ROTATING BIOLOGICAL CONTACTOR TREATMENT
OF HYPERSALINE WASTES
Paul L. Bishop, Associate Professor
Nancy E. Khmer, Graduate Student
Department of Civil Engineering
University of New Hampshire
Durham, New Hampshire 03824
Many industrial manufacturing processes generate wastewaters containing high salinity.
For example, tannery wastes, pickle processing wastes, oil field brines and many chemical
production wastes contain high concentration of chloride. This can have a serious impact
on wastewater treatment since high chloride concentrations can inhibit or impair the microorganisms operating in the biological treatment system.
Several biological treatment methods have been evaluated for dealing with these wastes,
including both suspended growth and fixed growth systems, with varying degrees of success.
This research was performed to examine the effects of high salinity on the operating of rotating biological contactors or RBCs.
Structurally, RBCs are composed of circular plastic media mounted centrally on a horizontal shaft with the assembly partially submerged in a tank containing wastewater. The
shaft is rotated to alternately provide wetting of the disks with wastewater followed by contact with atmospheric oxygen. To increase the efficiency of the treatment process, the tank
is normally divided into several compartments, each containing a section of media. Various
types of media are manufactured with high density designs to maximize the surface area per
unit volume available to microorganisms for attachment. Disk diameters range from 0.5 to
3.7 meters.
The characteristics of activated sludge dispersed cultures and trickling filter attached bio-
films are combined in RBCs. During the start-up period microorganisms adhere to the disk
surfaces and within one to four weeks a significant biofilm develops. Up to 97% of the carbonaceous biochemical oxygen demand (BOD) can be converted by suspended floes in the
liquid phase and by the biofilm on the medium into new cell biomass, effectively removing
this material from the waste stream. The biofilm continually sloughs off the disk after it has
reached some critical thickness and is removed from the effluent along with the suspended
floes by second clarificiation.
LITERATURE REVIEW
Until recently there has been little concentrated research in the area of hypersaline wastewater treatment. Most of the research on saline biological wastewater treatment has been
conducted using the activated sludge process [1-4], especially extended aeration [5,6].
Only a few studies have used trickling filters [7-9|. These studies concluded that, with an
acclimation period of 1 to 3 weeks, freshwater bacterial cultures subjected to salinities up to
35,000 mg/1 could attain organic removals equivalent to those obtained during non-saline
operation. Shock loading with wastewater of varying salinity, however, could impair the
removal capacity of the biological growth.
Most previous research on saline domestic wastewater treatment has been conducted on
the activated sludge process. Using a bench scale unit Ludzack and Noran [3] found that
free swimming ciliates survived in a continuous high chloride artificial waste made from NaCl
(3.5% salinity). When the chloride content alternated between high and low concentrations,
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