Human- and infrastructure-associated bacteria in greywater

Greywater, the wastewater from sinks, showers and laundry, is an understudied environment for bacterial communities. Most greywater studies focus on quantifying pathogens, often via proxies used in other wastewater, like faecal indicator bacteria; there is a need to identify more greywater-appropriate surrogates, like Staphylococcus sp. Sequencing-based studies have revealed distinct communities in different types of greywater as well as in different parts of greywater infrastructure, including biofilms on pipes, holding tanks and filtration systems. The use of metagenomic sequencing provides high resolution on both the taxa and genes present, which may be of interest in cases like identifying pathogens and surrogates relevant to different matrices, monitoring antibiotic resistance genes and understanding metabolic processes occurring in the system. Here, we review what is known about bacterial communities in different types of greywater and its infrastructure. We suggest that wider adoption of environmental sequencing in greywater research is important because it can describe the entire bacterial community along with its metabolic capabilities, including pathways for removal of nutrients and organic materials. We briefly describe a metagenomic dataset comparing different types of greywater samples in a college dormitory building to highlight the type of questions these methods can address. Metagenomic sequencing can help further the understanding of greywater treatment for reuse because it allows for identification of new pathogens or genes of concern.     

Comparative life cycle sustainability assessment of urban water reuse at various centralization scales

Purpose

Population growth and urbanization lead to increasing water demand, putting significant pressure on natural water sources. The rising amounts of domestic wastewater (WW) in urban areas may be treated to serve as an alternative water source that may alleviate this pressure. This study examines sustainability of utilizing reclaimed domestic wastewater in urban households for toilet flushing and garden irrigation. It models a city characterized by water scarcity, using a coal-based electricity mix.

Methods

Four approaches were compared: (0) Business-as-usual (BAU) alternative, where the central WW treatment plant effluent is discharged to nature; (1) central WW treatment and urban reuse of the effluent produced; (2) semi-distributed greywater treatment and reuse, at cluster scale; (3) Distributed greywater treatment and reuse, at building scale. Environmental life cycle assessment (LCA), social LCA (S-LCA), and life cycle costing (LCC) were applied to the system model of the above scenarios, with seawater desalination as the source for potable water. System boundaries include water supply, WW collection, and treatment facilities. Analytical hierarchy process (AHP), a multi-criteria decision analysis (MCDA) methodology, was integrated into the life cycle sustainability assessment (LCSA) framework as a means for weighting sustainability criteria through judgment elicitation from a panel of 20 experts.

Results and discussion

Environmentally and socially, the two distributed alternatives perform better in most impact categories. Socially, semi-distributed (cluster scale) reuse is somewhat advantageous over the fully distributed alternative (building scale), due to the benefits of community engagement. Economically, the cluster-level scenario is the most preferable, while the building-scale scenario is the least preferable. A hierarchical representation of the problem’s criteria was constructed, according to the principals of AHP. Each criterion was weighted and those of extreme low importance were eliminated, while maintaining the integrity of the experts’ judgments. Weighted and aggregated sustainability scores revealed that cluster level reclamation, under modeled conditions, is the most sustainable option and the BAU scenario is the least sustainable. The other two alternatives, centralized and fully distributed reclamation, obtained similar intermediate scores.

Conclusions

Distributed urban water reuse was found to be more sustainable than current practice. Different alternative solutions are advantageous in different ways, but overall, the reclamation and reuse of greywater at the cluster level seems to be the best option among the three reuse options examined in this assessment. AHP proved an effective method for aggregating the multiple sustainability criteria. The hierarchical view maintains transparency of all local weights while leading to the final weight vector.

