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उपचार आर्द्रभूमियााँ ‘जैविक अपमिष्ट जल’ िें सातिाृं खृंड है उपचार श्ृंखर ला, जो सीिेज उपचार के विज्ञान और तकनीक की अत्याधुननक प्रस्तुनत देती है। आर्द्रभूमि प्रणामलयों के प्रिुख प्रकार इस खृंड िें िामिल हैं, नाितः: (i) क्षैनतज प्रिाह आर्द्रभूमि; (ii) ऊध्िारधर प्रिाह आर्द्रभूमि; (iii) फ्रें च ऊध्िारधर प्रिाह आर्द्रभूमि; (iv) सघन आर्द्रभूमि; (v) िुक्त जल सतह आर्द्रभूमि; (vi) उपचार आर्द्रभूमि के अन्य अनुप्रयोि। पुस्तक िुख्य अिधारणाओृं, कािकाजी मसद्धाृंतों, अपेक्षक्षत प्रदिरन, डडजाइन िानदृंड, डडजाइन उदाहरण, ननिारण पहलुओृं और पररचालन द्रदिाननदेिों को स्पष्ट और उपचारात्िक तरीके से प्रस्तुत करती है। पुस्तक को उपचार के क्षेत्र के िीर्र वििेर्ज्ञों की एक अृंतरराष्रीय टीि ने मलखा है। श्ृंखर ला के बारे िें: इस बहुप्रिृंमसत श्ृंखर ला िें सात पाठ्यपुस्तकें िामिल हैं - वप्रटृं िें या िुक्त-अमभिि ई-पुस्तकों के रूप िें उपलब्लध - जो जैविक अपमिष्ट जल उपचार के विज्ञान और तकनीक की एक अत्याधुननक प्रस्तुनत प्रदान करती हैं। विकमसत और विकासिील देिों िें छात्रों, िोधकतारओृं और अभ्यासकों द्िारा श्ृंखर ला के सभी खण्डों का व्यापक रूप से उपयोि क्रकया िया है। जैविक अपमिष्ट जल उपचार श्ृंखर ला िें िीर्कर हैं: खृंड 1: अपमिष्ट जल के लक्षण, उपचार और ननपटानखृंड 2: अपमिष्ट जल उपचार के िूल मसद्धाृंतखृंड 3: अपमिष्ट स्स्िरीकरण तालाबखृंड 4: अिायािीय ररएक्टरखृंड 5: सक्रिय कीचड़ और िायुजीिी बायोक्रिल्ि ररएक्टरखृंड 6: कीचड़ उपचार और ननपटानखृंड 7: उपचार आर्द्रभूमियााँ आईएसबीएन: 9781780408767 (पेपरबैक) आईएसबीएन: 9781789062564 (ई-पुस्तक)

Treatment wetlands (TWs) efficiently remove many pollutants including a several log order reduction of pathogens from influent to effluent; however, there is evidence to suggest that pathogen cells are sequestered in a subsurface wetland and may remain viable months after inoculation. Escherichia coli is a common pathogen in domestic and agricultural wastewater and the O157:H7 strain causes most environmental outbreaks in the United States. To assess attachment of E. coli to the TW rhizosphere, direct measurements of E. coli levels were taken. Experiments were performed in chemostats containing either Teflon nylon as an abiotic control or roots of Carex utriculata or Schoenoplectus acutus. Flow of simulated wastewater through the chemostat was set to maintain a 2 hour residence time. The influent was inoculated with E. coli O157:H7 containing DsRed fluorescent protein. Root samples were excised and analyzed via epifluorescent microscopy. E. coli O157:H7 was detected on the root surface at 2 hours after inoculation, and were visible as single cells. Microcolonies began forming at 24 hours post-inoculation and were detected for up to 1 week post-inoculation. Image analysis determined that the number of microcolonies with >100 cells increased 1 week post-inoculation, confirming that E. coli O157:H7 is capable of growth within biofilms surrounding wetland plant roots.

