An experimental hybrid system based on an anaerobic reactor followed by three stages of different constructed wetland configurations was evaluated when operating under a high hydraulic loading rate (HLR = 0.27 m d-1, considering the area of the VF beds) for one year, which corresponds to four times the nominal hydraulic loading rate, with the purpose of reducing the specific area required. Moreover, in order to assess its buffer capacity, a major storm event was simulated by increasing the HLR 10 times during 1 h. A tracer experiment was also performed to determine the experimental hydraulic retention time (HRT). The system consisted of a hydrolytic upflow sludge blanket (HUSB) reactor followed by two alternating 1.5 m2 vertical subsurface flow, a 2 m2 horizontal subsurface flow and a 2 m2 free water surface constructed wetlands operating in series. The system achieved very high values of removal of solids, organic matter and nutrients (82, 93, 96 and 75% for COD, BOD5, TSS and NH4-N, respectively). Removal of PO4-P and SO42- were though fairly low, of 11 and 10%, respectively. There was a seasonal effect in the system for parameters whose removal highly depends on biodegradation, being enhanced under warmer conditions (98 and 92% removal of BOD5 and NH4-N in summer vs. 87 and 67% removal of BOD5 and NH4-N in winter). The experimental HRT of the entire system was of about 38 h, which is greater than the theoretical HRT (28 h). During the simulation of the storm event removal efficiencies did not vary significantly from the ones obtained under normal conditions (average of 83, 99 and 80% for COD, TSS and NH4-N removal, respectively). The system showed a very good buffer capacity coping with sharp fluctuations in flow to be treated, showing to be an adequate solution for wastewater treatment in small communities. The specific area requirement under the long-term operation showed to be as low as 2 m2/PE.
Green and grey stormwater management infrastructures, such as the filter, swale and infiltration trench (FST), can be used to prevent flooding events. The aim of this paper was to determine the environmental and economic impacts of a pilot FST that was built in São Carlos (Brazil) using Life Cycle Assessment (LCA) and Life Cycle Costing (LCC). As a result, the components with the greatest contributions to the total impacts of the FST were the infiltration trench and the grass cover. The system has a carbon footprint of 0.13 kg CO2 eq./m3 of infiltrated stormwater and an eco-efficiency ratio of 0.35 kg CO2 eq./USD. Moreover, the FST prevented up to 95% of the runoff in the area. Compared to a grey infrastructure, this system is a good solution with respect to PVC stormwater pipes, which require a long pipe length (1070 m) and have a shorter lifespan. In contrast, concrete pipes are a better solution, and their impacts are similar to those of the FST. Finally, a sensitivity analysis was conducted to assess the changes in the impacts with the varying lifespan of the system components. Thus, the proper management of the FST can reduce the economic and environmental impacts of the system by increasing its durability.
Labella, A.; Caniani, D.; Hughes, T.; Morrison, R.; Newton, M.; Hawes, P.; Puigagut, J.; Garcia, J.; Uggetti, E. Ecological engineering Vol. 83, p. 184-190 DOI: 10.1016/j.ecoleng.2015.06.028 Data de publicació: 2015-10 Article en revista
Constructed wetlands including aeration and heating were studied to improve treatment efficiency and prevent clogging. The experiments were carried out in a pilot plant (0.4 m(2)) treating urban wastewater with an organic loading rate of 40-60 g COD/m(2) d. Continuous and intermittent aeration was performed from the bottom on 8% of the wetland surface, leading to different dissolved oxygen concentrations within the wetlands (from 0.2 to 5 mg O-2/L). Continuous aeration increased organic matter (COD) and ammonium nitrogen removal by 56% and 69%, respectively. Improvements in wastewater treatment caused by aeration can result in reduction of the surface area requirement of future systems. This work demonstrated that for the studied configuration the cost of the power consumption of the continuous aeration was largely covered by the reduction of the wetlands surface. Even if the heating of 8% of the wetland surface at 21 degrees C had no effects on treatment performance, positive results showed that solids accumulation rate within the granular medium, which is closely related to the development of clogging. It has been demonstrated that heating for 10 days per year during 20 year period would delay the equivalent of 1 year of solids accumulation.
