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. It “looks” bad – human aesthetic.

2. It causes filter contamination – financial aesthetic.

3. 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

light

Detect

Cloudy water

light

Detect

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 100-110°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 Undissolved solids Settleable

Suspended

Organic Inorganic Volatile 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 gSuspended 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/LTotal volatile solids = 14.8630 g/1 L = 14,863.0 mg/L

Solution Summary

Total solids = 21.3177 g/L = 21,317.7 mg/LTotal fixed solids = 6.4547 g/1 L = 6454.7

mg/LTotal volatile solids = 14.8630 g/1 L =

14,863.0 mg/LSettleable solids = 15.3 mL/LSuspended solids = 59.2 mg/LTotal 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.