Turbidity & Solids
What you see is what you get…
Turbidity
What is “turbidity”?
Turbidity is the technical term for “cloudy”. In water
sources, cloudiness is an indication of “suspended”
material.
What is “suspended” material?
Suspended compounds are those species that are
insoluble in the water but because of their size,
density, or composition won’t settle to the bottom but
remain “hanging” in the water.
Is Turbidity a problem?
Turbidity is an issue because:
1.
2.
3.
It “looks” bad – human aesthetic.
It causes filter contamination – financial
aesthetic.
It causes interference in analysis,
especially optical – chemist’s aesthetic
How to define “turbidity”
Joe’s 1st rule of chemistry is:
UNITS! UNITS! UNITS!
What units should turbidity have?
Turbidity can only be quantified relative to
a reference.
It’s all about the sand…
…well, it used to be…
Turbidity was originally measured relative to
SiO2 (sand). This gave a standard material
with a standard grain size.
Today, formazin polymer beads are used as the
reference material in a nephelometer!
Nephelo-who?
A nephelometer measures scattered light
at right angles to the source.
Pure water
Detect
Cloudy water
Detect
light
light
Turbidity indicates Solids
Turbidity is a visible indicator of the
presence of “solids” in a water sample.
What are “solids”?
Solids

Solids, as the term is used in water analysis,
refers to residue left upon evaporation and
may be dissolved or undissolved species. The
more common chemical usage would be
undissolved material which may include
sediment or “suspended material”.
Sometimes, water analysis will refer to
“dissolved solids” which are determined by
evaporating the water and drying the material.
Types of Solids
Solids come in many specific flavors:
Dissolved solids are responsible for the
hardness of water. Dissolved solids specifically refers
to samples isolated by drying at 180°C which removes
any bound water.
Undissolved solids are responsible for turbidity
or sediment. These can be isolated simply by filtering.
More flavors of solids:

Volatile solids are those wastes that will burn off at
550°C or lower. This includes the vast majority of
organic compounds.

Fixed solids are those remaining after pyrolysis
(“burning”) and consist largely of inorganic salts.
These salts are most directly related to hardness.

Settleable solids refers to those solids that will form
sediment if not stirred up. Can be determined by
simply allowing the material to sit in an Imhoff cone for
an hour.
Total solids
Total solids is the combination of all
solids. The “total solids” can be
determined by evaporation of a water
sample and drying of the residue (at 100110°C). The mass of remaining solids
relative to the volume of water
evaporated is the measure (mg/L for
units, yet again).
Total solids
What compounds make up total solids?
Everything that isn’t a gas or doesn’t
evaporate below 110°C!
Metal salts, inorganic salts, organic
material, insoluble salts, soluble salts,
etc.
Related tests

Specific conductance is an easy way to
measure the dissolved inorganic solids.
Usually measured in mhos (ohms,
backwards), the larger the conductance, the
higher the ionic concentration. This is a quick
test that should not be sensitive to most
organic contamination.

Dissolved organic solids are best
determined by COD or BOD or even TOC
(spectrophotometric determination of CO2
from combustion).
Other tests

Settleable solids are best determined
by settling in an Imhoff cone (1 hour
settling time). In this case the solids are
measured by volume (mL/L) in the tip of
the cone.

