Simulation and reaction parameter estimation in subsurface flow constructed wetland for greywater treatment

Abstract

Subsurface flow constructed wetland (SSFCW) is widely adopted for the removal of BOD5 and TKN from greywater. The design of SSFCW is normally based on thumb rules or using a first-order reaction kinetic model. However, the applicability of this model is system/environment-specific which necessitates the assessment of the potential applicability of other reaction kinetic models. In the present study, experiments were planned on SSFCW during initial and established phases to collect the data on BOD and TKN for assessing the system-specific application of plug flow, K-S* and CSTRs in series models. The reaction rate parameters along the length of SSFCW and overall for the system were estimated. There was no variation in values of rate parameter along the length in an initial phase, but the values increased along the length of SSFCW in established phase. Further, the applicability of these models was assessed for predicting BOD5 in SSFCW based on error analysis. And overall reaction rate parameters were estimated. Based on the average absolute error and RMS error it is concluded that plug flow and K-S* reaction kinetic models are more applicable for BOD5. The volumetric reaction rate parameter is recommended to be 0.612/day (plug flow) and 0.742/day (K-S*) for the design of SSFCW in tropical climate for BOD5 removal. The volumetric reaction rate parameter for TKN removal by plug flow model is recommended to be 0.389/day.