GUIDANCE ON SPILL RESPONSE TO BIOFUELS

A detailed analysis and response guidance was released as a Technical Bulletin to all ISAS Accredited Contractors in January 2021- this is an abridged version – for the full version, and other Technical Bulletin join ISAS – info@isasaccreditation.org

Introduction

International Spill Accreditation Scheme (ISAS) were asked by the Environment Agency to provide guidance on the appropriate spill response to biofuels.

A biofuel is a fuel that is produced from biomass (e.g. vegetable oil, animal oil/ fats, waste cooking oil) rather than fossil fuels. Biofuels offer a more sustainable energy source than petrol or diesel and they can produce significantly lower emissions and toxins than fossil fuels, however, these environmental benefits will depend on how the biofuels are produced and used.

Biofuels can be used in their pure form but are commonly blended with existing products such as petrol and diesel, in order to reduce emissions.

Biofuels are increasing in usage across a range of sectors from bulk transport to commercial and home heating and mobile power generation, and their use will further increase as we strive towards a net zero carbon world.

In the UK transport sector currently, the percentage of biofuel derived from a sustainable renewable source is 5% in petrol and 7% in diesel. This will increase to 10% ethanol in petrol from September 2021. There is no doubt that further increases will follow. The Renewable Transport Fuel Obligation Order (RTFO) compel owners of transport fuel who supply at least 450,000 litres a year or more, to make sure the mix is at least 12.4% biofuel by 2032.

This has an environmental benefit, in 2018 the use of biofuels saved 3,727 kilotonnes of CO2, the equivalent of 1.5 million average car emissions per year.

With respect to liquid fuel heating, OFTEC have completed research on the use of biofuels, and the research revealed that biofuels, both 100% pure biofuel and a 30% blend of FAME (fatty acid methyl ester) and kerosene, provided the best carbon reducing routes for the least financial outlay. OFTEC state that renewable liquid fuels manufactured from waste material could provide a ‘drop-in’ replacement for heating oil and that these fuels can quickly be brought to market and have the potential to virtually remove emissions from the UK’s 1.5 million and RoI’s 686,000 oil-heated homes.

It is clear that the use of biofuels is going to increase dramatically in the coming years and owing to the differing chemistry of the pure and blended biofuels, once released to the environment, they behave differently to fossil fuel derived products and therefore present a challenge to spill responders.

Biofuels are often broken into threecategories, 1st, 2nd and 3rd generationbiofuels.

UK GHG emission savings from the use ofrenewable fuels 2018 ENC0503

First generation biofuels are produceddirectly from food crops and include, forexample, ethanol and FAME (Fatty AcidMethyl Esters). Ethanol is derived fromplant-based material, like palm oil, oilseedrape, sugar cane, cereals and reprocessedvegetable oil. FAME is produced fromvegetable oils, animal fats or waste cookingoils by transesterification. In the processa glyceride reacts with an alcohol in thepresence of a catalyst, forming a mixtureof fatty acid esters and an alcohol. Usingtriglycerides results in the production ofglycerol. Rapeseed, sunflower, soybean,palm oils and animal fat are the mostcommon raw materials being used for theproduction of biodiesel.

Whilst ethanol and FAME are now in general use, the second generation of biofuels is being introduced that is promoted as being cleaner, more stable in storage and can be mixed with the hostels at higher % than currently used and deliver improved emission savings. These second-generation biofuels are produced more sustainably using materials consisting of the non-food parts of current crops, such as stems, leaves, husks that are left behind once a food crop has been extracted as well as other non-food crops grown for this production like grasses, jatropha and miscanthus. This generation of biofuel ensures that its production is not prioritised before food production in a world that is already short of food.

Second generation biofuels fall into various categories:

Paraffinic diesel produced from coal,natural gas or biomass - Shell GTL is a sucha fuel. It is similar to fossil diesel regardingenergy content, density, viscosity and flashpoint; however, it is characterized by highercetane number and near zero sulphurand aromatic content. CO, HC, NOx, andsmoke emissions from an unmodified dieselengine operating on DME (Dimethylether)type diesel were lower when comparedwith those of conventional diesel.

