Conjunctive use of Inter-Basin Transferred and Desalinated Water in a Multi-Source Water Supply System Based on Cost-Benefit Analysis

Water shortage has forced coastal cities to seek multi-source water supply with a focus on inter-basin water and desalinated seawater. The differences of water supply costs pose a challenge in the optimal use of multiple water resources. This paper aims to understand the impact of desalinated seawater’s variable costs on multi-source water supply through a cost-benefit analysis method based on a multi-objective optimization model, considering different combination scenarios of desalination yield, streamflow condition, seawater desalting plant (SDP) scheme, water shortage index and utilization ratio of the SDP. The application in the coastal city Tianjin, China shows that the desalination yield has an impact on the tradeoff between the water shortage index and the total water supply cost and an optimal desalination yield can be determined at a turning point. And where the turning point appears is influenced by the utilization ratio of the SDP and streamflow conditions of inter-basin water. Moreover, a single centralized SDP is found to have an overall lower water supply cost than several decentralized small-sized SDPs. Lower water shortage index leads to higher cost, and the unit decrease of shortage index will need more added cost when the shortage index is very low. This method is proven to be effective in identifying the best conjunctive use of inter-basin water and desalinated seawater, which can contribute to relieve urban water shortage.     

The application of economic-engineering optimisation for water management in Ensenada, Baja California, Mexico.

Mathematical optimisation is used to integrate and economically evaluate wastewater reuse, desalination and other water management options for water supply in Ensenada, Baja California Mexico with future levels of population and water demand. The optimisation model (CALVIN) is used to explore and integrate water management alternatives such as water markets, reuse and seawater desalination, within physical capacity constraints and the region's water availability, minimising the sum of economic costs of water scarcity and operating costs within a region. The modelling approach integrates economic inputs from agricultural and urban water demand models with infrastructure and hydrological information, to identify an economically optimal water allocation between water users in Ensenada. Estimates of agricultural and urban economic water demands for year 2020 were used. The optimisation results indicate that wastewater reclamation and reuse for the city of Ensenada is the most economically promising alternative option to meet future water needs and make water imports less attractive. Seawater desalination and other options are not economically viable alone, but may have some utility if combined with other options for the Ensenada region.     

Desalination and water security in the US–Mexico border region: assessing the social,environmental and political impacts

In the western US–Mexico border region, both countries’ authorities look to desalination as a means to meet increased demands for dwindling supplies. In addition to several existing or planned desalination plants, plans exist to develop projects along Mexico’s coasts to convert seawater into freshwater primarily for conveyance and consumption in the United States. Even though desalination systems have the potential to increase water supply in the region, there are associated consequences, costs and constraints. To understand the impacts of such binational desalination systems, this paper assesses, through a water-security framework, the case of a proposed desalination plant on the Upper Gulf of California. The analysis suggests that for binational desalination systems, there are several key areas of impact against which the benefits of increased water supply must be weighed.     

滨海城市非常规水源供水规模优选

滨海地区河流源短流急、地表水资源开发难度大,将再生水、淡化海水等非常规水纳入滨海城市水资源统一配置是缓解水资源短缺矛盾的有效途径。考虑地表水等常规水资源丰枯不确定性,科学确定非常规水源工程建设规模,是实现常规与非常规水资源统一配置的关键。以威海市区为例,建立了考虑水库来水不确定性的海水淡化与再生水厂建设规模优选模型,采用多目标遗传算法进行求解,以可靠性、弹性和脆弱性为指标,评价整个供水系统的性能,并进行多方案比较。结果表明:2030规划水平年威海市区适宜的再生水和海水淡化规模分别为23和15万m3/d;在此规模下,威海市区的供水保证率可由63.8%提高到95.2%,多年平均供水成本为6.6亿元。研究结果可为区域供水规划提供决策参考。     

Use of flavour profile and consumer panels to determine differences between local water supplies and desalinated seawater.

