Supersized Biowaste Treatment to Admire

Tank you very much: the facility has a capacity of 120,000 tonnes of food waste Packaging often proves a challenge for biowaste processing facilities. A new 'super' £24 million anaerobic digestion facility in the UK has the technology to overcome this and well as set the standard for large-scale infrastructure, explains Ben Messenger. Around 10 million people in East Africa are currently at risk of starving, in what aid agencies are calling the worst drought for 60 years. It is more than a little perplexing, therefore, that a recent study by the United Nations Food and Agriculture Organisation (FAO) shows that one third of the entire World's food production - about 1.3 billion tonnes - goes to waste. Every year, consumers in rich countries waste 230 million tonnes of food, almost as much as the entire net food production of sub-Saharan Africa. According to the FAO, North American and European consumers are each discarding an average of 100 kg food waste per year, with the largest constituent being fresh fruit and vegetables. Financial incentives In the UK, figures from the Department for Environment, Food and Rural Affairs (Defra) and the Waste & Resources Action Programme (WRAP), show that around 16 million tonnes of food waste is generated each year, with around half of this coming from businesses, and at least 40% currently ending up in landfill. And all that waste raises more than just moral questions. It causes half of all waste related CO2 equivalent emissions in the UK - 3% of the national total. Because of this, as in many countries around the world, the UK government has identified food as a priority waste stream. While the government's recent Waste Review identifies prevention as the most effective means of tackling the issue of food waste, it also recognises that some food waste is unavoidable. The the key to negating the impact of such waste lies in treating it in the most sustainable way, it says. By aiming to treat food waste as high up the waste hierarchy as possible, the government has identified Anaerobic Digestion (AD) and in-vessel composting as the most appropriate technologies with which to treat food waste. To this end a number of financial incentives are being offered by the government to encourage the development of AD, including Renewable Obligation Certificates (ROCs) per MWh, Feed in Tariffs (FiTs) and a Renewable Heat Incentive (RHI) for biogas combustion. As a result, a number of companies are investing in food waste infrastructure projects around the country. One example of a company tackling food waste in a 'super sized' fashion is waste management firm Biffa, which recently opened its 120,000 tonne per year capacity food waste AD facility adjacent to its landfill site in Poplars, Staffordshire. The UK's new big hitter Speaking at the opening of the £24 million Poplars facility, Ian Wakelin, Biffa chief executive, explains that this 'super' facility is a strategically important step forward in the company's plans, and makes more sense than having lots of small plants dotted around the country. "Firstly it's cheaper," he says. "It's cheaper for us and it's cheaper for our customers. Secondly you can deploy more technology in bigger plants." John Casey and Ian Wakelin at the opening of Biffa's new 'Super AD' facility With plans to roll out a further three to five such facilities in the coming years, this is a strategy that Biffa intends to follow. The idea sounds like a good one. Scale up the facilities and use economies of scale to invest in more sophisticated technologies that will allow for greater yields, less downtime and higher quality outputs. But what makes this facility 'super'? According to Wakelin one of the problems that AD food waste facilities typically face is that of packaging. When Biffa began designing this plant two years ago it was very keen that it should be able to accept as wide a range of food wastes as possible. By leveraging its size the Poplars facility has been able to install sophisticated machinery that will strip the packaging away from the food and send the plastics for recycling. The development of the plant was heavily influenced by lessons the company learned in extracting gas from mixed black bag waste at the Mechanical Biological Treatment (MBT) plant in Leicester, which it has been running since 2003, explains Dr John Casey, director of engineering and quality at Biffa. As such the company applied the same design principles of creating a robust system, with built in redundancy that allows for one part of the plant to undergo maintenance without shutting down the whole operation. The whole design and build of the facility has been completed in two years, with work continuing through winter temperatures that sank as low as -20°C. The process Upon arriving at the 120,000 tonnes per annum facility, vehicles enter through rapid open/shut doors and unload in a waste reception area. Solid and liquid waste is emptied into a bunker then crushed before grit and packaging is removed. The reception hall has been designed with four bunkers. The idea behind this is to allow the control room to remove any contaminants from the waste stream before it can damage the process, and also to ensure that different wastes, with different gas yield potential, are optimally fed into the digester. This ensures that limited waste alcohol enters the digesters at any one time. This is claimed to be a unique design, and has been developed by Biffa and environmental engineering firm Ros Roca envirotec, which was awarded the contract for the installation of the food waste AD technology in 2009. Once cleaned the biogas is sent to an 850 m3 buffer bag From the bunkers, waste is processed through a series of crushers and macerators that break down the packaging and the waste fraction to a size where the organic matter can be recovered, and the plastics and other contaminants are separated in a series of trommels and washed to clean it of all organic matter. Casey says that the company is also working with its partner, Biffa Polymers to develop the capability in the next four to six months to recycle the separated packaging. The heavy fraction such as glass is also removed and used in aggregate applications. Organic material is then passed through a range of sanitisation tanks where any pathogens are killed. This pasteurisation process heats the material to 70°C for at least one hour to meet the requirements of the Animal By-Products Regulations. Waste is then piped into one of five digester tanks in which naturally occurring microbes already present in the waste break the material down over a certain time frame, creating methane and carbon dioxide (biogas) and water. The optimum gas yield for the facility is between 160 and 200 cubic metres per tonne of food waste, with the process taking around 20 days to complete. Before the resultant gas can be use to fuel the three 2 MW spark ignition reciprocating gas engines at the site, it has to first be cleaned, before being sent to an 850 m3 buffer bag, enough for about an hour to an hour and a half of generation. Self sufficiency Operators aim to keep the buffer between 30% and 70%, and match the demand from the engines to gas output in order to minimise the need to flare any excess gas. Once at full throughput the three 2 MW gas engines are expected to be running at full capacity for around 93% of the time. In addition the engines generate more heat than is required by the AD facility, and alternative uses for the surplus are being investigated. The plant will also be entirely self sufficient in electricity, with surplus being exported to the grid. By leveraging its size the Biffa has been able to install sophisticated machinery The wet mixture is transferred into two centrifuges to reduce the water content, with the remaining solids used by local farms as a soil improver. This digestate is to be produced to meet PAS110 certification, which is a specification for whole digestate, separated liquor and separated fibre derived from the anaerobic digestion of source-segregated biodegradable materials. According to WRAP the purpose of PAS110 is to remove a major barrier to the development of AD by encouraging markets for digested materials, and to create an industry specification against which producers can check that the digested materials are of consistent quality and fit for purpose. PAS110 quality allows the material to be used as a composting agent, or for soil restoration. The future's big "All of our customers that we talk to want to do more," adds Wakelin. "They want to do more because waste is now quite expensive. It gets more expensive every year and in terms of CSR (Corporate Social Responsibility) getting to zero waste to landfill at some point is an objective for most of our customers. We try to look at waste as an asset, but we need to embrace technology. Now the cost has got more and more expensive it has enabled us to do that." Large scale AD facilities do not solve the ethical dilemma of discarding so much food, much of it still edible. Developed countries will continue to waste yet developing countries will continue to go hungry. For that the solution lies in education further up the waste hierarchy. However, with increasingly tough landfill diversion targets, and such a large volume of waste to deal with, facilities like this will look increasingly attractive to policy makers, waste management companies and their customers. Ben Messenger is associate editor of Waste Management World magazine, email: benm@pennwell.com More Waste Management World Articles Waste Management World Issue Archives