Constructed wetlands are a widely adopted technology for the treatment of wastewater in small communities. The understanding of their internal functioning has increased at an unprecedented pace over recent years, in part thanks to the use of mathematical models. BIO_PORE model is one of the most recent models developed for constructed wetlands. This model was built in the COMSOL Multiphysics (TM) software and implements the biokinetic expressions of Constructed Wetlands Model 1 (CWM1) to describe the fate and transport of organic matter, nitrogen and sulphur in horizontal subsurface-flow constructed wetlands. In previous studies, CWM1 was extended with the inclusion of two empirical parameters (M-bio_max and M-cap) that proved to be essential to provide realistic bacteria growth rates and dynamics. The aim of the current work was to determine the effect of these two parameters on the effluent pollutant concentrations predicted by the model. To that end, nine simulations, each with a different M-bio_max-M-cap pair, were launched on a high-end multi-processor computer and the effluent COD and ammonia nitrogen concentrations obtained on each simulation were qualitatively compared among them. Prior to this study, a finite element mesh optimization procedure was carried out to reduce computational cost. Results of the mesh optimization procedure indicated that among the 5 tested meshes of different element size, the mesh utilized for this model in previous studies represented a fair compromise between output accuracy and computation time. Results of the sensitivity analysis showed that the value of M-cap has a dramatic effect on the simulated effluent concentrations of COD and ammonia nitrogen, which clearly decreased for increasing values of this parameter. On the other hand, the model output was also sensitive to the values of M-bio_max, but its effects were less important and no clear relation could be established between its value and the simulated effluent concentration of COD and ammonia nitrogen. (C) 2014 Elsevier B.V. All rights reserved.
A full-scale hybrid constructed wetland (CW) system based on three stages of different wetlands configurations showed to be a very robust ecotechnology for domestic wastewater treatment and reuse in small communities. It consisted of a 317-m(2) vertical subsurface flow (VF), a 229-m(2) horizontal subsurface flow (HF), and a 240-m(2) free water surface (FWS) CWs operating in series. VF and HF wetlands were planted with Phragmites australis and the FWS contained a mixture of plant species. An excellent overall treatment performance was exhibited on the elimination of conventional water quality parameters (98-99% average removal efficiency for TSS, BOD5 and NH4-N; n = 8), and its final effluent proved to comply with existing Spanish regulations for various reuse applications. The removal of studied emerging contaminants, which included various pharmaceuticals, personal care products and endocrine disruptors, was also very high (above 80% for all compounds), being compound dependent (n = 8). The high rates were achieved due to high temperatures as well as the differing existing physico-chemical conditions occurring at different CW configurations, which would allow for the combination and synergy of various abiotic/biotic removal mechanisms to occur (e.g. biodegradation, sorption, volatilization, hydrolysis, photodegradation). While aerobic metabolic pathways and solids retention are enhanced in the VF bed, other removal mechanisms such as anaerobic biodegradation and sorption would predominate in the HF bed. At last, photodegradation through direct sunlight exposure, and less importantly, sorption onto organic matter, seem to take an active part in organic contaminant removal in the FWS wetland. (C) 2014 Elsevier B.V. All rights reserved.
Methane is emitted in horizontal subsurface flow constructed wetlands (HSSF CWs) during wastewater treatment. The objective of this work was to determine the influence of primary treatment and organic loading rate on methane emissions from constructed wetlands. To this aim, methane emissions from a HSSF CW pilot plant were measured using the closed chamber method. The effect of primary treatment was addressed by comparing emissions from wetlands receiving the effluent of an anaerobic (HUSB reactor) or a conventional settler as primary treatments. Alternatively, the effect of organic loading was addressed by comparing emissions from wetlands operated under high organic loading (52 g COD m (2) day (1)) and low organic loading (17 g COD m (2) day (1)). Results showed that methane emission rates were affected by the type of primary treatment and, to a lesser extent, by the organic loading applied. Accordingly, lower redox conditions and slightly higher organic loading of a wetland receiving the effluent of a HUSB reactor resulted in methane emissions twelve times higher than those of the wetland fed with primary settled wastewater. Moreover, systems subjected to three times higher organic loading than that recommended lead to higher methane emission rates, although high data variability resulted in no statistically significant differences.
tAn experimental hybrid constructed wetland system consisting of 3 stages of different wetland config-urations (i.e. two vertical flow beds (1.5 m2each) alternating feed-rest cycles followed by a horizontalsubsurface flow (2 m2) and a free water surface (2 m2) wetlands in series) and the quality of its finaleffluent were evaluated for about one year. Mean overall removal rates were as 97% TSS, 78% COD, 91%BOD5, 94% NH4-N, 46% TN and 4% PO4-P. Vertical flow beds achieved high organic matter retention (77%BOD5) and great nitrification capacity (74% NH4-N removal). Although horizontal and free water surfacewetlands accomplished little denitrification, they enabled water disinfection to produce an effluent suit-able for various reuse applications. Authors suggest partial bypass from the Imhoff tank to the horizontalsubsurface flow wetland so as to provide a carbon source to promote denitrification. The treatment sys-tem performed equally well in terms of organic matter and ammonium removal both in warm and coldseasons. However, reduced nitrate retention took place in horizontal and free water surface wetlands inthe cold season, presumably due to low denitrification activity at low water temperatures. In general, thethree-stage hybrid constructed wetland system has proven to constitute an appropriate ecotechnology for wastewater treatment and reuse in small communities of warm climate areas.