This study aimed to investigate the effects of constructed wetland design (unsaturated, saturated and aerated saturated) and plant species (Juncus, Typha, Berula, Phragmites and Iris) on the mass removal and removal kinetics of the pharmaceutical ibuprofen. Planted systems had higher ibuprofen removal rates (29%–99%) than in the unplanted ones (15%–85%) in all designs. The use of forced aeration improved ibuprofen removal only in the unplanted mesocosms. In general, ibuprofen removal followed an area-based first-order removal kinetics model with removal rate coefficients (kA) varying between 3 and 35 cm/d. The ibuprofen removal was mainly attributed to microbial degradation by the fixed bed biofilm, but plant uptake and degradation within plant tissues also occurred. The ibuprofen removal was positively correlated with the oxygen concentration in the water and the removal of nutrients, indicating that degradation may be due to co-metabolisation processes.

In this study, a mathematical biofilm reactor model based on the structure of the Constructed Wetland Model No.1 (CWM1) coupled to AQUASIM's biofilm reactor compartment has been used to reproduce the sequence of transformation and degradation of organic matter, nitrogen and sulphur observed in a set of constructed wetland mesocosms and to elucidate the development over time of microbial species as well as the biofilm thickness of a multispecies bacterial biofilm in a subsurface constructed wetland. Experimental data from 16 wetland mesocosms operated under greenhouse conditions, planted with three different plant species (Typha latifolia, Carex rostrata, Schoenoplectus acutus) and an unplanted control were used in the calibration of this mechanistic model. Within the mesocosms, a thin (predominantly anaerobic) biofilm was simulated with an initial thickness of 49 μm (average) and in which no concentration gradients developed. The biofilm density and area, and the distribution of the microbial species within the biofilm were evaluated to be the most sensitive biofilm properties; while the substrate diffusion limitations were not significantly sensitive to influence the bulk volume concentrations. The simulated biofilm density ranging between 105,000 and 153,000 gCOD/m(3) in the mesocosms was observed to vary with temperature, the presence as well as the species of macrophyte. The biofilm modeling was found to be a better tool than the suspended bacterial modeling approach to show the influence of the rhizosphere configuration on the performance of the constructed wetlands.

Constructed wetlands offer an effective means for treatment of wastewater from a variety of sources. An understanding of the microbial ecology controlling nitrogen, carbon and sulfur cycles in constructed wetlands has been identified as the greatest gap for optimizing performance of these promising treatment systems. It is suspected that operational factors such as plant types and hydraulic operation influence the subsurface wetland environment, especially redox, and that the observed variation in effluent quality is due to shifts in the microbial populations and/or their activity. This study investigated the biofilm associated sulfate reducing bacteria and ammonia oxidizing bacteria (using the dsrB and amoA genes, respectively) by examining a variety of surfaces within a model wetland (gravel, thick roots, fine roots, effluent), and the changes in activity (gene abundance) of these functional groups as influenced by plant species and season. Molecular techniques were used including quantitative PCR and denaturing gradient gel electrophoresis (DGGE), both with and without propidium monoazide (PMA) treatment. PMA treatment is a method for excluding from further analysis those cells with compromised membranes. Rigorous statistical analysis showed an interaction between the abundance of these two functional groups with the type of plant and season (p

