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Interest in greywater reuse is increasing in South Africa, because of the potential to supplement scarce freshwater resources in the face of increasing demand and aridity. This paper aims to inform the water savingrisk trade-of associated with residential untreated greywater use, through a statistical analysis of greywater quality results as sourced from prior South African studies. Greywater sources included in this review were the bathroom, kitchen, laundry, mixed and general residential sources. Variability in terms of each of the reported physical, chemical and microbiological constituents by source and between result sets was noted. Statistically significant diferences were evident between the pH, conductivity and phosphorus values of certain sources. A risk assessment undertaken for each of the constituents revealed further variability. The constituent with the highest number of high-risk samples was total dissolved solids. The relatively high risk and negative consequences in greywater practices in terms of public health, the environment, and infrastructure, given this variability, provide insight into the trade-of with potential water savings. It is recommended that a more nuanced view of the potential potable savings associated with greywater reuse and also improved risk management is required by the user.

Granular filtration systems are often used for onsite treatment of greywater. In this study, sand filters modified with the introduction of aluminium-based water treatment sludge were used for treating greywater. Using real greywater, the performance of the modified filters was compared with that of a sand filter in long-term study spanning 73 days. The performance was evaluated in terms of the removal of organic matter, nutrients, solids and faecal coliforms with modified filters operated at different hydraulic loading rates (HLR). Results of the study shows that the modification improved the performance of the filters in terms of chemical oxygen demand (COD), phosphate and faecal coliform removals. Best removals were obtained at the lowest HLR used (9 m 3 /m 2 /day). At this HLR, the mean turbidity, COD, PO 4 3− -P and faecal coliform removals were 91, 54, 65 and 99.5%, respectively for this filter which were significantly higher than those observed for the sand filter (89, 39, 32 and 76.9% respectively). The study thus revealed the potential of water treatment sludge for improving the performance of sand filters treating greywater. Graphical Abstract

A year-long study was conducted to assess the quantity and quality characteristics of greywater generated from different sources of an Indian household. The effect of source separation on greywater quantity and pollutant load contribution was also assessed. Composite samples were collected separately over a period of 24 h from each of the greywater source, namely hand basin, bathroom, kitchen, and laundry, and were analysed for different physico-chemical and microbiological parameters. The mean greywater generation averaged 62 L per person per day. Quantitatively, kitchen and bathroom greywater contributed 37 and 31% of the total greywater volume, respectively, while hand basin and laundry greywater accounted for 11 and 21% of the total greywater generation. Kitchen greywater contributed about 60% of the organic load in terms of biochemical oxygen demand (BOD) and chemical oxygen demand (COD), while laundry greywater was the major contributor of heavy metals and PO 4 -P loads. Hand basin and bathroom greywaters were the major sources of total coliforms. The analysis shows that separation of kitchen and laundry greywater is beneficial as it reduces pollutant load considerably.

This study explores the optimization of iron electrocoagulation for treating laundry greywater, which accounts for up to 38% of domestic greywater. Characterized by high concentrations of surfactants, detergents, and suspended solids, laundry greywater presents complex challenges for treatment processes, posing significant environmental and health risks. Utilizing response surface methodology (RSM), this research developed a second-order polynomial regression model focused on key operational parameters such as the area-to-volume ratio (A/V), current density, electrolysis time, and settling time. Optimal treatment conditions were identified: an A/V ratio of 30 m 2 /m 3 , a current density of 10 mA/cm 2 , an electrolysis duration of 50 min, and a settlement period of 12 h. Under these conditions, exceptional treatment outcomes were achieved, with turbidity removal reaching 94.26% and COD removal at 99.64%. The model exhibited high effectiveness for turbidity removal, with an R 2 value of 94.16%, and moderate effectiveness for COD removal, with an R 2 value of 75.90%. The interaction between the A/V ratio and electrolysis time particularly underscored their critical role in electrocoagulation system design. Moreover, these results highlight the potential for optimizing electrocoagulation parameters to adapt to daily fluctuations in greywater production and meet specific household reuse needs, such as toilet flushing. This tailored approach aims to maximize contaminant separation and coagulant efficiency, balance energy use and operational costs, and contribute to sustainable water management.

The use of greywater reduces the consumption of many resources and is an effective tool for achieving Sustainable Development Goals. In order to assess the rationality of its use as an alternative source of energy and water in buildings, a holistic literature review was carried out based on a bibliometric analysis of publications in these fields. The main bibliographic source was the Web of Science database. This review contributed to a better understanding of the analyzed research field. It also revealed trends in greywater energy recovery and recycling research, indicating that these are developing fields. In recent years, there has been a marked increase in the number of publications on the most popular ways of using greywater in buildings, with the territorial scope of research carried out in the greywater recycling domain being considerably larger than research on greywater energy recovery. The analysis revealed poor cooperation between different universities, especially in the field of greywater energy recovery. In light of previous literature reviews, some important research gaps and further proposals for future research were also identified. They concern, in particular, the simultaneous use of greywater as an alternative source of energy and water. Together with the findings of other researchers and people related to the subject matter, this review can contribute to the further development of greywater energy recovery systems and greywater recycling systems.

