Quantity and quality characteristics of greywater: A review

Deciphering the roles of nitrogen source in sharping synchronous metabolic pathways of linear alkylbenzene sulfonate and nitrogen in a membrane biofilm for treating greywater

Nitrogen (N) source is an important factor affecting biological wastewater treatment. Although the oxygen-based membrane biofilm showed excellent greywater treatment performance, how N source impacts the synchronous removal of organics and N is still unclear. In this work, how N species (urea, nitrate and ammonia) affect synchronous metabolic pathways of organics and N were evaluated during greywater treatment in the membrane biofilm. Urea and ammonia achieved efficient chemical oxygen demand (>97.5%) and linear alkylbenzene sulfonate (LAS, >98.5%) removal, but nitrate enabled the maximum total N removal (80.8 ± 2.6%). The nitrate-added system had poor LAS removal ratio and high residual LAS, promoting the accumulation of effluent protein-like organics and fulvic acid matter. N source significantly induced bacterial community succession, and the increasing of corresponded functional flora can promote the transformation and utilization of microbial-mediated N. The nitrate system was more conducive to the accumulation of denitrification related microorganisms and enzymes, enabling the efficient N removal. Combining with high amount of ammonia monooxygenase that contributing to LAS and N co-metabolism, LAS mineralization related microbes and functional enzymes were generously accumulated in the urea and ammonia systems, which achieved the high efficiency of organics and LAS removal.

Optimization of iron electrocoagulation parameters for enhanced turbidity and chemical oxygen demand removal from laundry greywater

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 m2/m3, a current density of 10 mA/cm2, 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 R2 value of 94.16%, and moderate effectiveness for COD removal, with an R2 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.

A critical review of characteristics of domestic wastewater and key treatment techniques in Chinese villages

As of 2022, China's rural sewage treatment rate is only approximately 31 %. Rapid rural development has led to higher demand. However, China's rural areas are complex and face many problems, such as uneven economic development, population distribution, and water availability. Long-lasting and low-cost wastewater treatment measures are needed for application in rural areas. The quantity and quality of rural domestic wastewater in China were characterized first. Next, the hot topic of domestic wastewater in Chinese villages was confirmed via bibliometric analysis using CiteSpace, and the treatment technologies for rural domestic wastewater were compared. Specifically, the technical status and challenges of the most common technology in rural domestic wastewater treatment, constructed wetlands, were summarized.

Household water use and greywater management in Khulna city, Bangladesh

While substantial progress has been made in improving water and sanitation services in low- and middle-income countries, aligned basic services such as greywater, stormwater, and solid waste management have progressed little in recent decades. Data was collected in Khulna city, Bangladesh via a household survey (n = 192) of low-income areas exploring domestic water use and greywater volumes, characteristics, and disposal practices. Most households (71%) use a piped water supply for domestic purposes, supplemented by seasonal rainwater harvesting (26%) and greywater use (13%). Of the total water used by households (mean: 594 L/household/day and equivalent to 116 L/person/day), approximately 58% becomes greywater through bathing, dishwashing, religious practices, handwashing, laundry, and mopping. Greywater produced ranges from 61-1274 L/household/day, with a mean of 345 L/household/day and equivalent to 78.4 L/person/day. Greywater characteristics vary depending on the activity, individual behaviours and any products used during cooking, bathing, or cleaning. After generation, households dispose greywater to open drains (67%), nearby waterbodies (17%) directly to the ground (9%), or decentralised wastewater treatment system (7%). Without services for greywater management, greywater disposal may have considerable public and environmental health implications, necessitating careful attention and oversight from service-providers and stakeholders beyond the household-level.

Electrochemical oxidation of surfactants as an essential step to enable greywater reuse

The practical application of electrochemical oxidation technology for the removal of surfactants from greywater was evaluated using sodium dodecyl sulfate (SDS) as a model surfactant. Careful selection of electrocatalysts and optimization of operational parameters demonstrated effective SDS removal in treating a complex greywater matrix with energy consumption below 1 kWh g-1 COD (Chemical Oxygen Demand), paving the way for a more sustainable approach to achieving surfactant removal in greywater treatment when aiming for decentralized water reuse. Chromatographic techniques identified carboxylic acids as key byproducts prior to complete mineralization. These innovative approaches represent a novel pathway for harnessing electrochemical technologies within decentralized compact devices, offering a promising avenue for further advancements in this field.

A pilot-scale assessment of five common weeds in the sustainable treatment of sewage utilizing SHEFROL®, with prospects of a closed-loop biorefinery

