PERFORMANCE AND STABILITY OF THE ANAEROBIC CONTACT
PROCESS AS AFFECTED BY WASTE COMPOSITION,
INOCULATION AND SOLIDS RETENTION TIME
L. van den Berg, Research Officer
C. P. Lentz, Research Officer
Division of Biological Sciences
National Research Council of Canada
Ottawa Kl A OR6
INTRODUCTION
The anaerobic contact process was the first of several advanced digestion technologies
incorporating retention of microorganisms in the digester independent of hydraulic renten-
tion time. It was originally developed for meat packing waste [ 1-7] and has been studied in
detail for use with food processing wastes at the National Research Council of Canada
[8-13]. A comparison between the anaerobic contact process and another advanced technology is presented in a comparison paper [14]. The present paper deals with the performance and stability of the anaerobic contact process at 35 C as affected by the composition
of the waste, overloading, changes in waste composition, reinoculation and solids separation.
EXPERIMENTAL
The design and operation of the seven fermenter units used in this study have been described in detail earlier [8-13]. Briefly, each fermenter unit (Figure 1) consisted of a 36-liter
cylindrical fermenter (holding 30 liters of liquid), a 4-liter settling flask, a refrigerated feed
tank, peristaltic pumps for adding waste and returning sludge from the settling flask to the
fermenter and variable speed stirrers. Fermenters were located in a room maintained at
35 C. Moderate agitation in the fermenter ensured adequate mixing with minimum effect on
settleability. Feed was pumped into the fermenter continuously at the required rate, with
effluent obtained after settling of fermenter liquid being removed at the same rate.
Widely differing types of wastes were used: (a) pear peeling waste, containing mostly
carbohydrate, (b) rum stillage waste without easily degradable carbohydrates, (c) bean
blanching waste, containing mostly soluble protein and carbohydrate, (d) dry caustic potato
peeling waste with a high sodium content, (e) a waste made of whole potatoes and (f) a
simulated sewage sludge waste, a complex waste containing cellulose, protein, fat and hemi-
celluloses. The preparation and characteristics of these wastes have been described earlier
[11-14]. Most of these wastes were used both without and with added yeast extract to test
for nutrient deficiencies. Ammonia nitrogen and phosphate were added when necessary to
obtain COD:N:P ratios in the range 300:5:1 to 100:5:1 [12].
-•EXISTED LIQUID
Figure   t.  Sketch   of  anaerobic  contact
fermenter.
— OGtSTIB LlCWD
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