Keeping bioenergy safe: From feedstock to fuel

INTRODUCTION

Bioenergy encompasses a wide range of technologies and feedstocks, and depending on the conversion route used, can support applications ranging from power generation and industrial heat through to transport fuels and, in some cases, carbon removal through integration with carbon capture technologies.

Understanding how these systems operate – and the hazards they can introduce – is therefore increasingly important. While the risks vary by technology, careful management of flammable materials, combustible dusts, toxic atmospheres, elevated temperatures, and pressurised systems is essential across the sector.

This article explores what bioenergy is, how different technologies convert biomass into useful energy, the hazards commonly associated with bioenergy systems, and how established process safety management (PSM) principles can help ensure bioenergy plays its part in the energy transition safely and effectively.

Understanding the terminology

Terms such as biomass, bioenergy, biofuels, biogas, biomethane, and sustainable aviation fuel (SAF) are often used interchangeably, despite referring to different parts of the bioenergy system.

At a simple level, bioenergy involves converting a biomass feedstock through a conversion process into an energy product for an intended end use. Figure 1 provides a simplified overview of this journey and helps illustrate where some of the commonly used terms fit.

Figure 1 – The bioenergy journey

Biomass: where it begins

Biomass refers to biological material used as a feedstock for energy production. Typical feedstocks include:

• Agricultural residues
• Forestry residues and wood waste
• Food waste
• Sewage sludge
• Animal manure
• Organic industrial wastes

The nature of the feedstock plays an important role in determining the technologies used, operational complexity, and hazard profile of a facility.

Bioenergy: the umbrella term

Bioenergy is the energy derived from biomass. Depending on the selected conversion process, bioenergy can produce:

• Heat
• Electricity
• Renewable gas
• Liquid transport fuels

Biofuels: powering the transition

Biofuels are fuels derived from biomass and are particularly important in sectors where electrification may be challenging. Examples include:

• Bioethanol – an alcohol-based fuel commonly blended into petrol.
• Biodiesel – a fuel produced from vegetable oils, waste oils, and fats.
• Biogas – a methane-rich gas produced through biological decomposition, comprising primarily methane and carbon dioxide alongside trace constituents such as hydrogen sulphide and water vapour.
• Biomethane – purified biogas suitable for gas grid injection or transport fuel use.
• Bio-oil – an energy-rich liquid that can be used for heat and power generation, or refined into lower-carbon fuels.

Sustainable aviation fuel

Sustainable aviation fuel (SAF) is a lower-carbon alternative to conventional jet fuel produced from sustainable feedstocks such as waste oils, agricultural residues, municipal waste, and biomass.

As aviation remains difficult to electrify at scale, SAF is expected to play an important role& in reducing emissions from air travel.

Bioenergy with carbon capture and storage

Because biomass absorbs carbon dioxide during growth, capturing emissions released during energy conversion creates the potential for net carbon removal.

This makes bioenergy with carbon capture and storage (BECCS) different from many other decarbonisation technologies. While most approaches focus on reducing emissions, BECCS has the potential to remove carbon dioxide from the atmosphere overall – provided feedstocks are sustainably sourced and the carbon captured is permanently stored.

For this reason, BECCS is increasingly being considered within some net zero pathways as a means of addressing harder-to-abate residual emissions from sectors where complete decarbonisation may prove difficult.

BIOMASS CONVERSION PATHWAYS

The conversion pathway used to transform biomass into usable energy is one of the main factors influencing how a bioenergy system operates, the form of energy produced, and the types of risk introduced.

The route selected depends largely on the characteristics of the feedstock and the intended energy output – whether electricity, heat, gas, or transport fuel.

Broadly, bioenergy conversion technologies tend to fall into three groups.

1. Biological conversion

Biological routes are typically used for wetter feedstocks such as food waste, sewage sludge, and animal manures.

Anaerobic digestion (AD)

Anaerobic digestion uses naturally occurring microorganisms, primarily bacteria, to break down organic material in an oxygen-free environment, producing:

• Biogas – primarily methane and carbon dioxide
• Digestate – a residual nutrient-rich material

Biogas can be used directly for heat and electricity generation, or upgraded into biomethane for gas grid injection or transport fuel applications.

Fermentation

Fermentation converts biomass rich in sugars or starches into liquid fuels through controlled biological processes, typically involving microorganisms such as yeast.

Common feedstocks include crops such as maize, wheat, and sugar cane. The most widely produced output is bioethanol, which is commonly blended with petrol for use in road transport.

