A comparison of the suitability of different willow varieties to treat on-site wastewater effluent in an Irish climate

A preliminary experimental study simulating evapotranspiration process in TEvap tanks cultivated with different forages

The evapotranspiration tank (TEvap) is a 'zero-discharge' ecotechnology for toilet water disposal. This work refers to a preliminary study to evaluate the influence of forages and the addition of a vertical soil strip on evapotranspiration (ET), electrical conductivity (EC) and pH in TEvap receiving fresh water. The factors studied were the forages and the soil strip, resulting in four treatments with three replications. Two plant growing seasons, cycle 1 and cycle 2, were monitored, during which the variables were measured every three and seven days, respectively. Weather variables were used to estimate the reference evapotranspiration and determine the TEvap coefficient (KTEvap). The accumulated ET for TEvap with Capiaçu was 27.93% and 45.89% greater than for TEvap cultivated with Tifton-85 during the first and second cycles, respectively. There were no significant differences in ET for TEvap with and without the soil strip. BRS Capiaçu also showed lower values for EC and pH. High values were obtained for KTEvap: 2.37 and 1.76 for TEvap cultivated with BRS Capiaçu and Tifton-85 grass, respectively. Considering the period of this study, the minimum area for 'zero-discharge' would be 5.70 m2 inhab-1 and 7.77 m2 inhab-1 by TEvap planted with BRS Capiaçu and Tifton-85 grass, respectively. Due to its greater capacity for evapotranspiration, it can be concluded that the BRS Capiaçu forage is suitable for a 'zero-discharge' constructed wetland systems. It is suggested that further, more-thorough studies be carried out to design a 'zero-discharge' TEvap, considering different weather conditions, crops and inlet toilet water. HIGHLIGHTSEvapotranspiration tank (TEvap) is a 'zero discharge' ecotechnology for disposing toilet water;A preliminary study was conducted to simulate the evapotranspiration in TEvap receiving fresh water;Two forages - Cynodon spp. (Tifton-85 grass) and Pennisetum spp. (BRS Capiaçu) - were cultivated in the tanks;5.70 m2 inhab-1 were estimated for evapotranspiration with BRS Capiaçu and 7.77 m2 inhab-1 with Tifton-85 grass.

X, Barbeau LC, Comeau Y, Pitre FE, Labrecque M. Treatment of Landfill Leachate by Short-Rotation Willow Coppice Plantations in a Large-Scale Experiment in Eastern Canada

The treatment of leachate by vegetative filters composed of short-rotation willow coppice (SRWC) has been shown to be a cost-effective alternative to conventional and costly methods. However, few studies have considered the treatment capability of willow filters at a scale large enough to meet the industrial requirements of private landfill owners in North America. We report here on a field trial (0.5 ha) in which a willow plantation was irrigated with groundwater (D0) or aged leachate at two different loadings (D1 and D2, which was twice that of D1). Additionally, half of the D2-irrigated plots were amended with phosphorus (D2P). The system, which operated for 131 days, was highly efficient, causing the chemical oxygen demand concentration to drop significantly with the total removal of ammonia (seasonal average removal by a concentration of 99-100%). D2P efficacy was higher than that of D2, indicating that P increased the performance of the system. It also increased the willow biomass 2.5-fold compared to water irrigation. Leaf tissue analysis revealed significant differences in the concentrations of total nitrogen, boron, and zinc, according to the treatment applied, suggesting that the absorption capacity of willows was modified with leachate irrigation. These results indicate that the willow plantation can be effective for the treatment of landfill leachate in respect of environmental requirements.

Wastewater-Fertigated Short-Rotation Coppice, a Combined Scheme of Wastewater Treatment and Biomass Production: A State-of-the-Art Review

Vegetated filters based on short-rotation coppice (SRC) can be used to treat various industrial and municipal wastewater while producing valuable biomass in an economical and sustainable way, showing potential in the field of pollution control and bio-based circular economy. This study provides an overview of the state of the art in wastewater-fertigated SRC systems (wfSRCs) worldwide. Different designs, wastewater sources, tree species and varieties, planting schemes, geographic locations, and climates for wfSRC implementation were identified after conducting a literature review. The performance review includes standard water quality parameters, BOD5, COD, nitrogen, phosphorous, and potassium, as well as the extent of pathogen and emergent contaminant removal and biomass production rates. Identified knowledge gaps and important factors to support the practical implementation of wfSRCs are highlighted. Europe leads the research of wfSRC, followed by North America and Australia. The available publications are mainly from developed countries (73%). The most applied and studied tree species in wfSRC systems are willows (32%), followed by eucalyptus (21%) and poplars (18%). Most of the reviewed studies used domestic wastewater (85%), followed by industrial wastewater (8%) and landfill leachate (7%). Most data show high BOD5 and COD removal efficiencies (80%). There are large differences in the documented total nitrogen and total phosphorus removal efficiencies (12%–99% and 40%–80%, respectively). Enhanced biomass growth in wfSRC systems due to wastewater fertigation was reported in all reviewed studies, and biomass production varied from 3.7 to 40 t DM/ha/yr. WfSRCs seem to have high potential as viable and cost-effective wastewater treatment alternatives to conventional treatment technologies.

