Storage as the Weak Link of the Biomass Supply Chain

Abstract

Biomass such as wood, straw or agricultural wastes are a worldwide abundant resource offering high potential for a decentralized energy production and supply which is especially interesting for rural areas. However, substance and energy loss caused by microbial degradation is one major reason for high feedstock costs. As a consequence of the microbial activity and further exothermic processes, heat is produced inside stored piles, leading to temperatures >200°C, causing partial pyrolysis and self-ignition. This work investigates the degradation process of spruce forest residues in order to generate a better knowledge about underlying processes and possible counteractions. Therefore, the microbial metabolic activity has been described in dependency on the moisture content (MC), particle size distribution and pH by respirometric tests. Respirometric tests revealed the microbial activity over time showing a maximum within the first few days of storage. Our results show that the moisture content is a key factor during wood degradation. No microbial activity could be verified for a MC < 20%. A moisture content of 46% led to a monthly dry matter loss of 5.4%. Raising the pH to an alkaline environment reduced the monthly dry matter loss from 3.1 to 1.8% per month proofing it´s influence on microbial metabolic activity. Further investigations have to be conducted to clarify underlying mechanism and countermeasures.

Evaluation of the Effect of a Spray Coating Applied on Open-Air-Stored Woodchips

“…For the dry piles, we can assume that the microbial activity and dry matter losses were minimal due to the a low initial MC and the low air temperatures, representing limiting factors for microbial development [6], as also demonstrated by Dumfort et al [24] through respirometric tests, indicating lower production of CO 2 when the MC decreased below 35%. Thus, the unique cause for mass variation is an increased MC, which caused an important reduction in the energy content of the dry piles (approximately −2.8%).…”

Supply Chain Uncertainties of Small-Scale Coffee Husk-Biochar Production for Activated Carbon in Vietnam

“…Harvested Robusta coffee beans are dried to a water content of around 13% [8]. In Vietnam, after drying, the outer parts of the cherry that surrounds the bean, which is referred to as coffee husk, is usually disposed of or burned inefficiently to dry coffee beans (Dzung et al, 2013; Vietnam Coffee-Cacao Association, 2019) [6,9]. The coffee husk accounts for roughly 14% of the coffee production weight, meaning that every year, almost 1.4 million tonnes of waste needs to be disposed of (Montilla-Pérez et al 2008) [10].…”

“…This would also reduce their workload. However, a third source as well as the literature stated that farmers currently use the husk for drying coffee cherries or spreading it on the fields as fertilizers (Dzung et al, 2013; Vietnam Coffee-Cacao Association, 2019) [6,9], while further literature claimed that 26% of the husk is separately collected at the farmers by private companies without further stating for what purpose (Nguyen and Sarker, 2018) [15]. This makes it difficult not only to assess the incentives but also to assess the amount of husk that would be available in terms of actual supply, as the husk could be a crucial component of the business model of some actors.…”

“…Lastly, it could be stated that the supply chain is highly dependent upon long-term relationships and structures, which are often related to different financing structures toward the farmers (Dzung et al, 2013) [9]. For example, both processors and buying agents tend to lend money to farmers for larger parts of the year, which is later repaid during the harvest period (Nguyen and Bokelmann, 2019) [14].…”

“…When the coffee cherry is dried correctly-to 12-13% moisture-the husk can be stored for long periods of time if later stored correctly, which does not increase the supply uncertainty. According to Dumfort et al (2018) [27], below 20% moisture, the biomass will not start degrading. The intermediaries have better opportunity for correct handling of the husk, as farmers have been observed to have limited opportunities for dedicated storing, but they are still in the hands of the farmers who provide the raw material.…”