     

Quantification of diarrhea risk related to wastewater contact in Thailand

Wastewater reuse contributes to closing the nutrient recycling loop as a sustainable way of managing water resources. Bangkok has over a thousand man-made drainage and irrigation canals for such purposes. Its use for agricultural and recreational purposes has a long tradition in rural and peri-urban areas. However, the continuation of these practices is increasingly questioned since potential health risks are an issue if such practices are not appropriately managed. The microbial and chemical quality of canal water has considerably deteriorated over the last decade, mainly because of discharged, untreated domestic and industrial wastewater. It is important to understand the health risks of wastewater reuse and identify risky behaviors from the most highly exposed actors promote the safe use of wastewater. This study assessed diarrhea infection risks caused by the use of and contact with wastewater in Klong Luang municipality, a peri-urban setting in Northern Bangkok, using quantitative microbial risk assessment. Wastewater samples were collected from canals, sewers at household level, and vegetables grown in the canals for consumption. Samples were also collected from irrigation water from the agricultural fields. Two protozoa, Giardia lamblia and Entamoeba histolytica, were quantified and analyzed by real-time PCR, exposure assessment was conducted, and finally, the risk of infection due to contact with wastewater in different scenarios was calculated. The results showed that canal water and vegetables were heavily contaminated with G. lamblia and E. histolytica. Infection risk was high in tested scenarios and largely exceeded the acceptable risk given by WHO guidelines.     

Anaerobic Treatment in Decentralised and Source-Separation-Based Sanitation Concepts

Anaerobic digestion of wastewater should be a core technology employed in decentralised sanitation systems especially when their objective is also resource conservation and reuse. The most efficient system involves separate collection and anaerobic digestion of the most concentrated domestic wastewater streams: black or brown water and solid fraction of kitchen waste. Separate collection using minimal amount of transport water besides saving this resource allows to apply a targeted treatment. A relatively small volume of digested effluent can be directly reused for fertilisation or processed when a high quality product is required. Clean nutrient production requires advanced multi-step treatment but the quality of products is risk-free. The issue of organic micro-pollutants and their accumulation in the environment is recently often addressed. Anaerobic treatment of total domestic wastewater stream can be applied as well. Treated in this way wastewater can be discharged or used for irrigation or fertilisation. The post-treatment will be usually required and its rate of complexity depends on the anaerobic effluent quality and local requirements for final effluent quality. A variety of technological solutions for treatment of domestic wastewater streams and reuse of resources is discussed in this paper.     

Potential changes in soil properties following irrigation with surfactant-rich greywater

The use of insufficiently treated greywater (GW) for irrigation is becoming increasingly common, a practice mistakenly considered safe. Concentrations of surfactants found in greywater effluents range from 0.7 to 70 mg L⁻¹ and on average are higher than concentrations in raw domestic wastewater. However, there is little information regarding the environmental impact of surfactants. Pollutants such as boron, salt, and faecal coliforms are also commonly found in greywater but are not the focus of this study. The capillary rise in sand that was pre-treated with a laundry detergent solution was lower than that in sand pre-treated with fresh water, and exhibited hydrophobic properties. As with the capillary rise, a flow pattern typical of hydrophobic soil was noted when the imbibition of fresh water into sands pre-treated with laundry detergent solution was tested. It is suggested that surfactant accumulation in the soil due to greywater irrigation can create water-repellent soils, thereby affecting their flow patterns and productivity.     

Current research trends on microplastic pollution from wastewater systems: a critical review

Microplastics have been widely considered as contaminants for the environment and biota. Till now, most previous studies have focused on the identification and characterization of microplastics in freshwater, sea water, and the terrestrial environment. Although microplastics have been extensively detected in the wastewater, research in this area is still lacking and not thoroughly understood. To fill this knowledge gap, the current review article covers the analytical methods of microplastics originating from wastewater streams and describes their sources and occurrences in wastewater treatment plants (WWTPs). Studies indicated that microplastic pollution caused by domestic washing of synthetic fibers could be detected in the effluent; however, most microplastics from personal care and cosmetic products (PCCPs) can be efficiently removed during wastewater treatment. Moreover, various techniques for sampling and analyzing microplastics from wastewater systems are reviewed; while, the implementation of standardized protocols for microplastics is required. Finally, the fate of microplastics during wastewater treatments and the environmental contamination of effluent to environment are presented. Previous studies reported that the advanced wastewater treatment (e.g., membrane bioreactor) is needed for improving the removal efficiency of small-sized microplastics (<?100 µm). Although the role of microplastics as transport vectors for persistent organic pollutants (POPs) is still under debate, they have demonstrated abilities to absorb harmful agents like pharmaceuticals.

