IMPROVED BIOLOGICAL TREATMENT OF FOOD PROCESSING
WASTES WITH TWO-STAGE ABF PROCESS
Brian W. Hemphill, Product Engineer
Richard G. Dunnahoe, Product Manager
Neptune Microfloc, Incorporated
Corvallis, Oregon 97330
INTRODUCTION
Biological treatment of food processing and combined food processing/municipal wastes
has historically presented unique problems because of:   (a) highly erratic flows and wastewater strengths; (b) high soluble organic concentrations; and (c) tendencies to contribute
to operational problems such as bulking of activated sludge due to the presence of high
levels of carbohydrate materials [ 11.   Traditional fixed-film treatment systems such as
trickling filters have often been used on these wastes because of their relative stability
under changing loads and low operating costs [2,3].   However, they are limited because
of high land area requirements, high capital costs, and inferior effluent qualities.   Suspended growth systems (activated sludge) have been used because of their lower first cost,
higher effluent quality, and lower land requirements.   The success of these systems has
been hindered by their operational complexity, their sensitivity to shock loadings and
tendency to be unstable under conditions such as those typically imposed by food-processing plants.
The activated biofiltration (ABF) process has been developed to make use of the advantages of both the fixed-film and suspended growth treatment systems while minimizing the disadvantages.   A superior process stability is realized over a wide range of wastewater characteristics and treatment problems.   This paper will summarize the development
of the ABF process in treatment of food-processing waste and will present operating data
from both pilot-scale studies and full-scale plants.
ABF PROCESS DESCRIPTION
Figure 1 shows the flow schematic for the ABF process.   After primary treatment,
the wastewater is combined with return sludge from the secondary clarifier and Bio-Cell
recycle to form a mixed liquor which is then pumped to the Bio-Cell.   The Bio-Cell reactor contains horizontal biomedia, to which fixed-film organisms attach.   The suspended
growth organisms combine with the fixed-film to oxidize the biodegradable organics.   The
Bio-Cell underflow is split, with a portion being returned as Bio-Cell recycle and the remainder proceeding to a short-term aeration basin.   The aeration basin acts as a complete-
mix activated sludge basin, which further oxidizes organic materials and provides a floc-
culent mixed liquor prior to final sedimentation.   Settled biological solids are recycled to
the Bio-Cell lift station with a portion going to waste.   For roughing applications, the
aeration basin is often deleted from the flow scheme.
The horizontal ABF biomedia consists of individual racks made of wooden lath fixed
to supporting rails, as shown in Figure 2.   The horizontal configuration of the media provides turbulent conditions, which are necessary to maintain a high dissolved oxygen environment and particle-micTOorganism contact.   Oxygen transfer is provided by the dual
action of wastewater continually moving in a film across the biota, and splashing between
layers.   The open design permits free flow of air in all directions  and prevents ponding or
bridging.
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