A simulation model based on Constructed Wetland Model No. 1 (CWM1) using the AQUASIM mixed reactor compartment as a platform was built to study the dynamics of key processes governing COD and nutrient removal in wetland systems. Data from 16 subsurface-flow wetland mesocosms operated under controlled greenhouse conditions with three different plant species (Typha latifolia, Carex rostrata, Schoenoplectus acutus) and an unplanted control were used for calibration and validation in this mechanistic model. Mathematical equations for plant related processes (growth, physical degradation, decay, and oxygen leaching), physical re-aeration, as well as adsorption and desorption processes for COD and ammonium were included and implemented alongside CWM1 in the AQUASIM software, while some CWM1 parameters were adjusted to better fit the model predictions to experimental data during calibration. The simulation results showed that the model was able to describe the general trend of COD (R2 = 0.97–0.99), ammonium (R2 = 0.85–0.97) and sulphate (R2 = 0.71–0.93) removal in the wetland mesocosms and also in their controls (unplanted) through the experimental temperature range of 12–24 °C. Oxygen transfer by physical re-aeration was found to be 0.05 and 0.09 g m−2 d−1 at 12 °C and 24 °C, respectively. The amount of root oxygen transfer was the highest for the planted mesocosms at 12 °C at rates of 1.91, 0.94, and 0.45 g m−2 d−1 in the Carex, Schoenoplectus and Typha mesocosms, respectively, indicating that COD of the bulk wastewater was removed mainly by anaerobic processes under the specific experimental situations. Measured COD removal was better in the planted mesocosms than in the control; differences were effectively modelled by varying the bacteria concentration. The sorption process was found to be important in simulating COD and ammonia removal under these experimental conditions.

Floating islands are a form of treatment wetland characterized by a mat of synthetic matrix at the water surface into which macrophytes can be planted and through which water passes. We evaluated two matrix materials for treating domestic wastewater, recycled plastic and recycled carpet fibers, for chemical oxygen demand (COD) and nitrogen removal. These materials were compared to pea gravel or open water (control). Experiments were conducted in laboratory scale columns fed with synthetic wastewater containing COD, organic and inorganic nitrogen, and mineral salts. Columns were unplanted, naturally inoculated, and operated in batch mode with continuous recirculation and aeration. COD was efficiently removed in all systems examined (>90% removal). Ammonia was efficiently removed by nitrification. Removal of total dissolved N was ∼50% by day 28, by which time most remaining nitrogen was present as NO3-N. Complete removal of NO3-N by denitrification was accomplished by dosing columns with molasses. Microbial communities of interest were visualized with denaturing gradient gel electrophoresis (DGGE) by targeting specific functional genes. Shifts in the denitrifying community were observed post-molasses addition, when nitrate levels decreased. The conditioning time for reliable nitrification was determined to be approximately three months. These results suggest that floating treatment wetlands are a viable alternative for domestic wastewater treatment.

Plants have many well-documented influences in treatment wetlands, but differences in individual species’ effects on year-round and seasonal performance are poorly understood. In this study, we evaluated plant effects on seasonal patterns of organic carbon removal (measured as COD) and sulfate concentration (used as an indicator of rootzone oxidation) in replicated, batch-loaded, greenhouse microcosms simulating subsurface treatment wetlands. Microcosms were planted with monocultures of 19 plant species or left unplanted as controls, dosed every 20 days with synthetic secondary wastewater, and operated over 20 months at temperatures from 4 to 24 °C. Study-long COD removal averaged 70% for controls and 70–97% for individual species. Most species enhanced COD removal significantly and the benefits of plants were greatest at 4–8 °C because COD removal decreased at low temperatures in controls but displayed limited seasonal variation in planted microcosms. Removal was significantly better at 24 °C than 4 °C with two species ( Panicum virgatum and Leymus cinereus ), significantly poorer with two species ( Carex utriculata and Phalaris arundinacea ), and did not differ with 15 species. Only one species showed a significant positive correlation between temperature and COD removal ( Iris missouriensis , r = 0.67), while two species showed significant negative correlations (better when colder: Carex nebrascensis , r = −0.67; C. utriculata , r = −0.93). High COD removal throughout the study was strongly associated with high SO 4 concentrations at low temperatures, suggesting that plant performance is related to rootzone oxidation and species’ abilities to promote aerobic over anaerobic microbial processes, particularly in winter. Results indicate that improved year-round and cold-season COD removal is common across diverse wetland plant species and novel species can be as good or better than those typically used. Better performing species were largely in the sedge and rush families ( Cyperaceae and Juncaceae ), while poorer performing species were largely in the grass family ( Poaceae ).

This review summarizes the microbial mechanisms responsible for removal of carbon, nitrogen. and sulfur compounds in treatment wetlands (TWs) and identifies, categorizes and compares various techni ...

