Developing on-site anaerobic digestion for smaller businesses in the food and drink sector

The British market for anaerobic digestion (AD) can be divided into three sectors (municipal, on-farm and industrial). Clearfleau is a leading technology provider specialising in on-site industrial plants, treating biodegradable residues. On-site AD also has a role on farms (for manure, slurry and other residues) and in rural communities (converting food waste to energy for local use).

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Aug 22, 2017
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Author(s): Mr Richard Gueterbock and Ms Bunmi Sangosanya


  • The bio-economy: encompasses the production of renewable biological resources and their conversion into food, bio-based products and bio-energy using innovative technologies. It offers new opportunities and solutions to a number of social, environmental and economic challenges, including climate change mitigation, energy and food security and enhanced resource efficiency.
  • On-site AD: smaller scale deployment of the process used to generate bio-energy in a biological degradation process whereby micro-organisms that thrive without oxygen convert bio-degradable (volatile) process residues into renewable energy. Clearfleau’s industrial AD plants convert liquid effluents and production residues into valuable bio-energy.
  • Digestion plant scale – small, medium and large scale AD plants: A classification for AD was developed by the Renewable Energy Association (REA) and other partners for dealings with policy makers:
    • small: on-site AD plants generating under 100 Nm3 of biogas or 200 kW thermal output,
    • medium: plants generating >200 kW thermal but <2 MW thermal output,
    • large: plants generating over 2 MW thermal (increasingly using gas to grid technology).



a natural organism that thrives or a process that can occur in air or free oxygen


an organism that thrives or a process that occurs in the absence of air or free oxygen


gas produced from the biological degradation of bio-residues in the absence or air or free oxygen comprising of mainly methane and carbon dioxide

Biological oxygen demand

measurement of dissolved oxygen used by aerobic microorganisms in the degradation of organic material


enriched biogas achieved by purification/removal of carbon dioxide


biodegradable materials produced as part of a manufacturing process (also co-products)


renewable (non-fossil fuel) energy derived from organic biomass, including bio-residues


residual solid material (containing nutrients) produced as result of a bio-degradation process

Chemical oxygen demand

measurement of degradable organic compounds in effluent and results of COD test can be used to indicate the presence of decomposing pollutants that absorb oxygen from water

Digestate liquor

residual liquid after AD containing non-biodegradable materials

Merchant AD

commercial, centralised AD plants that are designed to handle a range of biodegradable materials from household or high street collection, operated for municipal authorities


linked processes where one process cannot proceed for very long without the other process


Amongst a range of smaller scale renewable energy technologies, on-site digestion has a value for industrial sites because demand for heat or power can be met at the point where bio-degradable residues are produced. On-site bio-energy cuts fossil fuel use, while reducing emissions that would be released from biodegradable residues and cutting disposal costs.

There needs to be a greater synergy between Britain’s industrial and energy policies within the Department of Business, Energy and Industry Strategy (BEIS), if we are to do more to encourage the transition to a more circular bio-economy. The previous Government’s Policy Green Paper ‘Building our Industrial Strategy’ [1] highlights the value of sustainability and clean technologies but does not indicate how the bio-engineering and renewables sectors will be supported after Brexit.

Existing on-site bio-energy plants are illustrating the benefits of decentralised generation. For instance, at one of the UK’s largest cheese creameries (see Fig 1 – plant built for the farmer owned dairy company, First Milk), an on-site AD plant is converting cheese residues into biogas, while discharging cleansed water to the nearby river Ellen. It supplies upgraded biomethane to the creamery and other users on the gas grid and is an example of innovative bio-engineering.

Fig 1: Arial photo of Lake District Biogas on-site AD plant

Clearfleau’s approach to on-site digestion is based on tailoring each facility to the specific requirements of the site where the plant is located. Also, by developing a more modular approach to plant design we aim to facilitate export opportunities and help make plants affordable on smaller SME (small or medium enterprise) industrial sites, with a comparable return on investment (ROI) to larger projects. From 2017, Clearfleau will be installing on-site bio-energy facilities on smaller industrial sites and we hope to boost deployment in the SME sector in future.

On-site AD technology

AD is a bio-chemical process, where bacteria breakdown organic material in the absence of oxygen to produce biogas which is predominantly methane (CH 4) and carbon dioxide (CO 2). The technology has existed for many years. However, applications that treat residues other than those originating from municipal sources are a more recent development. The digestion process relies predominantly on two types of organism in a symbiotic relationship – acid forming and methane forming bacteria [2]. The process occurs in the stages shown in Fig 2[3].

