SUSTAINABLE WASTE MANAGEMENT
Waste – is anything which is no longer useful and needs to be got rid of
Waste Management
Effective management of wastes is a fundamental requirement of ecologically sustainable development
Objectives of WM
Protection of human health
Promotion of hygiene
Protection of environment
Recycling of materials
Avoidance of waste
Reduction of waste quantities
Reduction of emissions and residuals
Protection of natural resources
Waste Management Strategy (WMS)
Waste management strategy (WMS) sets out to deal comprehensively with waste issues
identifies the most effective options for dealing with specific needs and problems
WMS enable a country to achieve a state of sustainable waste management
Waste Management Strategy (WMS)
Primary Objective
Provide a framework within which waste can be managed effectively to minimize or avoid adverse impacts on the environment, while at the same time allowing economic development and improvement in the quality of life
Secondary Objectives
Promote more efficient use and conservation of resources
Reduce the need for waste treatment facilities
Reduce inspection and enforcement costs
Greater cost efficiency within industry by reducing the volume of raw materials and lowering disposal costs
Compatible with international strategies and regulations
Principles of WMS
Integrated waste management
waste management from the point of generation to final disposal
The principles of ‘polluter pays’ and ‘user pAays’
The EU End-of-Life Vehicles Directive (2000/53/EC)
Waste generators and product designers
responsibility for the fate of their wastes and products
Waste management hierarchy
Waste management should be based on a waste management ‘hierarchy’ of
Waste Prevention/Source reduction
avoidance and reduction of waste creation
Recycling & Reuse
reuse and recycling of waste
Treatment
destroying, detoxifying or neutralising wastes
Disposal
discharging wastes
The internationally accepted approach to
waste management
Based on zero waste philosophy
Waste management hierarchy Example 1
ASK FOR THE DIAGRAM... IN CLASS
Waste management hierarchy Example 2
ASK FOR THE DIAGRAM... IN CLASS
Waste prevention/Minimisation
involves altering the design, manufacture, purchase, or use of products and materials to reduce the amount and toxicity of what gets thrown away
Waste prevention is sometimes called source reduction because it reduces or eliminates pollution at the source
donating an unwanted computer to a charity
photocopying on both sides of a sheet of paper
Altering material specifications so that fewer hazardous constituents are used in a manufacturing process
WASTE MANAGEMENT AND POLLUTION CONTROL
Basic consideration and concepts in
Environmental Quality
Development
An evolutionary process which uses the resource endowment of the planet to improve the welfare of the beneficiary community
Traditionally evaluated by economic and technological growth (measured in terms of GND and GDP)
Human Development Index (HDI) embraces
Health and nutrional status
Education achievement
Assess to resources and information
Equitable distribution of income
Well-paid employment opportunities
Basic freedom
All development activities inevitably lead to
some environmental changes (degradation)
Environment
Where we live, or our surroundings of air, water and land
Health
A state of complete physical, mental and social well being
Determined by population, environment, behavior and level of health services
Pollution
Contamination of the environment by biological, chemical, and/or physical agents and may arise through material events, volcanic eruptions, flooding, drought or human activity
Major driving forces of pollution (environmental decline)
Poverty
Resource-consumption
Economic growth
Rapid population growth
Sustainable Development
A development that meets the needs of the present without compromising the ability of future generations to meet their needs
Environmental Health
The control of all those factors in man’s physical environment which exercise or may exercise a deleterious effect on his physical environment, health and survival
Major components
Water resources management
Air quality management
Sanitation and waste management
Housing
Food safety
Occupational health and safety (incl. chemical safety and safe use of chemical
Control of environmental health
Public Health
The science and art of preventing disease, prolonging life and promoting health through organized efforts of society
Definitions of Waste
Several definitions used by different countries and organizations (e.g. UK EPA, EEC, US EPA, Botswana WMA 98, etc
Four major classes of waste are recognized
General waste
Controlled waste
Special waste
Hazardous waste
General waste
World Bank definition
A waste is a mixable object which has no direct use and is discarded permanently
UK EPA 1990 definition
Any substance which constitutes a scrap metal or an effluent or other unwanted surplus substance arising from the application of a process
Any substance or article which requires to be disposed of as being broken, worn out, contaminated or otherwise spoiled but excluding Explosives Act 1875
Botswana Waste Management Act 1998
Waste includes the following substances and any combination thereof which are discarded by any person or are accumulated or stored by any person for the purpose of recycling
Undesirable or superfluous by-products;
Residue or remainder of any process or activity;
Any gaseous, liquid or solid matter
Controlled waste
Households
Commercial
Industrial
Or any such waste
Special waste
These are waste “dangerous to life" as a result of their toxicity, corrosivity, volatility and inflammability and restrictive nature
Hazardous waste
Hazardous waste mean waste (solids, sludges, liquids and containerized infectious) which by reason of their chemical activity or toxic, explosive, corrosive and other characteristics, cause danger to health or the environment, whether alone or when coming into contact with other wastes