Hydrotreated Vegetable Oil (HVO) is aparaffinic bio-based liquid fuel originatingfrom many kinds of vegetable oils, such asrapeseed, sunflower, soybean, and palm oil,as well as animal fats. However alternativenon-food oils such as jatropha as well aswaste cooking oils are being preferred inproduction. It can be used in conventionaldiesel engines, pure or blended withstandard diesel. This technology is amodern way to produce high-quality biobaseddiesel fuels without compromisingfuel logistics, engines, or exhaust aftertreatmentdevices and storage stability ishigh as water solubility is low though notunlimited.

Recent analysis of an HVO productcompleted by UK & Ire Spill Membersconfirms it has a very low aromaticcontent with negligible concentrationsof mono-aromatic and polyaromatic

hydrocarbons and is principally comprisedof aliphatic C12-C21 hydrocarbons. HVOis a potential replacement for kerosene indomestic heating installations and owingto its reduced aromatic content it has thepotential to pose a much lower risk tohealth, building structures and services andthe environment following a spill incident.

Soon to arrive are third generation biofuelswhich are algae-based fuels and no doubtmany others in the necessary drive toreduce harmful emissions. Previously, algaederived biofuels were grouped with secondgeneration biofuels. However, it becameapparent that algae are capable of muchhigher yields with lower resource inputsthan other feedstock, and many suggestedthat they be moved to their own category.

Biofuel releases to the environment

The biodegradation potential of acompound is affected by severalfactors, including the concentration,complexity of the chemical structure, thepresence of suitable electron acceptors,and bioavailability (ITRC, 2011). Mosthydrocarbons in conventional fuels arecharacterized by branching, saturation,and high hydrophobicity and these can allnegatively affect biodegradation rates. Incontrast, biofuels, such as FAMEs, ethanol,and butanol, have simple structures and arereadily biodegradable under both aerobicand anaerobic conditions. Therefore, diluteconcentrations of biofuels in groundwaterexhibit smaller plumes with shorterlongevity than plumes associated withconventional fuel components. However,spills of blended biofuels will presenta challenge owing to the mixture ofhydrophobic and hydrophilic components.

The release of a readily degradable biofuel to soil or water results in the rapid consumption of oxygen in the receiving media. This can be particularly detrimental in surface waters where low oxygen levels can adversely affect biological communities. The impact of a highly biodegradable fuel on surface waters or groundwater is strongly dependent on the ability of the receiving water to dilute the load. In spills where a highly soluble and highly biodegradable biofuel reaches groundwater, rapid biodegradation induces anaerobic conditions. Near source zones, added oxygen demand can reduce biodegradation rates of petroleum hydrocarbons in saturated and unsaturated environments, which can potentially allow petroleum vapours to migrate further, both horizontally and vertically.

Where biofuels are rapidly metabolized by aerobic and anaerobic organisms, ethanol releases to shallow groundwater are likely to produce dark-coloured microbial slimes near the water table. These slimes have been noted in soil cores following Denatured Fuel Ethanol (DFE) spills and may encapsulate high concentrations of ethanol in the capillary fringe, preserving them for several years. The presence of biomass indicates a high density of organisms growing in the source zone, likely leading to reduced transport of ethanol and degradation products in groundwater.

At very high concentrations (30%–70%, depending on the biofuel), highly watersoluble biofuels with solvent properties (e.g. ethanol) can dissolve other separate-phase hydrocarbons that may already be present in the ground and mobilize these dissolved components as a migrating bulk phase. For example, for ethanol-water hydrocarbon mixtures >70% ethanol, the mixture exists as a single phase with properties very similar to neat ethanol. Therefore, for a spill of considerable ethanol volume that encounters residual nonaqueousphase liquid (NAPL), the hydrocarbons are dissolved by the ethanol and migrate with the bulk fuel until the ethanol dilutes to <70%. At this point, the hydrocarbons phase-separate from the bulk fuel.

