Biodegradation of nonionic and anionic surfactants in domestic wastewater under simulated sewer conditions

The ultimate disposition of chemicals discarded down the drain can be substantially impacted by their fate in the sewer, but to date limited data have been published on the biodegradability of chemicals in sewer systems. The recently established OECD 314 guideline (Simulation tests to assess the biodegradability of chemicals discharged in wastewater, 2008) contains a simulation method (314A) for evaluating the biodegradation of chemicals in sewage under simulated sewer conditions. This research used the OECD 314A method to evaluate the rates and pathways of primary and ultimate biodegradation of a suite of ¹⁴C-labeled homologues representing four classes of high volume surfactants including nonionic alkyl ethoxylates (AE), and anionic alkyl ethoxysulfates (AES), alkyl sulfate (AS) and linear alkyl benzene sulfonate (LAS). All the tested homologues exhibited >97 % loss of parent, formation of metabolites, and some level (16-94 %) of CO₂ production after being incubated 96-100 h in raw domestic wastewater. Comparison of C₁₂E₃, C₁₄E₃, and C₁₆E₃ showed that the first order biodegradation rate was affected by alkyl chain length with rates ranging from 6.8 h^-1 for C₁₂E₃ to 0.49 h^-1 for C₁₆E₃. Conversely, comparison of C₁₄E₁, C₁₄E₃, and C₁₄E₉ showed that the number of ethoxy units did not impact the biodegradation rate. AES and AS degraded quickly with first order kinetic rates of 1.9-3.7 and 41 h^-1 respectively. LAS did not exhibit first order decay kinetics and primary degradation was slow. Biodegradation pathways were also determined. This work shows that biodegradation in the sewer has a substantial impact on levels of surfactants and surfactant metabolites that ultimately reach wastewater treatment plants.