The San Diego County Water Authority of California has initiated planning for coastal desalination facilities to augment their water supplies. Integration of the different water qualities from these facilities into existing pipelines must be achieved. This investigation determined whether, and to what degree, consumers can discriminate between desalinated seawater and imported water supplies and how these investigations can contribute to decision making regarding the need for construction of facilities to blend such supplies prior to delivery. Based upon the results of the flavour profile analysis panel and the consumer evaluation sessions, it was concluded that free chlorine versus chloramine disinfection or different concentrations of disinfectants did not significantly affect consumer perception of the taste and odour of desalinated seawater or blends with Colorado River water and State project water. Consumers were able to discern between desalinated seawater and imported water, preferring imported water when forced to make a choice. However, the investigators did not believe that the difference in consumer perception was significant enough to warrant special blending facilities to mitigate the relatively minor aesthetic quality differences between imported water supplies and desalinated seawater.     

Viability of increasing the tariff of freshwater for irrigation as a tool to stimulate wastewater reuse in the MENA region.

Despite water scarcity and high agricultural water demand in the Middle East and North Africa region, substantial proportions of treated wastewater are discharged into the environment and seas without proper utilization. All countries of the region, low pricing of reclaimed wastewater is a common tool to make reuse attractive. However, low pricing of reclaimed wastewater is ineffectual due to farmers' access to freshwater for irrigation at low tariff. Therefore, increasing the prices of freshwater in such a way that does not jeopardize feasibility of agriculture would promote irrigation with reclaimed wastewater even at increased prices. On one hand, it increases the gap between the price of freshwater and that of reclaimed wastewater, making the later more attractive. On the other hand, it would be used as a financial resource for funding the investment costs of the infrastructure needed for conveyance and distribution of reclaimed wastewater. This paper studies the viability of increasing the prices of freshwater and reclaimed wastewater. The results show that irrigation with reclaimed wastewater even for restricted irrigation can be as profitable as, and sometimes better than, freshwater irrigation. Some of the permitted crops such as fruit trees can be more profitable than vegetables. Thus, it appears that the level of knowledge farmers and others on the benefits of reclaimed wastewater is still limited.     

Issues and challenges of reclaimed water usage: a case study of the dragon-shaped river in the Beijing Olympic Park

Increased use of reclaimed water could be one of the solutions to Beijing’s growing water shortage, particularly for non-potable (e.g. landscaping) purposes. The dragon-shaped river, a large artificial waterscape built on the site of the 2008 Beijing Olympic games, offers a useful case study of the issues and challenges attendant on wastewater reclamation and reuse. Of particular interest is the use of phytoremediation techniques for bioremediation of nutrient loads. This article presents the results of ongoing monitoring which indicate that phytoremediation is succeeding in preventing eutrophication, though some challenges, notably management of aquatic biomass, remain.     

Reusing Urban Wastewater—An Alternative and a Reliable Water Resource

ABSTRACT

Fundamental concepts of reusing urban wastewater as an alternative and a reliable source of water supply are discussed, along with the categories for water reuse, planning methodologies, wastewater reclamation technologies, and economics. The rational basis for integration of urban reclaimed water into water resources planning is proposed and the safe use of reclaimed water is evaluated. Special attention is paid to tertiary or advanced wastewater treatment systems that are capable of producing essentially pathogen-free effluent for a variety of uses such as irrigation of urban landscape, flushing of toilets served by dual plumbing systems in large commercial buildings, and groundwater recharge for eventual potable reuse. The motivating factors for wastewater reclamation and reuse are summarized and the costs of water reclamation projects are discussed with several examples. The integration of this alternative water supply into water resources planning is proposed and the safe use of reclaimed water is emphasized.     