Fig 2: Metabolic pathways and microbial groups

The main phases of the anaerobic process are outlined below:

  • Hydrolysis: complex compounds are converted into simpler substances by fermentative bacteria and some fungi. These compounds are carbohydrates, fats and proteins which are converted into simple sugars, fatty acids and amino acids, respectively.
  • This stage is followed by acidogenesis, where fermentative bacteria again convert the simpler substances produced in the hydrolysis phase to organic acids and alcohols.
  • The next stage, acetogenesis sometimes cannot be distinguished from acidogenesis. Here organic acids and alcohols are converted to acetates prior to methane production.
  • The final stage, methanogenesis is carried out by methanogenic bacteria that form the methane, plus CO2 and hydrogen gas (H2), from acetates created in the previous stage.

In the industrial sector, the substrate (or feedstock) fed to the AD plant is measured in terms of its organic strength – commonly called chemical oxygen demand (COD). Although digestion is a highly effective way of treating biodegradable residues on industrial sites, most AD plants built in the past decade are processing municipal bio-waste feedstocks or purpose grown crops. However, there is increasing interest in deployment of on-site AD in the agri-food sector.

Technology innovation

Clearfleau’s liquid digestion plants utilise the continuously stirred reactor system, adapted to optimise COD removal and hence gas output. The main innovation is breaking the link between the liquid retention time to minimise the size of the digester tank) and extended bio-solids retention period (to about 50 days to optimise COD removal and gas output) (see Fig 3).

Fig 3: Basic process schematic

In optimising the effectiveness of the bio-degradation process two key operating parameters are:

  • Temperature: microorganisms can be mesophilic – meaning they grow best in a range between 20 and 40°C (although operating experience shows the optimum to be from 35 to 38°C). They can also be thermophilic (operating range 50 and 60°C, with an optimum of 55°C). Operating under mesophilic conditions generally means less energy is required to maintain temperature, which can be beneficial for running costs.
  • Alkalinity or pH: The pH of the digester is important as microorganisms in the digester, in particular methanogenic bacteria, can be sensitive to pH outside a range of between 6.8 and 7.2. With pH values outside this range, a reactor will still degrade the substrate, however, the level of COD removal and biogas production will be severely compromised.

To optimise performance and hence payback, process management is crucial. Unlike, municipal sludge digestion systems or dry fermentation processes, where the incoming waste composition is fixed and each tonne of material is equated to a specific gas and sludge output, Clearfleau’s mass balance is correlated to the organic strength of the feed (COD) and level of degradability.

COD values can vary greatly, suitable biodegradable food or drink residues can include wash waters and effluents, plus co-products from production processes, plus product discards and other processing residues. Even as sites become more efficient and able to recycle water for other site operations, there is often a liquid residue with a related disposal cost. Harnessing the available energy from such materials cuts costs and supplies energy to substitute fossil fuels (see Fig 4).

Fig 4: Outputs from on-site digestion

Clearfleau’s process is better suited than other systems for handling both fatty and non-fatty food residues, dairy and bio-fuel sectors, due to the ability to break the link between solids and liquid retention time, reducing cost and tank capacity, while facilitating more cost effective operation. Also, by achieving over 95% degradability, these plants maximise associated biogas output.

The proprietary method of solids retention maintains an elevated biomass content within the reactor, to deliver efficient COD reduction and quality effluent for discharge. The system produces gas with optimal methane content, due to effective mixing of liquors in the anaerobic reactor and sustained exposure of active biomass to incoming COD load. Post digestion, aerobic treatment will remove any residual COD and nutrients before discharge to river or re-use as grey water.

Industrial on-site digestion

The AD market is subdivided into three sectors: merchant sites (predominantly handling municipal bio-wastes) farm plants (digesting manures or crop residues – plus less appropriate purpose grown crops) and plants on industrial sites (treating bio-effluents and residues). On-site digestion can process biodegradable residues generated by the site where a plant is located.

On-site industrial digestion systems have only three outputs: biogas, clean water and bio-solids. The bio-solids produced from the digestion process are rich in nutrients, in particular nitrogen and phosphorous. The bio-solids often undergo a dewatering process to remove the liquid fraction and create a spreadable material that can be spread to land as a fertiliser or soil improver.

Regardless of the source of feedstock, biogas produced can be combusted in a boiler to supply hot water or steam, or a combined heat and power (CHP) plant to generate electricity and heat. Gas can also be upgraded to produce biomethane (and fed into the natural gas grid or pressurised to produce compressed biomethane for use as fuel). Options for biogas use mean that digestion offers a flexible alternative to renewable technologies that just supply electricity.

The food and beverage industry is devoting greater attention on its environmental impact. For instance, the Scotch Whisky Association (SWA) sustainability strategy is setting tougher targets but also encouraging members to access sources of renewable energy. A range of feedstocks from whisky distillation and brewing processes are suited to digestion including pot ale (residue from initial distillation) and spent lees/wash (also from distillation), plus residual wash waters.

