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Water scarcity has prompted the recycling of wastewater and reclaiming it for reuse in agricultural and domestic purposes. All the same, a well planned reuse has just started to gain importance globally, as the demand for potable water is increasing dramatically owing to high population and advancement in technology. This coupled with urbanization and climatic change has put pressure on the available fresh water for human needs. Reuse of waste water for activities that demand large supply of fresh water has been engineered to function just as the natural hydro-cycle does. Previously several studies on the topic have paved the way for technical confidence for safe usage of recycled water. Reclaimed water has been used for agricultural, industrial and domestic purposes. However, fears of toxic organic pollutants, regulations and precautions of ‘grey water’ and ‘sewage’ use have led to the search of other alternatives to supplement water resources globally.
Recycled water is wastewater that has been treated in a process of reclaiming it through the removal of dissolved solids and other impurities (Lens et al, 2002). After recycling, the water can be used in sustainable landscape irrigation or in recharging groundwater aquifers. The main purpose of such process of reclaiming water is to ensure sustainability and conservation of water instead of discharging the already treated water to the surface waters like in oceans and rivers. Water recycling provides financial and resource savings. The treatment of wastewater can be applied to meet the requirements of water quality in order to be re-used. Recycling water for different uses requires different levels of treatment. Recycled water for drinking would certainly require a thorough recycling process than the case would be landscape irrigation. The recycling of wastewater has been of great use and benefit. Most importantly, water is very scarce in some regions and the recycling process offers a great solution. There are no documented cases concerning the health of human beings as a result of having contact with water that has been recycled to criteria, standards and regulations.
Aims and Objectives
With changes experienced in the environment through global warming, water is becoming scarce by the day. The activities of man have mainly contributed to the diminishing level of water in different environments. Therefore, there is much communication needed that highlights the importance of maximizing the use of the water that is already available. Water is a very important resource that is used very much. The increasing need of water prompts the need to come up with better and cheaper methods of recycling wastewater and other water sources. Therefore, this report seeks to attain the following aims and objectives.
- To determine the issues with buildup of potentially toxic organic pollutants from recycling
- To determine the different regulations and precautions involved with recycling water for ‘grey water’ use to those required for full ‘potable’ water.
- To establish the social impact of water recycling
- To seek for alternatives to water recycling to secure water in ‘water poor’ areas
According to Eckhardt (1995, par. 1), a typical water recycling process is ideally a remarkably simple procedure that makes use of very fundamental, physical, chemical and biological principles to get rid of contaminants out of water. The use of physical or mechanical systems of treating wastewater is normally referred to as the initial treatment whereas the application of biological procedures comes in as the secondary level of treatment. Further treatment after the secondary processes and procedures normally involves the use of chemical systems on top of the biological procedures (Lens et al, 2002). These include the injection of chlorine in disinfecting the water. Tertiary level can also apply once the primary and secondary methods of treatment have been applied. Tertiary treatment of water mainly involves the removal of chemical traces and other dissolved solids. Tertiary treatment is however expensive and is not practiced to a wider extent except in places where it is deemed important to get rid of industrial contaminants.
Figure I below shows an integrated system of all the physical, biological and chemical processes involved in the treatment of waste water. Generally, the physical processes are the initial move in the process of recycling water. In this set up, the raw sewage is taken through bar screens which are essentially metal rods that have been immersed in the flow of the influent to get rid of large solid objects like rags and other solids from the water (Lens et al, 2002). These are used to protect pumps as well as other rotating mechanisms further in the process of treatment. After the stage of bar screens, water is let through a grit chamber. The influent flow at this point is taken down slowly to facilitate the falling off of gravel and sand to the base of the chamber. Primary clarifiers make it possible for further gradual flow of the wastewater so that organic precipitates can settle at the bottom while greases, oils and fats float at the top. The mechanical and physical process is said to get rid of about 50% of the water contaminants.
