46    TREATMENT OF TUNA PROCESSING WASTEWATER IN
LABORATORY AND PILOT SCALE
DSFF ANAEROBIC REACTORS
M.C. Veiga, Postdoctoral Student
Michigan Biotechnology Institute
Lansing, MI 48909
R.J. Mendez, Associate Professor
J.M. I.ema, Professor
Department of Chemical Engineering
University of Santiago de Compostela
Santiago de Compostela, Spain
INTRODUCTION
The tuna processing industry generates large volumes of high strength wastewaters (20-50 g COD/
L). Contrary to many other kinds of wastewaters, those produced by tuna processing industry
generally do not contain carbohydrates. About 80% of their total COD is proteinaceous material.
They also contain some lipids and present a relatively high salt content (9.2 g/L). Moreover, in the
first step of anaerobic digestion, the degradation of proteins leads to the formation of high amounts
of ammonium-nitrogen which may be inhibitory. Due to these characteristics, wastewaters from the
fish processing industry are difficult to biodegrade. Only few reports have been published in the
literature regarding their treatment by anaerobic digestion.1"4 Some studies have also been reported
on the biodegradation of proteins in synthetic media.5"7
In the present study we evaluate the treatment by anaerobic digestion of wastewaters from a tuna
processing industry, at laboratory-(l L) and pilot-scale (15 m3), in downflow stationary fixed film
reactors under mesophilic conditions. The adhesion of biomass was compared for three different
support media (clay, polystyrene and polyvinyl chloride) and was related to the kind of methanogenic
bacteria present.
MATERIALS AND METHODS
Reactor Design and Operation
The experimental set-up and the characteristics of the laboratory-scale reactor are shown in Figure 1
and Table I. The packing of the laboratory reactor was made of three different materials: polyvinylch-
loride, needle punched polystyrene and clay, fashioned into cylinders located along the reactor. The
characteristics of the pilot-scale reactor appear in Table I. It was filled with an oriented film support
material consisting of straight vertical channels (Figure 2). The support was made of polyvinyl
chloride. A recirculation feed ratio of 10:1 was applied in both cases. The results of mixing studies
indicated that both reactors behaved like completely mixed reactors, with active volumes of 88% and
98% at laboratory-scale and pilot-scale respectively.
The feed was pumped into the top of the reactor and the effluent was withdrawn from the bottom
for disposal and recirculation. Biogas exited at the top of the reactor through a wet gas meter. The
level of liquid in the reactor was maintained a few centimeters above the top of the support media in
order to protect the biofilm.
Tuna Wastewater
Wastewater was obtained from a tuna processing industry near La Coruna (Galicia, Spain). During
the tuna processing a wide range of discharges with different characteristics are generated. The
effluents generated by the tuna cookers posess most of the organic content (65% of total COD)
46th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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