     

Dispersal through stream networks: modelling climate‐driven range expansions of fishes

Aim To incorporate dispersal through stream networks into models predicting the future distribution of a native, freshwater fish given climate change scenarios. Location Sweden. Methods We used logistic regression to fit climate and habitat data to observed pike (Esox lucius Linnaeus) distributions in 13,476 lakes. We used GIS to map dispersal pathways through streams. Lakes either (1) contained pike or were downstream from pike lakes, (2) were upstream from pike lakes, but downstream from natural dispersal barriers, or (3) were isolated from streams or were upstream from natural dispersal barriers. We then used climate projections to model future distributions of pike and compared our results with and without including dispersal. Results Given climate and habitat, pike were predicted present in all of 99,249 Swedish lakes by 2100. After accounting for dispersal barriers, we only predicted pike presence in 31,538 lakes. Dispersal barriers most strongly limited pike invasion in mountainous regions, but low connectivity also characterized some relatively flat regions. Main conclusions The dendritic network structure of streams and interconnected lakes makes a two‐dimensional representation of the landscape unsuitable for predicting range shifts of many freshwater organisms. If dispersal through stream networks is not accounted for, predictions of future fish distributions in a warmer climate might grossly overestimate range expansions of warm and cool‐water fishes and underestimate range contractions of cold‐water fishes. Dispersal through stream networks can be modelled in any region for which a digital elevation model and species occurrence data are available.     

Addressing water quality in water footprinting: current status,methods and limitations

Purpose

In contrast to water consumption, water pollution has gained less attention in water footprinting so far. Unlike water scarcity impact assessment, on which a consensus has recently been achieved, there is no agreement on how to address water quality deterioration in water footprinting. This paper provides an overview of existing water footprint methods to calculate impacts associated with water pollution and discusses their strengths and limitations using an illustrative example.

Methods

The methods are described and applied to a case study for the wastewater generated in textile processing. The results for two scenarios with different water quality parameters are evaluated against each other and the water scarcity footprint (WSF). Finally, methodological aspects, strengths and limitations of each method are analysed and discussed and recommendations for the methods application are provided.

Results and discussion

Two general impact assessment approaches exist to address water quality in water footprinting: the Water Degradation Footprint (WDF) calculates the impacts associated with the propagation of released pollutants in the environment and their uptake by the population and ecosystem, while the Water Availability Footprint (WAF) quantifies the impacts related to the water deprivation, when polluted water cannot be used. Overall, seven methods to consider water quality in water footprinting were identified, which rely upon one or a combination of WDF, WAF and WSF. Methodological scopes significantly vary regarding the inventory requirements and provided results (a single-score or several impact categories). The case study demonstrated that the methods provide conflicting results concerning which scenario is less harmful with regard to the water pollution.

Conclusions

This paper provides a review of the water pollution assessment methods in water footprinting and analyses their modelling choices and resulting effects on the WF. With regard to the identified inconsistencies, we reveal the urgent need for a guidance for the methods application to provide robust results and allow a consistent evaluation of the water quality in water footprinting.

