Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
7-1 SECTION 7 CONCLUSIONS This section presents the significant conclusions drawn from the findings of this research, organized by topic. General Conclusions A candidate alternative Type IV formulation was identified with significantly reduced toxicity compared to current use products. The final candidate formulation has aquatic toxicity values that are an order of magnitude or more improved over the least toxic commercial Type IV products tested. This formulation would need addition of a dye and additional certification testing that my warrant formulation modification. Toxicity identification techniques were successful in helping to improve the toxicity profile of alternative fluids. The Toxicity Identification Evaluation (TIE) approach used in evaluation of current-use products identified surfactants as the primary contributor to aquatic toxicity. Using this information to choose alternative surfactants resulted in a candidate Type IV formulation with substantially lower aquatic toxicity. The physical properties of the candidate alternative Type IV formulations were affected by interactions between the surfactants and thickeners. For diethylene glycol/water formulations containing the surfactant and thickener, the viscosity was only slightly lower than mixtures without the surfactant, while the thickener tends to increase the contact angle (or surface tension) over mixtures containing just the surfactant. For glycol/water formulations containing the surfactant and thickener, the viscosity was about 60-70 percent higher than without the surfactant, while there didnât appear to be an effect of the thickener on the contact angle. Numerous potential alternative components were identified. This research resulted in one candidate alternative Type IV formulations using several alternative components; however, numerous potentially viable alternative components were identified that have potential to improve environmental performance. Empirical testing with all possible alternatives was beyond the scope of this research, but this information could be used in future work attempting to formulate alternative deicers. The techniques used in identifying a less-toxic Type IV formulation have potential applicability to developing Type I formulations with reduced toxicity. The focus of the research was directed towards the identification of alternative Type IV formulations with significantly less toxicity than currently available products. The final candidate Type IV formulation is less toxic than the least toxic Type I commercial product currently in use, indicating that there is a potential for applying the same methods which led to substantial improvement in toxicity for Type IV formulations to reformulating Type I products. There is no current evidence to suggest that either the alternative FPD or thickener present significant concerns relative to degradation pathways and degradation products. The evidence in the literature suggests that the biodegradation by-products of the alternative surfactant and corrosion inhibitor may be have greater aquatic toxicity than the parent
ALTERNATIVE AIRCRAFT ANTI-ICING FORMULATIONS 7-2 products. Both of these additives are used in a wide range of products. Further investigation of concentrations resulting from degradation would be needed to fully evaluate this. The use of molecular modeling can significantly improve efficiency of the chemical product development process. The search for an improved formulation necessitated the evaluation of thousands of candidate components. Experimentally evaluating each of these candidates would have been costly and highly unproductiveâthe large majority of these candidates were not viable. Physical property estimation techniques were able to quickly and inexpensively evaluate these candidates computationally, selecting only the most promising compounds for experimental evaluation. Oxygen Demand ThOD is a good screening criterion for oxygen demand of freezing point depressants. The COD results for FPDs compared well with ThOD. Conventional BOD tests produced unreliable results for some of the FPDs. The success of BOD testing was highly variable and dependent on how well microorganisms acclimated to FPDs. COD was the most useful metric in down-selecting FPDs for oxygen demand. The reliance on COD was necessary because of the uncertainties encountered with BOD tests. FPDs are the predominant source of oxygen demand in all deicer formulations. The relative concentrations of all other components are so small that any contribution to oxygen demand is insignificant. No candidate FPD was found with potential for improvement of BOD characteristics compared to the least toxic current-use Type I fluids and pavement deicer formulations. Of the candidate FPDs with improved aquatic toxicity compared to Type I fluids and pavement deicers, BOD and COD were not improved compared to current-use products. DEG and glycerol were identified as promising alternative FPDs for Type IV fluid formulations. Of the FPDs with favorable performance characteristics, DEG and glycerol were the most promising candidates to provide improvements in aquatic toxicity and BOD characteristics as compared to current-use products. Concerns regarding the potential for glycerol to dry out and form residuals after application led to the selection of DEG as the preferred FPD. Parameters such as molecular weight, freezing point depression, application rates, and transport phenomena would need to be considered to gain a comprehensive understanding of the potential impact of PDMs on dissolved oxygen in receiving waters. These characteristics were recognized as potentially significant factors in the actual oxygen demand load from deicer applications, but further investigation of these properties was beyond the scope of this research. Aquatic Toxicity Screening-level toxicity testing identified potentially viable alternative components in each of the categories of FPDs, surfactants, corrosion inhibitors, and thickeners. Identified candidates included 7 FPDs, 11 surfactants, 9 corrosion inhibitors, and 6 thickeners.
SECTION 7â6BCONCLUSIONS 7-3 a reliable predictor of formulation toxicity. However, in several instances this was not the case, demonstrating the importance of laboratory confirmation of predictions based on theoretical values. Pavement Deicers There were apparent synergistic interactions between sodium formate and tripotassium citrate that increased absorption of water and cannot be readily explained. Resolution of the counter-intuitive results is beyond the scope of this investigation.
