Synergistic effect of process parameters and nanoparticles on spent lubricant oil waste biodegradation by UV-exposed Scenedesmus vacuolatus: Process modelling, kinetics and degradation pathways

Abstract

The study examines the impact of process parameters and nanoparticles (NPs) on the degradation of spent coolant waste (SCW) by UV-exposed S. vacuolatus. The model was experimentally optimized using response surface methodology (RSM) with high coefficient of determination (R2) >0.99. Upon validation of the model, total petroleum hydrocarbon (TPH) degradation of 100 % was obtained after 15 days under the optimized conditions of 25 °C temperature, 10 % (v/v) substrate concentration and 10 % (v/v) inoculum concentration. Moreover, the sensitivity of the process parameters on the degradation process assessed using artificial neural network (ANN) revealed high sensitivity of the degradation process to operational temperature. Metabolites obtained provide strong evidence for terminal oxidation and subterminal oxidation metabolic pathways in SCW degradation. In addition, the incorporation of NPs in the SCW degradation significantly enhanced the biodegradation efficiency of UV-exposed S. vacuolatus resulting in shortened degradation period from 15 to 12 days. Likewise, the inclusion of NPs substantially improved UV-exposed S. vacuolatus affinity (1/Ks) for SCW, growth constant (Kg) and maximum specific growth rate (μmax). The degradation kinetics followed the second-order reaction with degradation rate constant (K) in the range of 0.029 to 0.288 m−1 t−1 for monoaromatics and 0.972 to 4.130 m−1 t−1 for PAHs, at half-life (T1/2) ranges of 0.75 to 1.52 day−1 and 0.08 to 0.23 day−1, respectively. This knowledge will enhance the design of waste pollutant degradation towards sustainable green environment.