ADAF Research Articles

Research on the Heating of Deicing Fluid in a New Reshaped Coiled Tube

Aircraft ground deicing operation is significant to ensure civil flight safety in winter. Helically coiled tube is the important heat exchanger in Chinese deicing fluid heating system. In order to improve the deicing efficiency, the research focuses on heat transfer enhancement of deicing fluid in the tube. Based on the field synergy principle, a new reshaped tube (TCHC) is designed by ring-rib convex on the inner wall. Deicing fluid is high viscosity ethylene-glycol-based mixture. Because of the power function relation between high viscosity and temperature, viscosity has a negative influence on heat transfer. The number of ring-ribs and inlet velocity are two key parameters to the heat transfer performance. For both water and ethylene glycol, the outlet temperature rises when the number of ring-ribs increases to a certain limit. However, the increasing of velocity reduces heating time, which results in lower outlet temperature. The heating experiment of the original tube is conducted. The error between experiment and simulation is less than 5%. The outlet temperature of TCHC increases by 3.76%. As a result, TCHC efficiently promotes the coordination of velocity and temperature fields by changing the velocity field. TCHC has enhanced heat transfer of high viscosity deicing fluid.

Numerical simulation and experimental validation of aircraft ground deicing model

Aircraft ground deicing plays an important role of guaranteeing the aircraft safety. In practice, most airports generally use as many deicing fluids as possible to remove the ice, which causes the waste of the deicing fluids and the pollution of the environment. Therefore, the model of aircraft ground deicing should be built to establish the foundation for the subsequent research, such as the optimization of the deicing fluid consumption. In this article, the heat balance of the deicing process is depicted, and the dynamic model of the deicing process is provided based on the analysis of the deicing mechanism. In the dynamic model, the surface temperature of the deicing fluids and the ice thickness are regarded as the state parameters, while the fluid flow rate, the initial temperature, and the injection time of the deicing fluids are treated as control parameters. Ignoring the heat exchange between the deicing fluids and the environment, the simplified model is obtained. The rationality of the simplified model is verified by the numerical simulation and the impacts of the flow rate, the initial temperature and the injection time on the deicing process are investigated. To verify the model, the semi-physical experiment system is established, consisting of the low-constant temperature test chamber, the ice simulation system, the deicing fluid heating and spraying system, the simulated wing, the test sensors, and the computer measure and control system. The actual test data verify the validity of the dynamic model and the accuracy of the simulation analysis.

Electrolyte Effects on Polyacrylic Acid-Polyvinylpyrrolidone Aqueous Glycol Mixtures for Use as De-Icing Fluids

Rheological and wind tunnels measurements are presented for mixtures of polymer polyacrylic acid [PAA] and polyvinylpyrrolidone [PVP] polymers dispersed in water-1,2 propylene glycol mixture to examine their use as potential aircraft de-icing fluids. PAA solutions which form the basis of de-icing fluids are known to result in undesirable gelation which may lead to undesirable and catastrophic consequences in such applications. In this study, we examine the blending of PVP with PAA blends as alternative de-icing fluid formulations that can reduce the likelihood of forming such irreversible gel deposits. Through adjustment of the electrolyte concentration, the ratio of PAA to PVP as well as the molecular weight of PVP, it is possible to achieve a required viscosity profile to that exhibited by a model de-icing fluid across a range of appropriate temperatures. Wind tunnel tests indicate that the mixtures are capable of meeting the necessary requirements for boundary layer depletion as well as having sufficient capability of retaining a stable layer required during aircraft taxiing.

