Investigation of aerobic degradation kinetics of surfactants using respirometric batch experiments

The mineralization of a non-ionic alcohol ethoxylate (AEO) surfactant was i nvestigated over the concentration range occurring in rinsing water from su rfactant production processes. For this, an experimental set-up for respiro metric batch experiments was developed. The set-up and the method were vali dated by experiments with glucose as the single carbon source. It was possi ble to calculate substrate decay from the time course of exogenously consum ed oxygen during respirometric batch experiments. The kinetic coefficients calculated by respirometry showed a lower standard deviation than those cal culated from measured glucose concentrations. The degradation mechanism of AEO was investigated by identification of meta bolites, occurring during the mineralization process of AEO, using Flow Inj ection Mass spectrometry (FI-MS). It was concluded that the degradation of AEO occurs in two main steps. First, the enzymatic hydrolysis of AEO into a lcohol and polyethylene glycol (PEG) is performed. Second, the mineralizati on of both substances takes place, while the mineralization of the alcohol is faster than that of the PEG. The mineralization kinetics were investigat ed in respirometric batch experiments. The model used is based on double MO NOD kinetics for the substrates being produced by hydrolysis (mu(max1) = 0. 047 h(-1), K-S1 = 15 mg/l DOC for alcohol; mu(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 b acteria recycle was successful.