ENV 382 notes

Natural water is not just H2O

it can have many additional components from micrograms to grams per litre

Criteria are needed to judge it by

Relate to physical, chemical and
biological characteristics of the
water

These characteristics need to be
measured and judged against
appropriate criteria

Several guidelines for water quality with,
perhaps, the most quoted being the
WHO guidelines


Natural water is not just H2O

it can have many additional components from micrograms to grams per litre

Criteria are needed to judge it by

Relate to physical, chemical and
biological characteristics of the
water

These characteristics need to be
measured and judged against
appropriate criteria

Several guidelines for water quality with,
perhaps, the most quoted being the
WHO guidelines

Physical Characteristics

Temperature
Affects solubility and, therefore, taste and odour

Taste, odour
Presence of volatile chemicals and decomposing organic matter
Affects consumer acceptability

Colour
Minerals such as iron, manganese, organic material, coloured wastes
Affects consumer acceptability

Turbidity
Turbidity is a measure of the suspended solids or cloudiness of the water
Turbidity can affect a waterway by

preventing light from reaching submerged aquatic plants and reducing photosynthesis

absorbing sunlight and raising the temperature of the water

clogging gills and causing harm to aquatic animal life

causing suspended particles to act as carriers for nutrients, pesticides, herbicides and bacteria.

Factors that result in increased turbidity include:
algae blooms
sediment run-off from exposed or bare soil
industrial waste
sewage
chemical spills

Electrical Conductivity (EC)

Dissolved ionisable compounds (mainly inorganic)
Approx. EC x (0.6-0.8) = TDS mg/l

Chemical characteristics

Often more specific than physical ones and therefore, are often of more use in the immediate assessment of water quality

pH

pH is a measure of the acidity or alkalinity of a waterway

The optimal pH for most organisms for most waters is pH 6.5 to pH 8.2

Changes in pH outside this normal range will cause a reduction in species diversity
Only causes problems high (alkaline) and low (acidic) pH
pH will vary depending on the geology of the area
Water flowing through limestone will be alkaline and water flowing through sandstone or basaltic soils will be slightly acidic
Natural seawater is slightly alkaline pH 8.2 so as the water is tested in estuarine environments the pH is naturally above fresh water levels.


Hardness
due to the presence of calcium and magnesium salts
Sources are limestone
Measure of the capacity of water to react with soap
Scaling of hot water pipes, boilers, etc

BOD
Biological Oxygen Demand is a measure of the amount of organic matter in water

COD
Chemical Oxygen Demand is commonly used to indirectly measure the amount of organic compounds in water

Oxygen levels are affected by pollutants, which in turn affect biological characteristics of the water e.g. for DO<4mg/l fish die


Dissolved Oxygen

Dissolved oxygen (DO) is the amount of oxygen dissolved in the water

Dissolved oxygen is essential for the health of aquatic ecosystems and for the survival of most aquatic organisms

Factors that cause the levels of DO to decrease include:

 the decay of organic matter such as leaves, grass clippings and sewage.

Sulphates
Corrosion of concrete
Reduction to sulphides, deposition
Laxative effect

Chloride
From salt deposits, saline intrusion, sewage
Cause corrosion at higher temp, affects taste

Fluoride
Occurs naturally if water flows over fluoride containing minerals such as fluorapatite
Fluorosis (teeth and bones) if conc. are too high (> 2 mg/l)
If too low then tooth decay (< 0.3 mg/l)

Nutrients - Phosphorous and Nitrates

Too many nutrients in fresh-water leads to algal bloom

increasing turbidity
blue-green algae blooms (some toxic)
an increase in aquatic weeds that eventually choke a waterway
the displacement of native riparian vegetation with introduced weed species
increased BOD
reduced DO levels leading to fish kills

Nitrate
infant methaemoglobinaemia
commonly referred to as “the blue baby syndrome”


sewage
manure from feedlots
phosphate-based detergents
decomposing organic material
fertilizers and industrial wastes

Pesticides

Pesticides can potentially pollute the soil, water and air
Pesticide effects on human health can include:

Injury to the stomach and intestines, resulting in nausea, vomiting, abdominal cramps, or diarrhea

Injury to the nervous system, causing excessive fatigue, sleepiness, headache, muscle twitching, and numbness
Trace heavy metals

Trace heavy metals
aluminium, arsenic, cadmium, chromium, copper, iron, lead, manganese, mercury, nickel, silver and zinc