Aerodynamic Effects of Anti-Icing Fluids on a Thin High-Performance Wing Section

The Federal Aviation Administration has worked with Transport Canada and others to develop allowance times for aircraft operating in ice-pellet precipitation based upon wind-tunnel experiments with a thin high-performance wing. These allowance times are applicable to many different airplanes. Therefore, the aim of this work is to characterize the aerodynamic behavior of the wing section in order to better understand the adverse aerodynamic effects of anti-icing fluids and ice-pellet contamination. Aerodynamic performance tests, boundary-layer surveys, and flow visualization were conducted at a Reynolds number of approximately and a Mach number of 0.12. Roughness and leading-edge flow disturbances were employed to simulate the aerodynamic impact of the anti-icing fluids and contamination. In the linear portion of the lift curve, the primary aerodynamic effect is the thickening of the downstream boundary layer due to the accumulation of fluid and contamination. This causes a reduction in lift coefficient and an increase in pitching moment (nose up) due to an effective decambering of the wing. The stalling characteristics of the wing with fluid and contamination appear to be driven at least partially by the effects of a secondary wave of fluid that forms near the leading edge as the wing is rotated in the simulated takeoff profile. These results have provided a much more complete understanding of the adverse aerodynamic effects of anti-icing fluids and ice-pellet contamination on this wing.

Understanding and managing de-icer contamination of airport surface waters: A synthesis and future perspectives

De-icers containing propylene glycol and potassium acetate are a major source of organic pollution in airport surface waters. Direct discharges of these pollutants into receiving waters, even at very low concentrations, can result in detrimental environmental impacts and may breech regulatory requirements. The airport operator is responsible for devising a de-icer management plan (DMP) which outlines the pollution prevention strategies adopted to manage contaminated runoff. This poses one of the most significant environmental management challenges in the aviation sector. Within this review article, we conceptualise the transport and fate of de-icing fluids in the environment and consider the implications for management of runoff from airports. We examine the treatment technologies that are currently incorporated into DMPs in the aviation industry. Finally, we review the current application of subsurface flow treatment wetlands, an eco-innovative technology for advanced treatment of industrial strength wastewaters, and consider priorities for future research related to this emerging technology.

Bubbly Two-Phase Flow: Part I- Characteristics, Structures, Behaviors and Flow Patterns

An important topic in fluid dynamics is multiphase flows. Multiphase flows can be found in numerous fields in engineering, e.g. aerospace, biomedical, chemical, electrical, environmental, mechanical, materials, nuclear and naval engineering. There is an enormous variation in applications, e.g. rocket engines, chemical reactors, contamination spreading, multiphase mixture transport, cavitation, sonoluminescence, ink-jet printing, particle transport in blood, crystallization, multiphase cooling, fluidized beds, drying of gases, air entrainment in oceans/rivers and anti-icing fluids. The number of papers on multiphase flow in the field of fluid dynamics is enormous and still growing. The diversity of flow types makes a general description almost impossible. This makes fundamental research necessary. Especially, controlled experiments are needed for a better physical understanding and as test cases for numerical and theoretical work. The purpose of this paper is the desire to demonstrate, review and summarize the major finding of the previous research of bubbly two-phase flow characteristics, structures, behaviors and flow patterns. Moreover, to elucidate some important models and techniques to measure the two-phase bubbly flow parameters such as bubble motion, flow regime, bubble shape which play a considerable role in many engineering applications.

Treatment performance of an aerated constructed wetland treating glycol from de-icing operations at a UK airport

