Water condition in biotrickling filtration for the efficient removal of gaseous contaminants

Biofiltration (BF) facilitates the removal of organic and inorganic compounds through microbial reactions. Water is one of the most important elements in biotrickling filters that provides moisture and nutrients to microbial biofilms. The maintenance of proper trickle watering is very critical in biotrickling filtration because the flow rate of the trickling water significantly influences contaminant removal, and its optimal control is associated with various physicochemical and biological mechanisms. The lack of water leads to the drying of the media, creating several issues, including the restricted absorption of hydrophilic contaminants and the inhibition of microbial activities, which ultimately deteriorates the overall contaminant removal efficiency (RE). Conversely, an excess of water limits the mass transfer of oxygen or hydrophobic gases. In-depth analysis is required to elucidate the role of trickle water in the overall performance of biotrickling filters. The processes involved in the treatment of various polluted gases under specific water conditions have been summarized in this study. Recent microscopic studies on biofilms were reviewed to explain the process by which water stress influences the biological mechanisms involved in the treatment of hydrophobic contaminated gases. In order to maintain an effective mass transfer, hydrodynamic and biofilm conditions, a coherent understanding of water stress and the development of extracellular polymeric substances (EPS) in biofilms is necessary. Future studies on the realistic local distribution of hydrodynamic patterns (trickle flow, water film thickness, and wet efficiency), integrated with biofilm distributions, should be conducted with respect to EPS development.