Investigation of aerobic degradation kinetics of surfactants using respirometric batch experiments

Abstract

The mineralization of a non-ionic alcohol ethoxylate (AEO) surfactant was investigated over the concentration range occurring in rinsing water from surfactant production processes. For this, an experimental set-up for respirometric batch experiments was developed. The set-up and the method were validated by experiments with glucose as the single carbon source. It was possible to calculate substrate decay from the time course of exogenously consumed oxygen during respirometric batch experiments. The kinetic coefficients calculated by respirometry showed a lower standard deviation than those calculated from measured glucose concentrations. The degradation mechanism of AEO was investigated by identification of metabolites, occurring during the mineralization process of AEO, using Flow Injection Mass spectrometry (FI-MS). It was concluded that the degradation of AEO occurs in two main steps. First, the enzymatic hydrolysis of AEO into alcohol and polyethylene glycol (PEG) is performed. Second, the mineralization of both substances takes place, while the mineralization of the alcohol is faster than that of the PEG. The mineralization kinetics were investigated in respirometric batch experiments. The model used is based on double MONOD kinetics for the substrates being produced by hydrolysis (μ max1 = 0.047 h -1 , K S1 = 15 mg/l DOC for alcohol; μ max2 = 0.027 h -1 , K S2 = 4 mg/l DOC for PEG). The validation of the model by calculating the results obtained from measurements in a continuously operated lab scale CSTR with bacteria recycle was successful.