Biofilms in the gravity sewer interfaces: making a friend from a foe

Abstract

Sewer systems are an integral part of our modern civilization and are an imperative underground infrastructure asset that our society relies on. In Western Europe alone, 92% of the resident pollution is connected to sewer systems. This extensive coverage of sewerage systems presents an ideal habitation for microorganisms to strive. Sewers can be considered continuous flow bioreactors. They are always colonized by bacteria, either in a planktonic state traveling along the pipe with the water flow or dragged in sediment, or organized as biofilms. Many studies have been devoted to the detrimental effects of microorganisms on sewer systems made of concrete. However, their metabolic activity can also be beneficial, lead to more effective wastewater treatment, or be beneficial for concrete pipes. This aspect has not been thoroughly studied to date and requires further investigation. Therefore, in this Review, we highlighted the positive and negative activity of biofilms and their participation in five proposed mass exchange points in gravity sewers. Furthermore, we systematized and reviewed state of the art regarding methods that could be potentially used to remove or engineer these biological structures to increase the sustainability of sewers and achieve a better pre-treatment of wastewater. We have also indicated research gaps that could be followed in future studies.