77    ANAEROBIC TREATMENT OF OLIVE MILL EFFLUENTS
Izzet Ozturk, Associate Professor
Suleyman Sakar, Research Associate
Gulseven Ubay, Research Associate
Veysel Eroglu, Associate Professor
Istanbul Technical University
Maslak, Istanbul, Turkey
INTRODUCTION
The olive oil extraction industry is principally located around the Mediterranean, Agean and
Marmara seas. Typical olive oil producing countries are Turkey, Tunisia, Syria, Lebanon, Portugal,
Spain, Greece, and Italy. Turkey has a significant share in the world, ranking fourth in olive oil
production, which amounts to 150,000 tons per year.1 Olive oil extraction is mainly carried out by
means of the traditional discontinuous press or by the more recent continuous solid-liquid centrifuge
system. Both processes produce two waste streams: the residual solids (prina), which contain oiUo be
recovered by means of solvent extraction, and olive mill wastewaters (black water). In general, the
organic pollution load from olive oil extraction process is practically independent of the processing
method and amounts to 45-55 kg BOD5 per ton of olives. The corresponding volume of black water
from the traditional press process is 0.4 to 0.5 m3 per ton of olives.2
Olive oil processing is a seasonal operation which starts in September and ends in February at the
latest. Individual olive crops are brought to the plant which processes the crop of each customer
separately and gives back the processed oil and soap stock to the customer. In Turkey, olive oil
processing is generally carried out by many small plants rather than by large edible oil refineries. An
appropriate treatment technology has not been developed to solve the environmental pollution problem from olive oil extraction plants. Traditional production capacity of olive oil plant is about 100 t
per day. Most of the treatment processes used for high strength industrial wastewaters have been
applied on olive mill effluents. Aerobic biological processes are not appropriate due to various factors
including high energy and nutrient consumption, production of large amounts of secondary biological
sludges and high capital cost. Incineration and concentration by distillation are reliable but very
expensive and energy consuming. Evaporation in shallow lagoons is also not practical due to ground
water pollution, bad odor and flies. Anaerobic biological treatment processes, however, have distinct
advantages including energy and chemical saving and low biological sludge yield. Seasonal operation
of olive oil mills is not a disadvantage for anaerobic treatment systems since anaerobic digesters can be
easily restarted after several months of shut-down.3
In this study, anaerobic treatability of olive mill effluents and bioenergy recovery from this high
strength wastewaters have been investigated. The study was conducted in a laboratory scale upflow
anaerobic sludge blanket reactor (UASBR) with a volume of 10.35 L. Experimental studies were
continued for about six months. The effects of feed strength and hydraulic retention time on the
stability of the anaerobic treatment process have been searched.
PRODUCTION OF OLIVE OIL
The traditional olive oil extraction process includes the following operations: sorting and rinsing,
grinding, extraction, oil-water separation and/or centrifugation. A flow diagram of a traditional olive
oil mill plant is shown in Figure 1.
46th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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