Applying Process Separation to Enhance the AnaerobicTreatment of Aircraft Deicing Fluid

Large quantities of aircraft deicing fluid (ADF) comprised mainly of ethylene glycol (EG) and propylene glycol (PG) are used for aircraft deicing/anti-icing during cold weather operations at airports throughout the world. Several different formulations of ADF have been developed and are used, but PG-based deicers are generally used in the United States because of their lower toxicity.In this paper the use of process separation to enhance the treatment of a PG-based ADF under anaerobic conditions is evaluated under laboratory conditions and the results are reported. The systems evaluated included:A single Anaerobic Fluidized Bed Reactor (AFBR)A two-stage system consisting of a CFSTR and AFBR in series, andA two-phase system consisting of two AFBR's in seriesThe performance of each reactor system was evaluated under steady state conditions at a organic loading rate (OLR) of approximately 13.3 kg/m3 · day, and in response to a stepwise increase in OLR to approximately 50 kg/m3 · day. In addition, the stability and robustness of each system was compared by evaluating system response to a short duration high loading condition after stable operation at an OLR of approximately 13.3 kg/m3 · day had been achieved. For these spike studies, the transient loading rate to the reactors was increased to ten times the steady state loading level, or approximately 133.1 kg/m3 · day, and the response of the reactor system to this condition over time was observed.Testing of the three reactor systems indicated that each reactor system was capable of achieving a high degree of COD removal (>95%) at steady-state loading rates of up to 50 kg/m3 · day. The testing also demonstrated that process separation in two-phase and two-stage systems could be achieved by using reactor hydraulic residence time as a process control. Although there was little difference in performance between the single AFBR and the process separated systems under steady-state conditions, the two-phase and two-stage systems exhibited greater stability and produced better effluent quality than the single AFBR when exposed to an OLR spike. Hydrogen measurements made during the spike tests show that process separation was useful in regulating hydrogen levels and this may have contributed to the improved performance of the phased and staged reactor systems.