1. Introduction
Up until the 1990s, the olive oil production process
was based on the so-called ‘‘three-phase system’’, which
produced three streams: pure olive oil, a watery liquid
called alpechı´n, and a solid cake called three-phase orujo
or olive cake. The alpech´ın contained soluble organic
matter and fine solids, and was extremely hazardous to
the environment because of its high biochemical oxygen
demand (BOD). The olive cake had a variable oil content
of around 3% that could be economically recovered
in oil extracting plants after moisture content had been
reduced to 8%.
In order to eliminate the alpech´ın, a new process technology
with only two effluent streams (olive oil and alpeorujo)
has emerged. The wet solid stream or two-phase
orujo contains all the substances that, in the three-phase
system, were contained in the alpechı´n and in the olive
cake.
The characteristics of this two-phase orujo are, obviously,
very different from those of olive cake (3-phase
orujo). It is a thick sludge that contains pieces of pit
and pulp of the olive fruit, as well as vegetation water.
It has a moisture content of around 65%, while olive
cake only had around 40–45%. This greater moisture,
together with the sugars and fine solids, that in the
three-phase system were contained in the vegetation
water, give the two-phase orujo sludge a doughy consistency
and makes transport, storage, and handling diffi-
cult (it cannot be piled and must be kept in large ponds).
Anyway, the main problems associated with the
processing of orujo during oil extraction occur in the
dryers. These dryers were designed for three-phase olive
cake, made up of loose particles of pit and pulp with a
homogeneous moisture distribution that can easily be
piled up and fed through rotary dryers.