Planning an urban wastewater system with centralised greywater reuse: a case in Beijing

This paper presents a proposed centralised greywater reuse (CGR) system for Daxing New City, Beijing. This system would use separate greywater and blackwater discharge pipes in residences and public buildings. Greywater would be treated in a centralised plant and reused for public purposes. Water supply–demand balance analysis showed that this system would conserve 28.5% of freshwater resources. A centralised wastewater reuse system that would conserve the same water resources and serve the same consumers was developed for comparison. The greywater reuse system would cost 1.2% more than the reference system, but would decrease the pollution load by 10% and improve the water-quality compliance of the Xinfeng River (total phosphorous: 24–42%, total nitrogen: 0–7%). The proposed CGR system exhibited acceptable water conservation, environmental impact, and construction and operation costs, and would thus be suitable in urbanising areas that face water shortages and aqueous environmental deterioration.     

Reuse of greywater for irrigation around homes in Australia: Understanding community views,issues and practices

We examined people's views on a number of water issues and their motivation, practices and concerns about greywater reuse for irrigation of around homes. Survey participants (275) from different socio-economic background from 125 suburbs in the Western Sydney region, Australia took part in the study. Regardless of their age and gender, when asked which was the most important issue regarding water in their region from a prescribed list, the majority of participants identified water quality as the most important and availability without water restriction as the least important. About half of the participants reused greywater regularly or at some time during the last few years. The cost of plumbing and health risks to people, plants and soil are critical issues for greywater reuse and need attention. For the reusing widely and sustainably, there is a need for easily accessible, user-friendly information packages to create ‘greywater reuse literacy’ in the community.     

Decentralized water management: rainwater harvesting and greywater reuse in an urban area of Beijing,China

Large-scale centralised wastewater treatment system has often prevailed in industrial countries, and has been regarded as a successful approach during the last century. However, transfer of this highly water-consuming system and so-called ‘end-of-pipe’ technology to developing countries, especially in fast-growing cities with scarce water resources, has been extremely limited. Decentralized water treatment is not a new technology and has been successfully implemented in many rural areas worldwide. However, there are few applications in urban areas. This study at Tianxiu Garden in Beijing, China, investigated the potential and feasibility of water management based on a decentralized approach, but modified for application of greywater recycling and rainwater harvesting in a densely populated semi-urban area. A high degree of drinking water substitution (more than 25%) could not be attained by rainwater harvesting. Recycling of treated greywater for toilet flushing was shown to be an efficient method for minimisation of drinking water consumption, and a more suitable technique than rainwater harvesting for saving water in Beijing, China.     

Evaluation of the effects of greywater reuse on domestic wastewater quality and quantity

This simulation study, based on experimental and literature data, evaluates the influence of onsite greywater reuse on domestic wastewater quality and quantity. For this, three scenarios were studied: no reuse; reuse for toilet flushing; reuse for toilet flushing and garden irrigation. Light greywater reuse reduced the daily household wastewater flows by 25–40%. These reductions mainly occurred during the morning and evening peak wastewater generation. Although daily loads of all pollutants decreased, their concentrations in the discharged wastewater increased owing to exclusion of potable water from the wastewater and replacing it by treated light greywater. The proportional concentration increase of most pollutants was lower than the decrease in wastewater discharge, due to degradation during treatment. The highest concentration increase occurred during the morning peak, coinciding with the highest flow reduction. This study is a first step towards quantification of the effects of onsite greywater reuse on sewers and wastewater treatment plants.     

The management of greywater in the non-sewered areas of South Africa

The management of greywater in the non-sewered areas of South Africa has been identified as a key area of research owing to the fact that very little, if any, provision has been made for it. Without water-borne sanitation, the disposal of greywater becomes a problem that has the potential to create a host of environmental and health problems, and this is particularly evident in the high density informal settlements that surround the major South African cities. The main aim of this study was to understand the use and disposal of greywater in the non-sewered areas in South Africa, determine typical quantities and qualities, and develop a preliminary guide for its management, both in terms of reducing health and environmental risks as well as possibly providing benefits through controlled reuse.     

Seasonal patterns and socio-economic predictors of household rainwater and greywater use

Seasonal water insecurity is a growing concern in many countries. For some households, rainwater and greywater are important alternative water sources. This study examines household patterns and socio-economic predictors of using rainwater and greywater in urban Philippines, in rainy versus dry seasons. Results from a household survey (N = 396) and in-depth interviews (N = 18) suggest that rainwater and greywater use are widespread, particularly among households with more members, less financial resources, and less access to the public utility, in seasonal ways. Future research into the adoption and diffusion of these practices may inform policies that promote equitable water access year-round.     

