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The aim is to review the importance of water recycling and the unending effects of hard water all round us. Objective is to achieve a clear understanding of the present and future benefits of water recycling and why it is still practised today. A number of up-to-date water recycling tehnologies are studied to an extent. The perpetual need for the various solutions in softening hard water is looked into retrospectively carefully highlighting typical problems likely to occur.
Water is a common substance that is essential to all forms of life. A massive 75 percent of planet earth is covered in water and is mostly found in oceans and large water bodies. Of this total volume of water, 97 percent is saltwater and 3 percent is freshwater. 69 percent of this freshwater is glacial and 31 percent is groundwater. For billions of years, earth has been reusing water over and over again in a natural process called the hydrologic cycle (BENEFITS OF RECYCLING., 2010). This cycle is the path water takes as it circulates from the land to the sky and back again.
1.1 Water Recycling
Water recycling is a natural process which relies on technology to speed up such projects. It is sometimes described as ‘unplanned’ and ‘planned’ (GREYWATER RECYCLING SYSTEMS., 2010). By unplanned, this means for example, when cities draw their water supplies from rivers that receive waste water upstream from these cities. Water from these rivers has been reused, treated and piped into the water supply a number of times before the last downstream use withdraws the water (GREYWATER RECYCLING SYSTEMS., 2010). However, that of planned water recycling projects is developed with the aim of reusing a recycled water supply.
Recycled water is waste water that has been treated and processed for useful nonpotable purposes such as agricultural, landscape, public parks, and golf course irrigation (GREYWATER RECYCLING SYSTEMS., 2010). Other nonpotable applications include cooling water for power plants and oil refineries, industrial process water for facilities such as paper mills and carpet dyers, toilet flushing, dust control, construction activities, concrete mixing, and artificial lakes (GREYWATER RECYCLING SYSTEMS., 2010). In an industrial facility, water is recycled and reused onsite used in cooling processes for example (GREYWATER RECYCLING SYSTEMS., 2010).
Although most water recycling projects have been developed to meet the demands of nonpotable water, a number of them use recycled water indirectly for potable purposes (GREYWATER RECYCLING SYSTEMS., 2010). These projects include recharging ground water aquifers and augmenting surface water reservoirs with recycled water (OASIS DESIGN., 2009). Recycled water can be spread or even injected into ground water aquifers to augment ground water supplies, and to prevent salt water intrusion in coastal areas. Environmentally, water recycling provides tremendous benefits. Water recycling can help us find ways to reduce the diversion of water from sensitive ecosystems by providing a supplementary source of water. The lack of sufficient water flow, as a result of diversion for agricultural, urban, and industrial purposes, can cause impairment of water quality and ecosystem health for plants, wildlife, and fish which depend on adequate water flow to their habitat for sustenance and reproduction (OASIS DESIGN., 2009). For streams that have been dried from water diversion, recycled water may be used to build these habitats (GREYWATER RECYCLING SYSTEMS., 2010). Water flow can be augmented with recycled water to develop and sustain the aquatic and wildlife habitats (GREYWATER RECYCLING SYSTEMS., 2010).
Greywater is water that has been used domestically (from baths, showers, clothes washers, and wash-hand basins) except for water from toilets (GREYWATER RECYCLING SYSTEMS., 2010). Greywater takes up 50 – 80% of household wastewater (OASIS DESIGN., 2009). Wastewater produced by toilets is called ‘black water’ (OASIS DESIGN., 2009). However wastewater from kitchen sinks and dish-washers is also considered to be black water as well due to the presence of organic contents (OASIS DESIGN., 2009). The clearest purpose of recycling domestic grey water is that it replaces potable water use (OASIS DESIGN., 2009).
2 BUILD-UP OF TOXIC ORGANIC POLLUTANTS FROM RECYCLING
In water treatment, a wide range of chemicals are added in excess due to poor operation or accidents (GRAY N. F., 2005). However, most of these chemicals are discharged with the finished water product due to the nature of the processes themselves. These include iron, aluminium, and organic compounds used as coagulates, such as polycrylamide (GRAY N. F., 2005). These chemicals result in odour and discolouration in the water as well as poor taste. Furthermore, the new Drinking Water Directive sets limit values for all these compounds. Chemicals such as chlorine and fluorine are added intentionally to protect the public from pathogens and teeth decay respectively (GRAY N. F., 2005).
