polymer as a reference turbidity standard
  suspension.
• Turbidity of seawater
• Affects light penetration.
• 2. Affects marine fauna.
• caused by suspended particles (silt, clay,
  organic matter, algae)

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In HK, greatest turbidity near Pearl River Delta.
Also dredging, dumping, reclamation and airport
core projects affect turbidity in other areas.
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Nutrients in seawater Algal growth arises from
high levels of a nutrient, and leads to
eutrophication. High levels of inorganic
phosphate (gt0.2 mg dm-3, depth average) were
found in 1994 in inner Deep Bay inner Tolo
Harbour.
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The various determination of phosphorus
Direct
Ortho - P
Total sample (no filtration)
Sample
H2SO4 Hydrolysis
Hydrolyzable Ortho - P
Filter 0.45 micron membrane filter
Persulfated Digestion or Kjeldahl Digestion
Residue
Filtrate
Total P
H2SO4 Hydrolysis
Persulfated Digestion
Kjeldahl Digestion
Direct
or
Dissolved Hydrolyzable Ortho - P
Dissolved Ortho - P
Dissolved Phosphorus
Source US EPA
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Principle of chemical determination of P as
orthophosphate (PO43-) PO43- reacts with
ammonium molybdate antimony potassium tartrate
under acidic conditions to form a complex.This
complex is reduced by ascorbic acid to form a
blue complex which absorbs light at 880nm.The
absorbance is proportional to PO43- in
sample. Interferences See notes in library file
7131-14
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Characteristics of FlA 1. Unsegmented flow. 2.
Direct injection into the flow. 3. Controlled
partial dispersion or dilution of the analyte. 4.
Reproducible operational timing. Four components
as indicated in diagram. System requirements 1.
Pulse free. 2. Reproducible injection. 3.
Changeable flow-path. 4. Sensitive, rapid,
reproducible detection.
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Manifold Diagram
PUMP FLOW from water from wash bath
drain orange orange CARRIER Blue SAMPLE Gree
n
to wash bath fill
to waste
molybdate color reagent
1?
ascorbic acid
1
60o
2 3 1 4 6
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Sample Loop 30cm Filter 880nm
To flow cell
to port 6 of next valve or waste
CARRIER is helium degassed water.
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Basic principles of FIA
General arrangement of an FIA system, showing its
essential components propelling unit
(peristaltic pump or gas-pressure unit),
injection system, tube zone (linear, coiled, with
reactor/mixing minichamber), detection system
(flow-cell) recorder. Its automation would
require a sampling unit an electrically-controll
ed injection valve.
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Operational scheme for a four-way rotary valve
showing the sample filling emptying positions.
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Schematic drawing of a peristaltic pump.
(a)Detail of the drum bearing the rollers on
which the tubes are accommodated. (b)The entire
pump showing the situation of the drum.
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Lachat optical-fibre photometric flow-cell
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Lachat optical-fibre photometric flow-cell

• The splitting of the light from the halogen
  lamp results in two beams (measurement and
  reference) equidistant from the emissive source.
  The detector head can be adjusted to accommodate
  two cells with different optical paths and has a
  pre-amplifying circuit and two optical detectors.

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Calibration graph from Lachat FIA for phosphate