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.     

浅谈再生污水地下回灌的健康危害风险

针对目前污水再生利用越来越广泛的现状,探讨了再生污水的健康危害风险评价方法,分析了非饮用回用及饮用回用时要注意的问题和对策。并对北京高碑店污水处理厂二级生化出水经深度处理地下回灌后用作饮用回用的健康危害风险进行了实例分析评价。     

Integrated Management of Non-conventional Water Resources in Anhydrous Islands

Anhydrous islands are dependent either on non-conventional water resources, such as desalinated seawater or reclaimed water from wastewater, or on water importation from the mainland. The latter option is often expensive and non-sustainable. Desalinated water can be used for potable and non-potable water applications, while reclaimed water can be used for non-potable water applications. Thus all water needs can be satisfied by an optimal blend of desalinated and reclaimed water. It is important to calculate the optimal capacities and locations of seawater desalination plants, wastewater treatment plants and water reclamation plants, and to estimate the water/wastewater conveyance system, in order to minimise water production and distribution costs. Mathematical modelling and optimisation techniques can be employed for calculating the optimum scenario: the satisfaction of all water needs at minimum cost. In this article, we have estimated the water demands taking into account water quality for the anhydrous Greek island of Syros, in the Aegean Sea. Syros has been subdivided into 6 regions, taking into account geographical and population distribution criteria. All water needs are to be satisfied by desalinated seawater and reclaimed water. A mixed-integer linear programming algorithm is used here to calculate the optimal scenario (location and capacities of desalination plants and wastewater treatment and water reclamation plants, as well as the desalinated water, reclaimed water and wastewater conveyance infrastructure needed) by minimising the annualised total cost including capital and operating costs.     

The effect of reclaimed wastewater on the quality and growth of grapevines

The effect of the use of treated wastewater on the growth of cabernet sauvignon and merlot grapes from the Guadalupe Valley, Mexico was evaluated. Secondary advanced effluent was used to irrigate the grapevines at a rate of 66 L/vine/week. Wastewater quality results confirmed that all parameters complied with Mexican legislation for crop irrigation as well as reuse in activities in which the public would be in direct or indirect contact with the reclaimed water. Results showed that the number of leaves per shoot and the overall biomass increased in plants irrigated with wastewater and grape production per plant was 20% higher. The concentration of carbohydrates, organic acids and pH were similar in grapes from vines irrigated with wastewater to those irrigated with groundwater. Throughout the experiment, no fecal coliform bacteria were detected in the cultivated grapes. The wastewater caused an increase in the biomass of the grapevines and there was no presence of microbial indicators in the final product so a higher wine production could be achieved without an increase in health risk related problems. If 200 L/s of reclaimed wastewater would be returned to be used for grapevine irrigation in Valle de Guadalupe (the same amount that is currently being sent as drinking water to Ensenada), assuming an irrigation application of 6,000-7.500 m3/ha/year, approximately 837-1046 hectares (ha) of grapevines could be irrigated. Part of ongoing research includes an economical analysis of the best options for Ensenada and the Valle de Guadalupe in order to establish the optimum volume of water to be returned, the cost of its transportation, as well as the cost of irrigation.     

The membrane biofilm reactor: the natural partnership of membranes and biofilm.

Many exciting new technologies for water-quality control combine microbiological processes with adsorption, advanced oxidation, a membrane or an electrode to improve performance, address emerging contaminants or capture renewable energy. An excellent example is the H2-based membrane biofilm reactor (MBfR), which delivers H2 gas to a biofilm that naturally accumulates on the outer surface of a bubbleless membrane. Autotrophic bacteria in the biofilm oxidise the H2 and use the electrons to reduce NO3-, CIO4- and other oxidised contaminants. This natural partnership of membranes and biofilm makes it possible to gain many cost, performance and simplicity advantages from using H2 as the electron donor for microbially catalysed reductions. The MBfR has been demonstrated for denitrification in drinking water; reduction of perchlorate in groundwater; reduction of selenate, chromate, trichloroethene and other emerging contaminants; advanced N removal in wastewater treatment and autotrophic total-N removal.     

