December 19, 2007 | General

Composting Plants Tap Biomass Markets (Germany)

BioCycle December 2007, Vol. 48, No. 12, p. 53
Renewable energy policies, along with strong demand for biomass fuels, are leading some green waste composting facilities to alter operations to service both biomass and compost markets.
Joachim Hirtenfellner

IN JANUARY 2007, the European Commission (EC) proposed its Roadmap for Renewable Energy in the 21st Century. The proposal included an overall binding 20 percent renewable energy target and a binding minimum target of 10 percent for transport biofuels for the European Union (EU) by 2020. To achieve this objective, a massive effort will be needed across a range of sectors, in particular power generation, heat generation, cooling and biofuels.
As valuable as the new objectives may be, it should not be forgotten that the EC also set renewable energy targets in 1997 – namely to achieve 12 percent renewable energy in total energy consumption by 2010. In addition, in March 2006, the European Council put forward a target of 15 percent of the EU’s primary energy supply to come from renewable energy sources by 2015. At the time, the European Parliament sought a higher target of 25 percent by 2020. Regrettably, it seems most unlikely that Europe will reach more than 10 percent renewable energy by 2010.
A key part of the response to the 1997 strategy was the Directive on Electricity Production from Renewable Energy Sources (2001/77/EC). This Directive established individual aims for each Member State in terms of the share of renewable energy in total power generation. When all States have met their target values, the EU-25 should be able to reach a total share of 21 percent renewable energy in power consumption. As things stand, with the current strategies employed, only 19 percent will be achieved. Nine Member States are set to reach their individual targets, a few of them even before 2010. But the others still have to push to make up for their shortfalls.
Biomass Fuels And Compost
In the first few years of this decade, renewable electricity received greater focus than renewable heating. As the renewable heat market now becomes more mature, it is attracting increased attention. The European Union is banking on the enormous potential of biomass as a cost-efficient fuel, as concluded by the EU Commission Biomass Action Plan from December 2005. This requirement for more renewable energy from biomass has resulted in long-term stimulation of the market for biomass materials. In Spring 2006 in Austria, there were shortfalls in the supply of wood pellets for the first time, resulting in a sustained price increase of up to 50 percent. While supply now seems secure, the pricing situation has not improved dramatically. Despite increased production capacities, there is still a huge backlog to satisfy the continually increasing demand for heating material in the long term.
Some composting operations are adopting processing methodologies to maximize production of both compost and biomass. From the source material delivered to the plant, fuel is generated either directly or following a short, intensive rotting process, depending on the wood and green fraction. In the first step, woody biomass – which can include dry branch wood, root stocks and driftwood – is shredded down to the size required by the biomass plant.
Following shredding, the next step is windrow composting. The coarse nature of the shredded biowaste allows a high air pore volume in the windrow, accelerating the biological decomposition process. After about 10 days, material not intended for biofuel applications can be screened off. The fine fractions are then composted further and used afterwards as fertilizers and soil conditioners. Up to 50 percent usable fuel fraction can be generated during screening of partially composted material. This approach to composting and biomass fuel production can improve a plant’s operating efficiency. First , there are the high revenues generated by the fuel; second, plant throughput can be increased considerably by significantly reducing processing time.
This approach is now being used in many composting plants, particularly ones in central Europe. For example, the Hahn-Kompost plant near Pfatter, Regensburg, Germany has been using this system for three years and represents a good example of this strategy working in practice. High quality compost and fuel are both generated from green garden waste. This process has a higher throughput than conventional treatment methods due to shorter rotting periods.
Hahn-Kompost was founded in 1993 and processes more than 25,000 metric tons of green garden waste and wood annually. Material is generated by communities and municipalities in the district of Regensburg. Green waste is collected at community recycling centers and transported to the plant. Additional material from commercial or household sources can also be added directly into this waste stream. The spectrum of waste accepted includes grass, leaves, green waste, garden cuttings, root stocks, fruit and graveyard wastes (e.g. flowers), branches and also untreated waste wood that is free from foreign matter (such as glue).
Incoming material is shredded using Komptech’s CRAMBO dual-shaft shredder. Screen baskets can be integrated within the system to shred to defined particle size. Shredded garden waste is composted in windrows for about a 10-day period, then processed through a Komptech MULTISTAR screen to separate out a clean fuel fraction with a particle size from 25 to 70 mm (roughly 1 to 3 inches). This fraction makes up 40 to 50 percent by weight of the original waste biomass and is accepted as a fuel by district heating plants in the region. Approximately 40 percent of the original waste biomass is processed further to generate high quality compost, with a particle size of less than 25 mm. Approximately 10 percent of the material – an oversized fraction (> 70 mm) – is shredded again for further composting. This process makes maximum use of available plant space, which increases operating efficiency. The throughput was increased by more than 30 percent within the first year using the new treatment process.
At the Schernthaner GmbH biomass and compost production plant in Fichtenstrabe, Germany, a similar system is used. Starting in 2002, the company began shredding and screening a small amount of incoming green waste for sale as biomass fuel. Demand for that material grew rapidly. Today, Schernthaner produces a fuel fraction by screening and shredding root stocks, driftwood, uncontaminated pallets and other materials without doing any composting. Green waste collected by local authorities is precomposted and then screened to capture the biomass fuel fraction.
The site uses a CRAMBO equipped with a biocutter. It primarily uses 250 mm screen baskets to produce the desired particle size for fuel. Materials composted in windrows are screened through Komptech’s MULTISTAR XXL, which generates three fractions. The medium particle size – between 25 and 70 mm – comprises about 30 to 40 percent of the volume of what is being screened and can be used in most biomass plants. A total of 50,000 cubic meters of this biomass fuel was produced and marketed in 2006. The undersized particles are composted in windrows, then screened down to 15 mm and sold as plant soil.
Joachim Hirtenfellner is Marketing and Public Relations Manager at Komptech GmbH, Austria. He can be contacted at This article was adapted from one written by the author for Waste Management World.

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