Thermal properties of treatment wetlands operated under freezing conditions.

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.

Establishment and potential use of woody species in treatment wetlands.

Plant 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.

Impacts of Continuous Inflow of Low Concentrations of Silver Nanoparticles on Biological Performance and Microbial Communities of Aerobic Heterotrophic Wastewater Biofilm.

Attached-growth wastewater processes are currently used in water resource recovery facilities (WRRFs) for required upgrades due to an increase in influent loading or to reach more stringent discharge criteria. Yet, the distribution and long-term inhibitory effects of silver nanoparticles (AgNPs) in attached-growth biological wastewater processes and their impact on involved microbial communities are poorly understood at relevant, low concentrations. Retention, distribution, and long-term inhibitory effect of polyvinylpyrrolidone (PVP)-coated AgNPs were evaluated in bench-scale moving bed biofilm reactors (MBBRs), achieving soluble organic matter removal, over a 64 day exposure to nominal concentrations of 10 and 100 µg/L. Distributions of continuously added AgNPs were characterized in the influent, bioreactor, and effluent of MBBRs using single particle inductively coupled plasma mass spectroscopy (spICP-MS). Aerobic heterotrophic biofilms in MBBRs demonstrated limited retention capacity for AgNPs over long-term exposure, with release of AgNPs, and Ag-rich biofilm sloughed from the carriers. Continuous exposure to both influent AgNP concentrations significantly decreased soluble chemical oxygen demand (SCOD) removal efficiency (11% to 31%) and reduced biofilm viability (8% to 30%). Specific activities of both intracellular dehydrogenase (DHA) and extracellular α-glucosidase (α-Glu) and protease (PRO) enzymes were significantly inhibited (8% to 39%) with an observed NP dose-dependent intracellular reactive oxygen species (ROS) production and shift in biofilm microbial community composition by day 64. Our results indicated that long-term exposure to AgNPs in biofilm processes at environmentally relevant concentrations can impact the treatment process stability and the quality of the discharged effluent.

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 ±â€¯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.

Activated Sludge Production Parameters and Nutrient Content of Organic Sludge Components.

An important part of biological treatment system design is quantifying the sludge production and the nutrient removal capacity. Influent wastewater COD fractionation, biomass growth and endogenous respiration directly impacts the composition of the mixed liquor solids in activated sludge systems. The objectives of this project were to determine the model kinetic and stoichiometric parameters associated with activated sludge production and the nutrient content (N and P) of unbiodegradable organic matter components. A complete sludge retention experiment was conducted over 70 days in a pilot-scale membrane bioreactor fed with a real municipal wastewater, and operated with alternating growth and famine periods. Experimental results were simulated and compared using the default values from two well-accepted model parameter sets. The General ASDM parameter set was found to better fit the experimental data than the Metcalf and Eddy parameter set, mainly to characterize endogenous respiration and the heterotrophic biomass concentration. An influent unbiodegradable organic particulate fraction (fXU,Inf) value of 0.16 g COD/g COD was determined by calibration of the accumulated sludge total COD, suspended solids and heterotrophic biomass concentrations. The nutrient content of the accumulated endogenous residue (XE) and influent unbiodegradable organic particulate (XU,Inf) components were calibrated to 0.030 and 0.100 g N/g COD and 0.035 and 0.008 g P/g COD, respectively. These values are in the range of those reported in the literature except for the high P content found in the endogenous residue, possibly due to the presence of coagulants added for P removal in the accumulated sludge. These results were consistent under the wide range of dynamic conditions tested and could improve model prediction of sludge production and composition.

Sludge reduction via biodegradation of the endogenous residue (XE): experimental verification and modeling.

The feasibility of sludge reduction via the XE biodegradation process was explored both experimentally and through modeling, where the main focus was on determining the value of the bE parameter (first order degradation of XE) from a continuous process. Two activated sludge (AS) systems (30 L) were operated in parallel with synthetic wastewater during 16 months: a conventional activated sludge (CAS) system and a modified low-sludge production activated sludge (LSP-AS) process equipped with a side-stream digester unit (DU). First, the long term data of the CAS reactor (1 year) were used to calibrate the ASM model and to estimate the heterotrophic decay constant of the cultivated sludge (bH = 0.29 d-1, death-regeneration basis). Second, pre-simulations were performed to design the LSP-AS system and to estimate the DU volume required (40 L), to avoid XE accumulation in the process. Third, the LSP-AS process was built, put in operation and monitored for more than 9 months. This allowed assessment of the actual behavior of the quasi-complete solids retention system. Once calibrated, the modified AS model estimated the value of the bE parameter to be in the range of 0.003-0.006 d-1, satisfactorily describing the overall sludge yield reduction of up to 49% observed in the experiments.