Strategien und Potenziale zur Energieoptimierung bei der Wasserwiederverwendung

The energy and materials derived from treating sewage are becoming increasingly important worldwide and are thus progressively considered resources rather than a disposal problem. This is also apparent in the growing interest in recycling water from municipal wastewater for both non-potable and potable purposes, supplementing the drinking water supply in the latter case. However, the energy consumption of about 0.9–1.8 kWh/m³, required to recycle drinking water, is not insignificant. Due to the lack of national as well as international standardized regulatory specifications for recycled water quality, very different technical solutions for potable water reuse have been deployed worldwide. Therefore, energy-saving measures often can only be applied to internal operational optimizations and the achievable savings are rather limited. Strategies for integrated energy recovery, the increased use of anaerobic biological processes and combined heat and power (CHP) for water recycling are hence very promising. These provide opportunities for internal power provision and therefore options to reduce the specific energy requirements for potable water reuse to well below 1 kWh/m³, despite the necessary treatment processes. However, the greatest potential for energy-efficient water recycling is at the regional planning level. Recycling water is only attractive where local freshwater resources are insufficient or there is a dependency on imported water, and it is the significantly more cost-effective option than the treatment of brackish or sea water.     

Interbasin water transfers at the US–Mexico border city of Nogales,Sonora: implications for aquifers and water security

Nogales, Sonora, on the US–Mexico border, employs interbasin water and wastewater transfers to address water scarcity in the context of a rising population, a warming climate, and cross-border institutional asymmetries. A unique feature of its geography and border context is Nogales's export of wastewater both north to the US and, starting with the August 2012 commissioning of a strategically positioned wastewater treatment plant, south to the Alisos basin, which is its principal drinking-water source. Thus, when the new plant is fully operational, it will result in indirect potable reuse of effluent via recharge of the source-water aquifer. This paper finds that such strategies contribute to increased water scarcity in Nogales, and to detrimental health, livelihood and environmental impacts in the source basin, thus raising questions about interbasin transfers as a principal water management strategy.     

Technical and Environmental Sustainability Assessment of Water Distribution Systems

An environmental and technical sustainability assessment methodology is developed for both centralized and dual water distribution systems (WDSs) with and without fire flow scenarios. Technical sustainability of potable and reclaimed water networks is measured by a sustainability index (SI) assessment using reliability, resiliency, and vulnerability performance criteria. The U.S. Environmental Protection Agency EPANET software is used to simulate hydraulic (i.e. nodal pressure) and water quality (i.e. water age) analysis in a WDS. Total fresh water use and total energy intensity are considered as environmental sustainability criteria. The procedure considers two separate alternatives for meeting fire flows: (1) adding pumping to a system or (2) adding a non-potable WDS. The reclaimed system is designed using linear programming (LP) optimization. For each alternative, multi-criteria decision analysis (MCDA) is used to combine technical and environmental sustainability criteria for an urban WDS.     

Helminth eggs removal by microscreening for water reclamation and reuse.

Irrigation with reclaimed water is becoming a practical alternative to conventional irrigation in semi-arid areas of the Mediterranean like Spain, but it requires a reliable treatment process to provide a safe water supply. Helminth eggs are one of the main concerns for the safe use of reclaimed water, as they can survive adverse environmental conditions and they are highly infective. Spanish water quality criteria and International guidelines set a limit of 0.1 eggs/l for water uses with unrestricted human exposure. Two microscreening processes have been tested to determine their potential for helminth eggs removal, after a conventional physic-chemical reclamation process. Hydrotech Drum and Discfilters, provided with 10 microm pore size filter cloth, were tested to determine their efficiency for helminth eggs straining. An experimental test was conducted using 20 microm spherical latex particles, as surrogates for helminth eggs, to test the removal efficiency of a small full-scale drumfilter. In a subsequent laboratory test, actual Trichuris suis eggs were strained using a 10 microm pore size filter cloth from a discfilter. Results from both tests indicate that drum and discfilters are able to achieve 99% removal efficiency for spherical latex particles and a complete removal for helminth eggs in reclaimed water.     

A critical evaluation of combined engineered and aquifer treatment systems in water recycling.

