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

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.

Evaluating a vertical greening system mesocosm for kitchen greywater treatment: Comparison among vegetation species in water consumption, biomass growth and pollutants uptake and removal

The escalating climate imbalance, coupled with rising water demands in rapidly expanding urban areas, is forcing scientists and policymakers to seek alternative strategies for efficient water resource management. Nature Based Solutions (NBS) are gaining prominence due to their ability to provide multiple ecosystem services. However, the quantification of benefits and drawbacks mediated by different vegetation species remains inadequate. In this study, we investigated the performance of a pot-based vertical greening system (VGS) designed to integrate the functions of green facades with those of treatment wetlands. The VGS was vegetated with Mentha aquatica L. (hereafter Mentha), Oenanthe javanica (Blume) DC. (hereafter Oenanthe) and Lysimachia nummularia L. (hereafter Lysimachia), and their respective effects on water balance and mass removal of common greywater pollutants were compared. Results indicated that VGS lines vegetated with Oenanthe and Mentha exhibited comparable pollutant removals. Oenanthe showed a preference for greywater that had already undergone partial treatment, while Mentha was not affected by any pollutant load in water removal -48.1 % of total inflow- and in nutrients uptake in aboveground biomass -14.3 % N and 7 % P- due to sustained and robust growth, outperforming Oenanthe and Lysimachia. This has suggested the potential use of Oenathe in combination with Mentha for enhanced performances, particularly given Oenanthe's rapid growth in the early season and high biomass and nitrogen content following initial greywater treatment.

A systematic analysis on the efficiency and sustainability of green facades and roofs

In the modern urban space, green infrastructures have been gaining increasing relevance due to their positive impacts on sustainability issues, visual appeal, and the well-being of individuals. On the other hand, environmental sustainability has become mandatory in the agenda of governments and organizations. Thus, a systematic analysis on the efficiency and sustainability of green facades and roofs spanning key applications, benefits and implementation constraints is welcome. In this paper, we employed the PRISMA method to investigate how these matters were addressed in the recent literature, comprising articles published in scientific journals indexed to the SCOPUS database. Following the web search, selection, systematization, and analysis of that literature, it was revealed that the efficiency of green facades and roofs has been mostly associated with energy and thermal performance in buildings, which brings unequivocal multiple benefits (e.g., consumption savings, mitigation of urban heat island effects) despite of some barriers (e.g., installation and maintenance costs). Other discussions about green facades and roofs involved their valuable roles in stormwater management, considering their retention capacity, and in the treatment of wastewater for reuse in non-potable applications, considering their filtering capacity. It was also discovered the need to improve green infrastructures through the use of cleaner technologies and recycled materials, selection of plants that are appropriate for the local climate, and minimization of construction, transportation, disposal and maintenance costs. Efficiency and sustainability in these cases was prognosed to succeed if the costs were minimized throughout the entire life cycle, and complemented with incentive policies (e.g., tax reduction, agile administrative processes) and collaboration among multidisciplinary teams comprising designers, builders, municipality planners and the academic and market worlds.

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.

Removal of hydrophilic, hydrophobic, and charged xenobiotic organic compounds from greywater using green wall media

Green walls offer a novel on-site approach for greywater treatment and reuse in densely build urban environments. However, they need to be engineered for effective removal of a wide range of emerging contaminants such as xenobiotic organic compounds (XOCs), which may be present in greywater due to extensive use of personal care products and household chemicals. This study used laboratory column design and batch experiments to investigate the performance of three lightweight green wall media (coco coir, zeolite, and perlite) and their mixture in three different combinations for the removal of twelve XOCs, covering wide range of hydrophilic, hydrophobic, and charged pollutants in greywater. The experiments were designed to assess the removal of targeted XOCs under different operational condition (i.e., hydraulic loading, infiltration rate, drying) and uncover the dominant mechanisms of their removal. Results showed excellent removal (>90%) of all XOCs in coco coir and media mix columns at the start of the experiment (i.e., fresh media and initial 2 pore volume (PV) of greywater dosing). The removal of highly hydrophobic and positively charged XOCs remained high (>90%) under all operational conditions, while hydrophilic and negatively charged XOCs exhibited significant reduction in removal after 25 PV and 50 PV, possibly due to their low adsorption affinity and electrostatic repulsion from negatively charged media. The effect of infiltration rate on the removal of XOCs was not significant; however, higher removal was achieved after 2-weeks of drying in coco coir and media mix columns. The dominant removal mechanism for most XOCs was found to be adsorption, however, a few hydrophilic XOCs (i.e., acetaminophen and atrazine) exhibited both adsorption and biodegradation removal processes. While findings showed promising prospects of unvegetated media for removing XOCs from greywater, long term studies on vegetated green wall systems are needed to understand any synergetic contribution of plants and media in removing these XOCs.