Relative efficacy of five common weeds-of the kind that are either rooted in soil or which freely float over water-was assessed in rapid, effective and sustainable treatment of sewage at pilot plant scale in the recently developed and patented SHEFROL® bioreactors. The plants were utilized in a unit of capacity 12,000 liters/day (LPD) which, after two years of use, was enlarged to handle 40,000 LPD of sewage. It was then further expanded after an year to treat 57,000 LPD. All the five weeds, of which none has previously been tested in a pilot-scale SHEFROL, were able to foster highly efficient primary treatment (in terms of suspended and total solids) and secondary treatment (in terms of BOD and COD) to levels exceeding 85% in most cases. Additionally, the weeds also helped in achieving significant tertiary treatment. At different hydraulic retention times, and at steady state, the five weeds achieved treatment of BOD, COD, suspended solids, nitrogen, phosphorous, copper, nickel, zinc, and manganese in the ranges, 80-95, 79-91, 82-95, 61-71, 51-73, 37-43, 30-38, 39-47, and 27-35%, respectively. It all occurred in a single process step and without the use of any machine or chemical. This made the system not only simple and inexpensive to install but also to maintain. Over continuous long-term operation for four years, the system was seen to be very robust as it was able to handle wide variations in the volumes and characteristics of sewage, as well as absorb shock loads without compromising the reactor performance. The sustainability of the system can be further enhanced by upgrading it to a circular biorefinery. Energy sources in the form of volatile fatty acids (VFAs) can be extracted from the weeds removed from SHEFROL and then the weeds can be converted into organic fertilizer using high-rate vermireactors recently developed by the authors.

Exploring effects of carbon, nitrogen, and phosphorus on greywater treatment by polyculture microalgae using response surface methodology and machine learning

The microalgae-based wastewater treatment is a promising technique that contribute to achieving sustainable development goals (SDGs), such as SDG-6, "Clean Water and Sanitation". However, it is strongly influenced by the initial composition of wastewater. In this study, the impact of initial organics and nutrient concentration on the removal of total organic carbon (TOC), total carbon (TC), ammonium (NH4+), total nitrogen (TN), and phosphate (PO43-) from greywater using native polyculture microalgae was explored. Response surface methodology was employed along with two machine learning approaches, AdaBoost and XGBoost, to evaluate the interactions among three main factors: TOC, NH4+, and PO43-, and their effects on treatment efficiency. The C/N ratios for achieving maximum TOC and TC removal efficiency of 99.2% and 97.7% were determined to be 10.3, and 65.4-73.6, respectively. Notably, the N/P ratio did not significantly affect their removal. The highest NH4+ removal efficiency, reaching 96.2%, was attained at C/N ratios of 4.3, 24.0, 38.2, and 212.9, coupled with N/P ratios of 0.3, 2.6, and 23.4. Highest TN removal efficiency of 77.2% was achieved at C/N and N/P ratios of 12.2 and 2.0, respectively. Highest PO43- removal of 78.8% was obtained at N/P ratio 12.8. However, C/N ratio did not affect the removal efficiency. Maintaining these specified C/N and N/P ratios in the influent greywater would ensure that the treated greywater meets the required standards for various reuse applications, including flushing, groundwater recharge, and surface water discharge. The integration of RSM with AdaBoost and XGBoost provided accurate predictions of removal efficiencies. For all the models, XGBoost had the highest R2, and lowest MAE and MSE values. The cross validation of RSM models with AdaBoost and XGBoost further reinforced the reliability of these models in predicting treatment outcomes.

Identification of Membrane Fouling with Greywater Filtration by Porous Membranes: Combined Effect of Membrane Pore Size and Applied Pressure

Membrane fouling caused by complex greywater synthesized by personal care products and detergents commercially available for household applications was investigated using dead-end microfiltration (MF) and analyzed systematically by a multistage Hermia blocking model as a first attempt. The highest flux decline was associated with the smallest pore size of the membrane (0.03 μm). This effectiveness was more pronounced at higher applied pressures to the membrane. A cake layer was formed on the membrane consisting mainly of silica particles present as ingredients in greywater. Although organic rejection was low by the porous MF membrane, the organic compound contributed to membrane fouling in the filtration stage. With a 0.03 μm pore size of the membrane, dominant fouling mechanisms were classified into three stages as applied pressure increased, such as complete pore blocking, intermediate pore blocking, and cake layer formation. Specifically, during the early stage of membrane filtration at 1.5 bar, membrane fouling was determined by complete pore blocking in the 0.10 μm pore size of the membrane. However, the later stage of membrane fouling was controlled mainly by intermediate pore blocking. Regardless of the applied pressure, pore constriction or standard blocking played an important role in the fouling rate with a 0.45 μm pore size of the membrane. Our results also support that complex formation can occur due to the concentration of organic and inorganic species present in simulated greywater. Thus, strategic approaches such as periodic, chemically enhanced backwashing need to be developed and tailored to remove both organic and inorganic fouling from MF membranes treating greywater.

Development of data-driven models for the optimal design of multilayer sand filters for on-site treatment of greywater

Greywater, with limited content of pathogens, makes up more than half of the produced wastewater in urban areas. Given the high cost of wastewater management and treatment, it causes sense to collect greywater separately at the source and employ an on-site treatment system to increase opportunities for on-site water reuse. For this purpose, this paper aims to propose a multilayer granular filter as an inexpensive and simple on-site treatment method for greywater reuse. Furthermore, as determining the optimal structure of multilayer filters is a serious challenge, a simulation-optimization model is developed for determining the best filter configuration. An Artificial Neural Network (ANN) is trained based on experimental results to simulate the filter performance with different combinations of layers and the Genetic Algorithm (GA) is used to find the optimal thickness of different layers based on ANN simulation results. The proposed filter in this paper for greywater treatment consists of silica sand (in three different gradings) and activated carbon (with fixed grading) and treatment measures for evaluation of filter performance are considered as Chemical Oxygen Demand (COD) and Electrical Conductivity (EC). Due to difficulties in collecting, transferring, and storing the real greywater, synthetic greywater was used in this study. 49 experiments with different combinations of filter media thicknesses were performed and the performance of the filter was analyzed. Generally, three-layer filters perform better in COD and EC reduction, however, the average COD and EC elimination equals 36.3% and 15.1%, respectively, which indicates more efficiency of filter in COD reduction in comparison with EC. Based on the optimization-simulation model and experimental results, a filter consisting of 33 cm of fine sand, 20 cm of activated carbon, and 7 cm of medium sand results in the maximum efficiency and can reduce the COD and EC of greywater by 72% and 30%, simultaneously. According to the optimization outputs, the ideal filter can treat greywater up to having EC of 1000 μS/cm and COD of 321 mg/L, which is generally suitable for irrigation purposes.