Raw sewage is almost 99.9% water (Eckhardt 1995, par. 3). Biological processes come in handy to get rid of all other contaminants. In a biological system, water gets through aeration basins where it is allowed to mix with oxygen. The oxygen is added to enhance the survival of micro-organisms. Micro-organisms eat up the organic material as food. This helps a lot in reducing the Biochemical Oxygen Demand (BOD) in the water. They make a conversion of the solids that can settle to be able to do so. With such a process, these solids can now be captured in the last clarifiers resulting into wastewater bio-solids. Due to the fact that this is a biological process, any harmful chemical substance can interrupt the functioning of the plant in use for the water recycling process. This is the reason why many urban centers do not allow the discharge of industrial wastes that are not treated directly into sewers. These urban authorities enlighten their citizens concerning the harmful effects that can be induced trough the dumping of household chemicals. In the event that the chemicals kill the micro-organisms causing malfunctioning of the recycling plant, the reuse programs of water are put to danger (Lens et al, 2002). Again, the quality of the water that has been discharged to the receiving water streams goes down significantly.
The chemical process may include such chambers as those of chlorine contact. These chemical chambers are applied to kill the micro-organisms that remain after the preceding processes. It is not essentially desirable to have any residual chlorine in the lakes and the rivers. Chlorine is later on removed with the use of sulphur dioxide (SO2). This offers protection for the aquatic life in stream that receives the water. The use and storage of highly lethal chlorine gas has risks. In modern times, some facilities are starting to make use of ultraviolet radiation in the place of chlorine to offer the last disinfection of water (Lens et al, 2002).
Example: Sydney Airport’s Water Treatment Plant
The water treatment plant in Sydney’s airport is a very good example of an industrial water recycling system. This plant in the Sydney’s airport takes sewage effluent from an international terminal. The process of treatment involves physical, chemical and microbiological procedures. The recycling is made possible through a dedicated network of pipes for refuse in toilet flushing together with cooling towers for the purposes of the air-condition apparatus. Generally, the sewer is collected from an already existing pumping point. The sewage then goes through inlet screens to remove foreign objects prior to the reception at the flow balance tank (See Figure 2 below).
Another physical process in the system takes place in the flow balance tank where there is a primary mixing of the sewage controlling the highs and lows of the flow of sewage as it permits a steady sewage flow into the biological reactor. The harvesting cycle is governed by the volume of the sewage inside the flow balance tank. In the biological reactor, there is an anoxic and aerobic tank. The anoxic tank gets rid of any nitrogen form the waster before it enters the aerobic area. The aerobic tank mainly allows biomass to grow and eat up any matter that is biodegradable in the wastewater. The air blowers provide the oxygen needed at this stage. All nitrogen and organic components are removed through oxidation and absorption in the cell tissues. The already grown biomass population is known as the mixed liquor suspended solids (MLSS). The MLSS is fed constantly to the membrane tank through overflow from the outlet box. Recirculation is also done into the anoxic area through return activated sludge (RAS).
The MLSS is fed through gravity to the membrane tank from the aerobic tank. A membrane cassette in the membrane tank contains hollow fibre made from a material that is resistant to oxidants. The MLSS then passes through the membrane fibre surface. Some bit of suction is sufficiently provided at the fibre side to draw through the treated water hence leaving contaminants like pathogens and solids behind (Sydney Airport). The by-products at this stage are the waste activated sludge taken back to the pumping station of the sewage and RAS re-circulated back into the biological reactor.
The filtrate tank is mainly used to collect and store water that passes through the process in the membrane and makes it possible for the creation of tow separate recycled streams of water. Stream 1 is for recycled water. It has an ozone system which gets rid of colour from the water that has been recycled and again disinfects the water. Chlorination is also provided through two stand-alone contact tanks with a combined volume of 350kl (Sydney Airport, n.d). These tanks offer the ultimate water storage point and time of contact for the dosing of chlorine to facilitate disinfection of the recycled water. There are also booster pumps that deliver the water that has been recycled to the international terminal to be reused in flushing urinals and toilets.
Stream 2 is meant for reverse osmosis water. There are reverse osmosis membranes in this stream through which the recycled water is pumped. The procedure gets rid of organic compounds, nutrients, dissolved salt and inorganic compounds from the recycled water. This procedure also offers an additional blockade against contaminants of microbiological nature like protozoa and viruses. There is also a calcite filter which re-mineralizes the water. This process limits any likelihood of corrosion of the infrastructure of the cooling tower. The booster pumps deliver the water that has been recycled to the central services building for used in the cooling towers for air-conditioning (Sydney Airport, n.d).