3 THE NEGATIVE PUBLIC PERCEPTION OF DRINKING ‘SEWAGE WATER’
The increasing concern of the public is reflected by a large rise in the sales of bottled water and home treatment systems (GRAY N.F., 2008). The view of reusing sewage water for the purpose of drinking water ignorantly puts people off now and again. However, the knowledge of water recycling plays a big role here so educating the consumer about water quality and the regulatory functions of water undertakers is mandatory (GRAY N.F., 2008). All water is reused and with the system of treatment in place, sewage water can be drinkable. The use of chlorine in water treatment is a major source of complaint with consumers (GRAY N.F., 2008). The prevailing reasons for boiling water, buying bottled water or the use of home treatment systems are over an improvement in taste and health concerns. There is a strong belief that bottled water is safer and purer to drink which unfortunately is not always true. The media also plays a role in the influence of attitudes towards water and the assessment risk (GRAY N.F., 2008).
In protecting public health, conditions and regulations have been made to allow for the safe use of reclaimed water. Reclaimed water often provides a vital water supply and fertilizer source (METCALF & EDDY., 2003). For most developing countries, the greatest concern with the use of wastewater for irrigation is that untreated or treated wastewater can possess quite a number of intestinal nematodes (e.g., Ascaris and Trichuris species and hookworms) and bacterial pathogens which are often difficult to control (METCALF & EDDY., 2003). The health of the general public consuming farm produce that have been contaminated by the wastewater infected by these viral and bacterial agents can deteriorate over time. The world health organisation suggest that irrigation of farm produce prone to be eaten uncooked, sports fields, and public parks should be irrigated with wastewater dealt with stabilization ponds (METCALF & EDDY., 2003). From country to country, regulations in reusing water and wastewater vary. In England and Wales, Drinking Water Inspectorate control the standard of drinking water provided (GRAY N. F., 2005). However, the quality of the water is the privatised water companies’ responsibility (GRAY N. F., 2005).These responsibilities are regulated by the Office of Water Services and it also controls the price of water before hitting the market. The Environment Agency for England and Wales is responsible for controlling water pollution, regulating waste and manage integrated pollution control (IPC) licensing (GRAY N. F., 2005). It also has the duty to issue licenses for water control functions, promote the conservation and enhancements of freshwater to promote the recreational use of freshwater, to improve and develop fisheries and regulate them, to issue flood warnings and the provision of defences to reduce the risk of sea and river flooding, the issuing of land drainage consents and many other tasks (GRAY N. F., 2005). The Agency points out water protection zones, protects groundwater and sets the objectives for water quality (GRAY N. F., 2005).
Don’t store grey water
Grey water should be used within 24 hours before the build up of bacteria develops. After this period, it is on its way to becoming septic, that is, black water (LETS GO GREEN., 2009).
Avoid contamination and contact
Identify grey water plumbing by labelling it. The use of gloves is vital when in contact with grey water filters or anything that has come in contact with it (LETS GO GREEN., 2009).
Use only grey water that is fairly clean to start with. If otherwise, it should be diverted to a sewer or septic system (LETS GO GREEN., 2009).
Microorganisms on consumable goods
Untreated grey water possesses some microorganisms which affect lawns, or fruits and vegetables that are eaten raw (e.g., strawberries, lettuce, carrots) to an extent (LETS GO GREEN., 2009).
Contamination of surface water
Grey water should be disposed of properly either underground or in a mulch (a mulch is a covering made up of rotten vegetable matter which prevents evaporation and soil erosion). The addition of grey water to an already soaked soil should be avoided (LETS GO GREEN., 2009).
Desalination involves removing dissolved minerals from aquatic bodies to create drinking water (CITY OF RYDE, 2009). 15-50% of water is recovered with the other portion being brine (CITY OF RYDE, 2009). A few technologies have been produced for the execution of this process, including the best known and common membrane process is the reverse osmosis (CITY OF RYDE, 2009).
Figure 2: Diagram showing osmotic and reverse osmotic flow (Source: Courtesy of FWPBDP., 2010)
Countries which do not have the advantage of continual fresh water supplies, competition for fresh water continually soars (TENE A. 2010). Israel is regarded pioneer in the area of desalination (TENE A. 2010). Following the water crisis in Israel, the state of water economy improved to an extent that even during harsh drought years, the water economy will continue to flourish since the water in the sea would not be running out anytime soon (TENE A. 2010). This sea water is pumped to as much volume is required and the final desalinated water is supplied as necessary. Another type of separation technique is the evaporation process (PEREIRA H.C. 1973). Developing economies such as California have warm climates of high evaporation rates (PEREIRA H.C. 1973). Its primary water resource is the sea where the evaporation process is practised. It is an effective alternative to water recycling in ‘water poor’ regions (PEREIRA H.C. 1973).
7 FUTURE OF WATER RECYCLING
Recycling is generally vital to our planet’s future. The rate at which the earth’s highly valued resources are been consumed is taking a rapid turn and many of these resources are not renewable (U.S. EPA., 2009). Recycling as a process takes considerably less energy to reuse an existing product than to source and make one from scratch (U.S. EPA., 2009).
