BioCycle June 2007, Vol. 48, No. 6, p. 53
This description from the Warmer Bulletin explains how green wastes are being composted for peat-free media using mobile biovessels and separators. “What could be more natural?”, asks the author.
Arnie Rainbow

WHEN I launched my consultancy in 1993, most UK composting companies seemed to regard their “product” as a worthless nuisance, with the gate fee being their sole raison d’etre. Since then, the industry has been shaped by the increasingly effective Composting Association and its quality standard/accreditation scheme. Markets have been developed for green compost significantly through research, capital funding and education. Market conditions have improved markedly for composting firms that are “market-led” rather than “disposal-driven.” The Vital Earth site at Ashbourne near Derby, UK epitomizes the trend.
Vital Earth’s first composting operation was established four years ago to compost curbside-collected green waste from North Shropshire District Council. The site processes 11,000 metric tons per year using a system based on mobile biovessels developed in-house to meet special requirements. In October 2006, Vital Earth launched a second operation to process additional green waste.
At Ashbourne, the scale is impressive: Three hectares of concrete, half under cover and 75 40m3 mobile biovessels processing up to 60,000 tons of collected green waste per year. The first thing visitors notice is the site’s neatness and cleanliness, then the very low odor levels. An earthy odor exists in the main building, where maturation, screening, blending and bagging are managed. (Each bag of Vital Earth product can be traced back to the green waste batch from which it is derived.)
Deliveries of green waste pass through a picking line where plastic bags and other “contraries” are removed. A JCB 300 grab loads the organics into a Comptech Crambo 600 shredder fitted with an electromagnetic belt. In-house software helps monitor temperature and optimize airflow through the ventilated floor.
After a “double bout of sanitization,” the steaming compost is formed into 800 m3 windrows within the maturation hall, where recontamination from weed seeds and pathogens are prevented. Maturation is enhanced by forced aeration and monitored by transmitter-thermistors. After six to eight weeks, windrow temperatures have fallen to just above ambient. Approved compost is then screened using 40 mm and 10 mm trommels, and then passed for blending and bagging.
MARKETS FOR PEAT-FREE COMPOST
Launched in September 2006, the Genie™ products are the only peat-free composts endorsed by the John Innes Foundation and are manufactured exclusively by Vital Earth. The fact that they are much lighter, more consistent and more storage-stable is welcome news to hobby gardeners and the retail trade.
Complementing this range of peat-free growing media is the Vitalizer® Plant Food range based on finely-graded compost and recycled organic plant foods. The three grades provide extended nutrient release, including soil improver plus, lawn dressings and sterilized topsoils.
There is a delightful logic in such recycling of crop wastes into growing media and other products designed to grow more plants – a classic win-win in terms of carbon fixation. And what could be more natural?
For further information, contact Arnie Rainbow, Rainbow Wilson Associates Ltd., Walton House, 218 High Street, Felixstowe, Suffolk, IPII 9DS, United Kingdom. E-mail: arnie@rainbowwilson. co.uk. This report originally appeared in Warmer Bulletin, Issue 109, April 2007, the “journal for sustainable waste management.” To find out more about this publication, write Editor Kit Strange at Warmer Bulletin, 1st floor, The British School, Otley Street, Skipton, North Yorkshire, BD23 lER, United Kingdom. E-mail: bulletin@residua.com.