The modified k–C* first-order degradation model proposed by Kadlec and Knight [Kadlec, R.H., Knight, R.L., 1996. Treatment Wetlands. Lewis Publishers, Boca Raton, FL] was fit to 192 data sets of COD concentration versus time measured in batch-loaded wetland microcosms. The time series sets were divided into four replicates of four plant species treatments; Carex utriculata (sedge), Schoenoplectus acutus (bulrush), Typha latifolia (cattail) and unplanted controls housed in a controlled-environment greenhouse in which temperature was cycled in 4 °C increments from 24 to 4 °C and back to 24 °C over a yearlong period. One 20-day batch incubation was conducted at each temperature setting during which seven chemical oxygen demand (COD) samples were drawn from each of 16 wetland columns. Non-linear mixed effects regression was used to fit parameters of the model. Best-fit values of the rate parameter k and the background concentration C* varied significantly by plant species and greenhouse temperature setting. An Arrhenius relationship was used to assess the effect of temperature on these parameters. Species greatly influenced the value of volumetric rate parameter at 20 °C (k20) and ranked Carex > Schoenoplectus > Typha > unplanted control (0.925, 0.743, 0.612 and 0.366 day−1, respectively). All displayed decreasing values for increasing temperature but species variation was much less (θk = 0.945, 0.957, 0.953 and 0.936, respectively). Background COD concentration values at 20 °C (C20*) ranked Carex

Three polar organic solvents, acetone, tetrahydrofuran (THF) and 1-butanol, were added at 100 mg/l each to post-primary municipal wastewater in order to simulate a mixed waste stream. This mixture was applied to an experimental microcosm subsurface constructed wetland system consisting of replicates of Juncus effusus, Carex lurida, Iris pseudacorus, Pondeteria cordata and unplanted controls in a series of 14-day batch incubations over a yearlong period simulating a summer and winter season. 90% removal of 1-butanol typically took less than 3 days. 90% removal of acetone required from 5 to 10 days in summer and 10 to 14 days in winter. 90% removal of THF required at least 10 days and was frequently not achieved during the 14-day incubations. Initial experiments confirmed that the majority of solvent removal was via microbial bioremediation. Solvent removal was typically better in planted replicates, especially Juncus, regardless of season. The removal rate of all solvents was slower in winter, but the seasonal effect was most pronounced in the unplanted control replicates and least in the Carex and Juncus replicates. Plant and seasonal effects are believed to be due, in part, to variation in metabolic pathways induced by plant and seasonal variation in available root-zone oxygen. Variation in transpiration also influenced species and seasonal effects on THF removal, but not the other more biodegradable solvents. A model based on a prediction of plant uptake of nonionic dissolved chemicals suggests that as much as 39% of the THF in solution could have been removed through plant transpiration.

We evaluated ammonium nitrogen removal and nitrogen transformations in three-year-old, batch-operated, subsurface wetland microcosms. Treatments included replicates of Typha latifolia, Carex rostrata, and unplanted controls when influent carbon was excluded, and C. rostrata with an influent containing organic carbon. A series of 10-day batch incubations were conducted over a simulated yearlong cycle of seasons. The presence of plants significantly enhanced ammonium removal during both summer (24 degrees C, active plant growth) and winter (4 degrees C, plant dormancy) conditions, but significant differences between plant species were evident only in summer when C. rostrata outperformed T. latifolia. The effect of organic carbon load was distinctly seasonal, enhancing C. rostrata ammonium removal in winter but having an inhibitory effect in summer. Season did not influence ammonium removal in T. latifolia or unplanted columns. Net production of organic carbon was evident year-round in units without an influent organic carbon source, but was enhanced in summer, especially for C. rostrata, which produced significantly more than T. latifolia and unplanted controls. No differences in production were evident between species in winter. COD values for C. rostrata microcosms with and without influent organic carbon converged within 24 hours in winter and 7 days in summer. Gravel sorption, microbial immobilization and sequential nitrification/denitrification appear to be the major nitrogen removal mechanisms. All evidence suggests differences between season and species are due to differences in seasonal variation of root-zone oxidation.

