Oil shale is one of the most important natural resources in Estonia. In the
year 2002, 12 million tons of oil shale was mined. From this amount about
9 million tons were burnt in thermal power plants to produce energy, and
about 3 million tons were treated thermally to produce oil.
Thermal processing of Estonian oil shale and refining of the products of
its semicoking process (retorting) is accompanied by the formation of large
amounts of different process water and wastewaters containing phenols, tar
and several other products heavily separable and toxic to the environment.
The solid waste of the thermal treatment process, semicoke, is discharged
from the retorts and disposed of in an ash dump. Water enters the technological
process of oil shale thermal treatment from different sources: physical
moisture in mined oil shale; water from oil shale semicoking process
(process water); precipitation on the factorys territory; leakages in the cooling
water system; used potable water and washwater, etc.