Heading up the class

Biowaste management in the UK What do 800 tonnes of misplaced cocoa have to do with 4800 pigs? Two new organic waste management facilities, both using imported technology, have recently opened in the UK In March this year, the UK Environment Agency (EA) published the UK’s first quality protocol for compost. Martin Brocklehurst, Head of Environmental Protection External Programmes for the EA, commented ‘Under the quality protocol for compost, producers will be able to create compost which is no longer classed as a waste, making it a more marketable product to those who buy it, as it allows them to spread compost on to land without the need to register with the Environment Agency for a waste exemption.’ John Ibbett, Biogen’s Chairman shaking hands with HRH the Princess Royal at the opening of the new facility Click here to enlarge image This is a vital step on the road to a healthy by-products market; and it is indicative of a UK waste industry that is chomping at the bit to support serious landfill diversion and throw off the shackles of being a disappointment in the class of Europe. But the UK is a willing student and is now learning from its European neighbours. This was the first characteristic that linked two biowaste treatment facilities recently opened in south east England — one being an in-vessel composting facility and the other an anaerobic digestion plant. Both plants integrate imported technology. Other similarities include close ties with the agricultural sector and a clear focus on developing end-markets. Farming: it’s in the genes The Biogen Twinwoods facility in Bedfordshire was officially opened on 11 September 2007 by HRH the Princess Royal. The operators of the integrated anaerobic digestion (AD) facility have a background in farming and it is this backdrop that sets the context for efficient operation of the plant. Such expertise is invaluable when the processing strategy depends on integrating the needs of both farming and waste management communities. External expertise from the waste sector came primarily in the form of German partners who provided the biogas technology for the plant and were involved in its installation. Integrated AD technology Phil Moffat, Operations Manager for Biogen, informed me that the throughput of the plant will be approximately 30,000 tonnes of food waste and 12,000 tonnes of pig slurry per annum. The pig slurry comes from 4800 pigs on a nearby farm from sister company Bedfordia Farms. Cawleys waste management company supplies the food waste, mostly from commercial sources, and Biogen has installed depackaging equipment to remove unwanted packaging materials in this stream. The Powerscreen shredder is put to good use, preparing green and kitchen waste for composting and shredding willow waste for use in Envar’s biofilter Click here to enlarge image On arrival at the plant, the food waste is pasteurized at 70ºC for one hour — using process heat from combined heat and power technology to comply with the Animal By-Product Regulations (ABPR). The two waste streams are then mixed together within the reception building and fed into storage tanks, each with a capacity of 2200 m3. Lime can be added to adjust the pH as needed. Subsequently the mixture is added to the digesters — about six times per day — and frequently mixed, to be extracted after about 30 days. Prior to extraction, the material undergoes various chemical changes, including a decrease in the concentration of fatty acids which lessens the smell of the waste. These changes are supported by maintaining a constant temperature inside the tanks of approximately 40ºC. As the solids sink, the biogas produced by these reactions, primarily methane, is collected in a dome at the top of each tank. This biogas is tapped off to be burned on-site via combined heat and power (CHP) units. Biogen plans to produce about 1.1 MW from these CHP units when the plant operates at full capacity and to sell excess electricity back to the grid. (Currently it uses one 536 kW unit and one 256 kW unit; it is awaiting imminent delivery of another 256 kW unit.) A new field of vision for biowaste management in the UK. This aerial shot overlooks the Twinwoods Biogen facility in Bedfordshire, UK Click here to enlarge image In terms of odour control, currently the plant does not have an advanced treatment strategy; however, this is not urgent bearing in mind that the plant is in the middle of the countryside without any residential buildings close-by. That said, Biogen does plan to invest in an odour management system in the future and all of the company’s second generation plants will incorporate effective odour management systems. The treatment facility produces approximately 30,000 tonnes of biodigestate fertilizer per year. It is not economical to truck the biodigestate, but that is not necessary for the current output levels since there is a ready market for this material locally in the form of the nearby farm. As a result the biodigestate is piped to be spread as a liquid fertilizer on the farm. Future expansion Looking to the future for this facility, there are two elements worth mentioning. First, there is the planned expansion of infrastructure. A planning application has been submitted for a 2 MW plant on the northern block of the farm. Secondly, and of more significant and general interest, is the role that this type of plant will play in helping to push for a digestate quality protocol for the AD process within the UK. During my visit to the plant I discovered that a consultation on an AD protocol is due to occur early next year. Clearly the aim is to follow in the footsteps of the compost quality protocol mentioned earlier, and this will involve collaboration between the EA, the UK Waste and Resources Action Programme (WRAP) and industry. The main problem faced by Biogen at present is that everything produced by this plant is currently labelled as a waste. This limits the scope for market development and it is hoped that a quality protocol will assist in removing such a restrictive operational framework. In-vessel composting of biowaste Also at the vanguard of the UK biowaste industry is the second plant I visited recently, which is part of the new technologies demonstrator programme (NTDP) run by the UK Department for Environment, Food and Rural Affairs (Defra). The Envar plant is not the only in-vessel composting programme on Defra’s new technology