On-site AD of such energy rich residues offers several benefits:

  • Energy – on-site bio-energy cuts fossil fuel use, helping meet energy reduction targets,
  • Emissions – replacing fossil fuel with bio-energy, will reduce food sector emissions,
  • Water use – after digestion, cleansed water fit for river discharge can be re-used on site,
  • Land fertility – residual bio-solids provide nutrients for crops (e.g. grain for distilleries),
  • Efficiency – extracting value from residues offers a more circular (zero-waste) approach.

Most industrial sites are coming under pressure to curtail their wider environmental impact and on-site digestion offers a cost effective treatment option with an attractive return on investment. Also a number of national agencies (for instance, the Scottish Environment Protection Agency – SEPA) are promoting a more circular approach to resource use – while encouraging lower carbon emissions, better use of materials and a reduction in fossil fuel use. This approach could eventually be extended to the imposition of penalties on sites that are more profligate or do not take measures to cut energy use or deploy renewables.

Despite the benefits for industrial sites, AD development across the UK has been slanted towards larger municipal plants, often using imported technology. While this is an effective use of AD technology, there have been issues with process efficiency and residual digestate disposal, plus impacts on nearby communities (transport, noise or odour). This is partly due to the involvement of major utility companies that tend to favour larger scale projects. After rapid expansion but with uncertain investment returns from a number of plants, this sector appears to have stalled.

Also, there are concerns about use of purpose grown crops for farm AD plants and Government will be limited support for this sector from 2017, in part due to concerns about the land use impact and carbon efficiency. Despite potential for greater use of AD to treat manures or crop residues, it is a development of the on-site industrial AD sector (fed with materials at or close to the place where they are created) that has the most potential for further growth and is the focus of this paper.

Harnessing the potential for on-site bio-energy

With the food industry becoming increasingly concerned about its impact on the environment, there is an opportunity to replace the energy intensive aerobic disposal of energy rich process residues with on-site anaerobic plants. Growing interest in the benefits of the circular economy, will transform business models created when the level of resource use was of less concern.

Improved resource use should be part of Britain’s business strategy prior to Brexit – in part to ensure the UK can meet sustainability requirements in other markets. The 2017 Green Paper ‘Building our Industrial Strategy’ [1] places the switch to the low carbon economy within the ten pillars of this new strategy but is less explicit than it could be on future support for industrial transition. Moreover, the Brexit White Paper [4] published in February 2017 underlines the Government’s aspiration for a cleaner environment, with the UK a ‘leading actor’ on climate change, without being specific on how it will support delivery for industry and specifically in the agri-food sector.

Decentralised energy supply

Investment in decentralised (on-site) bio-energy will enable the British food and beverage industry to reduce its environmental footprint and overcome a perceived ambivalence about resource use and levels of waste in the food chain. Such investment can be justified as follows:

  1. A processing residue is no longer a waste but a resource used to generate energy on site, while minimising off-site disposal of unwanted bio-materials and liquid effluents.
  2. Disposal costs associated with such residues are converted into a source of revenue. These costs not only include energy used for aerobic treatment but also transport off site for approved treatment or disposal – not only costly but a significant use of fossil fuel.
  3. Alternative solutions (often aerobic treatment) use more energy to achieve the same goal without generating renewable energy that can be harnessed by the industrial user.
  4. Importantly (and something we have experienced recently) on-site AD can help improve the position of sites facing competition pressure or the impact of rising fuel and disposal costs. AD enables a site to provide more sustainable treatment as well as secure energy supplies that can offer a variable proportion (10–30%) of site energy needs.

With a number of multinational businesses like Unilever, Nestle and Arla already investing in on-site AD in the UK, there is scope to build the market for industrial solutions, also for the smaller SME businesses that proliferate across the European food and drink industry.

In addition to the potential to export modular plants to other markets, we are developing plants on smaller sites – e.g. the plant being installed on a craft distillery in southern Scotland (see Fig 5).

Fig 5: 3D image of craft distillery with planned AD plant in the background

Expected increases in costs of energy and the handling of process residues will support the business case for on-site bio-energy. However, to encourage investment in renewables (AD plants can take over a year to fund, design, install and commission) businesses need to be able to predict their return on investment. While there are still incentives available, ultimately future on-site bio-energy plants must be viable without current renewable generation support.

In the shorter term, to deliver more widespread deployment of such bio-energy systems on industrial sites, we need for a more creative approach from Government, including support for industrial low carbon demonstration sites. While it is helpful that the recently published Brexit White Paper and the Industrial Strategy Green Paper make passing references to carbon reduction and clean technologies, greater clarity on what is expected from the business community would be helpful. All too often, actions of Ministers and key Government departments do not necessarily match up to the fine words in policy documents.

