Biofilm development in a subsurface flow wastewater treatment wetland

Abstract

This study describes the investigation the development of biofilms on rock media in a subsurface flow, wastewater treatment wetland in South Auckland, New Zealand. The study includes investigation of initial adsorption of microorganisms to different substrata, the early phases of biofilm development in the wetland and mature biofilm development. Various methodologies were optimised for use during the study including in situ hybridisation and confocal scanning laser microscopy. During laboratory investigations into the initial stages of biofilm development on the common rock media, greywacke, scoria and slag, it was found that the hydrophobic substrafum, slag, adsorbed a greater number of bacterial cells than the more hydrophilic greywacke or scoria. A model was developed, based on these results, which linearly correlated the kinetics of adsorption of bacteria to the hydrophobicity of the substratum to which they adsorbed. Further studies using isolates indicated that the initial stages of adsorption were influenced by the hydrophobicity of the cell surface and the substratum, the presence of a conditioning film on the substratum surface and the motility of the individual bacterial cells. Substrata ceased to influence adsorption after 3 weeks of exposure in the Clark farm wetland.