total solids and total dissolved solids in water
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Total Solids and Total Dissolved Solids in Water
Objective
In this lesson we will answer the following questions:
What are Total Dissolved Solids? Where do dissolved solids come from? What is the effect of solids on drinking water? How are solids taken care of?
Reading Assignment
Along with the online lecture, read chapter 25 in Simplified Procedures for Water
Examination.
Lecture
Introduction to Solids
Water is a good solvent and picks up impurities easily. Pure water - tasteless,
colorless, and odorless - is often called the universal solvent. Dissolved solids refer to
any minerals, salts, metals, cations or anions dissolved in water. Total dissolved solids
(TDS) comprise inorganic salts (primarily calcium, magnesium, potassium, sodium,
bicarbonates, chlorides and sulfates) and some small amounts of organic matter that
are dissolved in water.
TDS in drinking water originate from natural sources, sewage, urban runoff, industrial
wastewater, and chemicals used in the water treatment process, and the nature of the
piping or hardware used to convey the water, i.e. the plumbing. In the U.S. elevated
TDS has been due to natural environmental features such as mineral springs,
carbonate deposits, salt deposits, and sea water intrusion, but other sources may
include salts used for road de-icing, drinking water treatment chemicals, stormwater
and agricultural runoff, and point/non-point wastewater discharges.
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Solids analyses are performed in a variety of applications in the fields of
environmental engineering and science. For example, one of the most important
parameters used in making control decisions in the activated sludge process of
wastewater treatment systems is mixed liquor suspended solids(MLSS)
and/or mixed liquor volatile suspended solids(MLVSS). Total solidscan be
subdivided into total suspended solids(TSS) and total dissolved solids (TDS). Eachdivision can be further subdivided into fixedor volatile.
Total solidsis the term applied to the material residue left in a vessel after
evaporation of a sample and its subsequent drying in an oven at a defined temperature
(either 103C or 180C) Total solids includes total suspended solids, the portion of
total solids retained by a filter, and total dissolved solids, the portion that passes
through the filter.
The type of filter holder, the pore size, porosity, area, and the thickness of the filter
and the physical nature, particle size, and amount of material deposited on the filterare the principal factors affecting separation of suspended from dissolved
solids. Dissolved solidsis the portion of solids that passes through a 2.0 m
(micrometer) or smaller nominal pore size filter. Suspended solidsis the portion
retained on the filter.
Fixed solidsis the term applied to the residue of total, suspended, or dissolved solids
remaining after combustion at 500C. The weight lost during combustion is referred
to as volatile solids. Fixed and volatile may not be the best measure of inorganic or
organic material. For example, the loss of mass during combustion is not confined to
organic material, and may include the decomposition or volatilization of some mineral
salts. Most appropriate methods of characterizing organic material include total
organic carbon (TOC), BOD and COD. More appropriate methods of characterizing
inorganic material include alkalinity, hardness, and chromotography techniques for
the analysis of specific constituents. The selection of the most appropriate method
requires knowledge of both sample characteristics and the intended use of the data.
Settleable solidsis the term applied to the material settling out of suspension within a
defined period of time. Settleable solids are not directly related to total solids, total
suspended solids or total dissolved solids.
Total Suspended Solids
Total Suspended Solids (TSS) are solids in water that can be trapped by a filter. TSS
can include a wide variety of material, such as silt, decaying plant and animal matter,
industrial wastes, and sewage. High concentrations of suspended solids can cause
many problems for stream health and aquatic life.
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High TSS can block light from reaching submerged vegetation. As the amount of light
passing through the water is reduced, photosynthesis slows down. Reduced rates of
photosynthesis causes less dissolved oxygen to be released into the water by plants. If
light is completely blocked from bottom dwelling plants, the plants will stop
producing oxygen and will die. As the plants are decomposed, bacteria will use up
even more oxygen from the water. Low dissolved oxygen can lead to fish kills. HighTSS can also cause an increase in surface water temperature, because the suspended
particles absorb heat from sunlight. This can cause dissolved oxygen levels to fall
even further (because warmer waters can hold less DO), and can harm aquatic life in
many other ways.
High TSS in a water body can often mean higher concentrations of bacteria, nutrients,
pesticides, and metals in the water. High TSS can cause problems for industrial use,
because the solids may clog or scour pipes and machinery.
The flow rate of the water body is a primary factor in TSS concentrations. Fastrunning water can carry more particles and larger-sized sediment. Heavy rains can
pick up sand, silt, clay, and organic particles (such as leaves, soil, tire particles) from
the land and carry it to surface water. A change in flow rate can also affect TSS; if the
speed or direction of the water current increases, particulate matter from bottom
sediments may be resuspended.
