U N E S C O - E O L S S S A M P L E C H A P T E R WASTEWATER RECYCLE, REUSE, AND RECLAMATION - Recycle and Reuse of Domestic Wastewater - S. Vigneswaran, M.Sundaravadivel RECYCLE AND REUSE OF DOMESTIC WASTEWATER S. Vigneswaran Faculty of Engineering, University of Technology, Sydney, Australia M. Sundaravadivel Graduate School of the Environment, Macquarie University, Sydney, Australia Keywords: Blackwater, Dual reticulation, Graywater, Pathogens, Reclamation,Recycle, Reuse, Sludge Contents 1. Introduction2. History of Wastewater Reuse3. Motivational Factors for Recycling/Reuse4. Quality Issues of Wastewater Reuse/Recycling5. Types of Wastewater Reuse6. Future of Water ReuseAppendixGlossaryBibliographyBiographical SketchesTo cite this chapter Summary Reuse of wastewater for domestic and agricultural purposes has been occurring sincehistorical times. However, planned reuse is gained importance only two or three decadesago, as the demands for water dramatically increased due to technological advancement,population growth, and urbanization, which put great stress on the natural water cycle.Reuse of wastewater for water-demanding activities, which, so far consumed limitedfreshwater resources is, in effect, imitating the natural water cycle through engineeredprocesses. Several pioneering studies have provided the technological confidence forthe safe reuse of reclaimed water for beneficial uses. While initial emphasis was mainlyon reuse for agricultural and non-potable reuses, the recent trends prove that there aredirect reuse opportunities to applications closer to the point of generation. There are alsomany projects that have proved to be successful for indirect or direct potable reuse. Allthe case studies presented in this article point towards the potential wastewater has toserve as a viable alternative source of water, in future. 1. Introduction The total supply of freshwater on earth far exceeds human demand. Hydrologistsestimated that if all the water available on the planet—from oceans, lakes and rivers, theatmosphere, underground aquifers, and in glaciers and snow—could be spread over thesurface, the earth would be flooded to an overall depth of some three kilometers. About97 percent of this water is in the oceans, and out of the remaining three percent, only about one-hundredth is the accessible freshwater that can be used for human demand. If this available water could be evenly distributed, still it is enough to support a populationabout ten times larger than today. The foremost use of water by humans is for thebiological survival. However, water need for the biological survival is not the only issuebeing discussed in the world today. Because, apart from drinking, water is required alsofor household needs such as cooking, washing, and is vital for our development needs,such as for agriculture and industry.Unfortunately, the available freshwater supplies are not evenly distributed in time andspace. Historically, water management has focused on building dams, reservoirs, anddiversion canals etc., to make available water wherever needed, and in whatever amountdesired. Soaring demands due to rapidly expanding population, industrial expansion,and the need to expand irrigated agriculture, were met by ever larger dams anddiversion projects. Dams, river diversions, and irrigation schemes affected both waterquality and quantity.Demands on water resources for household, commercial, industrial, and agriculturalpurposes are increasing greatly. The world population will have grown 1.5 times overthe second half of the twenty-first century, but the worldwide water usage has beengrowing at more than three times the population growth. In most countries humanpopulations are growing while water availability is not. What is available for use, on aper capita basis, therefore, is falling. Out of 100 countries surveyed by the WorldResources Institute in 1986, more than half of them were assessed to have low to verylow water availability, and quality of water has been the key issue for the low wateravailability. Given the rapid spread of water pollution and the growing concern aboutwater availability, the links between quantity and quality of water supplies have becomemore apparent. In many parts of the world, there is already a widespread scarcity,gradual destruction and increased pollution of freshwater resources.In industrialized countries, widespread shortage of water is caused due to contaminationof ground and surface water by industrial effluents, and agricultural chemicals. In manydeveloping countries, industrial pollution is less common, though they are severe nearlarge urban centers. However, untreated sewage poses acute water pollution problemsthat causes low water availability. Development of human societies is heavily dependentupon availability of water with suitable quality and in adequate quantities, for a varietyof uses ranging from domestic to industrial supplies. An estimate infers that every year,the wastewater discharges from domestic, industrial and agricultural practices pollutemore than two-thirds of total available run-off through rainfall, thereby, what can becalled a “man-made water shortages.” Thus, in spite of seeming abundance, waterscarcity is endemic in most parts of the world. It is because of these concerns, theAgenda 21 adopted by the United Nations Conference on Environment andDevelopment, popularly known as the “Earth Summit” of Rio de Janeiro, 1992,identified protection and management of freshwater resources from contamination asone of the priority issue, that has to be urgently dealt with to achieve globalenvironmentally sustainable development.The need for increased water requirement for the growing population in the new centuryis generally assumed, without considering whether available water resources could meet these needs in a sustainable manner. The question about from where the extra water is tocome, has led to a scrutiny of present water use strategies. A second look at strategieshas thrown a picture of making rational use of already available water, which if usedsensibly, there could be enough water for all. The new look invariably points out atrecycle and reuse of wastewater that is being increasingly generated due to rapid growthof population and related developmental activities, including agriculture and industrialproductions. 