Fumigation monitoring and modeling of hopper-bottom railcars loaded with corn grits

Authors: Brabec, Daniel - Dan; KALOUDIS, EFSTATHIOS - Centaur Analytics, Inc; ATHANASSIOU, CHRISTOS - University Of Thessaly; Campbell, James - Jim; AGRAFIOTI, PARASKEVI - University Of Thessaly; Scheff, Deanna; BANTAS, SOTIRIS - Centaur Analytics, Inc; SOTIROUDAS, VAILIS - Centaur Analytics, Inc

Submitted to: Journal of Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2022
Publication Date: 8/4/2022
Citation: Brabec, D.L., Kaloudis, E., Athanassiou, C., Campbell, J.F., Agrafioti, P., Scheff, D.S., Bantas, S., Sotiroudas, V. 2022. Fumigation monitoring and modeling of hopper-bottom railcars loaded with corn grits. Journal of Biosystems Engineering. 47:358-369. https://doi.org/10.1007/s42853-022-00148-8.
DOI: https://doi.org/10.1007/s42853-022-00148-8

Interpretive Summary: Transportation by rail accounted for ~25% of total US grain shipments and is the predominant method for long distance transport (>1,000 miles) of grain and grain-based commodities within the US. During rail transportation it is a common practice to fumigate commodities with phosphine to eliminate potential infestations and prevent infestations occurring during transportation. However, little information is available on the effectiveness of these treatments given that it is difficult to monitor gas concentrations over time in moving railcars. The efficacy of fumigations is likely to vary with railcar type and their gas-holding ability, environmental temperatures, airflow across the railcar during movement, and duration of transport. Recent commercial development of wireless phosphine measurement devices that can store data provides an opportunity to evaluate fumigations in railcars. These electronic devices were deployed on individual hopper bottom railcars shipping corn grits and data collected on gas concentration and temperature over time while moving from a grain mill to a processor. The hopper bottom railcars displayed good gas-holding abilities, with monitoring data confirming lethal levels of phosphine in the headspace above the grain in each railcar. Supplemental experiments to confirm model predictions using fumigation of grits in barrels revealed that lethal concentrations of phosphine could penetrate the commodity to depths of over 2 m. A computational fluid dynamics (CFD) model was evaluated as well and it provided estimates of the phosphine concentration and distribution which matched well the observed data. This study showed hopper bottom cars can hold the fumigant phosphine at concentrations and exposure times to provide pest suppression and that the CFD fumigation model can be successfully used for railcars and provide the inferences necessary to plan a judicious fumigation strategy for in-transit grain shipments.

Technical Abstract: Bulk railcars are a common method of moving commodities in the United States. Allowances are given for the practice of treating railcars with fumigates during transit because the routes are limited access and not on public roads. Recent technology has become available for monitoring phosphine gas (PH3) fumigation on railcars which log the phosphine concentration and temperature of the test point in the railcars. Industrial cooperators allowed for the monitoring of fumigations for two shipments of corn grit, which were being transported in hopper bottom railcars. Several sensing units were used in each railcar and spaced across the top layer. Data were collected during the eight-day trip from grain mill to processor. The phosphine concentrations at the top varied with time with phosphine spiking over 1600 ppm and gradually settling to over 300 ppm at the end of the eight days. Total gas dosage was estimated as concentration*time (CT) over the eight days as 115,000 and 125,000 ppm*hr at the top of each railcar. Because access to lower depths in the railcar were not available, supplement experiments were performed with small columns of corn grits (2.5 m height x 0.55 m dia) to test for phosphine below the top surface. A higher and lower phosphine treatments were applied to the columns. These tests found significant phosphine penetration into the bulk at 2 m depth with ~380 ppm after two days and going down to ~260 ppm after eight days with the high phosphine treatment. Bioassays of both phosphine susceptible and resistant, adult Rhyzopertha dominica (F.), lesser grain borer, and Tribolium castaneum (Herbst), red flour beetle, were included at both the surface (0 cm), 25 cm and 60 cm below the surface. All insect, at all locations, were dead after eight days. The railcar and the fumigation treatments were additionally modeled with a CFD simulation approach. The simulation models were shown to provide estimates of the phosphine concentration and distribution which matched well the observed data, validating the CFD approach as an efficient tool for future planning and analysis of similar fumigations.