Accurate estimates of evapotranspiration from constructed wetlands are required to establish design flow estimates and to assess the effectiveness of wetland water quality amelioration. Water consumption by two wetland plant species, Typha latifoilia (broadleaf cattail) and Scoenoplectus acutus (hardstem bulrush), was measured in a greenhouse for eight months. Measurements of actual evapotranspiration (ETC) from replicates of both plant treatments were related to potential evaporation (ET0) as approximated by evaporation from saturated gravel beds. Ratios of ETC to ET0 were used to develop crop coefficients (Kc) for each plant species. The relationship between cattail ETC/ET0 and the ratio of vegetative to open water surface area (SV/S0) agreed with previous investigations. A linear relationship was used to account for advective energy fluxes due to peripheral canopy area. Cattail crop coefficients were scaled according to this relationship. The resulting scaled crop coefficient curve may be transferable ...

Two side-by-side experimental sub-surface flow systems allowed direct comparison of wetland performance under batch and continuous-flow operation. One system consisted of microcosm “columns” operated in 20-day batch mode while the second consisted of continuous-flow “cells” operated at a five-day residence time. Both systems treated identical synthetic domestic wastewater for two years and then treated identical synthetic mine-impacted water for one year. Each system had replicates planted with Typha latifolia, Scirpus acutus and unplanted controls. Temperature was cycled annually between 4 to 24°C. Results indicated that plant species, season, and mode of operation interacted strongly in controlling dynamics of COD, nitrogen species, phosphate, sulfate, and redox potentials. In batch-loaded columns, between-species differences in oxidation and COD removal were large in winter, during plant dormancy, but absent in summer; COD removal, sulfate concentration, and redox potentials were closely correlated, suggesting that variation in root-zone oxygenation due to seasonal plant growth patterns and temperature-dependent plant and microbial respiration may explain observed differences. In the continuous-flow cells, species and seasonal differences were minimal or non-existent, indicating that under continuous-flow operation plants either did not influence root zone oxidation or that this influence had no effect on wetland performance for COD and nutrient removal or sulfate reduction.

Total nitrogen (TN) removal in treatment wetlands (TWs) is challenging due to nitrogen cycle complexity and the variation of influent nitrogen species. Plant species, season, temperature and hydraulic loading most likely influence root zone oxygenation and appurtenant nitrogen removal, especially for ammonium-rich wastewater. Nitrogen data were collected from two experiments utilizing batch-loaded (3-, 6-, 9- and 20-day residence times), sub-surface TWs monitored for at least one year during which temperature was varied between 4 and 24 °C. Synthetic wastewater containing 17 mg/l N as NH 4 and 27 mg/l amino-N, 450 mg/l chemical oxygen demand (COD), and 13 mg/l SO 4 -S was applied to four replicates of Carex utriculata , Schoenoplectus acutus and Typha latifolia and unplanted controls. Plant presence and species had a greater effect on TN removal than temperature or residence time. Planted columns achieved approximately twice the nitrogen removal of unplanted controls (40–95% versus 20–50% removal) regardless of season and temperature. TWs planted with Carex outperformed both Typha and Schoenoplectus and demonstrated less temperature dependency. TN removal with Carex was excellent at all temperatures and residence times; Schoenoplectus and Typha TN removal improved at longer residence times. Reductions in TN were not accompanied by increases in NO 3 , which was consistently below 1 mg/l N.