Total Dissolved Solids
Total Dissolved Solids (TDS) are solids in water that can pass through a filter. TDS in
a measure of the amount of material dissolved in water. This material can include
carbonate, bicarbonate, chloride, sulfate, phosphate, nitrate, calcium, magnesium,
sodium organic ions, and other ions. A certain level of these ions in water is necessary
for aquatic life. Changes in TDS concentrations can be harmful because the density of
the water determines the flow of water into and out of the organism's cell. However, if
TDS concentrations are too high or too low, the growth of many aquatic life can be
limited, and death may occur.
Similar to TSS, high concentrations of TDS may also reduce water clarity, contribute
to a decrease in photosynthesis, combine with toxic compounds and heavy metals, and
lead to an increase in water temperature. TDS is used to estimate the quality of
drinking water, because it represents the amount of ions in thew ater. Water with high
TDS often has a bad taste and/or high water hardness.
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In general, the total dissolved solids concentration is the sum of the cations (positively
charged) and anions (negatively charged) ions in the water. Therefore, the TDS test
provides a qualitative measure of the amount of dissolved ions, but does not tell us the
nature or ion relationships. In addition, the test does not provide us insight into the
specific water quality issues, such as elevated hardness, salty taste or corrosiveness.
Therefore, the TDS test is used as an indicator test to determine the general quality ofthe water. The sources of total dissolved solids can include all of the dissolved cations
and anions, but the following table can be used as a generalization of the relationship
of TDS to water quality problems.
Cations combined with Carbonates
(CaCO3, MgCO3, etc)
Associated with hardness, scale
formation, bitter taste
Cations combined with Chloride (NaCl,
KCl)
Salty or brackish taste, increase
corrosivity
Some rock and soil release ions very easily when water flows over them; for example,
if acidic water flows over rocks containing calcite (CaCO3), such as calcareous shales,
calcium (Ca2+
) and carbonate (CO32-
) ions will dissolve into the water. Therefore,
TDS will increase. However, some rocks, such as quartz-rich granite, are very
resistant to dissolution, and don't dissolve easily when water flows over them. TDS of
waters draining areas where the geology only consists of granite or other resistant
rocks will be low (unless other factors are involved.)
Factors Affecting TSS and TDS
Soil Erosion
Soil erosion is caused by disturbance of a land surface. Soil erosion can be caused by
building and road construction, forest fires, logging and mining. The eroded soil
particles can be carried by stormwater to surface water. This will increase the TSS and
TDS of the water body.
Urban Runoff
During storm events, soil particles and debris from streets and industrial, commercial,
and residential areas can be washed into streams. Because of the large amount of
pavement in urban areas, infiltration is decreased, velocity increases, and natural
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settling areas have been removed. Sediment is carried through storm drains directly to
creeks and rivers.
Decaying Plants and Animals
As plants and animals decay, suspended organic particles are released and can
contribute to the TSS and TDS concentration.
Wastewater and Septic System Effluent
The effluent from wastewater treatment plants can add suspended solids to a stream.
The wastewater from our houses contain food residue, human waste, and other solidmaterial that we put down our drains. Most of the solids are removed from the water
at the treatment plant before being discharged to the stream, but treatment plants only
remove some of the TDS. Important components of the TDS load from the treatment
plants include phosphorus, nitrogen, and organic matter.
Measurement of TSS
To measure TSS, the water sample is filtered through a pre-weighed filter. The
residue retained on the filter is dried in an oven at 103 to 105C until the weight of the
filter no longer changes. The increase in weight of the filter represents the total
suspended solids. TSS can also be measured by analyzing for total solids and
subtracting total dissolved solids. You will read more about this in the lab section of
this lesson.
Measurement of TDS
To measure TDS, the water sample is filtered, and then the filtrate (the water that
passes through the filter) is evaporated in a pre-weighed dish and dried in an oven at
180C, until the weight of the dish no longer changes. The increase in weight of the
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dish represents the total dissolved solids, and is reported in milligrams per liter
(mg/L). You will read more about this in the lab section of this lesson.
Interpreting Test Results
The Environmental Protection Agency (EPA) establishes standards for drinking water
which fall into two categories - Primary Standards and Secondary Standards. Primary
Standards are based on health considerations and Secondary Standards are based on
taste, odor, color, corrosivity, foaming, and staining properties of water. There is no
Primary drinking water standard for total dissolved solids, but the Secondary standard
for TDS is 500 mg/L.
The treatment options for an elevated total dissolved solids really depends on the
nature of the cations and anions. If the elevated total dissolved solids is due to cations
like calcium, magnesium, and iron, it may be possible to remove these ions using a
water softner. This process may not reduce the TDS concentration, but reduce the
aesthetic problems with the water. If the problem is associated with an elevated
concentration of sodium, potassium, etc, the primary recommendations would include
a reverse osmosis system or distillation unit.