Toxic Organic Pollutants from Water Recycling
There are quite a number of issues with buildup of potentially toxic organic pollutants from recycling. One of the troubling issues is the build up of estrogen or pharmaceutical medications in the water supply. Some pharmaceuticals were initially developed to promote the well being and health of human beings but have in the recent past attracted a lot of attention as a potential emerging class of water pollutants (University Of Wisconsin-Madison 2004, par. 3-7). These pharmaceuticals include birth control pills, anti-depressants, cancer treatments, cholesterol-lowering compounds, seizure medication and antibiotics. All these substances have been detected in different sources of water. These substances come from hospitals, pharmaceutical industries and other medical facilities as well as households. The disposal of unused medicines through flushing down in toilets and the excreta from humans can contain different types of partly metabolized medicines. The drugs can get their way intact through traditional facilities of treating sewage into waterways, aquifers and into lakes. Moreover, the discarded pharmaceuticals usually end up at landfills and dumps increasing danger to underlying groundwater (Pharmaceuticals in Our Water Supplies n.d, par. 4-7). Another substance is estrogen, the female sex hormone which is basically responsible for the deformation of reproductive systems of fish considering that blood plasma from male trout living under sewage treatment facilities has been reported having the female egg protein vitellogenin.
Social Impact of Water Recycling
Regardless of the long history of global water management, the concern of water safety is still a dilemma because of the standard and quality of the recycled water. This is more especially the negative public perception of drinking ‘sewage’. The disagreement between the hydrologists and supporters of waste water reuse about the safety of wastewater reuse is always there. Other controversies include hydro-geologic matters and social-economic considerations. The issue of using waste water for irrigation is tackled by all the standards and the guidelines for waste water management. This phenomenon is experienced where large tracts of land need to be irrigated. The University Of Wisconsin-Madison (2004, par. 1) raised concerns about the efficiency of the water recycling plants due to the many hormones like estrogen and human pharmaceuticals that make their way into wastewater. There were fears that were indicated that sewage water could not safely turn into water that can be reused by completely removing these chemicals.
6. Regulations and Precautions in Water Recycling
There are different regulations and precautions involved with recycling water for ‘grey water’ use as in the case for gardening and washing systems to those required for full ‘potable’ or drinking water. While water recycling processes and procedures yield a lot of benefits, there are regulations and precautions that govern the people, the environment and the economy of the land (Water recycling facts from California 2004, p. 3). Thus any water recycling scheme for ‘grey water’ use must adhere to the following directives as provided for by the governing authority and based on the laws of the land.
- They should be a promotion of the kinds of water recycling that can be undertaken safely
- Local governing bodies have a duty to take into account the local community in making plans for the complete management of the water cycle
- The local community should be made aware of the performance of water recycling schemes
- The recycled water should only be applied for beneficial use
- Recycled water must be used as a resource and a suitable price charge for the use
- Recycled water must be applied to such uses that produce the highest added value
- Recycled water must be treated to levels that are fit for the intended use. The treatment of water above the required levels is a waste of money, chemicals, human resources and energy
Water Recycling Alternatives
With the need for water recycling and the high cost involved in some water recycling systems, there are a number of alternatives to water recycling to secure water in ‘water poor’ areas. In the arid and semi-arid areas, wastewater reuse is highly practiced (University Of Wisconsin-Madison 2004, par. 4). Despite this, most of the large-scale facilities used in treatment of water for reuse are headquartered in the developed countries like Israel, US and South Africa where water finds many uses but there is minimal supply. The reduction in the cost of wastewater reuse has been the key attraction for many establishments. Reuse is regularly practiced as an approach of resources management. Prevention of ecological problems resulting from discharge of untreated waste to the environment is a major factor that encourages reuse of wastewater. Though the nutrients in the wastewater may be profitable to the crops in case of sewage farming, there is a need to regulate the amount of the components in the wastewater; this calls for reuse. In a semi-arid area like California, the public policy makes emphasis on the recycling of water. Therefore, treated wastewater for non-potable uses is vital for such places like in California (Water recycling facts from California 2004, pp. 1-2).
