Biofilms in Water and Wastewater Treatment

Biofilms were used for the treatment of municipal water and wastewater before the invention of the activated sludge process, and long before they were called biofilms; for example, in slow sand filters and trickling filters. This chapter describes unifying biofilm principles that are of importance to both research as well as modern biofilm reactor design and operation. The application of biofilm mechanics and fundamental principles to understand biofilms and design biofilm reactors represents a paradigm shift from the historical approach, which was based on empirical criteria and design formulations. Fundamental principles describing biofilms exist as a result of focused research. Biofilm technology studies using modern scientific methods and equipment have resulted in a substantial improvement in understanding of the biological processes, structure, and function of biofilms. However, many facets of biofilms remain poorly understood, namely the fate or particulate organic matter, dynamics and rate of biofilm detachment, and factors influencing concentration gradients external to the biofilm surface, to name a few. While it is expected that the results of these studies can be used to improve the design and operation of biofilm reactors, there is a need to guide future research to the same end. Nevertheless, process designers exploit our newfound understanding to improve biofilm reactor and supporting control system designs. In essence, leading researchers and practitioners are working together to apply knowledge obtained in research and practice toward environmental protection and the safeguard of human health. Unfortunately, little information exists to bridge the gap between our current understanding of biofilm fundamentals and reactor-scale empirical information. Therefore, there is a clear dichotomy in literature: micro- (biofilm) and macro- (reactor) scales. This chapter highlights the division. Part I is dedicated to basic research and communicating the state of the art with respect to understanding biofilms. Part II is practice oriented and describes the use of biofilms for the sanitation of municipal wastewater, groundwater, and water treatment plant waste streams. A basis for addressing this disconnection is presented by (1) describing the fundamental biofilm principles that can be uniformly applied to biofilms in several disciplines extending from medicine to environmental biotechnology, and (2) the presentation of a fundamental-based approach to understanding and applying biofilms in reactors. Finally, Part III of this chapter gives examples of deleterious biofilms in the water sector and describes attempts to mitigate their effects.