Plant performance assessment using radioactive tracer technology and conventional techniques: case study of an edible oil refinery wastewater treatment plant

Performance assessment of industrial wastewater treatment plants (WWTPs) is crucial to ascertain design flaws and efficiency. The edible oil refinery (EOR) industry generates large amounts of wastewater necessitating treatment to ensure discharge of urbane effluent into catchment water bodies. The study assessed the performance of the WWTP of an EOR using radioactive tracer technology (RTT) and conventional wastewater quality assessment (WWQA) techniques. Results obtained (in ranges) for effluent quality parameters are: pH [7-7.89]; Temp [25.3-31.3 °C]; EC [1012-1328 µS/cm]; TDS [543-9480 mg/L]; TSS [9-13 mg/L]. Others are turbidity [13-17 NTU]; colour [246-249 TCU]; COD [118-190 mg/L]; BOD [0.99-1.70 mg/L]; O&G [1.25-1.99 mg/L]. The removal efficiencies [RE] (%; in ranges) for the parameters were: EC ([-324.67] - [-148.89]); TDS ([-111.61] - [-74.59]); TSS (97.4 - 98.1); turbidity (96.8 - 97.5); colour (94.8 - 95.3); COD (95.5 -96.2); BOD (68.5 - 68.8); O&G (48.4 - 51.4). Effluent parameters met Ghana's Environmental Protection Agency and World Health Organization's recommended limits except for EC and colour. The relatively high REs of the parameters indicate efficient wastewater treatment (WWT). The calculated Biodegradability Index (BI) of 0.001 indicates that a stand-alone biological treatment plant will be inadequate for the WWT. The results of the RTT demonstrated that the respectiveexperimental mean residence times (MRTs) of 53.4 and 85 min obtained for cavitation air flotation tanks (CAFTs) 1 and 2 (of the WWTP) were lower than their design MRTs of 161 min; suggesting the presence of dead volumes (V_d) in the CAFTs. This may be attributed to the accumulation of sludge at the bottom of the tanks over time. CAFTs 1and 2 had dead volumes of 67% and 53% with their corresponding effective volumes of 33% and 47% respectively. The mixing in CAFT 2 was better than CAFT 1; based on the variances (evaluated using the Method of Moments) of 1.62×10⁷ for CAFTs 1 and 2 respectively. The IAEA-developed RTD analysis software used to model the flow type in the CAFTs revealed that the perfect mixer in series with exchange (PMSE) and perfect mixers in series (PMS) models best described the flow regimes in CAFTs 1 and 2 respectively. Based on the results of the entire study, it can be concluded that the performance of the WWTP was appreciably high; and the two techniques (RTT and WWQA) employed are complementary. (Author)