Influence of airflow, material type, and dripline density on gas transfer and bubble pathways in a pilot-scale aerated vertical flow treatment wetlands

Abstract

ABSTRACT Oxygen transfer is a crucial element in the design of aerated wetlands. The presence or absence of dissolved oxygen has a significant impact on biological processes, and consequently, the efficiency of the degradation process. Typically, the air distribution system is sized by matching the air supply to the stoichiometric requirements of the incoming pollutant load to be treated. Despite the widespread use of aerated treatment wetlands worldwide, many practical questions remain unanswered, including how filter media size, diffuser density, airflow rate, and air distribution within the reactor volume influence gas transfer. In order to gain knowledge about gas/liquid transfer in aerated wetlands, a series of laboratory-scale column experiments were conducted under controlled conditions using three distinct sizes of gravel. The experiments included clean water oxygen transfer tests, in which oxygen concentrations were measured at various depths and in the gas at the outlet of the column. Additionaly, combining 3D time-lapse electrical resistivity tomography with these techniques successfully characterized air homogeneity, oxygen transfer, and gas retention.The results show that particle size alters medium tortuosity and bubble dynamics, yielding oxygen transfer efficiencies of 5% to 18%/m.