Improving Water's Quality with Water Purification

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Water purification is a process that removes suspended solids and gases, biological contaminants and undesirable or potentially harmful chemicals from water to achieve water that is suitable for a certain purpose. This extended response is based around safe drinking water and how it is achieved in WA. Naturally, water contains many contaminants and impurities, by removing these through a series of processes, odours, repelling taste and poor appearances can also be removed. Monitoring techniques help ensure that the water is safe to drink and contaminant levels are controlled. According to the World Health Organisation (WHO) an approximate 1.5 million people die from bacterial diseases caused by unsafe drinking water every year, and an estimated 94% of these cases could have been prevented if access to safe water was more prevalent on a global scale.

As previously mentioned, many processes must be undergone before drinking water can be clarified as ‘safe drinking water’, in Western Australia (WA), these steps include; aeration, coagulation and flocculation, sedimentation, filtration, chlorination and fluoridation. Aeration is the addition of air to water. This process allows dissolved gasses, such as carbon dioxide and hydrogen sulphate (that cause increased acidity and bad odour) that are trapped in the water to escape. In addition to this, it also helps remove dissolved metals through oxidation (as the excess oxygen makes the water corrosive). This is achieved by pumping air in an upward motion into flowing water that flows over a stair-case like structure, this causes the water to bubble and as a result of this the gasses can escape into the surrounding environment. This process can also be achieved by spraying water into air. Aeration keeps the oxygen concentration levels high throughout the entire process which prevents anaerobic conditions, averting taste and odour problems. This also reduces the amount of organic matter (such as nitrate or phosphorus) and disease-causing microorganisms. The removal of manganese compounds ensures that the water stays clear rather than appearing black, or in the case of iron compounds, prevents that water from appearing brown.

Coagulation, also know as clarification is the use of alum (aluminium sulphate) to bind particles of dirt and other solids. Rapidly mixing the water disperses the coagulants evenly, for a complete chemical reaction. As a result, clumps of alum and sediment are formed by fine particles that are chemically stuck together. A long period of gentle agitation encourages particle collision (this is flocculation). Through neutralising negatively charged particles and forming a gelatinous mass that traps particles, a larger mass can be formed that can either settle or become trapped in the filter. Then when flocculation occurs, the masses can become even larger so they can be filtered from the solution. The end result of this process being the removal of dirt and other solids, to therefore clean the water of these contaminates.

Sedimentation is the use of gravity to pull coagulated solids to the bottom of the solution, allowing clean water to be drained off. Filtration is used to remove the remaining impurities and particles in the solution. The water is percolated downward into a layer/bed of pores (sand), where particles (including chemicals and heavy metals) are suspended and become trapped within the pore surface. There are often two layers of pores, one consisting of a sand, and the other consisting of coal (anthracite (coal with up to 98% carbon)). This process adsorb organic materials (anthracite is extremely effective at absorbing organic materials), and as a result improves the taste and odour of water.

Disinfection purifies water by eliminating infectious elements such as pathogenic bacteria. Ultra Violet light (UV light) and chlorine are often used for disinfection. UV light is able to penetrate harmful pathogens in the water by attacking their genetic core. By using UV light, no additional undesirable chemicals are added to the water throughout the purification Process. If chlorine is used in this process, its accompanied by ammonia, producing a longer lasting disinfectant. Chlorine breaks down the chemical bonds in the bacterias molecules, killing all pathogens.

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Chlorination is the addition of chlorine to drinking water, usually as sodium hypochlorite (NaOCl) solution or as solid calcium hypochlorite (Ca(OCl)2) Chlorine levels are added at 5 parts per million. This is the last treatment of all the treatment processes to kill any remaining parasites, bacteria and viruses. Fluoridation is purely part of the purification processes in WA to help prevent tooth decay. Fluoride is added in many two forms, fluorosilicic acid ( a by-product of the production of phosphate fertiliser) and sodium fluoride. According to the Fluoridation of Public Water Supplies Advisory Committee, acceptable levels of fluorine in drinking water range from 0.6 to 0.9 milligrams per litre, with an absolute maximum of 1.0 milligrams per litre.

The pH of drinking water often needs to be adjusted by either decreasing or increasing the pH level to acquire optimum pH level for drinking water, 7 (but can vary from 6.5-8.5). The addition of lime, CaO (a very strong chemical base) which is an alkaline reagent used for acidic neutralisation. By dissolving carbon dioxide gas (CO2), which is slightly acidic, with a pH of approximately 6. Lime will increase the pH of water, while CO2 will decrease the pH of water. Stronger or weaker acids or bases can be used to neutralise water for safe consumption, which acid or base is used and how strong or weak it is, is depended upon the current pH of the water. The purpose of this process is to ensure the water is not too acidic or basic. If the water is too acidic, over a period of time the water will start eat away at our teeth and cause several dental issues, such as tooth decay. It may also effect out body internally. If the water is too basic, like alkaline water, the body’s normal pH may become agitated, leading to metabolic alkalosis.