Australian experience at five research sites where stormwater and reclaimed water have been stored in aquifers prior to reuse, have yielded valuable information about water treatment processes in anaerobic and aerobic aquifers. One of these sites is the stormwater to potable water ASTR project at the City of Salisbury, a demonstration project within the broader EC project 'RECLAIM WATER'. A framework for characterising the effectiveness of such treatment for selected organic chemicals, natural organic matter, and pathogens is being developed for inclusion in new Australian Guidelines for Management of Aquifer Recharge. The combination of pre-treatments (including passive systems such as reed beds) and aquifer treatment effectiveness in relation to source waters and intended uses of recovered water will be described. Advantages and disadvantages of various types of pre-treatments in relation to effectiveness and sustainability of managed aquifer recharge will be discussed taking account of aquifer characteristics. These observations will be consolidated into a draft set of principles to assist in selection of engineered treatments compatible with passive treatment in aquifers.     

The water framework directive -can we reach the target?

The WFD is an overarching piece of legislation that aims to harmonize existing European water policy; since 2000 it requires managing the river basins so that the quality and quantity of water does not affect the ecological services and to promote sustainable water use of any specific water body. Nevertheless the goals of other directives, such as drinking water, bathing water and urban wastewater treatment (UWWT), are not yet harmonised mainly concerning microbiological and PS/PSR/PHS contamination. Great challenges are due to emerging contaminants especially the technical improvement and harmonisation for risk identification and risk assessment: for biological effects and for chemical analysis and, finally integrate this knowledge to preserve the "good status". The methodologies implemented have as aim the identification of acceptable or unacceptable risks. This identification provides the basis for the regulatory decisions, which follow from the risk assessment. After priority setting the UWWT needs to be adjusted and existing or new treatment options should comply with the requirements of the different directives. This will be another step on the way to reach the targets given in EU water legislation and in the achievements of millennium development goals.     

The role of physical-chemical treatment in wastewater reclamation and reuse

Amid the heightened public health concerns for emerging microorganisms such as cryptosporidium and enteropathogenic E. coli in the water environment, there have been many instances where optimization of chemical coagulation-flocculation processes and filtration of wastewater was not achieved in practice, resulting in waste of coagulant chemicals and breach of the multiple barriers to pathogen removal and inactivation; thus, unnecessarily endangering public health. In addition, lack of information on the optimization of these processes has hampered the establishment of alternative and more cost-effective wastewater reclamation methods for tertiary and advanced wastewater treatment.Thus, the purpose of this paper is to evaluate the basic factors affecting the optimization of chemical coagulation-flocculation and filtration processes in municipal wastewater reclamation and reuse, based on the theoretical developments and practical applications. Reference is also made to the wastewater treatment processes and operations that can produce reclaimed water with an extremely small probability of enteric virus contamination.     

Chihuahua: a water reuse case in the desert.

Water supply for all kind of uses in Chihuahua is mainly groundwater. During the last decade this city has been damaged with a heavy hydrologic crisis because of a persistent drought. This came up with the overexploitation of groundwater aquifers; therefore a deficit between demand and offer was done. To minimize this problem the government authorities have started an integral plan of optimizing hydrologic resources which considers the treatment of wastewater and the use of reclaimed water. The secondary wastewater treatment facility of the city treats about 30,000 m3/d of a wastewater with high organic contents, and produces an effluent with low concentration of suspended solids, organic matter, fats, detergents, and metals. Reclaimed water is conveyed toward strategic sites for the irrigation of great green areas in sport clubs, educational institutions and industrial zones, besides of its utilization on some manufacturing processes, road service, and also over construction industry. The potential reuse of this water goes farther from those activities; the treatment of the secondary effluent until the required levels of the water-bearing recharge criteria are met for drinking water supply is considered as the next step to achieve through a suitable planning strategy for the best integral resource advantage.     