Mechanisms for Reduced Excess Sludge Production in the Cannibal Process.

Reducing excess sludge production is increasingly attractive as a result of rising costs and constraints with respect to sludge treatment and disposal. A technology in which the mechanisms remain not well understood is the Cannibal process, for which very low sludge yields have been reported. The objective of this work was to use modeling as a means to characterize excess sludge production at a full-scale Cannibal facility by providing a long sludge retention time and removing trash and grit by physical processes. The facility was characterized by using its historical data, from discussion with the staff and by conducting a sampling campaign to prepare a solids inventory and an overall mass balance. At the evaluated sludge retention time of 400 days, the sum of the daily loss of suspended solids to the effluent and of the waste activated sludge solids contributed approximately equally to the sum of solids that are wasted daily as trash and grit from the solids separation module. The overall sludge production was estimated to be 0.14 g total suspended solids produced/g chemical oxygen demand removed. The essential functions of the Cannibal process for the reduction of sludge production appear to be to remove trash and grit from the sludge by physical processes of microscreening and hydrocycloning, respectively, and to provide a long sludge retention time, which allows the slow degradation of the "unbiodegradable" influent particulate organics (XU,Inf) and the endogenous residue (XE). The high energy demand of 1.6 kWh/m³ of treated wastewater at the studied facility limits the niche of the Cannibal process to small- to medium-sized facilities in which sludge disposal costs are high but electricity costs are low.

Phosphorus removal by steel slag filters: modeling dissolution and precipitation kinetics to predict longevity.

This article presents an original numerical model suitable for longevity prediction of alkaline steel slag filters used for phosphorus removal. The model includes kinetic rates for slag dissolution, hydroxyapatite and monetite precipitation and for the transformation of monetite into hydroxyapatite. The model includes equations for slag exhaustion. Short-term batch tests using slag and continuous pH monitoring were conducted. The model parameters were calibrated on these batch tests and experimental results were correctly reproduced. The model was then transposed to long-term continuous flow simulations using the software PHREEQC. Column simulations were run to test the effect of influent P concentration, influent inorganic C concentration and void hydraulic retention time on filter longevity and P retention capacity. High influent concentration of P and inorganic C, and low hydraulic retention time of voids reduced the filter longevity. The model provided realistic P breakthrough at the column outlet. Results were comparable to previous column experiments with the same slag regarding longevity and P retention capacity. A filter design methodology based on a simple batch test and numerical simulations is proposed.

Modelling the degradation of endogenous residue and 'unbiodegradable' influent organic suspended solids to predict sludge production.

Activated sludge models have assumed that a portion of organic solids in municipal wastewater influent is unbiodegradable. Also, it is assumed that solids from biomass decay cannot be degraded further. The paper evaluates these assumptions based on data from systems operating at higher than typical sludge retention times (SRTs), including membrane bioreactor systems with total solids retention (no intentional sludge wastage). Data from over 30 references and with SRTs of up to 400 d were analysed. A modified model that considers the possible degradation of the two components is proposed. First order degradation rates of approximately 0.007 d(-1) for both components appear to improve sludge production estimates. Factors possibly influencing these degradation rates such as wastewater characteristics and bioavailability are discussed.

Physico-chemical characteristics and biodegradability of primary effluent and particulate matter removed by microscreens.

In this study, the physical, chemical, and biological characteristics of raw wastewater were compared with the liquid and solid streams generated by a primary clarifier (PC), a rotating belt filter (RBF, 350 µm), and a drum filter (DF, 60 µm) and series (SER) combination of an RBF with a PC or a DF using pilot-scale primary treatment units. The RBF removed about 36% of the influent total suspended solids. The DF and PC yielded an influent total suspended solid removal of 47% to 55% in both individual (parallel) and SER configurations. The size fractionation and chemical characterizations of the liquid fractions indicated a significant change in the wastewater composition in both filter configurations with no variation in the biodegradability of liquid fractions. The solids recovered by RBF had a higher total solids (TS) concentration and a higher volatile solids (VS) content (0.92 g VS/g TS) than that of DF and PC treatments (0.58 to 0.84 g VS/g TS). DF and PC sludge demonstrated a higher biodegradability rate (k1 ; 0.11 d-1 < k1 < 0.20 d-1 ) than solids recovered by RBF (0.09 d-1 ). The retained solids in the SER configuration demonstrated a significantly lower theoretical biochemical methane potential than the parallel configuration, likely due to the presence of smaller particles with a significantly higher ratio of particulate chemical oxygen demand over volatile suspended solids (1.86 to 2.40 g chemical oxygen demand/g volatile suspended solids). These results indicated that the physical, chemical, and biological characteristics of liquid and solids from different filter configurations are required to determine design criteria to upgrade or retrofit water resource recovery facilities using an RBF or a DF. PRACTITIONER POINTS: A rotating belt filter (RBF) removed less solids than a drum filter (DF) or a primary clarifier (PC). A series configuration of an RBF with either a DF or PC resulted in an effluent with a lower proportion of slowly biodegradable organic matter than in a parallel configuration. Solids from an RBF, a DF, or a PC had similar theoretical biochemical methane potential.

