A thermal analysis of a sub-surface, vertical flow constructed wetland

1997 ◽  
Vol 35 (5) ◽  
pp. 55-62 ◽  
Author(s):  
Ian D. Smith ◽  
George N. Bis ◽  
Edgar R. Lemon ◽  
Lloyd R. Rozema
Keyword(s):  
Thermal Energy ◽  
Constructed Wetland ◽  
Transport Model ◽  
Thermal Design ◽  
Sensitivity Analyses ◽  
Municipal Sewage ◽  
Deep Soil ◽  
Design Assessment ◽  
South Central ◽  
Thermal Data

Since November of 1991, an experimental constructed wetland has successfully treated municipal sewage effluent on a year round basis in a cool climate. The sub-surface, vertically pulsed flow system is located at a latitude of approximately 43 degrees, 15 minutes north latitude in south-central Canada. The 5 metre long by 5 metre wide by 1.2 metre deep constructed wetland cells were designed to operate through extended freezing periods via a number of specific features. The most important features being the allowance of thatch accumulation atop the system, ice accretion within the upper cell strata both acting as insulating layers, and the transfer of thermal energy to the system from warmer deep soils. The cells were hydraulically loaded below this frozen layer of granular matrix six times a day. A dense three dimensional array of thermocouples was planted within the first of the three constructed wetland cells in a series to allow for the assessment of thermal data at a high level of temporal and spatial resolution. Thermal data were sampled every five minutes and averaged and stored every hour over a two year period (1994 and 1995). The data were reviewed statistically to determine the operating envelope experienced at the Niagara-On-The-Lake experimental constructed wetland site. A detailed review of winter thermal data was made to provide parameters for the use of the HEATFLOW density-dependent ground water flow and thermal energy transport numerical model (Molson and Frind, 1995). The use of this coupled Darcy flux, thermal transport model has allowed for a better understanding of the importance of various thermal design considerations, and has allowed for the undertaking of sensitivity analyses for design assessment and optimization. The sensitivity analyses indicate that the retention of deep soil heat and top insulation from plant thatch are the most important thermal features. It is likely that this technology can be used in areas colder than Niagara-On-The-Lake.

scholarly journals Modelling both the continual erosion and regeneration of discolouration material in drinking water distribution systems

2013 ◽  
Vol 14 (1) ◽  
pp. 81-90 ◽  
Author(s):  
W. R. Furnass ◽  
R. P. Collins ◽  
P. S. Husband ◽  
R. L. Sharpe ◽  
S. R. Mounce ◽  
...  
Keyword(s):  
Distribution System ◽  
Distribution Systems ◽  
Water Distribution ◽  
Transport Model ◽  
Water Distribution Systems ◽  
Sensitivity Analyses ◽  
Drinking Water Distribution Systems ◽  
Proactive Management ◽  
Drinking Water Distribution ◽  
Mass Transport Model

The erosion of the cohesive layers of particulate matter that causes discolouration in water distribution system mains has previously been modelled using the Prediction of Discolouration in Distribution Systems (PODDS) model. When first proposed, PODDS featured an unvalidated means by which material regeneration on pipe walls could be simulated. Field and laboratory studies of material regeneration have yielded data that suggest that the PODDS formulations incorrectly model these processes. A new model is proposed to overcome this shortcoming. It tracks the relative amount of discolouration material that is bound to the pipe wall over time at each of a number of shear strengths. The model formulations and a mass transport model have been encoded as software, which has been used to verify the model's constructs and undertake sensitivity analyses. The new formulations for regeneration are conceptually consistent with field and laboratory observed data and have potential value in the proactive management of water distribution systems, such as evaluating change in discolouration risk and planning timely interventions.

Modelling uranium leaching from agricultural soils to groundwater as a criterion for comparison with complementary safety indicators

2006 ◽  
Vol 932 ◽  
Author(s):  
D. Jacques ◽  
J. Šimůnek ◽  
D. Mallants ◽  
M.Th. van Genuchten
Keyword(s):  
Soil Profile ◽  
Reactive Transport ◽  
Transport Model ◽  
Agricultural Soils ◽  
Solid Phase ◽  
Water Flux ◽  
Fertilizer Application ◽  
Mineral Fertilizers ◽  
Deep Soil ◽  
Long Time

