Household attitudes toward wastewater recycling in Saudi Arabia

Domestic water supply is an essential but challenging public service, especially in countries with rapid population growth and limited freshwater resources. Wastewater recycling has now become a sustainable source of domestic water supply worldwide. In Saudi Arabia, the energy-intensive desalination process meets over 60% of municipal water demand, rising by about 6% within the last two decades. The government has set an ambitious target of complete recycling of treated wastewater in major cities by 2040. Based on a questionnaire survey of 625 households, this study investigates household willingness to reuse treated greywater (TG) for non-drinking domestic applications and the factors that influence their attitudes toward wastewater recycling. The findings indicate more acceptability (agree or strongly agree) of reusing TG for laundering (males: 36.9%, females: 31.7%) than bathing (males: 11.6%, females: 12.1%). Chi-Square analyses show that residential location, age, and education significantly influence household attitudes to reuse TG, but gender and nationality do not. There is more prospect of agreeing to reuse TG for laundering than bathing across all ages groups, residential locations, nationalities, and genders. Educational attainment is the only significant predictor of the likelihood of using TG for bathing and laundering with an odds ratio of 1.26 and 1.04, respectively. Age and gender are significant predictors of the odds of reusing TG for laundering only. Behavioral change campaigns are key to scaling up wastewater recycling to reduce reliance on expensive seawater desalination and dwindling freshwater resources.     

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.     

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.     

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.     

Assessing integrated water management options for urban developments – Canberra case study

Urban water services in the Australian Capital Territory (ACT) are currently provided through conventional centralised systems, involving large-scale water distribution, wastewater collection, water and wastewater treatment. A study was conducted to assist Environment ACT in setting broad policies for future water services in Canberra. The current paper presents the outcomes of a study examining the effects of various water servicing options on water resources and the environment, for two townships in Canberra, one existing and one greenfield site. Three modelling tools were used to predict the effects of various alternative water servicing scenarios, including demand management options, rainwater tanks, greywater use, on-site detention tanks, gross pollutant traps, swales and ponds. The results show that potable water reductions are best achieved by demand management tools or a combination of greywater and rainwater use for existing suburbs, while third pipe systems are preferred for greenfield sites. For this specific climatic region and end use demands, modelling predicted increased water savings from raintanks compared to greywater systems alone, with raintanks providing the additional benefit of reduced peak stormwater flows at the allotment scale. Rainwater and stormwater reuse from stormwater ponds within the catchments was found to provide the highest reduction in nutrient discharge from the case study areas. Environment ACT amended planning controls to facilitate installation of raintanks and greywater systems, and commenced a Government funded rebate scheme for raintanks as a result of this study.     

建筑污水回用网络的优化设计

结合污水回用网络的优化模型设计，介绍了两个较简单的用水网络中最优污水回用网络设计实例，从而使污水得到最大程度的回用，并满足用水要求。     

Greywater reuse systems for toilet flushing in multi-storey buildings – over ten years experience in Berlin

Water reuse in Germany has gained in significance in the last 10 years. Several greywater systems, built according to guidelines introduced in 1995, operate today with no public health risk. Two greywater treatment systems are described in this paper: a rotary biological contactor (RBC) built in 1989 for 70 persons, and a fluidized-bed reactor for a one-family household built in 1995 as the biological stage for the treatment of household greywater for use in toilet flushing. Both systems were optimized in the following years with consideration of a minimal energy and maintenance demand. As numerous investigations have shown, biological treatment of the greywater is indispensable in order to guarantee a risk-free service water for reuse applications other than potable water.     

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.     

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.     

Inventory of water management practices in Harare, Zimbabwe

Lake Chivero, in Zimbabwe, is the major water supply source for the greater Harare area. This paper looks at the sustainability of current practices of the urban water cycle in relation to water quantity and quality management in the Chivero catchment. Data on population, water supply, water and wastewater treatment and river flows were obtained from urban councils and government departments. The data were used to assess water consumption, wastewater generation, treatment and disposal practices, river flow trends, raw water abstractions and water demand patterns. The results showed that the current situation is not sustainable as water quantity in the catchment will soon be a problem at current levels of consumption while water quality is already a problem, especially with regard to nutrient levels. Water and nutrient management strategies, which include water use efficiency, treatment and water recycling and nutrient reuse in controlled urban agriculture, are recommended as matters of urgency.     

Nutrient addition to enhance biological treatment of greywater.

This study compares the chemical oxygen demand (COD) removal and respiration rates of a microbial population treating real and synthetic greywaters dosed with nutrient supplements. The nutrient composition of the real and synthetic greywaters was analysed and the dosing regime for nitrogen, phosphorus and a range of trace metals planned accordingly. The doses consisted of eight single additives (macronutrients and trace metals) to the control greywater and six trace metal additions to C: N : P balanced greywater. The COD removal for the control real and synthetic greywater in lab-scale activated sludge systems (0.038 and 0.286 kg COD kg MLSS(-1) d(-1), respectively) confirmed nutrient limitation and the poor degree of greywater treatment. Nutrient dosing increased the COD removal rate and oxygen uptake rate in many cases. The greatest stimulation of microbial activity was observed with zinc additions to C: N: P balanced real greywater (1.291 kg COD kg MLSS(-1) d(-1) over 30 times the control). Inhibitory effects to various extents were rare and limited mainly to the additions of metals to synthetic greywater. The dominance of chemicals effects was observed on addition of some micronutrients; notably iron and aluminium, metals on which many coagulants for use in biotreatment of other wastewaters are based. The data indicate that the impact of understanding microbial processes and the nutrients required for wastewater treatment can only serve to optimise process efficiency for the proposed treatment of 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.     