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.

Removal of pathogens from greywater using green roofs combined with chlorination

Greywater is an important alternative water resource which could be treated and reused in buildings, reducing the freshwater demand in drought affected areas. For the successful implementation of this solution, it is important to ensure the microbial safety of treated greywater. This study examined the microbiological quality of treated greywater produced by an emergent nature-based technology (green roofs) and a chlorination process. Specifically, the effect of substrate, substrate depth, and vegetation on the removal of total coliforms, Escherichia coli, and enterococci in experimental green roofs treating greywater was examined for a period of about 12 months. In addition, the ability of chlorination to inactivate the abovementioned pathogen indicators was evaluated and their potential regrowth was examined. Results shown that green roofs filled with 10 cm of perlite reduce total coliform concentration by about 0.4 log units while green roofs filled with 20 cm of vermiculite reduce total coliform concentration by about 1.2 log units. In addition, the use of vegetation in green roofs improves the removal of pathogenic bacteria by about 0.5 log units in comparison with unvegetated systems. In all cases, the effluents of green roofs failed to satisfy the criteria for indoor reuse of treated greywater for non-potable uses such as toilet flushing without a disinfection process. The addition of 3 mg/L of chlorine in the effluent provided safe greywater microbiological quality for storage periods of less than 24 h, while longer periods resulted in the significant regrowth of pathogens. In contrast, a chlorination dose of 7 mg/L completely secured inactivation of pathogen indicators for periods of up to 3 days.

Evaluation of the multifunctionality of a vertical greening system using different irrigation strategies on cooling, plant development and greywater use

Vertical greening systems (VGS) are implemented in the building envelope to address challenges such as the urban heat island effect, energy reduction, air purification, support of biodiversity and recently greywater treatment (wastewater without urine and faeces) for reuse purposes. In this context, providing and using treated wastewater is a crucial point, as generally VGS are irrigated with tap water and thereby increase urban water depletion and pollution. In this study, we evaluate the multifunctionality of a pot-based VGS irrigated with untreated greywater and capable, as well, of acting as a greywater treatment system. The full-scale experimental system uses a low-tech irrigation technique and was investigated for different irrigation water volumes to identify the needed water demand to maximize local cooling by evapotranspiration and suitable plants for the different water conditions and water types. Plant development and greywater treatment capabilities were monitored from April 2020 until September 2021. Based on the highest irrigation volume, a local air temperature reduction of up to 3.4 °C was measured. The removal efficiencies for treating greywater were COD 80 %, TOC 74 %, TNb 70 %, NH₄-N 81 % and Turbidity 79 %, respectively, and showed a decrease in the second year of operation. Therefore, the results support the need to develop more robust systems, since up to now mainly short-term experiments have been reported in literature.

Measurement of the Green Façade Prototype in a Climate Chamber: Impact of Watering Regime on the Surface Temperatures

Green façades with an active water regime and the water flowing through the substrate itself are not common. This system reduces the temperatures and incorporates the evapotranspiration, which could be more effective than by the regular green façades. The use of a double-skin façade with a ventilated air cavity can reduce the heat load, but the evapotranspiration can reduce it even more with additional benefits. Green façades could also serve as a key element for reducing the surface temperatures of the insulated metal panels (IMP), which are mostly used as a façade system for production facilities or factories. In this paper, a prototype of a double-skin façade, which consisted of vegetation board from recycled materials and IMP, is tested in a climate chamber to evaluate the function and benefits of such a combination. The outdoor skin is made from board, the surface of which is covered by the rooted succulent plants. Measurement results are represented as a direct comparison of single sunny day surface temperatures with and without a double-skin (green) façade. The use of the green façade reduces the indoor surface temperature of IMP by 2.8 °C in this measurement. The use of water circulation through the outdoor skin reduces the temperature of the vegetation board by 28 °C. This could have a great impact on the microclimate around the façade. Because of the controlled environment and ventilation system in a climate chamber, it is not possible to investigate the airflow and solar chimney effect within the ventilated cavity. In addition, it is complicated to show the potential of microclimate change caused by the wet vegetation surface. For the mentioned reasons, the need to carry out “in situ” tests on a model wall under the real conditions was indicated.