Water recycling has certainly established beyond doubt to be effective and resourceful in developing a new and reliable water supply. Nonpotable reuse is a widely accepted practise that will continue to expand (YOSHIKAWA N., 2006). Advances in wastewater treatment technology and health studies of indirect potable reuse will become common soon (YOSHIKAWA N., 2006). As water and environmental needs becomes urgent, water recycling would play a greater role in our long-term water supply (U.S. EPA., 2009).
8 WATER RECYCLING TECHNOLOGY
The type of wastewater is essential for determining the kind of treatment plant and technologies to employ. Wastewater primarily arises from water usage by residential, commercial and industrial institutions including groundwater, surface water and storm water as shown in Figure 3.
Figure 3: Sources of Wastewater (Source: Courtesy of ESCWA., 2003).
Typical examples of water recycling systems in the domestic or industrial field are flotation and sedimentation, of which both are relevant to the chemical industry.
Flotation is a unit process used to remove solid or liquid from any form of liquid by releasing fine gas, usually air bubbles into it (ESCWA., 2003). The gas bubbles would stick to the liquid or would get trapped in the particle structure of the suspended solids, raising the floaty force of the particle and gas bubbles put together (ESCWA., 2003). Particles having a higher density than the liquid would be able rise. Flotation is used to remove suspended matter and to concentrate biological sludge in wastewater treatment (ESCWA., 2003). Flotation has an advantage over the sedimentation process in that; very minute and light particles are easily removed in a quicker time frame (ESCWA., 2003).
Table 1: Data of Flotation Methods
Dissolved Air Flotation
Wastewater is subjected to the pressure of several atmospheres while air is introduced into it. The pressure then returns to atmospheric level, allowing the air to be released as small bubbles after a short time. These bubbles which stick to the suspended matter where it is removed by a skimming device.
By the application of a revolving impellers or through diffusers, gas is passed into the liquid directly at atmospheric pressure
Wastewater is saturated with air. With the application of a partial vacuum, the dissolved air results in escaping as minute bubbles where they form a scam blanket. This blanket is removed by a skimming device.
Source: Courtesy of ESCWA., 2003.
Figure 4: A typical Flotation unit (ESCWA., 2003).
Sedimentation is a widely used unit operation in water and wastewater treatment (ESCWA., 2003). It involves the gravitational settling of suspended solids in a mixture usually water (ESCWA., 2003). These suspended solids are removed from suspensions by allowing it gravitate to the floor of a tank to form a sludge under near still conditions (ESCWA., 2003). This tank is referred to as a clarifier (ESCWA., 2003). It comprises of three main designs. They are;
Horizontal flow clarifiers
They can either be rectangular, square or circular in shape. The flow in rectangular clarifiers is rectilinear and parallel to the long axis of the basin. Furthermore, the water flows radially from the centre towards the outer edges in circular clarifiers. The clarifiers are usually made up of steel or reinforced concrete (ESCWA., 2003).
Solid contact clarifiers
They get solids into contact with a suspended layer of sludge near the bottom that acts as a blanket. The solids put in cumulate and remain trapped within the sludge blanket. As the solids remain below, the liquid is able to rise upwards (ESCWA., 2003).
Inclined surface basins
The flow here is laminar and there is little or no wind effect. Inclined trays are used to divide the depth into shallower sections, reducing the settling times in the process (ESCWA., 2003).
Figure 5: Parts of a circular clarifier (Source: Courtesy of ESCWA., 2003).
9 HARD WATER
Hard water is simply referred to as water that contains more minerals than ordinary water (FREE DRINKING WATER., 2009). Water that is said to be hard possesses minerals made up of calcium and magnesium compounds (FREE DRINKING WATER., 2009). This water usually comes from aquifers and other underground sources that collect dissolved minerals from rocks (FREE DRINKING WATER., 2009). Minerals of these sought reduces the ability of soap to lather and the ease of rinsing anything being washed made difficult. On the other hand, soft water is treated water that contains only sodium ion (FREE DRINKING WATER., 2009).
Figure 6: Diagram showing hard and soft water processes (Source: Courtesy of LENNTECH., 2009).
