1. Biochemical Basis for Environmental Management of Aircraft Deicing Fluid Waste Using Vegetation Sigifredo Castro (1), Lawrence C. Davis (2), Larry E. Erickson (1) (1) Department of Chemical Engineering and (2) Department of Biochemistry, Kansas State University, Manhattan, KS Phytoremediation can be employed as a natural and feasible strategy for treating the waste generated by aircraft deicing operations. The environmental concern is due to the high oxygen demand of ethylene glycol (EG) and propylene glycol (PG) and the toxicity associated with corrosion inhibitors, such as benzotriazole (BT) and methyl-benzotriazole (MBT). Land application of this waste can take advantage of vegetation by two mechanisms: enhancement of EG and PG biodegradation by the rhizosphere effect and transformation of BTs by plant enzymatic activities. This study focused on the uptake of BTs in hydroponic culture of sunflowers (Helianthus annuus L.). Introduction Find toxicity thresholds for plants to EG and BTs Estimate kinetic parameters for phytotransformation of different BTs Establish the rate-controlling mechanism by comparing rates of phytotransformation under different environmental conditions Determine whether phytotransformation is linked to photosynthesis and /or plant metabolism Evaluate effect of temperature and estimate activation energy Confirm observations on uptake and fate of BTs in plants by experimenting with 14 C-MBT Objectives For benzotriazoles: Detector: UV ( 275 nm) Eluent: methanol/water Column: Polymeric Reverse Phase EG: Indirect analysis by oxidation Detector: UV (260 nm) Eluent: Acidified sodium periodate Reaction: 4 min, 65°C, on high- density polyethylene tubing Aqueous solutions analyzed by HPLC: Analytical Methods Effect of lighting period Experimental methodology Plant: Sunflower Artificial lighting: 40-watt cool white fluorescent light Media: -Sandy top soil mixed with vermiculite -Hydroponics in Hoagland ’ s solution  reduce water uptake during dark 12h Effect of temperature T = 18°C Cooling Circulator Heating pump T = 24°CT = 31°C Effect of induced convection Magnetic Stirrers  Reduce mass transfer resistance  Determination of activation energy for transformation Toxicity Thresholds Ethylene and propylene glycol: Healthy plant growth for aerobic conditions: EG concentration < 2 g/L in soil solution, drip irrigation, Hoagland’s 1X solution supplied. No accumulation of EG in soil and possible plant uptake leading to accumulation in leaves. Benzotriazoles: Healthy plant growth for concentrations < 100 mg/L in soil solution Hoagland’s 1X solution supplied Concentration decreased with time. For continuous feeding, plants reached a “steady-state” condition, lower than dose concentration. Loss of benzotriazole was greater than water uptake  disappearance due to an active uptake process Insignificant recovery of MBT from plant material by methanol extraction  irreversibly binding and/or change in chemical structure Triazole concentration Linear Michaelis-Menten Experimental data -20 0 20 40 60 80 100 120 140 050100150200250300350400450500550 Average triazole concentration (μmol / L) Influx (μmol / kg.hr) (a) MBT Phase 1 I max = 384 μmol / hr.kg K M = 503 μmol / L R 2 = 0.930 During dark period, evapo- transpiration was reduced but triazole uptake did not stop  phytotransformation in/on the roots and not directly linked to photosynthesis. Apparent kinetics fitted a Michaelis-Menten model. Large variation in parameters (K M, I max ) among treatments and stages of plant growth. Normalizing the rates by plant fresh weight was not successful. Phytotransformation Kinetics and Photoperiod 0 1 2 3 4 5 6 7 8 9 0123456 Elapsed time (days) Total mg triazole lost / mg triazole lost by water uptake BTTTMBTMBT12 Estimated activation energy ranged from 24 to 69 kJ/mol (18 to 30 °C)  process is kinetically limited. Decrease in activation energy with plant age and plant size. Stirring improved growth  better aeration and nutrient uptake, higher temperature (23°C vs. 26°C). Phytotransformation rates normalized to plant fresh weight were similar. Effect of Stirring and Temperature Methanol soluble by-products, more polar than the MBT, corresponded to 77% of the recovered material. Remaining 23 % irreversibly bound to the plant structure, with the majority (85 %) located in the roots. Phytotransformation confirmed with 14 C-MBT. About 46% of estimated losses were recovered. Preliminary Study with 14 C-MBT When enough nutrients are supplied and at concentrations less than 100 mg/L, BTs are phytotransformed into a soluble fraction and a bound fraction located mostly in the roots. Phytotransformation followed Michaelis-Menten kinetics, occurred on the roots, was not directly linked to the photosynthetic activity or plant transpiration, and was not diffusion-limited. Phytotransformation of BTs is the most promising biological treatment technology since microbial degradation in waste water treatment has not been demonstrated. Main Findings Castro, S., L. Davis, and L. Erickson, “Plant-enhanced remediation of glycol-based aircraft deicing fluids,” Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management, 5, 3, 141-152, 2001. Castro, S., L. Davis, and L. Erickson, “Phytotransformation of benzotriazoles,” International Journal of Phytoremediation, 5, 3, 245- 265, 2003. References