Biomass Feedstock Storage for Quantity and Quality Preservation - Engineering and Science of Biomass Feedstock Production and Provision - page 162

Microbial oxidation of C6 sugars in anaerobic conditions causes losses in
water-soluble carbohydrates and hydrolyzed cellulose. Sugars are fermented by
bacteria in anaerobic conditions as well to produce lactic acid (ensilage). Oxidation
due to air infiltration also increases cellulose loss. These causes are discussed in
detail and effective storage options to minimize them, such as drying, compacting,
sealing, temperature control, and freezing or cooling, are also presented.
Storage can also be used to prepare biomass for processing into ethanol by reduc-
ing the recalcitrance [ 5 ]. Other undesirable properties such as high moisture content
may also be addressed during storage to improve subsequent handling and conver-
sion. Shredding and compaction are pretreatments that typically take place before
storage and affect particle size. Particle size and pH can be optimized for the pre-
treatment stage in the biorefinery. Lignin content can be manipulated through the
plant age at harvest. Lignin is broken down through acid hydrolysis, enzymes, ultra-
sound treatment, and drying. The design of a storage structure also needs to take
into account biomass coefficient of friction and angle of repose.
The goal of this chapter is to discuss these aspects in detail and provide a com-
prehensive review of the existing literature. The information presented here can
ultimately be used to create a storage design model for a storage system, optimized
to preserve biomass quality and quantity for ethanol production.
The chapter is arranged as follows. The next section summarizes the important
storage methods that can be employed for biomass feedstock storage. Section 7.3
discusses the important properties of biomass feedstock that play a key role in stor-
age. Section 7.4 briefly summarizes the causes for dry matter loss and then presents
the alternatives to minimize the loss. Section 7.5 discusses the alternatives to reduce
the biomass recalcitrance during storage so as to prepare the biomass for pretreat-
ment and further processing. Section 7.6 presents general guidelines for selecting a
storage method, and the chapter ends with a summary and future research directions
in Sect. 7.7 .

7.2 Storage Methods

The storage methods can broadly be classified as dry or wet methods [ 6 ]. Table 7.1
summarizes the methods that have been considered in the literature as potential
alternatives. Apart from ensilage, which is a method for wet storage, all others are
dry methods for biomass storage.
For dry storage, biomass needs to be harvested at moisture content less than
20-25 %. If high-moisture biomass is harvested, it must be dried on-field using
windrows. Sufficiently dry biomass is then prepared for storage by further opera-
tions such as baling or grinding. For wet storage, high-moisture biomass, typically
greater than 45 %, is harvested and shredded and ground immediately. The ground
biomass is sent to silage pits or packed in air tight bags for long-term storage.
Most of the methods mentioned in Table 7.1 are currently used for storage of
agricultural residue for various end uses. The table also provides a qualitative,