Comparison between batch aerobic biodegradation of paracetamol and glucose with open mixed microbial cultures: experimental data and kinetic modelling

Biodegradation of man-made chemicals (xenobiotics) in biological wastewater treatment processes is essential to avoid the accumulation of these substances with negative effects on the environment and on human health. This study investigated the aerobic biodegradation of paracetamol as sole carbon and energy source and compared it to a model biogenic substrate (glucose). Batch experiments with unacclimated open mixed cultures from soil were carried
out with glucose or paracetamol in a range of concentrations (100-2,000 mg/L), measuring the rate of substrate removal, the acclimation time, the oxygen consumption and the COD (chemical oxygen demand) removal. The experimental data were used for kinetic modelling, using several different models based on the Monod kinetics with modifications for inhibition or for acclimation. Paracetamol was biodegraded as sole carbon and energy source at all concentrations (90-97 % COD removal), with slower degradation rate and longer acclimation time than for glucose. From the COD balance, a slightly higher production of microorganisms per unit of substrate COD was calculated for paracetamol than for glucose. The kinetic modelling of the experimental data achieved a good fit with the simple Monod model, but with different parameters for each substrate concentration. Combined fitting of all the experiments with the same set of parameters was attempted, and overall the best fitting was observed with a new model that includes an empirical time constant for acclimation. Compared to glucose, microbial growth on paracetamol was characterised by lower maximum specific growth rate, slightly higher growth yield and higher time constant for acclimation.