TREATMENT OF MILK WASTE BY ROTATING
BIOLOGICAL CONTACTORS USING PURE OXYGEN
Ju-Chang Huang, Professor
Department of Civil Engineering
University of Missouri—Rolla
Rolla, Missouri 65401
Valentino T. Bates, Sanitary Engineer
CH2M-Hill Consulting Engineers
Milwaukee, Wisconsin 53222
INTRODUCTION
The traditional rotating biological contactor (RBC) for waste treatment consists of a
series of circular discs mounted on a horizontal shaft placed in a semicircular or semi-
trapezoidal tank with approximately 40-45% submergence. The discs are rotated at an
appropriate speed so that adequate growths of microorganisms can develop on the disc
surface. In rotation, each disc carries a film of wastewater into the air, which then
trickles down the surface and absorbs atmospheric oxygen. The organisms in the biomass
then utilize the absorbed oxygen to oxidize organic matter present in the wastewater
film. This type of treatment was first conceived in Germany by Weigand in 1900 [ 1 ].
In the U.S. the first RBC was tested by Doman in 1929 [2] using metal discs. However,
the results were not encouraging and no further work was done. The major development
work and commercialization of the RBC treatment system actually began in early 1960
in both the U.S. and some European countries. In the last several years when the public
has become increasingly concerned about energy utilization, this type of treatment has
become more and more popular because of its low energy need and ease of operation
and maintenance.
Due to its gaining popularity, numerous research studies have been conducted to obtain a better understanding of the RBC system in order to optimize its performance. In
the literature it has been well documented that the rate of organic stabilization in an
RBC system is generally limited by the oxygen flux rather than by the substrate diffusion
into the biological film [3,4]. It is only in a multistage system that the substrate concentration may become a rate-limiting factor in the last stages of the system [5,6]. In fact,
many researchers [5,7-9] have experienced that the substrate utilization rate increases
with the disc rotating speed since higher speeds incur greater oxygen transfer efficiencies.
However, the rotating speed cannot be increased indefinitely without causing major drawbacks. First, power requirement increases exponentially with the disc rotating speed [5,
10]. Secondly, excessively high rotating speeds would create high hydraulic shearing forces
which tend to interfere with satisfactory development of biomass on the disc surface.
Antonie [10,11] has suggested that the optimal peripheral speed for treating domestic
wastewater is about 18.2 m/min (60 ft/min). Therefore, in order to increase the oxygen
transfer in an RBC system, some appropriate means other than unlimitedly increasing
the rotating speed is necessary. It appears that there are at least two possible methods to
accomplish this. One is to replace air with pure oxygen in an enclosed RBC system and
the other is to pressurize the enclosed RBC system using either air or pure oxygen. In
both cases, the partial pressure of oxygen in the gaseous phase is increased and the oxygen
flux into the biofilm is thus accelerated. The objective of this study was to investigate the
feasibility of using these two approaches to improve the RBC performance.
METHODS AND MATERIALS
A synthetic milk waste was used as the influent feed throughout this study. The
relative performance results of treating this waste by three specially built, bench scale
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