There are many heavy metal contaminants that are found in water, the main ones of which being; cadmium, with recommenced amounts of 0.005 milligrams per litre; chromium, with a standard of 0.1 milligrams per litre; copper, with acceptable amounts ranging from 1 to 5 milligrams per day; lead, with a safe consumption of 0.1 milligram per litre; mercury, with acceptable standards of 0.01 milligrams per litre. The main source if these heavy metal contaminants is a result of mining, where an acid mine drainage system is used to release heavy metals from ores. Heavy metals are very soluble in acidic solutions. The pipes, generally made of copper which carry the water from the water supply to our household, can start to erode and contaminate the water in the pipes. Pipes made pre-1960 where made of iron and steal, which rust and as a result have an obvious effect on heavy metal contaminants in drinking water.

Heavy metal concentration can be reduced using several methods, such as carbon filtration and ion exchange. Carbon filtration uses activated carbon (either granular or powder activated carbon), a solid black material. The carbon is traded with oxygen to open thousands on tiny pores between the carbon atoms, helping provide a large internal surface area which accounts for its ability to hold contaminants and impurities. As carbon is positively charged, it attracts the impurities that are negatively charged, this is called adsorption. The contaminants become trapped in the small pores on the internal surface area of the activated carbon.

Ion exchange uses ion exchange resins as polymers (polymers are materials that are made up of long, repeating chains of molecules. The materials consist of unique properties which are dependent upon how the molecules are bonded and the type of molecules within the bond), they can exchange particular ions within the polymer with ions in the solution that’s passed through them. Ion exchanges are bases or acids that are not soluble and have salts that are also insoluble, allowing them to exchange their either positive or negative ions. Once the resin can no longer have ions bound to it, the cations and anions must be removed from the resin so it can be used again (regenerated). To ensure the water is suitably purified, techniques have ben developed to monitor the quality of drinking water. There are several analysis methods including microbiological tests that test for bacteria and viral pathogens and there are chemical quality tests that test the pH level, turbidity (thick, cloudy quality), heavy metals and dissolved solids.

Microbiological analysis test for coliform bacteria and faecal coil form, it shows the number of bacterias present in the water sample and can also determine what bacterias are present. The most suitable and accurate method of this analysis is the direct count method. A sample is placed in a media containing bile salts, which then promotes the growth of gram negative and gram positive (staining technique displaying bacteria presence). The media also contain lactose which is broken down by lactose fermenting bacteria, producing colonies which can then be identified. Throughout this process the samples must be sealed and incubated at 22 degrees Celsius to unsure the conditions remain controlled. This method is quick, so results can be obtained in a short time period, minimum equipment is required and the morphology of the bacteria can be counted. However, this method is not one-hundred percent accurate as it is not sensitive to populations that are fewer than one million and Both living and dead cells are counted making the results inaccurate as the amount of viable cells cannot be determined.

Chemical quality tests identify heavy metals that may affect odour, taste and appearance or oppose a risk to the health of consumers, causing problems such as kidney damage, cancers, still births, and much more. Artificial mussels (AM) technology accumulates heavy metals via a passive sampling device. The device independently collects heavy metals onto a sorbent medium through a diffusion barrier. The device is comprised of a permeable (meaning liquids and gases can pass through it) perspex tubing, where chelex-100, a chelating material used to purify substances via ion exchange which encourages the binding of metal ions. This is suspended in a sample of the water. A layer of polyacrylamide gel is used to cap both ends of the tube, the water diffuses through this gel into the metal-binding agent and the metals are removed, several weeks later, the chelex-100 is sampled to determine the metal contents.

An advantaged of this technique is that no energy or power is required, making it more convenient, cost effective and environmentally friendly, and accumulation of metals are no affected by biotic (living organisms) or abiotic factor (non-living materials) which ensures the accuracy of this technique is high, and it gives a sample to be analysed. It also not only detects heavy metal contaminants, but organic pollutants and pathogens as well. This process can be performed on a large scale and yet have no negative affect on the environment. However this technique requires continues monitoring, and a long process of collecting this equipments and ensuring the equipment meets a required standard can take up to several weeks or even months, both of these factors contribute to making it less convenient. It also cannot be applied to materials that are unstable under alkaline conditions.

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