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MULTI-SCALE BIOFILM BASED MODELING FOR VEGETATED SUBMERGED BED SYSTEMS REATING DOMESTIC WASTEWATER

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  701P0104,  . (doi: 10.13031/2013.15766)
Authors:   W. E. Woldt, R. C. Marahatta, D. D. Schulte, M. F. Dahab
Keywords:   Subsurface flow constructed wetland, vegetated submerged bed, biofilm, clogging, multi-scale modeling, on-site wastewater treatment

A new approach for modeling vegetated submerged bed (VSB) wastewater treatment systems based on subsurface flow and transport principles is presented. Advection and diffusion based transport and biological transformation both in bulk liquid and biofilm is discussed. Macroscopic fluctuations in hydraulics of the system due to subsurface flow in porous media, precipitation and evapotranspiration are included in the model. Transport of substrate and microorganisms in the bulk media due to advection, dispersion and diffusion in the saturated porous media along with biological transformation both in biofilm and bulk liquid is expected to give better system insights than traditional models using reaction rate constants. Biofilm on the porous media is considered as a microscale process, allowing substrate diffusion into the biofilm from the bulk liquid and transformation of substrate in the biofilm. The process of attachment and detachment of the microorganisms, into and out of the biofilm, can be incorporated using empirical relationships. The mesoscale processes include biological transformation of substrate in the bulk water, transport of substrate and microorganisms in the bulk media, due to advection, dispersion and diffusion in the saturated porous media. The effect of evapotranspiration, influent flow and effluent flow on the subsurface hydraulics is included broadly in macroscale process. The volume of biofilm and the inert solid deposition in the system are considered in the model to estimate the time for hydraulic failure of the system from clogging. A theoretical development of a generalized model, and potential applications of the approach are presented. This new modeling approach in the vegetated submerged beds is expected to broaden understanding of the complex processes in VSB wastewater treatment systems.

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