An excess shear sediment detachment relation is commonly used in erosion prediction models. Traditional field methods for calibration of soil-dependent empirical constants are both expensive and conceptually suspect. The subprocesses of sediment detachment and transport cannot be physically separated, therefore they cannot be calibrated independently. Impingement of a clear-water jet on a soil bed produces detachment without transport at the point of maximum scour. In this article, a mathematical description of the impinging jet scour process is used to calibrate an excess shear detachment relation. Four calibration models are developed based on variants of the jet-scour rate equations (differential and integral form, each evaluated using arithmetic and logarithmic values for dependent variables). All models assume detachment is linearly related to excess shear. The validity of this calibration technique has been tested in the laboratory by measuring scour depth versus time for six different soils, all evaluated in a disturbed, saturated condition. A total of 14 replicates on the soils were conducted where hydraulic inputs were varied with replicate. Statistical analyses were used to place confidence limits about the optimal sediment detachment values for each of the four models. Only the arithmetic differential model produced results considerably different than the other three. The integrated log model produced the tightest confidence intervals and this is suggested for further use. The size of the confidence intervals demonstrates the replicability of the technique. The technique produced detachment rate constants that are similar to field calibration studies for soils of similar properties. Critical shear values are an approximate order of magnitude lower, but all soils were evaluated only in the highly erosive, disturbed, unconsolidated, and saturated condition. The technique can be applied to soils in other conditions and it is possible that this discrepancy is due to different soil conditions.

Timevarying sediment concentration exiting a plunge pool is analyzed by considering the effect of freeoverfall jet diffusion on sediment detachment and scour. The analysis results in dimensionless ...

Scour immediately downstream of a headcut is analyzed by considering the effect of jet diffusion on sediment detachment. The analytical development results in equations for: 1. the equilibrium scou...

Two modes of headcut migration are generally recognized: (1) rotating headcuts that tend to flatten as they migrate; and (2) stepped headcuts that tend to retain nearly vertical faces. A mathematical description of the sediment detachment potential immediately upstream and downstream of the headcut is used to delineate these modes of migration. The delineating parameter is the ratio of the time required to erode the headcut face from above to the time required to undermine the headcut face from below. This erosional time-scale ratio is a dimensionless function of flow, sediment, and geometry parameters. For the limiting case of homogeneous cohesive soils, the time-scale ratio is a simple function of a Froude number and the aspect ratio of drop height to normal flow depth. This relationship is calibrated using original laboratory experiments of headcut migration in initially vertical headcuts and verified by independent field experiments of headcuts propagating in four different homogeneous cohesive soils.

Publisher Summary This chapter deals with wet well design, pump piping, and selection of pumping equipment. The pump intake design must satisfy several requirements for proper approach conditions by avoiding poor velocity distribution at the entrance to the pump, excessive swirling in the pump intake piping, air entrainment in the pumped flow, unstable approach conditions in multiple pump operation, and vortices. Model studies are useful for finding and correcting faults in the hydraulic flow patterns in wet wells. The ANSI/HI 9.8-1998 standard requires a physical model study if the sump or piping geometry differs from the standard, the approach flow is non-uniform or unsymmetrical, and the flow rate is more than 2520 L/s (40,000 gal/min) per pump or the total flow exceeds 6310 L/s (100,000 gal/min) with all pumps running. Several factors that need to be considered during pipe selection include quality of the fluid to be pumped, required design capacity (initial minimum, average, and maximum flow rates), operating conditions (best-case and worst-case system head curves, maximum and minimum flow rates, submergence, and/or NPSH). A step-by-step procedure for selecting pumps involves developing the calculations for the performance requirements completely and on the basis of the best- and worst-case assumptions for system dynamic headlosses, specifying materials that are suitable for the application, specifying the proper balance grade number, and deciding the number of pumps to be used and the type of pump.