2. Thermochemical conversion

Thermochemical routes are often associated with drier feedstocks such as wood, forestry residues, and agricultural biomass, although some processes – such as hydrothermal liquefaction – are specifically designed to handle wetter biomass streams.

Combustion

Combustion converts biomass by burning it in the presence of oxygen. The heat released is typically used to produce steam, which can then drive turbines to generate electricity, or be used directly for heating and industrial processes. Combustion remains one of the most mature and widely deployed bioenergy technologies, particularly for large-scale heat and power generation.

Gasification

Gasification converts biomass by heating it at high temperature using a controlled and limited supply of oxygen or steam. Rather than fully burning the biomass, the process partially breaks it down into a combustible gas mixture known as syngas. This typically contains hydrogen, carbon monoxide, carbon dioxide, and nitrogen – with the balance of these components varying depending on whether air, oxygen, or steam is used as the gasification agent. Syngas can be used for heat and power generation, or further processing into fuels and chemicals.

Pyrolysis

Pyrolysis converts biomass by heating it to high temperatures in the absence of oxygen.

Rather than combusting the material, the process thermally breaks the biomass down into a range of products, with the exact mix influenced by the feedstock and operating conditions. These outputs typically include bio-oil, combustible gases, and biochar – a stable, carbon-rich, charcoal-like material.

The energy-rich gases and bio-oil can be used for heat and power generation or further refined for fuel production. Biochar, by contrast, is often used for soil improvement or longer-term carbon storage. Because the pyrolysis process converts biomass into a stable form of carbon that resists decomposition, biochar can lock carbon away for extended periods, creating the potential for some applications to contribute to wider carbon removal objectives.

Liquefaction

Liquefaction converts biomass into liquid products under elevated temperature and pressure, typically using wet feedstocks where drying would be inefficient.

A common example is hydrothermal liquefaction (HTL), which converts materials such as sewage sludge, food waste, or algae into a crude-like liquid known as bio-crude. Unlike other thermochemical routes, HTL exploits the properties of hot pressurised water as the reaction medium, rather than requiring the feedstock to be dried first. This can then be refined into lower-carbon fuels, including potential pathways to SAF.

Interest in liquefaction is growing because it can process high-moisture feedstocks without extensive drying, making it potentially attractive for some waste streams and advanced fuel applications.

3. Mechanical conversion

Mechanical extraction, typically cold or expeller pressing, is used to recover oils from biomass feedstocks, typically as a precursor to fuel production.

Rather than converting biomass directly into usable energy, the process produces an intermediate oil that can be refined into liquid fuels such as biodiesel and other lower-carbon transport fuels.

Where the risks arise

Bioenergy facilities vary considerably in scale and technology, ranging from anaerobic digestion plants and biomass-fired generation, through to advanced fuel production processes.

Despite these differences, many share a common hazard profile involving combustible fuels, elevated temperatures, pressurised systems, and variable feedstocks. As a result, similar accident pathways often emerge across the sector.

Fire and explosion

Many bioenergy facilities routinely generate, process, or store flammable materials as part of normal operation. Examples include:

• Methane-rich biogas from anaerobic digestion
• Biomethane following gas upgrading
• Fuel gases generated through gasification or pyrolysis
• Combustible biomass dusts and powders

Releases of flammable gases or combustible dusts can create flammable atmospheres which, if ignited, may result in fire or explosion. The likelihood and potential consequences of such events are exacerbated in enclosed or poorly ventilated areas, where flammable materials may accumulate and confinement can increase the severity of an explosion.

Loss of containment and overpressure

Loss of containment is one of the most critical process safety risks facing bioenergy facilities. Combustible gases, liquids, and solids are often processed at elevated temperatures and pressures, and failure of the containment system can lead to the release of hazardous materials with the potential for fire, explosion, environmental harm, or asset damage.

Feedstock variability, fouling, blockages, equipment degradation, and abnormal operating conditions can all challenge the integrity of a process system. In some cases, these conditions can result in overpressure, ultimately causing a loss of containment through leaks or ruptures.

As with many industrial processes, the greatest risks often arise during startup, shutdown, maintenance, and process upset conditions, when systems are operating outside their normal envelope and safeguards may be unavailable, bypassed, or less effective. This highlights the importance of identifying hazards across all operating conditions, rather than focusing solely on normal operation.