Water consumption assessment and classification in industrial buildings - The case study of Continental Advanced Antenna, Vila Real, Portugal

Water abstraction for the industrial, domestic, and agricultural sectors increased from 0.67 trillion m3/year in the 1900s to 3.79 trillion m3/year in 2000, and it is expected to increase by 55 % in 2050 when the majority of the world's population will live in urban areas. Concerning the industrial sector, despite the efforts to a more sustainable use, water is still an essential and irreplaceable resource, and this situation tends to increase due to modern industrial installations that require large-scale and complex water distribution systems. Usually, industries consume a large volume of water, however due to more and severer regulations, it is necessary to propose strategies for the aid of water conservation. This article presents a methodology to analyse, classify and optimize water consumption in industrial installations, using a real case study located in Vila Real, Portugal. The daily water consumption per worker, the daily record of use of each type of device and the hourly usage pattern were analysed and a classification was achieved according to the ANQIP (National Association for Quality in Building Installations) calculator. The case study revealed a great opportunity of improvement in what concerns to water efficient use. Some measures to improve the efficiency of water use in the building were pointed out, such as the use of rainwater harvesting systems, the use of aerators and replacements of taps and faucets when possible. The methodology is expeditious and user-friendly, and easy to replicate in similar cases, however it reveals some difficulties (especially in the data collection process that is made by inquiry, once it is always dependent on the respondent sensibility and willingness).

Nutrient treatment of greywater in green wall systems: A critical review of removal mechanisms, performance efficiencies and system design parameters

Greywater has lower pathogen and nutrient levels than other mixed wastewaters, making it easier to treat and to reuse in nature-based wastewater treatment systems. Green walls (GWs) are one type of nature-based solutions (NBS) that are evolving in design to support on-site and low-cost greywater treatment. Greywater treatment in GWs involves interacting and complex physical, chemical, and biological processes. Design and operational considerations of such green technologies must facilitate these pivotal processes to achieve effective greywater treatment. This critical review comprehensively analyses the scientific literature on nutrient removal from greywater in GWs. It discusses nutrient removal efficiency in different GW types. Total nitrogen removal ranges from 7 to 91% in indirect green facades (IGF), 48-93% for modular living walls (MLW), and 8-26% for continuous living walls (CLW). Total phosphorus removal ranges from 7 to 67% for IGF and 2-53% for MLW. The review also discusses the specific nutrient removal mechanisms orchestrated by vegetation, substrates, and biofilms to understand their role in nitrogen and phosphorus removal within GWs. The effects of key GW design parameters on nutrient removal, including substrate characteristics, vegetation species, biodegradation, temperature, and operating parameters such as irrigation cycle and hydraulic loading rate, are assessed. Results show that greater substrate depth enhances nutrient removal efficiency in GWs by facilitating efficient filtration, straining, adsorption, and various biological processes at varying depths. Particle size and pore size are critical substrate characteristics in GWs. They can significantly impact the effectiveness of physicochemical and biological removal processes by providing sufficient pollutant contact time, active surface area, and by influencing saturation and redox conditions. Hydraulic loading rate (HLR) also impacts the contact time and redox conditions. An HLR between 50 and 60 mm/d during the vegetation growing season provides optimal nutrient removal. Furthermore, nutrient removal was higher when watering cycles were customized to specific vegetation types and their drought tolerances.

Modeling the effect of improved sewage disposal rates on ecological status for aquatic organisms in Japan

Improving sewage disposal rates is an important policy for maintaining the health of aquatic organisms in river environments. In Japan, the rate is not yet 100 %. Two measures are necessary to eliminate the discharge of untreated greywater: (1) increase the number of households connected to sewage lines in areas with sewage systems, and (2) replace single-type household onsite wastewater treatment systems (OWTSs) with combined-type systems. To estimate the effect of improving the disposal rate on river water quality, we developed a hydrology-based organic pollution assessment model with a gridded spatial resolution of 250 m to estimate the biochemical oxygen demand (BOD) in rivers in Gunma Prefecture, Japan. We considered three scenarios based on the sewage disposal rate of 70.5 % in 2015. In Scenario A, the disposal rate is increased to 75.2 % in 2030 by increasing the connection rate to sewage lines. In Scenario B, the rate is increased to 88.2 % in 2030 through additional progress in converting from single-to combined-type OWTSs. In Scenario C, the rate reaches 100 % by 2040. The ecological status of rivers was evaluated using taxon richness of Ephemeroptera, Plecoptera, and Trichoptera estimated from its reported relationship to BOD. The number of sites in Gunma Prefecture polluted by organic waste classified as III (poor) and IV (very poor) was estimated to be 1610 under the present state (2015) and decreased to 1212 (25 % reduction) in Scenario A, 619 (62 % reduction) in Scenario B, and 50 (97 % reduction) in Scenario C, with the improvements mainly in small branch rivers. The effects of improved disposal rates were mainly evident in areas with relative high population densities using single-type OWTSs outside of areas with a sewage system, and measures taken in these areas were shown to be effective.