Mayfield Farm Treatment System receives effluent collected from the Southern Catchment of Heathrow Airport, a total of 290ha. During winter operations, weather-related de-icing activity results in large shifts in the flow and concentrations of airport run-off. The biological treatment of spent de-icing fluids is challenging because it involves the treatment of a cold and nutrient-deficient wastewater of variable flow and strength. After a successful full scale trial to determine the efficacy of aerated wetlands, the entire treatment system was upgraded and optimized in 2010. It consisted of a primary reservoir, partial and complete mix zones, a balancing lagoon, and 12 aerated horizontal sub-surface flow (HSSF) treatment wetlands operating in parallel, with a total wetland area of 2.08ha. The original non-aerated HSSF wetland system, commissioned in 2001 had a design cBOD5 loading rate of 374kg/day at a flow rate of 40l/s (Revitt et al., 2001; Richter et al., 2003). The aerated HSSF wetlands now have a design cBOD5 loading rate of 2073kg/day at a maximum flow rate of 80l/s. Due to the weather conditions of the UK, the system is event-driven with highly variable flows and loads, with peak cBOD5 loadings of up to 12,188kg/day.The entire treatment system is now designed to remove 3500kg/day cBOD5 at a design flow of 40l/s. It has a combined capacity of >44,000m3 of wastewater with a retention time of approximately 21 days, depending on the pump flow rate which varies between 40 and 80l/s. Nutrient dosing points have been positioned at strategic points throughout the whole system to prevent nutrient deficiency becoming a limiting factor in the development of a stable and viable mass of bacteria necessary to achieve the design criteria.

Vertical and horizontal distributions of microbial abundances and enzymatic activities in propylene-glycol-affected soils

The natural microbial activity in the unsaturated soil is vital for protecting groundwater in areas where high loads of biodegradable contaminants are supplied to the surface, which usually is the case for airports using aircraft de-icing fluids (ADF) in the cold season. Horizontal and vertical distributions of microbial abundance were assessed along the western runway of Oslo Airport (Gardermoen, Norway) to monitor the effect of ADF dispersion with special reference to the component with the highest chemical oxygen demand (COD), propylene glycol (PG). Microbial abundance was evaluated by several biondicators: colony-forming units (CFU) of some physiological groups (aerobic and anaerobic heterotrophs and microscopic fungi), most probable numbers (MPN) of PG degraders, selected catabolic enzymatic activities (fluorescein diacetate (FDA) hydrolase, dehydrogenase, and β-glucosidase). High correlations were found between the enzymatic activities and microbial counts in vertical soil profiles. All microbial abundance indicators showed a steep drop in the first meter of soil depth. The vertical distribution of microbial abundance can be correlated by a decreasing exponential function of depth. The horizontal trend of microbial abundance (evaluated as total aerobic CFU, MPN of PG-degraders, and FDA hydrolase activity) assessed in the surface soil at an increasing distance from the runway is correlated negatively with the PG and COD loads, suggesting the relevance of other chemicals in the modulation of microbial growth. The possible role of potassium formate, component of runway de-icers, has been tested in the laboratory by using mixed cultures of Pseudomonas spp., obtained by enrichment with a selective PG medium from soil samples taken at the most contaminated area near the runway. The inhibitory effect of formate on the growth of PG degraders is proven by the reduction of biomass yield on PG in the presence of formate.

Poly(acrylic acid)–poly(vinyl pyrrolidone)-thickened water/glycol de-icing fluids

In this study we consider the use of poly(vinyl pyrrolidone) (PVP) in conjunction with poly(acrylic acid) (PAA) as a thickener for water/glycol solutions. PAA in water/glycol formulations has wide application in the aviation industry for aircraft de-icing and prevention of ice build-up. Routinely sprayed onto the surface of wings and fuselage of aircraft in winter, they are designed to be retained on surfaces under zero shear and actively removed under high shear corresponding to take-off velocities. PAA deposited in aerodynamically quiet regions can produce gel deposits which have adverse effects on the performance of aircraft control systems. In this study we examine the rheological properties of solutions produced using a combination of PAA with PVP, with the aim of reducing the sensitivity of the solutions to added electrolytes. Various PVP–PAA formulations were examined rheologically and in a wind tunnel, across a range of sub-zero temperatures. The conclusions were that these blends can be used as alternative de-icing fluids. In these fluids, hydrogen bonding between the PVP and the PAA achieves the required level of polymer–polymer interactions to exhibit viscoplastic flow at lower electrolyte content. Gels which are formed are less stable that those formed with PAA alone.

The distribution, fate, and effects of propylene glycol substances in the environment.

