TEMPERATURE AND NUTRIENT EFFECTS ON THE
ANAEROBIC EXPANDED BED TREATING A HIGH STRENGTH WASTE
C. Richard Kelly, Research Assistant
Michael S. Switzenbaum, Assistant Professor
Department of Civil Engineering
University of Massachusetts
Amherst, Massachusetts 01003
INTRODUCTION
Since 1974, the anaerobic film expanded bed (AFEB) process has seen development from bench
scale tests through pilot scale operation and several full scale designs. The process has proven successful for the treatment of several wastes at both high and low concentrations with lab scale reactors.
The AFEB process basically consists of inert sand-sized particles which expand as a result of the
upward direction of recycle flow. The inert particles provide a support surface for the growth of
microorganisms. Since the support particles are small, the system has a large surface area to volume
ratio and can maintain a large population of bacterial mass. The AFEB process is also a completely
mixed system and provides excellent contact between biomass and substrate. Since the microorganisms are attached, the system enables long solid retention times with concomitant short hydraulic
retention times.
Common to previous studies concerning the AFEB process is the evaluation of process performance as a function of influent concentration and hydraulic retention time. Except for a study by
Switzenbaum and Jewell [1], the evaluation of process performance as a function of temperature has
been limited, and virtually no study has been conducted to examine the effects of nutrient limitation
on the process.
The purpose of this study was to more accurately define the effect of temperature on the AFEB
process treating a high strength waste and to compare the results obtained to other results in the literature.
EXPERIMENTAL CONDITIONS
The design of the experiment involved housing a bench scale AFEB reactor in an incubator to control temperature. Influent substrate was stored in a refrigerator and continuously pumped to the reactor at an average rate of 614 cm3 per day. Gases and liquid effluent left the reactor in separate lines
and were collected outside of the incubator. Figure 1 is a schematic of the reactor designed for the
experiment. The reactor was constructed from cast acrylic and contained a total volume of 2729 cm3.
The tapered portion of the reactor resembled an inverted pyramid and contained 368 cm3 of aluminum oxide particles which served as the support media for the biofilm.
Attached above the tapered portion of the reactor was a sealed tank which served as a reservoir for
the recycle pump. Reactor recycle was provided by a small centrifugal force pump. The flow was controlled with a metering ball valve. During the course of the experiment, the expanded bed volume of
the support media was maintained at approximately 605 cm3.
Gas produced by the reactor was collected and measured daily with a gas collection device specifically constructed for the experiment. The device resembled and operated in the same manner as a respirometer. Daily gas production rates were calculated at room temperature and then converted to
standard temperature (0 C). Pressure changes were not accounted for as the resultant volume change
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