The objective of the present work was the enhancement of the efficienc
y of microbiological processes in purification of high-salinity oil-fi
eld brine by adding the powdered activated carbon (PAC) to the bioreac
tor and by diluting the brine with surface water. The investigation wa
s carried out in a laboratory setup. Results show that the nature of p
ollutants and the high salinity (about 29 g/l) of oil-field brine had
an unfavourable effect on the activated sludge process. Higher hydraul
ic loads (above 2.5 d(-1)) increased wash-out of the activated sludge
from the bioreactor, so that an increased concentration of the suspend
ed matter in the settler was observed. The addition of PAC to the bior
eactor, combined with the dilution of oil-field brine with surface wat
er, produced a substantial improvement in the sludge volume index. Als
o, under the given conditions, it was possible to maintain the given c
oncentration of the activated carbon in the bioreactor. The procedure
involving PAC and dilution with surface water resulted in an increased
rate of pollutant degradation. The positive effect of PAC on the proc
ess of oil-field brine purification with the activated sludge was expl
ained by the possibility of immobilization of microorganisms on the ac
tivated carbon surface in the form of a biofilm.