Desalination has been one of the major alternatives used in securing water in areas faced with scarcity of water. Salty waters beyond the recommendations made by World Health Organization (WHO) present the biggest challenge for Adelaide, Australia (O’Loughlin and Vidal 2009, par. 2-5). According to O’Leary (2009, par. 11-26) desalination appears to be a key process in reclaiming water through a reverse osmosis process like in Australia, San Diego and Virginia. A reversed osmosis system comprises of such components as: a supply pump or a supply of pressurized raw water, pre-filtration stages, chemical injection agents, pressure pump, carbon membrane array with either one or a series of membranes installed in either a single or several pressure tubes (pressure vessels), gauges, flow meters, relief valves (or safety pressure switches), pressure regulating valve. Post treatment includes a sterilization form using chlorine, Ultra-Violet or Ozone. Carbon filters, mineral injection or PH adjustment for certain applications can also be used in post treatment.
In a reverse osmosis process, water goes through a number of filters including an activated carbon filter to get rid of chlorine. After this, the water then goes through a semi-permeable membrane capable of rejecting and removing a wide spectrum of contaminants, impurities and bacteria producing pure water. See figure 2 below.
b) Rainwater Harvesting
To supplement the available water for use, rainwater harvesting has been of great help in such places like Delhi, India where the government and private developers are seeking to address water scarcity (Swaraj, n.d). India is faced with a lot of challenges in having enough supply of water for its people owing to the large population and the scarcity of the resource. Recycling of wastewater and the digging of ground water do not seem to suffice. A rainwater harvesting system can be a very prudent alternative which can be used to address the scarcity of water. Figure 3 below is a diagrammatic representation of a rainwater harvesting system.
With the increasing demand and the unlikely scarcity of water, the need to recycle water was prompted and water recycling schemes have been of great use in addressing the issue. The demand of water by human beings is exceeded by the supply of the commodity globally. There is hardly any enough water to cater for the needs of the current world population. As seen from the research in this report many parts of the world from the United States, Africa and Asia among others are plagued with the lack of sufficient water for industry and domestic use. The most important usage of water by human beings is for the biological survival (Lens et al, 2002). Nevertheless, water demands for the biological survival are not the sole issue of discussion in the world. Apart from direct consumption, water is also needed for cooking, and other domestic usages, and other human developments such as agricultural and industrial needs.
While waste water treatment has in the past been of great use, there have been a lot of concerns about the buildup of potentially toxic organic pollutants from recycling. The build up of estrogen or pharmaceutical medications in the water supply has raised a lot of questions across the world and people are reluctant to make use of the already reclaimed water for some domestic uses. The social impact of recycling water is also affecting the efforts of reclaiming waste water. Again, with the regulations and precautions concerning wastewater treatment, there are still some hurdles that are experienced with the process. Therefore, this has prompted the need to come up with other alternatives. Desalination of water through a reverse osmosis system has also proved to be useful but may not be in a position to suffice for the ever growing world population (Lens et al, 2002). Adelaide in Australia has been faced with the same challenges and reverse osmosis process has seemed to work for the region to get rid of the salt from the regional waters. The search for groundwater has been in the process but also with some controls and regulations. This has led to the adoption of the Rainwater harvesting systems as the case has been in such places like Delhi in India.
Summary and Conclusion
Generally, water recycling has proven to be efficient in creating a reliable source of water putting into consideration the public health. Non-potable reuse is accepted widely. Advancement in technologies of wastewater reuse and health researches of non-potable reuse has been misinterpreted by many as the final destination of the idea of reuse. Though, water reuse is a sustainable approach, the treatment of wastewater for reusing and the setting up the facilities can be bearing a high cost in comparison to other sources such as ground water, imported water or the grey water. Educating the local people on the importance of setting up a facility before implementation is very crucial for any agency. Due to the rapid change of the climate it is evident that demand for waste water will increase to supplement the shortage in supply. However, meeting the global water demand is not a one day activity a number of factors has to be put in place e.g. preservation of water, rainwater harvesting and increasing the water usage efficiency. This combination of measure will assure the world of sustainable management of the water sources. Thus, it is everyone's responsibility to work towards meeting the water needs in a way that supports the environment and brings harmony in people’s lives.