Plant species contribution to bioretention performance under a temperate climate.

Bioretention systems are green infrastructures increasingly used to manage urban stormwater runoff. Plants are an essential component of bioretention, improving water quality and reducing runoff volume and peak flows. However, there is little evidence on how this contribution varies between species, especially in temperate climates with seasonal variations and plant dormancy. The aim of our study was to compare the performance of four plant species for bioretention effectiveness during the growing and dormant periods in a mesocosm study. The species selected (Cornus sericea, Juncus effusus, Iris versicolor, Sesleria autumnalis) are commonly used in bioretention and cover a wide range of biological forms and functional traits.All bioretention mesocosms were effective in reducing water volume, flow and pollutant levels in both of the studied periods. Plants decreased runoff volume and increased contaminant retention by reducing water flow (up to 2.7 times compared to unplanted systems) and increasing water loss through evapotranspiration during the growing period (up to 2.5 times). Plants improved removal of macronutrients, with an average mass removal of 55 % for TN, 81 % for TP and 61 % for K compared to -6 % (release), 61 % and 22 % respectively for the unplanted systems. Except for Sesleria, mass removal of trace elements in planted mesocosms was generally higher than in unplanted ones (up to 8.7 %), regardless of season. Between-species differences in exfiltration rate and improved water quality followed the same order as their evapotranspiration rate and overall size, measured in terms of plant volume, leaf biomass, total leaf area and maximum average root density (Cornus > Juncus > Iris > Sesleria). By increasing evapotranspiration, plants decreased runoff volume and increased contaminant retention. Nutrient removal was partly explained by plant assimilation. Our study confirms the importance of plant species selection for improving water quality and reducing runoff volume during bioretention under a temperate climate.

Impact of synthetic silver nanoparticles on the biofilm microbial communities and wastewater treatment efficiency in experimental hybrid filter system treating municipal wastewater.

Silver nanoparticles (AgNPs) threaten human and ecosystem health, and are among the most widely used engineered nanomaterials that reach wastewater during production, usage, and disposal phases. This study evaluated the effect of a 100-fold increase in collargol (protein-coated AgNP) and Ag+ ions concentrations in municipal wastewater on the microbial community composition of the filter material biofilms (FMB) and the purification efficiency of the hybrid treatment system consisting of vertical (VF) and horizontal (HF) subsurface flow filters. We found that increased amounts of collargol and AgNO3 in wastewater had a modest effect on the prokaryotic community composition in FMB and did not significantly affect the performance of the studied system. Regardless of how Ag was introduced, 99.9% of it was removed by the system. AgNPs and AgNO3 concentrations did not significantly affect the purification efficiency of the system. AgNO3 induced a higher increase in the genetic potential of certain Ag resistance mechanisms in VFs than collargol; however, the increase in Ag resistance potential was similar for both substances in HF. Hence, the microbial community composition in biofilms of vertical and horizontal flow filters is largely resistant, resilient, or functionally redundant in response to AgNPs addition in the form of collargol.

Effects of macrophyte species and biochar on the performance of treatment wetlands for the removal of glyphosate from agricultural runoff.

Glyphosate is the most widely used herbicide in the world, and consequently has polluted numerous water bodies through agricultural runoff. Treatment wetlands (TWs) have shown great promise for mitigating such pesticide contamination. The objectives of our study were to determine the effects of adding biochar to subsurface flow TW substrate, and to evaluate the performance of three North American macrophyte species (Phragmites australis subsp. americanus, Scirpus cyperinus and Sporobolus michauxianus) for removal of glyphosate. A synthetic agricultural runoff comprising 50 µg/L of glyphosate was applied to water-saturated TW mesocosms with mature vegetation during a 5.5-week period. Average removal efficiency, calculated on a mass balance basis, reached 78 and 82% for mesocosms with biochar (without and with plants, respectively), and 54 to 76% for those with macrophytes. Sporobolus michauxianus showed a lower evapotranspiration rate and less anoxic conditions in the lower part of the substrate, which resulted in lower overall removal performance. Aminomethylphosphonic acid (AMPA), the main toxic metabolite of glyphosate, was detected in all mesocosms, but at higher levels in planted ones. Results show that both the sorption capacity of biochar and the biodegradation processes associated with macrophytes contribute to glyphosate removal in TWs. Additionally, our results suggest that species selection is important to enhance favorable conditions and maximize removal of targeted pollutants.

