BioCycle December 2007, Vol. 48, No. 12, p. 50
A 30,000 metric tons/year in-vessel tunnel composting plant is receiving source separated household organics. The facility received its Animal By-Products Regulation authorization in October.
OPERATIONS got underway in April 2007 at an in-vessel composting plant at Etwall in Derbyshire, England that is designed to compost 30,000 metric tons/year of source separated household organics from three area solid waste councils. Accepted feedstocks include garden waste (e.g., leaves, prunings, grass clippings) and kitchen organics – meat, fish and bones; vegetable and fruit peelings; bread; tea bags and coffee grounds; and egg shells. No soiled cardboard or paper is accepted in the bin.
The composting plant is owned and operated by Biffa Waste Services, Ltd., a solid waste management company in the United Kingdom (UK). The company already was composting garden waste at this site, which is located on land owned by a water company. It is adjacent to a biosolids dewatering plant. This is Biffa’s second composting facility processing source separated organics. “We have had a composting facility on the Isle of Wight for about 10 years,” says David Morgan, Biffa’s Composting Manager. “That plant uses Wright composting tunnels.” The new facility is the company’s first using aerated concrete tunnels, which were supplied by Christiaens Group in The Netherlands. Technology selection was driven in large part by the UK’s Animal By-Products Regulations (ABPR) that essentially eliminates use of windrow composting when food waste that includes animal by-products is being processed.
Biffa has contracts with the East Staffordshire Borough Council, South Derbyshire District Council and Lichfield District Councils to receive source separated residential organics. East Staffordshire, for example, provides composting collection service to 40,000 households, equating to 90 percent coverage of all residents, says Andrew Bird, who works with East Staffordshire Borough Council’s Environmental Services Division. “The scheme has been progressively rolled out over the last four years, initially collecting garden waste only. Food waste could start to be added in April 2007, which is when the last 6,000 households were provided with the service. We collect compostable waste every two weeks. Every household on the scheme has been supplied with 240-litre, brown wheeled bins. Extra bins can be requested at no additional cost.” Compostable liners for the brown bin are accepted. Recyclables are collected biweekly as well, and trash weekly.
The £3 million project (roughly $6.2 million USD) was supported by £560,000 (about $1.2 million USD) of funding from the Waste & Resources Action Programme’s (WRAP) Organics Capital Support Programme. The maximum support that WRAP will offer is 30 percent of the total eligible costs (operating costs are not eligible for support) towards land, plant, equipment (fixed or mobile) and infrastructure (access roads, buildings, etc). The aim of this capital program – launched in 2006 – is to deliver an additional 450,000 metric tons per annum of processing capacity across England, Scotland and Northern Ireland by the end of March 2008.
COMPLYING WITH ABPR
Biffa went through a lengthy technology selection process before deciding it wanted to use a tunnel system to compost the source separated waste stream. “We decided on batch tunnel composting on the grounds of proven technology within the mushroom composting industry,” explains Morgan. “They are simple to operate and don’t rely on any specialized piece of equipment. We did trials with the waste stream we would be processing at a facility making mushroom compost and became confident that batch tunnels were the way to go. We went through a tendering exercise and Christiaens came out well in terms of price, sophistication of its process control system and on-time delivery.”
The ABPR rules specify treatment criteria, and there are different time/ temperature requirements that processors can select. Biffa chose to use a two-stage process where it has to ensure that the compost reaches at least 60°C for 48 hours; that process needs to be done twice. “Essentially, we load a tunnel with material, and temperatures are self-generated by the feedstocks,” says Morgan. “Temperature is maintained in the tunnel above 60°C for at least 48 hours. We then cool that down and move that batch to the next tunnel, or reload the same tunnel, and repeat the process. Once that is completed, the compost is effectively ‘sanitized’ and the heat treatment has essentially killed any potential animal disease. At that point, we can take the compost outside to complete the maturation process in a ‘normal’ manner.”