     

Water Quality of Effluent-dominated Ecosystems: Ecotoxicological, Hydrological, and Management Considerations

In arid and semi-arid regions of the southwestern United States and other parts of the world, flows of historically ephemeral streams are now perennially dominated by municipal and/or industrial effluent discharges, particularly in urbanized watersheds. Because effluent-dominated and dependent water bodies have previously received limited scientific study, we reviewed select contemporary topics associated with water quality of ephemeral streams receiving effluent flows. Our findings indicate that these ecosystems present numerous challenges to aquatic scientists and water resources managers, including: 1) appropriate ecosystems or upstream conditions used reference sites in biomonitoring are difficult to locate or do not exist; 2) water quality criteria, particularly for metals, are dramatically influenced by unique site-specific stream and land use conditions; 3) effluent-dominated streams represent worse-case scenarios for evaluating and predicting aquatic responses to emerging contaminants (e.g., pharmaceuticals and personal care products); 4) low-flow and drought conditions often preclude effective biomonitoring and water quality interpretation, or skew ambient assessment results; 5) chemical-physical water quality parameters (e.g., dissolved oxygen, conductivity, temperature) are dramatically altered by effluent and stormwater characteristics; and 6) beneficial reuse of reclaimed effluent waters potentially conflict with sustainability of ecological integrity. Subsequently, we recommend several water quality research priorities for effluentdominated water bodies.     

A sustainability analysis of a municipal sewage treatment ecosystem based on emergy

“Discharge of treated wastewater and sewage sludge landfilling” are the most common practice, which poses threats to the local environment. In this work we first constructed a general sewage treatment ecosystem (STE) which integrated the three systems. Emergy synthesis, with several improved emergy-based indicators which considered the waste input contribution and impacts of emissions, was applied to evaluate two alternative scenarios (scenario 1: sewage treatment system + treated water discharge + sludge landfilling; scenario 2: sewage treatment subsystem + reclaimed water reuse subsystem + aerobic compost production subsystem) for Mingjingtan sewage treatment plant in Wanzhou City of Chongqing in China. Results point out the environmental pressure of scenario 2 is much smaller than scenario 1 although its economic performance is somewhat poorer than scenario 1, and finally the sustainability of scenario 2 is still much better than scenario 1. Therefore, the treated water and sewage sludge reuse can further improve the environmental benefit of the sewage treatment process; however, the STE should be optimized in order to enhance its economic benefit. The proposed methods can help policy-makers make decisions and guide designers and operators to improve the comprehensive performance of sewage treatment processes. In addition, this paper also briefly discusses wastewater integrated management strategy.     

Recycling of aquaculture wastewater using charcoal based constructed wetlands

Abstract

The competitive demand for water makes it a scarce resource for agricultural use. This necessitates wastewater reuse for irrigation and any other agricultural purpose, especially in developing countries where treatment of wastewaters is not a priority. The aim of this study was to evaluate the performance of a charcoal-based constructed wetland (CBCW) in treating aquaculture wastewater. Aquaculture wastewater from a Research Fishpond Farm was treated in a CBCW planted with Sacciolepsis africana and Commelina cyannae for 5?days retention time. Raw wastewater and the treated wastewater from the constructed wetland (CW) was sampled and the physicochemical parameters determined. The performance of the CW in treating aquaculture wastewater was conducted. The result showed that the CBCW was capable of removing 50% TSS, 88% COD, 93% BOD_5, and 100% nitrate nitrogen. The pH and DO of the wastewater before treatment and after treatment ranged from 6.68 to 6.91 and 4.13 to 6.30?mg/l, respectively. Thus, CWs have great potential for the treatment of aquaculture wastewater and prevention of environmental degradation through wastewater treatment, thereby solving the problem of water scarcity for agriculture for optimum food production.     

Potential infection of grazing cattle via contaminated water: a theoretical modelling approach

