Chemistry Research Task - Catchment Areas Essay

Gather information on the features of you local water supply in terms of: The Catchment Area: Sydney’s water supply is made of 5 main catchments: Warragamba, Woronara, Hawkesbury Nepean, Shoalhaven and Blue Mountains. Warragamba Catchment covers 9,051km?. My local area is Blacktown, in an image shown below; all the catchment areas are linked to Warragamba Catchment Area. Possible Sources of Contamination: Water quality in Warragamba catchment is affected by: * Wastes and runoff from industry and urban development * Poor sewage and storm water management * Agricultural activities * Mining * Fertilizers * Forestry * Chemical fuel spills Erosion * Uncontrolled bush ? res * Fallen Tree Branches Chemical tests available to determine levels and types of contaminants: Turbidity test is used to indicate microbial contamination such as algal growth and faecal contamination, and to detect insoluble solids such as sludge suspended in the water. Dissolved oxygen (DO) is used to determine possible increase in organic wastes. Low DO indicates activity of aerobic microbes which use up the oxygen. BOD is a measure of organic matter in water. High BOD is due to paper and food processing industries. AAS is used by adding Na2S to test quantitatively for heavy metals and metal ons. Physical and Chemical Processes used to purify water: Physical Processes: Screening: Water from the dam is screened by removing large contaminants. E. g. : Fallen Trees. Sedimentation: Allowing floc particles to settle out to form a sludge, which can be removed from settling tanks periodically. Filtration: Water from the settling tanks is piped to filtration tanks to be filtered. The water at this stage should be clear. Chemical Processes: Aeration: The screened water is then sprayed into the air to increase oxygen levels so that iron salt becomes oxidised and forms insoluble salts oxides which can be removed.

Flocculation: Removes colloidal impurities. Alum (Aluminium Sulfate) is a chemical added to cause the impurities within the water to stick/thicken together forming a precipitate or floc of Al(OH)3 which would be large enough to be filtered out. Al3+(aq)+ 3H2O(l) >Al(OH)3 (s)+ 3H+(aq) All other compounds and iron oxides adhere to the flocs. Chlorination: The filtered water is then disinfected with chlorine gas to kill microorganisms such as bacteria. UV light: Emitted to kill bacteria. pH adjustment: Buffering chemicals such as carbonates are added, to achieve the required pH between 7 and 8. . Fluoridation: Fluoride is added to help prevent tooth decay. Chemical Additives in the water and the reasons for the presence of these additives: * Chlorine added for disinfectant purposes as it destroys bacteria and some viruses (1-2 ppm). If the starting water was reasonably clean and if the right amount of chlorine is used, there is no odour when it reaches the households. * Fluorine (sodium ? uoride) added to the water after it has passed the chlorination plant. Fluoride is added (1ppm) to strengthen tooth enamel ; to help prevent tooth decay. If needed, lime water, sodium carbonate is added to lower the acidity of the water. * Sulfuric acid is added to break down organic wastes and aids coagulation. Describe and assess the effectiveness of methods used to purify and sanitise mass water supplies Solid objects are removed by screening devices. Water treatment consists of removing very small particles by flocculation. The water is sand filtered to remove bigger particles. A 2m deep bed of sand is used. Finally, it is treated with chlorine to kill microorganisms as disinfection is needed to ensure concentrations are acceptably low.

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Water testing is carried out for ions, colour, pH, hardness, turbidity, conductivity, micro-organisms. Alternative methods of filtration such as membrane filtration may be both more efficient in removing particles including microorganisms such as Giardia and Cryptosporidium. However, these techniques are expensive to execute. Monitoring of catchment and treatment processes is necessary. If microbial levels are too great extra chlorine can be added, if organic matter is excessive, aeration of the water and longer storage can be done to allow decomposition to occur.

This means that constant monitoring and adjustment is required for the process to be effective. Our water purifying methods are highly effective. However the methods were not completely effective as of one occasion. Sydney’s water contained high levels of the organisms, giardia and cryptosporidium which caused illness. This could be prevented, and our purification of water supplies improved, by installing membrane filters which would be able filter out these microscopic particles.

As a result, water supplies are monitored daily at water treatment plants and throughout each catchment during storms or other events that cause a rise in stream water levels and could influence water quality. This is considered effective, as the cost of treatment of all water supplies with membrane filters would make treatment very expensive. Describe the design and composition of microscopic membrane filters and explain how they purify contaminated water Microscopic membrane filters are used to remove solutes, colloidal particles and microorganisms from water than cannot be removed by other treatment processes.

Composition: Microscopic membrane filters are made from synthetic polymers such as cellulose acetate, PVC and polypropylene. They have extremely tiny pores, so that large organic molecules and micro organism including viruses cannot pass through, although water can. The polymer is made into a thin film, so that it acts like a sieve, removing particles larger than pore size. Microfiltration membranes can remove micro-organisms including virus and colloidal particles down to 200nm in diameter. Ultrafiltration removes large organic molecules and can remove metal ions.

Nanofiltration membranes will remove even smaller molecules such as those with molecular masses down to 300, and can reduce hardness as well as removing toxic heavy metals. Nanofiltration is the most expensive membrane filter. They can be cleaned (back-flushed) and reused. How they purify water: The porous material is made into hollow capillaries. Dirty water flows from outside the wall of the capillary ; clean water comes out of the inside. Large numbers of capillaries are bundled together to make a filtering unit with a very large surface area.


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