programme, but — like the Biogen plant — the plant has recently opened and it integrates imported technology, in this case from Gicom Composting Systems BV in the Netherlands. The project seeks to assess the technical, economic and environmental performance of the system, to develop optimized composting regimes that will: Produce high-quality composts from a variety of municipal waste in the shortest possible time Minimize environmental impact Minimize energy usage Determine essential technical data to fill gaps in current knowledge For those unfamiliar with Envar Envar is a wholly owned subsidiary of Adas UK Ltd. It runs the operational site that I visited in St. Ives, near Huntingdon in Cambridgeshire, as well as an office in Leeds, concentrating mainly on recycling of organic wastes to land. Envar has worked on a wide variety of projects since its conception, including soil bioremediation after the severe contamination incident from an air crash in Greece in 2004. It is now an active operator of a waste treatment facility, which doubles up as a research and development centre for composting and biowaste management; indeed, it lays claim to being the largest combined R&D commercial composting site in the UK. The site operates under a waste management licence of 105,000 tonnes of waste per year. It currently operates well below capacity (approximately 44,000 tonnes per year) and so there is plenty of room for expansion. The company occupies about 50% of the site at the moment, and interestingly composting occurred on the site before Envar arrived. The site was previously run by Hensby Composting, which specialized in mushroom composting, accepting manure and straw. Understandably the old infrastructure has proved a mixed blessing, with some features proving ideal for adaptation; others less so. A visitors’ centre was opened on 5 October — the week before I visited the site — by MP for Northwest Cambridgeshire, Shailesh Vara. As part of the Defra Demonstrator Programme, informing the public is an important aspect; for example, Envar expects to welcome over 75 local authorities during the duration of the project. The technology basics The facility is valuable as a test site and, as mentioned, integrates Dutch expertise. Gicom was wholly responsible for the building of the new system and has offered continual support since commissioning was completed. Currently the site includes three different designs of in-vessel composting tunnels. Six tunnels were built (not by Gicom) in the 1980s. At present these six tunnels are compliant with the ABPR but not for meat included wastes and are starting to show their age; but there are plans to develop them to become fully ABPR compliant. The next phase of development occurred about ten years ago when Gicom constructed two tunnels that remain in regular use. And the final upgrade was completed in May 2007 with the commissioning of four new tunnels constructed by Gicom, which I shall cover in more detail later. First, let us examine the basics of the process. Seven days for basic processing ‘The site complies with the Animal By-Product Regulations (ABPR)’ commented Mark Fowles, NTDP Project Manager. ‘Most of the waste accepted into the site is category 3 — meat included — under the ABPR. These wastes include kerbside collected kitchen wastes, combined with green and kitchen wastes and catering wastes. The site does not accept category 1 or 2, but it does accept some ABPR-exempt materials.’ Initially, waste material arriving on-site is shredded using a Powerscreen shredder 1800 to achieve a basic particle size of about 40 mm. The shredded waste is then loaded into an appropriate tunnel by a Volvo L60E front loader where it is kept at 60ºC for about two days. The aim is for the enclosed tunnel to reach 60ºC during day one and then hold this temperature for two days (48 hours) to pasteurize the waste. Thereafter, the waste material remains in the tunnel and the temperature is brought down to 55ºC for three to four days. Finally the tunnel temperature is decreased further to allow the waste to be removed. (For category 3 waste, the material then goes through exactly the same process a second time in a second tunnel — this type of waste needs double treatment to comply with current legislation.) For catering waste and green waste (which Envar is accustomed to dealing with), the pasteurized material is then placed in windrows for a period of eight to 12 weeks, and is turned regularly. The company employs two turners: one a basic loader and one TIM Windrow Turner, ENVPRO, ENV-300. Very recently Envar accepted an unusual delivery from a local supplier, namely 800tonnes of cocoa powder. Apparently the powder had been misplaced by the distributor and hence had exceeded its ‘best before’ date. During my visit, this added a rather pleasant, sweet aroma to the proceedings since it had been placed on the windrows nearest me. More commonly, Envar accepts fruit and vegetables from local suppliers, which can also be put straight on the windrows without treatment. After the eight to 12 week windrow period, screening of the waste occurs to bring the particle size down to less than 10 mm. This is achieved using a McCloskey 621 trommel screen, currently on hire-purchase. The trommel screen has two main outputs in this context: oversized material which can go through the entire in-vessel process at least one more time to ensure maximum organic material is tapped, and compost. Most of the compost is currently spread directly to land by a local farmer. Small quantities are also sent to several test sites to explore the potential for using this type of compost to support the growth of bioenergy crops. The interesting part For those thinking ‘so what?’ here comes the particularly interesting part. Envar has the capacity to heat the walls of the four new Gicom tunnels already mentioned. And in the coming few weeks it will embark on a test phase of this operation using one of these four tunnels. The selected tunnel is the primary focus of the Defra interest. When using this new facility, waste input material is loaded into the tunnels, which can each accept up to approximately 160tonnes of material. The tunnel is fully enclosed and air is circulated from vents in the tunnel roof, down into a concrete plenum chamber and up into the compost through an underfloor piping system. Ducts above the compost then direct the air either back into the plenum or into