Performance evaluation of various individual and mixed media for greywater treatment in vertical nature-based systems

Simultaneous removal of nutrients and biological pollutants via specialty absorbents in a water filtration system for watershed remediation

To investigate watershed remediation within a Total Maximum Daily Load program, this study examined the field-scale filtration performance of two specialty absorbents. The goal was to simultaneously remove nutrients and biological pollutants along Canal 23 (C-23) in the St. Lucie River Basin, Florida. The filtration system installed in the C-23 river corridor was equipped with either clay-perlite with sand sorption media (CPS) or zero-valent iron and perlite green environmental media (ZIPGEM). Both media were formulated with varying combinations of sand, clay, perlite, and/or recycled iron based on distinct recipes. In comparison with CPS, ZIPGEM exhibited higher average removal percentages for nutrients. Findings indicated that ZIPGEM could remove total nitrogen up to 49.3%, total Kjeldahl nitrogen up to 67.1%, dissolved organic nitrogen (DON) up to 72.9%, total phosphorus up to 79.6%, and orthophosphate up to 73.2%. Both ZIPGEM and CPS demonstrated similar efficiency in eliminating biological pollutants, such as E. coli (both media exhibiting an 80% removal percentage) and chlorophyll a (both media achieving approximately 95% removal). Seasonality effects were also evident in nutrient removal efficiencies, particularly in the case of ammonia nitrogen; the negative removal efficiency of ammonia nitrogen from the fifth sampling event could be attributed to processes such as photochemical ammonification, microbial transformation, and mineralization of DON in wet seasons. Overall, ZIPGEM demonstrated a more stable nutrient removal efficiency than CPS in the phase of seasonal changes.

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.

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.

The comparative performance of lightweight green wall media for the removal of xenobiotic organic compounds from domestic greywater

Green walls can provide an aesthetic approach to treat domestic greywater in urban landscapes. However, the widespread adoption of green walls for greywater treatment depends on its performance to remove the emerging contaminants from greywater such as xenobiotic organic compounds (XOCs). In this study, the performance of five lightweight green wall media types (zeolite, perlite, date seeds, coffee grinds, and coco coir) was evaluated for the removal of six XOCs representing a range of hydrophilic to hydrophobic organic micropollutants in domestic greywater (acetaminophen, diethyltoluamide, bisphenol A, oxybenzone, triclosan, nonylphenol). The adsorption affinity of targeted XOCs on different green wall media types, the role of contact time on XOCs removal, and the impact of background pollutants in greywater matrix on the adsorption of XOCs were analysed. Results indicate that removal of XOCs was higher using carbonaceous waste materials (date seeds, coffee grinds, and coco coir) as compared to natural minerals (zeolite and perlite). Moreover, the adsorption of XOCs increased with the increase in pollutant hydrophobicity. All XOCs showed highest removal using coco coir with fast adsorption kinetics, achieving 90% of the removal in 30 min. The only exception was acetaminophen that showed best removal using zeolite but exhibited slow adsorption kinetics with 90% of the removal attained in 24 h. The initial adsorption kinetics (<30 min) of XOCs in greywater were adversely affected by the presence of background pollutants, indicating the need of higher residence time of greywater in green wall system for better removal of XOCs. Based on the findings of this batch study, it is recommended to design a green wall system with more than 30 min of greywater residence time using a mixture of coco coir and zeolite for effective removal of XOCs from domestic greywater.

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.

Green Roof Enhancement on Buildings of the University of Applied Sciences in Neubrandenburg (Germany) in Times of Climate Change

The reduction in evaporative surfaces in cities is one driver for longer and hotter summers. Greening building surfaces can help to mitigate the loss of vegetated cover. Typical extensive green roof structures, such as sedum-based solutions, survive in dry periods, but how can green roofs be made to be more effective for the longer hot and dry periods to come? The research findings are based on continuous vegetation analytics of typical extensive green roofs over the past 20 years. -Survival of longer dry periods by fully adapted plants species with a focus on the fittest and best adapted species. -Additional technical and treatment solutions to support greater water storage in the media in dry periods and to support greater plant biomass/high biodiversity on the roofs by optimizing growing media with fertilizer to achieve higher evapotranspiration (short: ET) values. The main findings of this research: -The climate benefits of green roofs are associated with the quantity of phytomass. Selecting the right growing media is critical. -Typical extensive green roof substrates have poor nutrition levels. Fertilizer can significantly boost the ecological effects on CO2 fixation. -If the goal of the green roof is a highly biodiverse green roof, micro-structures are the right solution.