Waste lubricating oil removal in a batch reactor by mixed bacterial consortium: a kinetic study

The growth kinetics and biodegradation of two waste lubricating oil samples including waste engine oil (WEO) and waste transformer oil (WTO) were studied using pure isolates and mixed culture of Ochrobactrum sp. C1 and Bacillus sp. K1. The mixed culture significantly influenced degradation efficiency of the pure isolates through bioaugmentation process. In particular, the mixed culture was capable of growing on various n-alkanes and polycyclic aromatic hydrocarbons and was able to tolerate unusually high concentrations of waste lubricants (WEO-86.0 g/L and WTO-81.5 g/L). The initial concentration of waste lubricating oils has been varied in the range of 1-10 % (v/v). Under this experimental range, the bacterial growth has been observed to follow Haldane-type kinetics characterizing the presence of substrate inhibition. Haldane model was used to fit the exponential growth data and the following kinetic parameters were obtained: mu(max) = 0.078 h(-1), K-S = 23.101 g/L, K-i = 43.844 g/L for WEO; and mu(max) = 0.044 h(-1), K-S = 10.662 g/L, K-i = 58.310 g/L for WTO. The values of intrinsic kinetic parameters, like specific growth rate mu(max), half saturation constant, K-S, inhibition constant, K-i and the maximum substrate concentration, S-max and growth yield coefficient Y-x/s , have been determined using each model hydrocarbon and their mixture as limiting substrate. Relative changes in the values of the kinetic parameters have been correlated to the number of carbon atoms present in n-alkanes. The metabolites from degradation of model hydrocarbon compounds have been identified by GC-MS to elucidate the possible pathway of waste lubricating oil degradation process.