Macrophyte Potential to Treat Leachate Contaminated with Wood Preservatives: Plant Tolerance and Bioaccumulation Capacity.

Pentachlorophenol and chromated copper arsenate (CCA) have been used worldwide as wood preservatives, but these compounds can toxify ecosystems when they leach into the soil and water. This study aimed to evaluate the capacity of four treatment wetland macrophytes, Phalaris arundinacea, Typha angustifolia, and two subspecies of Phragmites australis, to tolerate and treat leachates containing wood preservatives. The experiment was conducted using 96 plant pots in 12 tanks filled with three leachate concentrations compared to uncontaminated water. Biomass production and bioaccumulation were measured after 35 and 70 days of exposure. There were no significant effects of leachate contamination concentration on plant biomass for any species. No contaminants were detected in aboveground parts of the macrophytes, precluding their use for phytoextraction within the tested contamination levels. However, all species accumulated As and chlorinated phenols in belowground parts, and this accumulation was more prevalent under a more concentrated leachate. Up to 0.5 mg pentachlorophenol/kg (from 81 µg/L in the leachate) and 50 mg As/kg (from 330 µg/L in the leachate) were accumulated in the belowground biomass. Given their high productivity and tolerance to the contaminants, the tested macrophytes showed phytostabilization potential and could enhance the degradation of phenols from leachates contaminated with wood preservatives in treatment wetlands.

Bacterial community activity and dynamics in the biofilm of an experimental hybrid wetland system treating greywater.

The objectives of this study were to determine the biofilm microbial activity and bacterial community structure and successions in greywater treatment filters and to relate the treatment efficiency to the bacterial community parameters. This 10-month study was performed in a newly established experimental system for domestic greywater treatment that consisted of three parallel vertical flow filters (VFs) followed by a horizontal flow filter (HF). A rapid increase in the bacterial community abundance occurred during the first 85 days of filter operations, followed by a short-term decrease and the stabilization of the 16S rRNA gene copy numbers at average levels of 1.2 × 109 and 3.2 × 108 copies/g dw in VFs and HF, respectively, until the end of the experiment. The dominant bacterial phyla and genera differed between the VFs and HF. The temporal variation in the bacterial community structure was primarily related to the species replacement, and it was significantly affected by the influent organic carbon and nitrogen compounds in the VFs and the ammonia and organic carbon in the HF filters. Despite the differences in the community structure and assembly mechanisms, the temporal dynamics of the bacterial community showed high congruence between the filter types. The treatment efficiency was related to the biofilm bacterial community diversity and abundance and the abundance of certain bacterial genera in the VF filters. The results suggest that the dominant pathway of nitrogen removal by greywater treatment VFs occurs via coupled heterotrophic nitrification and denitrification, while the contribution of aerobic denitrification is temporally variable in these filters.

Biochar enhances plant growth and nutrient removal in horizontal subsurface flow constructed wetlands.

Biochar has shown great potential as an amendment to improve soil quality and promote plant growth, as well as to adsorb pollutants from water. However, information about the effect of biochar on the wastewater treatment efficiency in horizontal subsurface flow (HSSF) constructed wetlands (CWs) is still scarce. In this study, we assessed the effect of biochar amendment on the purification efficiency of pretreated municipal wastewater in planted (Typha latifolia) experimental horizontal subsurface flow filters filled with lightweight expanded clay aggregates (LECA). The addition of wood-derived biochar (10% v/v) to LECA significantly increased plant biomass production and enhanced the wastewater treatment efficiency of the planted filters. Both the aboveground plant biomass and belowground plant biomass were higher (1.9- and 1.5-fold, respectively) in the filters of the LBP (LECA + biochar + plants) treatments compared to the LP (LECA + plants) filters. The water pH was significantly lower in the planted filters (LBP < LP < LB-LECA + biochar). The efficiencies of TN and TP removal from wastewater were highest in the LBP filters (20.0% and 22.5%, respectively), followed by the LP (13.7% and 16.2%, respectively) and LB (9.5% and 15.6%, respectively) filters. More N and P were incorporated into the plant biomass from wastewater in the presence of biochar in the filter medium. The study results confirm that biochar can be an advantageous supplement for planted HSSF CWs to enhance the treatment efficiency of these systems.