Water Pollution and Quality Flashcards
Defining Water Pollution
o Water is considered ‘polluted’ when it is unfit for its intended use
o Common uses: drinking, aquatic ecosystems, recreation, irrigation, water source
Water Pollutants
o Oxygen demanding substances
• Reduce dissolved oxygen (DO) concentrations
• Typically biodegradable substances (sewage, food processing effluents)
• Dissolved oxygen is a critical parameter
Oxygen Depletion
Aerobic digestion of organic matter consumes O2
Organic matter + O2 + (microorganisms) = CO2 + H2O + new cells + stable products
Anaerobic digestion:
Organic matter (+ microorganisms) = CO2 + CH4 + new cells + unstable products
Chemical oxygen demand (COD)
Amount of O2 needed to chemically oxidise wastes
Faster, but not a good indicator of oxygen demand
Biochemical oxygen demand (BOD)
Amount of O2 required to oxidise organic matter aerobically (mg/L)
Determined by 5 day BOD test (BOD5)
BOD5 test
Total amount of O2 consumed during first 5 days of biodegradation
BOD_5=(DO¬_initial-DO¬¬_final )/P
DO_initial→initial DO of diluted wastewater
DO_final→final DO of diluted wastewater after 5 days
P→dilution fraction (volume wastewater / total test volume)
Pathogens
o Bacteria
o Viruses
• E.g. hepatitis, polio
o Protozoans
• E.g. amoebic dysentery, giardiasis
o Parasitic worms
• Common class is schistosomiasis
• Larvae enter blood stream & liver after burrowing through skin
o Waterborne diseases
• E.g. cholera and typhoid
• Spread by ingestion of contaminated water
o Water-based diseases
• E.g. schistosomiasis & dracunculiasis
• Involve water contact but not ingestion
o Water-washed diseases
• E.g. trachoma & scabia
• Associated with lack of sufficient water to maintain cleanliness
o Water-related diseases
• E.g. malaria & dengue fever
• Involve a host that depends on water for its habitat
o Water management and water treatment systems to address these
Infectious Diseases
o Morbidity, mortality and population at risk for diseases associated with water
o E.g. diarrheal diseases, schistosomiasis, malaria, onchoecerciasis
o Morbidity: ill health in a population
o Mortality: death in a population
Nutrients
o Chemicals essential for growth of living things: nitrogen, phosphorous, carbon etc.
o Contained in sewage, feedlot runoff, fertilisers
o Considered pollutants if levels are high enough to allow excessive algae growth
o Causes eutrophication in lakes and reduces DO concentrations when this algae dies and decomposes
Role of limiting nutrients
o Algal photosynthesis
• 106CO2 + 16NO3- + HPO42- + 122H2O → C106H263O110N16P + 138O2
• Redfield-Richards ratio C:N:P = 106:16:1
• Practical range of N/P = 10-20
• N/P < 10: possibly nitrogen limited
• N/P > 20: possibly phosphorous limited
Sediment
o Caused by accelerated soil erosion
o Suspended sediment reduces light penetration and disrupts photosynthesis
o Can drastically change stream morphology
o Nutrients often ‘bound’ to sediment particles
Dissolved Solids
o Mineral salts dissolved in water • Sodium, potassium, magnesium, chloride, sulphate, bicarbonate o Total dissolved solids (TDS) • Freshwater < 1500 mg/L • Brackish 1500-5000 mg/L • Saline > 5000 mg/L • Seawater = 30 000 mg/L • Influences appearance, taste & odour o Clogs pipe networks – formation of scale o Reduce agricultural productivity o Saltwater intrusion in groundwater
Other Pollutants
o Heat (industrial cooling waters) o Heavy metals o Pesticides o Acidity o Litter o Endocrine disruptors
Water Quality Guidelines
o Various standards/criteria
o Various across states and federal bodies
o Based on organism toxicity (ecological & human)
Lakes
o Age of a lake • Young: oligotrophic (few floods) • Old: eutrophic (many floods) o Light penetration • Euphotic zone: water • Profundal/aphotic zone: ground o Stratification (layering) • Chemical & thermal • Epilimnion: warm, light & well mixed • Thermocline • Hypolimnion: relatively cold & dark • Eutrophic lake: hypolimnion is cut off from re-oxygenation and can become anaerobic, as stratification occurs in spring & summer • Oligotrophic lake: nutrient poor and don’t have this problem, they are clear so light penetrates further for photosynthesis to add O2 • Autumn overturn: oxygenated cold water sinks into the hypolimnion and the lake mixes (nutrients, DO, temperature more evenly distributed)
Eutrophication
o Excessive richness of nutrients in a lake
o ‘Cultural’ eutrophication: accelerated input of nutrients from catchment, stimulates excess algal growth and degrades water quality
o Limiting nutrient: usually N or P
o Stratification exacerbates eutrophication impact, hypolimnion suffers major DO drop
Emerging Issues
o Endocrine disrupting chemicals (EDCs) interfere with natural hormones
• As low concentrations, can disrupt embryo development
• Sources: dioxins, pesticides, polycarbonates
Nanoparticles
- Materials with functionalities at the near-atomic scale
* Commonly found in paint, food additives, polishing compounds