The propylene glycol substances comprise a homologous family of synthetic organic molecules that have widespread use and very high production volumes across the globe. The information presented and summarized here is intended to provide an overview of the most current and reliable information available for assessing the potential environmental exposures and impacts of these substances across the manufacture, use, and disposal phases of their product life cycles.The PG substances are characterized as being miscible in water, having very low octanol-water partition coefficients (log Pow) and exhibiting low potential to volatilize from water or soil in both pure and dissolved forms. The combination of these properties dictates that, almost regardless of the mode of their initial emission, they will ultimately associate with surface water, soil, and the related groundwater compartments in the environment. These substances have low affinity for soil and sediment particles, and thus will remain mobile and bio-available within these media.In the atmosphere, the PG substances are demonstrated to have short lifetimes(I. 7-11 h), due to rapid reaction with photochemically-generated hydroxyl radicals.This reactivity, combined with efficient wet deposition of their vapor and aerosol forms, lends to their very low potential for long-range transport via the atmosphere.In the aquatic and terrestrial compartments of the environment, the PG substances are rapidly and ultimately biodegraded under both aerobic and anaerobic conditions by a wide variety of microorganisms, regardless of prior adaptation to the substances.Except for the TePG substance, the propylene glycol substances meet the OECD definition of "readily biodegradable", and according to this definition are not expected to persist in either aquatic or terrestrial environments. The TePG exhibits inherent biodegradability, is not regarded to be persistent, and is expected to ultimately biodegrade in the environment, albeit at a somewhat slower rate. The apparent ease with which microorganisms and higher organisms can metabolize the PG substances, along with their low log Pow and very high water solubility values, portends them to have very low potential for bioaccumulation and/or biomagnification in aquatic and terrestrial organisms. These same properties, along with their neutral structures and lack of biological reactivity, are the reasons for which the PG substances exhibit a base-line, non-polar narcosis mode of toxicity.The PG substances have been shown here to be practically non-toxic to essentially every aquatic and terrestrial animal and plant species tested. Collectively, the available wealth of information relating to persistence, bioaccumulation, and eco-toxicity of these substances allows a definitive conclusion of their categorization as not being PBT (i.e., persistently bioaccumulative/toxic). The PBT screening and categorization of substances on the Canadian Domestic Substances List (DSL) by Environment Canada has formally concluded that each member of this substance family is "not P", "not B", and "not T' according to their associated PBT criteria.Similarly, the preceding evaluations of these high production volume substances within the OECD SIDS program concluded that MPG, DPG, and TPG are low priorities for further examination of potential impacts to humans and the environment.More extensive evaluations of potential risks to human health and the environment were recently completed by industry, as required for their registration under the European Union REACh legislation; each evaluation demonstrated that current uses, associated exposures, and controls thereof, will not result in exposures that exceed predicted no effect concentrations in the environment.

Scaling of Lift Degradation Due to Antiicing Fluids

In recent years, North American civil airworthiness authorities have conducted research to develop the allowance times for aircraft operations in ice-pellet precipitation. These allowance times are critical to ensure the safety and efficient operation of commercial and cargo flights. Wind-tunnel testing with uncontaminated antiicing fluids and fluids contaminated with simulated ice pellets has been carried out to better understand the flowoff characteristics and resulting aerodynamic effects. The percent lift loss was determined at an 8 deg angle of attack and used as one of the evaluation criteria in determining the allowance times. This paper describes how the lift loss was related to the loss in the maximum lift of a Boeing 737-200ADV airplane through the aerodynamic acceptance test performed for fluids qualification. A loss in the maximum lift coefficient of 5.24% on the B737-200ADV airplane (which was adopted as the threshold in the aerodynamic acceptance test) corresponds to a lift loss of 7.3% on the test model at an 8 deg angle of attack. A statistical analysis was performed to account for data scatter in the correlation and indicated that the upper limit of lift loss on the test model was 9.2%. Therefore, for cases resulting in lift loss from 7.3 to 9.2%, extra scrutiny of the visual observations is required for evaluating fluid performance with contamination and establishing appropriate allowance times.