Greywater treatment in a green wall using different filter materials and hydraulic loading rates

Green walls in urban environments can be both an aesthetic feature and be of practical use in greywater treatment. This study evaluates the effect of different loading rates (4.5 l/d, 9 l/d, and 18 l/d) on the efficiency of treating actual greywater from a city district in a pilot-scale green wall with five different filter materials as substrates (biochar, pumice, hemp fiber, spent coffee grounds (SCG), and composted fiber soil (CFS)). Three cool climate plant species, Carex nigra, Juncus compressus, and Myosotis scorpioides, were chosen for the green wall. The following parameters were evaluated: biological oxygen demand (BOD), fractions of organic carbon, nutrients, indicator bacteria, surfactants, and salt. Three of the five materials investigated - biochar, pumice, and CFS - showed promising treatment efficiencies. The respective overall reduction efficiencies of BOD, total nitrogen (TN) and total phosphorus (TP) were 99%, 75%, and 57% for biochar; 96%, 58%, and 61% for pumice; and 99%, 82% and 85% for CFS. BOD was stable in the biochar filter material with effluent concentrations of 2 mg/l across all investigated loading rates. However, higher loading rates had a significantly negative effect on hemp and pumice for BOD. Interestingly, the highest loading rate (18 l/d) flowing over pumice removed the highest levels of TN (80%) and TP (86%). Biochar was the most effective material in removing indicator bacteria, with a 2.2-4.0 Log₁₀ reduction for E. coli and enterococci. SCG was the least efficient material, giving a higher BOD in the effluent than in the influent. Therefore, this study presents the potential of natural and waste-derived filter materials to treat greywater effectively and the results can contribute to the future development of nature-based greywater treatment and management practices in urban areas.

Recent advances in aqueous virus removal technologies

The COVID-19 outbreak has triggered a massive research, but still urgent detection and treatment of this virus seems a public concern. The spread of viruses in aqueous environments underlined efficient virus treatment processes as a hot challenge. This review critically and comprehensively enables identifying and classifying advanced biochemical, membrane-based and disinfection processes for effective treatment of virus-contaminated water and wastewater. Understanding the functions of individual and combined/multi-stage processes in terms of manufacturing and economical parameters makes this contribution a different story from available review papers. Moreover, this review discusses challenges of combining biochemical, membrane and disinfection processes for synergistic treatment of viruses in order to reduce the dissemination of waterborne diseases. Certainly, the combination technologies are proactive in minimizing and restraining the outbreaks of the virus. It emphasizes the importance of health authorities to confront the outbreaks of unknown viruses in the future.

Granular media filtration for on-site treatment of greywater: A review

Rapid urbanization and industrialization have put pressure on water resources and centralized wastewater treatment facilities and the need for greywater treatment at decentralized levels is increasing. This paper reviews the studies that used granular filtration for the treatment of greywater. Filter media characteristics that helps in the selection of suitable sustainable and environmental friendly materials without compromising the quality of treated greywater is first reported. The effect of type of filter media, media size and media depth along with the effect of operating conditions are discussed in detail. The choice, role and effect of different pre-treatment alternatives to granular media filtration are also presented. The efficiency of the filters to remove different physicochemical and microbial parameters was compared with different reuse guidelines and standards. Reported studies indicate that not only filter media characteristics and operating conditions but also the quality of raw greywater significantly influence the filter performance. Based on the source of greywater and desired reuse option, different granular media filtration alternatives are suggested. Operation of filters with properly selected media at optimum conditions based on the source of greywater helps filter in achieve the different reuse standards.

Application of leaf analysis in addition to growth assessment to evaluate the suitability of greywater for irrigation of Tilia cordata and Acer pseudoplatanus

Water is the key resource in fulfilling the cooling function of plants in urban environments and needs to be supplied reliably and adequately, especially during dry periods. To avoid an unsustainable use of high-quality drinking water for irrigation, the reuse of greywater should be implemented for Green Infrastructure irrigation in the sense of the circular economy. In this study, the influence of greywater irrigation on vitality of two trees species, Tilia cordata and Acer pseudoplatanus, was determined by investigating the effect of irrigation with raw or treated greywater in comparison to municipal tap water. Plant growth parameters were measured, including leaf area, number of leaves, average leaf area and annual growth. In addition, the relative chlorophyll content was determined and image analysis was used to identify vital and necrotic leaf parts. While treatment did not affect growth after one growing season A. pseudoplatanus had significantly higher leaf necrosis (34.8%) when irrigated with raw greywater compared to treated greywater (15.5%) and tap water (5.8%). Relative chlorophyll content of T. cordata irrigated with tap water decreased over time until it was significantly lower (28.5) then the greywater treatments (34.5 and 35). Image analysis of leaves to quantify necrosis proved to be a sensitive method to quantify plant health and showed negative effects earlier than an analysis of growth. Anionic surfactants and electrical conductivity had a significant influence on plant vitality. Therefore, plant selection should take these parameters into account, when planning green infrastructure irrigated with greywater.

