Biological Treatment of Organic Loads in Surface Flow Constructed Wetland Using Convective Dispersion Mixing Flow Model.

Moharram, Saad Hamed Saad; Zidan, Abd- ElRazek Ahmed El-Sayed; Rashed, A. A.; Abedel Gawad, S. T.

doi:10.21608/bfemu.2020.131639

Biological Treatment of Organic Loads in Surface Flow Constructed Wetland Using Convective Dispersion Mixing Flow Model.

Document Type : Research Studies

Authors

¹ irrigation and Hydraulics Department., Faculty of Engineering., El-Manosura University., Mansoura., Egypt

² The Chair person and Researcher, National Water Research Center, MWRI.

10.21608/bfemu.2020.131639

Abstract

Wastewater treatment through constructed wetland is a combination of physical, biological and chemical treatment processes. These processes are described by plug flow, mixed flow or by the plug - mixing flow combination. The concept for describing removal of organic loads biologically with treating the wetland as a series of completely stirred tanks reactors is practically applied (Chen et al, 1999). Each of stirred tank reactors is presumed to be completely mixed and the concentration departing each is equal to the uniform, internal concentration.
A model is used to assess the BOD removal through free water surface (FWS) constructed wetland in a pilot scale project treating drainage wastewater before dumping at Lake Manzala on the North of Egypt. Two assumptions are used in the model application; the fully mixing stirred tank reactor with fully dispersion and diffusion inside and between the wetland subsystems. The other assumption is proposed as a new idea based on the fully mixed flow assumption, namely; the partially mixing stirred tank reactor with fully dispersion and diffusion inside and a plug flow between the wetland subsystems. Sensitivity analysis of the two assumptions is presented as well as a comparison between the BOD treatment results and the corresponding results obtained from field data.
Sensitivity results shows that for both model assumptions, BOD treatment improves with increasing number of internal mixing tanks, removal rate constant, and hydraulic detention time and with decreasing the aspect ratio (length/width). In both model assumptions the BOD concentration values were nearly comparable with the corresponding measured BOD values along the wetland length with a mean absolute error of 11.7% for the case of fully mixed flow and 12.5% the case of partially fully mixed flow.

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