Wastewater discharge and agricultural activities may pose microbial risks to natural water sources. The impact of different sources can be assessed by water quality modelling. The aim of this study was to use hydrological and hydrodynamic models to illustrate the risk of exposing grazing animals to faecal pollutants in natural water sources, using three zoonotic faecal pathogens as model microbes and fictitious pastures in Sweden as examples. Microbial contamination by manure from fertilisation and grazing was modelled by use of a hydrological model (HYPE) and a hydrodynamic model (MIKE 3 FM), and microbial contamination from human wastewater was modelled by application of both models in a backwards process. The faecal pathogens Salmonella spp., verotoxin-producing Escherichia coli O157:H7 (VTEC) and Cryptosporidium parvum were chosen as model organisms. The pathogen loads on arable land and pastures were estimated based on pathogen concentration in cattle faeces, herd prevalence and within-herd prevalence. Contamination from human wastewater discharge was simulated by estimating the number of pathogens required from a fictitious wastewater discharge to reach a concentration high enough to cause infection in cattle using the points on the fictitious pastures as their primary source of drinking water. In the scenarios for pathogens from animal sources, none of the simulated concentrations of salmonella exceeded the concentrations needed to infect adult cattle. For VTEC, most of the simulated concentrations exceeded the concentration needed to infect calves. For C. parvum, all the simulated concentrations exceeded the concentration needed to infect calves. The pathogen loads needed at the release points for human wastewater to achieve infectious doses for cattle were mostly above the potential loads of salmonella and VTEC estimated to be present in a 24-h overflow from a medium-size Swedish wastewater treatment plant, while the required pathogen loads of C. parvum at the release points were below the potential loads of C. parvum in a 24-h wastewater overflow. Most estimates in this study assume a worst-case scenario. Controlling zoonotic infections at herd level prevents environmental contamination and subsequent human exposure. The potential for infection of grazing animals with faecal pathogens has implications for keeping animals on pastures with access to natural water sources. As the infectious dose for most pathogens is more easily reached for calves than for adult animals, and young calves are also the main shedders of C. parvum, keeping young calves on pastures adjacent to natural water sources is best avoided.     

Evaluation of water services system through LCA. A case study for Iasi City,Romania

Purpose

The main objective of this paper is to analyse through life cycle assessment (LCA), the entire water services system in Iasi City (Romania): a representative city for the problems faced by the water services sector in Romania. Furthermore, the study is aimed at demonstrating the usefulness of the LCA approach as a support instrument for water resources management.

Methods

The life cycle inventory (LCI) of the Iasi water system was organized considering the water system components, as well as their function related to the water use life cycle: before the tap system as production phase (water abstraction, transport, treatment and distribution) and after the tap section as post-use phase (wastewater collection, treatment and discharge). The foreground data describing the LCI processes were provided directly by the company operating the Iasi water system, while the data for the background processes were sourced or selected from Ecoinvent 2.0 database. The assessment considers the quantification of environmental impacts (according to the CML 2000 baseline and Ecological Scarcity 2006 methodologies) of water supply (abstraction, treatment and distribution) and wastewater disposal (collection and treatment) relative to 1 m³ of tap water.

Results and discussion

For this given system, the results have pointed out that the before the tap system generates higher impacts than the after tap system, mainly due to the energetic effort needed for water supply and the fairly high water losses in the distribution system. However, the after the tap system, specifically the discharge of treated wastewater is still responsible for many of the water-related impact such as Eutrophication (when using CML) or Emissions to surface waters (when using the Ecological Scarcity method). Apart from the LCA approach, this study presents several scenarios for the improvement of the environmental performance of the water services, such as: changing between water sources, improving the distribution system and upgrading the wastewater treatment plant.

Conclusions

This study has demonstrated the usefulness of LCA to describe, compare and predict the environmental performance of complex water services systems (and all its components). The results have provided a reference case for the environmental profile of Iasi city water system, and have enabled the identification of its improvement alternatives. Also, this study, which represents a premiere for Romania, has opened future research directions which may include the development perspectives of the Iasi water services system, as well as improvements of LCIA methodologies to better represent the local specific water-related impacts.     

