A biotechnological method for metalworking fluids (MWF) wastewater treatment was developed. The research, conducted in a lab-scale bioreactor, proved that the process of eliminating pollutants from MWF wastewater proceeds effectively when the following are applied: multiple reinoculating of biomass by adding active microorganisms into the bioreactor, immobilizing microorganisms on the PVC foam carrier, and carrying out the process in the anoxic/aerobic conditions at phase durations of 0.5 and 5.5 hours, respectively. The above parameters allowed us to obtain the following eliminations: 87% of chemical oxygen demand (COD), 97% of biochemical oxygen demand (BOD₅), 98% of petroleum ether extractable organic (PEEO) and more than 96% of total content of hydrocarbons determined by infrared (IR) spectrophotometry. The chromatographic analyses showed almost complete reduction of oily hydrocarbons contained in the used MWF.