ABSTRACT
Rotating biological contactors (RBCs) employ aerobic fixed film treatment to degrade either organic and/or nitrogenous (ammonia-nitrogen) constituents present in aqueous waste streams. Treatment is achieved as the waste passes by the media, enabling fixed-film systems to acclimate biomass capable of degrading organic waste [1, p. 91]. 2 Fixed-film RBC reactors provide a surface to which soil organisms can adhere; many indigenous soil organisms are effective degraders of hazardous wastes.
An RBC consists of a series of corrugated plastic discs mounted on a horizontal shaft. As the discs rotate through the aqueous waste stream, a microbial slime layer forms on the surface of the discs. The microorganisms in this slime layer degrade the waste’s organic and nitrogenous constituents. Approximately 40 percent of the RBCs surface area is immersed in the waste stream as the RBC rotates through the liquid. The remainder of the surface area is exposed to the atmosphere, which provides oxygen to the attached microorganisms and facilitates oxidation of the organic and nitrogenous contaminants [2, p. 6]. In general, the large microbial population growing on the discs provides a high degree of waste treatment in a relatively short time. Although RBC systems are capable of performing organic removal and nitrification concurrently, they may be designed to primarily provide either organic removal or nitrification singly [3, p. 1–2].
RBCs were first developed in Europe in the 1950s [1, p. 6]. Commercial applications in the United States did not occur until the late 1960s. Since then, RBCs have been used in the United States to treat municipal and industrial wastewaters. Because biological treatment converts organics to innocuous products such as CO2, investigators have begun to evaluate whether biological treatment systems like RBCs can effectively treat liquid waste streams from Superfund sites. Treatability studies have been performed at at least three Superfund sites to evaluate the effectiveness of this technology in removing organic and nitrogenous constituents from hazardous waste leachate. A full-scale RBC treatment system is presently operating in at least one Superfund site in the United States.
