Modelling of Biodegradation Kinetics for Binary Mixtures of Substituted Phenols in Sequential Bioreactors

Substituted phenols are extensively produced and utilized in chemical industry and therefore they are largely present in wastewater. In this paper we considered phenolic mixtures which are representative of industrial wastewater, usually containing multiple substrates. In these conditions, degradation process is strongly affected by the complex interactions among substrates, which include enhancement, inhibition and co-metabolism so a process model is an useful tool to explore and predict the process evolution. Objective of this work was to formulate a kinetic model for the biodegradation of binary mixtures performed in a sequencing batch reactor (SBR). Two model mixtures were investigated: a 4-nitrophenol (4NP) and 2,4-dimethylphenol (2,4DMP) mixture, and a more recalcitrant mixture of 4NP and 2,4-dichlorophenol (2,4DCP). Kinetic tests were performed at different feed concentrations, with single compounds and mixtures and each biodegradation process was kinetically characterized. Haldane equation was utilised to model the substrate inhibited kinetics for single compound while for the mixtures the model was modified with a "switching function" to account the mutual substrate interaction. The proposed model was initially calibrated with a preliminary set of data to evaluate the best-fitting parameters, then validated by simulating different runs with the estimated parameters. Satisfactory results with high correlation coefficients (>= 0.98) and reliable predictions were obtained for the two investigated mixtures.