To prepare for a future without renewable incentives, the industry needs a period of policy stability to enable bio-energy to fulfil its potential in delivering decentralised bio-energy and to boost carbon savings. Also, the priorities of policy makers must switch from further investment in larger centralised plants towards multiple smaller on-site units that treat biodegradable feedstocks where they are produced.

Developing a more circular economy

There is considerable potential for on-site re-use of processing residues, as part of the transition to a more circular resource use and enhanced industrial sustainability. To stimulate industrial investment in smaller scale renewables, policy makers must recognise that on-site digestion of process residues saves costs and helps meet carbon reduction targets. Bio-energy generation can help protect sites from future energy cost increases and enhance overall sustainability.

Despite the failure of past Governments to recognise the value of smaller scale bio-energy, an increasing proportion of our energy could come from decentralised installations at the point where energy is used. In a more circular economy, as part of a more integrated industrial and renewables policy, investing in smaller scale, on-site renewables should help boost industrial competitiveness. Interrelated drivers for increased industrial investment in bio-energy, include

  • Increased focus on resource use – There is growing pressure to embrace a more circular approach to production but much of this is superficial commentary by politicians, academics and consultants. On-site generation allows businesses to address concerns over resource use and levels of water loss and energy demand in the food chain.
  • Energy costs and carbon emissions – The food industry is aware of the need to address future energy cost rises, as well as greater price instability. Some degree of on-site generation is a partial solution. Also, energy from biodegradable residues supports de-carbonisation of the food chain, reducing the carbon footprint of individual sites.
  • Handling biodegradable residues – Disposal costs for process residues continue to rise, driven by regulatory factors and practices that deny access to the available energy. Rather than disposal of bio-residues to sewer or landfill, businesses need effective, low-risk solutions that do not require excessive space or undermine production processes.
  • On-site renewable energy – Pressure to develop lower cost renewable energy will increase with stakeholder (retail and regulator) pressure for low carbon manufacture. On-site AD and biomass solutions will allow sites to generate base load power (or heat), while exporting electricity when on-site demand is lower (or times of peak demand).

Greater awareness is encouraging British manufacturers to evaluate bio-energy or develop better resource use practises, looking for robust solutions that do not impact on manufacturing processes. However, for bio-energy to fully contribute to the transition to a more circular economy, SME businesses also require reassurance from policy makers that it will be cost effective to access the energy value of their residues.

Targeting the food and drink sector

After the 2015 Paris COP21 Climate Change Convention, a group of leading food and beverage sector multi-nationals made commitments to change their practices. CEO’s of global companies like Unilever and Nestle signed a statement of intent: ‘We want the facilities where we make our products to be powered by renewable energy, with nothing going to waste, as corporate leaders, we have been working hard toward these ends, but we can and must do more.’

With global food companies setting ambitious targets for reducing their GHG emissions and developing the circular economy, what should British firms, large and small, be doing to match this? Those UK companies that have installed on-site bio-energy plants are benefiting from incentive revenue and cost savings while boosting their CSR profile.

Industrial deployment of bio-energy

Progressive improvement in AD technology (e.g. process control, biogas yields, COD removal efficiency, ability to recycle grey water and plant footprint) has enhanced payback. In the past decade about 30 AD plants have been built on UK factory sites – cutting emissions and producing a decent return on investment.

AD is now more attractive for off-balance sheet finance providers, with an increasing appetite among the investor community for on-site plants that can provide a better return than is available from merchant plants. In any case, the ROI for industrial investment in renewables needs to be higher than the circa 15% targeted by municipal projects.

Clearfleau has taken a lead in developing the on-site liquid AD sector but other technology suppliers (of higher and ultra-low solids systems) are active in the UK market. Some higher solids systems can be found in the food sector (mainly on vegetable processing sites) but they require more space (for multiple digestion tanks). More effective residue management solutions will help companies to recognise the calorific value of their bio-residues and the carbon impact of other disposal systems. Enabling smaller sites to use such residues rather than exporting potential energy value should be part of progress to a more circular economy.

Despite reduced incentive support for renewables, businesses will consider on-site alternatives to fossil fuel derived energy, not just biomass systems and bio-digestion but also fuel cells and hydrogen energy, if there is an adequate return. Benefits also include improved bio-security and less handling on site, as residues are fed to the AD plant as they arise and do not have to be stored or transported. Fossil fuel substitution (with biomethane, biodiesel and hydrogen) brings a commercial advantage, by adding value to discarded materials and reducing production costs.

The beneficial impact of on-site bio-energy is clear but how do we make it easier for SME firms to invest, given the challenges that arise with smaller sites? Choices must be made regarding the best match for a site based on space available, energy needs, grid access and fluctuations in energy demand. There are specific issues to be addressed on smaller sites.