An integrated pilot-scale treatment system consisting of a vertical subsurface flow (317 m2), a horizontal subsurface flow (229 m2) and a free water surface (240 m2) constructed wetlands operating in series for the treatment of a combined sewer effluent was put into operation and monitored over a period of about 1.5 years. The goal of the treatment system was to provide effluents suitable for various water reuse applications. Moreover, the influence of pulses of high flow resulting from several rain events over the treatment performance of the system was evaluated. An intensive sampling campaign was also carried out following an intense storm (45 mm in one-hour span) to have a further insight into the characteristics of the inflowing water at the early part of it or so-called ‘first-flush’. Results under dry weather conditions showed a good performance on the removal of BOD5, COD and TSS taking place already in the vertical flow wetland (94, 85 and 90%, respectively). A high removal of total nitrogen occurred also in the vertical flow wetland (66%) suggesting both nitrification and denitrification to take place, presumably due to the existence of both aerobic and anoxic microenvironments within the bed. Removal of Escherichia coli along the treatment system was of almost 5 log units. To this respect, the horizontal flow and free water surface wetlands proved to be crucial treatment units to achieve a water quality suitable for further reuse (e.g. recharge of aquifers by percolation through the ground, silviculture and irrigation of green areas non accessible to the public). Although the occurrence of the storm event caused a prompt raise of COD and TSS within the first 30 min of rainfall (868 and 764 mg L-1, respectively), it was soon followed by a dilution effect. In general the storm events did not jeopardize the correct functioning of the system, proving its robustness for the treatment of a combined sewer effluent.
An integrated pilot-scale treatment system consisting of a vertical subsurface flow (317 m2), a horizontal subsurface flow (229 m2) and a free water surface (240 m2) constructed wetlands operating in series for
the treatment of a combined sewer effluent was put into operation and monitored over a period of about 1.5 years. The goal of the treatment system was to provide effluents suitable for various water reuse applications. Moreover, the influence of pulses of high flow resulting from several rain events over the treatment performance of the system was evaluated. An intensive sampling campaign was also carried
out following an intense storm (45 mm in one-hour span) to have a further insight into the characteristics of the inflowing water at the early part of it or so-called ‘first-flush’. Results under dry weather conditions showed a good performance on the removal of BOD5, COD and TSS taking place already in the vertical flow wetland (94, 85 and 90%, respectively). A high removal of total nitrogen occurred also in the vertical
flow wetland (66%) suggesting both nitrification and denitrification to take place, presumably due to the existence of both aerobic and anoxic microenvironments within the bed. Removal of Escherichia coli along the treatment system was of almost 5 log units. To this respect, the horizontal flow and free water surface
wetlands proved to be crucial treatment units to achieve a water quality suitable for further reuse (e.g. recharge of aquifers by percolation through the ground, silviculture and irrigation of green areas non accessible to the public). Although the occurrence of the storm event caused a prompt raise of COD and TSS within the first 30 min of rainfall (868 and 764 mg L−1, respectively), it was soon followed by a dilution effect. In general the storm events did not jeopardize the correct functioning of the system, proving its robustness for the treatment of a combined sewer effluent.
Reactive-transport models have been widely used to describe biogeochemical processes in subsurface environments. Horizontal subsurface-flow constructed wetlands fall in that category, and have experienced an exponential widespreading as an alternative wastewater treatment technique in recent years. As a result, the interest in modelling the processes occurring within these systems has proportionally increased. However, the functioning of wetlands is still poorly understood and the applicability of the available models is still limited. BIO_PORE model was built using COMSOL Multiphysics™ platform to help accelerating the development of constructed wetland models and to shed light on their internal functioning. The biokinetic equations of Constructed Wetlands Model number 1 describe bacteria-induced degradation and transformation processes of organic matter, nitrogen and sulphur. Small changes of such equations were required in order to include attachment and detachment of influent particulate components.
