Influence of Hydrophobe Type and Extent of Branching on Environmental Response Factors of Nonionic Surfactants

A number of ethoxylated nonionic surfactants differing in hydrophobe branching and chain lengths have been evaluated for environmental responses. Screening biodegradation tests show those non-ionics having more than one methyl group per hy-drophobe degrade considerably slower than those having less extensive branching. Continuous flow-through activated sludge tests, simulating actual waste treatment, show the more highly branched nonionics biodegrade more slowly and less extensively than do those with less hydro-phobe branching. In addition, treated effluents originating from influents containing the more highly branched nonionics tend to be more surface active and more toxic to aquatic species than those originating from influents containing surfactants with less hydrophobe branching. Under conditions simulating plant stress, such as high surfactant concentrations in the influent or low temperature, biodegradation of the highly branched nonionics was considerably less extensive while biodegrada-tion of the linear nonionics was not affected to any measurable degree compared to more normal operating conditions. Introduction Surfactants are used increasingly in household cleaning products, personal care and a variety of industrial and institutional applications.' Owing to the tendency of these surfactants to foam and exhibit toxicity to aquatic organisms at relatively low concentrations, they must be removed prior to entering receiving waters in order to meet regulatory requirements. Secondary waste treatment, employing aerobic biodegradation, is the most widely used approach to reducing the undesired properties of organic materials, like surfactants, which enter domestic waste treatment plants. In this approach , bacteria provide enzymatic systems which utilize oxygen to convert organic materials to C02, H20 and cellular mass. The process is complex with biodegradation rate dependent on the structure of the organic material. Alcohol-based surfac-tants having essentially linear hydrophobes have been shown in many extensive studies2-9 to biode-grade rapiaiy to produce non-foaming non-toxic products in treatment plant effluents. However, biodegradation of those alcohol-based surfactants having highly branched hydrophobes has been studied less extensivelylO~ii than the linear surfac-tants, since demand for the highly branched sur-factants has not been as great as those based on linear hydrophobes. All surfactants must show acceptable biodegradability in order to meet effluent regulatory criteria. This paper discusses an environmental response study of three of the major types of surfac-tants derived from linear primary alcohols, highly branched primary alcohols and branched nonyl-phenols. Nonionics derived from the nonylphenols have also been studied e x t e n ~ i v e l y. ~ ~ ~ ~-~ ~ Each of these nonionic classes …