A comparative analysis for the development and recovery processes of different types of clogging in lab-scale vertical flow constructed wetlands

Abstract

Clogging is a major operational and maintenance issue associated with the use of constructed wetlands. In this study, four lab-scale vertical flow constructed wetlands (VFCW) were used to fully understand the development mechanisms of various types of clogging and their recovery characteristics. The VFCWs were fed with glucose solution, starch suspension with and without bacteriostat, glucose, and starch mixed solution, respectively, to simulate Bio-clogging, organic particle clogging (Op-clogging), inert particle clogging (Ip-clogging), and the combination of Bio-clogging and Op-clogging (C-clogging). Resting operations with water decline were applied to relieve the clogging in the VFCWs. The results indicate that Op-clogging occurred first, followed by C-clogging and Bio-clogging. Ip-clogging took the longest time to develop and did not occur by the end of this study. The microscope analysis found that the extracellular polymeric substances (EPS) bonded the starch particles together to form a dense membrane-like structure and promoted the clogging process. In addition, surface clogging was observed in all four experimental beds. Op-clogging occurred much closer to the surface than those caused by soluble organic matter and inert particles. Furthermore, the growth of biofilm caused significant decline in hydraulic conductivity, whereas its influence on porosity was relatively slight. Moreover, applying resting operation with water decline was effective for recovery from Bio-clogging, Op-clogging, and C-clogging in VFCWs except for Ip-clogging. The results also implied the recovery rates through applying resting operation with water decline were much higher than that with constant water level.

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