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- ItemInfluence of Tree Species, Harvesting Method and Storage on Energy Demand and Wood Chip Quality When Chipping Poplar, Willow and Black Locust(Basel : MDPI AG, 2020) Pecenka, Ralf; Lenz, Hannes; Jekayinfa, Simeon Olatayo; Hoffmann, ThomasThe cultivation of fast-growing wood (e.g., poplar, willow or black locust) in short rotation coppices and agroforestry systems presents an opportunity for producing biomass sustainably in the agricultural sector. Cost-efficient agricultural wood production requires the availability of high-performance machinery and methods with which high-quality wood chips can be produced at low cost. It is known from harvesting short rotation coppices in practice that both the wood chip quality and the performance of the harvesting machinery depend on a variety of factors (e.g., harvesting method, weather conditions, tree species). That is why this study examines in detail the influence of the tree species (different varieties of poplar, willow, black locust) and the wood condition (fresh, stored or dried, frozen) on the specific energy demand for comminution in a stationary drum chipper and on the particle size distribution of the wood chips produced. For all the tree species examined, the chipping of dried as well as frozen stems was connected with a significant increase in the specific energy demand for comminution. An increase of 31% has been measured if poplar stems are chipped in frozen conditions (max. 6.31 kWh t−1). Drying led to an increase of 59% for dried willow stems (max. 6.67 kWh t−1). Drying and frost had also an influence on the size and quality of the wood chips, but no globally significant connection could be established for the examined tree varieties.
- ItemMolecular monitoring of the poplar wood chip microbiome as a function of storage strategy(Barking : Elsevier, 2021) Zöhrer, Julia; Probst, Maraike; Dumfort, Sabrina; Lenz, Hannes; Pecenka, Ralf; Insam, Heribert; Ascher-Jenull, JudithOne of the most challenging aspects of using wood chips as renewable energy source is the loss of biomass related to storage. Therefore, we installed three outdoor industrial-scale piles (250 m³) of poplar wood chips and monitored the bacterial and fungal communities by next-generation sequencing over a storage period of 120 d. Two of the three piles were supplemented with calcium dihydroxide (Ca(OH)2) (1.5%, 3% w/w) in order to test its potential as alkaline stabilization agent to preserve woody biomass during storage. Shifts in the microbial community composition occurred almost entirely in the beginning of the storage experiment, which we attribute to the temperature rise of up to 60 °C within the first week of storage. Later, however, we found little changes. Independent of Ca(OH)2 concentration, a consortium of lignocellulolytic and thermotolerant microorganisms dominated the stored wood chip microbiota emphasizing their role as key players during wood decomposition. Although the addition of Ca(OH)2 altered the physicochemical properties of wood chips, it did not prevent loss of biomass. Especially the pH was increased in Ca(OH)2 treated piles. However, only minor differences in the microbial communities’ composition were detected following Ca(OH)2 addition, highlighting the microbes tolerance towards and adaptation to changing environmental conditions.
- ItemEstablishment of a Laboratory Scale Set-Up with Controlled Temperature and High Humidity to Investigate Dry Matter Losses of Wood Chips from Poplar during Storage(Basel : MDPI, 2022) Hernandez-Estrada, Albert; Pecenka, Ralf; Dumfort, Sabrina; Ascher-Jenull, Judith; Lenz, Hannes; Idler, Christine; Hoffmann, ThomasThe aim of this work was to improve the understanding of dry matter losses (DML) that occur in wood chips during the initial phase of storage in outdoor piles. For this purpose, a laboratory scale storage chamber was developed and investigated regarding its ability to recreate the conditions that chips undergo during the initial phase of outdoor storage. Three trials with poplar Max-4 (Populus maximowiczii Henry Populus nigra L.) chips were performed for 6–10 weeks in the storage chamber under controlled temperature and assisted humidity. Two different setups were investigated to maintain a high relative humidity (RH) inside the storage chamber; one using water containers, and one assisted with a humidifier. Moisture content (MC) and DML of the chips were measured at different storage times to evaluate their storage behaviour in the chamber. Additionally, microbiological analyses of the culturable fraction of saproxylic microbiota were performed, with a focus on mesophilic fungi, but discriminating also xerophilic fungi, and mesophilic bacteria, with focus on actinobacteria, in two trials, to gain a view on the poplar wood chip-inhabiting microorganisms as a function of storage conditions (moisture, temperature) and time. Results show that DML up to 8.8–13.7% occurred in the chips within 6–10 storage weeks. The maximum DML were reached in the trial using the humidifier, which seemed a suitable technique to keep a high RH in the testing chamber, and thus, to analyse the wood chips in conditions comparable to those in outdoor piles during the initial storage phase.