Two-year performance of single-stage vertical flow treatment wetlands planted with willows under cold-climate conditions

Climate-related issues constitute an important obstacle for the development of treatment wetland (TW) applications in regions with freezing winter temperatures. The aim of the present study was to evaluate the efficiency of a new configuration of TWs based on the vertical flow (VF) configuration. The proposed TWs system is planted with a willow species (Salix miyabeana SX67) and including design adaptations for cold climate operation. Two different flow modes for winter-time operation were proposed: percolated and saturated with continuous artificial aeration. The pilot-scale systems were tested with municipal wastewater, at an organic loading ranging from 5 to 20 g CBOD5 m−2 d−1. The pilot TWs were successfully operated for 22 months despite freezing winter temperatures reaching as low as −32 °C. Willow development was normal, with evapotranspiration ranging from 19 to 23 mm/d in July 2017 for the pilot TWs at an organic loading of 10 g CBOD5 m−2 d−1. Organic matter removal efficiency was high for all pilot TWs, with an average 91% COD and 81% TSS removal. Nitrification was essentially complete during the summer period and remained high for pilot TWs operated under percolating flow mode in winter but was lower for the saturated flow mode, probably due to insufficient air supply. Our study confirms the successful application of a modified version of VF TW in regions with freezing air temperatures

Evapotranspiration of a willow cultivar (Salix miyabeana SX67) grown in a full-scale treatment wetland

Since woody plants like willow are used increasingly in treatment wetlands, there is a growing need to characterize their ecophysiology in these specific growing conditions. For instance, evapotranspiration (ET) can be greatly increased in wetlands, due to factors like high water availability as well as oasis and clothesline effects. Few studies report willow ET rates measured in full-scale constructed wetland conditions, and fewer still in a temperate North-American climate. The objective of this study was to measure and model evapotranspiration of a commonly used willow cultivar, Salix miyabeana (SX67), to provide the ET rates and crop coefficient for this species. During two growing seasons, we studied a 48 m2 horizontal subsurface flow willow wetland located in eastern Canada, irrigated with pretreated wood preservative leachate. Over two seasons, from May to October, we measured a mean monthly evapotranspiration rate of 22.7 mm/day (16.5 mm/d modelled), for a seasonal cumulative ET of 3954 mm (2897 mm modelled) and a mean crop coefficient of 6.4 (4.2 modelled). Both the evapotranspiration results and leaf area index (LAI) were greater than most results reported for open field willow plantations. Maximal stomatal conductance () was higher than that expected for deciduous trees and even for wetland plants, and mean values correlated well with temperature, solar radiation, relative humidity and day of the year. We demonstrated that an ET model using , LAI and water vapor pressure deficit (VPD) as parameters could predict the evapotranspiration rate of our wetland. This simplification of traditional ET models illustrates the absence of evapotranspiration limitations in wetlands. Furthermore, this study also highlights some factors that can enhance ET in treatment wetlands. Our results should both improve the design of treatment wetlands using willows, and provide a simple ET predictive model based on major evapotranspiration drivers in wetlands

Thermal properties of treatment wetlands operated under freezing conditions

ABSTRACT: The use of treatment wetlands (TWs) presents particular challenges in regions with sub-zero winter temperatures, due to reduced biological activity and risk of pipe breakage or clogging due to freezing. We studied the vertical temperature distribution in four pilot-scale TWs exposed to winter temperatures in order to determine the impact of operational system parameters and the role of insulation on heat conservation inside the filtering bed. The overall temperature pattern was similar in all wetlands, with a trend of increasing temperature from the surface toward the bottom during the cold season. No freezing was detected in the wetlands despite average daily temperatures as low as −20 °C. Influent water temperature and hydraulic loading had a stronger influence on TW temperatures in winter than air temperature. The vertical distribution of temperatures in TWs is more sensitive to hydraulic loading variation in the percolating operating condition than in the saturated flow with forced aeration configuration. Our results suggest that TW systems can remain operational under cold winter conditions provided the surface is properly insulated by vegetation, mulch and/or snow

improving treatment wetland systems for municipal wastewater treatment under northern continental climate