Natural and enhanced biodegradation of propylene glycol in airport soil

Aircraft de-icing fluids (ADF) are a source of water and soil pollution in airport sites. Propylene glycol (PG) is a main component in several commercial formulations of ADFs. Even though PG is biodegradable in soil, seasonal overloads may result in occasional groundwater contamination. Feasibility studies for the biostimulation of PG degradation in soil have been carried out in soil slurries, soil microcosms and enrichment cultures with and without the addition of nutrients (N and P sources, oligoelements), alternative electron acceptors (nitrate, oxygen releasing compounds) and adsorbents (activated carbon). Soil samples have been taken from the contaminated area of Gardermoen Airport Oslo. Under aerobic conditions and in the absence of added nutrients, no or scarce biomass growth is observed and PG degradation occurs by maintenance metabolism at constant removal rate by the original population of PG degraders. With the addition of nutrient, biomass exponential growth enhances aerobic PG degradation also at low temperatures (4°C) that occur at the high season of snowmelt. Anaerobic PG degradation without added nutrients still proceeds at constant rate (i.e. no biomass growth) and gives rise to reduced fermentation product (propionic acid, reduced Fe and Mn, methane). The addition of nitrate does not promote biomass growth but allows full PG mineralization without reduced by-products. Further exploitation on the field is necessary to fully evaluate the effect of oxygen releasing compounds and adsorbents.

Reverse selective NH3/CO2 permeation in fluorinated polymers using membrane gas separation

The analysis of the process of gas and vapour permeation through dense polymers is of primary importance for packaging, controlled release and membrane separation processes. A significant amount of polymer permeability data has already been reported, especially for permanent gases, such as N2, O2, H2, CH4 and CO2, although a very small amount of data is available for ammonia (NH3). In this case, the experimental results show the faster permeation of NH3 in comparison to CO2, which is in agreement with the solution diffusion model predictions. NH3 is smaller and more condensable than CO2. In this study, the solubility, diffusion coefficient and permeability of NH3, CO2 and N2 in ten different polymers were investigated between 5 and 50°C. A reverse NH3/CO2 permeation selectivity is occasionally observed for dense fluorinated polymers (PTFE, FEP, Hyflon AD and Teflon AF). This unusual behaviour is interpreted in the light of the diffusion and sorption coefficients obtained from time lag experiments which tend surprisingly to show in fluorinated polymers: a NH3/CO2 solubility selectivity systematically lower than expected by the usual correlations and, in some cases, lower diffusion coefficients for NH3 than for CO2. This peculiar result is interpreted from the differences between NH3 and CO2 interactions with fluorine atoms, similarly to the differential solubility phenomena of these two species which have previously been clearly established in fluorinated liquids.

Rheology of Poly(acrylic acid) in Water/Glycol/Salt Mixtures

Aqueous mixtures of 1,2-propylene glycol with added poly(acrylic acid), neutralized and with added salt, are used for aircraft deicing. This study reports data on the effects of varying the salt concentration, architecture, and temperature of a series of different mixtures. For a deicing fluid to be effective, it is desirable that it be able to create a liquid layer that is stable under low-shear conditions yet can be completely removed during the initial stages of takeoff. A number of the mixtures examined show a viscosity profile that is either almost independent of temperature or exhibits a peak. To gain a greater understanding of the factors responsible for the observed rheological behavior, a theoretical model was fitted to oscillatory data. Using two fitting parameters, it was possible to describe the changes in the observed behavior, suggesting that, as the temperature is varied, the extent of shielding of carboxylic acid groups and the conformation of the chain balance one another to give an apparent temperature independence of the viscosity. The rheological data were used to interpret the boundary-layer displacement thickness data obtained from wind-tunnel measurements.