Harmful effects can include death  (lethal effects) or inability to reproduce

The toxicity of heavy metals will be affected by their bioavailability

Organisms uptake metals through the food they consume, through absorption onto gills and through the skin

Toxic substances can enter water from sewage overflows and stormwater run-off

Stormwater carries lead deposited in streets
car exhausts, oil, grease and copper worn from metal plating and brake linings, etc

Biological characteristics
Natural waters contain many types of living organisms: viruses, bacteria, fungi, protozoa, algae, etc

Most pathogenic organisms found in the water are not free-living but of faecal or urinary origin (> 107 microbes/ gram of faeces)

Most organisms found in water are NOT pathogens

Harmful organisms are of major concern

Possible diseases –
Cholera, typhoid, bilharzia, etc

Not possible to test for all samples for all possible diseases causing organisms
too costly, too time consuming, need special expertise, etc.)

Test for organisms that occur only in faeces and not as free-living forms in nature - Indicator organisms

If indicators are present – faecal pollution and possibility of pathogen presence
If indicators absent, it is essentially assumed that pathogens are absent
If indicator organisms are bacteria, then viruses may occur

Escherichia coli (Ecoli)

Each person excretes 1013 (10 million million) per day
most of these are NOT pathogenic
Relatively easily detected organism
Yet indicates possible pathogen presence if detected
Are part of a large group of bacteria called coliforms
Some are naturally occuring coliforms, 37 oC
Others are faecal coliforms, 44.5 oC
Most commonly used indicator organism

Also used, but to a much smaller extent, are
Streptococcus faecalis - (faecal streps)
Clostridium welchii – (clostridia)

Faecal coliform enter our water through:

leaking sewers or septic tanks

feedlot and dairy run-off or any other intensive animal husbandry farming

stormwater run-off carrying animal and bird faeces (including pet droppings)

sewage overflows during wet weather

waterfowl and livestock defecating directly into water


Macroinvertebrates

Small organisms that live on the bottom of streams and rivers are known as benthic macro invertebrates

Collecting these water bugs can provide a greater understanding of a waterway's condition

They are a useful indicator of water quality because:
they are sensitive to physical and chemical changes in their habitat
they are present in the water over extended periods of time and can thus indicate cumulative impacts
They cannot easily escape pollution
they are easy and fun to collect

Microscopic examinations of raw
water sample will show many micro-
organisms and also larger organisms

TITRIMETRIC METHODS 

Principle - the analyte is determined titrimetrically through a chemical reaction with a reacting species of known concentration

Titrimetric methods of analysis
require dispensing accurately measured volumes of reagents of known concentration

At the "end point" of a titrimentric analysis, the added reagent exactly balances the concentration of the material of interest.

A knowledge of the volume and concentration of the reacting species allows the analyst to determine the total amount of analyte present

A chemical indicator is frequently used to indicate the end of the reaction by signaling that the analyte has been fully consumed

Titrimetric analysis consists in determining the number of moles of reagent (titrant), required to react quantitatively with the substance being determined

The titrant can be added volumetrically, with a glass or automatic burette or with a low flow-rate pump

Chloride

is the most common inorganic anion found in water and wastewater

Salt (sodium chloride) passes through the human digestive system unchanged to become the principal source of chlorides in raw sewage

A limit of 200 mg/l chloride (BOBS) has been placed on drinking water supplies, as this is the level at which water begins to taste salty

A limit of 250 mg/l chloride when sodium is the cation; and

When calcium or magnesium is the cation, up to 1000 mg/l chloride can be tolerated with no salty taste (WHO)

Natural sources of salt are the ocean and various salt deposits above and below ground.

Chloride is very corrosive to most metals in systems with elevated pressures and temperatures such as boilers and oil drilling equipment

In coastal areas

higher than normal chloride concentrations in drinking water can indicate seepage of seawater into the water supply or the presence of industrial effluents.

