Evaluation of Antimicrobials in Liquid Fuels Boiling Below 390°C (ASTM E1259-23 Standard).

Test not accredited in our laboratory.

This standard is designed to evaluate antimicrobial agents to prevent liquid fuel deterioration caused by problems associated with uncontrolled microbial growth in fuels and fuel systems. Treatment with effective antimicrobial agents is one element of a fuel contamination control strategy. This procedure should be used to evaluate the relative effectiveness of microbicides on liquid fuels boiling below 390°C. The effect of certain conditions, such as various fuel additives, metal surfaces, and environmental conditions, are variables that can be included in specific tests using this protocol, when required by the client.

Tests use the required number and capacity of microcosms, in duplicate, for each control and each test treatment. Controls can include any combination of filter-sterilized test fuel over filter-sterilized water, and reference fuel (supplied by the client) without microbicides and tested over water. Some commercially available fuels contain additives with antimicrobial properties that must be filtered through activated carbon filters before use for microbicide performance testing. Microbicide-treated fuel (supplied by the client) placed over background water can be used as a positive reference control.

Tests can be conducted with a single dose or multiple doses (dose range). Typically, the minimum and maximum doses permitted by the microbicide registration are used. To compare cost-effectiveness, dose selection can be based on the treatment costs of the microbicide with which the test product is being evaluated.

To determine the number of microcosms required for the test matrix, the total number of control and test treatments and the number of replicate microcosms used (usually duplicates) must be taken into account. The microcosm volume for preliminary screening of the microbicidal product can be carried out in 1 or 2 liter microcosms, with a fuel-to-water ratio of 1000:1, although fuel-to-water ratios between 50:1 and 500:1 can also be used (at the client's discretion), depending on factors such as sample availability and the volume of the test system available.

Any type of isolated or associated microorganism can be used, but the standard recommends some that can use fuel alone as the sole carbon source: Pseudomonas aeruginosa, Hormoconis resinae, and Candida viswanathi (syn. Candida tropicalis and Yarrowia tropicalis).

All fuel types covered by this standard have vapor pressures high enough to release harmful and potentially toxic volatile organic carbon (VOC) molecules, so they are used inside a fume hood for small fuel:water ratios (50:1). For higher fuel:water ratios, e.g., 500:1, a closed microcosm with an extraction system for vapor removal through carbon filtration (not currently performed at IVAMI) must be used.

Depending on the intended end application, as specified by the client, the composition of the bottom water can vary from distilled water (simulating the accumulation of condensed water) to seawater. Since the chemical composition of the bottom water varies considerably between fuel tanks, site-specific testing must be performed using filter-sterilized water from the fuel tanks (provided by the client).

The client can specify whether they wish to determine the rate of elimination or the rate of elimination. Samples are taken during the test at the indicated times, such as after 30 minutes, 4, 8, 16, 24, 48, and 72 hours. The persistence of the effect can also be assessed, with samples taken periodically at daily, weekly, or monthly intervals, or until the microcosm with the maximum dose of microbicide fails (as requested by the client).

Tests for fuel biodeterioration, corrosion, or changes in the chemical distribution of its component molecules are not performed in our laboratory.