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.     

The potential for decentralized reclamation and reuse of household greywater in peri‐urban areas of Bangkok

A survey was conducted of 400 households in the peri‐urban area of Bangkok to investigate typical household water consumption, daily water use activities, public perception towards wastewater reuse and detergent consumption. Four categories of greywater, including cooking, dish washing, bathing and laundry washing wastewater, their properties and potential application for reuse were examined. Average water consumption was estimated to be 208 L/person/day. The wastewater was already reused in 42% of households, and that laundry wastewater was widely used for plant watering and floor washing. More than 80% of households accepted the use of treated greywater, while 50% of households did not accept the use of treated blackwater. Biochemical oxygen demand (BOD), chemical oxygen demand (COD) and suspended solid (SS) were high in cooking, dish washing and laundry, and lower in bathing wastewater, while anionic surfactant were high in laundry and dish washing wastewater. The finding results clearly demonstrate the possibility of greywater reclamation and reuse in the area.     

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.     

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%).     

Microbial quality assessment of household greywater

A monitoring program was undertaken to assess the microbial quality of greywater collected from 93 typical households in Melbourne, Australia. A total of 185 samples, comprising 75 washing machine wash, 74 washing machine rinse and 36 bathroom samples were analysed for the faecal indicator Escherichia coli. Of these, 104 were also analysed for genetic markers of pathogenic E coli and 111 for norovirus (genogroups GI and GII), enterovirus and rotavirus using RT-PCR. Enteric viruses were detected in 20 out of the 111 (18%) samples comprising 16 washing machine wash water and 4 bathroom samples. Eight (7%) samples were positive for enterovirus, twelve (11%) for norovirus genogroup GI, one (1%) for norovirus genogroup GII and another (1%) for rotavirus. Two washing machine samples contained more than one virus. Typical pathogenic E. coli were detected in 3 out of 104 (3%) samples and atypical enteropathogenic E. coli in 11 (11%) of samples. Levels of indicator E. coli were highly variable and the presence of E. coli was not associated with the presence of human enteric viruses in greywater. There was also little correlation between reported gastrointestinal illness in households and detection of pathogens in greywater.     

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.     

Fouling control of a membrane coupled photocatalytic process treating greywater

Fouling in membrane coupled photocatalytic reactors was investigated in the case of greywater treatment by establishing the link between product type, dose, irradiation time and fouling rates in a cross flow membrane cell fitted with a 0.4 μm pore sized polyethylene membrane. Rapid fouling occurred only with shower gels and conditioners and was linked to changes in the organo-TiO₂ aggregate size postulated to be caused by polymers within the products. Fouling was reduced to a negligible level when sufficient irradiation was applied demonstrating that the membrane component of the process is not the issue and that scale up and implementation of the process relates to effective design of the UV reactor.     

Potential for potable water savings by using rainwater and greywater in a multi-storey residential building in southern Brazil

Studies on the use of rainwater and greywater to promote potable water savings have been performed in different countries. The main objective of this article is to evaluate the potential for potable water savings by using rainwater and greywater in a multi-storey residential building composed of three blocks, located in Florianópolis, southern Brazil. Water end-uses were estimated by applying questionnaires and measuring water flow rates. An economic analysis was performed to evaluate the cost effectiveness of using rainwater and greywater either separately or together. Results show that the average potential for potable water savings range from 39.2% to 42.7% amongst the three blocks, considering that water for toilet flushing, clothes washing and cleaning does not need to be potable. By using rainwater, the potable water savings would actually range from 14.7% to 17.7%. When greywater is considered alone, potable water savings are higher, i.e., ranging from 28.7% to 34.8%. As for the use of rainwater and greywater combined, the potable water savings range from 36.7% to 42.0%. The main conclusion that can be made from the research is that the three systems that were investigated are cost effective as the payback periods were lower than 8 years, but the greywater system was the most cost effective one, followed closely by the rainwater one.     

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.     

Presence and fate of priority substances in domestic greywater treatment and reuse systems

A wide range of household sources may potentially contribute to contaminant loads in domestic greywater. The ability of greywater treatment systems to act as emission control barriers for household micropollutants, thereby providing environmental benefits in addition to potable water savings, have not been fully explored. This paper investigates the sources, presence and potential fate of a selection of xenobiotic micropollutants in on-site greywater treatment systems. All of the investigated compounds are listed under the European Water Framework Directive as either “Priority Substances” (PS) or “Priority Hazardous Substances” (PHS). Significant knowledge gaps are identified. A wide range of potential treatment trains are available for greywater treatment and reuse but treatment efficiency data for priority substances and other micropollutants is very limited. Geochemical modelling indicates that PS/PHS removal during treatment is likely to be predominantly due to sludge/solid phase adsorption, with only minor contributions to the water phase. Many PS/PHS are resistant to biodegradation and as the majority of automated greywater treatment plants periodically discharge sludge to the municipal sewerage system, greywater treatment is unlikely to act as a comprehensive PS/PHS emission barrier. Hence, it is important to ensure that other source control options (e.g. eco-labeling, substance substitution, and regulatory controls) for household items continue to be pursued, in order that PS/PHS emissions from these sources are effectively reduced and/or phased out as required under the demands of the European Water Framework Directive.     

