Water Pollution Basics - Sources, Effects & Treatment

Water Pollution Talaes sunt aquae quam terrae perfluunt (Water becomes like the ground through which they have flowed) -Pliny the Elder , 74 CE  Basics  Water pollution: Refers to a degradation of water qua...

Water Pollution Talaes sunt aquae quam terrae perfluunt (Water becomes like the ground through which they have flowed) -Pliny the Elder , 74 CE  Basics  Water pollution: Refers to a degradation of water quality  In defining pollution we consider the following:  The intended use of the water  How far the water departs from the norm  Its effects on public health  Its ecological impacts  Originates from either point or non-point sources  Basics  Pollutant: Any biological, physical, or chemical substance that, in an identifiable excess, is known to be harmful to desirable living organisms  Pollutants Include:  Heavy metals  Sediment  Certain radioactive isotopes  Heat  Faecal coliform bacteria  Phosphorous  Nitrogen  Sodium  Pathogenic bacteria and viruses Sources of Water Pollution Biochemical Oxygen Demand (BOD)  Dissolved oxygen is needed for a healthy aquatic ecosystem  BOD: A measure of the amount of oxygen necessary to decompose organic material in a unit volume of water  Concept  Dead matter in a stream decays  Bacteria carrying out this decay use oxygen  If there is enough bacterial activity the amount of O2 available to fish and other organisms can be reduced to a point where they die  A stream with low O2 levels is considered polluted Biological Oxygen Demand (BOD)  Waterborne Diseases  Effects can vary from upset stomach to death  Faecal Coliform Bacteria: Bacteria that occur naturally in human intestines and are used as a standard measure of microbial pollution and an indicator of the disease potential of a water source  The presence of these bacteria indicate that the faecal material from mammals or birds are present  E.g. Escherichia coli (E. coli)  Causes human illness and death  In US (developed nation) 73 000 cases per year & 60 deaths  Nutrients  P & N are important nutrients that lead to pollution  Eutrophication: The process whereby a body of water develops a high concentration of nutrients such as nitrogen and phosphorous  Concept  Nutrients increase the growth of aquatic plants, photosynthetic blue-green bacteria, and algae  Algae can form surface mats preventing sunlight from entering water body (reduces photosynthesis)  Death of bacteria and algae leads to increased BOD  Nutrients  Types of lakes:  Oligotrophic:  A lake with a relatively low concentration of chemical elements required by life  Water is clear and relatively low abundance of life  Eutrophic:  A lake that has a naturally high concentration of chemical elements required by life  Water is murky and abundant with life often with mats of bacteria and algae  Cultural Eutrophication: When eutrophication is accelerated by human activities  Acid Mine Drainage (AMD)  AMD: Water with a high concentration of H2SO4 that drains from mines, typically coal, but also metal mines (copper, lead, zinc, and gold) 4𝐹𝑒𝑆2 + 15𝑂2 + 14𝐻2 𝑂 → 4𝐹𝑒(𝑂𝐻)3 + 8𝐻2 𝑆𝑂4  Acid produced when surface water or shallow groundwater runs through or moves into and out of mines and mine tailings  If AMD runs off to a natural stream or pond significant pollution and ecological damage may result  Even abandoned mines can cause a severe problem AMD (Iron mine, Colorado USA)  Saltwater Contamination of Groundwater Prior to pumping of groundwater Fresh Groundwater Ocean Salt Groundwater After excessive pumping of groundwater Fresh Groundwater Ocean Salt Groundwater  Wastewater Treatment  Wastewater Treatment: The process of treating wastewater (primarily sewage) in specially designed plants that accept municipal wastewater  Septic tank systems in rural areas and centralized waste water treatment in cities  Wastewater Treatment Plants  Primary treatment  Secondary treatment  Advanced wastewater treatment Wastewater Treatment  Water Reuse  Inadvertent  Results when water is withdrawn, treated, used, treated, and returned to the environment followed by further withdrawals and reuse  Indirect  Planned endeavour. E.g. reuse for agriculture or municipal uses  Direct  Refers to use of treated wastewater that is piped directly from the treatment plant to the next user