Potential Health Effects
An elevated total suspended solids (TSS) or total dissolved solids (TDS)
concentration is not a health hazard. The TDS concentration is a secondary drinking
water standard and therefore is regulated because it is more of an aesthetic rather than
a health hazard. High total dissolved solids may affect the aesthetic quality of water,
interfere with washing clothes and corroding plumbing fixtures. An elevated TDS
indicates the following:
The concentration of the dissolved ions may cause the water to be corrosive,salty or brackish tase, result in scale formation, and interfere and decrease
efficiency of hot water heaters; and
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Many contain elevated levels of ions that are above the Primary or SecondaryDrinking Water Standards, such as: an elevated level of nitrate, arsenic,
aluminum, copper, lead, etc.
Calculations
where:
A = weight of filter + aluminum dish, g
B = weight of filter + aluminum dish + residue, g
Review
Dissolved solids refer to any minerals, salts, metals, cations or anions dissolved in
water. This includes anything present in water other than the pure water molecule and
suspended solids. Suspended solids are any particles that are neither dissolved norsettled in the water, such as wood pulp. Some dissolved solids come from organic
sources such as leaves, silt, plankton, and industrial waste and sewage. They can also
come from inorganicmaterials such as rocks, calcium bicarbonate, nitrogen, iron and
other minerals. Water may also pick up metals such aslead or copper as they travel
through pipes used to distribute water to consumers.
An elevated total dissolved solids conentration does not mean that the water is a
health hazard, but it does mean the water may have aesthetic problems or cause
nuisance problems. These problems may be associated with staining, taste, or
precipitation. With respect to trace metals, an elevated total dissolved solids maysuggest that toxic metals may be present at an elevated level. It is important to keep in
mind that water with a very low TDS concentration may be corrosive and corrosive
waters may leak toxic metals such as copper and lead from the household plumbing.
This also means that trace metals could be present at levels that may pose a health
risk.
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Assignment
Complete the questions for Assignment 20, which deals with the TSS, MLSS and
MLVSS labs. When you have gotten all the answers correct, print the page and either
mail or fax it to the instructor. You may also take the quiz online and directly submit
it into the database for a grade.
Lab
Read the Total Suspended Solids andMixed Liquor Suspended Solidslabs and do theassignment listed above, there are questions concerning the virtual labs included.
Quiz
Answer the questions in the Lesson 20 quiz . When you have gotten all the answers
correct, print the page and either mail or fax it to the instructor. You may also take thequiz online and directly submit it into the database for a grade.
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Lab 17:
Total Suspended Solids
Reading Assignment
Read Chapter 25 in Simplified Procedures for Water Examination .
Introduction
The laboratory exercises you have performed up until this point have been primarily
concerned with water treatment. This lab, and the rest of the labs in this course, are
primarily used for testing wastewater and should be carried out in a wastewater
treatment plant.
The primary purpose of wastewater treatment is to remove solids from water, so this
lab will be concerned with testing for one of the types of solids found in water. There
are a variety of terms referring to solids in wastewater, each of which is defined
below:
Total solids- all solids in water. Total solids are measured byevaporating all of the water out of a sample and weighing the
solids which remain.
o Dissolved solids- solids which are dissolved in the waterand would pass through a filter. Dissolved solids are
measured by passing the sample water through a filter, then
drying the water which passes through. The solids
remaining after the filtered water is dried are the dissolved
solids.
o Suspended solids- solids which are suspended in the waterand would be caught by a filter. Suspended solids are
measured by passing sample water through a filter. The
solids caught by the filter, once dried, are the suspended
solids.
Settleable solids- suspended solids which wouldsettle out of the water if given enough time.
Settleable solids are measured by allowing the
sample water to settle for fifteen minutes, then by
recording the volume of solids which have settled to
the bottom of the sample.
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Nonsettleable solids- suspended solids which aretoo small and light to settle out of the water, also
known as colloidal solids. Nonsettleable solids are
measured by subtracting the amount of settleable
solids from the amount of suspended solids.
This lab focuses on the total suspended solids, which includes both settleable and
nonsettleable solids. Total suspended solids should be tested at least five times per
week using 24-hour, flow-proportioned composite samples. The test should be
performed on both raw water (to determine the solids content of water entering the
plant) and on finished water (to determine the efficiency of treatment at the plant.)