Le système de filtres plantés (FP) représente une solution alternative pour le traitement des eaux usées domestiques des petites communes et permet de respecter les normes de rejet dans de nombreux pays aux climats tempérés ou tropicaux. Dans la province de Québec (Canada), environ 49% des municipalités ont une taille inférieure à 1000 équivalent-habitants (EH) et sont partiellement ou pas équipées d'installation d'assainissement, ce qui met en évidence un besoin important. Toutefois, les dispositifs les plus intéressants de type filtres plantés à flux vertical ne peuvent pas être utilisés comme tel en climat froid et nécessitent des adaptations. Ce manuscrit propose donc l'étude d'innovations permettant de mettre en œuvre une solution de filtres plantés adaptés aux particularités du climat continental froid. Dans ce travail de thèse, la mise en œuvre d'un système à filtre planté vertical compact a été étudiée selon trois axes : 1) étude du fonctionnement général et des performances épuratoires, 2) suivi des propriétés thermiques durant la période hivernale et 3) étude sur le choix et l'utilisation d’espèces ligneuses. Ce travail de thèse a validé la filière de FP proposé pour l’application en climat froid en mettant en évidence le haut niveau de performances épuratoire ainsi qu’une forte résistance du lit filtrant aux conditions de gel. Les espèces ligneuses sont une solution appropriée pour ce type de système de traitement.A treatment wetland (TW) system represents a promising solution for wastewater treatment for small-scale communities and allows meeting the discharge criteria in many countries with a temperate or tropical climate. In Quebec province (Canada), almost 49% of municipalities are small-scale communities (< 1000 people-equivalent (PE)) with nonexistent or partial equipment of sewage facilities. This situation demonstrates a serious need of alternative solutions of wastewater treatment. However, the most interesting systems as a vertical flow TW can’t be used as such in cold climate, and so need to be adapted. Therefore this manuscript proposes an innovative study allowing an implementation of a TW solution appropriate to specific features of a cold continental climate. In this thesis research the compact version of a vertical flow TWs was studied through three principal axes: 1) a study focused on an overall functioning taken in account a treatment performances, 2) a thermal properties study focused on a winter-period and 3) a study of woody species using on TWs. This research validates a proposed TW design forcold climate application highlighting a high level of treatment performances as well as a great frost resistance of filtering bed. It was confirmed that woody species is an appropriate solution for this kind of treatment system

Optimisation de la filière de filtres plantés pour l'épuration d'eaux usées municipales en climat continental nordique

A treatment wetland (TW) system represents a promising solution for wastewater treatment for small-scale communities and allows meeting the discharge criteria in many countries with a temperate or tropical climate. In Quebec province (Canada), almost 49% of municipalities are small-scale communities (< 1000 people-equivalent (PE)) with nonexistent or partial equipment of sewage facilities. This situation demonstrates a serious need of alternative solutions of wastewater treatment. However, the most interesting systems as a vertical flow TW can’t be used as such in cold climate, and so need to be adapted. Therefore this manuscript proposes an innovative study allowing an implementation of a TW solution appropriate to specific features of a cold continental climate. In this thesis research the compact version of a vertical flow TWs was studied through three principal axes: 1) a study focused on an overall functioning taken in account a treatment performances, 2) a thermal properties study focused on a winter-period and 3) a study of woody species using on TWs. This research validates a proposed TW design forcold climate application highlighting a high level of treatment performances as well as a great frost resistance of filtering bed. It was confirmed that woody species is an appropriate solution for this kind of treatment system.Le système de filtres plantés (FP) représente une solution alternative pour le traitement des eaux usées domestiques des petites communes et permet de respecter les normes de rejet dans de nombreux pays aux climats tempérés ou tropicaux. Dans la province de Québec (Canada), environ 49% des municipalités ont une taille inférieure à 1000 équivalent-habitants (EH) et sont partiellement ou pas équipées d'installation d'assainissement, ce qui met en évidence un besoin important. Toutefois, les dispositifs les plus intéressants de type filtres plantés à flux vertical ne peuvent pas être utilisés comme tel en climat froid et nécessitent des adaptations. Ce manuscrit propose donc l'étude d'innovations permettant de mettre en œuvre une solution de filtres plantés adaptés aux particularités du climat continental froid. Dans ce travail de thèse, la mise en œuvre d'un système à filtre planté vertical compact a été étudiée selon trois axes : 1) étude du fonctionnement général et des performances épuratoires, 2) suivi des propriétés thermiques durant la période hivernale et 3) étude sur le choix et l'utilisation d’espèces ligneuses. Ce travail de thèse a validé la filière de FP proposé pour l’application en climat froid en mettant en évidence le haut niveau de performances épuratoire ainsi qu’une forte résistance du lit filtrant aux conditions de gel. Les espèces ligneuses sont une solution appropriée pour ce type de système de traitement

