47. Bioreactors: rotating biological contactors

Abstract

Presently there is a wide variety of bioreactors in wastewater treatment, which may be broadly categorized as suspended or attached growth processes. During the 1970s and 1980s, due to its advantages, the rotating biological contactor (RBC), an efficient attached biofilm system, became very popular and thousands of RBC units were installed all around the world. Many of these facilities did not perform as predicted and experienced mechanical failures well before their expected lifetime. As a consequence, the process has fallen into disfavor with many consulting engineers. However, experience with existing installations, over the last forty years, has established the appropriate range of applications for the RBC process, as well as the range of operating conditions resulting in acceptable performance. Furthermore, RBC manufacturers have re-examined the basic process to identify shortcomings and deficiencies and while many design parameters have remained unaltered, significant changes have been made in other areas to produce a low cost, robust process where unnecessary costs are eliminated. For these reasons we believe that the RBC system should deserve greater consideration than what is currently paid during process selection. Existing RBC facilities can now be reliably upgraded and expanded. Plant owners and operators can also properly evaluate RBCs as an alternative for new applications. This has resulted in an increase of interest from both academic and industrial sources. Indeed, there are recent publications detailing the development of RBC technology to accomplish higher levels of treatment and documenting its appropriate range (1–5). This chapter provides an overview of rotating biological contactors, focusing on their main characteristics, advantages and drawbacks, hydrodynamics, factors affecting performance, biofilm characteristics, some aspects about design and scale-up. The main operational problems and their resolution as well as the general application areas of this reactor are also presented.