Alternative Aircraft Anti-Icing Formulations with Reduced Aquatic Toxicity and Biochemical Oxygen Demand (2010)

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1-1 SECTION 1 INTRODUCTION The current research was conducted to identify alternative aircraft and pavement deicer and anti-icer formulations with improved environmental characteristics compared to currently used commercial products (2007). The environmental characteristics of primary concern are the biochemical oxygen demand (BOD) and aquatic toxicity of the fully formulated products. Except when the distinction among products is necessary for clarity, “deicer” will refer to aircraft-deicing fluids (ADFs), aircraft anti-icing fluids (AAFs), and pavement- deicing materials (PDMs). A previous report presented the results of the first phase of the research, consisting of a review of available literature and data, and the results of laboratory analyses of commercial aircraft and airfield pavement deicers(1). These analyses characterized the oxygen demand and aquatic toxicity of the commercial products, and identified the relative contribution of constituent components to these characteristics. This current report presents the results of the second phase of the research, wherein candidate alternative components were evaluated and mixtures were built up through a progressive series of performance and environmental testing and down-selecting. At the direction of the research panel, the research objectives in this phase were the development of a Type IV aircraft anti-icing fluid formulation with reduced toxicity compared to commercially available products, and identification of an additive for solid pavement deicers to reduce caking. The following activities were conducted to achieve these research objectives: • Candidate freezing-point depressants (FPDs), thickeners, surfactants, and corrosion inhibitors with improved environmental qualities were identified and compared to components of commercial aircraft deicers and anti-icers. • Laboratory analysis of the candidate components were conducted for oxygen demand and toxicity. • Candidate components were down-selected to identify a subset for use in building candidate formulations. • A series of testing and down-selecting of increasingly complex mixtures was conducted to arrive at a final formulation that is equivalent to, or better than current commercial formulations in terms of deicing performance and environmental characteristics. • Candidate anti-caking agents were identified and tested in solid FPD formulations to evaluate performance. • The environmental characteristics of the final formulations were determined. The procedures developed and applied in this research would be applicable to developing additive packages for formulations based on other FPDs.

ALTERNATIVE AIRCRAFT ANTI-ICING FORMULATIONS 1-2 Background The aviation industry faces a formidable combination of tasks in ensuring the safety of winter flight operations. These include removing ice and snow from aircraft surfaces, preventing ice and snow from accumulating on aircraft surfaces before takeoff, maintaining ice- and snow-free taxiways and runways, maintaining flight schedules, and minimizing the environmental impact of aircraft and airfield deicer and anti-icer formulations through deicer-runoff management programs. The industry has made steady progress over the past two decades in collecting and containing deicing runoff; however, a more comprehensive and more practical approach to reducing the environmental impacts of deicers includes reducing BOD and the potential toxic impact of components in the products and, by extension, in discharges to the environment. Deicer manufacturers have made progress to reduce these impacts in formulations within recent years, but BOD and aquatic toxicity in deicing runoff entering receiving waters continues to be a concern. FPDs in ADFs and AAFs are most commonly propylene glycol or ethylene glycol, or, rarely, diethylene glycol (DEG). New formulations have appeared in recent years using glycerol and 1,3-propandiol, although their use is currently limited. ADFs and AAFs also contain water and various additives, collectively referred to as the “additive package,” which enhance the fluids’ performance and are required to meet strict Society of Automotive Engineers (SAE) international performance standards(2). Classes of chemicals in additive packages include corrosion inhibitors, surfactants, thickeners, dyes, flame retardants, defoamers, and pH buffers (3, 4). Although it is recognized that the primary source of BOD in all aircraft and airfield deicers is the FPD, the source of toxicity has not been as clear. The first phase of this research found that aquatic toxicity in aircraft deicers is associated with additives, principally polyethoxylated nonionic surfactants, including both alkyphenol ethoxylate surfactants and aliphatic alcohol ethoxylate surfactants. In the case of one Type IV aircraft anti-icer, triazole- based corrosion inhibitors were also implicated as contributing significantly to toxicity, although this class of chemicals is being phased out of commercial formulations. Toxicity in pavement deicers was found to be associated primarily with the FPDs in those products. Objectives of the Phase 2 Research The primary objective of the Phase 2 research was to identify and characterize commercially viable alternative deicing formulations with reduced aquatic toxicity and BOD and to generate a data base for use by the air transport industry. Another objective was to present this information to chemical manufacturers so they could use it to produce more environmentally friendly deicing formulations and to aircraft operators so they could look at alternatives for meeting discharge requirements. Report Structure Section 2 presents a summary of the rationale for the selection of alternative candidate aircraft and runway deicing/anti-icing components evaluated in the test program. The components included FPDs, thickeners, surfactants, corrosion inhibitors, anti-caking agents and other additives.

SECTION 1—0BINTRODUCTION 1-3 A summary of the test plan used to evaluate the alternative components is presented in Section 3. The test program was divided into two parts: Tier 1 and Tier 2. Tier 1 testing evaluated pure components and mixtures of pure components with water. Candidate components were down-selected for Tier 2 testing that involved more-complex mixtures. After evaluation of the Tier 1 results, Tier 2 tests were redirected to focus on aircraft Type IV anti-icing formulations and sodium formate runway deicers. Details of the Tier 1 experimental results are presented in Section 4 and the Tier 2 results in Section 5, including a summary of the aquatic toxicity results for the final Type IV formulation. Degradation pathways for the deicing components are detailed in Section 6. Conclusions of the study are presented in Section 7, and suggested future research topics are provided in Section 8.