Chloride

is analyzed using the argentometric method

The Argentometric method (Mohr method)
consists of titration with silver nitrate using potassium chromate indicator
Chloride in solution reacts with the silver ions to form silver chloride and the appearance of a red silver chromate precipitate is the end point
This method is applicable to samples containing > 20 mg/L chloride
The Argentometric method

Principle
In neutral or slightly alkaline solution, potassium chromate can indicate the end point of sliver nitrate titration of chloride

Interference
sulphite, thiosulphate and sulfite ions – removed by hydrogen peroxide

If silver ion (Ag+) is added to water which contains chloride ion (Cl-)

The two combine to form silver chloride, which is insoluble

Ag+ + Cl- = AgCl (ppt)

Silver and chromate ion (CrO4-2) also combine to form silver chromate

Ag+ + CrO4-2 = Ag2CrO4 (ppt)


a solution of silver nitrate with a known molarity is used to titrate the unknown chloride until the moles of silver equals the moles of chloride

this technique depends on measuring volumes very exactly by using pipets and burets.

the other key is the use of potassium chromate as an indicator which allows us to stop the titration when the moles of silver equals the moles of chloride

the potassium chromate reacts with any excess silver to form a red precipitate of silver chromate


the solution turn from a cream yellow to a pinkish yellow within a few drops indicating the endpoint of the titration.

since the ratio of silver to chloride is 1:1 in the precipitate, it is easy to calculate the molarity of the chloride using:
mols of chloride = mols of silver
MAg x VAg = MCl x VCl
MCl = (MAg X VAg)/VCl

Water Hardness

Hard water is due to metal ions (minerals) that are dissolved in the ground water

These minerals include Ca2+, Mg2+, Fe3+, SO42-, and HCO3-.

Sources

limestone, CaCO3, that occurs in some aquifer.

this is why we measure hardness in terms of CaCO3

Industrial products

The determination of water hardness is a useful test that provides a measure of quality of water for households and industrial uses

Originally, water hardness was defined as the measure of the capacity of the water to precipitate soap.

Hard water is not a health hazard. People regularly take calcium supplements.

Hard water does cause soap scum, clog pipes and clog boilers.

Soap scum is formed when the calcium ion binds with the soap. This causes an insoluble compound that precipitates to form the scum you see. Soap actually softens hard water by removing the Ca2+ ions from the water.

When hard water is heated, CaCO3 precipitates out, which then clogs pipes and industrial boilers. This leads to malfunction or damage and is expensive to remove.

Water Softeners
Add salt to water to remove hardness
Na ion replace Ca ion – causes water to be too salty

Types of Hardness

Two types : temporary and permanent

Temporary Hardness
is due to the bicarbonate ion, HCO3-, being present in the water. This type of hardness can be removed by boiling the water to expel the CO2, as indicated by the following equation:
HCO3- H2O + CO2

Bicarbonate hardness is classified as temporary hardness.
Permanent hardness
is due to the presence of the ions Ca2+, Mg2+, Fe3+ and SO4-.

This type of hardness cannot be eliminated by boiling.

The water with this type of hardness is said to be permanently hard


EDTA Titrimetric Method

Principle
When EDTA or its salts is added to water containing both Ca and Mg, it combines first with Ca. Ca can be determined directly with EDTA, when pH is made sufficiently high that the Mg is largerly precipitated with hydroxide and indicator is used that combines with Ca only

Interferences
Cu, Fe, MN, Zn, Pb, Al, Sn – no interference




Procedure

Ca

Determined of sample to which had been added NaOH to exceed pH value of 12, thus precipitating Mg as Mg(OH)2

Ca ion in the unfiltered sample are treated with EDTA using Eriochrome Blue SE indicator

Colour change at endpoint from wine red to violet


Mg

The solution after titration of calcium is acidified with dilute HCl acid to dissolve Mg(OH)2 and then buffered at pH 10.1

Eriochrome Black T indicator is added and Mg is titrated with EDTA

Ca (mg/l) = Vol EDTA (A)x400 /ml sample

Mg (mg/l) = Vol EDTA (B)x 243/ml sample

Total hardness as mg CaCO3/l
= A+B x 1001/ml of sample

Analytical Chemistry

The branch of chemistry that deals with the separation, identification and determination of components in a sample

Qualitative analysis

Attempting to identify what materials are present in a sample

Quantitative analysis

Determining how much a material is present in a sample

Types of methods

Gravimety

Methods based on a measured weight

Titrimetry

Methods based on a measured volume

Spectral methods

Interaction of an analyte with EM radiation

Quantitative analysis

What types of information do you need?