a water scrubber (to remove any ammonia) and biofilter (to ensure odour reduction). Working up a head of steam in biowaste management Click here to enlarge image Water is collected from the composting mass in the same pipes that deliver the air flow underneath the compost. The water is recycled through the compost sprinkling system and the scrubber, and is then stored in an underground tank. In fact, Envar has two of these tanks in the new complex: one for tunnels 4, 5 and 6 and a second for the NTDP tunnel. The leachate from each of these tanks will be regularly monitored for heavy metals, ammonia, pH, and other chemicals. The biofilter is located in three structures adjoining the new system, incorporating obsolete cooling tunnels constructed when the site produced mushroom compost. Envar has used recycled willow waste as biofilter material. Windrows at Envar, which has plenty of space for further expansion Click here to enlarge image ‘It is important to pick the right material for the biofilter’ commented Mark Fowles; ‘If the material is too soft, it breaks down too quickly and needs replacing within a few months. If it has a small particle size, the air cannot filter through it easily. We have assessed several different types of waste and the willow was found to be the most appropriate.’ Envar was put in contact with the company providing the willow waste through Eastex, the materials exchange for the East of England. In using this material in the biofilter, Envar has diverted a significant quantity of biodegradable waste from landfill. Heating of the tunnel will be arranged in a manner similar to underfloor heating run off a domestic boiler. ‘The aim is to see how well it works — it is hoped that it will drastically speed up the composting process in the winter months, when high temperatures are hard to achieve rapidly’ Mark explained. ‘Some might say that using propane gas for this type of heating is another fuel and this is undesirable, but the plan is simply to find out realistically what this approach can achieve. Once we have proved the system works, we will look for different sustainable fuels, which will reduce our carbon footprint even further. The trial is due to start in the next few weeks and is expected to last approximately 18 months.’ After the testing programme has begun, Envar will take mass balance readings on a weekly basis and will monitor aspects such as methane, ammonia and CO2. As you might expect, the system is also special in that it includes advanced control systems (supplied by Gicom), which can measure and regulate up to 30 process parameters. Temperatures are monitored using probes (six probes per tunnel) and data loggers spread throughout the composting mass, particularly to check on cold spots which do not reach ABPR compliant temperatures. The company has an odour monitoring kit too, which will measure the odour at three points in the system: on the windrows, in the ducting of the NTDP tunnel and off the biofilter. Look out for a report from this test in the summer of 2009. Future expansion of Envar Like Biogen, Envar is tuned to expansion — particularly of end-markets. With this in mind the company is working toward PAS 100 accreditation for its compost material and thereafter to selling its compost. Currently a local farmer is taking all compost material for free and Envar simply charges a gate fee for the waste it accepts. But that is not the only area of interest. One of the main headaches encountered so far is what to do with the oversized material left after screening. Currently Envar has enough space to store it, in the hope of avoiding landfilling in the future. The company is currently carrying out a long-term research project looking at cleaning the compost to remove plastic and glass contamination, and is also looking into the generation of refuse-derived fuel (RDF). Conclusions These two plants exemplify the potential for imported technology to develop in the UK market. For instance, Gicom might find this a valuable opening gambit in terms of expansion in this emerging market. Another plus point is the local interest that is attracted to flagship projects of this type. A farm open day organized by Biogen and Bedfordia Farms earlier this summer attracted approximately 1200 people, indicating an encouraging level of local interest. Michael Chesshire, Director of Greenfinch — a UK company specializing in AD and biogas — was one of the many who attended the opening of the Biogen plant. He is also Chairman of the biogas committee for the UK’s Renewable Energy Association (REA). The committee has only been going six months and is intended to be a channel from industry to Defra. While challenges in biowaste management remain, such as making an AD plant viable in the UK using only pig slurry, the excitement shown by stakeholders such as Michael was palpable. These two plants and others like them suggest that the UK is no longer at the bottom of the class. Guy Robinson is Editor of Waste Management World email: wmw@pennwell.com Anaerobic digestion in Germany According to Michael Hannes from the Germany-based Enspar consultancy (who was involved in the development of the Twinwoods facility and who I met at the plant opening in September), AD in Germany has evolved along two separate paths, whereby the kitchen and green waste stream tends to be kept separate from the agricultural waste stream. While this separation contrasts with the integrated approach of Biogen, comparisons are largely inappropriate, not least because the German market is considerably more mature. And linked to this maturity, the demand for by-products from the numerous AD plants across the country has levelled off. The next significant change looks likely to be an amendment in the law regarding payment for electricity (one of the key outputs from AD) in 2009. Michael Hannes comments: ‘The change in prices will probably be a positive step for AD plants that use only agricultural feedstock, driven in part by rising prices for this feedstock. The position regarding ‘codigestion’ AD [as in the Biogen plant] is unlikely to change. The aims of the German approach are to stabilize basic energy production from agricultural products and to upgrade the energetic use of organic waste. Also important, of course, are the development of energy self-sufficiency within a region, the creation of new jobs, and the domestic use and export of German ‘green’ technology.’