Fitting plants on a confined footprint

When fitting plants on clients’ sites, the footprint available is often less than ideal. On some sites containerised units for ancillary equipment can be part of the solution. The considerations that should be taken into account in the preliminary design and evaluation phases include:

  • Space saving and whether equipment can be housed in existing buildings. For instance, for the craft distillery project, to create space for the digester, all the related equipment is housed in a 2-storey building, therefore maximising use of the limited area available.
  • Is there potential for shared technical services? Consideration is given to a shared laboratory and other facilities, although the boiler or CHP unit must biogas dedicated.
  • Integration with production is a key consideration – manufacturing processes cannot be compromised by the AD plant. Production needs to always take precedence.

It may also be possible for smaller sites to combine and share the energy produced as well as to develop centralised plants for locations where there are a number of smaller businesses.

Matching biogas output to thermal demand

On industrial AD plants with thermal output below 1 MW, a common concern is finding the best way to match output with clients’ energy demand. When more energy is generated than can be used in production, can it be exported as power? On some sites there may be a need to find other uses for the surplus biogas – there are three main options for utilisation of biogas on-site:

  • Combustion in a boiler (biogas dedicated to qualify for incentives) to produce hot water or steam. On sites where there are no incentives biogas and natural gas can be co-fired.
  • Combustion in a CHP engine to produce power for the site. Power can be exported if not required but grid access can be an issue on some sites.
  • Upgrade to biomethane for injection into the local grid or compression for use as vehicle fuel. Gas grid injection is not really viable for sub 1 MW (thermal) plants due to upgrade costs but vehicle fuel conversion could be an attractive option for product transport.

The two Case Studies 1 and 2 (see Figs 9 and 10) illustrate how decisions have been made at different sites.

The effective use of energy is often key to the viability of individual projects but this is affected by incentive rates and the changes in incentive rules. However, a biogas boiler will tend to be the simplest solution on smaller sites. As well as optimising the use of (and revenue from) energy produced, there is a need to curtail capital costs for smaller plants. For SME sites (plus potential export projects) we are developing solutions based on modular units, to reduce construction costs and improve ease of deployment on the site.

There are a range of technical options that if combined can provide cost-effective solutions for smaller SME sites. We have developed a micro test plant for use in EU funded research into low temperature AD (the Ambigas project), as well as an earlier containerised unit for on-site trials. This modular approach should allow on-site AD to be deployed on a wider range of industrial sectors:

  • Modular design for the ancillary equipment mounted on skids or containers.
  • Lower temperature operation of the digester to run it at ambient temperature.
  • Inclusion of grey water recycling, enabling sites to improve use of water resources.
  • Pre-treatment of higher solids feedstock to extract further value from site residues Fig 6.

Fig 6: Micro trials plant for the EU funded Ambigas Project

Making the business case

In addition to addressing technical and engineering issues for smaller more compact sites, there is also a need to make the business case for on-site bio-energy generation and demonstrate an attractive return on investment. Despite the successful experience with existing plants, concerns remain about impact on the core business, access to funding (either internal capital sanction or from third party funders) and the unexpectedly rapid degression of incentive rates. Hence, bio-energy technology providers must develop solutions that fit with individual requirements of the site but also offer an attractive investment proposition.

The plant built for Nestle on their Fawdon site (treating confectionery residues) included containerisation of the main process elements to allow off-site assembly and reduced construction time on site. This approach could also be applied for export projects (see Fig 7). Other design configurations can also be used on confined sites such as the craft distillery and the rural distillery site in Speyside (see Fig 8).

Fig 7: On-site AD plant on Nestle’s Fawdon Confectionery Site

Fig 8: 3D image of smaller AD plant serving a distillery to be operational in early 2018

While companies like Unilever or Nestle will consider investing in sustainable manufacturing, as part of longer term strategy, the reality for smaller businesses is that internal funds are allocated to core production activity. Thus, external funders are needed to support on-site renewables.

If on-site AD is to be deployed more widely on SME sites, some key issues must be addressed:

  • Access to funding: Smaller companies are less able to devote scarce resources to sustainability and require external funding, from specialist funders that understand AD and recognise the better returns that can be available from on-site projects.
  • On-site solutions: Traditional practices (like aerobic treatment) or access to off-site solutions, combined with limited financial resources, tend to make SME managers to be less open to novel technology and we need to raise the profile of on-site options.
  • Carbon savings: To date pressure from stakeholders and regulators has had limited impact. But, as landfill costs rise (and Scotland and Wales banning disposal of biodegradable residues to landfill) less carbon intensive solutions will come to the fore.
  • Internal resources: Many SME sites have limited staff time available for activities that are not directly related to core production activity. Hence reliance can be placed on external consultants who may prefer to stick to established technologies, that do not offer access to on-site energy for the factory or the extent of carbon and cost savings.
  • Incentives rates: Despite pressure to reduce emissions SMEs and family companies are being deterred by declining incentives. Also, there is perceived lack of Government interest in addressing climate change, the circular economy or supporting bio-energy (support for nuclear plants is being contrasted with falling renewables incentives).
  • Political support: It is in the wider interests of the British economy (post Brexit) that Government helps successful British bio-energy companies to compete in the EU and globally. This should include supporting he market for industrial on-site renewables.