Life Cycle Assessment of Urban Wastewater Reclamation and Reuse Alternatives

Continuous population growth is causing increased water contamination. Uneven distribution of water resources and periodic droughts have forced governments to seek new water sources: reclaimed and desalinated water. Wastewater recovery is a tool for better management of the water resources that are diverted from the natural water cycle to the anthropic one. The main objective of this work is to assess the stages of operation of a Spanish Mediterranean wastewater treatment plant to identify the stages with the highest environmental impact, to establish the environmental loads associated with wastewater reuse, and to evaluate alternative final destinations for wastewater. Tertiary treatment does not represent a significant increment in the impact of the total treatment at the plant. The impact of reclaiming 1 cubic meter (m³) of wastewater represents 0.16 kilograms of carbon dioxide per cubic meter (kg CO₂/m³), compared to 0.83 kg CO₂/m³ associated with basic wastewater treatment (primary, secondary, and sludge treatment). From a comparison of the alternatives for wastewater final destination, we observe that replacing potable water means a freshwater savings of 1.1 m³, whereas replacing desalinated water means important energy savings, reflected in all of the indicators. To ensure the availability of potable water to all of the population—especially in areas where water is scarce—governments should promote reusing wastewater under safe conditions as much as possible.     

Integrated Cryptosporidium Assay To Determine Oocyst Density,Infectivity, and Genotype for Risk Assessment of Source and Reuse Water

Cryptosporidium continues to be problematic for the water industry, with risk assessments often indicating that treatment barriers may fail under extreme conditions. However, risk analyses have historically used oocyst densities and not considered either oocyst infectivity or species/genotype, which can result in an overestimation of risk if the oocysts are not human infective. We describe an integrated assay for determining oocyst density, infectivity, and genotype from a single-sample concentrate, an important advance that overcomes the need for processing multiple-grab samples or splitting sample concentrates for separate analyses. The assay incorporates an oocyst recovery control and is compatible with standard primary concentration techniques. Oocysts were purified from primary concentrates using immunomagnetic separation prior to processing by an infectivity assay. Plate-based cell culture was used to detect infectious foci, with a monolayer washing protocol developed to allow recovery and enumeration of oocysts. A simple DNA extraction protocol was developed to allow typing of any wells containing infectious Cryptosporidium. Water samples from a variety of source water and wastewater matrices, including a semirural catchment, wastewater, an aquifer recharge site, and storm water, were analyzed using the assay. Results demonstrate that the assay can reliably determine oocyst densities, infectivity, and genotype from single-grab samples for a variety of water matrices and emphasize the varying nature of Cryptosporidium risk extant throughout source waters and wastewaters. This assay should therefore enable a more comprehensive understanding of Cryptosporidium risk for different water sources, assisting in the selection of appropriate risk mitigation measures.     

Technological aspects of the microbial treatment of sulfide-rich wastewaters: A case study

Thiobacillus denitrificans has been shown to be an effective biocatalyst for the treatment of a variety of sulfide-laden waste streams including sour water, sour gases, and refinery spent-sulfidic caustics. The term 'sour' originated in the petroleum industry to describe a waste contaminated with hydrogen sulfide or salts of sulfide and bisulfide. The microbial treatment of sour waste streams resulting from the production or refining of natural gas and crude oil have been investigated in this laboratory for many years. The application of this technology to the treatment of sour wastes on a commercially useful scale has presented several technical barriers including substrate inhibition (sulfide), product inhibition (sulfate), the need for septic operation, biomass recycle and recovery, mixed waste issues, and the need for large-scale cultivation of the organism for process startup. The removal of these barriers through process improvements are discussed in terms of a case study of the full-scale treatment of sulfide-rich wastewater. The ability of T. denitrificans to deodorize and detoxify an oil-field produced water containing sulfides was evaluated under full-scale field conditions at Amoco Production Co. Salt Creek Field in Midwest, WY. More than 800 m³/d of produced water containing 100 mg/L sulfide and total dissolved solids of 4800 mg/L were successfully biotreated in an earthen pit (3000 m³) over a six-month period. Complete removal of sulfides and elimination of associated odors were observed. The system could be upset by severe hydraulic disturbances; however, the system recovered rapidly when normal influent flow rates were restored.     