The initial fate of biofuel spills at the ground surface is largely controlled by vaporization of the product, consumption by fire (if appropriate), infiltration, surface drainage, and surface water dilution. Ignition of vapours can be catastrophic and are the greatest concern for first responders at large alcohol-based biofuel release sites. Unless precautions are taken, biofuel not consumed by fire may be more rapidly transported to nearby lakes, rivers, and streams due to firefighting efforts.

When low-density biofuels such as ethanol and butanol are released into surface water bodies, their lower specific gravities initially cause them to be buoyant as they mix in the upper water column. However, this buoyancy is not expected to last, as dilution and mixing (e.g. by waves and currents) are likely to be rapid. Hydrocarbons from the petrol fraction quickly phase-separate, generating LNAPL on the biofuel’s contact and dilution with water. For low hydrocarbon fractions, such as the 2%–5% in DFE, LNAPL is not likely to be observed due to rapid dispersion, spreading, and the evaporation of the

relatively small quantities of hydrocarbons. For higher hydrocarbon fractions (e.g.>50%), LNAPL and/or sheens are expected to result from the turbulent mixing of the ethanol fuel and surface waters, as long as the amount of water exceeds the amount that can be held within the fuel. Sincebutanol has a vapour pressure of 7 mm Hg and is highly volatile, loss by vaporization from the LNAPL phase is significant. In addition, because the vapour density of butanol is 2.6, the vapours are heavier than air and can accumulate in low-lying areas. Because the explosive range for butanol in the air is 1.4%–11.2% (as compared to 5%–15% for ethanol), vaporization from surface spills could quickly result in conditions favourable for combustion.

Unlike ethanol and butanol based biofuels,spills of biodiesel blends typically behavesimilarly to standard diesel at first (i.e. theyremain on the surface and spread veryquickly to a thin film). However, biodieselscontain mild surfactants, and blends willnaturally ultimately disperse much morethan standard diesels. The rate of naturaldispersion can increase droplet formationand slow the rate of droplet resurfacing,and when released to water they form

Milky white emulsion resulting from biodiesel spill (Source: USEPA, 2009)

a white, milky emulsion. Biodiesel isslightly more viscous than standard diesel,especially at lower temperatures.

Biodiesels are slightly soluble in water,with a water-soluble fraction of typically13-60 milligrams per litre (mg/L) forpure biodiesels, but as high as 110 mg/L;whereas biodiesel blends (5% and 20%have a water-soluble fraction of 20-30mg/L). Standard diesels have a watersolublefraction of 20-40 mg/L. However,the water-soluble fraction of purebiodiesel lacks the acutely toxic aromaticcomponents and volatiles that drive thetoxicity of standard diesels.

Releases of biofuel can have immediateshort-term impacts on aquatic ecology;this impact can be due to highly watersolublebiofuels (alcohol biofuels) thatcan potentially disperse throughout the

entire water column or that, in the case of relatively insoluble biofuel such as biodiesel, can coat shorelines and vegetation. In general, alcohols may impact larger volumes of surface water than equivalent petroleum releases due to their higher solubilities and the inability to capture separate-phase product.

Biodegradation is an important fate process for biofuels in aquatic environments. Compared to aquifers, surface water environments have a greater capacity to rapidly decrease concentrations of dissolved organic compounds through biodegradation and dilution. Sudden large biofuel releases can result in surface water zones with large BOD loadings, resulting in enhanced and rapid bacterial growth. The increased biological activity is due in part from exposure to sunlight, wind, and atmospheric oxygen. DO drives microbial processes, resulting in rapid biological transformation. The rate of DO depletion depends on the rates of biodegradation and volatilization. For example, the half-life due to volatilization of butanol in streams (2.4 hours) and lakes (125 days) may result in DO depletion as great or greater than that following an ethanol release of similar size, and DO depletion can cause significant fish kills.

Pure ethanol and blended fuels can easily infiltrate into the subsurface. The liquid will then percolate through the unsaturated zone soils, moving through the gas filled pore spaces, until it ultimately reaches the water table. Due to its affinity to reside in the water phase, migrating ethanol will partition into soil moisture; this partitioning can slow the downward migration of ethanol. Dissolved ethanol present in soil pore water typically is subject to biodegradation, which can further attenuate the rate of ethanol migration to the water table.