Recent insights into greywater treatment: a comprehensive review on characteristics, treatment technologies, and pollutant removal mechanisms

With the rapid socio-economic and industrial development, the problem of water shortage is becoming increasingly serious. Seeking alternative water sources to reduce the need for freshwater resources is an increasing concern. Household greywater production is high and accounts for about 50-80% of domestic wastewater. In recent years, the in situ treatment and reuse of greywater have received widespread attention. Treated greywater can be used for non-potable purposes such as toilet flushing and irrigation, which can greatly reduce the pressure of freshwater resource shortage. This paper reviews the sources and characteristics of greywater and analyzes its quantity and quality. In addition, this paper outlines and summarizes various greywater treatment technologies commonly used, including physical, biological, and chemical treatment technologies, as well as combination technologies. Understanding the mechanisms of contaminant removal is essential for effective greywater treatment. While discussing different treatment technologies, we focus on the removal mechanisms of pollutants from greywater, including organics, nutrients, surfactants, and emerging contaminants. Finally, future perspectives on greywater management and reuse are presented. Through a comprehensive review, we expect that this review will help the reader to better understand the characteristics of greywater and to more rationally select the appropriate treatment technology based on the removal mechanism of pollutants.

Unconventional water resources: Global opportunities and challenges

Water is of central importance for reaching the Sustainable Development Goals (SDGs) of the United Nations. With predictions of dire global water scarcity, attention is turning to resources that are considered to be unconventional, and hence called Unconventional Water Resources (UWRs). These are considered as supplementary water resources that need specialized processes to be used as water supply. The literature encompasses a vast number of studies on various UWRs and their usefulness in certain environmental and/or socio-economic contexts. However, a recent, all-encompassing article that brings the collective knowledge on UWRs together is missing. Considering the increasing importance of UWRs in the global push for water security, the current study intends to offer a nuanced understanding of the existing research on UWRs by summarizing the key concepts in the literature. The number of articles published on UWRs have increased significantly over time, particularly in the past ten years. And while most publications were authored from researchers based in the USA or China, other countries such as India, Iran, Australia, and Spain have also featured prominently. Here, twelve general types of UWRs were used to assess their global distribution, showing that climatic conditions are the main driver for the application of certain UWRs. For example, the use of iceberg water obviously necessitates access to icebergs, which are taken largely from arctic regions. Overall, the literature review demonstrated that, even though UWRs provide promising possibilities for overcoming water scarcity, current knowledge is patchy and points towards UWRs being, for the most part, limited in scope and applicability due to geographic, climatic, economic, and political constraints. Future studies focusing on improved documentation and demonstration of the quantitative and socio-economic potential of various UWRs could help in strengthening the case for some, if not all, UWRs as avenues for the sustainable provision of water.

Quantity and quality characteristics of greywater from an Indian household

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 PO₄-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.

Greywater characteristics, impacts, treatment, and reclamation using adsorption processes towards the circular economy

The gap between water demand and available water supply led to wastewater treatment, particularly greywater. Due to specific characteristics of grey wastewater, treatment and recycling of this type of wastewater capture global attention. This paper presents a literature review of the remediation of greywater by adsorption processes. Besides, the reclamation of the grey wastewater in the context of the circular economy is highlighted. In this regard, the characterization of various types of grey wastewater, the potential risks associated with greywater, and the properties of reclaimed water as per the regulation or guideline are summarized. These standards vary based on the application of reused water and from a country to another country. Furthermore, this review elucidates the adsorption process in terms of the type of adsorbents, modification of adsorbents and their regeneration process, adsorption isotherm, kinetics and thermodynamic of adsorption, and optimization of adsorption system. Finally, the removal of different pollutants from greywater by various adsorbents and techno-economic aspects are illustrated.

Modelling Treated Laundry Greywater Reuse for Irrigation Using an Affordable Treatment Method and Seed Germination Test

A potential solution in areas facing water shortages is greywater (GW) reuse. GW is produced in bathrooms, laundry rooms, and kitchens of households. With proper treatment, it can be an alternative source for the agriculture sector, which consumes approximately 70% of the world’s water. This paper represents the characterization of synthetic laundry GW fraction (LGW), its treatment and modelling of treated LGW reuse for irrigation using a seed germination test. LGW’s constant quality (pH = 8.0 ± 0.3, turbidity = 174 ± 73 NTU, BOD5 = 300 ± 60 mgL−1, TOC = 162 ± 40 mgL−1) is suitable for testing the treatment method’s efficiency. Coagulation–flocculation, applying iron(III) chloride and sand filtration as a simple treatment combination, generates good-quality irrigation water (pH = 7.27 ± 0.23, turbidity = 0.6 ± 0.4 NTU, BOD5 = 17 ± 8 mgL−1, TOC = 16 ± 6 mgL−1). Seed germination tests with different waters, and elemental analysis of water, roots, and stems of the plants were done to verify the plants’ quality. The sodium adsorption ratio (SAR) for the raw LGW (SAR = 4.06) was above the threshold (<3) for safe irrigation, thus it is not recommended for this purpose. Based on the elemental analysis results and SAR value of treated LGW (SAR = 2.84), it can potentially be used for irrigation purposes.