Health-based targets for greywater reuse in residential schools in Madhya Pradesh,India

In line with developments in the water reuse sector, this paper applied quantitative microbial risk assessment (QMRA) techniques to seven greywater reuse systems used for recycling shower water for toilet flushing. The objective of the study was to establish a scientific basis for health-based greywater targets for India. It involved qualitative risk assessments and quantitative microbiological analysis using Enterococci, thermotolerant coliforms (TTC) and coliphage indicator organisms. Four conclusions are drawn from this study. Firstly, the systems indicated a low risk and high quality, and secondly that low levels of risk were present in systems, resulting in the recommendation of guideline of 5000 cfu/100 mL rather than 10 000 cfu/100 mL for greywater utilised for direct toilet flushing. Thirdly, disability adjusted life years (DALYs) are a useful indicator of risk for evaluating the performance of a greywater reuse system in addition to chemical/microbiological indicators DALYs, and finally that TTC are a useful surrogate microbial indicator for analysis of greywater in developing countries with limited analytical facilities.     

Evaluation of a portable in-house greywater treatment system for potential water-reuse in urban areas

This study aims at improving greywater reuse potential. An advanced physical filtration system named as GAC-MI-ME was developed to attain multi-grade effluents for versatile reuse of greywater. It consists of a matrix of treatment trains including coarse filtration, microfiltration, activated carbon, ultrafiltration, ultraviolet, and reverse osmosis. A preliminary set of experiments were conducted to characterize the greywater originating from shower, washbasin, and laundry. The samples were subsequently treated through GAC-MI-ME system. It was observed that the activated carbon along with microfiltration and coarse filtration played vital roles as pre-filtration for ultrafiltration and reverse osmosis. The contaminant load distributions of GAC-MI-ME system were observed with an average of 90.4% turbidity and 53.2% of biochemical oxidation demand (BOD₅₎ as the pre-filtration, whereas the effluents at ultrafiltration and reverse osmosis showed unrestricted water reuse possibilities. The GAC-MI-ME system can be envisioned as advancement to the conventionally applied greywater treatments.     

The role of free water surface constructed wetlands as polishing step in municipal wastewater reclamation and reuse

In Europe, the last two decades witnessed growing water stress, both in terms of water scarcity and quality deterioration, which prompted many municipalities for a more efficient use of the water resources, including a more widespread acceptance of water reuse practices. Treatment technology encompasses a vast variety of options. Constructed wetlands are regarded as key elements in polishing conventionally treated wastewater for recreational and environmental applications. A survey was conducted to assess the performance of tertiary free water surface constructed wetlands in treating both key and emerging contaminant categories in the perspective of water reuse. A database was created with information concerning systems with emerging and free-floating macrophytes. The database includes results from both full- and pilot-scale systems, and considers a broad variety of operating conditions. This paper provides an overview of the treatment performances of the constructed wetlands in the database and discusses their significance in the optic of water reclamation and reuse practices.     

城市污水回用深度处理方法及其研究进展

介绍了城市污水回用深度处理的概念,总结了几种常见的城市污水回用深度处理方法,对它们的原理和特点进行了简单概述,并阐述了近年来这些深度处理方法的研究进展,从而使城市污水作为新的资源得以循环利用,提高了城市资源的利用率。     

Assessment of greywater reuse as a potential mitigation measure for water shortages and sanitation problems in senior high schools

The study assessed water shortages and its effects on sanitation in Senior High Schools using structured questionnaires involving water availability, water use pattern and perception of greywater reuse. Additionally, an observation of the sanitation situation was done to validate the responses. The study found that water availability was an issue as this caused students to use more than an hour round trip to access water resulting in poor sanitation and hygiene practices. Meanwhile, an average greywater generation rate of 14.5 L per person per day, is always disposed of despite its potential reuse. Greywater reuse was accepted by respondents as 59% proposed reusing it if available for non‐potable applications (94%) such as toilet cleaning and flushing. This is because, there is a significant association between cleanliness of the toilet facilities and usage (P < 0.05). Respondents who declined greywater reuse cited health risks (58%), uncomfortable feeling (37%) and cultural issue (5%).     

The implications of household greywater treatment and reuse for municipal wastewater flows and micropollutant loads

An increasing worldwide interest in water recycling technologies such as greywater treatment and reuse suggests that additional research to elucidate the fate of xenobiotics during such practices would be beneficial. In this paper, scenario analyses supported by empirical data are used for highlighting the potential fate of a selection of xenobiotic micropollutants in decentralised greywater treatment systems, and for investigation of the possible implications of greywater recycling for the wider urban water cycle. Potential potable water savings of up to 43% are predicted for greywater recycling based on Danish water use statistics and priority substance monitoring at a greywater treatment plant in Denmark. Adsorption represents an important mechanism for the removal of cadmium, nickel, lead and nonylphenol from influent greywater and therefore the disposal route adopted for the generated sludge can exert a major impact on the overall efficiency and environmental sustainability of greywater treatment.     