There is greater recognition of the need for industry to invest in the circular economy and decentralised energy generation. However, there must also be a clear benefit from investment in on-site renewables, in terms of cost saving and manufacturing efficiency. However, to help keep the UK economy competitive post Brexit, access to bio-energy solutions must be extended beyond the larger food sector businesses.

Delivering bio-energy in the SME sector

Interest in more sustainable manufacturing models is being led by food multinationals, as indicated by their support for investment in on-site bio-energy after the Paris Climate change summit. However, extending this approach more widely in the British food sector will require a more supportive policy and regulatory framework focused on changing existing practises.

Decentralised micro-generation from production residues and by-products can reinforce efforts to reduce reliance on fossil fuels and cut industrial carbon emissions. Policy makers still need to be persuaded of the value of the bio-economy and smaller scale on-site generation of renewable energy. In the past decades, incentive support has been focused on larger centralised merchant and crop based plants, not all of which are delivering cost effective, low carbon energy.

Developing the bio-economy

Decentralised bio-energy can support the transition to a more circular bio-economy, helping more UK industrial sites to limit their environmental impact with low carbon solutions. Adapting bio-energy policy to help promote smaller on-site plants that generate value from bio-residues will boost emissions reduction. The installation of multiple bio-energy plants should be encouraged alongside the development of novel technologies and the supply of raw materials for more resource efficient bio-refinery technologies.

The bio-economy (which includes forestry and the agri-food sector) already contributes £36 billion in gross value added (GVA) to the UK economy, of which over 80% is from food and farming. In 2012, industrial biotechnology and bio-energy contributed 3% to the sectors’ GVA, accounting for at least 1% (6,000 jobs) of sector employment [5]. With growth that has taken place since 2012, this should be significantly higher (perhaps 10% of employment in the renewables sector currently which exceeds 100,000). Policy makers should value the number of engineering and related jobs being created in the bio-energy supply chain.

However, development of Britain’s bio-economy requires industry confidence in available technologies plus a stable, supportive regulatory framework. Future growth in bio-engineering and the bio-energy sector also depends on the policy framework and Government investment in research. With support for companies investing in collaborative or on-site projects, the bio-economy could a key growth sector for the post Brexit economy. While the UK may be leading research in this field it is commercial exploitation that drives economic growth. Hence more attention needs to be paid to motivation of businesses to invest in this sector.

Enhancing resource efficiency

Assessment of site potential for investment in bio-energy should be a first step in the evaluation of how to boost resource efficiency. Companies should start by looking at issues such as site energy requirements or feedstock suitability. This includes specific site criteria (such as seasonality, discharge requirements or energy demand) and access to the space to build on-site AD plants, alongside the evaluation of biogas potential and degradability of available residual materials and their suitability for a particular digestion system (higher or lower solids).

Investing in better resource use and bio-energy should provide a competitive advantage while supporting commercial goals, such as cost reduction, sustainability and plans for expansion or brand development. Other factors influencing decision making include access to in-house skills to support and champion a project, plus access to funding or credibility for an external investor. Also, whether a site is facing regulatory pressures (e.g. due to a failing aerobic plant) and the planning landscape, particularly for urban sites.

Commercial interest in resource use and access to bio-energy will increase but more political engagement is required if bio-engineering is to play a more prominent role in development of the economy. Also, if technology providers are to capitalise on opportunities for wider deployment of on-site renewables, we must overcome reservations about investing in non-core activities like energy generation and carbon reduction.

Commercial and political drivers

In addition, as suppliers, we need to continue to develop the technology to provide solutions that will minimise capex cost while limiting operating costs to help keep rates of return close to 20%. We also seek to keep core technology as simple as possible with limited operator input but also to minimise the risk of interruption to manufacturing processes. For smaller businesses with restricted funds, improved access is required to external funding for more innovative on-site energy solutions, on a build and operate basis but this also requires a stable incentive regime.

As energy prices start to rise again, we can demonstrate how reduced energy costs and other operating expenditure (OPEX) savings can boost on-site efficiency and cost recovery. However, there is still a need for more demonstration sites, other than on factories run by the large multinational companies and Clearfleau hopes to have several such reference sites in operation in the next 12 months.

Wider adoption of bio-energy generation on food and beverage manufacturing sites (the sector is one of the largest consumers of energy in the UK) requires a more strategic support to help smaller businesses follow the lead from the multinationals. It is perhaps not surprising that most of our current projects are in Scotland, where the devolved administration is enthusiastic about renewables. Government should do more to engage with industry and facilitate more sustainable industrial development.