Evaluation of the influence of filter medium composition on treatment performances in an open-air green wall fed with greywater

According to the European Research and Innovation Policy Agenda, nature-based solutions (NBSs) are key technologies to improve the sustainability of urban areas. Among NBSs, green walls have been recently studied for several applications, among the others the treatment of lowly polluted wastewater flows as greywater (GW, e.g. domestic wastewater excluding toilet flushes). This work is aimed at the evaluation of the influence of four additives (compost, biochar, granular activated carbon, polyacrylate) mixed with a base filter medium made of coconut fibre and perlite, on the performances of a green wall fed in batch mode with synthetic GW. The green wall was operated with a high hydraulic loading rate of GW (740.8 L/m²/day) in open-air winter conditions (3.5-15 °C measured for GW) between January and April. The performances of the green wall have been assessed though the monitoring every 1-2 weeks of physicochemical and biological parameters (pH, electric conductivity, total suspended solids, dissolved oxygen, BOD₅ and COD, nitrogen and phosporus compounds, chlorides and sulphates, anionic surfactants and E. coli). Removal performances were excellent for BOD₅ (>95%) and E.coli (>98%) for all additives; compared to the base medium, biochar was the best performing additive over the highest number of parameters, achieving removals equal to 51% for COD, 47% for TKN and nitric nitrogen and 71% for anionic surfactants. Compost also achieved high removal performances, but the frequent clogging events occurred during the monitoring period do not make its use recommendable. Granular activated carbon and the combination of biochar and polyacrylate performed better than the base medium, but only about the removal of nitric nitrogen. These results demonstrated that, in the considered experimental boundaries, biochar could improve the overall treatment performances of a green wall fed by GW and operated in challenging conditions.

Removal of personal care products in greywater using membrane bioreactor and constructed wetland methods

Personal care products (PCPs) are contaminants of emerging concern because of their continuous input into the environment. In this study, membrane bioreactor (MBR) and constructed wetland (CW) methods were used to investigate the effect and mechanism of conventional pollutant and PCP removal from greywater. The effluent of both the MBR- and CW-treated greywater met the reclaimed water reuse standard in China. Conventional pollutants and five target PCPs had a higher removal efficiency in the MBR than in the CW. The removal rates of the PCPs, including Tuina musk (AHTN), were >80% using MBR and CW methods. The main pathway of removing PCPs in the MBR was sludge adsorption and biodegradation, whereas the contribution of the membrane module was weak. The main pathway of removing PCPs in the CW was the combined action of plant absorption, microbial biodegradation, and substrate adsorption, depending on the PCP type. Ethyl hexyl methoxycinnamate (EHMC) has strong biological oxidizability and was mainly removed by biodegradation, whereas Jiale musk (HHCB) and AHTN were mainly removed by adsorption. Six types of CW substrates were investigated, and perlite showed the best adsorption effect for the five target PCPs. The optimal substrate adsorption pH was 7. This study provides important technical information on the effective removal of conventional pollutants and PCPs in greywater and the preparation of high-quality reclaimed water.

Total value wall: Full scale demonstration of a green wall for grey water treatment and recycling

Greywater treatment and reuse for non-potable purposes in urban areas has become a widely researched topic to reduce the burden on fresh water resources. This study reports on the use of a green wall for treating grey water and reusing the effluent for toilet flushing, called Total Value Wall (TVW). Initially, the effectiveness of (mixtures of) different substrates, i.e. lava, lightweight expanded clay aggregates, organic soil and biochar was investigated by means of column tests. All substrates were first examined for hydraulic characteristics and later on the columns were fed with synthetic grey wastewater and followed up in terms of removal efficiency of COD and detergents. The mixture consisting of lava (50%), organic soil (25%) and biochar (25%) proved to be optimal both in terms of percolation rates and removal efficiencies, and was thus selected for the full-scale system. The full-scale TVW of 14.4 m² was installed at a terraced house in Ghent (Belgium), and was loaded with grey water at 100 L per day. Influent and effluent quality were routinely monitored by grab sampling, water savings were monitored by means of flow meters, and electricity consumption was also accounted for. The TVW was further equipped with sensors that measure temperature, Particulate Matter (PM₁₀) and CO₂ in the air. The full-scale system obtained effluent concentrations of 13 mg.L^-1 TSS, 91 mg.L^-1 COD and 5 mg.L^-1 BOD₅. Ammonium and total coliforms were removed with removal rates of 97% and 99% (2 log units) respectively. However, an increase in effluent concentration of nitrate and phosphate was observed due to leaching from the selected substrate. Available data from the temperature sensors have clearly demonstrated the additional benefit of the TVW as an insulating layer, keeping the heat outside on warmer days, and keeping the heat inside on colder days. Overall, this study demonstrated that the TVW is a sustainable system for greywater treatment and reuse.