Complete analysis

The goal is to determine the amount of each component in a sample

Ultimate analysis

The amount of each element present without regard to actual composition


Partial analysis

Determining one or a limited number of species in a sample

Examples

Presence of lead in a water sample
Iron in an ore sample


Basic steps in an analysis

Factors to consider

Technique to be used
Sampling and sample preparation
Proper application of the method
Data analysis and reporting

Technique to be used

Factors to consider

Accuracy and sensitivity
Cost
Number of samples to be assayed
Number of components in a sample

Samples

Must be representative
Sample selection
Requires some knowledge as to sample source and history

Sample preparation

Convert the sample to a form suitable for the method of analysis

Based on method
Drying to ensure an accurate weight
Sample dissolution
Elimination or masking of potential interferences
Conversion of analyte to a single or measurable form

Sample replicates

All methods have errors associated with them

Using multiple samples and replicates helps track and identify this error

Multiple samples

Identically prepared from another source
Used to verify if your sampling was valid

Replicates samples

Splits of the same sample
Helps track and identify errors in method

Error and uncertainty

Error

Difference between your answer and the ‘true’’ one

Systematic
Problem with a method
Determinate errors

Random
Based on limits and precision of a measurement
Indeterminate errors

Blunders
Best to just repeat the work

Determinate errors

Potential instrumental errors

Variations in temperature
Contamination of the equipment
Power fluctuations
Component failure

All of these can be corrected by Calibration or proper instrument maintenance

Method errors

Slow or incomplete reactions
Unstable species
Nonspecific reagents
Side reactions

Can be corrected with proper method development
Personal errors

Misreading of an instrument or scale
Improper calibration
Poor technique/sample preparation
Personal bias
Improper calculation of results

These blunders can be minimized or eliminated with proper training and experience


Random errors

Each value reported - is the result of many different factors and variables

Many of these variables – beyond analyst control and are random in nature

Example

Reading an electronic balance

Sample reported as 1.0023g
Actually weigh somewhere in the range of 1.0022 -1.0024g


Accuracy & Precision

Accuracy is the measure of how close the test results are to the true value

Precision is the measure of how close the results of replicate analyses are

Accuracy is telling the truth . . . Precision is telling the same story over and over again.
Yiding Wang


GRAVIMETRIC METHODS

Gravimetric analyses rely on some final determination of weight as a means of quantifying an analyte

There are 3 fundamental types of gravimetric analysis:

physical gravimetry
thermogravimetry
precipitative gravimetric analysis


Physical gravimetry

most common type used in environmental science

involves the physical separation and classification of matter in environmental samples based on volatility and particle size (e.g., total suspended solids).

Thermogravimetry

samples are heated and changes in sample mass are recorded (e.g. volatile solids analysis )


Precipitative gravimetry

relies on the chemical precipitation of an analyte

the most important application in the environmental field is with the analysis of sulphate.


Common Procedures in Gravimetric Analysis

Drying to a Constant Weight

All solids have a certain affinity for water, and may absorb moisture from the laboratory air

Reagents that readily pick up water are termed hygroscopic (e.g. silica)

Those that absorb so much water that they will dissolve in it and form a concentrated solution are called deliquescent (e.g. sodium hydroxide)

These types of substances will continually increase in weight while exposed to the air

For this reason, many types of laboratory procedures require that a sample be dried to a constant, reproducible weight

the sample is dried in a 103° C to 110° C oven for about 1 hour and allowed to cool to room temperature in a desiccator

It is then weighed, and heated again for about 30 minutes

The sample is cooled and weighed a second time. The procedure is repeated until successive weighings agree to within 0.3 mg.


b. Use of the Analytical Balance

The analytical balance is the most accurate and precise instrument in an environmental laboratory

Significance to Environmental
Science

Most of the impurities in potable waters are in the dissolved state, principally as inorganic salts

Thus, the parameters, "total solids" and especially "total dissolved solids" are of primary importance

Waters containing high concentrations of inorganic salts are not suitable as sources of drinking water
such materials are often difficult to remove during treatment

unpleasant
unsuitable for many industrial applications
Unsuitable for bathing/swimming purposes

Drinking waters containing more than 1000 mg/l TDS are generally considered unacceptable

unsuitable for agricultural purposes due to the harmful effects of high ionic concentrations on plants

In most natural waters, the TDS concentration correlates well with total hardness (i.e., [Ca] + [Mg])

This is useful in assessing the corrosivity of a water and the need for softening

TSS content of natural waters is of interest for the purpose of assessing particle bed load and transport

High concentrations of suspended matter may be detrimental to aquatic life

municipal wastewater - suspended solids analysis is by far the most important gravimetric method

used to evaluate the strength of the raw wastewater as well as the overall efficiency of treatment

WWTP's have effluent standards of 10 to 30 mg/l suspended solids which may be legally enforceable.

