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

Role of advanced cleaning and sanitation techniques in biofilm prevention on dairy equipment

Biofilm formation on dairy equipment is a persistent challenge in the dairy industry, contributing to product contamination, equipment inefficiency, and economic losses. Traditional methods such as manual cleaning and basic chemical sanitation are discussed as foundational approaches, followed by an in-depth investigation of cutting-edge technologies, including clean-in-place systems, high-pressure cleaning, foam cleaning, ultrasonic and electrochemical cleaning, dry ice blasting, robotics, nanotechnology-based agents, enzymatic cleaners, and oxidizing agents. Enhanced sanitation techniques, such as dry steam, pulsed light, acidic and alkaline electrolyzed water, hydrogen peroxide vapor, microbubble technology, and biodegradable biocides, are highlighted for their potential to achieve superior sanitation while promoting sustainability. The effectiveness, feasibility, and limitations of these methods are evaluated, emphasizing their role in maintaining dairy equipment hygiene and reducing biofilm-associated risks. Additionally, challenges, such as equipment compatibility, cost, and regulatory compliance, are addressed, along with insights into future directions and innovations, including automation, smart cleaning systems, and green cleaning solutions. This review provides a comprehensive resource for researchers, industry professionals, and policymakers aiming to tackle biofilm formation in dairy production systems and enhance food safety, operational efficiency, and sustainability.

Resilience to flow variability of an open-air green wall for greywater treatment

Water management in urban areas is challenged by climate change and increasing population, and the reduction of water consumption in urban areas is becoming a major issue. Thus, domestic greywater (GW) can be a valuable water source for non-potable purposes, coupled with the benefits provided by a nature-based treatment approach. In this context, green walls have been proposed for GW treatment and local reuse, hence coupling the advantage of GW reuse with the benefits provided by a nature-based treatment approach. The amount of available GW is linked with the occupancy and habits of the inhabitants, but there is still limited knowledge on the impact of variations of GW flow rate on the treatment efficiency and on the health of the green wall. Therefore, this study aims to test the resilience of a modular green wall to variations in GW flow rate over 7 months. The experiments were performed on two configurations fed with synthetic GW: one was fed with a constant flow rate (equivalent to daily GW production per capita) as a reference, while the other received a variable flow schedule. The variable schedule included three phases: underload (-50 %), overload (+50 %) and maintenance flow. Input and output water were analysed to evaluate the treatment performances on fourteen physical-chemical parameters. Results showed that neither underload nor maintenance caused any detrimental effect on GW treatment efficiency or plants. Overload conditions caused a slight decrease in the treatment efficiency (e.g., 93.8 % for BOD5 compared to 100 % recorded in the control configuration), and plants exhibited visual signs of distress. However, these negative effects disappeared after re-establishing the standard flow rate. These findings demonstrated the resilience of green walls to inflow rate variations. The results provide useful indications for the application of green walls for GW treatment and provide important indications for design guidelines, in terms of maximum values of organic loading rate (∼20 gBOD5 m-2 d-1) and oxygen transfer rate (∼15 gO2 m-2 d-1), and focusing on building maximum capacity as driving parameter.

Green walls for greywater treatment: A comprehensive review of operational parameters and climate influence on treatment performance

Green walls for greywater treatment have emerged as a solution to increase green spaces in densely urbanized areas while providing treated greywater for reuse. Over the past decade, numerous studies have focused on optimizing these systems, though most address specific operational conditions and evaluate a limited set of performance parameters. This review synthesizes the existing literature using a meta-analysis to identify key operational factors and treatment performance metrics. A systematic search was conducted across Google Scholar, Scopus, and Web of Science, resulting in the selection of 33 studies. These studies were classified using the Köppen-Geiger climate classification, and a comprehensive database with over 8500 entries was built to analyse performance of COD, BOD, TOC, TSS, NH₄⁺, TN, TP, and bacteriological parameters across different climate zones. Results revealed performance variations across climate zones, with temperate climates outperforming dry regions. Regression equations between areal mass load and removal efficiency are proposed as design guidelines, and recommendations are made regarding optimal filling media. Additionally, for specific reuse applications, the inclusion of a disinfection unit is advised to meet microbiological quality standards.

Potential reuse of greywater for irrigation of tomato (Solanum lycopersicum) plants and its effect on plants growth and soil

The goal of this study is to examine the reactions of tomato (Solanum lycopersicum) plants to both untreated greywater and treated greywater filtered through a zeolite. In a randomized block arrangement, tomato plants were irrigated with greywater, treated greywater, or tap water. Number and total fecal coliforms were found in soil, tomato leaves, and fruits. Compared to tap water, greywater has higher levels of Ec, TDS, and COD. The average fruit weight and number for plants irrigated with tap water was 64.42 g and 4.2, while those irrigated with treated greywater were 55.4 g and 3.6, exceeding those irrigated with untreated greywater 39.6 g and 3.2. Treated greywater irrigation increased total chlorophyll content (SPAD) from 57.6 to 62.4 and relative water content from 49.6% to 63%. The leaves contained lower levels of proline (55.9 μmol/g) and total soluble sugar (32.24 mg/g). Researchers found total fecal coliforms in the soil, tomato leaves, and fruits. According to the research, treated greywater may prevent contamination of soil and save water.

Treated greywater as a novel water resource: The perspective of greywater treatment for reuse from a bibliometric analysis

The current global water crisis has prompted research into technologies that can reuse different water resources to mitigate water scarcity. The use of treated greywater can be proposed to provide additional water resources. By reusing this water in different applications, this water crisis can be mitigated at the local scale. This study presents a bibliometric analysis to assess the state of the art of greywater treatment and its reuse technologies. This analysis is based on the scientific literature published until 2023 in Scopus regarding greywater treatment and 1,024 documents were found. The results showed a clear exponential increase in the accumulated number of publications in this topic, which was spurred during the mid-1990s. The most prolific country was the United States, while China, the other typical scientific superpower in most fields, occupied the sixth position in the ranking. Environmental Sciences was the knowledge subject with more documents, followed by Engineering and Chemical Engineering. The bibliometric study was complemented using SciMAT to create bibliometric networks that represent the dynamic evolution of the themes. The most important themes were identified, among which three key points stand out: greywater characterization, technologies for greywater treatment, and water management, including the reuse of treated greywater.

Examining the efficacy of the legal framework governing the management of greywater in South Africa's informal settlements

The management of greywater and sanitation in South Africa's urban informal settlements is a pressing concern. This review critically examines the legal framework that governs greywater management in South Africa's informal settlements, aiming to shed light on the existing regulations, gaps, and opportunities for sustainable greywater reuse. By scrutinizing the legal framework, the review identifies gaps and challenges in the regulatory environment, including inconsistencies, lack of clarity, and limited enforcement mechanisms. It explores the potential for international best practices to inform possible amendments to the existing legal framework. This was a quantitative research design utilizing a cross sectional survey model. Questionnaires were administered electronically to a sample of 17 municipal leaders from the City of Tshwane, City of Johannesburg and Buffalo City municipalities whose responsibilities were on water management. Descriptive statistics were employed in analysis of the data. Outcomes were reviewed against the alignment or the lack thereof with the SANS 1732:201x standards. This paper underscores the critical need for a coherent and robust legal framework to support responsible greywater management in South Africa's informal settlements. The paper's insights contribute to the ongoing discourse on water governance, shedding light on the pathways toward a more equitable water future.

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.