Regulators could do more to support smaller companies that are keen to invest in renewables. Perhaps assisting companies to access the most appropriate technologies and showcasing novel solutions that are contributing to the bio-economy. Also, food sector trade bodies should work with Government and the industry to promote the benefits of a more circular economy and low carbon solutions, including:

  • Challenging industry to find ways of cutting emissions and fossil fuel demand.
  • Promoting the economic and wider benefits of on-site decentralised generation.
  • Developing a more coordinated approach across the food and beverage supply chain.
  • Encouraging more collaboration between businesses, particularly on adjacent sites.
  • Developing drivers and incentives based on carbon (GHG) emissions reduction.

Hopefully, in time, commercial interest in better resource use within the circular economy will see greater use of bio-feedstocks not only for energy generation but also alternative industrial raw materials in the emerging bio-economy. Improving resource use across industry could also include the ‘mining’ of landfill to extract discarded materials and adding value to a wider range of residues.

However, the future of the bio-energy sector (and wider bio-engineering solutions) requires a fundamental change of approach within Government, in relation to energy and resource use priorities. BIES should follow Scotland’s example and look at setting targets for decentralised energy generation, while adjusting the imbalance between levels of taxpayer support for the nuclear sector and for renewables. A switch of 5% of funding from nuclear will stimulates growth, support engineering jobs and boost technology innovation.

Moreover, future taxpayer support should focus on British technology as Britain risks handing a major share of its renewables market to EU suppliers. We need to see more overt support for developing the Circular Economy by deploying British technology. On-site bio-energy will not just help the UK curb agri-food sector emissions and meet renewable energy targets, as it is also able to provide baseload power and peak lopping capabilities, unlike solar or wind energy.

Conclusion – technical and policy drivers

The UK has the technical solutions, engineering skills and pioneering instincts to challenge the traditional approaches to resource use and commercial energy supplies but we need to find technical and funding solutions to help smaller businesses embrace lower carbon manufacturing and on-site bio-energy.

In the run up to Brexit, the UK’s food and beverage industry needs to be more competitive in Europe and develop new markets elsewhere. Also, with global food sector leaders pushing for more investment in on-site renewables, the British supply chain needs to match action by EU companies on emissions, resource efficiency and decentralised energy supply. However, to be technically viable on smaller sites in the food and drink sector in Britain and across Europe, the on-site digestion sector needs to be:

  • Innovative – reducing costs and increasing operational efficiency, such as by limiting the liquid retention time and extending bio-solids retention to optimise COD removal and biogas output.
  • Flexible – recognising that energy requirements vary on each site and being able to meet this with a combination of options for use of biogas, while matching peaks and troughs of site demand.
  • Reliable – acknowledging that the site’s production capacity cannot be compromised by a plant that is not available all the time or not able to handle expected variation in flows and loads.
  • Commercial – delivering a credible return on investment that in line with industry expectations, and well in excess of the 8–10 years payback that is the norm for other renewable technologies.

The on-site bio-energy sector can also generate base load energy on factory sites where it is required but wider adoption needs a more sustained commitment from policy makers. If Minsters are keen to promote a cleaner, more circular economy, including low carbon manufacturing, can they do more to back the deployment of decentralised energy generation from process residues on industrial sites?

Government should collaborate with industry stakeholders on the delivery of a low carbon industrial strategy. The actions of large multinationals may be determined by different drivers to those of smaller firms but all businesses should be contributing to the improved management of our natural resources.

Modest support for smaller on-site bio-energy plants over the next five years will increase decentralised energy production. More efficient management of residues and carbon emissions will provide a boost to the circular economy. British technology and engineering skills can embed the circular economy in our manufacturing strategy and we should be challenging companies to embrace this.

The UK has the engineering skills to deliver technical solutions. But, if British industry is to match the lead being taken by global business leaders, it will require technology providers, trade associations and bodies concerned with our industrial competitiveness to challenge politicians to help with the transition.


  1. Building Our Industrial Strategy – Government Green Paper January 2017,, accessed May 2017.
  2. Cheremisinoff N. P.: ‘Biotechnology for waste and wastewater treatment – 3.5.9 anaerobic digestion (treatment)’ (William Andrew Publishing/Noyes, 1996), p. 136. Available at:
  3. Adapted from Carlos Augusto de Lemos Chernicharo: ‘Biological wastewater treatment series’ (Anaerobic Reactors, IWA Publishing, 2007, 1st edn.), vol. 4, p. 6.
  4. The United Kingdom’s exit from and new partnership with the European Union – Government White Paper February 2017,, accessed May 2017.
  5. Glyn Chambers, Alexandra Dreisin and Mark Pragnell: ‘The British Bio-economy - an assessment of the impact of the bioeconomy on the United Kingdom economy’ Capital Economics Ltd, 11 June 2015,, accessed June 2017.