The mechanisms controlling the entry of biofuel to groundwater under different site conditions are not well understood; however, laboratory and field investigations have provided some insight into important properties and variables that influence downward transport. For large releases of DFE, ethanol has been detected in source zone groundwater soon after the release except in cases where deep soil excavation occurred immediately following the release. In shallow groundwater areas, large DFE releases appear capable of creating sufficient head pressures to quickly transport 1%–5% of the ethanol beneath the water table. These releases have an immediate impact on the geochemistry and biodegradation reactions in the source zone. The figure below illustrates the relative behaviours and NAPL distributions of conventional gasoline, gasoline with 10% Ethanol (E10), and DFE for approximately equal-volume releases. Darker red shading indicates greater NAPL pore saturations; yellow indicates the extent of detectable ethanol prior to dilution and attenuation.

Hydrocarbon constituents are slowly released to groundwater according to their solubility and mass fraction in the hydrocarbon phase if a sufficient mass of hydrocarbon from the fuel mixture remains as a residual LNAPL source near the water table. The longevity of residual LNAPL as a source of hydrocarbons (e.g. BTEX) to groundwater is on the scale of years to decades. Because biofuel blends have lower fractions of petroleum hydrocarbons than conventional fuels, concentrations of aromatic hydrocarbons are expected to be lower, and the longevity of LNAPL as a continuing source to groundwater is expected to be shorter.

Biodiesel is predicted to be highly adsorbed to soil organic matter in the unsaturated zone. The log Kow values for some biodiesel FAMEs are higher than those for diesel, suggesting that groundwater impacts will mostly be limited to large releases on excessively well-drained soil with a shallow depth to groundwater.

Ethanol in groundwater has been investigated at several experimental sites and a few DFE release sites. At these sites, the concentration of ethanol in groundwater ranged 220 – 55,000 mg/L

The most frequent release scenarios are small releases of fuel with low percentages of ethanol biofuel (e.g. <10% ethanol). These are not expected to produce a detectable plume downgradient of the source zone due to retention of ethanol above the water table, rapid biodegradation, and low initial ethanol concentrations. Ethanol that does reach the saturated zone may temporarily influence the biodegradation potential of coexisting hydrocarbons as discussed above, but these effects are expected to be minor.

Conclusion

Biofuels are reducing the greenhouse gas and other harmful emissions from the use of hydrocarbon-based fossil fuels. The first generation biofuels (e.g. FAME and ethanol), helped to reduce annual emissions by the equivalent of 1.5 million family cars in 2018. However, as they readily absorb water they pose problems when stored through microbial contamination, phase separation and biofilm which can allow acidity to attack the infrastructure used to store and deliver fuel.

Second generation biofuels are being introduced and further developed to enable their use as a total replacement of diesel or their use as a high % drop-in substitute. At a financial cost, they represent the opportunity to considerably reduce harmful emissions with no performance deficit.

Whilst some are said to be biodegradable, this takes time to be achieve and any loss of product should be treated as if it is a loss of petrol / diesel.

Response to spills of biofuel must consider the chemistry of the pure biofuel or the blend which has been released to the environment, and must also consider how the biofuel will partition in the environment and the health and safety hazards associated with the response to these fuels.

A key challenge to responders will be the tendency for some biofuels to readily dissolve once released to water rendering the traditional use of some techniques (e.g. floating oil absorbents) of limited application.

The response should focus on stopping the source, contain and recovering the lost product and then remediating any residual contamination using an ISAS Accredited Contractor.

An International Spill Accreditation Scheme (ISAS) accredited responder should be mobilised to ensure that the spillage is comprehensively cleaned up and any impact from its loss is properly remediated.

A guide for an initial immediate response, specific product hazards, flash points, PPE and how to make an initial response to a spillage of fuel containing biofuel is presented at Annex A.

If the spillage presents a risk to controlled waters it MUST be reported to the relevant environmental regulator (e.g. EA, SEPA, NRW, NIE, EPA) using the emergency hotline, providing site address, details of product lost and any likely environmental impact. The ISAS accredited contractor can assist in liaising with environmental regulator visits or follow up thereafter.