ANAEROBIC DIGESTION OF AIRCRAFT DEICING FLUID WASTES: INTERACTIONS AND TOXICITY OF CORROSION INHIBITORS AND SURFACTANTS

Corrosion inhibitors and surfactants are present in aircraft deicing fluids (ADF) at significant concentrations (>1% w/w). The purpose of this research was to study the interactions of a common nonionic surfactant (Tergitol NP-10) with the commercially significant corrosion inhibitors used in modern ADF [4-, and 5-,methylbenzotriazole (MeBT)], and determine the effects of their mixture on the conventional anaerobic digestion process. In mesophilic anaerobic microcosms co-digesting sewage biosolids, propylene glycol, and MeBT, increasing Tergitol NP-10 (TNP-10) levels resulted in enhanced MeBT sorption on digester solids. As judged by anaerobic toxicity assay, responses from digesters containing surfactant concentrations below their critical micelle concentration (CMC), suggested that low nonionic surfactant concentrations could facilitate a reduction in the apparent toxicity of MeBT. In microcosms exposed to surfactant concentrations above the CMC, no increase in MeBT solubility was observed, and the anaerobic toxicity response corresponded to control systems not containing TNP-10. Direct microscopic measurements of digesting biomass using fluorescent phylogenetic probes (FISH), revealed that members of the domain Bacteria were more sensitive to MeBT in the presence of Tergitol NP-10 than were members of the domain Archaea.