ABSTRACTNaturally occurring radionuclides can also end up in soils and groundwater due to human practices, such as application of certain fertilizers in agriculture. Many mineral fertilizers, particularly (super)phosphates, contain small amounts of 238U and 230Th which eventually may be leached from agricultural soils to underlying water resources. Field soils that receive P-fertilizers accumulate U and Th and their daughter nuclides, which eventually may leach to groundwater. Our objective was to numerically assess U migration in soils. Calculations were based on a new reactive transport model, HP1, which accounts for interactions between U and organic matter, phosphate, and carbonate. Solid phase interactions were simulated using a surface complexation module. Furthermore, all geochemical processes were coupled with a model accounting for dynamic changes in the soil water content and the water flux. The capabilities of the code in calculating natural U fluxes to groundwater were illustrated using a semi-synthetic 200-year long time series of climatological data for Belgium. Based on an average fertilizer application, the input of phosphate and uranium in the soil was defined. This paper discusses calculated U distributions in the soil profile as well as calculated U fluxes leached from a 100-cm deep soil profile. The calculated long-term leaching rates originating from fertilization are significantly higher after 200 years than estimated release rates from lowlevel nuclear waste repositories.

scholarly journals The fate of saharan dust across the atlantic and implications for a central american dust barrier

2011 ◽  
Vol 11 (16) ◽  
pp. 8415-8431 ◽  
Author(s):  
E. Nowottnick ◽  
P. Colarco ◽  
A. da Silva ◽  
D. Hlavka ◽  
M. McGill
Keyword(s):  
Central America ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Saharan Dust ◽  
Sensitivity Analyses ◽  
Transport Barrier ◽  
Dust Transport ◽  
Transport Dynamics ◽  
The Caribbean ◽  
Wet Removal

Abstract. Saharan dust was observed over the Caribbean basin during the summer 2007 NASA Tropical Composition, Cloud, and Climate Coupling (TC4) field experiment. Airborne Cloud Physics Lidar (CPL) and satellite observations from MODIS suggest a barrier to dust transport across Central America into the eastern Pacific. We use the NASA GEOS-5 atmospheric transport model with online aerosol tracers to perform simulations of the TC4 time period in order to understand the nature of this barrier. Our simulations are driven by the Modern Era Retrospective-Analysis for Research and Applications (MERRA) meteorological analyses. Compared to observations from MODIS and CALIOP, GEOS-5 reproduces the observed location and magnitude of observed dust events, but our baseline simulation does not develop as strong a barrier to dust transport across Central America as observations suggest. Analysis of the dust transport dynamics and loss processes suggest that while both mechanisms play a role in defining the dust transport barrier, loss processes by wet removal of dust are about twice as important as transport. Sensitivity analyses with our model showed that the dust barrier would not exist without convective scavenging over the Caribbean. The best agreement between our model and the observations was obtained when dust wet removal was parameterized to be more aggressive, treating the dust as we do hydrophilic aerosols.

Laboratory Studies of the Effects of Dissolved Organic Material on the Adsorption of Organochlorine Pesticides by Sediments and Transport in Rivers

1993 ◽  
Vol 28 (8-9) ◽  
pp. 199-208 ◽  
Author(s):  
J.-Y. Ding ◽  
S.-C. Wu
Keyword(s):  
Organic Matter ◽  
Molecular Diffusion ◽  
Transport Model ◽  
Water System ◽  
High Rate ◽  
Sensitivity Analyses ◽  
Overlying Water ◽  
Sediment Bed ◽  
Three Phase ◽  
Phase Transport

In this study experiments simulating sediment/water system were carried on with sediments spiked with aldrin, heptachlor epoxide and p,p'-DDE. It was expected that these hydrophobic contaminants would be released to the overlying water column from sediment bed with molecular diffusion and co-diffusion with dissolved organic matter (DOM) as well. A three-phase-transport model including aqueous, solid and mobile adsorptive phases was developed and used to describe the behavior of these contaminants and to explain the results of the experiments. Sensitivity analyses show that observable effects of DOM occur only under conditions of high partition coefficient (Koc) of the contaminant and high rate of transfer from sediment organic matter to DOM. In this study, owing to the low concentration of DOM and relatively low hydrophobicity of the compounds, the DOM-associated pollutant flux does not significantly contribute to the total flux. Also, the simulated results of the model can reasonably explain the variations of the concentrations of the spiked compounds observed in the microcosms.

scholarly journals Attribution of recent increases in atmospheric methane through 3-D inverse modelling

2018 ◽  
Author(s):  
Joe McNorton ◽  
Chris Wilson ◽  
Manuel Gloor ◽  
Rob Parker ◽  
Hartmut Boesch ◽  
...  
Keyword(s):  
Growth Rate ◽  
Transport Model ◽  
Energy Sector ◽  
Total Carbon ◽  
Sensitivity Analyses ◽  
Northern Eurasia ◽  
Atmospheric Methane ◽  
Chemical Transport Model ◽  
Bottom Up ◽  
Source And Sink