ABPR compliance also dictated layout of the composting site, he adds. Operators need to ensure that unprocessed waste is kept separate from processed material. “We essentially run the plant from dirty to clean,” he says. “There is an area in the building to receive the materials, an unloading area to swap them between tunnels, and then a clean area for material that has been processed twice. There are doors at both ends of the tunnels, so we can unload at the opposite end of the ‘dirty side.'”
The plant has six tunnels. At this time, each batch remains in the tunnels for a total of two weeks – one week for stage one and one week for stage two. In the second stage, temperature of the material is reduced to about 50°C before moving the compost outdoors. “We do that so the material doesn’t go into biological shock,” says Morgan. “If we bring it out at too high a temperature, it takes time for the biological process to recover.” Compost is matured in windrows turned with a front-end loader.
ABPR rules require that feedstocks have to be less than 40 cm going into a composting process like Biffa uses. Material is shredded to that coarse size. The UK’s Animal Health Group, which is part of the Department for Environment, Food and Rural Affairs (DEFRA), makes the determination that a composting facility is in compliance with ABPR requirements. “The authorization process involves proving to the state veterinarian assigned to the plant that the composting process achieves 60°C all the way through the material in the tunnel, including the edges,” explains Morgan. “We went through roughly a 4-month phase of having extra monitoring probes in the tunnels to record temperatures at the edges of the tunnel at the same time we were recording temperatures throughout the rest of the material. In order for the temperature to reach and be maintained at 60°C at the edges for the 48-hour kill stage, the temperature in the center of the material needs to be at 63°C. We received approval for our process from the state veterinarian on October 18, 2007, which we believe was fairly quick. The vet became confident in our system early on.”
Odor control at the plant has been effective, using water-based ammonia scrubbers and an open-box biofilter. There are two residential properties close to the site, one 250 meters and the other 400 meters away.
The European Union’s Landfill Directive established fairly aggressive deadlines for reducing the amount of unprocessed organic waste going into landfills in EU countries. As of October 30, 2007, England and Wales can no longer landfill untreated municipal solid waste. In addition, the UK’s Environment Agency set statutory targets for composting and recycling that must be met by municipal waste authorities. The Environment Agency also established a landfill tax escalator and the Landfill Allowance Trading Scheme (LATS) as incentives to comply with the directive. (A full report on these initiatives can be downloaded from the DEFRA website: http://www.defra.gov.uk/environment/waste/strategy/index.htm.)
“As a collection authority, we don’t have a target for landfill avoidance,” explains Andrew Bird. “That lies with the waste disposal authority, which covers eight districts in Staffordshire. However, the target for them, which we will help deliver, is 90 percent by 2011. East Staffordshire’s combined composting and recycling rate is currently 41 percent. The ability to compost food waste is a key objective for us and will help deliver the reduction targets for landfill through Staffordshire’s Joint Municipal Waste Strategy.”
There isn’t a mandatory requirement for households to use the service, because it isn’t allowed under UK law at this time, he adds. “Currently, average participation rates in East Staffordshire are around 75 percent, which is accepted as very good,” notes Bird. “The scheme has been popular with residents and is successful. However, we wish to increase performance further and will be rolling out more educational awareness campaigns over the coming months.” He explains that the service is part of the standard council tax charge to all households. East Staffordshire’s waste collection cost per household per year is £41 (about $85 USD/year).
The quality of the material arriving at the plant is “very good,” says Morgan, and doesn’t require any hand sorting prior to the coarse shredding step. He explains that Biffa discouraged including cardboard in the brown bins because it doesn’t break down at the same rate as the food and garden waste in their system. The final product is initially screened to 40-mm (1.5-inches) and then to 10-mm (about one-third-inches), using a Doppstadt trommel. “One key aspect of this site is to make sure the compost is sold,” he notes. “We are selling into the local landscape market as well as for applications such as sports pitches. Compost is bagged as well and sold back to the public.” Finished compost is PAS 100 compliant, which enables distribution to all types of end users. – Nora Goldstein
December 19, 2007 | General
Residential Organics Composting Kicks Off In Derbyshire (United Kingdom)
BioCycle December 2007, Vol. 48, No. 12, p. 50