2. History of Wastewater Reuse The term “wastewater” properly means any water that is no longer wanted, as no furtherbenefits can be derived out of it. About 99 percent of wastewateriswater, and only onepercent is solid wastes. An understanding of its potential for reuse to overcome shortageof freshwater existed in Minoan civilization in ancient Greece, where indications forutilization of wastewater for agricultural irrigation dates back to 5000 years. Sewagefarm practices have been recorded in Germany and UK since 16 thand 18th centuries,respectively. Irrigation with sewage and other wastewaters has a long history also inChina and India. In the more recent history, the introduction of waterborne sewagecollection systems during the 19 thcentury, for discharge of wastewater into surfacewater bodies led to indirect use of sewage and other wastewaters as unintentionalpotable water supplies. Such unplanned water reuse coupled with inadequate water andwastewater treatment, resulted in catastrophic epidemics of waterborne diseases during1840s and 50s. However, when the water supply links with these diseases became clear,engineering solutions were implemented that include the development of alternativewater sources using reservoirs and aqueduct systems, relocation of water intakes, andwater and wastewater treatment systems. Controlled wastewater irrigation has beenpracticed in sewage farms many countries in Europe, America and Australia since theturn of the current century.For the last three decades or so, the benefits of promoting wastewater reuse as a meansof supplementing water resources and avoidance of environmental degradation havebeen recognized by national governments. The value of wastewater is becomingincreasingly understood in arid and semi-arid countries and many countries are nowlooking forward to ways of improving and expanding wastewater reuse practices.Research scientists, aware of both benefits and hazards, are evaluating it as one of theoptions for future water demands. 3. Motivational Factors for Recycling/Reuse Major among the motivational factors for wastewater recycle/reuse are: •opportunities to augment limited primary water sources; •prevention of excessive diversion of water from alternative uses, including thenatural environment; •possibilities to manage in-situ water sources; •minimization of infrastructure costs, including total treatment and discharge costs;reduction and elimination of discharges of wastewater scope to overcome political, community and institutional constraints.Reuse of wastewater can be a supplementary source to existing water sources,especially in arid/semi-arid climatic regions. Most large-scale reuse schemes are inIsrael, South Africa, and arid areas of USA, where alternative sources of water arelimited. Even in regions where rainfall is adequate, because of its spatial and temporalvariability, water shortages are created. For example, Florida, USA is not a dry area, haslimited options for water storage, and suffers from water shortages during dry spells.For this reason wastewater reuse schemes form an important supplement to the waterresource of this region.Costs associated with water supply or wastewater disposal may also make reuse of wastewater an attractive option. Positive influences on treatment costs of wastewaterand water supplies, and scopes for reduction in costs of headworks and distributionsystems, for both water supply and wastewater systems has been the motivation behindmany reuse schemes in countries like Japan.Reuse is frequently practiced as a method of water resources management. For example,depleted aquifers may be “topped-up” by injection of highly treated water, thusrestoring aquifer yields or preventing saltwater intrusion (in coastal zones).Avoidance of environmental problems arising due to discharge of treated/untreatedwastewater to the environment is another factor that encourages reuse. While thenutrients in wastewater can assist plant growth when reused for irrigation, their disposal,in extreme cases, is detrimental to ecosystems of the receiving environment. In addition,there may be concerns about the levels of other toxic pollutants in wastewater.Concern about water supply or environmental pollution may emerge as a political orinstitutional issue. Community concern about the quality of wastewater disposed tosensitive environments may lead to political pressures on the water industry to treatwastewater to a higher level before discharge, that can be avoided through reuse of wastewater. Institutional structures may also provide incentives for reuse. Becauseresponsibility for different parts of water use and disposal system may rest withdifferent organizations, a water utility may also be faced with standards of service set inagreements with other industry bodies. 4. Quality Issues of Wastewater Reuse/Recycling Despite a long history of wastewater reuse in many parts of the world, the question of safety of wastewater reuse still remains an enigma mainly because of the quality of reuse water. There always have been controversies among the researchers andproponents of extensive wastewater reuse, on the quality the wastewater is to meet. Ingeneral, public health concern is the major issue in any type of reuse of wastewater, beit for irrigation or non-irrigation utilization, especially long term impact of reuse practices . It is difficult to delineate acceptable health risks and is a matter that is stillhotly debated.
Posted on: Wed, 03 Jul 2013 01:34:54 +0000
Trending Topics
Recently Viewed Topics
© 2015