Study on De-Icing Fluid Pump Station’s Flow Pulsation Suspension Methods

This article studies the flow pulsation of de-icing fluid pump station. First, find the factors affect the extent of flow pulsation through kinetics analysis. Then, base on the summary of the existing pulsation suspension methods (Include combining work of several pumps with an equal original phase differences, changing a single acting pump with a double acting pump), we put forward the method by optimizing the structure of the reciprocating pump to inhibit the flow pulsation. Use system simulation software AMESim to simulate the effect of these methods. Ultimately get the conclusion that the flow pulsation can be controlled at about 12% through these methods. All these works may provide a reference for the design of a de-icing fluid pumping station.

Properties of rigid polyurethane foams prepared from recycled aircraft deicing agent with hexamethylene diisocyanate

AbstractPolyurethane (PUR) rigid foams were prepared from recycled aircraft deicing agent (aircraft deicing fluid) with reaction of hexamethylene diisocyanate at temperature of 55°C. The effect of [NCO]/[OH] ratio on properties of microscopic structure, cell size distribution, compressive strength, apparent density, as well as thermal conductivity (k) was studied. Higher [NCO]/[OH] ratio helped achieve better micromorphology, higher apparent density, and compressive strength of the PUR foams. With the [NCO]/[OH] ratio of 0.75 and 0.8, some shrinking happened during foam rising, causing a decrease in total volume of the PUR foam, and leading to higher apparent density as well as sharply increased compressive strength. All PUR foams displayed good thermal insulation properties in this study. With [NCO]/[OH] ratio increased from 0.7 to 0.8, the k value increased significantly from 34.3 to 42.2 mW m−1 K−1. The k value here was chiefly governed by the apparent density of the foams, which was in turn a function of the ratio of [NCO]/[OH]. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci., 2013

Seasonal source influence on river mass flows of benzotriazoles

The anticorrosive agents 1H-benzotriazole (1H-BT), 4-methyl-1H-benzotriazole (4 Me-BT) and 5-methyl-1H-benzotriazole (5 Me-BT), which are usually added to dishwasher detergents, automotive antifreeze formulations and aircraft de-icing/anti-icing fluids (ADAFs), were measured in river water. Samples were collected from 15 sampling sites in the mainstream and selected tributaries of a medium-sized catchment area during summer and winter periods. The aim of this study was to assess a seasonal source influence on mass flows of benzotriazoles (BTs). The study area was representatively selected for an area with a possible influence of airport surface runoff. River discharge measurements were also performed. Moreover, BT concentrations were measured in an anti-icing and a de-icing fluid used at German airports as well as in several dishwasher detergents. The highest concentrations of all three compounds in river water were measured during the winter seasons. The maximum BT mass flows were calculated for all three substances in January when the mean monthly air temperature was the lowest; mass flows were the lowest in July when the mean monthly air temperature was the highest. A significant seasonal influence on BT mass flows in river water was observed for monitoring stations with a possible influence of airport surface runoff and for sampling locations where such an influence could be excluded. This indicates an input of BTs from other temperature-dependent applications, e.g. the use of antifreeze formulations in automotive windscreen wiper or cooling systems. 1H-BT was detected in two dishwasher tablets; 4 Me-BT and 5 Me-BT were not detected. BTs were measured in the anti-icing fluid with concentrations of 715 ng g(-1) (1H-BT), 1425 ng g(-1) (4 Me-BT) and 536 ng g(-1) (5 Me-BT); none of the BTs were detected in the de-icing fluid. Distribution patterns of BTs in ADAF and dishwasher detergents differed from those in river water.