Optimization Approach to Designing Water Supply Systems in Non-Coastal Areas Suffering from Water Scarcity

This article presents a novel optimization approach to designing water supply systems in non-coastal areas with water scarcity. In such areas, high water demand caused by population increases and economic development can only be satisfied with seawater supply. Furthermore, most of the non-coastal users are located at long distances and sometimes at altitudes very diverse from the coastline, meaning long pipelines and several pumping stations will be required to effectively supply water. The proposed optimization approach based on a mixed integer nonlinear programming model offers optimal designs of water supply systems from an economic and technical perspective. It determines the location and size of desalination plants and the design of the water transport network including pipelines of specified length and diameter and pumping stations that minimize capital and operational costs of the whole system. A case study in a hyper-arid region of Chile was used to validate the applicability of the proposed model and the results show its aptitude for determining global optimal solutions to real-scale problems.     

The water reclamation and reuse project of El Prat de Llobregat, Barcelona, Spain.

Water reclamation and reuse have become essential components of water resources management in the Metropolitan Area of Barcelona, by helping to develop additional water resources in the lower Llobregat River, one of its main sources of water supply. By generating a reliable flow of 300,000 m3/day of high quality reclaimed water, the options available for integrated water resources management have widely expanded to allow in-stream river water substitution, restoration of natural wetland areas, agricultural irrigation, and supply to a seawater intrusion barrier. Those management options have been possible thanks to the implementation of an extensive water distribution system that allows distribution of reclaimed water to a point 15 km upstream of the reclamation facility, and to a seawater intrusion barrier within a few kilometres of the plant. The cost of producing reclaimed water using a physico-chemical process (0.05 euro/m3) and the investment required for such a facility (0.21 euro/m3 annual capacity) are very close to those of similar large scale projects in Spain. However, higher degrees of treatment, such as demineralization for agricultural irrigation and for injection into a seawater intrusion barrier, result in considerable increases of both water reclamation cost and investment costs.     

Heat island mitigation using water retentive pavement sprinkled with reclaimed wastewater.

In Japan, reclaimed wastewater has been recycled widely for non-potable urban applications and it is to be used for sprinkling roads to mitigate heat island in urban areas. To assess the heat island mitigation effects of the sprinkling reclaimed wastewater on water retentive pavement, we carried out a survey at Shiodome-District, Tokyo. The temperatures of air and roads, humidity, and WBGT (Wet-bulb globe temperature) were measured and heat flux was estimated to compare the condition of the areas with/without sprinkling. The following results were obtained. 1) Sprinkling reclaimed wastewater decreased the road surface temperature by 8 degrees during the daytime and by 3 degrees at night: temperatures equal to those on planting zones. Nevertheless sprinkling was done only in the daytime, the temperature decrease effect was not only obtained during the daytime: it continued through the night, due to the water retentive pavement. 2) Sprinkling reclaimed wastewater reduced the amount of sensible heat flux and increased that of latent heat flux. These results suggest that sprinkling reclaimed wastewater on water retentive pavement can effectively mitigate the heat island phenomenon.     

