Biomass from landscape conversation and maintenance work (LCMW) is mostly not utilised in Europe, although it originates as a residue from necessary maintenance measures and its utilisation is in accordance with the principles of sustainability. To support an efficient treatment of LCMW biomass, the data on its potential, types and possible utilisation technologies need to be reviewed.
Occurrence of LCMW biomass
Available estimates of the potential
The potential of LCMW feedstock in the EU has already been assessed in the course of different projects (e.g. BioBoost; Biomass Futures; EUwood). But the data from potentials in different studies are hardly comparable as in most cases the assessed feedstock type differs in its specification and the assessed areas vary in size, this can be seen in the table below. Also the source area is often given in various units as well. Therefore, it is necessary to consider the type of estimated potential, the investigated area and the methodology more closely.
Table1: Potential of various LCMW feedstock types in EU according to different resources
In a number of regions as for example in Rotenburg (Wümme) and Elmshorn in Germany, Asturias and León in Spain and Vitebro in Italy LCMW biomass has been recognised and studies on the occurrence and potential of LCMW biomass are available. Regarding the example of the regions Vest-og-Sydsjaelland in Denmark and Paris in France the assessed feedstock potentials of green urban areas were found to be very promising.
For further information on the factors determining biomass potentials (biomass yield, concurrent use, etc.) and a list of studies analysing the potential of LCMW biomass in whole Europe and for single EU countries or regions see chapter 2.1 in the „Report on the state of the art of the occurrence and use of LCMW material for energy consumption in Europe and examples of best practice“.
Seasonal occurrence of LCMW biomass
The timing and frequency of conservation and maintenance operations is given by the seasonal fluctuations during the year and is determined by legal regulation and safety requirements. Where possible the LCMW is kept at low frequency in order to prevent unnecessary costs. Additionally, special management regimes can occur where, for example, extensive maintenance work is avoided during peak holiday season or mowing in the evening is reduced due to negative effects of transportation.
Timing of the harvest also differs between herbaceous and woody biomass. Grass is usually moved during the vegetation season while tree maintenance proceeds outside of it. The seasonality of the LCMW feedstock occurrence is important because it determines its logistic concepts. For the further utilisation it has to be taken into account that fresh biomass harvested in summer and in autumn has different characteristics because of its different composition. The biomass collected in July has a higher content of hemicellulose and cellulose, while the October harvest has a higher content of lignin and consequently lower biogas yield in anaerobic fermentation.
Harvest and collection
The first steps in the utilization chain of LCMW biomass are harvest and collection, which are the most costly steps. The lack of convenient and efficient machinery seems to be a common problem. There is often the need for specific measures for the harvest and the extraction of the cut biomass. In reduced accessibility areas like steep slopes, in nature conservation areas or areas with protected species, special treatments and selective strategies are required.
In a common pathway for roadside biomass the grassy residues are mostly cut and mulched. The woody material is preferably left in place, chipped and blown on the marginal areas. Where this is not possible, the grassy residues are collected and transported, stored in intermediate storage, chopped and then composted or used as mulch.
In a common pathway for woody biomass from hedges the biomass is harvested either fully mechanized or by manual harvest. The fully mechanized harvest is done e.g. with a hydraulic hedge trimmer which can be used for shrubs and woody growths. The manual harvest proceeds with a chainsaw and is used for hardly accessible growths or trees over 20 cm in diameter. The processing of the biomass (chipping) mostly precedes the transport. Wood chips can be produced on site with help of mobile chippers or directly at the power plant with large stationary chippers.
Authors: Kathrin Ludewig, Aline Clalüna