60    AEROBIC BIOFILTER TREATMENT OF
SLAUGHTERHOUSE EFFLUENT
Alexandra Kantard jieff. President
Ekokan Incorporated
Rock Forest, Canada
J. Peter Jones, Professor and Director
Department of Chemical Engineering
University of Sherbrooke, Canada
INTRODUCTION
Food processing wastewaters can generally be categorized as containing a high concentration
of BOD (can be greater than 1000 mg/L), which is predominantly soluble (greater than 80%). It
is not unusual for these wastewaters to exhibit a deficiency of biologically accessible nutrients. If
not properly pretreated, these effluents can also have a high total suspended solids, and a high oil
and grease content. Operation of different types of suspended growth processes, such as extended aeration, activated sludge, and sequential batch reactor, is becoming commonplace. Performance of those systems depend upon maximizing pretreatment and very close operation in
order to prevent microbiological disturbances, mainly bulking. The suspended growth systems
require large volumes, are rather high energy consumers, and produce high quantities of biological solids, exhibiting poor dewatering characteristics.
Biological fixed film processes are considered one potentially interesting alternative from a
process and economic point of view.1 Since an industrial aerobic biofilter has been piloted extensively in Canada over the last five years on several types of pulp and paper mill effluents,2-3 resulting in one full-scale operational facility at a fine paper mill,4 it was decided to verify the applicability of the process to slaughterhouse industry wastewaters.
The majority of the red meat slaughterhouses and/or meat processing industries are located either near the urban areas or in the middle of the populated villages and cities. Often their effluents are treated jointly with the municipal wastewaters and the associated user fees in this case
were the main motivating agent to search for an alternative, more economical treatment process.
THE AEROBIC BIOFILM REACTOR
The fixed biofilm reactor combines aeration and clarification in one unit by using a granular
media for biomass attachment and a certain degree of suspended solids removal. The schematic
diagram of the biological aerated filter is presented in Figure 1.
The core of the system is a rectangular (large-scale treatment systems) or circular (small-scale
systems) aerobic upflow packed bed reactor, packed with 3 to 6 meters of porous media with
grain sizes between 10 and 20 mm. The packing media and typical bacterial colonization are
shown in Figure 2.
Compressed air and untreated effluent are injected at the base of the media, providing process
oxygen and substrate to the attached microbial community. Retained suspended solids and accumulated excess biomass are wasted periodically by automatic backwashing using air and final effluent water.
Full-scale measurements of the oxygen transfer characteristics of aerobic submerged biofilter
aeration system indicated KLa as high as 36 h"1. It was ascertained that packing material in an
aerobic submerged biofilter controls the air bubble size, bubble rising velocity, and the spiral liq-
51st Purdue Industrial Waste Conference Proceedings, 1996, Ann Arbor Press, Inc.. Chelsea, Michigan 48118.
Primed in U.S.A.
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