Lecture (4): Water quality
Lecture (4): Water quality
Lecture (4): Lecture objectives:
By the end of this lecture students should be able to:
1. To know the Water quality: Physical Factors.
2. To know the Water quality: Chemical Factors.
3. To know the Water quality: Biological Factors.
Lecture (4): Water quality: Physical Factors
1-1: Solids:
Other than gases.
All contaminants of water contribute to the solids content.
Classified by their (size / state/ chemical characteristics/ size distribution) solids can be dispersed in water in both suspended and dissolved forms.
TSS – Total Suspended Solids.
TDS – Total dissolved solids.
1-2.Turbidity:
One of the first things we notice about water is its clarity. The clarity of water is usually measured by its turbidity.
Turbidity is a measure of the extent to which light is either absorbed or scattered by suspended material in water.
There are various parameters influencing the cloudiness of the water. Some of these are:
• Phytoplankton.
• Sediments from erosion.
• Waste discharge.
• Algae growth.
• Urban runoff.
Causes of Turbidity
1-3: Color:
Pure water is colorless.
Water color causes by foreign substances such as:
organic matter from soils.
Vegetation.
Minerals.
aquatic organisms are present.
municipal and industrial wastes.
1-4: Taste and odour
In drinking water, taste and odor are not normally a problem until the consumer complains.
consumers find taste and odor in water displeasing.
Taste and odor do not directly present a health
Many consumers consider water to be tasteless and odorless.
When water has both taste and odor, however, the likely cause is organic materials.
1-5.Temperature:
• Heat is added to surface and groundwater in many ways. Some of these are natural, some artificial.
• When water temperature is high, the result:
higher chlorine demand (increased reactivity)
increased level of algae and other organic matter in raw water
Chemical Factors:
2.1 pH
• pH is a measure of the increase of Hydrogen ions in water
• Additional carbon dioxide in freshwater can decrease the pH, making the water body more acidic (dissolved gases)
• Runoff including the addition on ions in water is also important (i.e. – phosphates, chlorides, etc… that are dissolved solids)
pH of natural waters
Modified from www.waterwatch.org http://www.vic.waterwatch.org.au/fortheteacher/manual/sect4f.htm due to humic acid
Limestone, marble, CO3 rich Pure rain, snow
Sea water
Factors that affect pH
• Algal blooms
• Bacterial activity
• Water turbulence
• Chemicals flowing into the water body
• Sewage overflows
• Pollution
2.2 Total Dissolved Solids:
solvent properties of water.
minerals dissolve from rocks and soil.
produce total dissolved solids (TDS).
(TDS) are any minerals, salts, metals, cations, or anions dissolved in water.
Conductivity
Ability of a substance to conduct an electrical current.
In water, conductivity determined by types and quantities of dissolved solids. (Commonly called Total Dissolved Solids = TDS)
Current carried by ions (negatively or positively charged particles).
Eg: NaCl(aq) = Na + + Cl –
Cl-
Na+
Na+ Na+
Na+
Na+ Cl-
Cl- Cl-
Cl-
Na+ Na+Na+ Na+Na+ Na+Na+ Na+
Cl- Cl-
Na+ Na+ Na+Na+
Cl- Cl- Cl- Cl-
Na+ Na+ Na+Na+
Cl- Cl- Cl- Cl-
Na+ Na+ Na+ Na+Na+
Na+
Na+
Na+ Na+
Na+ Na+
2.3 Alkalinity
Alkalinity is a measure of the ability of water to neutralize acid,
The major chemical constituents of alkalinity in natural water supplies:
1. bicarbonate, 2. carbonate,
3. hydroxyl ions.
2.4 Hardness:
Hardness is due to the presence of multivalent metal ions.
Hardness is based on the ability of these ions to react with soap to form a precipitate or soap scum.
In freshwater, the primary ions are calcium and magnesium.
2.5 Fluoride:
Fluoride is seldom found in appreciable quantities in surface waters and appears in groundwater in only a few geographical regions.
fluoride is sometimes found in a few types of sedimentary rocks.
Fluoride is toxic to humans in large quantities.
Fluoride is also toxic to some animals.
USEPA has set the upper limits for fluoride based on ambient temperatures. Because people drink more water in warmer climates.
2.6 Metals:
Metal ions are dissolved in water when the water is exposed to rock or soil containing the metals,
The metals most often found in the highest concentrations in natural waters are calcium and magnesium.
In natural water systems, other nontoxic metals are generally found in very small quantities.
Arsenic, cadmium, lead, and mercury, all cumulative toxins, are particularly hazardous.
2.7. Dissolved Oxygen (DO)
DO is the measurement of oxygen dissolved in water and available for fish and other aquatic life.
Indicates health of an aquatic system.
Can range from 0-18 ppm.
Most natural water systems require 5-6 ppm to support a diverse population.
Varies with time of day, weather, temperature.
Nitrate (NO3-)
naturally-occurring form of nitrogen found in soil.
Forms by microbial decomposition of fertilizers, plants,
manures or other organic residues
Plants uptake nitrates (Spinach a good source).
Phosphate (PO4-3) naturally occurs in rocks and
minerals.
Plants uptake weathered-out elements and compounds.
Animals ingest plants.
Water soluble.
Nitrates Phosphates
Nitrates
Artificial sources:
• Livestock manure/urine
• Failing septic systems
• Synthetic fertilizers
Can lead to:
eutrophication of natural water systems
(overproduction of vegetation) Blue baby syndromne
Biological
Microbiological
Viruses, Bacteria - Pathogens Human: e.g E. coli