Suspended matter can be determined
by filtration.
The Whole Solids Picture
Total Solids
Dissolved solids
Organic
Volatile
Undissolved solids
Settleable
Suspended
Inorganic
Fixed
Sample Problem
1 L of waste water is collected. 1 hour settling in an Imhoff cone
results in 15.3 mL of sediment. The remaining liquid is decanted
and filtered using a 1 micron filter (initial weight 2.0460 g), the
solid isolated in the Imhoff cone is dried at 105 C and found to
weigh 20.0210 g. The filter paper is dried and weighed = 2.1052
g. The remaining liquid is evaporated and dried at 105 C
resulting in 1.2375 g of residue. Further drying at 180 C results in
0.9467 g of remaining residue from the evaporation. All three
residues were combined and ignited at 550 C, resulting in 6.4547
g of residue.
What is the concentration of settleable solids, suspended solids,
total solids, total volatile solids, and total dissolved solids? (With
appropriate units.)
Sample Problem
1 L of waste water is collected. 1 hour settling in an Imhoff cone
results in 15.3 mL of sediment. The remaining liquid is
decanted and filtered using a 1 micron filter (initial weight 2.0460
g), the solid isolated in the Imhoff cone is dried at 105 C and
found to weigh 20.0210 g. The filter paper is dried and weighed =
2.1052 g. The remaining liquid is evaporated and dried at 105 C
resulting in 1.2375 g of residue. Further drying at 180 C results in
0.9467 g of remaining residue from the evaporation. All three
residues were combined and ignited at 550 C, resulting in 6.4547
g of residue.
What is the concentration of settleable solids, suspended solids,
total solids, total volatile solids, and total dissolved solids? (With
appropriate units.)
1st – The Settleable solids
The settleable solids are easy - they come
directly from the Imhoff cone:
15.3 mL sediment/1 L waste water = 15.3
mL/L settleable solids.
Sample Problem
1 L of waste water is collected. 1 hour settling in an Imhoff cone
results in 15.3 mL of sediment. The remaining liquid is
decanted and filtered using a 1 micron filter (initial weight
2.0460 g), the solid isolated in the Imhoff cone is dried at 105
C and found to weigh 20.0210 g. The filter paper is dried and
weighed = 2.1052 g. The remaining liquid is evaporated and
dried at 105 C resulting in 1.2375 g of residue. Further drying at
180 C results in 0.9467 g of remaining residue from the
evaporation. All three residues were combined and ignited at
550 C, resulting in 6.4547 g of residue.
What is the concentration of settleable solids, suspended solids,
total solids, total volatile solids, and total dissolved solids? (With
appropriate units.)
Suspended Solids
Suspended solids are equally easy to determine, but
they SOMETIMES INCLUDE SETTLEABLE SOLIDS
(usually for natural systems where time is less limited):
Including settleable solids, total suspended
= 20.0210 g + (2.1052 g -2.0460 g) = 20.0802 g
Suspended solids = 20.0802 g/L = 20,080.2 mg/L
Excluding settleable solids, total suspended
= 2.1052 g - 2.0460 g = 0.0592 g
Suspended solids = 0.0592 g/1L = 59.2 mg/L
Sample Problem
1 L of waste water is collected. 1 hour settling in an Imhoff cone
results in 15.3 mL of sediment. The remaining liquid is decanted
and filtered using a 1 micron filter (initial weight 2.0460 g), the
solid isolated in the Imhoff cone is dried at 105 C and found to
weigh 20.0210 g. The filter paper is dried and weighed = 2.1052
g. The remaining liquid is evaporated and dried at 105 C
resulting in 1.2375 g of residue. Further drying at 180 C results
in 0.9467 g of remaining residue from the evaporation. All three
residues were combined and ignited at 550 C, resulting in 6.4547
g of residue.
What is the concentration of settleable solids, suspended solids,
total solids, total volatile solids, and total dissolved solids? (With
appropriate units.)
Total Solids
Total solids would include everything left
after drying at 105 C (settleable +
suspended + dried residue):
Total solids mass = 1.2375 g + 20.0802 g
= 21.3177 g
Total solids = 21.3177 g/L = 21,317.7 mg/L
Sample Problem
1 L of waste water is collected. 1 hour settling in an Imhoff cone
results in 15.3 mL of sediment. The remaining liquid is decanted
and filtered using a 1 micron filter (initial weight 2.0460 g), the
solid isolated in the Imhoff cone is dried at 105 C and found to
weigh 20.0210 g. The filter paper is dried and weighed = 2.1052
g. The remaining liquid is evaporated and dried at 105 C
resulting in 1.2375 g of residue. Further drying at 180 C results
in 0.9467 g of remaining residue from the evaporation. All