Polymer-based immobilized Fe2O3-TiO2/PVP catalyst preparation method and the degradation of triclosan in treated greywater effluent by solar photocatalysis

The present study involves a novel protocol to develop a ternary composite catalyst for an effective post-treatment technique for greywater. The ternary film of Fe₂O₃-TiO₂/polyvinyl pyrrolidine (PVP) is coated on a glass tube using spray coating with annealing at 320 °C. The structure, thermal, microstructure, and surface properties of the coated film are characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and Thermo Gravimetric Analysis (TGA). The scratch hardness of photocatalysts at different Fe₂O₃/TiO₂ compositions is investigated based on the width measurement of scratch using FESEM analysis. Results show that at an optimum coating of 5% of Fe₂O₃/TiO₂ composition catalytic film, the maximum scratch hardness (7.984 GPa) is obtained. Also, the photocatalyst has the highest cohesive bond strength and wearing resistance. The degradation of triclosan (TCS) in treated greywater, discharged from the anaerobic-aerobic treatment system, is investigated at a lab-scale using a solar photocatalytic reactor. The response surface analysis has been performed from the different sets of experimental trials for various optimal parameters. It is observed that the TCS degradation efficiency of 83.27% has resulted under optimum conditions.

Effect of operating mode on the performance of sand filters treating greywater

A long-duration laboratory study spanning more than 6 months was conducted to evaluate the effect of operating mode on the performance of sand filters for greywater treatment. Performance of saturated and unsaturated filters operated in continuous or intermittent mode was evaluated using settled real greywater. Effects of pause period and higher loading rate on their performance were also evaluated. Furthermore, the effect of the depth of the filter medium on the performance of the filters was also assessed. The saturated filters operated continuously or intermittently performed significantly better than the respective unsaturated filters. Saturated continuous (SC) and unsaturated intermittent (UI) filters were the best and worst performers amongst the different filters. SC filter removed on an average 98% turbidity, 76% BOD, 88% COD, 84% ammonia-N (NH₄-N) and 95% phosphate (PO₄-P). Up to 99.68% (2.40 log) removal of faecal coliforms was also achieved by this filter. SC filter showed stable and reliable performance as its effluent quality was insensitive to fluctuations in influent quality. The pause period significantly affected the removal of some of the parameters. Doubling the hydraulic loading rate significantly affected the performance of continuous filters. Though most of the pollutant removal occurred in the top 10 cm in all the filters, a depth of 50 cm was found optimum for the removal of different pollutants. Whilst all the filters produced effluent conforming to different reuse standards except microbial standards, saturated continuous filter (SC) could also meet the faecal coliform standards towards the end of the filter operation.

An Assessment of Treated Greywater Reuse in Irrigation on Growth and Protein Content of Prosopis and Albizia

This study investigated the influence of treated greywater on growth and protein content of multipurpose (forage and ornamental) transplants, Prosopis juliflora L., Prosopis tamarugo L., and Albizia lebbeck L. Transplants of tested species were irrigated with treated greywater, diluted greywater (grey + distilled water, 1:1/by volume), and distilled water (control) for seven months. Water quality analysis showed that the concentrations of nutrients and heavy metals found in the greywater were within the acceptable range compared with Jordan Institution for Standard and Metrology (JISM) and the World Health Organization (WHO) thresholds for safe use of greywater. Escherichia coli found in the greywater were lower compared to JISM and WHO guidelines for the safe use of greywater. Irrigation with treated greywater increased shoot fresh weight by 24–39% and dry weight by 34–40% compared to diluted greywater and control. No significant difference in crude protein was noticed between water treatments. Prosopis species (P. juliflora Albizia lebbeck L. and P. tamarugo Albizia lebbeck L.) had higher shoot fresh (35%) and dry weight the same species had lower crude protein (44%) when compared to Albizia lebbeck Albizia lebbeck L. The reuse of treated greywater for landscaping or forage production alleviates the demand for water resources and reduces the pressure on wastewater treatment plants. However, considering the controversial findings of previous studies on greywater quality (especially, long-term reuse), the reuse of treated greywater needs to be considered with caution and periodic quality analyses and economic assessments are required.

Insights into the effects of heavy metal pressure driven by long-term treated wastewater irrigation on bacterial communities and nitrogen-transforming genes along vertical soil profiles

Irrigation with treated wastewater (TWW) influences soil ecological function due to the accumulation of heavy metals (HMs) and nutrients in soils. However, the interaction between HMs and microbial processes in TWW-irrigated soil has not been fully explored. We investigated the effect of HMs on bacterial communities and nitrogen-transforming (N-transforming) genes along vertical soil profiles irrigated with domestic TWW (DTWW) and industrial TWW (ITWW) for more than 30 years. Results indicate that long-term TWW irrigation reshaped bacterial community structure and composition. Irrigation with ITWW led to increased accumulation of Cd, Cr, Cu, Pb, Zn, and Ni in soils than DTWW. Accumulation of inorganic N, soil organic carbon, and HMs in topsoil irrigated with ITWW contributed to the activities of Micrococcaceae. The effect of the activation of nutrient factors on Bacillus, which was the dominant species in DTWW-irrigated soils, was greater than that of HMs. HM pressure driven by ITWW irrigation changed the vertical distribution of N-transforming functional genes, increasing the abundance of amoA gene and decreasing that of nifH through soil depth. ITWW irrigation enhanced the denitrification capacity in topsoil; ammonia-oxidizing capacity in deeper soil was increased after long-term irrigation with DTWW and ITWW, suggesting a potential risk of nitrogen loss.