Urban Water Management in Developing Arid Countries

Urbanization, industrialization and rapid population growth in developing countries of the Arabian Peninsula are putting increasing pressure on local water authorities and water planners to satisfy the growing urban water and sanitation demands. In the Arabian Peninsula, water resources are limited, average rainfall is low and the seawater and brackish water desalination in addition to limited groundwater resources are the major water supply sources. The population increased from about 17.688 million in 1970 to 38.52 million in 1995 and is expected to reach 81.25 million in 2025. The urban population is expected to rise from 60% in 1995 to more than 80% in 2025. The domestic water demand is expected to rise from 2863 million cubic metres (MCM) in 1990 to about 4264 MCM in 2000 and 10580 MCM in 2025. In Saudi Arabia, the population increased by 143.6% between 1970 and 1995; and it is expected to reach about 40.426 million in 2025, with about 80% urban population. The domestic water demand in the Kingdom is expected to be about 2350 MCM in 2000 and 6450 MCM in 2025. Specialized agencies have been established for water production and distribution, and for wastewater collection, treatment and reuse. Special legislation has been introduced to manage water demands and to protect the interests of the community and its natural resources. Fifty-seven costly desalination plants have been constructed in the Peninsula on the Gulf and Red Sea coasts, as well as water transmission lines to transport the desalinated water to coastal and inland major cities. The seawater desalination unit cost is about US$0.70/m 3 for a large desalination plant with energy priced at world prices. More than $30 billion has been invested on water and sanitation projects. Present desalination production is about 46% of the total domestic demand, and the rest is pumped from deep and shallow aquifers. In general, fragmented legislation and institutional arrangements and low water charges have indirectly resulted in over-usage of domestic water, production of excessive quantities of wastewater, significant leakage, and enhancement of shallow water-table formation and rise in some cities. Facing the challenges of satisfying the growing urban water demands requires several essential measures such as: (a) introduction of new technologies to reduce water demands, and losses, and to enhance wastewater recycling and water conservation; (b) the updating of legislation to coordinate both responsibilities and actions among different water agencies; (c) the introduction of a strong and transparent regulatory framework to adopt different forms of water supply privatization, to reduce the costs of building, operation and maintenance of water and sanitation facilities, and to improve the level of services and billing, leakage and wastewater collection and treatment; (d) an increase in water tariffs to reflect the actual value of the water, and to enhance the awareness of public as to the value of water; and (e) development of short-term and long-term national water plans based on realistic water demand forecasting.     

Comparative Evaluation Of Surface Water Availability,Wastewater Reuse And Desalination In Saudi Arabia

ABSRTACT

There is a growing concern in the Kingdom of Saudi Arabia to exploit water resources of acceptable quality to meet demands in domestic, industrial, and agricultural sectors. The agricultural water need, which constitutes approximately 84% of the total demand, was estimated to be 7430 million cubic meters in 1985. The annual domestic and other demands amounted to 1400 million cubic meters for 1985. Various alternative supplies to meet these demands are surface water, renewable groundwater resources, reclaimed wastewater, desalinated water, and non-renewable groundwater. Due to excessive withdrawal of water from deep aquifers, considerable drawdown has recently been noticed.

This paper reviews the existing and future trends in developing surface water resources, reclamation of waste-water from various towns and cities and its use, and the role of desalination plants in the coastal regions of the Arabian Gulf and Red Sea. These alternatives are evaluated and compared in economic terms. Cost-capacity relationships are developed for various alternatives which will be used in developing long-term plans for optimum allocation of available resources in different parts of the Kingdom.     

The Optimal Reuse of Reclaimed Water: A Mathematical Model Analysis

As recycling effluent from municipal sewage plants is technically a feasible way, this paper presents a mathematical model to analyze the extent to which effluent should be reclaimed for industrial use and examine the factor affecting reuse of reclaimed water. The resulting data shows that the low price of fresh water leads to reduced use of reclaimed water and impedes the investment of the effluent purification plant. A mandated regulation on the substitution rate of reclaimed water is suggested to impose on the industry. Theoretically, the optimal substitution rate as well as the water quality is determined by maximizing the total social welfare that results from the construction of conveyance channels and effluent purification plants. A case example is employed to derive the optimal substitution rate and water quality of reclaimed water. Through the numerical analysis, an effluent plant for treating 20,000 kl/day effluent with the substitution rate of 21.24 % is selected as the optimal solution.     

城市再生水利用输水形式分析研究

近年来再生水已经成为北京市水资源的重要组成部分。为了保证再生水利用输水方案合理可行,安全可靠,文中以永定河再生水供水北线工程为例,首先通过大量的调研、实地踏勘,充分了解工程区间情况,完成了明渠输水和管道输水方案,并对两方案工程内容、湿地方案、工程投资、工程实施难度、水质水量保障、水环境和原有工程功能影响分析、工程管理及汛期输水保障等方面进行了详细的分析研究。经比选,虽然明渠方案具有增加沿线河道水面,改善区域生态环境的优点,但存在对北京市自来水第三水厂水源地造成水质污染风险,与区域蓄滞洪功能矛盾,汛期输水调度管理难度大,工程投资高等问题,因此推荐采用管道输水方案。本文提出的再生水明渠输水和管道输水形式的分析论证可供类似城市再生水利用输水方式的选择参考。     

