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

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.

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.

Performance evaluation of modified Living Wall garden for treating septic tank effluent

The Living Wall (LW) garden system has been employed as a post-treatment system to improve the effluent quality of septic tanks. This improvement primarily involves reducing nutrient levels, as well as facilitating the removal of organic matter and solids in accordance with effluent discharge guidelines. The objective of this study was to investigate the treatment performance of the LW system connected to a septic tank, along with an examination of the microbial communities within the LW units. A laboratory-scale LW system, comprising LW1, LW2, and LW3 units, was employed. The system was fed with effluent obtained from septic tanks and varied by theoretical hydraulic retention time (HRT) of 6, 12, and 24 h. The TCOD, SCOD, TSS, TVS, TKN, and TP removal efficiencies of the LWs were achieved at 62 ± 24, 42 ± 19, 72 ± 21, 66 ± 15, 80 ± 15, and 58 ± 21%, respectively. To classify microbial communities in the soil and gravels collected from each LW unit, the Illumina MiSeq System Sequencer was employed. Nitrospirota was consistently found in all LW units, aiding in the conversion of nitrogen. Fusobacteriota were detected in specific layers of the LW units, indicating varying oxygen levels in the LW system.

Comparative evaluation of different pre-treatment alternatives for granular media filters treating greywater and their ranking using analytical hierarchy process

In this study, the performance of four different pre-treatment alternatives for granular media filtration, namely, settling, aeration, coarse media filtration and chemical coagulation were compared experimentally. Further, analytical hierarchy process (AHP) was used to compare their performance based on economic, environmental, technical and performance criteria. Performance of settling and aeration were evaluated up to 24 h duration. The coarse media filter was intermittently operated with 10 L of greywater in downflow mode while alum was used for chemical coagulation. Experimental results showed that settling up to 6 h did not show significant removal of different pollutants whereas 24 h settling resulted in moderate removal of turbidity and organic content but was not efficient in the removal of nutrients and faecal coliforms. Chemical coagulation reduced 93, 66, 48 and 97% of turbidity, COD, NH4-N and faecal coliforms, respectively from greywater but resulted in excessive sludge generation and is difficult to adopt on-site and requires skilled supervision. Coarse filtration of greywater resulted in 61, 41, 36 and 35% removal of turbidity, COD, PO4-P and faecal coliforms, respectively. Considering different criteria AHP gave coarse filtration as the best pre-treatment option to the granular media filters treating greywater.

What does it take to renature cities? An expert-based analysis of barriers and strategies for the implementation of nature-based solutions

This paper uses an expert-based methodology to survey the barriers and strategies related to the implementation of nature-based solutions (NBS). The ambition of the paper is to offer a bird's eye overview of the difficulties encountered by NBS deployment and ways to overcome them. With a wide participation of 80 experts from COST Action Circular City, we identify barriers specific to 35 pre-defined NBS of the following four categories: Vertical Greening Systems and Green Roofs; Food and Biomass Production; Rainwater Management; and Remediation, Treatment, and Recovery. The research sheds light on how a major interdisciplinary - yet predominantly technically-oriented - community of scientists and practitioners views this important topic. Overall, the most relevant barriers are related to technological complexity, lack of skilled staff and training programs and the lack of awareness that NBS is an option. Our results highlight concerns related to post implementation issues, especially operation and maintenance, which subsequently affect social acceptance. The paper identifies a "chain" effect across barriers, meaning that one barrier can affect the existence or the relevance of other barriers. In terms of strategies, most of them target governance, information, and education aspects, despite the predominantly technical expertise of the participants. The study innovates with respect to state-of-the-art research by showing a fine-grained connection between barriers, strategies and individual NBS and categories, a level of detail which is not encountered in any other study to date.

Vertical flow constructed wetlands as green facades and gardens for on-site greywater treatment in buildings: Two-year mesocosm study on removal performance

This study focuses on the performance and clogging of vertical flow constructed wetlands (VFCWs) planted with climbing ornamentals and ornamental plants for greywater treatment, after two years of operation at mesocosm level. Different substrate (sand, vermiculite) and vegetation (Trachelospermum jasminoides, Lonicera japonica, Callistemon laevis) types were evaluated to determine the optimal removal of pollutants. Results revealed that, during the second year of operation, removal efficiencies of turbidity and COD were significantly higher (1st year: 54-94 %; 71-89 %, 2nd year: 82-98 %; 86-95 %, respectively) for both studied planted substrates, compared to the first year. Moreover, it was found that sand systems from each studied plant as well as from the unplanted systems, were more effective compared to vermiculite for most of the studied parameters (turbidity, TSS, COD, anionic surfactants, pathogens). Sand systems were also quite effective in removing total coliforms (5 log reduction) and Escherichia coli (4 log reduction). At the end of the two-year experiment, all planted systems with sand had significantly higher hydraulic conductivity than the unplanted ones. With reference to evapotranspiration, even though planted systems had significantly higher losses, C. laevis systems demonstrated less water losses than the other vegetated systems. According to the findings, the studied plants managed to continue growing without facing added stress. Therefore, the application of climbing and ornamental plants in VFCWs for greywater treatment in buildings seems a promising option for developing green infrastructures in urban areas and enhancing the removal efficiency of such systems.