城市再生水利用风险评价指标体系初探

水的再生利用是破解我国水资源短缺问题的重要途径之一,但是再生水利用对人体健康和环境的影响也是生活污水处理必须面对的挑战,从而受到人们普遍关注。根据我国再生水回用途径和天津市纪庄子再生水厂的出水水质情况,构建了再生水利用风险评价指标体系(包括健康风险指标和生态环境风险指标),并对纪庄子再生水厂的出水与景观用水和地表水分别进行了风险评价,得出再生水用在不同用途时存在的不同环境风险。     

Managed aquifer recharge using quaternary-treated wastewater: an economic perspective

An excess of 31 million m³/y of tertiary-treated wastewater is expected in Muscat, Oman, by 2015. This paper addresses the technical and cost estimation of managed aquifer recharge after reverse-osmosis treatment. The results indicate that the project is appealing from an economic perspective. The total cost varies between USD 0.353 and USD 0.550 per cubic metre, depending on the cost of electricity, the interest rate and the life span of the project. The project may face rejection from domestic users, who may be unwilling to accept mixing treated wastewater with the current water supply due to health risks. An alternative to indirect potable reuse is the installation of a separate network to service industrial users.     

Screening health risk assessment of micropullutants for indirect potable reuse schemes: a three-tiered approach.

Indirect potable reuse schemes are an important consideration in the sustainable management of scarce water resources. However, communities still hold real concerns about the potential health risks of micropullutants in recycled water entering their potable water supply. Microfiltration or ultrafiltration followed by reverse osmosis is currently the standard treatment technology for potable use of recycled water. Nevertheless, membranes are not 100% efficient in the removal of trace organic contaminants and the potential health risks of these micropullutants need to be assessed. The aim of this paper is to present a three-tiered approach for the preliminary assessment of micropullutants in recycled water. A risk quotient is calculated by comparing measured concentrations against benchmark values. Tier 1 corresponds to regulated chemicals; the maximum contaminant level in drinking water is used as benchmark value. Tier 2 corresponds to unregulated chemicals with toxicity information; slope factors or risk specific doses are used to calculate benchmark values. Tier 3 corresponds to unregulated chemicals without toxicity information. The "Threshold of Toxicological Concern" concept is used to calculate benchmark values. The characterization of chemicals of concern following reverse osmosis in a water reclamation plant and the application of the three-tiered approach for the evaluation of the potential health risks is presented.     

Research on wastewater reuse planning in Beijing central region.

The need to implement wastewater reuse in Beijing is discussed. Based on the investigation of the built wastewater reuse projects in Beijing, the differences between small wastewater reuse system and large systems were analyzed according to the technical, economical and social issues. The advantages and disadvantages of the small system and the large system were then given. In wastewater reuse planning in Beijing urban region, the large system was adopted. The rations of reclaimed water for difference land use type, including industrial reuse, municipal reuse, grass irrigation, and scenes water reuse were determined. Then according to the land use information in every block in central Beijing, using GIS techniques, the amounts of the reclaimed water needed in every block were calculated, and the main pipe system of reclaimed water was planned.     

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.     

完善中水利用管理政策的探讨

针对我国再生水回用行业在管理中存在的问题,提出相应的对策和建议.制定和完善污水回用的政策法规体系;完善技术规范标准;确定合理的价格体系,政府应给予污水处理行业优惠的政策,建立奖惩激励制度;改变运营机制,使污水处理行业由事业型向经营型转变;建立统一协调的管理机制.     

Economic considerations and decision support tool for wastewater reuse scheme planning.

The reuse of upgraded wastewater for beneficial uses is increasingly adopted and accepted as a tool in water management. However, funding of schemes is still a critical issue. The focus of this paper is on economic considerations of water reuse planning. A survey of pricing mechanisms for reclaimed water revealed that most schemes are subsidised to a great extent. In order to minimise these state contributions to the implementation and operation of reuse projects, their planning should identify a least cost design option. This also has to take into account the established pricing structure for conventional water resources and the possibility of gaining revenues from reclaimed water pricing. The paper presents a case study which takes into account these aspects. It evaluates different scheme designs with regard to their Net Present Value (NPV). It could be demonstrated that for the same charging level, quite different amounts of reclaimed water can be delivered while still producing an overall positive NPV. Moreover, the economic feasibility and competitiveness of a reuse scheme is highly determined by the cost structure of the conventional water market.