The k - C * first order model was fit to time-series COD data collected from batch-loaded model wetlands. Four replicates of four plant species treatments; Carex utriculata (sedge), Schoenoplectus acutus (bulrush), Typha latifolia (cattail) and unplanted controls were compared. Temperature was varied by 4 °C from 24 °C to 4 °C to 24 °C over a year-long period. One mathematical fit was made for each wetland replicate at each temperature setting (192 fits). Temperature effects on both parameters were subsequently estimated by fitting the Arrhenius relationship to the estimated coefficients. Inherent interactions between k and C * make values dependent on sample timing and statistical technique for either time series (batch load) or distance profile (plug flow) data. Coefficients calibrated using the Levenberg–Marquardt method are compared to values previously reported using a nonlinear mixed effect regression technique. Overall conclusions are similar across approaches: (a) the magnitude of the coefficients varies strongly by species; (b) the rate constant k decreases with increasing temperature; and (c) temperature and species variation in the residual concentration C * is greater than the variation in k , such that variation in k alone is a poor predictor of performance. However, the magnitudes of the coefficients, especially the rate parameter k , vary between the statistical techniques, highlighting the need to better document the statistical routines used to calibrate the k - C * model.

To characterize the effects of season, temperature, plant species, and chemical oxygen demand (COD) loading on sulfate reduction and metals removal in treatment wetlands we measured pore water redox potentials and concentrations of sulfate, sulfide, zinc and COD in subsurface wetland microcosms. Two batch incubations of 20 day duration were conducted in each of four seasons defined by temperature and daylight duration. Four treatments were compared: unplanted controls, Typha latifolia (broadleaf cattail), and Schoenoplectus acutus (hardstem bulrush), all at low COD loading (267 mg/L), plus bulrush at high COD loading (534 mg/L). Initial SO4-S and zinc concentrations were 67 and 24 mg/L, respectively. For all treatments, sulfate removal was least in winter (4 degrees C, plant dormancy) greatest in summer (24 degrees C, active plant growth) and intermediate in spring and fall (14 degrees C), but seasonal variation was greater in cattail, and especially, bulrush treatments. Redox measurements indicated that, in winter, plant-mediated oxygen transfer inhibited activity of sulfate reducing bacteria, exacerbating the reduction in sulfate removal due to temperature. Doubling the COD load in bulrush treatments increased sulfate removal by only 20-30% when averaged over all seasons and did not alter the basic pattern of seasonal variation, despite tempering the wintertime increase in redox potential. Seasonal and treatment effects on zinc removal were broadly consistent with sulfate removal and presumably reflected zinc-sulfide precipitation. Results strongly suggest that interactive effects of COD loading rate, temperature, season, and plant species control not only sulfate reduction and zinc sequestration, but also the balance of competition between various microbial consortia responsible for water treatment in constructed wetlands.

The influence of temperature and plant-mediated oxygen transfer continues to draw attention from researchers, practitioners and regulators interested in the use of constructed wetlands for wastewater treatment. Because the vast majority of research on constructed wetland performance has been conducted during periods of active plant growth, the true influence of temperature, season, and plant species selection on constructed wetlands performance has not yet been evaluated adequately. In this article, we briefly summarize changes in the understanding of these influences on wetland performance, and suggest that effects of temperature and oxygen transfer are not readily separable because both factors respond to seasonal cycles and because effects of one can offset the other. We further speculate that the net effect of seasonal variation in these factors is such that plant-mediated oxygen transfer affects water treatment most in winter. Results of controlled-environment experiments conducted at Montana State University support these perspectives. Different plant species' capacities to oxidize the root zone responded differently to seasonal cycles of growth and dormancy, and species' effects on wastewater treatment were most pronounced in winter.

A basin-wide assessment of fish passage through culverts was performed in the upper Seeley Lake watershed in western Montana. The watershed has many small streams that support a variety of trout species, predominately cutthroat trout and brook trout, but with some bull trout and brown trout too. A total of 47 culverts were studied, and at these culverts the FishXing model and a screening tool that is a composite of several flowchart-based models were used to predict fish passage success. At a subset of 21 culverts, fish were collected above and below the culvert to check for population differences with respect to species, size, and abundance. At another subset of 10 culverts, fish passage was directly assessed using fish traps. Results indicate that the FishXing model and the composite screen are conservative estimators of fish passage in culverts. The direct passage assessment indicated that more fish passage occurred during low flow than was expected, and the population (above/below) sampling results gave little evidence to indicate that many of the culverts were functioning as barriers to fish passage. However, there was evidence that fish passage was restricted at many of the culverts at low flow. High flow was not examined in detail at the field sites in this study.