Case study: Glendullan bio-energy plant

The AD plant (commissioned in 2014) converts 1000 m3 of distillery co-products per day into 1 MW of heat, feeding biogas to a dedicated biogas boiler that supplies renewable energy to the distillery, reducing its carbon footprint. Following completion of an initial digestion facility at the Dailuaine malt distillery (in 2013, also in Speyside) Diageo requested Clearfleau to build a second facility. The on-site plants optimise energy output from distillery co-products and involved close collaboration between Clearfleau’s in-house design, installation and commissioning engineers, their Diageo counterparts and an extended supply chain (Fig 9).

Fig 9: Case study 1, Glendullan bio-energy plant

The Glendullan plant also receives feedstock from other distilleries in the Dufftown area, fed via a recently completed pipeline, reducing local truck movements. The bio-energy facility is generating 2 million cubic metres of biogas per year – producing about 8000 MW hours of thermal energy for the distillery. Diageo has set an example to British food and beverage companies (plus other distillery sites). Engineering challenges involved developing a plant able to handle higher strength materials such as pot ale, and variability in strength and volume of feedstocks being fed to it. They also included the location of the plant on a sensitive location in a valley adjacent to the river Fiddich and achieving the complex water course discharge standards.

Case study: Lake District biogas plant

The innovative bio-energy plant built and operated by Clearfleau for Lake District Biogas converts over 1000 m3 per day of cheese whey into biomethane, generating 5 MW hours of thermal energy for the site and local community. Located on First Milk’s Aspatria creamery in Cumbria (one of the UK’s largest cheese creameries) the plant demonstrates how the circular economy can be applied to food processing sites. The main project objective was to replace a failing and costly aerobic treatment plant (seen on the right of the image) with AD to reduce carbon emissions, generate energy and make the site more sustainable (Fig 10).

Fig 10: Case study 2, Lake District biogas plant

The largest on-site digestion plant in Europe’s dairy processing sector and the only creamery site that is producing biomethane generated entirely from its processing residues, without inclusion of additional non-dairy feedstocks. Biomethane, supplied to the nearby gas grid, is supplied to the creamery’s boilers, and to households or local businesses. In addition, power is generated from a 500 kW CHP unit run on biogas generated from the AD process and cleansed water is discharged to the nearby river. By treating process residues from the creamery, it is reducing its use of fossil fuels by over 25% and provides a long-term sustainable solution for process residues from cheese making that can be deployed on comparable large scale food and beverage sites. This approach is now being replicated on other dairy sites in the UK.

Case study: urban craft distillery

In the case of a craft distillery being built in lowland Scotland, the most significant energy demand will be in the form of steam, with less demand for electricity. Hence, a biogas fired boiler producing steam has been designed to produce a proportion of distillery heat requirements. The distillery will be able use its modest output of co-product to produce about 20% of its energy needs and the biogas can provide a guaranteed price per kWh for a proportion of steam supplied to the distillery (Fig 11).

Fig 11: Case study 3, urban craft distillery

However, there were issues with fluctuating demand for heat at certain times of the week and this has been a major feature of the initial design phase. In addition, with the distillery being located on a derelict industrial site in an urban location, it was essential that the client and plant provider work closely with planners and other local stakeholders. The new distillery that will help regenerate the area and will have a minimal impact on the environment, with zero off-site waste disposal and effective re-use of all its process residues (all the residual bio-solids will be sent for composting). This site will combine optimal on-site energy generation combined with zero off-site disposal of residues. It is hoped that this approach will be replicated on other smaller malt distilleries.

Case study: cheese dairy

On smaller sites the power output from the biogas can be sufficient to meet the dairy’s electricity demand, avoiding the need for an export connection. However, a significant fluctuation in site energy demand during the day and over weekends, can result in periods where no energy is required for the production process. Dealing with periods of significant peak demand can be an issue when the AD plant is producing biogas at constant output (Fig 12).

Fig 12: Case study 4, cheese dairy

Options for optimal gas use can include storing biogas and combusting it when required in a CHP if there is no ability to export power. Running a second CHP unit on an adjacent site with its own power demand is an alternative, with the biogas being exported in a private pipeline or upgrading to biomethane, compressed for use as vehicle fuel in the milk collection fleet for the creamery. Smaller scale technologies are available and engines can be adapted for biogas offering demand for a proportion of the gas on some sites.

On the smaller sites energy use has a major bearing on viability and in most cases a comparison will be made on cost and revenue implications. For some sites viability will be enhanced where there is scope to use bio-fuel, heat and power in the creamery.

Go to the profile of Richard Gueterbock

Richard Gueterbock

Marketing director, Clearfleau

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