Investigation of the Impact of Wastewater from Waste Oil In-Stallation on the Activated Sludge Process, to Ensure the Proper Operation of Municipal Wastewater Treatment Plant

The study evaluated the feasibility of using the activated sludge process to treat real wastewater from used oil installations containing petroleum hydrocarbons, boron (B), and adsorbable organic halides (AOX). The aim was to determine the maximum ratio of this wastewater that could be added to the influent without impairing treatment efficiency. Tested shares ranged from 0.50% to 1.90%. An initial 1.30% of the tested share caused process instability, reflected in the elevated total nitrogen (TN) levels in treated wastewater. After reducing the share to 0.50%, an adaptation of the activated sludge was observed, manifested by a decrease in TN concentration to below 15.0 mg N/L. For the most favorable share of 1.60% (0.38 ± 0.10 kg_BOD5/kg_MLSS d, 0.51 ± 0.14 kg_COD/kg_MLSS d), the removal efficiencies of chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), TN, and total phosphorus (TP) were 95.0% ± 1.5, 99.1% ± 0.2, 89.3% ± 2.7, and 94.0% ± 5.0, respectively. Increasing the share to 1.90% decreased treatment efficiency and exceedances of COD, BOD₅, TN, and TP occurred. At this ratio, an increase in ammonium nitrogen (NH4⁺-N) and TN concentrations was observed, indicating the inhibition of nitrification. However, the average concentrations of mineral oil index, AOX and B in the treated wastewater remained within permissible levels throughout the study.