Diurnal patterns of micropollutants concentrations in domestic greywater

In recent years, much interest has been given to presence of micropollutants in municipal wastewater, some of which are suspected to be endocrine disruptors, toxic or carcinogenic. Much less attention has been paid to their presence in greywater. The present research studies the diurnal patterns of micropollutants in greywater and computes their daily loads. Monitoring was carried-out using auto-controlled sampling system, designed to overcome the erratic greywater generation. Two main generation periods were identified: morning (5:00–11:00) and evening-night (18:00–2:00), contributing about 20% and >50% of daily greywater discharge, respectively. Average specific daily greywater discharge was 57 L p^?1d^?1, which matches reported value for greywater generated by showers and washbasins in Israel. The most frequently detected micropollutants in this study were methylparben (preservative), galaxolide (fragrance) and oxybenzone (UV-filter), which are common ingredients in many personal care-products. Their daily loads were 2, 840, 1, 887 and 728 µg p^?1d^?1, respectively.     

Accumulation of oil and grease in soils irrigated with greywater and their potential role in soil water repellency

The potential impact of oil and grease (O and G) to soils irrigated with greywater (GW) was investigated. Greywater streams were sampled and analyzed for O and G content, along with corresponding GW-irrigated soils. Untreated kitchen GW averaged 200 mg L(-1) O and G, over an order of magnitude more than other GW streams. GW-irrigated soils showed O and G accumulation of up to 200 mg kg(-l) within the first 20-cm of depth. To determine the potential effects of such O and G accumulation on water movement in soil, capillary rise and water drop penetration time (WDPT) experiments were conducted. The results showed up to 60% decrease in capillary rise when sand containing 250 mg kg(-1) O and G was used. Interestingly, no additional reduction in capillary rise was observed at concentrations above 250 mg kg(-1). WDPT was observed to increase linearly with increased O and G content, up to 1000 mg kg(-1). This work demonstrated that O and G in GW used for irrigation can accumulate in soil and may lead to a significant reduction in the soils ability to transmit water.     

集中空调系统水质变化的原因及处理方法

分析了集中空调系统水质变化的原因,介绍了化学处理法、磁化处理法、电子处理法等常用的水质处理方法。     

天津市某污水处理及再生水利用工程设计探讨

结合GB 18918-2002城镇污水处理厂污染物排放标准,对天津市某污水处理及再生水利用工程设计进行了探讨,分别阐述了具体处理工艺及相关设计参数,并归纳了该设计方案中的节能措施,以指导今后同类工程项目。     

Soil salinity of urban turf areas irrigated with saline water: I. Spatial variability

With increasing use of saline water for irrigating urban landscapes, soil salinization is becoming a concern. This study examined spatial variation in soil salinity over the length of selected fairways at five golf courses, and of large turf areas at two public parks located in west Texas and southern New Mexico. Salinity of water used for irrigation ranged from 680 to 2700 mg L⁻¹, and the sites consisted mostly of Aridisols (upland soils) or Entisols (alluvial soils). Soil salinity distribution at sites consisting of deep Aridisols was spatially independent with the coefficient of variability (CV) ranging from 24 to 42%. The sites consisting of shallow Aridisols over a calcic horizon had erratic and random soil salinity distributions with an average CV of 37%. Since soil salinity distributions in Aridisols and Alfisols appeared to be spatially independent within the distance of fairways, soil sampling adequacy can be determined by the conventional probability statistics. However, salinity distributions at Entisols sites were spatially dependant to a length of 100 m or more. In addition, the clayey Entisols used for public parks had high levels of salt accumulation (>10 dS m⁻¹ in the saturation extract) with the CV exceeding 60%. When salinity readings were stratified by soil type distribution, the CV was reduced to 28% on the average. The number of samples required to obtain the mean salinity over a typical length of fairways (250–300 m) within a deviate range of 20% averaged 6 in deep sandy Aridisols and Alfisols, and 13 each in other cases, provided that sampling of Entisols is made based on soil type distributions. These sampling requirements are greater than those for field soil moisture or saturation water contents. The spacing to collect the required number of samples over the prevailing length of fairways was between 23 and 38 m. Soil sampling for salinity appraisal is most problematic in Entisols, but can be made simple if a detailed soil map is available. In Aridisols containing a calcic horizon, it is probable to have saline spots over poorly permeable caliche.     

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.     

Combined permeable pavement and photocatalytic titanium dioxide oxidation system for urban run‐off treatment and disinfection

Permeable pavement systems (PPS) are frequently associated with high removal efficiencies for water quality parameters. Their effluent can, therefore, be recycled, for example, for sprinkling onto gardens. Nevertheless, some stakeholders fear that potentially pathogenic organisms within the treated run‐off could be too high, and therefore they request disinfection before recycling. The aim of this paper is, therefore, to assess the efficiency of a batch flow combined titanium dioxide (TiO₂) and ultraviolet (UV) light photocatalytic reactor in removing water‐borne microbial contaminants from the effluent of PPS. Combined TiO₂ and UV photocatalytic reaction times between 80 and 100 min were required for the complete removal of Escherichia coli, total coliforms and faecal Streptococci, which had mean initial counts of 1.5 × 10⁷, 4.4 × 10⁶ and 6.9 × 10⁵ colony‐forming units (CFU) per 100 mL, respectively. In comparison, UV disinfection alone resulted in insignificant microbial removal. Suspended TiO₂ powder was more effective than small immobilised TiO₂ crystals.     

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。     

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.     

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.