基于成本加成的再生水阶梯定价方法研究

再生水作为城市的第二水源,能有效缓解水资源危机。以再生水管网建设的资金回收为前提条件,运用成本加成的方法,确定用户使用再生水的成本价格与需求量、输水距离之间的函数关系,并根据用户与水厂之间的距离划分不同的用户群;进而针对用户群内用户需求量的差异,采用阶梯定价的方法对再生水的价格制定进行研究,建立了基于再生水用户需水量、输水距离等因素的复合阶梯定价模型。最后,以西安市第二污水处理厂为例,运用模型计算其用户-西郊热电厂的再生水使用价格,验证了此定价模型的准确性与实用性,为再生水价格市场化发展提供了理论依据。     

Estimating willingness to pay for desalinated seawater: the case of Djerba Island,Tunisia

Water scarcity can be a growth-limiting factor. Non-conventional water resources, such as desalinated water, represent an alternative means of guaranteeing access to water while reducing water stress. In this study, a contingent valuation survey carried out in Djerba Island, Tunisia, allows the joint modelling of two decisions: societal support for the construction of a desalination plant and households’ willingness to pay for desalinated water. To the best of the authors’ knowledge, no study to date has addressed this relationship. We find that although a clear majority of households are in favour of using desalinated water, far fewer are willing to pay for it. The article concludes that it is worth studying willingness to pay for desalinated water in developing countries in order to avoid investing in projects where it is doubtful that costs will be recouped.     

我国海水利用现状、问题及发展对策研究

为解决淡水资源短缺、应对水资源危机,世界许多沿海国家及地区积极开展海水淡化和综合利用,为解决区域水资源短缺问题找到了一条有效途径。近年,我国沿海地区水资源短缺形势日益严峻,如何利用海水资源有效缓解水危机是我国长期以来十分关注的问题。从我国的基本国情水情出发,分析海水资源化利用的发展现状,分析海水利用发展过程中存在的问题及原因,在借鉴国外海水利用经验的基础上,分析我国海水淡化和综合利用的发展潜力、重点区域与领域布局,并提出促进海水利用发展的对策建议,为相关部门加强海水淡化和综合利用管理提供决策参考。     

Reasons for the Fast Growing Seawater Desalination Capacity in Algeria

Seawater/brackish water desalination has been widely adopted by the Algerian Government in the last few years to supply potable water to municipality for various purposes mainly for domestic and industrial uses especially in areas where demand is high due to shortage of fresh water resources, rapid population growth and development of industry and tourism. Ten years ago, desalination was confined to the industrial use only especially in oil and gas industry as the country was relying on rain water and other available sources to supply fresh water to municipalities. Due to chronic drought conditions, the Ministry of Water Resources reviewed the national water strategy and a strong option for desalination was adopted where an ambitious program was thus put into action. Sixteen mega-plants, with capacities ranging from 100,000 to 500,000 m³ per day, primarily based on Reverse Osmosis technology, were launched in the last few years making the Algerian desalination program one of the world’s fastest growing markets. Five desalination plants, including the Africa’s largest seawater reverse osmosis project with a total capacity of 200,000 m³ per day, are already in operation and the remaining projects are either under construction or in commissioning. An integrated water resources management was also adopted as additional option to cuter the increasing water demand as there is also a great potential for water reuse and conventional water treatment. An additional benefit of this would be reducing the volume of treated wastewater disposed into the environment.     

Responding to water challenges in Greece through desalination: energy considerations

Abstract

Desalination technology, and reverse osmosis in particular, is used by several island authorities in Greece to address water scarcity. However, this is a highly energy-intensive technique, requiring the consumption of significant quantities of fossil fuels. The case of Syros Island is presented, to demonstrate the strong water–energy link in the operation of desalination plants. The article also discusses the use of renewable energy sources as a means for reducing the energy intensity of desalination.