Anaerobic biodegradability testing of surfactants

Anionic and nonionic surfactants (5-50 mg C/g solids/L medium) were screened for anaerobic microbial decomposition to methane in an automated pressure transducer serum bottle assay system at 35C using municipal digester solids as a source of anaerobic bacteria. Analysis of the headspace gas recovered from tests with linear primary alcohol sulfates (A45S and A24S) and a linear alcohol ethoxylate (LAE-8) showed that these compounds were readily degraded (60-85% of the theoretical methane, TM) after a 15-30 day lag period at 50 ppm C. The extent of degradation of a branched alkyl phenol ethoxylate (NPE-9) was lower (30-40% TM). A survey of intact nonionic and anionic surfactants present in municipal digester sludges in the U.S. showed that these materials were present at levels of 0.5-8 mg CTAS or MBAS/g dry solids. A surfactant which was slower to biodegrade (NPE-9) at 50 ppm C was readily metabolized to methane when tested at 5 and 10 mg C/g solids/L. The pressure transducer serum bottle method described may be used to test biodegradability and inhibitory effects on methanogenesis at surfactant concentrations (e.g. 5 ppm C/g solids) typically present in digesters.