Section 8. DAIRY WASTES
ANAEROBIC TREATMENT OF DAIRY WASTES USING
FIXED-FILM AND WITHOUT-MEDIA REACTORS
Euiso Choi, Professor
Civil Engineering Department
Korea University
Seoul, Korea 132
Carl E. Burkhead, Professor
Department of Civil Engineering
University of Kansas
Lawrence, Kansas 66045
INTRODUCTION
An attractive industrial waste treatment alternative includes the aerobic biological processes.
However, anaerobic systems are receiving more recent attention because they require less energy to
operate than aerobic systems. Among the anaerobic systems, the fixed-film and sludge blanket (or
contact) processes are known to be the most efficient [1,2].
This study was conducted to determine the anaerobic treatability of a synthetic industrial waste
using laboratory batch reactors and to investigate the effects of plastic medium and temperature upon
process efficiency. Also, the results obtained from the batch media units were compared with the
results obtained from a laboratory continuous media unit. The units using plastic media can be classified as fixed-film anaerobic reactors, and the units operated without media are referred to as sludge
blanket or contact type of reactors.
MATERIALS AND METHODS
Reactors
All four batch units used in this study were 1.5 1. The media used for the fixed-film reactors were
1.6 cm Flexirings which have a specific surface area of 345 m2/m3 and 92% void space. The continuous fixed-film reactor had a 9.0 1 liquid volume with 3.8 cm Flexirings which have a specific surface
area of 132 m2/m3 and 96% void space. The effluent from the continuous unit was recirculated to the
bottom of the reactor at a rate of 43.2 1/day or about 5 times the reactor volume. Figures 1 and 2 illustrate the batch and continuous laboratory units, respectively. The batch units were operated at temperatures of 37, 50, and room temperatures ranging from 25 to 28 C. The continuous unit was operated at 38 C.
Substrate
The substrate used for this study was milk waste prepared from 0.5% low fat milk (Kroger brand)
mixed with Lawrence, Kansas primary effluent which provided the necessary micronutrients. The
combined waste composition was 40% protein, 5% fat, and 55% carbohydrates. The mineral content
was: 1,230 mg/l Ca, 0.4 mg/l Fe, 120 mg/l Mg, 980 mg/l P04, 1,620 mg/l K, 510 mg/l Na, 4 Mg/l Zn
and others [3]. The COD of the undiluted milk was 116 g/1.
Operation and Analysis
The feed solution was prepared and added daily into the reactors. For the 5 day hydraulic retention time (dHRT) batch unit, 500 ml of reactor supernatant was removed and allowed to settle in a
graduated cylinder for about 30 minutes. A portion of the second supernatant (300 ml) was discarded
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