Attenuation mechanisms and key parameters to enhance treatment performance in vegetation filters: A review

In times when environmental concerns are on the rise and the search of ways to reduce waste generation and to create a circular economy is booming, Nature Based Solutions (NBSs) play a very important role. Vegetation Filters (VFs) are a type of Land Application System (LAS) in which wastewater is used to irrigate a forestry plantation to treat the water and produce biomass. VFs show multiple benefits that render this technology a suitable solution for wastewater treatment, especially for scattered populations or isolated buildings that lack of connection to sewer systems. This review aims to provide a comprehensive state of the art of VF implementation, highlighting the do's and don'ts for a successful performance focusing on those factors that are essential to water treatment. Results show that VFs have a great treatment capacity when all involving factors are considered, and their efficiency tends to increase with time, as the VF develops and "gets older". Indeed, the presence of fine-textured soils, the selection of a proper vegetation species, the use of pre-treated wastewater and a water balance-based irrigation schedule alternating wetting and -drying cycles are all factors that help to achieve the best performance. However, it is necessary to design and follow a simple but rigorous operation and maintenance schedule to avoid system failure, which could lead to NO₃-N leaching towards groundwater.

Applying the nutrient transfer continuum framework to phosphorus and nitrogen losses from livestock farmyards to watercourses

Farmyards are commonly conceptualized as point sources of nutrient pollution nested within the wider agricultural landscape. However, within farmyards there are individual sources and delivery pathways, each of which is affected by a range of management practices and infrastructure. Rainfall mobilizes these nutrients, which may then be delivered to a receptor or to the wider drainage network. As such, the nutrient transfer continuum (NTC), which has been established as a framework to understand and mitigate nutrient loss at a landscape scale, can be similarly applied to disentangle the stages of nutrient transfer from farmyards. The NTC differentiates nutrient transfer into source, mobilization, delivery, and impact stages. This differentiation allows targeting of mitigation measures and evaluation of costs and benefits. This review paper applies the NTC template to farmyard nitrogen and phosphorus transport to conceptualize causative factors and to identify mitigation options.

Short-Rotation Willows as a Wastewater Treatment Plant: Biomass Production and the Fate of Macronutrients and Metals

Evapotranspirative willow systems (EWS) are zero-discharge wastewater treatment plants that produce woody biomass and have no discharge to surface or groundwater bodies. The influence of wastewater on the growth of three clones of Salix alba (‘V 093’, ‘V 051’ and ‘V 160’) and the distribution of macronutrients and metals in a pilot EWS receiving primary treated municipal wastewater was studied under a sub-Mediterranean climate. The influent wastewater, shoot number, stem height, and biomass production at coppicing were monitored in two consecutive two-year rotations. Soil properties and the concentrations of macronutrients and metals in soil and woody biomass were analyzed after the first rotation. S. alba clones in EWS produced significantly more woody biomass compared to controls. ‘V 052’ produced the highest biomass yield in both rotations (38–59 t DM ha−1) and had the highest nitrogen and phosphorus uptake (48% and 45%) from wastewater. Nitrogen and phosphorus uptake into the harvestable woody biomass was significantly higher in all clones studied compared to other plant-based wastewater treatment plants, indicating the nutrient recovery potential of EWS. The indigenous white willow clone ‘V 160’ had the lowest biomass yield but absorbed more nutrients from wastewater compared to ‘V 093’. Wastewater composition and load were consistent with the nutrient requirements of the willows; however, an increase in salinity was observed after only two years of operation, which could affect EWS efficiency and nutrient recovery in the long term.

Willows for environmental projects: A literature review of results on evapotranspiration rate and its driving factors across the genus Salix

Willows are increasingly used for a wide range of environmental projects, including biomass production, leachate treatment, riparian buffers and treatment wetlands. Evapotranspiration (ET), assumed to be high for most willow species used in environmental projects, affects hydrological cycles and is of key interest for project managers working with willows. Here, we present a comprehensive review of ET rates provided in the literature for the genus Salix. We aim to summarize current knowledge of willow ET and analyze its variability depending on context. We compiled and analyzed data from 57 studies, covering 16 countries, 19 willow species and dozens of cultivars. We found a mean reported ET rate of 4.6 ± 4.2 mm/d, with minimum and maximum values of 0.7 and 22.7 mm/d respectively. Although results reported here varied significantly between some species, overall interspecific standard deviation (±3.6 mm/d) was similar to intraspecific variation (±3.3 mm/d) calculated for S. viminalis, suggesting a greater influence of the growing context on ET than species identity. In terms of environmental and management variables, water supply, fertilization and contamination were identified as driving factors of ET across willow species. Effects of root age, experimental context, planting density and soil type were more nuanced. Our findings provide synthetic data regarding willow ET. We encourage practitioners who use ET data from the literature to be aware of the main drivers of ET and to consider the influence of the experimental aspects of a study in order to interpret data accurately and improve project planning.

Analysis of Salix humboldtiana to be used as the plant species in evapotranspirative willow systems in Latin American highland climate conditions

This study aims to evaluate the evapotranspiration (EVP) rate of the willow species Salix humboldtiana to be used as a plant species for evapotranspirative willow system (EWS) to treat domestic wastewater in highland climate conditions in Latin America. Twelve lysimeters were installed in Bogotá, Colombia (2,600 m.a.s.l.). Two parameters were evaluated to determine the effect on EVP rate as follows: (a) the plant's age at the plantation time (one year or six months), and (b) the type of water (domestic wastewater or fertilized water). The plant's age was the most important parameter influencing the EVP rate. In addition, the growth of plants was similar (p > 0.05) between individuals irrigated with domestic wastewater and fertilized water. Thus, Salix humboldtiana over one-year-old was recommended to be used in EWS because its EVP rate of 1456 mm y^-1, can treat 372 mm y^-1 of domestic wastewater under the highland climate conditions. Finally, one EWS planted with Salix humboldtiana to treat domestic wastewater for a Colombian family located in these climate conditions would need an area of 400 m². This value for area, although similar to other parts of the world, is higher when considering the solar radiation in tropical or sub-tropical climate conditions.