The use of Horizontal Subsurface Constructed Wetlands (HSCWs) for treating wastewaters in small communities has increased in the last years due to HSCW’s ecological singularities. Unfortunately, the same
singularities that differentiate HSCWs complicate any attempt to develop models and produce generic decision-support systems for them. Classical mathematical and statistical approaches used in other Wastewater Treatment Plants do not properly fit the particularities of HSCW and provide little insight in the domain of HSCW. We introduce a novel approach based on logic-based declarative specifications, i.e. non-monotonic causal logic, to capture explicit and implicit knowledge about HSCWs. By expressing all the relevant aspects of a HSCW in a declarative way, we produce a logic-based model which captures features that other approaches fail to formalize. At the end, we produce a complete decision-support system based on that model and test it against a set of realistic scenarios validated by experts. We discuss in which aspects this approach performs better than the most commonly proposed solutions in the
bibliography and why it does so.
Marianna Garfi'; Ferrer-Martí, L.; Pérez, I.; Flotats, X.; Ferrer, I. Ecological engineering Vol. 37, num. 12, p. 2066-2070 DOI: 10.1016/j.ecoleng.2011.08.018 Data de publicació: 2011-12 Article en revista
The aim ofthis research was to improve the anaerobic digestion of cow and guinea pig manure in low-cost unheated tubular digesters implemented at high altitude, by comparing different operating conditions and codigesting both manures
The aim of this study was to verify under lab conditions the reliability, repeatability and accuracy of the
falling head method (FHM) for hydraulic conductivity measurements. TheFHMis a reliable procedure that has slight variations (less than 10%) in repeated measurements and turns out to be a reliable technique to record the hydraulic conductivities typically described for clogged and unclogged subsurface-flow
constructed wetlands (from 4 to ca. 360 m/day). The accuracy of the method is acceptable considering difficulties in the measurement of hydraulic conductivity in highly conductive media. Accordingly, results
show measurement deviations of 20% when compared with a laboratory constant head method for highly conductive media (higher than 250 m/day), and 80% for media with low hydraulic conductivity (lower than 50 m/day). The main conclusion of the present paper is that of the FHM is a reliable and repeatable technique for hydraulic conductivity measurements and it is accurate enough for on-site clogging assessment in full-scale constructed wetlands.
This paper describes the development and operation of an Environmental Decision Support System (EDSS) to improve the operation and maintenance of horizontal subsurface-flow constructed wetlands (EDSS-maintenance). Constructed wetlands (CWs) allow wastewater treatment in a sustainable manner since they involve low energy consumption, low construction and functioning costs and low environmental impact. However, operation and maintenance activities are essential to guarantee reliability in CWs performance. The definition of operation and maintenance protocols depends on several quantitative and qualitative aspects such as wastewater treatment plant configuration, CW design, influent characteristics, sensitivity of the receiving media, etc. Bearing this in mind and considering the limited technical knowledge about CWs, the need for a new tool to support CW performance is clear. In this sense, EDSSs offer a new approach because they can tackle problems of complex and uncertain systems. The EDSS-maintenance provides operation and maintenance manuals specifically defined for every CW To achieve it, the required knowledge was implemented within a rule-based system, which forms the backbone of the EDSS. Several features presented in this paper demonstrate how the EDSS-maintenance provides a proper platform to support the necessary collaborative work in the ecological engineering problem of horizontal subsurface flow CWs operation and maintenance.
The main goal of this study was the development of a dynamic model that represents the thermal behavior of the complex ecological system of Biosphere 2, Nes. Tucson, AZ, USA. In this paper, a model that captures the thermal behavior of the ecological system in a non-controlled (i.e. passive) environment is presented. The bond graph methodology was used for modeling this highly complex system. The object-oriented nature of the bond graph approach enables the modeler to keep conceptually separated aspects of knowledge about the system’s comportment isolated from each other. Thereby, the individual modeling entities remain small and manageable. This makes it easier for the modeler to properly debug and validate individual models. Uniform power-flow interfaces between all bond graph models ensure energy conservation at the connections between the individual models, and support the modeler in validating the interconnected bond graph model of the overall system. Although plausible simulation results are presented at the end of this paper, no true simulation verification could be made, because the real system has never, since its completion, been allowed to be operated in a purely passive mode, i.e. without its air handlers, as in fact, such an experiment would kill most of the biomes inside Biosphere 2. Yet, simulation runs of the passive system are meaningful for model validation purposes. The control systems that operate the air handlers reduce the sensitivity of the simulation output to modeling errors, and may, in fact, not only correct for Tucson’s hot desert climate, but also for temperature deviations caused by an incorrect mathematical description of the system thermodynamics.