ENVIRONMENTAL LEGISLATION
Legislation
Is a law or set of laws passed by a parliament
Empower the environmental department or agency act on behalf of the environment and the community
Purpose
All waste disposal sites should be subject to legislative control
3 areas of concern
Planning for landuse
Pollution control
Waste management licenses
Environmental protection
Regulations and controls for health and safety
Botswana
Environmental legislation
Doesn’t exist
Fragmented both in substance and in terms of implementation mechanisms
Waste Management Act, 1998
Makes provision for efficient waste management in the country to prevent harm to human, animal and plant life and to minimize the pollution of the environment and cause provisions of the Basel Convention to prevail
Aim to control and regulate waste management in Botswana
Public Health Act, 1981
Designed to maintain a good environment for the protection of human health
It forbids the pollution of water resources by indiscriminate dumping of chemicals in the water
Local Authorities Bye-Laws
Provision for disposal of wastes
Enforcement by police officials
The Water Act, 1968
Provision on water pollution
Atmospheric Pollution (Prevention) Act, 1997
Aims to prevent atmospheric pollution by an industrial processes in any trade
Agricultural Resources (Conservation) Act, 1974
Aims at proper use and conservation of resources which are of agricultural importance
Agricultural Resources Board can issue regulations or conservation orders at controlling or preventing soil pollution
Environmental Impact Assessment Act, 2005
Mines and Minerals Act, (CAP.66:01 of 1977)
Mines, Quarries and Machinery Act (CAP.44:02 of 1978)
Explosives Act and Explosive Regulation Act (Cap 24:02)
Herbage Preservation (Preservation of fires) (CAP.38:02 of 1978)
United Nations Convention on Biodiversity (1992)
Wildlife Conservation Policy, 1986
National Conservation Strategy, 1990
National Policy on Natural Resources, Conservation and Development
Forestry Act (CAP.38:04 of 1976)
The Roads Act
Monuments and Relics Act (Cap 59:03)
Town and Country Planning Act (Cap.32:09 of 1980)
Basel Convention on the Control of
Transboundary Movements of
Hazardous Wastes and their Disposal,
1989
Botswana ratified convention in 2000
Aim to regulate movement and disposal of hazardous wastes from one country to another
Stockholm Convention on persistent
Organic pollutants (POPS), 2001
Botswana ratified convention in 2002
Aim to protect human health and the environment from persistent organic pollutants (POPs).
Bamako Convention on the ban of the
import into Africa and the Control of
Transboundary Movement of
Hazardous Wastes within Africa, 1991
Botswana ratified this convention in 2004
Aim to protect human health and the environment from dangers posed by hazardous wastes by reducing their generation to a minimum in terms of quantity and/or hazard potential
The Climate Change Convention,
1992
Botswana acceded to this convention in 1992
To regulate levels of greenhouse gas concentration in atmosphere in order to minimize the occurrence of climate change on a level that would impede sustainable development, or compromise food production.
Vienna Convention on the Protection
of the Ozone layer, 1985
Botswana ratified this convention in 1991
Its objective is to protect human health and the environment against adverse effects resulting from modifications of ozone layer
The Convention encourages and where necessary facilitates cooperation in research and the sharing of information relating to the depletion of ozone layer.
Montreal Protocol on Substances that
Deplete the Ozone layer, 1987
Botswana ratified this convention in 1991
Its objective is to encourage participants to take precautionary measures to control global emissions of the ozone layer depleting substances
It is responsible for the control and use of chlorofluorocarbons (CFCs) and other chlorine containing substances, with the ultimate objective of their elimination
Waste Management
3 (4) Rs of WM
The three (four) R’s of reduce, reuse and recycle (& refuse) should be looked as partial solutions
All three of these activities serve to lessen the impact that human activities have on the environment
Promote prevention and minimization
Waste prevention – 1st goal
Waste minimization
attitude of mind
Technique for industry
Input materials
Product design
Process change
Recycling
Recycling can be defined as making something new/useful from waste materials that could otherwise be thrown away
Benefits of recycling
Saves Landfill Space
Recycling is one way to reduce the amount of waste that is landfilled
Recycling Can Reduce the Cost of Waste Disposal
Getting rid of waste isn’t a free proposition
Garbage trucks must pay to dump their waste at a landfill
The payment is called a tipping fee, and it is based on the weight or volume of the garbage.
2008 Gaborone Landfill rates
General waste – P40 a ton
Garden waste – P60 a ton
Rubble/soil – P50 for 2tons
Medical waste – P50 a kg
In Vermont, one landfill charges about $65 a ton for the waste it receives
In 2003, recycling and composting diverted 72 million tons of material from landfill
Recycling Can Save Energy
It almost always takes less energy to make a product from recycled materials than it does to make it from new materials
Using recycled aluminum scrap to make new aluminum cans, for example, uses 95 percent less energy than making aluminum cans from bauxite ore, the raw material used to make aluminum
Recycling Saves Natural Resources
Natural resources are riches provided courtesy of Mother Nature
Natural resources include land, plants, minerals, and water
By using materials more than once, we conserve natural resources
In the case of paper, recycling saves trees and water. Making a ton of paper from recycled stock saves up to 17 trees and uses 50 percent less water.
