Aerobic biodegradability of surfactants at low concentrations using an automated pressure transducer system

We have developed a simple and reliable automated pressure transducer system (APTS) to evaluate the ready and ultimate aerobic biodegradability of surfactants in 28 days at low concentrations (5 mg C/L) using modifications of existing CO2 evolution assays (Sturm & Gledhill). Pressure transducers (PT) are fitted to Gledhill-type flasks containing Sturm minerals solution, dilute (50 mg/L) unacclimated activated sludge microbial seed and test compound. PT monitor microbial respiration through oxygen consumption from the headspace and CO2 from metabolism is absorbed in a 1M KOH solution within the flask. Results with nonionic ethoxylate (AE-7) and anionic sulfate (AS) surfactants prepared from linear or 2-alkyl branched C14−15 alcohol moieties show that sewage bacteria readily consumed 02 (70–140% ThO2) and degraded these compounds to C02 (65–75% ThCO2) in 12 days at 25C. However, when a more branched alcohol ethoxylate (NPE-9) was tested in the APTS, only 50% of both the ThO2 was consumed and ThCO2 was produced. Glucose and benzoic acid were biodegraded to CO2 similarly to the AE-7 and AS surfactants. Comparison of alcohol ethoxylate degradation data in the APTS with those published from traditional Sturm test methods demonstrated that the C02 recovery results were the same for readily metabolized compounds. Our experience with the APTS indicate that the method is reliable, less cumbersome and requires less manipulation than the Sturm and Gledhill assays. Furthermore, the method can be adapted to screen the ready biodegradability of volatile, insoluble and other organic compounds for which radiolabelled material is not available to study microbial degradation.