Constructed wetlands are widely used for wastewater treatment, but there is little information on processes affecting their performance in cold climates, effects of plants on seasonal performance, or plant selection for cold regions. We evaluated the effects of three plant species on seasonal removal of dissolved organic matter (OM) (measured by chemical oxygen demand and dissolved organic carbon) and root zone oxidation status (measured by redox potential [Eh] and sulfate [SO4(2-)]) in subsurface-flow wetland (SSW) microcosms. A series of 20-d incubations of simulated wastewater was conducted during a 28-mo greenhouse study at temperatures from 4 to 24 degrees C. Presence and species of plants strongly affected seasonal differences in OM removal and root zone oxidation. All plants enhanced OM removal compared with unplanted controls, but plant effects and differences among species were much greater at 4 degrees C, during dormancy, than at 24 degrees C, during the growing season. Low temperatures were associated with decreased OM removal in unplanted controls and broadleaf cattail (Typha latifolia L.) microcosms and with increased removal in beaked sedge (Carex rostrata Stokes) and hardstem bulrush [Schoenoplectus acutus (Muhl. ex Bigelow) A. & D. Love var. acutus] microcosms. Differences in OM removal corresponded to species' apparent abilities to increase root zone oxygen supply. Sedge and bulrush significantly raised Eh values and SO4(2-) concentrations, particularly at 4 degrees C. These results add to evidence that SSWs can be effective in cold climates and suggest that plant species selection may be especially important to optimizing SSW performance in cold climates.

[1] A two-dimensional model is developed to predict head cut migration rate for the specific case of a relatively erosion-resistant soil layer overlying a deep, relatively erosive base soil. For this geometry, head cut migration can occur as a series of discrete mass failures of the surface layer caused by undercutting in a plunge pool formed immediately downstream. The length scale of one failure episode is modeled as a cantilevered slab failing in bending. The timescale for each failure episode is controlled by the rate and geometry of base layer scour, which is modeled independently of cantilevered slab properties. An integration of the two model components for the case of steady flow and uniform soil properties predicts linear upstream head cut migration with time, occurring in discrete steps bounded by successive mass failure events. The model is calibrated and tested in a series of flume experiments representing ideal conditions of different initial geometries and flow conditions. Head cut migration occurred by the proposed mechanism in a nearly linear rate. Average error between the observed and predicted retreat rate is 40%, most of this error is attributable to prediction of the scour hole shape.

[1] Soil erosion due to head cut development and migration can devastate agricultural lands, yet current prediction technology does not address this important erosion process. Here an analytical model of this erosional phenomenon is presented. Realistic, physically based approximations to the laws governing mass, momentum, and energy transfer in the neighborhood of the scour hole result in closed-form predictive algorithms for the magnitude of the plunge pool erosion and the rate of head cut migration. The model introduces a special treatment of nonventilated overfall conditions, is limited to homogeneous, unbounded soil layers, and is validated by available experimental measurements.

The work on the STR started with a survey among the Wetland Systems SG members (about 140 SG members took part in the survey). In February 2018, a three-day workshop with approximately 20 participants was organised at BOKU University Vienna in Austria to kick off the STR work. During the workshop the main structure of the book and responsibilities for chapters were defined. The main outcomes were that the textbook should be the basis of the STR, and that the content of the STR should include useful information for practitioners and researchers aiming to design treatment wetlands. After the IWA Wetland Systems conference in October 2018 in Valencia, Spain, a meeting on the STR was organised in which the status of the work was reviewed and responsibilities for the remaining work were refined. The editors had the task to compile the new Scientific and Technical Report on Wetland Technology. The STR includes contributions from more than 50 wetland colleagues from academia and practice. The editors are very thankful for all the enthusiasm and effort put into this work and we hope that the STR will be a useful addition to the treatment wetland literature. We hope you will enjoy this Scientific and Technical Report on Wetland Technology.