Constraints of propylene glycol degradation at low temperatures and saturated flow conditions

Abstract

During snowmelt, the infiltration of large amounts of propylene glycol (PG), the major compound of many aircraft deicing fluids, affects redox processes and poses a contamination risk for the groundwater. To gain a better understanding about the degradation of PG and the associated biogeochemical processes under these conditions, we conducted saturated soil column experiments at 4 °C. During two successive PG pulses, we monitored the effect of the runway deicer formate (FO) and changing redox conditions on PG degradation. Furthermore, we applied first-order and simplified Monod kinetics to describe PG and FO transport. The transport of 50 mg l(-1) PG showed three stages of microbial degradation, which were defined as lag phase, aerobic phase, and anaerobic phase. During the second pulse, lag effects diminished due to the already accomplished microbial adaption, and the initial degradation rate of PG increased. Degradation of PG was most efficient during aerobic conditions (aerobic phase), while the subsequent drop of the redox potential down to -300 mV decreased the degradation rate (anaerobic phase). Formate addition decreased the overall degradation of PG by 50 and 15 % during the first and second pulse, illustrating the inhibitory effect of FO on PG degradation. The concurrent increase of Fe(III), organic carbon, and the turbidity in the column effluent after PG and FO application suggest the combined export of Fe adsorbed to fragments of detached biofilm. Neither the first-order nor the simplified Monod model was able to reconstruct the dynamic breakthrough of 50 mg l(-1) PG. The breakthrough of 1,000 mg l(-1), however, was described reasonably well with first-order kinetics. At low temperature and high water saturation, the application of first-order degradation kinetics seems therefore appropriate to describe the transport of high concentrations of PG.

Silk Fibroin Hydrogels Incorporated with the Antioxidant Extract of Stryphnodendron adstringens Bark

“…The first thermal event in all hydrogels occurred between 33.16 • C and 99.02 • C and was related to water evaporation [42]. For hydrogel PG and BT/PG, there was a higher loss of mass, which extended to approximately 240 • C and, possibly, was due to propylene glycol evaporation [46]. The main thermal event for the hydrogels occurred between 250 • C and 350 • C and was related to the thermal degradation of silk fibroin [42].…”

Environmental and Economic Impact of the Antifreeze Agents in Geothermal Heat Exchangers

“…(log 10 5.7 Re 0.9 2 (11) where Re = ρ f u f D/µ f is the Reynolds number and µ f (Pa•s) is the fluid dynamic viscosity.…”

“…Methanol and EG are the most toxic additives, with an oral chronic reference dose (RfD) of 2 mg/day per kg of weight, whereas PG is far less toxic (RfD = 20 mg/kg/day) [9]. Organic additives have a possible indirect impact represented by the redox alteration of groundwater, which may trigger the mobilization of heavy metals [10], as observed in several airports where these compounds are used as deicing agents [11,12]. On the other hand, calcium chloride has a negligible toxicity [13] and no groundwater potential chemical impact (in the case of a release into subsurface) other than an increase of Ca 2+ and Cl − ions.…”