Process water and phenols’ balances for the two processes of oil shale thermal
treatment, Kiviter (in vertical retort) and Galoter (with solid heat carrier)
were compiled. Options of wastewater treatment in the Kiviter process
were analyzed in more detail. Laboratory experiments of biological oxidation
of the process water after the dephenolation stage without other effluents and
municipal wastewater were carried out. Experiments indicated that the oil
shale phenols are generally quite easily degradable when the need for phosphorus
is covered by added reagents. The experiments indicated that, compared
to conventional aerobic bio-oxidation, the combined process, namely
aerobic bio-oxidation with ozonation in re-circulation system, enabled to increase
the efficiency of purification at relatively low ozone dosages. Application
of ozone at moderate doses (up to 30 mg/L) improved the rate of pollutant
removal. Injection of ozone at small dose – 2 mg/L – into the activated
sludge in the bioreactor increased the sludge activity: the specific oxygen uptake
increased about 15–20%. The biologically treated wastewater can be
used as some kind of technological water (cooling water) after chemical precipitation
and reduction of sulphate content. It can also been discharged to
nature, but only after additional treatment to reduce nitrogen content and after
filtration to remove the residual suspended solids.