Wastewater generated from households can be classified into greywater and blackwater. Greywater makes up a substantial portion of household wastewater. Such water consists of wastewater released from kitchen sinks, showers, laundries, and hand basins. Since the greywater is not mixed with human excreta and due to the low levels of pathogenic contamination and nitrogen, it has received more attention for recycling and reusing in recent decades. Implementing decentralized greywater treatment systems can be an effective solution to overcome water scarcity by supplying a part of water requirement, at least non-potable demand, and decreasing pollutant emissions by eliminating long-distance water transportation in remote regions, like rural and isolated areas. This review focuses on greywater management in terms of reducing environmental risks as well as the possibility of treatment. Effective management of water reclamation systems is essential for a decentralized approach and to ensure the protection of public health. In this regard, the environmental impacts of disposal or reusing the untreated greywater are discussed. Furthermore, the most appropriate technologies that can be employed for the decentralized treatment of greywaters like constructed wetlands, waste stabilization ponds, membrane systems, and electrochemical technologies are described. Finally, this review summarizes resource recovery and sustainable resource reuse.

This paper describes a pilot installation of a green wall treating greywater from an office building in Pune, Maharashtra State (NaWaTech project). The pilot installation is located at the main entrance of the state agency responsible for water supply and sanitation. The experimental analysis is in two phases. First phase analysed the results from green walls filled only with LECA® (lightweight expanded clay aggregate). Since results from the first phase were not satisfactory, a second phase was developed. In the second phase, LECA plus sand and LECA plus coconut fibres were tested as porous media in order to increase residence times and consequently green wall treatment performance. The expected improvements in treatment efficiency have been confirmed by the wider range of observed removal rates between Phase I (chemical oxygen demand, COD, 16–20%) and Phase II (i.e. COD removal in the order of 14–86% and 7–80% for LECA-coconut and LECA-sand, respectively), denoting higher treatment potentialities for the new configurations. The obtained effluent quality was fulfilling the Indian law specifications for reuse in irrigation for all the analysed samples, while only the last samples collected during Phase II were showing an appropriate quality for reuse by flushing toilets.

This study evaluates an integrated greywater reuse and rooftop solar photovoltaic (PV) concept for a luxury residential compound in New Cairo, Egypt (365 buildings; 7,512 units). Based on stated per‑capita end‑use assumptions, total greywater production is 6,300 m 3 /day (2,299,500 m 3 /year), while toilet flushing demand is 2,700 m 3 /day (985,500 m 3 /year). A physico‑chemical onsite treatment train (coagulation, multimedia filtration, chlorination) is specified at 6,300 m 3 /day; using a 5% filter backwash assumption, annual hydraulic recovery is 95% (2,184,525 m 3 /year). The recovered volume exceeds the flushing demand, indicating demand‑limited potable‑water offset for the quantified end use and potential surplus for additional non‑potable applications. The greywater system CAPEX is 3.37 million USD (535 USD/(m 3 /day)) with disaggregated components for in‑building supply, transfer networks, and the treatment plant. Total OPEX is 0.06 USD/m 3 (137,970 USD/year at design flow), yielding a straight‑line levelized cost of water (LCOW) of 0.133 USD/m 3 on a treated‑volume basis and 0.311 USD/m 3 on a potable‑offset basis over the 20‑year analysis horizon. For the PV system, the total initial cost for 365 buildings is 666,455,000 EGP, with modeled annual electricity cost savings of 5,348,550 EGP and an indicative simple payback of approximately 10 years. Overall, the results quantify the magnitude of potable‑water offset and cost metrics achievable at compound scale.

Water scarcity is a huge problem and is been consistently increasing every year. Many of the water systems that keep ecosystems flourishing and feed a growing human population became stressed. Ocean, river, lake, streams are too much polluted. A lot of technologies are available on water recycling. Greywater is around 50% of household water usage but unfailing information relating to both the characteristics of greywater and the variety of recycling technologies are not available. In this review paper we have discussed the relative merits of different options available in greywater recycling and viability of onsite recycling systems.

Addressing the Water-Energy-Food-Environment (WEFE) nexus is critical for sustainable resource management. This study investigates a novel hydroponic system integrating photovoltaic (PV) solar energy and treated greywater (System-II), compared to a grid-powered system (System-I). Key performance indicators, including energy consumption, energy efficiency indices, and CO 2 emissions, are evaluated for the two systems. Additionally, the morphological, physiological, and biochemical parameters of lettuce are measured. System-II achieved superior energy performance, with an energy ratio of 0.11, energy productivity of 0.16 kg/MJ, and specific energy of 6.14 MJ/kg, compared to System-I’s 0.05, 0.07 kg/MJ, and 14.89 MJ/kg, respectively. Additionally, the water use efficiency values were 0.071 kg/L for System-I and 0.073 kg/L for System-II. Moreover, System-II reduced CO 2 emissions by over 94%, emitting only 0.0861 kg CO 2 eq/m 2 , compared to 1.5386 kg CO 2 eq/m 2 from System-I. Morphological and physiological traits of lettuce irrigated with treated greywater remained optimal, showing a mean head weight of 682.9 g, head length and diameter of 17.7 cm and 18.3 cm, relative water content of 93.5%, 5.4% dry matter, and total chlorophyll content of 1.023 mg/g, comparable to those irrigated with tap water. This study highlights the potential of solar-powered hydroponics, utilizing treated greywater as a scalable and sustainable solution for efficient food production in alignment with WEFE nexus objectives. The findings provide insights into optimizing resource management in agricultural systems and contribute to the development of resilient, efficient, and sustainable food production systems in the face of global resource challenges.