TSS analysis is useful as a means of assessing the strength of industrial wastewaters and the efficiency of industrial wastewater treatment


PHYSICAL GRAVIMETRY

Total, Dissolved and Suspended Solids

Total solids - defined as all matter in a water or wastewater sample that is not water

solids are not a specific chemical compound, but rather a diverse collection of dissolved and particulate matter

must be defined by the procedure used to estimated their concentration

Total solids may be differentiated according to size into TDS and TSS


all solids passing through filter paper of a certain pore size (e.g., 1.5 microns, Whatman #934AH) are called dissolved, and those retained are termed suspended

overall definition of total dissolved solids is:

all matter that is not retained by a 934AH filter, and is not lost by evaporation and drying at 180oC for one hour


Procedures

Total Solids (Total Residue)

A well-mixed sample is evaporated in a weighed dish and dried to constant weight in an oven at 103-105 oC

the increase in weight over that of the empty dish represents TS

 Dissolved Solids (Filterable Residue)

A well-mixed sample is filtered through a standard glass fiber filter, and the filtrate is evaporated to dryness in a weighed dish and dried to constant weight at 108 oC

the increase in dish weight represents TDS

indirectly by determining the TSS and subtracting this value from the TS

Suspended Solids (Non-filterable Residue)

A well-mixed sample is filtered through a weighed standard glass fiber filter and residue retained on the filters is dried to constant weight at 103-105 oC

the increase in weight of the filter represents TSS

This approach is much more accurate for most waters than the indirect method of subtracting dissolved solids from total solids


Fixed and Volatile Solids

The residue from TS, TDS, TSS methods is ignited to constant weight at 500 oC

The remaining solids represents the fixed totals, dissolved or suspended solids while the weight lost on ignition is the volatile solids



THERMOGRAVIMETRY

Thermogravimetry and combustion analysis involve the heating of a sample to 500° C or more with the oxidation and/or volatilization of some of the sample constituents

Either the change of sample weight is determined (thermogravimetry), or the combustion gases are trapped and weighed (combustion analysis)

The former method is used for volatile solids analysis in environmental engineering


Volatile Solids and Fixed Solids

Fixed solids are those that remain as residue after ignition at 550° C for 15 minutes

The weight of material lost is called the volatile solids

Thus the total operational definition for volatile solids would be:

all matter lost upon ignition at 550° C for 15 minutes, but not lost upon drying at 103-105° C for 1 hour

The portion lost upon ignition is generally assumed to be equivalent to the organic fraction

The portion remaining is considered the inorganic fraction


For waters of moderate to high hardness, most of this is calcium carbonate which decomposes only at temperatures exceeding 800° C.

When igniting a filter with suspended matter, one must be especially careful of the temperature; above 600° C glass fiber filters begin to melt and can loose a significant amount of weight in 15 minutes.


Combining the fractionations resulting from ignition and filtration
a total of 9 separate categories

total solids (TS), fixed solids, volatile solids, total dissolved solids (TDS), fixed dissolved solids, volatile dissolved solids, total suspended solids (TSS), fixed suspended solids, and volatile suspended solids (VSS)

In practice, only four of these (TS, TDS, TSS, and VSS) are commonly used


PRECIPITATIVE GRAVIMETRIC
ANALYSIS

Precipitative gravimetric analysis requires that the substance to be weighed be readily removed by filtration

Sulphate

precipitative gravimetric procedure using barium (APHA et al., 1985)

If Ba(+II) is added in excess under acidic conditions, BaSO4 is precipitated quantitatively

The reaction is allowed to continue for 2 hours or more at 80-90oC. This is to encourage the formation of BaSO4 crystals (non-filterable) from the initially formed colloidal precipitate (partially filterable)


Chloride

Chloride may be determined by precipitation with silver

Interfering ions likely to form insoluble silver salts are the other halogens (bromide, iodide), cyanide, and reduced sulfur species (sulfite, sulfide, and thiosulfate)

reduced sulfur compounds can be pre-oxidized with hydrogen peroxide, and the others are rarely present at high concentrations

Although AgCl can be determined gravimetrically, the recommended procedure for water and wastewater (APHA et al., 1985) is to use a volumetric procedure with chromate as an indicator (ppt. of red silver chromate)