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<Proceedings of the International Symposium on Efficient Water Use in Urban Areas - Innovative Ways of Finding Water for Cities -> Session 3: Water Reuse for Non-potable Applications WASTEWATER REUSE FOR NON-POTABLE APPLICATIONS: Takashi Asano, Ph.D., P.E. ABSTRACT The role of wastewater reclamation and reuse in the context of efficient water use in urban areas is reviewed. Over the past few decades, the use of water increased rapidly and significantly. Frequent droughts, increasing water development costs, institutional and environmental concerns, and a growing conservation philosophy are key factors accounting for current surge of interest in wastewater reclamation and reuse throughout the world. Reclaimed water is, after all, a water resource existing right at the doorstep of the urban environment where water resources are needed most and priced the highest. Furthermore, reclaimed water provides a reliable source of water even in drought years because the generation of urban wastewater is affected little by drought. In this paper, fundamental concepts of wastewater reclamation and reuse are reviewed which include applicable wastewater treatment processes and operations, categories of water reuse, emphasizing the role of water reclamation and reuse in the context of more sustainable water resources development. In every wastewater reclamation and reuse operation, however, there is some risk of human exposure to infectious agents. Because of the public health concerns, special attention is paid to wastewater treatment systems that are capable of producing essentially pathogen-free effluent for variety of beneficial uses. Finally, regulatory aspects of wastewater reuse in developing countries are discussed. KEYWORDS Pathogens, planning, public health, water quality regulations, water resources, wastewater reclamation and reuse, wastewater treatment. INTRODUCTION As the worldwide demand for water increases, wastewater reclamation and reuse have become increasingly important in water resources management by allowing a water supply agency to plan for increasing long-term water supply reliability in agriculture, industry, and municipality. In industrialized countries, there are growing problems of providing dependable water supply, and municipal and industrial wastewater disposal. In developing countries, particularly those in arid parts of the world, there is a need to develop economically feasible new water supplies and protect existing water sources from pollution. The water pollution control efforts in many countries have made treated effluent available that may be an economical augmentation to the existing water supply when compared to the increasingly expensive and environmentally destructive new water resources development. However, wastewater reuse is only one alternative in planning to meet future water resources needs. Water conservation, water recycling in industries, efficient management and use of existing water supplies, and new water resources development based on environmentally conscious watershed management are the examples of other alternatives. The advantages as well as motivating factors for wastewater reuse are identified as follows:
However, a common misconception in planning for wastewater reclamation and reuse is that reclaimed wastewater represents a low-cost new water supply. This assumption is generally true only when wastewater reclamation facilities are conveniently located near large agricultural or industrial users and when no additional treatment is required beyond the existing water pollution control facilities from which reclaimed water is delivered. The conveyance and distribution systems for reclaimed water represent the principal cost of most proposed water reuse projects. Recent experience in California indicates that approximately four million U.S. dollars in capital cost are required for each one million m3 per year of reclaimed water that made available for reuse. Assuming a facility life of 20 years and a nine percent interest rate, the amortized cost of this reclaimed water is about $0.45/m3, excluding O & M costs. Wastewater reclamation and reuse involves considerations of public health and also requires close examinations of infrastructure and facilities planning, wastewater treatment and plant siting, treatment process reliability, economic and financial analyses, and water utility management involving effective integration of domestic water supply and reclaimed wastewater distribution. Whether wastewater reuse will be appropriate in a community depends upon careful economic considerations, potential uses for the reclaimed water, stringency in environmental protection and waste discharge, and public policy wherein the desire to conserve rather than develop new water resources with considerable environmental impacts. Today, technically proven wastewater treatment or purification processes exist to provide water of almost any quality desired. Thus, wastewater reuse has a rightful place and an important role in optimal planning and more efficient management and use of water resources in many countries. Wastewater reclamation is the treatment or processing of wastewater to make it reusable, and water reuse is the use of treated wastewater for a beneficial use such as agricultural irrigation and industrial cooling. In addition, direct wastewater reuse requires existence of pipes or other conveyance facilities for delivering reclaimed water. Indirect reuse, through discharge of an effluent to a receiving water for assimilation and withdrawals downstream, is recognized to be important but does not constitute planned direct water reuse. In contrast to direct water reuse, water recycling normally involves only one use or user and the effluent from the user is captured and redirected back into that use scheme. In this context, water recycling is predominantly practiced in industry such as in pulp and paper industry (Metcalf & Eddy, 1991). WASTEWATER TREATMENT TECHNOLOGIES FOR WATER REUSE In evaluating wastewater reclamation technologies, the overriding considerations are the operational reliability of each wastewater treatment process and operation, and the overall capability of complete treatment system to provide a reclaimed water that meets established water quality standards and/or criteria. As a result, additional treatment processes and operations may be required in certain water reuse applications for removal of chemical contaminants and removal or inactivation of microbiological pathogens. In conventional wastewater treatment, the general terms used to describe different degrees of treatment, in order of increasing treatment level, are preliminary, primary, secondary, and tertiary/advanced treatment. A disinfection step for removal or inactivation of pathogenic organisms is often the final treatment prior to storage and distribution for reuse. Because of cost considerations, preliminary and primary treatment in developing countries, and secondary treatments in industrialized countries are generally considered as water pollution control requirements; the additional treatment required for water reuse is normally designated as tertiary or advanced wastewater treatment. The goal in designing a wastewater reclamation and reuse system is to develop integrated cost-effective process combinations that are capable of reliably meeting the water quality objectives required for wastewater reuse. Figure 1 shows a generalized view of wastewater treatment processes and operations as well as effluent reuse schemes. Based on water quality requirements, any effluent stream can be used as reclaimed water for various beneficial uses. The range of applicable technologies may include: 1) septic tanks, lagoons, wetland, and natural treatment systems, 2) secondary wastewater treatment systems, 3) advanced physical-chemical treatment, 4) advanced biological treatment including biological nutrient removal (BNR), 5) advanced oxidation processes, 6) membrane separation and membrane bioreactors, 7) disinfection technologies, and 8) innovative reactor designs such as sequencing batch reactors and advanced mixing devices. Figure 1. Generalized wastewater treatment processes and operations, and effluent reuse schemes (Adapted from Asano, Smith, and Tchobanoglous, 1985). Advanced treatment plays a critical role in the effective treatment of municipal and industrial wastewater to meet higher water quality objectives for water reuse and to protect public health. Conventional and advanced wastewater treatment consist of a combination of physical, chemical, and biological processes and operations to remove settleable, suspended, and dissolved solids, organic matter, metals, nutrients, and pathogens from wastewater. Most of the current wastewater reclamation and reuse technologies are essentially derived from those used in water and wastewater treatment. However, opportunities for adopting technological innovations are much greater for water reuse applications, because reclaimed water will have an economic value as an alternative water supply. Furthermore, contrary to the disposal of treated effluent, where federal or national regulations are enforced by “command and control” methods of water pollution control, water reclamation and reuse allow more flexibility in water quality management, and consequently more possibilities for adopting innovative technologies. Table 1 shows a summary of major unit operations and processes used for wastewater reclamation. At present, the dominant wastewater reuse applications, worldwide, are irrigation of agricultural lands, parks and golf courses. However, there has been considerable progress in reclaimed water applications in the urban setting such as toilet flushing, cooling, fire fighting, and stream flow augmentation. Furthermore, future use of reclaimed water may involve a completely controlled "pipe-to-pipe" system with an intermittent storage step, or it may include blending of reclaimed water with non-reclaimed water, either directly in an engineered system or indirectly through a surface water supply reservoir or a groundwater recharge scheme.
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