Bioelectrochemical Greywater Treatment for Non-Potable Reuse and Energy Recovery

Greywater normally represents the largest fraction of wastewater generated in buildings and may be suitable for non-potable reuse after on-site treatment. Conventional technologies for greywater treatment include sequencing batch reactors, membrane filtration, and membrane biological reactors. Even though these can be very effective, they are highly energy consuming and may negatively impact the energy balance of the building where they are installed. Microbial fuel cells (MFCs) have emerged as a sustainable technology for contaminant removal and energy production from a variety of substrates. In this study, the application of MFCs for greywater treatment is reported, with a particular focus on the analysis of energy losses, in view of non-potable reuse. MFCs were fed with different types of greywater, characterized by either high or low conductivity, because greywater’s conductivity may greatly differ based on its origin; in either case, organic matter (chemical oxygen demand; COD) removal was higher than 85% and not influenced by the influent conductivity, coupled with a maximum power production of 0.46 mW L−1 and 0.38 mW L−1. Electrolyte overpotentials were dramatically higher in the case of low conductivity greywater (20% vs. 10%, compared to high conductivity influent); these overpotentials are related to the conductivity of the influent, showing that low conductivity hindered energy generation, but not COD removal. Polarization and power curves showed higher internal resistance in the case of low conductivity, confirming the overpotentials’ analysis. Results showed the feasibility of the use of MFCs in greywater treatment, with potential to reduce the energy demand connected to its reuse compared to conventional technologies; coupling with a disinfection stage would be necessary to fully comply with most non-potable reuse regulations.

Performance of a Micro-Scale Membrane Reactor for Greywater Treatment at Household Level

An aerated membrane reactor (25 L working volume) equipped with 1.5 m² hollow-fiber module was designed and operated using synthetic greywater for household water reuse. Activated sludge (MBR), activated carbon (PAC), zeolite (ZEO) and iron hydroxide (GEH) were added in separate experiments to optimize membrane hydraulic performance and removal efficiency of organics. The use of additives improved permeate quality (in terms of Chemical Oxygen Demand—COD) compared to the direct membrane filtration mode of operation. GEH and MBR were efficient for phosphorus removal, which was not the case for PAC and ZEO. No significant improvement of membrane flux was recorded when PAC, ZEO or GEH were added inside the membrane tank. The MBR system displayed optimum performance during medium-term operation, with COD removal efficiency 85% and permeate flux between 40 and 25 L m⁻² h⁻¹. The capital costs of the proposed technology were around 300 € and the operational costs below 80 € yr⁻¹, rendering the process feasible at household level. Greywater treatment systems for household applications are still on their infancy; however, this trend is expected to change due public perception towards circular economy, water conservation and reuse.

Reusing greywater for cultivation of Capsicum frutescens and Calendula officinalis

This study investigated the impact of greywater application for home yard gardening. Greywater was collected and treated using screening, sedimentation and solar disinfection methods. Finally, a field experiment was conducted to investigate the impact of untreated and treated greywater on a selected vegetable, Capsicum frutescens and flowering plant, Calendula officinalis for 2 months. The findings depicted that untreated greywater contains higher macro-nutrients with excessive bacterial population compared with tap water (control), however, the treatment process reduced the concentration of most of the unwanted parameters from greywater samples to bring them into irrigation standards. Overall, treated greywater irrigation showed the species-specific impact on experimental plants with more stimulation in Capsicum frutescens species compared with tap water irrigation. Both treated and untreated greywater irrigation increased the growth parameters of Calendula officinalis in comparison with control. The impact was not significant for most of the parameters of Calendula officinalis while compared between greywater (treated and untreated) and control, and between treated and untreated greywater irrigation. Treated greywater irrigation significantly stimulated most of the parameters of Capsicum frutescens while untreated greywater increased only moisture content, and number of branches compared with control. Most interestingly, treated greywater irrigation had significant impact on Capsicum frutescens particularly for number of branches and leaves compared with untreated greywater irrigation. In fine, the greywater, after treatment was bacterially safe and had positive impact on plant growth. The findings of this study will help to conserve irrigation water and to protect and manage aquatic ecosystem from the adverse impact of wastewater.

Sewers induce changes in the chemical characteristics, bacterial communities, and pathogen distribution of sewage and greywater

Sewers may affect the characteristics and bacterial communities of wastewater, and need be studied as they may impact treatment facilities and recycling operations. In this study, the wastewater characteristics and bacterial communities from the inflow and outflow of two sewers (sewage and greywater) were analyzed. The chemical oxygen demand was significantly reduced in the sewage and greywater sewer and the greywater sewer generated less sulfide and methane. Proteobacteria, Bacteroidetes, and Firmicutes as the major phyla in sewage and greywater and sewer biofilms. Sewer conveyance caused changes in the distribution and community interaction of suspended bacteria. Greywater contained abundant water-related pathogenic bacteria (WPB) and some WPB (e.g. Aeromonas, Klebsiella and Shigella) number in greywater were not lower than sewage. Sewers could increase the number of Shigella in sewage and decrease the number of Acinetobacter in greywater. Further treatment or disinfection of greywater collected by sewers was necessary and directly reuse of greywater without treatment should be avoided.