Fate and toxicity of aircraft deicing fluid additives through anaerobic digestion

The toxic effects and fate of the two commercially significant benzotriazole isomers used in aircraft deicing fluids (4-, and 5-, methylbenzotriazole (MeBT)) were studied in microcosms using mesophilic anaerobic biomass co-digesting sewage biosolids and propylene glycol. Sorption of MeBT to anaerobic digester solids could be approximated with a Fruendlich model. No anaerobic breakdown of either MeBT isomer was detected. Compared to digesters fed only settled sewage and glycol, digesters fed more than 300 mg/L MeBT responded with a significant decrease in methanogenic microbial activity and volatile solids production, and a concomitant increase in accumulation of volatile fatty acids. Direct microscopic measurements using fluorescent phylogenetic probes applied to digesting biomass revealed that members of both Archaea and Bacteria domains were sensitive to MeBT.; The impact of a nonionic surfactant (Tergitol NP-10), added (∼1% v/v) to ADF for more efficient application to airframe surfaces on anaerobic toxicity of MeBT was studied. Sorption to digester biomass was enhanced when exposed to surfactant in the MeBT concentration range observed (100–1,000 mg/L). Below the surfactant critical micelle concentration (CMC), a statistically significant decrease in methane production and corresponding increase in volatile fatty acid production was observed when microcosms were exposed to 1,000 mg/L MeBT; this suggested that low nonionic surfactant concentrations could facilitate a reduction in apparent toxicity of MeBT. In microcosms exposed to surfactant concentrations above the CMC, response corresponded to control microcosms absent of TNP-10. Granular activated carbon (GAC) (volatile solids/GAC = 10%) addition to microcosms nearly restored the baseline activity of digesters fed MeBT (500–1,000 mg/L).; Some modern airport waste management plans have instituted ADF waste disposal through anaerobic digestion. Results from this work suggest that (i) conventional anaerobic digester performance may be compromised by adding ADF diluted less than 20 times (solely due to MeBT toxicity); (ii) ADF waste will likely contain surfactant concentrations above the CMC resulting in increased MeBT toxicity due to significant surfactant-MeBT interactions; and (iii) GAC may prevent the toxic conditions induced by introducing ADF waste to full-scale digesters.