Determination of the fate and behavior of an alternative surfactant in a water recycle system (WRS)
The fate of a common commercial surfactant was investigated in biological reactors intended for long-term space applications. A NO2" reducing packed-bed bioreactor was employed to evaluate degradation of surfactant present in a typical space station greywater stream. The research was conducted to determine if a commercial surfactant could be used in the place of the current cleansing formulation and be degraded in biological water recycle system proposed for space travel. The commercial cleansing formulation used in the research was Pert Plus® for Kids (PPK), which contains sodium laureth sulfate (SLES) as the active surfactant. Experiments included a combination of microcosm experiments as well as a continuous-flow packed-bed bioreactor. The hydraulic retention time of the packed-bed bioreactor was varied through changes in flow rate to yield different steady-state values for NO2' reduction TOC, COD and SLES removal. Steady-state conditions allowed for the determination of degradation potential of both PPK and SLES. It was found that both constituents degraded well under NO2" reducing conditions. Stoichiometric relationships were used to determine if measured parameters could accurately predict the observed SLES degradation. Frora these relationships, it was found that other less common degradation pathways (biotic and/or abiotic) could have transformed SLES. Also, bacterial kinetics were determined for the currently used surfactant, Igepon T42 ™, and the commercial surfactant, SLES.
From the rates determined it was found that Igepon T42™ exhibits faster degradation rates compared to the SLES. It was also found that the rates determined for SLES were concentration dependent. During this evaluation both PPK and SLES were effectively degraded under NO2" reducing conditions indicating their possible use in a WRS.