Abstract. The atmospheric methane (CH4) growth rate has varied considerably in recent decades. Unexplained renewed growth after 2006 followed seven years of stagnation and coincided with an isotopic trend toward CH4 more depleted in 13C, suggesting changes in sources and/or sinks. Using surface observations of both CH4 and the isotopologue ratio value (δ13CH4) to constrain a global 3D chemical transport model (CTM), we have performed a synthesis inversion for source and sink attribution. Our method extends on previous studies by providing monthly and regional attribution of emissions from 6 different sectors and changes in atmospheric sinks for the extended 2003–2015 period. Regional evaluation of the model CH4 tracer with independent column observations from the Greenhouse gases Observing SATellite (GOSAT) shows improved performance when using posterior fluxes (R = 0.94–0.96, RMSE = 8.3–16.5 ppb), relative to prior fluxes (R = 0.60–0.92, RMSE = 48.6–64.6 ppb). Further independent validation with data from the Total Carbon Column Observing Network (TCCON) shows a similar improvement in the posterior fluxes (R = 0.90, RMSE = 21.4 ppb) compared to the prior (R = 0.71, RMSE = 55.3 ppb). Based on these improved posterior fluxes, the inversion results suggest the most likely cause of the renewed methane growth is a post-2006 1.8 ± 0.4 % decrease in mean OH, a 12.9 ± 2.7 % increase in energy sector emissions, mainly from Africa/Middle East and Southern Asia/Oceania, and a 2.6 ± 1.8 % increase in wetland emissions, mainly from Northern Eurasia. The posterior wetland increases are in general agreement with bottom-up estimates, but the energy sector growth is greater than estimated by bottom-up methods. The model results are consistent across a range of sensitivity analyses performed. When forced to assume a constant (annually repeating) OH distribution, the inversion requires a greater increase in energy sector (13.6 ± 2.7 %) and wetland (3.6 ± 1.8 %) emissions but also introduces an 11.5 ± 3.8 % decrease in biomass burning emissions. Assuming no prior trend in sources and sinks slightly reduces the posterior growth rate in energy sector and wetland emissions and further increases the amplitude of the negative OH trend. We find that possible tropospheric Cl variations do not to influence δ13CH4 and CH4 trends, although we suggest further work on Cl variability is required to fully diagnose this contribution. While the study provides quantitative insight into possible emissions variations which may explain the observed trends, uncertainty in prior source and sink estimates and a paucity of δ13CH4 observations limit the accuracy of the posterior estimates.

Thermal and mechanical analysis of an SU8 polymeric actuator using infrared thermography

2008 ◽  
Vol 222 (1) ◽  
pp. 73-86 ◽  
Author(s):  
B Solano ◽  
S Rolt ◽  
D Wood
Keyword(s):  
Heat Transfer ◽  
Infrared Thermography ◽  
Microelectromechanical Systems ◽  
Thermomechanical Analysis ◽  
Mechanical Analysis ◽  
Thermal Design ◽  
Conductive Heat ◽  
Transfer Coefficients ◽  
Design Assessment ◽  
Spatially Resolved

In the current paper, report the detailed thermomechanical analysis of a polymeric thermal actuator integrated in a microelectromechanical systems microgripper, is reported. The inclusion of an actuator design which eliminates completely the parasitic resistance of the cold arm improves considerably the thermal efficiency of the system and enables large displacements at lower input voltages and operating temperatures than reported previously. Two different microgrippers built using a trilayer polymer/metal/polymer combination of SU8/gold/SU8 have been modelled, fabricated, and tested. As opposed to standard models, heat transfer by conduction to the ambient as well as between adjacent beams has been modelled. A semi-empirical approach for the calculation of conductive heat transfer coefficients has also been provided. The analysis combines simulations with electrical, deflection, and spatially resolved temperature measurements. The latter was carried out using infrared thermography, its use in polymeric actuators reported here for the first time. The good agreement between the models and the experimental data support the conclusions of the basic analytical model, i.e. thermal losses are dominated by two conduction mechanisms (into the ambient and between the hot and cold arms), and encourage its use for qualitative thermal design assessment and optimization.

