Surfactant biodegradation for application to advanced life support water recycling systems

Complete reuse of graywater will be essential during long duration human space missions. The highest loaded and most important component to remove from graywater is surfactant, the active ingredient in soaps and detergents. When considering a biological treatment system for processing of graywater, surfactant biodegradability becomes a very important consideration. Surfactants should be chosen that are degraded at a fast rate and yield inconsequential degradation byproducts. Experiments conducted for this research examined the biodegradation of the surfactants in Pert Plus for Kids, disodium cocoamphodiacetate (DSCADA) and sodium laureth-3 sulfate (SLES), using respirometry. Rates of CO₂ production, or ultimate degradation, are reported. DSCADA was found to be toxic to bacteria when present at 270 ppm whereas no toxicity was observed during experiments with SLES. Several surfactants were identified that may be encountered in a biological graywater treatment system including SLES, DSCADA, sodium alkyl benzene sulphonate, and alcohol ethoxylates. Biodegradation pathways for these surfactants are discussed and potential degradation byproducts are identified. Future experiments will focus on determination of Monod growth kinetics for the above listed surfactants as well as examination of the potential persistence of their metabolites within a water reuse system.