9.1 PROBLEMS WITH HARD WATER
Every cleaning task from laundering and dish washing to bathing and personal care is made unreasonably difficult taking up time and energy. The quantity of hardness minerals in water would determine the soap and detergent level required for cleaning. Additional detergent would have to be added to achieve the desired goal. Dishes and glasses washed using hard water may not be totally clean possessing certain spots when dry. The same goes with clothes which may feel harsh and scratchy when worn. Furthermore, skin was led with hard water may leave the skin feeling itchy and dry certainly not a remedy for skins with conditions such as eczema (HEIDEKAMP A. J., 2005). A number of detergents have ingredients that would mix with hard water minerals leaving a white deposit on clothing, making it look faded and worn out. Heated hard water affects water-using appliances (HEIDEKAMP A. J., 2005). It forms a scale of calcium and magnesium minerals which contributes to the inefficient and costly of these appliances (HEIDEKAMP A. J., 2005). Pipes become clogged with scale that impedes water flow and would in no time require pipe replacement. When hard water is heated, calcium ions react with bicarbonate ions to form an insoluble compound called calcium carbonate which is responsible for the scaling in pipes (HEIDEKAMP A. J., 2005). This is depicted in the equation below;
9.2 SOFTEN WATER TECHNIQUES
9.2.1 Lime-Soda Ash Technique
It is the most common water softening method which involves the addition of slaked lime to hard water in water plants (FREE DRINKING WATER., 2009). Lime and soda ash are used because they are readily accessible and cost effective for softening water (FREE DRINKING WATER., 2009). Non-carbonate hardness is in turn reduced by the addition of soda ash to form insoluble precipitate which is also removed by filtration. Slaked lime is used to remove calcium bicarbonate from water (FREE DRINKING WATER., 2009). In this method, the slaked lime ions react with the calcium bicarbonate to form a slightly soluble calcium carbonate. This precipitate is usually removed by allowing it settle and then filtering (FREE DRINKING WATER., 2009). Additional lime is used in removing magnesium (FREE DRINKING WATER., 2009). This treatment becomes more costly as the hardness level has to be reduced to less than 5 grains. The use of the lime-soda ash treatment in homes was farfetched because of the equipment size and high cost involved in running one and even owning one (FREE DRINKING WATER., 2009).
9.2.2 Ion Exchange Columns Technique
Ions could either be positively or negatively charged. A positive charge ion is called a cation while a negatively charged ion is an anion. The minerals, calcium and magnesium, that result in hardness are positively charged cations (NORDEN R. L., 2010). An ion exchange water softener has three main parts;
A resin tank containing small beads of synthetic resin,
A brine tank,
The control valve (NORDEN R. L., 2010).
When using ion exchange equipment, calcium and magnesium are exchanged for sodium from the brine tank (NORDEN R. L., 2010). As water passes through the resin tank, the sodium ions are exchanged with calcium and magnesium ions (NORDEN R. L., 2010). This is because the calcium and magnesium ions have a higher positive charge than the sodium ions. As the calcium and magnesium attach themselves to the resin beads is released simultaneously into the water. After the sodium in the resin, medium is exhausted, the medium can be regenerated by the sodium from the brine tank (NORDEN R. L., 2010). People with health problems such as heart or circulation problems, or are on low sodium diets may need to avoid using the ion exchange because of the high sodium content (NORDEN R. L., 2010). It is not even recommended for watering lawns or plants due to the sodium content present. However, potassium can be used in replacing sodium but it costs more. It is highly recommended that only hot water in a home be softened because the hot water line and heater benefits and the rate of soap consumptions are reduced (NORDEN R. L., 2010). Another importance in using the ion exchange equipment is that, it removes traces of iron as well to an extent because it is a positively charged ion (NORDEN R. L., 2010).
9.2.3 Chemical Conditioners/Suppressants Technique
Chemical conditioning involves the addition of polyphosphates (SOUTHERN WATER., 2005). This reduces the availability of calcium in the formation of deposits. This would result in the water behaving as though softening although this would be false regarding the removal of calcium. A measure of this supposed softening is that such water would need less soap or detergent to lather. The polyphosphates can easily be set up by installing a relatively cheap dispenser in the pipework that could easily treat all the water going into the property (SOUTHERN WATER., 2005). When exhausted in the dispenser, the polyphosphates usually in solid glass-like balls are added at any appropriate time frame (SOUTHERN WATER., 2005). Alternatively, using polyphosphates helps to reduce traces of lead from any lead pipework but this should not be a guaranteed reason for using this technique (SOUTHERN WATER., 2005).
HARD WATER CONTAINING CALCIUM AND MAGNESIUM ENTERING SOFTNER
SOFTEN WATER CONTAINING SODIUM
Water is reusable. A high percentage of our water is recycled and the same water has been around for a long time. In this effect, water technologies have been cleverly developed in keeping this natural tradition alive.
Hard water is water that contains calcium and magnesium ions, and can be reversed by softening it thereby leaving it usable in homes and industries. It has a costly effect on most equipment in our homes and a health risk in humans. In softening hard water, the rate at which all these negative effects take its course would be minimised.
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