Equipment
Dessicator Drying oven, for operation at 103 to 105C Analytical balance, capable of weighing to 0.1 mg Magnetic stirrer with TFE stirring bar Wide-bore pipets Graduated cylinder Low-form beaker Glass-fiber filter disks with organic binder Filtration apparatus, which can be any one of the following:
o Membrane filter funnelo Gooch crucible, 25 mL to 40 mL capacity, with Gooch
crucible adapter
o Filtration apparatus with reservoir and coarse fritted disk(40 to 60 um) as filter support
Filter flasks, of sufficient capacity for sample size selected Vacuum pump Tubing Stop watch Aluminum weighing dishes
Reagents
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Reagent-grade water
Laboratory Procedure
1. Prepare the glass-fiber filter disks (unless they are pre-prepared.)
Insert the filter disk with wrinkled side up in filtration apparatus. Apply vacuum and
wash the disk with three successive 20 mL portions of reagent-grade water. Continue
suction to remove all traces of water, turn vacuum off, and discard washings.
Remove the filter from the filtration apparatus and transfer to an inert aluminum
weighing dish. If a Gooch crucible is used, remove the crucible and filter
combination. Dry in an oven at 103 to 105C for 1 hour.
Cool the filter in a desiccator to balance the temperature. Then weigh the filter and
record the weight.
Repeat the above cycle of drying, cooling, desiccating, and weighing until a constant
weight is obtained or until weight change is less than 4% of the previous weighing or
0.5 mg, whichever is less.
Store the filter in the desiccator until it is needed. You will need to prepare a filter
disk for each sample you plan to test.
2. Select the filter and sample sizes.
Choose a sample volume which will yield between 2.5 and 200 mg of dried residue.
If the volume filtered fails to meet the minimum yield, you will have to increase the
sample size up to 1 L. If the complete filtration takes more than 10 minutes, you will
have to increase the filter diameter or decrease the sample volume.
3. Analyze the sample.
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Assemble the filtering apparatus, as shown above, and begin suction. Wet the filter
with a small volume of reagent-grade water to seat it.
Stir the sample with a magnetic stirrer at a speed to shear larger particles, if practical,
to obtain a more uniform particle size.
While stirring, pipet a measured volume onto the seated glass-fiber filter. For
homogeneous samples, pipet from the approximate midpoint of the container but not
in the vortex. Choose a point both middepth and midway between the wall and thevortex.
Use the stopwatch to measure the amount of time it takes for the sample water to flow
through the filter. Remember that filtration should take no more than 10 minutes. If
filtration takes too long, choose a smaller sample size or a larger filter and repeat the
procedure. Record the filtration time.
Wash the filter with three successive 10 mL volumes of reagent-grade water, allowing
complete drainage between washings. (This washes down solids which may have
stuck to the glass on the upper filter holder and removes dissolved solids from the
suspended solids captured by the filter. Samples with high dissolved solids may
require additional washings.) Continue suction for about 3 minutes after filtration is
complete.
Carefully remove the filter from the filtration apparatus and transfer it to an aluminum
weighing dish as a support. Or remove the crucible and filter combination from the
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crucible adapter if a Gooch crucible is used.
Dry the filter for at least 1 hour at 103 to 105C in an oven, cool in a dessicator to
balance the temperature, and weigh. Repeat the cycle of drying, cooling, desiccating,
and weighing until a constant weight is obtained or until the weight change is less
than 4% of the previous weight or 0.5 mg, whichever is less.
At least 10% of all samples should be analyzed in duplicate. Duplicate determinations
should agree within 5% of their average weight.
4. Calculate the concentration of total suspended solids in the sample using the
following formula:
Where:
A = Sample and filter weight, mg
B = Filter weight, mg
5. If two samples were measured, then the average total suspended solids can be
calculated as follows:
Where:
C = Total suspended solids of sample 1, mg/L
D = Total suspended solids of sample 2, mg/L
6. Calculate the total suspended solids in kilograms per day (KGD) at the plant, as
follows:
Total suspended solids per day, KGD = (Average total suspended solids, mg/L) (Flow,
MGD) 3.785
Data
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Filter and sample preparation
Weight - Trial 1 Weight - Trial 2 Weight - Trial 3 Final Weight
Filter
Sample 1
Sample 2
Total suspended solids
Sample Sample
Source
Filter
weight
(mg)
Sample
volume
(mL)
Filtration
time (min)
Sample and
filter weight
(mg)
Total suspended
solids (mg/L)
1
2Average ---- ---- ---- ---- ----
Total suspended solids (KGD) =
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Virtual Lab
For more information on testing for total suspended solids, view the virtual lab.
Sources
American Public Health Association, American Water Works Association, and Water
Environment Federation. 1998. Standard Methods for the Examination of Water and
Wastewater. American Public Health Association, Washington, D.C.
Kerri, K.D. 1998. Operation of Wastewater Treatment Plants. California State
University: Sacramento.