Work is underway in England and Scotland on a series of landmark trials examining the potential for using anaerobic digestate as an alternative to commercial fertilisers in landscaping and regeneration projects.
The studies, organised by WRAP (Waste & Resources Action Programme), could have significant bearing for the UK's burgeoning anaerobic digestion (AD) industry by opening up potential new markets for digestate; the nutrient-rich bio-fertiliser produced as part of the AD treatment process for organic waste.
The results could offer a cost effective alternative to expensive commercial fertilisers for the UK's landscape and regeneration sectors; benefiting small independent firms and large environmental regeneration projects.
Paul Mathers, Programme Manager, Landscape & Regeneration at WRAP, explains
"We have seen significant improvement in how vegetation establishes itself in brownfield restoration and sport turfs through the use of BSI PAS 100 compost. I am confident that anaerobic digestate offers similar environmental and economic benefits.
"If successful, the results will have far reaching implications for a wide range of regeneration programmes and sports turf applications. The use of anaerobic digestate could open new markets on a national scale."
In Yorkshire, Walker Resource Management (WRM) is working in partnership with the Sports Turf Research Institute (STRI) to examine the effectiveness of anaerobic digestate when used as a sports turf fertiliser.
Two field trials, one held at the STRI grounds and the second at Marsden Park golf course in Lancashire, will compare the performance of anaerobic digestate when injected into golf greens and fairways against surface application. The trial plots will be compared with ones treated with conventional industry fertiliser, and with untreated control sites. Grass cover will be measured and photographed monthly, and assessed by chlorophyll meter. The trials will run until early spring.
A third trial will examine a very different use for digestate. The site in question is located at Stannon pit, a former China clay pit near Camelford in Cornwall which is deficient in all major and most minor nutrients. A five hectare test area has been established within the 150 hectare site, which is currently being restored as part of a landscape scheme implemented by South West Water and monitored by Cornwall Council. Here, Waste Treatment Water (WTW) is examining the use of anaerobic digestate, alongside water filter sludge and BSI PAS 100 quality compost, to assess the suitability of digestate as an aid to establishing vegetation on harsh landscapes.
The trial, which is being conducted by contractor Nexus Sustainability, will look at soil function and physical structure and will report its findings in late March 2011. If successful, the study will feed into current thinking guiding mine restoration sites, initially in Cornwall and the South West.
Further WRAP trials are also underway in Scotland, this time examining the use of anaerobic digestate in the establishment of newly planted trees and energy crops.
David Jarvis Associates, in partnership with Forest Research, is running the first of the three Scottish trials. Based at the Forestry Commission Newton nursery near Elgin, this study examines the effectiveness of anaerobic digestate when used in combination with BSI PAS 100 quality compost as a water retention 'blanket' to target root growth in trees, and in the retention of nutrients in soil. Alder trees will be used and soil quality and tree height will be assessed in the spring.
A second Scottish trial, located on the Heartlands brownfield restoration site at Polkemmet central Scotland, is being carried out by Earthcare to look at the benefits of using digestate in the growing of energy crops*.
The trial involves the planting of five hardwood tree species, including Red Alder, Cherry, Eucalyptus, Poplar and Birch into the site's poor quality soils - which have been blended with quality digestate and compost. Following the incorporation of the organic materials, the tree crops will be planted according to standard commercial practice.
The third Scottish trial is being run by the Forestry Commission. This will ascertain if silver birch, grown for biomass production, can be established on post-industrial land. Compost and digestate fibre will be cultivated into the existing soil and then planted in the tree plugs by spring. The project consists of two trial sites at Dalquhandy, a former open cast coal mine in Lanarkshire; and Addiewell, a former oil shale spoil tip in West Lothian.
The digestate used in all three Scottish trials is being provided by Scottish Water Horizons. The trials will assess improvements in the growing medium in the short term (by end of March 2011) by sampling the amended soils and assessing initial plant establishment.
Anaerobic digestion (AD) involves the breaking down of biodegradable material using micro-organisms in the absence of oxygen. It is currently used to treat wastewater at sewage treatment works in the UK, but can also be used to treat other organics wastes including household food waste, farmyard manures and energy crops. The process also provides a source of renewable energy in the form of biogas (a mixture of methane and carbon dioxide). Anaerobic Digestate, or biofertiliser, is the organic material produced during the process of anaerobic digestion. This is an organic material which is naturally high in valuable nutrients such as nitrogen, phosphorus and other elements required for healthy plant growth and fertile soil.