中水水箱技术研究

在水资源供需矛盾日趋严重的今天，建筑中水工程作为节水的重要技术手段已日益发展完善。但由于投资等因素制约，在实际推广应用方面仍相对滞后，针对城市中小型宾馆、饭店、招待所等建筑中的洗浴废水的回用问题，提出了中水水箱技术，并通过试验运行和技术、经济分析，证明了该技术的可行性以及所具有的推广应用价值。     

Potential for potable water savings by combining the use of rainwater and greywater in houses in southern Brazil

Research on rainwater and greywater have been performed all over the world as a way of promoting potable water savings. The main objective of this article is to evaluate the potential for potable water savings by using rainwater and greywater in two houses in southern Brazil. An economic analysis is performed to evaluate the benefits of using rainwater and greywater either separately or together. Results indicate that the potential for potable water savings in both houses range from 33.8% (house B) to 36.6% (house A), considering that water for toilet flushing and washing machine does not need to be potable. By using rainwater, the potable water savings in house A would be 35.5% and in house B, 33.6%. When greywater is considered alone, potable water savings are lower, i.e., 30.4% in house A and 25.6% in house B. As for the use of rainwater and greywater combined, the potable water savings are 36.4% in house A and 33.8% in house B. The three systems that were investigated seem not to be cost effective as the payback periods were very high (above 17 years), but the greywater system was the most attractive one. The main conclusion that can be made from the research is that there needs to be government incentives in order to promote the use of rainwater or greywater in houses in southern Brazil.     

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.     

Hazardous substances in separately collected grey- and blackwater from ordinary Swedish households

The objective of this paper is to present the mass flows of a number of selected hazardous substances in raw, separate grey- and blackwater from ordinary Swedish households. The Vibyasen housing area was selected for the investigation since its wastewater system has separate flows for grey- and blackwater. Due to the high analytical costs, a limited number of hazardous substances had to be selected and the number of samples restricted. The greywater flow was manually measured and the samples were collected at set time intervals. The blackwater samples were randomly collected from a blackwater tank. A total of 105 selected hazardous substances were measured in both fractions. Of the 24 elements (Ca, Fe, K, Mg, Na, S, Al, Ag, As, Ba, Bi, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Pt, Sb, Sn, Te, Zn) measured in both fractions, 22 were detected in the greywater and 23 in the blackwater. 81 organic substances were selected and measured in both fractions (nonylphenol- and octylphenol ethoxylates, brominated flame-retardants, organotin compounds, PAH, PCB, phthalates, monocyclic aromatics, and triclosan). 46 organic substances were found in greywater and 26 in blackwater. PCB was the only group found in neither grey- nor blackwater. The greywater flow fluctuated, with a specific average flow of 66 L per person and day. The composition of blackwater also fluctuated, with shifting proportions of urine, faeces, and flush water. The specific average blackwater flow was 28.5 L per person and day. The mixture of substances in separate wastewater fractions from Swedish households was too complex to exactly distinguish their specific sources.     

过冷水动态制冰冷冻法处理酸铜电镀废水研究

电镀中常用的酸铜工艺的水洗废水为强酸性,pH值超过了反渗透膜允许的范围,无法应用反渗透法进行浓缩回用于电镀槽。为此,采用全新的过冷水动态制冰技术,对酸铜工艺电镀水洗废水进行冷冻法处理。结果表明,一次冷冻结晶冰融水的溶质去除率超过90%,可满足一级水洗槽补充水洗水的要求;二次冷冻浓缩液达到电镀槽电镀液浓度的80%,可回用于电镀槽补充电镀液。     

Conceptual framework for decentralized green water‐infrastructure systems

We present a model for a decentralized green water‐infrastructure system (DGWIS) based on a new conceptual framework that optimises the use of captured rainwater, recycled wastewater and renewable energy resources. DGWIS is designed for building‐scale localised water supply systems that utilise rainwater and greywater and incorporate advanced small‐scale water treatment systems and renewable local energy sources such as solar and wind. Several constraints are considered: (i) available renewable energy; (ii) greywater production rate; (iii) potential captured rainwater; (iv) water demand; (v) water storage volumes required to accommodate greywater, harvested rainwater and separate water/energy supplies from the city and (vi) water treatment capacities. The proposed DGWIS optimisation framework demonstrates proof‐of‐concept and provides a solid foundation for an innovative paradigm shift towards water and energy sustainability.     

滤池反冲洗废水的直接回流利用研究

通过小试研究了滤池反冲洗废水直接回流利用对出水水质的影响.结果表明,反冲洗废水的直接回流利用对混凝过程有较为明显的强化作用,能够降低出水浊度和残余铝含量;当回流比例<10%时,对出水TOC没有影响;反冲洗废水的直接回流利用会导致出水细菌总数有少量增加,但不会影响消毒效果,同时对总余氯衰减的影响也很小.UFC试验的结果表明,反冲洗废水直接回流利用仅会造成消毒副产物前质含量轻微升高,其增幅为4.5%～7.6%.