Woody debris along an upland chronosequence in boreal Manitoba and its impact on long-term carbon storage

2005 ◽  
Vol 35 (2) ◽  
pp. 472-482 ◽  
Author(s):  
K L Manies ◽  
J W Harden ◽  
B P Bond-Lamberty ◽  
K P O'Neill
Keyword(s):  
Decay Rate ◽  
Soil Carbon ◽  
Carbon Storage ◽  
Net Primary Production ◽  
Woody Debris ◽  
Sensitivity Analyses ◽  
Balance Model ◽  
Deep Soil ◽  
Standing Dead

This study investigated the role of fire-killed woody debris as a source of soil carbon in black spruce (Picea mariana (Mill.) BSP) stands in Manitoba, Canada. We measured the amount of standing dead and downed woody debris along an upland chronosequence, including wood partially and completely covered by moss growth. Such woody debris is rarely included in measurement protocols and composed up to 26% of the total amount of woody debris in older stands, suggesting that it is important to measure all types of woody debris in ecosystems where burial by organic matter is possible. Based on these data and existing net primary production (NPP) values, we used a mass-balance model to assess the potential impact of fire-killed wood on long-term carbon storage at this site. The amount of carbon stored in deeper soil organic layers, which persists over millennia, was used to represent this long-term carbon. We estimate that between 10% and 60% of the deep-soil carbon is derived from wood biomass. Sensitivity analyses suggest that this estimate is most affected by the fire return interval, decay rate of wood, amount of NPP, and decay rate of the char (postfire) carbon pool. Landscape variations in these terms could account for large differences in deep-soil carbon. The model was less sensitive to fire consumption rates and to rates at which standing dead becomes woody debris. All model runs, however, suggest that woody debris plays an important role in long-term carbon storage for this area.

scholarly journals Effects of HRT on the efficiency of denitrification and carbon source release in constructed wetland filled with bark

2017 ◽  
Vol 75 (12) ◽  
pp. 2908-2915 ◽  
Author(s):  
Yinghe Jiang ◽  
Yao Li ◽  
Ying Zhang ◽  
Xiangling Zhang
Keyword(s):  
Carbon Source ◽  
Removal Efficiency ◽  
Constructed Wetland ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Municipal Sewage ◽  
First Order ◽  
N Removal ◽  
Carbon Release ◽  
The Relationship

Constructed wetland is widely used to treat municipal sewage. However, lack of carbon source always constraints the application of constructed wetland in advanced tailwater treatment process. Bark was used as the filler and external carbon source of constructed wetland in the study, and the effects of hydraulic retention time (HRT) on NO3−−N removal efficiency and carbon release velocity were explored. Results showed that the NO3−−N removal process was steady in the constructed wetland filled with bark without additional carbon source. The NO3−−N removal efficiency and NO3−−N concentration presented a first-order reaction. The reaction rate constant k was 0.4 day−1. The relationship between NO3−−N removal efficiency (η) and HRT (t) was η = 1-e−0.4t, and η was increased with increasing of HRT. η reached a maximum of 77% at HRT of 4.48 days. η obtained the minimum of 20% at HRT of 0.75 days. The relationship between the carbon source releasing velocity (v) by bark and HRT was v = 0.53(1.62/t-1/t2) + 0.32. v increased first and then decreased with HRT increasing. The maximum v was detected at t = 1.12 days.

Bacterial dynamics in the sub-surface constructed wetland

2001 ◽  
Vol 44 (11-12) ◽  
pp. 207-209 ◽  
Author(s):  
J. Vymazal ◽  
J. Balcarová ◽  
H. Doušová
Keyword(s):  
Constructed Wetlands ◽  
Constructed Wetland ◽  
Flow Direction ◽  
Anaerobic Bacteria ◽  
Root Surface ◽  
Coliform Bacteria ◽  
Municipal Sewage ◽  
Limited Information ◽  
Bacterial Pollution ◽  
Steep Decrease

Constructed wetlands have been shown to be capable of removing a wide variety of contaminants, including bacterial pollution. However, only limited information exists on the distribution of bacteria on roots of macrophytes growing in constructed wetlands. Constructed wetland with sub-surface horizontal flow at Nucÿice near Prague, Czech Republic, was put in operation in 1996. The system treats municipal sewage from 650 PE and the total area of the beds, planted with Phalaris arundinacea and Phragmites australis in alternate stripes perpendicular to the flow direction, is 3,224 m2 (2 beds 62×26 m each). Pea gravel (8/16 mm) was used as a filtration material. During the period 1998-1999, distribution of total aerobic and anaerobic bacteria, coliform bacteria and fecal streptococci was monitored in wastewater as well as on roots of both macrophyte species. Counts of bacteria on root surface in the system at Nucÿice indicate that there is a steep decrease in bacterial numbers within the first few metres of the bed and that there is significantly more bacteria on roots of Phragmites as compared to Phalaris. There was no statistically significant influence of the season on the bacterial counts on roots of macrophytes.

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