Toxic exposure

Some bioenergy processes can generate hazardous gases, contaminants, or by-products capable of causing acute harm. Within anaerobic digestion systems, for example, hydrogen sulphide (H₂S) may be present and can cause sudden incapacitation, respiratory failure, and severe toxic effects at elevated concentrations. Other toxic hazards may arise from process chemicals, combustion products, or abnormal releases.

Exposure risks often increase during maintenance, intrusive activities, or upset conditions, particularly where equipment is opened, lines are broken, or loss of containment occurs.

High temperature and thermal hazards

Thermochemical processes such as combustion, gasification, and pyrolysis operate at elevated temperatures and involve hot surfaces, ignition sources, and combustible materials. Risks can increase during startup, shutdown, and other transient operating states, where changing process conditions may increase the likelihood of fire, explosion, or process upset.

Asphyxiation and confined spaces

Many bioenergy facilities include enclosed or partially enclosed areas where hazardous or oxygen-deficient atmospheres may develop. Methane, carbon dioxide, and reduced oxygen levels can create risks associated with fire, explosion, toxic exposure, and asphyxiation, particularly during maintenance or intrusive activities.

Environmental and community impacts

Not all incidents directly harm people, but they can still cause significant environmental, operational, and reputational issues. Odour, visible emissions, noise, contaminated run-off, or the escape of process materials can affect surrounding communities and the environment, particularly where incidents lead to pollution or nuisance.

The consequences often extend beyond immediate operational disruption, adversely impacting regulatory compliance, stakeholder confidence, and long-term community acceptance.

The Common theme

Although all these hazards may appear diverse, most can be traced back to a relatively small number of recurring themes:

• Fuel + oxygen + ignition source
• Hazardous atmosphere + confined space
• Pressurised or high-temperature system + loss of containment

Understanding these pathways early is key to designing facilities that are not only lower carbon, but also safe, reliable, and operationally resilient.

BIOENERGY – A PROCESS SAFETY CHALLENGE

Although bioenergy technologies vary considerably, the underlying hazards are familiar.

Whether dealing with methane-rich biogas, combustible dusts, toxic atmospheres, elevated temperatures, or pressurised systems, many of the risks associated with bioenergy sit firmly within the discipline of process safety – understanding how hazardous materials and energy are generated, contained, controlled, and prevented from causing harm.

The good news is that these are not new problems. Across sectors such as oil and gas, chemicals, power generation, and manufacturing, decades of experience already exist in managing comparable hazards effectively. Established process safety management (PSM) approaches provide proven frameworks for identifying hazards, understanding risk, and maintaining safe and reliable operation.

For bioenergy, the challenge is therefore not to reinvent safety management, but to apply established PSM principles in a way that reflects the specific technologies, feedstocks, and operating conditions involved.

Alongside this, developers, owners, and operators need to understand the wider safety and regulatory framework relevant to their facilities. Depending on the technology and scale involved, this may include requirements relating to major accident hazards, dangerous substances, fire and explosion risk, pressure systems, environmental permitting, and occupational health and safety.

At its core, however, effective PSM boils down to three simple requirements, illustrated in Figure 2.

Figure 2 – Fundamental requirements of effective PSM

PSM is fundamentally technology agnostic. The same framework applies whether the hazardous substance is natural gas, chlorine, or biogas. It involves understanding what could go wrong, implementing the right safeguards, and assuring those safeguards continue to function effectively – providing a strong basis for safe and reliable operation throughout the asset lifecycle.

What bioenergy does introduce, however, is a degree of variability that is less common in conventional industries, as feedstocks, moisture content, process conditions, and operating modes can vary over time. Unlike more uniform fuel sources, changes in feedstock composition can influence how a facility behaves, how hazards arise, and how effectively safeguards perform.

This makes maintaining confidence in safeguard performance particularly important within bioenergy – and it is here that PSM principles prove their value most clearly. Variability in feedstock and process conditions should first be understood and accounted for during the design of the facility. Wherever practicable, inherent safety principles should be adopted to eliminate or reduce hazards at source, with equipment, control systems, and safeguards then designed to remain effective across the full range of anticipated operating conditions. Regular hazard assessments, ongoing monitoring of process conditions, and assurance that safeguards continue to perform as intended become essential to confirm that the assumptions made during design remain valid throughout the life of the facility.

CONCLUSION

Bioenergy has an important role to play in supporting the transition to net zero. The hazards it introduces are real, but familiar – and the tools to manage them already exist. With the right application of process safety principles, and attention to the variability that makes bioenergy distinctive, the sector can scale safely, reliably, and sustainably.