Microbes and Biodiesel

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The UK Renewable Transport Fuel Obligation Programme will, from April 2008, place an obligation on fuel suppliers to ensure that a certain percentage of their aggregate sales is made up of biofuels. Many major fuel suppliers are now introducing biodiesel blends into their fuel distribution networks on a scale far more widespread than has been seen to date. Although there has been experience in other European countries, we have a suspicion that the full impact of this implementation, in terms of the potential for microbiological contamination and growth, has not been fully appreciated.

Whilst there has been considerable focus on the operational and technical challenges presented by the introduction of bioethanol in gasoline, there has perhaps not been so much focus on the issues surrounding biodiesel. Biodiesel is degraded by microbes rapidly; some estimates put degradation rates at double those seen for conventional mineral diesel. This is potentially a good prospect in terms of the impact on the environment in the event of fuel spills, but there are also implications for the stability of diesel in storage. Wherever water gets into fuel, even in small amounts, microbial growth can be promoted. The resultant biomass produced can lead to serious fuel quality problems and operational issues (e.g. corrosion and filter clogging) for retailers and end-users. We can anticipate faster microbial growth in fuel tanks containing biodiesel blends. Anecdotal evidence and reported operational experiences back up our own investigations which suggest there is an increase in microbially related operational and quality issues associated with biodiesel. However, the issue may not be quite as simple as it first seems and there are contradictory factors at play . Biodiesel is hygroscopic, and it will have a tendency to scavenge free water from the fuel distribution network. Microbes need free water and hence, in some circumstances, introduction of biodiesel could reduce opportunities for microbiological growth. The Energy Institute (Inst. of Petroleum) Microbiology Committee, chaired by ECHA Director Graham Hill, is undertaking a project to fully assess the likely influence of biofuels on microbiological growth in fuel distribution and use. Its findings will hopefully be published later this year.

Some have seen continuous biocide use as the solution to the problem. In some cases this may be warranted but we stess the importance of fully appraising the impact of biocide use. Biocides do not necessarily make a bad situation better and adding biocides to heavily contaminated tanks can initially increase levels of particulates, both in the treated tank (if not cleaned) and in tanks downstream which receive biocide treated fuel. There is undoubtedly a place for biocide use where problems occur and indeed we are happy to recommend and supply biocide as required. In most cases we recommend GrotaMar71 on account of its widespread acceptability, fast action and relative ease of application and dispersion. But we believe use of biocides should not negate an emphasis on basic good housekeeping for terminal, depot and retail site tanks. We also believe microbiological monitoring of tanks and trend analysis is a key to succesful control. The monitoring programme need not be onerous and can be accomplished either by use of on-site tests, such as MicrobMonitor2, or by sending samples to a competent laboratory with expertise in fuel microbiology.

Please contact us if you would like to discuss the implications of biodiesel on your operations. We can offer a range of products and technical services to help you stay on top of microbiological contamination.