Food and drink manufacturers, as well as pharmaceutical companies and producers of biofuel that want to cut residue processing costs, might want to consider deploying on-site anaerobic digestion (AD). This green technology can pay for itself in under five years and will turn biodegradable production residues into energy for reuse in the production process. This has to be the most sustainable way forward argues Richard Gueterbock, Director of leading UK technology provider - Clearfleau.
So how does AD work?
Biodegradable liquid production residues can be diverted away from sewer discharge (or other offsite disposal routes) and fed to an on-site AD plant. Here bio-degradable solids are broken down by naturally-occurring bacteria. In the absence of oxygen this releases methane, a combustible gas which can be used to generate renewable heat or power. In the process of breaking down residues, anaerobic digestion can remove up to 95% of COD load, also facilitating grey water recycling.
Production residues from food, beverage, pharmaceutical and bio-fuel production sites have their own challenges and our solutions are tailored to site requirements. These include the composition of the production residues (including fatty and solid materials). Digester scale is affected by feedstock flows and loads and its composition, as well as location and physical constraints of each production site, budget and operational resources. What each site does have in common is a desire to minimise the cost and environmental impact of its production process and generate renewable energy.
As more industrial companies adopt on-site digestion technology to reduce costs and increase their sustainability KPIs, they can also contribute to the Government’s 20/20/20 targets: to reduce 20% of greenhouse gas emissions, increase energy efficiency by 20%, and supply 20% of energy needs from renewables by 2020. Nestlé, Diageo and First Milk (Lake District Biogas) are just three companies using on-site bio-energy systems to process bio-degradable production residues to generate heat and power. They are cutting fossil fuel use, becoming more energy efficient and minimising disposal costs. In the competitive marketplace, on-site AD can have a significant impact on sustainability by adding value to unwanted residues - a great example of the Circular Economy in practice.
Nestlé, as one of the world’s major food and nutrition companies, is committed to a sustainable approach to manufacturing. Nestlé chose Clearfleau in 2013 to install an AD plant at its confectionery factory at Fawdon, Newcastle where it produces a wider range of brands including Toffee Crisp, Fruit Pastilles and Rolos. Previously, all the site’s liquid production residues were discharged to the sewer with solids transported to local farms as pig feed. Nestlé is now generating significant revenue from disposal and energy savings and incentive payments. The company has also achieved the Dow Jones Index’s 'Environmental Dimension', its score of 99 is the highest in the industry, which underlines its commitment to water stewardship and environmental sustainability.
AD plant balance tanks at Nestle, Fawdon.
Alongside a detailed procurement exercise, the operation of Clearfleau’s mobile trials unit on the site confirmed its ability to process both liquid and solid residues. The design team was faced with the challenge of dealing with a range of solid residues as well as installing the new AD plant and CHP on a constrained footprint alongside a car park and adjacent to the Metro line. The plant is an integrated part of the manufacturing process and handles around 1,200 tonnes of solid production residues, by-product and residual ingredients each year. It also converts this plus over 200,000 litres per day of waste waters into renewable energy through the generation of biogas.
This gas fuels the combined heat and power engine which produces up to 200kW hours of electricity. This equates to about 10% of the factory's power requirements. This process generates at least 10% more biogas than other high-rate digestion systems. The annual electricity bill has been cut by about £100,000. Nestlé also registered the site for the feed-in tariff renewable generation incentive scheme.
Nestlé is looking at the potential benefits of AD on other manufacturing sites and has guaranteed that all its UK factories will no longer send waste to landfill by the end of 2015. This project demonstrates not only that on-site AD is a viable commercial proposition but also how to add value to unwanted residues. Most food processing plants will produce under 500kW hours of electrical power from their residues but this makes a significant contribution to energy requirements. We are starting work on a similar sized plant for a food processor, to supply additional power needed to expand output.
Combining energy extraction with post digestion water recycling delivers less tangible benefits to food manufacturers, such as minimising carbon and water footprints while boosting CSR credentials and upholding a hard-won brand image. On-site AD can deliver an attractive payback in under 5 years, based on savings and incentive payments. For Nestlé, what was previously a processing overhead is now a valuable financial and environmental asset and other manufacturers are keen to follow suit.
Diageo is a global name in alcoholic beverages. Its brands are produced in 200 sites in 30 countries, including the beautiful Scottish Highlands, where the heritage of whisky production is preserved, as Diageo converts its distilleries to renewable energy. The AD plant at Diageo’s distillery at Dailuaine became operational in 2013 and was the first distillery site to use Clearfleau’s on-site AD technology.