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.

Model of phosphorus precipitation and crystal formation in electric arc furnace steel slag filters.

The objective of this study was to develop a phosphorus retention mechanisms model based on precipitation and crystallization in electric arc furnace slag filters. Three slag columns were fed during 30 to 630 days with a reconstituted mining effluent at different void hydraulic retention times. Precipitates formed in columns were characterized by X-ray diffraction and transmission electronic microscopy. The proposed model is expressed in the following steps: (1) the rate limiting dissolution of slag is represented by the dissolution of CaO, (2) a high pH in the slag filter results in phosphorus precipitation and crystal growth, (3) crystal retention takes place by filtration, settling and growth densification, (4) the decrease in available reaction volume is caused by crystal and other particulate matter accumulation (and decrease in available reaction time), and (5) the pH decreases in the filter over time if the reaction time is too low (which results in a reduced removal efficiency). Crystal organization in a slag filter determines its phosphorus retention capacity. Supersaturation and water velocity affect crystal organization. A compact crystal organization enhances the phosphorus retention capacity of the filter. A new approach to define filter performance is proposed: saturation retention capacity is expressed in units of mg P/mL voids.

Effects of long exposure to low temperatures on nitrifying biofilm and biomass in wastewater treatment.

Attached growth biological treatment systems are a promising solution to ammonia removal in cold-temperature climates. Environmental scanning electron microscopy (ESEM) and confocal laser scanning microscopy in combination with fluorescent in situ hybridization (FISH) was used to investigate the effects of 4 months of exposure to 4 degrees C on nitrifying biofilm and biomass. These molecular and microscopic methods were modified to minimize loss of mass and distortion of in situ perspectives. Environmental scanning electron microscopy revealed that nitrifying biofilm did not exhibit significant changes in volume with exposure to 4 degrees C. Confocal laser scanning microscopy in combination with FISH showed that the number of ammonia-oxidizing bacteria (AOB) cells present in the biofilm was statistically consistent during exposure to 4 degrees C. The RNA content of AOB cells remained sufficient for FISH enumeration. The number of nitrite-oxidizing bacteria cells remained steady during exposure to 4 degrees C; however, the RNA content of the cells appeared to decrease with exposure to 4 degrees C, thereby preventing their enumeration using FISH.

Design of a zero liquid discharge leachate treatment system using an evapotranspiration willow bed.

While zero liquid discharge (ZLD) wetlands have been successfully used for domestic wastewater treatment, adapting this technology to treat other wastewaters such as leachate could be very attractive for some industries concerned with meeting increasingly stringent environmental regulations. Leachate treatment typically implies large volume of water that are entirely dependent on rainfall and therefore highly variable both throughout the year and between years. Current design guidelines for zero discharge willow systems limit system flexibility because they are based on rough theoretical estimates of evapotranspiration. This discuss the applicability of ZLD treatment through a willow bed evapotranspiration (ET) applied to the treatment of industrial leachate that has high and variable hydraulic loading rate and low contaminant and salt concentration. We propose a base design and, through detailed and long-term hydrological modeling of such a treatment system, investigate how various design and management decisions can affect sizing, efficiency, and overall feasibility of the technology. We showed that considering ET optimization factors (e.g. fertilization and organic substrate) was essential for ZLD to be achieved over a 20-year period in northern continental humid climate and that the ratio between cumulative annual ET of the willow bed and cumulative annual rainfall should be at least 1.5. When varying the leachate collection area, it was found that a ratio of willow bed area to collection area between 0.5 and 0.7 should be expected for an optimized design in this specific climate, were land area and storage volume remain the most limiting factors. Regarding storage volume, several management options can be applied to reduce the volume of storage required. We also highlight that a risk attenuation strategy should always be included in the design of a ZLD wetland system. Our study suggests that ZLD wetlands constitute a green technology that represents a serious alternative treatment method for pretreated leachate, while offering many benefits such as low maintenance and energy costs, valorization of contaminants such as nitrogen or phosphorus through biomass production, and, most importantly, zero contaminant discharge to the environment. Finally, we propose future research opportunities and other possible applications for further development of the technology.