An integrated environmental plan for the reuse of treated wastewater effluents from WWTP in urban areas

The reuse of treated wastewater effluents from wastewater treatment plants (WWTP) is a recent practice in the environmental restoration of marginal areas in combination with tree and shrub planting. In urban areas, an integrated approach to the application of this practice implies (a) reuse of treated domestic wastewater for irrigation of hardy plant species and (b) design of environmentally friendly outdoor landscape including the planting of species acceptable for irrigation with such kind of wastewater.     

城市更新中旧建筑再利用初探

通过对城市更新中旧建筑再利用的产生与发展历程的阐述，得出旧建筑再利用的必要性和其基本过程与理论方法，以期为我国城市更新旧建筑再利用的未来探索之路提供相关素材。     

The potential role of urban green areas for controlling ground surface and subsurface warming

Subsurface warming in urban areas is higher in magnitude than increases in surface air temperatures. However, little evidence exists on the effects of urbanization on subsurface environments, and there are few quantitative estimates of the effectiveness of adaptation measures. We analyzed the relationship between ground surface warming and the extent of landscape change using subsurface temperature anomalies as an indicator of surface warming in five urban areas in Japan. To interpret these results for urban planning, we presented the percentages of green areas that would be needed to achieve certain reductions in ground surface temperatures for areas with different urbanization levels. Accordingly, a 0.5 °C reduction in average ground surface temperatures can be achieved by an increased Normalized Difference Vegetation Index (NDVI) value of 0.035, which accounts for approximately a 17% increase in natural green areas in an area with 75% urbanization. This study provides quantitative estimates to cope with urban warming at the local scale in the face of climate change.     

Reducing inventory data requirements for scenario representation in comparative life cycle assessment (LCA), demonstrated on the urban wastewater system

Wastewater reuse has become an attractive option for alleviating the stress from water resources. Centralized wastewater reuse is a common and continuously expanding practice worldwide, but the advantages of centralized over decentralized approaches are lately being questioned. Life cycle assessment (LCA) is a well-accepted means of assessing the overall environmental performance of service systems, however, construction of a life cycle inventory (LCI) for complex systems such as urban wastewater systems, is very time consuming. Lack of resources and unavailability of data often enforce constraints on the scope of the assessment. In such cases it may be beneficial to consider the approach presented here, which manifests the differences between the studied alternatives. By eliminating processes that remain unchanged, less data and human resources are required in building the inventory, and less parameter uncertainty is introduced into the analysis. The proposed approach is demonstrated through the conceptual modeling steps of an assessment of decentralized urban wastewater reuse alternatives.     

连续运行卫星定位体系下城市测量现代基准的构建与应用

基于先进的连续运行卫星定位系统和城市似大地水准面等高新技术手段,广州市成功构建了新一代城市测量现代基准体系,实现了面向城市测量和各行业的应用,并围绕其开展了一系列拓展性研究工作。本文对该现代基准建设与应用中的关键问题进行了探索。     

Performance of UV disinfection and the microbial quality of greywater effluent along a reuse system for toilet flushing

This paper examines the microbial quality of treated RBC (Rotating Biological Contactor) and MBR (Membrane Bioreactor) light greywater along a continuous pilot-scale reuse system for toilet flushing, quantifies the efficiency of UV disinfection unit, and evaluates the regrowth potential of selected microorganisms along the system. The UV disinfection unit was found to be very efficient in reducing faecal coliforms and Staphylococcus aureus. On the other hand, its efficiency of inactivation of HPC (Heterotrophic Plate Count) and Pseudomonas aeruginosa was lower. Some regrowth occurred in the reuse system as a result of HPC regrowth which included opportunistic pathogens such as P. aeruginosa. Although the membrane (UF) of the MBR system removed all bacteria from the greywater, bacteria were observed in the reuse system due to “hopping phenomenon.” The microbial quality of the disinfected greywater was found to be equal or even better than the microbial quality of “clean” water in toilet bowls flushed with potable water (and used for excretion). Thus, the added health risk associated with reusing the UV-disinfected greywater for toilet flushing (regarding P. aeruginosa and S. aureus), was found to be insignificant. The UV disinfection unit totally removed (100%) the viral indicator (F-RNA phage, host: E. coli F_amp⁺) injected to the treatment systems simulating transient viral contamination. To conclude, this work contributes to better design of UV disinfection reactors and provides an insight into the long-term behavior of selected microorganisms along on-site greywater reuse systems for toilet flushing.     

Physical development planning and urban design in earthquake-prone areas

This paper argues that the application of physical development planning measures at national, regional and local level would reduce the risks to life and property of a potential earthquake in earthquake-prone countries and lessons are drawn from case studies. Basic definitions of hazard, vulnerability, sensitivity and risk are given. A check list of optimum physical planning measures, the goals to be achieved and level at which planning is envisaged is included in the paper. Measures to control vulnerability, in particular the use of low density development, and surrounding open space in densely populated urban areas are suggested.