Distribution of Enteric Pathogens in Wastewater Secondary Effluent and Safety Analysis for Urban Water Reuse

Through a 1-year monitoring of enteroviruses and pathogenic bacteria in the secondary effluent using real-time polymerase chain reaction (real-time PCR), the pathogen removal requirement was evaluated for safeguarding the reclaimed water quality for urban reuse. The distribution of each pathogen in the secondary effluent was found to follow a log-normal relationship, although 50% cumulative concentrations differed much from each other (1.4 GEC/L of infectious enteroviruses, 3.1 × 10² CFU/L of Salmonella typhi, 1.0 × 10³ CFU/L of Shigella, and 3.3 × 10⁵ CFU/L of Escherichia coli). By exposure analysis regarding two reuse scenarios (golf course irrigation and recreational impoundment), risks were analyzed for pathogens in reused water based on monitoring data and dose–response relation. For enteroviruses and pathogenic bacteria, there were obvious differences in the relationship between the reliability and removal efficiency. Under an acceptable annual risk level (10^–4/a), the pathogen removal requirement depends on the manner of water reuse. In the golf course irrigation, the removal efficiency of enteroviruses, Salmonella typhi, Shigella, and Escherichia coli reach to 3.8～4.0-log, 1.4-log, 3.3-log, and 2.0-log, respectively, in order to ensure 95% reliability. However, if wastewater is reused for recreational impoundment, only a further increase around 1.5-log removal efficiency of pathogens can meet the requirement for the same reliability.     

Identifying Drivers of China's Provincial Wastewater Reuse Outcomes Using Qualitative Comparative Analysis

In water‐scarce regions of China, wastewater reuse is increasingly considered as a potential component of China's future water resource management strategy. Currently, the percentage of wastewater reuse varies substantially across Chinese provinces, but conditions leading to a high rate of wastewater reuse have not been elucidated clearly. In this work, we use fuzzy‐set qualitative comparative analysis (fsQCA) to identify the drivers of high and low percentages of wastewater reuse in water‐stressed Chinese provinces in 2013. We find that among the five conditions studied (per capita water availability, urban population, access to sea, access to urban space, and access to agricultural land), a high percentage of wastewater reuse is primarily driven by water stress and access to urban green space. Consequently, policies should consider targeting provinces with these attributes where wastewater reuse is more likely to be successful. Further, our results show that there is asymmetry in the conditions that lead to high and low percentages of wastewater reuse, and that the drivers for and against reuse identified in this study are not completely analogous to those identified in previous studies. As such, the drivers for and against wastewater reuse should not be generalized without due consideration of the local context.     

Opportunities for woody crop production using treated wastewater in Egypt. I. Afforestation strategies

The Nile River provides nearly 97% of Egypt's freshwater supply. Egypt's share of Nile waters is fixed at 55.5 billion cubic meters annually. As a result, Egypt will not be able to meet increasing water demand using freshwater from the Nile and has been developing non-conventional wastewater reuse strategies to meet future demands. The USAID Mission in Cairo began promoting strategies for water reuse in 2004, and guidelines for safe and direct reuse of treated wastewater for agricultural purposes were approved in 2005 (Egyptian Code 501/2005). Twenty-four man-made forests were established that have been useful for assessing the efficacy of using treated wastewater for afforestation. At present, approximately 4,340 hectares are under irrigation with treated wastewater, utilizing a total daily volume of 467,400 cubic meters. Wastewater has been applied to trees along roads, greenbelts in cities, and woody production systems. Currently, a joint USDA Forest Service--Agricultural Research Service technical assistance team has been evaluating the feasibility of scaling up such afforestation efforts throughout Egypt. We describe information about: 1) suitable tree species that have been identified based on local soil characteristics, water quality, and quantity of water supply; 2) the benefits and consequences of using these species; 3) strategies to maximize the potential of afforestation with regard to improving water quality, maximizing resource production, increasing biodiversity, and limiting commercial inputs; and 4) potential long-term impacts on the natural resource base from afforestation. A companion paper addresses irrigation recommendations based on species and local conditions (see Evett et al. 2000).