Chemical_Monitoring_and_Management-_Local_Water_Catchment

Catchment Area The Sydney Catchment Authority drinking water catchments cover over 16,000 square kilometres. Nearly 60 per cent of the land is privately owned and 25 per cent is national park. Sydney relies on the Warragamba, Upper Nepean, Blue Mountains, Shoalhaven, and Woronora river systems to supply their drinking water. These catchments extend from north of Lithgow in the upper Blue Mountains, to the source of the Shoalhaven River near Cooma in the south - and from Woronora in the east to the source of the Wollondilly River west of Crookwell. Warragamba Dam is Sydney’s principle water storage dam. It is located 60 km west of Sydney in a narrow gorge on the Warragamba River and is one of the largest domestic water supply dams in the world. It has a capacity 2 million mega litres, almost 4 times the capacity of Sydney harbour. The catchment area of Warragamba dam is approximately nine thousand square kilometres. Water is delivered from Warragamba dam to the Prospect Water Filtration. Possible sources of contamination in this catchment Intensive agriculture such as market gardening is a potential source of contamination within the catchment especially the use of pesticides and fertiliser. Beef production has the potential to contaminate water sources if manure enters the waterways, especially if stock have direct access to water courses. This can result in bank erosion and faecal matter being directly deposited into the water. Water quality may be affected and have high measurements of nutrient concentrations and suspended solids. Land cultivation for agriculture can increase the sediments entering the waterways as erosion occurs. Land clearing to establish mining, infrastructure, processing, stockpiling and storage of waste materials leads to erosion and transportation of sediment to waterways. Less than 1% of land in the Sydney catchment area is used for urban development. Sewage and stormwater runoff are sources of possible water contaminants such as faecal coliform, greases and detergents. waterways. If not managed properly, this could result in high turbidity. Household waste and garbage are also possible sources of contamination which can affect water quality. Chemical tests available to determine levels and types of contaminants Sydney Water and other state water authorities are required to maintain high-quality water for domestic use. This involves monitoring the quality of water in catchment areas and throughout each stage of the system that delivers water to the consumer. Total dissolved solids- Total dissolved solids are determined by evaporation to dryness of a known volume of a filtered sample. The value is converted to parts per million (ppm) and expressed in mass per volume units, ppm. Hardness- Hardness is due to the presence of calcium and magnesium ions in the water. These form insoluble compounds with soap ions, resulting in a scum on the water surface. The test for hardness involves precipitating the calcium and magnesium ions from a known volume of the water sample with a solution of sodium carbonate, followed by filtering and drying of the precipitate. Most of the insoluble salt is assumed to be calcium and the concentration of calcium ions is calculated and reported in parts per million (ppm). Turbidity- Turbidity is a measure of suspended solids in water. High turbidity reduces penetration of light and decreases photosynthesis, which in turn reduces the oxygen concentration. The test for turbidity is conducted using a turbidity tube standing on a white tile. The tube has a black cross marked on the base. The water sample is poured into the tube until the cross just disappears when looking from above. Turbidity can also be measured by using a secchi disk, which is lowered into the body of water until it can no longer be seen. With both methods, the depth of the water is measured and a calibration graph is used to determine turbidity. Acidity- A pH reading below 7 would be expected where there are acid sulfate soils or where there is acid produced by decomposition of organic matter in stagnant situations. The test can be conducted with a data logger and pH probe, universal indicator solution or paper, or a pH meter. If using the universal indicator, comparison with a coloured pH scale provides the pH value. If it is less than 7, the solution is acidic. Biochemical oxygen demand- BOD measures the amount of oxygen used by bacteria and other micro-organisms during a five-day period. The sample bottles are held below the water surface and away from the bank. One sample is measured for DO as soon as possible while the other sample is kept in a dark place for 5 days and then tested for DO. The BOD is calculated by subtracting the DO value after 5 days from the initial DO value. The reading is given as milligrams per litre (mg L-1). Dissolved Oxygen-There are several tests for determining the DO in a water sample. The Winkler method fixes the amount of dissolved oxygen, which is later determined by titration. The amount of manganese dioxide produced by adding manganese(II) ions and hydroxide ions is a measure of the DO. Acidified iodide ions are added to cause the manganese dioxide to produce a yellow iodine solution. This is then titrated against a standard sodium thiosulfate solution using starch as the indicator. The indicator turns a blue colour with the iodine and the blue disappears at the endpoint. To conduct the test, no air is to be trapped with the sample and it is to be kept in the dark to reduce algae photosynthesis increasing the DO. Physical and Chemical process to purify water Step 1 – Aeration • Spray water into the air to increase the concentration of dissolved oxygen. • Any hydrogen sulfide gas dissolved in the water is oxidised to sulfate ions and iron salts are also oxidised to insoluble iron oxides which can later be removed. Oxygenated water also has a more pleasant taste. Step 2 – Flocculation • Water in rivers and reservoirs contains small suspended particles. The diameter of these clay colloids are very small, and are prevented from settling due to the repulsion between their negative surfaces. • These can be made to precipitate by a process called flocculation. • Alum (aluminium sulfate) is added to the water to produce a gelatinous precipitate or floc of aluminium hydroxide. This jelly-like precipitate traps other suspended particles, including some microbes. • The hydrogen ions produced in this hydrolysis reaction are attracted to the surface of the aluminium hydroxide flocs. The negative surfaces of the clay colloids are then attracted to the positive surfaces of the flocs and these larger particles settle out under gravity. Iron oxides and other soluble coloured compounds also adhere to the flocs. Step 3 – Sedimentation – settling of the flocs • The treated water is allowed to stand in a settling tank so that the flocs settle to the bottom to form sludge. • The sludge can be removed from these settling tanks periodically. By the end of step 3 about 95% of the suspended impurities (particle size >25 microns) have been removed. Step 4 – Filtration • Water from the settling tanks is then passed through a filter containing the sand and gravel to remove the remaining suspended particles and to remove other minerals, bacteria and coloured matter. The water at this stage should now by clear. If the water is still coloured, it can be passed through layers of activated charcoal, which adsorbs the coloured matter onto its surface. Step 5 – Chlorination and micro-biological tests • Water emerging from the filter is now chlorinated to kill bacteria and other microbes. Chlorination process produces hypochlorite ions which kill the microbes. Biochemists test the water for the presences of bacteria called coliforms (e.g. Escherichia coli) which are associated with pollution from animal manure. Drinking water should contain on average less than two colony-forming units (CFU) per 100mL of water throughout the year. The chlorine level must be constantly monitored to assure that carcinogenic chlorinated alkanes are not produced. Chemical additives in the water and the reason for the presence of these additives • Chlorine- added for disinfectant purposes. At a concentration of 1-2 ppm, the chlorine destroys bacteria and some viruses. If the starting water was reasonably clean and if the right amount of chlorine is used, there is no odour when it reaches the user. • Fluorine (sodium fluoride) - added at a concentration of 1ppm to the water supply generally just downstream of the chlorination plant. Fluoride is added to strengthen tooth enamel in growing children: it is a form of enforced medication. References Your water- Sydney water, Typical drinking Analysis http://www.sca.nsw.gov.au Water Quality- Sydney Water http://www.sydneywater.com.au/waterQuality Chemical monitoring and Management – Water http://hsc.csu.edu.au/chemistry/core/monitoring/chem945/945net.html