Waste-treatment facility will use anaerobic digestion

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Planning permission has been granted by Devon County Council for a £15m waste-treatment facility that will use autoclave processing and advanced anaerobic digestion (AD).

The facility will be located at the Imerys Minerals china clay works at Lee Moor, near Plymouth.

According to a statement, AAD (South West), an Aero Thermal company, will process up to 75,000 tonnes per annum of municipal and commercial/industrial waste to produce energy for export to the National Grid, in addition to digestate for use in local restoration as a soil conditioner.

The use of Aero Thermal’s autoclave technology upstream of the AD plant will involve using high temperatures (160ºC) and pressures to break down otherwise unsuitable paper, cardboard, packaging and woody plant wastes.

Unsorted municipal waste and high-organic-fraction supermarket and kitchen food waste can be processed simultaneously, while also making the AD process up to four times faster and enhancing biogas production rates.

The quality of recyclates removed at the screening stage, such as metals, plastics, glass and textiles, is also higher, since these are effectively cleaned and sterilised.

The biogas will be combusted in a CHP plant to produce up to 3.2MW of renewable electricity for export to the National Grid. It will also generate 3.8MW of heat, which will be used to raise steam for use in the autoclaves and to provide heat for the AD tanks, thereby reducing the amount of energy the system requires.

The digestate, an organic rich-soil conditioner containing nutrients including nitrogen, potassium and phosphorus that are essential for plant growth, will be used in the restoration scheme for the nearby Lee Moor china clay pits.

‘Our intention is to begin construction in early 2012, with a view to being fully operational from April 2013,’ said Tristan Lloyd-Baker, AAD (SW)’s managing director.