Intra-specific variability of the guaiacol peroxidase (GPOD) activity in roots of Phragmites australis exposed to copper excess

The intra-specific variability of the soluble guaiacol peroxidase (GPOD) activity in roots of 2-year-old Phragmites australis (Cav.) Trin. ex Steud. exposed to Cu excess (21 days) was investigated. The GPOD activity did not depend on the Cu exposure (0.08 vs. 25 μM) (p > 0.05) but was influenced by the sampling site (p < 0.05). The lowest GPOD activity (312-461 μM min−1) was found in roots of P. australis from the Capanne site, which displayed the highest total soil Cu (375 mg kg−1), while for plants from the three other sites the root GPOD activity remained steady, in the 1062-1389 μM min−1 range, independently of the sampling site. Copper excess did not affect the chlorophyll fluorescence for the four populations tested. Evidence of an intra-specific variability of the root GPOD activity, known for scavenging hydrogen peroxides in response to Cu excess, for P. australis provides new hints towards choosing relevant populations of this plant species for further use in constructed wetlands

Establishment and potential use of woody species in treatment wetlands

International audiencePlant species selection is an important criterion for improving treatment wetland performance. The aim of this work was to evaluate removal efficiency and potential uses of woody species in treatment wetlands during the establishment year. Plant development, removal efficiency and evapotranspiration rate of five woody species (Salix interior, Salix miyabeana, Sambucus canadensis, Myrica gale, Acer saccharinum) and four herbaceous taxa typically used in treatment wetlands (Typha angustifolia, Phragmites australis australis, Phragmites australis americanus, Phalaris arundinacea) were compared in a mesocosm-scale study during one growing season. Woody species showed significantly slower growth, but displayed several characteristics of interest for treatment wetland applications: good adaptation to wetlands conditions; high organic matter removal (76-88%); high nutrient accumulation in tissues and high evapotranspiration capacity. During the establishment year, herbaceous species showed greater biomass development (above- and belowground parts), higher evapotranspiration rate (>3.84 L m(-2) d(-1) compared to <3.23 L m(-2) d(-1) for woody species) and overall pollutant removal efficiency. These characteristics confirm the high efficiency of treatment wetlands planted with herbaceous species even in the first growing season. However, given their greater potential biomass development, woody species could represent an excellent alternative for improving treatment wetlands long-term performance

Copper removal from water using a bio-rack system either unplanted or planted with Phragmites australis, Juncus articulatus and Phalaris arundinacea

A bio-rack system was developed for treating Cu-contaminated freshwaters. Each pilot constructed wetland (CW, 110dm3) contained 15 perforated vertical pipes filled with a mixture of gravel (diorite; 80%) and perlite (20%) and assembled as a rack. The whole experimental device consisted of 12 CW planted either with Phragmites australis, Phalaris arundinacea or Juncus articulatus, and unplanted as control (in triplicates). All plants were sampled at a Cu-contaminated site. The CWs were filled with a mix of freshwater (30%) from the Jalle d'Eysines River (Bordeaux, France) and tap water (70%). Water was spiked with Cu (2.5μM, 158.5μgL-1). Three CW batches were carried out, i.e. in early spring (March, S#1), beginning of the growing season (May, S#2), and peak growing season (June, S#3). The S#3 water was initially acidified to pH 6. For all batches, water was recirculated in the CW during 14 days. Physico-chemical parameters (pH, electrical conductivity, redox potential, BOD5 and Cu2+ co