Odour and ecotoxicity in water from fuels of varying content of non-fossil components: Odour threshold values, predictive modelling and ecotox data

The composition of vehicle fuels has changed since 2018 due to the reduction obligation, which requires that an increasing proportion of bio-based content is mixed into fossil fuels. Since properties such as odour and ecotoxicity are complex and depend on the composition of substances' mixtures, information based on older studies is not applicable. Odour properties are essential for drinking water producers, and ecotoxicity is vital for prioritising remediation efforts in the event of spillage.

The objectives of this study have therefore been to 1) quantify the composition of standard diesel and petrol fuels sold in Sweden, 2) quantify odour thresholds for these fuels in drinking water, 3) investigate the ecotoxicity from HVO (hydrogenated vegetable oil) and diesel with RME additive (rapeseed methyl ester), and 4) investigate whether it is possible to predict odour in water based on concentrations in a fuel/water mixture.In the study, a total of eight fuels were tested, of which four were diesel fuels (HVO 100, MK1 diesel with HVO, MK1 diesel with RME and MK1 diesel) and four contained petrol/ethanol to varying degrees (E85, E05, E10 with bio-petrol and E10). HVO 100 and MK1 diesel with RME were used for ecotox tests on alga, bacteria, and crustaceans, as well as for degradation tests.Petrol/ethanol fuels were more efficiently dissolved in water than diesel fuels. This is because they contain a higher proportion of more water-soluble substances, such as ethers and light aromatic compounds, and the mixture of ethanol in the fuels. The E85 fuel resulted in the highest concentrations of hydrocarbons in the water mixture, even though the proportion of petrol is only 15%. A similar effect on solubility could be observed for RME in diesel fuels, although not to the same extent.The amounts of dissolved ether determined the odour properties of fuels in water.

The 98 octane E05 fuel had the highest ether concentration in the fuel product, while the ether content of E85 was most effectively dissolved in water due to the high ethanol content. The odour thresholds were at 0.0017% in a water/fuel mixture for the E05 fuel and 0.0042% for E85. The ethers so dominated the odour that the methyl tert-butyl ether (MTBE) concentration could accurately predict the smell in an aqueous solution.Overall, the ecotoxicological tests showed mild or no effect from the fuels on the tested organisms. The exception was for the reproduction of crustaceans that were disturbed by MK1 diesel with RME. The low solubility of the two tested diesel fuels in water resulted in too low concentrations of hydrocarbons in the fuel/water mixture for valid degradation tests. 

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