LuminUltra, the microbial monitoring specialist, has highlighted important concerns over the quality of some compliant fuels as the shipping industry gears up towards meeting the International Maritime Organization's sulphur cap, which enters into force in January.

Commenting on the blending of biodiesel with HSFO and distillates, which go towards reducing the amount of SOx emitted during the combustion process, Patrick Taylor, LuminUltra's newly appointed Director of Global Business Development, said: "The addition of biodiesel will reduce the sulphur content, but ship operators do need to be aware this can result in increased microbial influenced corrosion (MIC). Less sulphur means more bugs."

Taylor pointed out that the high sulphur content of residual fuel has been an "excellent inhibitor", preventing the build-up of microbial growth and, consequently, the microbial induced corrosion of fuel tanks and systems.

"There is an increased biodiesel content in Marine Gas Oil (MGO) and we are seeing HSFO now being blended with recovered distillates to reduce the sulphur level. As biodiesel has a high water content, these new fuels can be nutrient-rich breeding grounds for microbiological growth. There are real risks, real safety concerns," he said.

MIC tends to fall into two camps: aerobic, where microbes require oxygen, and those that don't, anaerobic. Water is the elixir of life for both these types, with microbes requiring little to form colonies and expand.

Yet while there is still a lack of information on water absorbance in biodiesel/diesel blends, research has shown that at constant relative humidity, biodiesel absorbed 6.5 times more moisture than diesel.

Referring to a paper published in 2016, in Volume 108 of International Biodeteriation & Biodegradation, published in 2016 by Elsevier, Taylor said that a strain of fungus degraded biodiesel at "a phenomenal rate" and resulted in enhanced 1018 steel corrosion due to acidification.

"If compliant fuels are not regularly monitored for their microbiological content, then at the very least biofilm will form and clog up the fuel filters. In the worst case, if microbial growth goes unchecked, then we are likely to see an increase in rapid microbiological induced corrosion of even the most well-maintained fuel tanks and pipework."

Seaborne Communications