Pasteurisation technology from HRS Heat Exchangers has helped waste-to-product business Shanks Group gain PAS 110 certification for its Westcott Park anaerobic digestion (AD) facility
Publicly Available Specification 110 (PAS 110) is a demanding industry specification which verifies the quality of digestate (the organic biofertiliser output from the AD process) and covers the product quality, standards for input materials and the management system for the AD process. Achieveing PAS 110 certification means that the digestate produced by Westcott Park is of a consistent high quality which can be sold and applied as an agricultural fertiliser.
The facility has also received a Certificate of Compliance by Organic Farmers & Growers. It has the capacity to process 48,000 tonnes of food waste, from sources such as the retail and catering sectors, each year, and supplies the National Grid with enough electricity to power 6,000 homes. As well as setting limits for physical contaminants, such as plastics, the PAS 110 standard requires pasteurisation of the material before or after it is digested at the AD facility. HRS designed and supplied a HRS 3 Tank Batch Sludge Pasteuriser System to pre-pasteurise the food waste feedstock before it is fed into one of the three digester tanks.
The system makes use of heat from the facility’s existing combined heat and power engine which would otherwise be wasted, helping to maximise overall site efficiency. It also recovers heat from the hot feedstock which has been pasteurised and uses it to pre-warm the feedstock as it enters the pasteuriser system. This provides energy savings of up to 70%. Ray Nattrass, head of Process Design & Engineering at Shanks Waste Management said: “We chose the HRS system because they offered a complete pasteurisation solution – we wanted the tanks, pumps, control system, control logic and everything built into that.
HRS demonstrated that they had the ability to design the facility as a stand alonesolution. It was their ability to do that which was key for us.” Digestate used as an organic fertiliser is a particularly good source of nitrogen and phosphorus for growing crops while also increasing soil organic matter. They also supply other important nutrients, and practical experience from farmers using digestate as a fertiliser suggests there are significant savings to be made. Matt Hale, international sales manager for HRS, said: “Our 3 Tank Batch Sludge Pasteuriser System ensured that the facility complied with the requirements for treating Animal By-Products when it was fully commissioned last year. Now it has been an integral part of achieving PAS110 certification.”