three residues were combined and ignited at 550 C, resulting in
6.4547 g of residue.
What is the concentration of settleable solids, suspended solids,
total solids, total volatile solids, and total dissolved solids? (With
appropriate units.)
Total Dissolved Solids
Total dissolved solids are those left after
filtering and 180 C drying (EXCLUDING
the suspended/settleable):
Total dissolved solids = 0.9467 g
= 0.9467 g/1 L = 946.7 mg/L
Sample Problem
1 L of waste water is collected. 1 hour settling in an Imhoff cone
results in 15.3 mL of sediment. The remaining liquid is decanted
and filtered using a 1 micron filter (initial weight 2.0460 g), the
solid isolated in the Imhoff cone is dried at 105 C and found to
weigh 20.0210 g. The filter paper is dried and weighed = 2.1052
g. The remaining liquid is evaporated and dried at 105 C
resulting in 1.2375 g of residue. Further drying at 180 C results in
0.9467 g of remaining residue from the evaporation. All three
residues were combined and ignited at 550 C, resulting in
6.4547 g of residue.
What is the concentration of settleable solids, suspended solids,
total solids, total volatile solids, and total dissolved solids? (With
appropriate units.)
We have Ignition!
The total solids are considered to include both volatile
and fixed solids. The ignition separates the two.
6.4547 g residue = 6.4547 g fixed solids (BY
DEFINITION)
Total solids = 21.3177 g
= fixed + volatile = 6.4547 + volatile
Volatile solids = 14.8630 g
Total fixed solids = 6.4547 g/1 L = 6454.7 mg/L
Total volatile solids = 14.8630 g/1 L = 14,863.0 mg/L
Solution Summary
Total solids = 21.3177 g/L = 21,317.7 mg/L
Total fixed solids = 6.4547 g/1 L = 6454.7
mg/L
Total volatile solids = 14.8630 g/1 L =
14,863.0 mg/L
Settleable solids = 15.3 mL/L
Suspended solids = 59.2 mg/L
Total dissolved solids = 946.7 mg/L
UNITS! UNITS! UNITS!
NOTE: Everything has units of mg/L
except for settleable solids which are
measured in mL/L!
Another Little Problem
300 mL of waste water is collected. 1 hour settling in an
Imhoff cone results in 6.6 mL of sediment. The
remaining liquid is decanted and filtered using a 1
micron filter (initial weight 1.8560 g), the solid isolated
in the Imhoff cone is dried at 105 C and found to weigh
8.3025 g. The filter paper is dried and weighed =
2.2713 g. The remaining liquid is evaporated and
dried at 105 C resulting in 0.6752 g of residue.
Further drying at 180 C results in 0.4567 g of
remaining residue from the evaporation. All three
residues were combined and ignited at 550 C,
resulting in 1.4547 g of residue.
What is the concentration of total volatile solids, and total
dissolved solids? (With appropriate units.)
Total Volatile Solids
How do you recognize the “total volatile
solids”?
It’s whatever burns off during the ignition at
550 C.
Another Little Problem
300 mL of waste water is collected. 1 hour settling in an
Imhoff cone results in 6.6 mL of sediment. The
remaining liquid is decanted and filtered using a 1
micron filter (initial weight 1.8560 g), the solid isolated
in the Imhoff cone is dried at 105 C and found to weigh
8.3025 g. The filter paper is dried and weighed =
2.2713 g. The remaining liquid is evaporated and
dried at 105 C resulting in 0.6752 g of residue.
Further drying at 180 C results in 0.4567 g of
remaining residue from the evaporation. All three
residues were combined and ignited at 550 C,
resulting in 1.4547 g of residue.
What is the concentration of total volatile solids, and total
dissolved solids? (With appropriate units.)
Total Volatile Solids
Add up the total solids, then subtract the residue:
Total solids mass= volatile solids + fixed solids
Total solids mass = settleable + suspended + in solution
= 8.3025 g + (2.2713 g – 1.8560 g) + 0.6752 g
= 9.393 g
Fixed solids mass = 1.4547 g
Volatile solids mass = 9.393 g – 1.4547 g = 7.938 g
?
UNITS! UNITS! UNITS!
The mass isn’t helpful. If you had twice the
sample size of the same water, you would
have twice the mass.
Volatile solids = mass of volatile solids
Volume of sample
Volatile solids = 7.938 g = 26.461 g/L
0.300 L
= 26, 461 mg/L
Easier test method
If you only cared about the volatile solids,
what would be the easiest way to
experimentally determine them in this
case?
Volatile solids
What are they?
The difference between total solids and fixed
solids.
What’s the easiest way to determine total solids?
Just dry everything at 105 C (no need to
separate them first)
Volatile solids
What’s the easiest way to determine fixed
solids?
Just take the dried residue and burn it at
550 C.