Diseño De Humedales

Ecological Engineering 16 (2001) 519 – 536

www.elsevier.com/locate/ecoleng

Development of a constructed subsurface-flow wetland simulation model
Theresa Maria Wynn a,*, Sarah K. Liehr b,1
a

Biological Systems Engineering, Virginia Tech 200 Seitz Hall (0303), Virginia Tech, Blacksburg, VA 24061 -0303, USA b Biological and Agricultural Engineering, P.O. Box 7625, NCSU, Raleigh, NC 27695-7625, USA Received 16 December 1998; received in revised form 1 May 2000; accepted 10 June 2000

Abstract This paper presents a mechanistic, compartmental simulation model of subsurface-flow constructed wetlands. The model consists of six submodels, including the nitrogen and carbon cycles, both autotrophic and heterotrophic bacteria growth and metabolism, and water and oxygen balances. Data froman existing constructed wetland in Maryland were used to calibrate the model. Model results reproduced seasonal trends well. Interactions between the carbon, nitrogen, and oxygen cycles were evident in model output. In general, effluent biochemical oxygen demand, organic nitrogen, ammonium and nitrate concentrations were predicted well. Because little is known about rootzone aeration by wetlandplants, oxygen predictions were fair. The model is generally insensitive to changes in individual parameters. This is due to the complexity of the ecosystem and the model, as well as the numerous feedback mechanisms. The model is most sensitive to changes in parameters that affect microbial growth and substrate use directly. This dynamic, compartmental, simulation model is an effective tool forevaluating the performance of subsurface-flow constructed wetlands. The model provided insights into treatment problems at an existing constructed wetland. With further evaluation and refinement, the model will be a useful design tool for subsurface-flow constructed wetlands. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Constructed wetlands; Monod; Wastewater treatment; CSTR;Subsurface-flow wetland; Nitrogen removal; BOD; Simulation model

1. Introduction Past research has shown constructed wetlands efficiently remove nitrogen and constituents that
* Corresponding author. Tel.: +1-540-2316509; fax: + 1540-2313199. E-mail addresses: tesswynn@vt.edu (T.M. Wynn), liehr@eos.ncsu.edu (S.K. Liehr). 1 Tel.: + 1-919-5156761; fax: + 1-919-5157760.

create biochemical oxygen demand (BOD)from municipal and industrial wastewaters (Hammer, 1989; Conley et al., 1991; Knight, 1994). While wetland systems are not well understood and few good design data exist, many of the individual processes have been studied in detail (Heliotis and DeWitt, 1983). Treatment processes in constructed wetlands include sedimentation and filtration, precipitation, sorption, and microbial

0925-8574/01/$ -see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 8 5 7 4 ( 0 0 ) 0 0 1 1 5 - 4

520

T.M. Wynn, S.K. Liehr / Ecological Engineering 16 (2001) 519–536

decomposition, nitrification, and denitrification. Unlike solids and phosphorus removal, nitrogen and BOD removal at low concentrations are mostly the result of complex, interdependent, microbialtransformations. Much of the treatment in wetlands is due to both heterotrophic and autotrophic microbes (Kadlec, 1986a; Mitsch and Jorgensen, 1989). Decomposition and ammonification rates are linked to microbial energy requirements, the carbon to nitrogen ratio (C/N) of the organic matter, and the growth rate of microbes (Parnas, 1975; Fyock, 1977; Patrick Jr, 1982; Reddy and D’Angelo, 1997). High removalrates can be sustained in constructed wetlands, although these reactions should be modeled concurrently to better understand and optimize the internal mechanisms (Howard-Williams, 1985; Kadlec, 1986b). In current wastewater wetland design models, the importance of microbial growth on nitrogen and carbon cycling is not explicitly addressed (Reed, 1990; Bavor et al., 1991; Watson et al., 1991; Reed...