Modeling thermomechanical pulp and paper activated sludge treatment plants to gain insight to the causes of bulking.

The Activated Sludge Model No. 1 was chosen as the basis for model development and was modified to take into account the specific characteristics of pulp and paper effluents. The model was incorporated to the GPS-X simulation environment (Hydromantis, Hamilton, Ontario, Canada) to study operating deficiencies and nutrient transformations, particularly in relation to bulking. The results show that the process of ammonification is not significant at the studied mill and that the process of phosphatification (transformation of soluble organic phosphorus into orthophosphates) seems to be related to settling problems, as indicated by the sludge volume index. The phosphatification rate and the standard oxygen-transfer efficiency were found to decrease as the system entered a bulking state. Understanding the behavior of pulp and paper activated sludge can be improved by the incorporation of industry-specific processes and components to comprehensive models. These models then can be used to gain insight to the causes of bulking.

Data reconciliation for wastewater treatment plant simulation studies-planning for high-quality data and typical sources of errors.

Model results are only as good as the data fed as input or used for calibration. Data reconciliation for wastewater treatment modeling is a demanding task, and standardized approaches are lacking. This paper suggests a procedure to obtain high-quality data sets for model-based studies. The proposed approach starts with the collection of existing historical data, followed by the planning of additional measurements for reliability checks, a data reconciliation step, and it ends with an intensive measuring campaign. With the suggested method, it should be possible to detect, isolate, and finally identify systematic measurement errors leading to verified and qualitative data sets. To allow mass balances to be calculated or other reliability checks to be applied, few additional measurements must be introduced in addition to routine measurements. The intensive measurement campaign should be started only after all mass balances applied to the historical data are closed or the faults have been detected, isolated, and identified. In addition to the procedure itself, an overview of typical sources of errors is given.

Uncertainty and variability in enhanced biological phosphorus removal (EBPR) stoichiometry: consequences for process modelling and optimization.

The overall potential for enhanced biological phosphorus removal (EBPR) in the activated sludge process is constrained by the availability of volatile fatty acids (VFAs). The efficiency with which polyphosphate accumulating organisms (PAOs) use these VFAs for P-removal, however, is determined by the stoichiometric ratios governing their anaerobic and aerobic metabolism. While changes in anaerobic stoichiometry due to environmental conditions do affect EBPR performance to a certain degree, model-based analyses indicate that variability in aerobic stoichiometry has the greatest impact. Long-term deterioration in EBPR performance in an experimental SBR system undergoing P-limitation can be predicted as the consequence of competition between PAOs and GAOs. However, the observed rapid decrease in P-release after the change in feed composition is not consistent with a gradual shift in population.

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.

In situ characterization of nitrifying biofilm: minimizing biomass loss and preserving perspective.

Methods for characterizing nitrifying bacteria within biofilms are of key importance to understand and optimize the nitrification kinetics of attached growth treatment facilities. In this work, we propose an analytical protocol based upon environmental scanning electron microscopy (ESEM) and confocal laser scanning microscopy (CSLM) in combination with fluorescent in situ hybridization (FISH) to characterize the structure of nitrifying biofilm as it remains attached to the original reactor substratum. This protocol minimizes the loss of mass and distortion of in situ perspective commonly associated with traditionally applied microscopic techniques and thereby enables a more accurate estimation of the nitrifying biomass within biofilm attached to the substratum. The use of ESEM eliminates the destructive preparatory procedures associated with traditional scanning electron microscopy and thus the loss of mass and shrinking of the samples. ESEM is used in this study to evaluate the percent coverage of the substratum with biofilm and the biofilm thickness. CLSM-FISH is used to determine cell counts in the biofilm and to characterize the undisturbed substratum/biofilm interface. By hybridizing and analyzing the nitrifying biofilm using CLSM as it remains attached to the substratum, the loss of material and distortion of in situ perspective associated with the biofilm detachment process is minimized. Moreover, by conducting the CLSM analysis directly on the nitrifying biofilm as it remains attached to the substratum it is shown that cell counts at the substratum/biofilm interface differ significantly from that located above the interface.