A key engineering challenge was in developing a bio-energy plant able to handle higher-strength materials such as pot ale, alongside other more dilute distillery co-products. After the digestion process, the residual COD and nutrients are removed in an aerobic plant before the cleansed water is discharged into the river Spey and the residual bio-solids are used as replacement for bought-in crop nutrients by local farms (replacing fossil-fuel based fertiliser) in some cases for the next barley crop.
In August 2015 a second Clearfleau bio-energy plant was completed at Diageo’s Glendullan distillery at Dufftown alongside the River Fiddich. This site was installed on land adjacent to the distillery and for such a large facility has been carefully integrated with the local environment.
This bio-energy plant can generate over 2 million m3 of biogas, delivering 8,000 MW hours of thermal energy from an on-site biogas boiler. By turning 1,000 m3 of co-products per day into 1 MW hour of heat, the site is saving over 1,000 tonnes of carbon each year. It is also cutting over 15 truck journeys daily, with a new pipeline supplying the AD plant from several nearby distilleries. Further carbon savings are derived from the change from aerobic to the more energy-efficient anaerobic treatment. Six months into operation, and the plant is delivering significant carbon reduction.
Clearfleau is now developing designs for further distillery bio-energy plants on sites across Scotland, including for a new micro distillery. Often located in places of natural beauty, distilleries need their bio-energy solutions to be fully integrated with the local environment, including the discharge of cleansed water into local watercourses. With scope to deploy on-site AD across the Whisky sector it can bring even greater benefits to smaller, more remote distilleries that have high energy costs.
First Milk (Lake District Biogas)
First Milk’s Aspatria creamery in Cumbria produces cheddar cheese under several brands names. Unable to fund the project due to other priorities, despite an expected payback of under 4 years, First Milk set up Lake District Biogas (www.lakedistrictbiogas.com) to fund, build, own and operate their new AD plant. The project will be a major boost for the creamery and for local farms that supply the milk, as it is minimising its impact on the environment (supported by the Environment Agency) as well as cutting energy and disposal costs while benefiting the local community. Clearfleau is now able to provide funding for its projects, in conjunction with its development partner Renewables Unlimited.
Dairy companies have stringent environment and health regulations to adhere to and a hard-won brand image to uphold. Like other businesses in the dairy sector, Lake District Biogas (LDB) was under pressure to reduce its costs and its impact on the environment. It is now doing both by addressing inefficiencies in the disposal of its unwanted whey permeates and other production residues.
Unlike other systems, Clearfleau’s liquid digestion process is able to accommodate fatty materials, so will reduce the chemical oxygen demand (COD) in the feedstock by over 95% to produce biogas with a methane concentration of at least 55%. The LBD project, which is about to enter the commissioning phase, is the first on-site AD project in Europe to supply up-graded bio-methane to the gas grid, based entirely on its production residues. It will also discharge cleansed water to a local watercourse. The equally innovative Wyke Farms project, which also puts gas into the grid, is a high solids system based on a wider range of inputs including local food waste and some locally grown crop feedstocks.
Feedstock will be pumped from the creamery to the AD plant which comprises two large digester tanks. The majority of the biogas generated is upgraded in a membrane based system to remove impurities prior to injection to the gas grid.
Downstream treatment will take place in an existing aerobic plant which we upgraded to enhance residual nutrient removal prior to watercourse discharge. The residual sludge from the plant will be dewatered in a screw-press and supplied to local farms for spreading to land as a soil improver. The entire plant is linked to the site SCADA (supervisory control and data acquisition) system to monitor key processes and provide operational data to all the parties involved in this complex project.
These three projects are being replicated on other sites in their sectors and we are also looking at projects that process residues from bio-fuel production. As businesses become more aware of the opportunities to reduce their carbon footprint, enhance their sustainability profile and add value to residues, we expect to see more on-site renewable energy plants being installed on industrial sites.
However, with a Government that is getting itself in a muddle over longer term energy policy, giving greater priority to expensive gas and nuclear generation over renewables, companies that do not take advantage of renewables in the next few years will miss out on current incentives and the opportunity to improve sustainability whilst generating significant revenue from process residues. In the longer term, these plants will have to be viable without access to taxpayer funded incentives but we also need to ensure that renewables are treated in the same way as other energy supply technologies.