Influence of the geometric configuration of unplanted horizontal subsurface flow constructed wetlands in the adjustment of parameters of organic matter decay models

Abstract

The aim of the present work was to evaluate the influence of the geometric configuration (aspect ratio) in unplanted horizontal subsurface flow constructed wetlands systems (HSSF-CWs), in the adjustment of reaction coefficients from different equations for estimation of organic matter decay. To that end, prototypes of unplanted HSSF-CW, of equal volumes and length-width ratios (L/W) of 1.0, 4.0 and 7.3, were utilized. The absence of plants is due to eliminate another factors of influence in reactor hydrodynamics. All HSSF-CWs were filled with gravel # 0 (D10 = 4.5 mm), and received pre-settled sewage during a period of 90 days, in which BOD5 and COD were monitored in the influent and effluent from the systems. To the experimental COD and BOD5 (total and soluble forms) data, the First-Order Kinetics Model (FOKM) and its modification (MFOKM), First-Order Kinetic Residual Concentration (RCM) and Retardation (RM) models were fitted. Higher Coefficients of Determination were obtained with the MFOKM and RM equations, with the poorer fitting being associated with the FOKM. The different geometric configurations of the HSSF-CWs did not lead to noticeable alterations in the removal of organic matter, however, the decay coefficient, that was obtained as a function of the hydraulic retention time in the systems (2,8 days), has indicated a tendency for increase with an increase of the L/W ratio (with the exception of soluble COD decay).