Acute and chronic toxicity of benzotriazoles to aquatic organisms

Resulting from their intensive use as corrosion inhibitors in aircraft deicing and anti-icing fluids (ADAF) and for silver protection in dishwasher detergents benzotriazoles (BTs) are widespread in European surface waters. The current study aimed on an ecotoxicological characterization of 1H-benzotriazole (1H-BT) and 5-methyl-1H-benzotriazole (5MBT). Acute and chronic OECD guideline tests were conducted with primary producers (Desmodesmus subspicatus, Lemna minor) and two daphnia species (Daphnia magna, Daphnia galeata) to characterize the hazard of these chemicals. Additionally, the estrogenic activity of both BTs was analyzed in vitro using a recombinant yeast estrogen screen (YES). Both BTs revealed significant effects in acute and chronic experiments, but exhibited no estrogenic activity in the YES. The algal growth test displayed an inhibited cell number increase with effect concentration (EC) values of EC(10) 1.18 and 2.86 mg l(-1) for 1H-BT and 5MBT, respectively. In the Lemna test, EC(10) values were 3.94 mg l(-1) (1H-BT) and 2.11 mg l(-1) (5MBT). D. magna was also affected with EC(50) (48 h) values of 107 mg l(-1) for 1H-BT and 51.6 mg l(-1) for 5MBT. D. galeata was more sensitive with an EC(50) (48 h) of 14.7 mg 1H-BT l(-1) and 8.13 mg 5MBT l(-1). In the 21-day reproduction tests with D. magna, the EC(10) for 5MBT was 5.93 mg l(-1) while 1H-BT showed no adverse effects. D. galeata turned out to be more sensitive in the chronic study with EC(10) values of 0.97 mg l(-1) for 1H-BT and 0.40 mg l(-1) for 5 MBT. Because BTs are regularly found in the aquatic environment at lower μg l(-1) concentrations reflecting their persistence and poor elimination during wastewater treatment processes, a preliminary risk assessment was conducted. There is little indication that BTs pose a risk for aquatic ecosystems at current exposure levels during most of the year. However, it cannot be excluded that in winter with a higher usage of ADAFs environmental concentrations may well exceed the level that is considered safe for aquatic organisms.

Laboratory-scale evaluation of a combined soil amendment for the enhanced biodegradation of propylene glycol-based aircraft de-icing fluids

A combined soil amendment was tested in microcosm experiments with an aim to enhance the aerobic biodegradation of propylene glycol (PG)-based aircraft de-icing fluids during and following the infiltration of contaminated snowmelt. A key objective under field conditions is to increase degradation of organic pollutants in the surface soil where higher microbial activity and plant rhizosphere effects may contribute to a more efficient biodegradation of PG, compared to subsoil ground layers, where electron acceptors and nutrients are often depleted. Microcosm experiments were set up in Petri dishes using 50 g of soil mixed with appropriate additives. The samples contained an initial de-icing fluid concentration of 10,000 mg/kg soil. A combined amendment using calcium peroxide, activated carbon and 1×Hoagland solution resulted in significantly higher degradation rates for PG both at 4 and 22°C. Most probable numbers of bacteria capable of utilizing 10,000 mg/kg de-icing fluid as a sole carbon source were about two orders of magnitude higher in the amended soil samples compared to unamended controls at both temperatures. The elevated numbers of such bacteria in surface soil may be a source of cells transported to the subsoil by snowmelt infiltration. The near-surface application of amendments tested here may enhance the growth of plants and plant roots in the contaminated area, as well as microbes to be found at greater depth, and hence increase the degradation of a contaminant plume present in the ground.

Analysis of Centralized Aircraft Deicing Process

This paper established a mathematical model for the centralized aircraft ground deicing processes which includes preparation, deicing operations and release after the deicing. To ensure the safety of aircraft, the proposed model has taken into account the constraint that the total time of deicing processes shall be less than the retention time of the deicing fluid so as to avoid secondary icing hazards. The proposed model has been verified through numerical simulations, where a first-come-first-service scheduling scheme is assumed. Simulation results show that the proposed model matches the current status of airport deicing very well.