Boyarsky Murphy's anaerobic digestion plant
Innovative facility in Cambridgeshire will turn food waste into energy
Architect Boyarsky Murphy Architects
Completion date End of 2012
In a pioneering new power plant, food waste normally destined for landfill will instead be processed to produce electricity and heat for a neighbouring potato packing factory. Any excess electricity will be sold on to the national grid.
Unusually for an industrial development, the buildings have been designed by an architect – in this case, London-based Boyarsky Murphy. The project has also endeavoured to be as sustainable as possible.
Three buildings will be built on the 4ha site: an anaerobic digestion building; an organic water recycling building; and a visitor centre.
The client, Local Generation, is a new company that provides low-carbon sources of renewable energy. Nicholas Boyarsky says it was keen to elevate the quality of the design from “crinkly tin sheds”, and, instead, ETFE cushions and locally sourced straw bales will be employed to form the building’s envelopes.
The digestion plant will be situated in the flat fenlands of Cambridgeshire just north of March.
It will process waste from the potato packing factory, along with imported food waste.
The east of England produces some 787,000 tonnes of food waste every year, with a large proportion of this going straight to landfill, and producing significant and potentially harmful quantities of methane.
The new anaerobic digestion plant is projected to process 30,000 tonnes of this waste into bio-gas and a digestate that can be used as a soil conditioner.
Organic water-recycling building
The function of the 46m-long organic water recycling building is to clean impurities from the water used in the anaerobic digestion building and the potato packing factory so it can be reused. This is done using organic processes that involve plant life, water creatures, aeration and filtration.
A key feature of the building will be the huge water-filled tanks cast in concrete and sunk 8m into the ground.
The building is essentially a glasshouse, though ETFE pneumatic cushions have been used as the main cladding material rather than glass since they require a far lighter support structure.
The supporting structure comprises a series of tubular steel frames (circular hollow sections) at approximately 3m centres. These members are supported on the walls of the concrete tanks and act as curved portal frames with mid-span vertical support provided by internal columns. Tie-rod bracing is incorporated into plan bays adjacent to the gable ends to provide overall stability to the structure.
Aluminium extrusions are bolted to tee-sections on the top of the steel frames to form the clamped boundaries to the ETFE cushions. The cushions are patterned with a frit that follows the curved frame profile.
The two-to-three layered ETFE elements are welded together to form an airtight deflated cushion. These are fixed into the aluminium extrusion on four sides and then inflated.
The cushions provide insulation and resist wind loads as well as allowing ultraviolet light to pass, thus enabling the plants to flourish within the tanks.
Anaerobic Digestion Building
The anaerobic digestion building receives and processes the food waste.
The main structural frame for the building, which will be 40m long x 29m wide, will be made from glue-laminated timber. The roof will be saddle-shaped and will support a sedum covering.
The 12m-high walls will be fabricated from locally sourced straw bales stacked in plywood cassettes with a render of lime wash both inside and out.
The visitor centre is connected to the south end of the organic water-recycling building.
It will provide facilities for lectures and school groups.
The grass-covered centre will provide a ramped auditorium, a café, and exhibition space, enabling visitors to gain an understanding of the way natural processes can be employed to recycle water and to learn about the anaerobic digestion process.
Like the anaerobic digestion building, the visitor centre employs a glue-laminated timber frame enclosed by lime-rendered straw bales.
How the Anaerobic Digestion Plant works
New equipment essential to the anaerobic digestion process is currently being built on the site and consists of tanks, water-treatment apparatus, combined heat and power units, a biofilter and pumping and water-management equipment.
The plant will take a mixture of waste from the existing potato packing factory and imported food waste from food processors, wholesalers, manufacturers and retailers near the site.
The food waste will be processed through the anaerobic digester to produce bio-gas and a digestate that will be used as soil conditioner. Digestate is the organic material that is left after the food waste has been processed and contains the nutrients that were originally present in the food waste.
The gas will be processed through a series of combined heat and power units that will produce electricity and heat. The heat provides hot water, space heating and refrigeration in the packing plant.
Water is added during pulping to create a nutrient-rich “soup” and to enable the bacteria to consume the organic matter. The matter that is left is then de-watered to produce a nourishing digestate that can be spread on to land as a soil conditioner, returning nutrients to the soil and completing the loop.
The water that remains needs to be cleaned before it can be reused in the anaerobic digestion process. While the water could have been treated chemically, the organic route – via the organic water-recycling building – was preferred since it uses less energy and is more sustainable. There will also be potential for the plants that are grown in the greenhouse to clean the water to be used to grow produce for sale.
Client Local Generation
Architect Boyarsky Murphy Architects
Structural engineer David Dexter Associates
Environmental engineer Wardell Armstrong