Recycling Can Reduce Air and Water Pollution
Using aluminum scrap instead of bauxite ore to make new aluminum products cuts air and water pollution by 95 percent
Recycling Creates Jobs
Recycling is estimated to create almost five times as many jobs as waste disposal
Recycling requires businesses that collect, haul, and process recyclables, as well as businesses that manufacture products from recycled materials
People employed in the recycling industry may be material sorters, truck drivers, sales representatives, process, engineers, or chemists. The National Recycling Coalition reports that recycling supports 1.1 million jobs in the U.S.
Why Recycling is needed?
Many residents, as well as shops and commercial establishments, dump indiscriminately at unofficial dumping sites, often old sand quarries
These unofficial sites present a direct hazard to people and livestock
They are unfenced, and contain anything from construction debris to plastic bags, tins, paint cans and possibly medical or other infectious wastes
Cows and goats routinely rummage through the sites, sometimes ingesting plastic bags or cutting themselves on glass.
People are also found at these sites, often barefooted, scavenging what reusable material they can find.
Materials that can be recycled include, but
not limited to:
Paper
Steel cans
Aluminum cans
Scrap metal
Plastics
Glass
Tires
Organic/ Garden Waste
Car batteries
Used Oil
Paper
Uncontaminated waste paper such as general office paper, news papers, magazines, food packaging, cement packets, cardboard boxes, corrugated brown and white cartons and craft paper of all kinds can be collected and taken for recycling
Some papers such as plastic-coated, tarred, carbon-paper and contaminated paper are not collected for recycling
In Botswana, the recycling companies collect various kinds of paper from different areas such as shopping malls, schools and institutions
The collected paper is then baled/ compacted into bundles and then loaded into trucks/ train wagons and sent to recycling plants either in Zimbabwe or South Africa.
Steel cans
Hard metal-cans which are often used for food packaging (tin-stuff)
Steel cans can be collected and thereby sent to recycling companies such as Collect-a-Can
Cans are then crushed into ingots and then taken to South African plants for recycling
The crushed cans can be used to make industrial steel products such as reinforcing wire and fencing wire
It takes 75% less energy to make steel from recovered metal than from raw materials
More cans can be made from fewer raw materials, and today every steel can contains 25% of recycled steel.
Aluminium Cans
Relatively soft metal-cans, which are often used to store beverages.
Aluminium drink cans can be recycled time and time again without loss of quality to enable them to be manufactured again and again into new drink cans of high quality
The recycling process of these cans happens in much the same way as steel cans
Recycling aluminium cans is economical and sustainable, i.e. 95 percent of the energy used in producing aluminium from its natural state (Bauxhite) is saved
Scrap Metal
Include old car bodies, engine blocks, gearboxes and any other metal component that is found in used motor-vehicles.
A number of companies around Gaborone collect scrap metal from various sources and send it to South Africa for recycling
Motor vehicle batteries
Old car batteries, which are potentially very polluting can be recycled
Lead acid batteries should be taken back to the supplier after their end of life use
Prevents the harmful substances that are contained in batteries from posing a health hazard to humans and other life forms.
Plastics
Plastics are used world-wide as a packaging material and are routinely classified into seven types according to the following number system:
PET (Polyethylene Terephthalate)
PE-HD (High Density Polyethylene)
PVC (Polyvinyl Chloride)
PE-LD (Low Density Polyethylene)
PP (Polypropylene)
PS (Polystyrene)
Other
The most common type of plastics found in the domestic waste stream in Botswana are polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) Each type of plastic is technically recyclable, however, in practice types 1, 2 and 4 are the easiest to recycle into new products
All plastics for recycling must be clean and label free
Plastic shopping bags are the least desirable for recycling but can be re-used for making bags, mats, and hats
Glass
Used glass bottles can be re-used again to store various liquid materials in the household
Some beverage bottles can be returned to retail stores or Kgalagadi Beverages for cash-deposit. Somarelang Tikologo currently collects glass bottles from schools, bars, hotels and shopping malls in and around Gaborone and take them to South Africa for recycling
Local entrepreneurs are encouraged to get into recycling of glass bottles as some financial benefits can be accrued with the environment being kept clean at the same time
Tyres
It takes over 800 years to decompose old tires
This makes them to be persistent in the environment and thereby posing health hazards to humans and other organisms
To remedy this problem, they can be recycled into road asphalt, shoes, and furniture
Some local entrepreneurs re-use tires to produce flowerpots, drinking/ watering troughs and other useful items
Organic Waste:
The non-animal kitchen waste can be easily composted to improve garden soil, for instance: vegetable waste, bread, fruit peels, and grains
These can be mixed with garden waste to enhance the formation of compost
This means that composting could save a large part of the land, which would otherwise be used for disposal of municipal and garden waste
Monday, September 14, 2009
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)
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)
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