Preservation of Microalgae, Lignocellulosic Biomass Blends by Ensiling to Enable Consistent Year-Round Feedstock Supply for Thermochemical Conversion to Biofuels

Abstract

Seasonal variation in microalgae productivity is a significant barrier to economical production of algae biofuels and chemicals. Summer production can be 3-5 times higher than in the winter resulting in uneven feedstock supplies at algae biorefineries. A portion of the summer production must be preserved for conversion in the winter in order to maintain a biorefinery running at capacity. Ensiling, a preservation process that utilizes lactic acid fermentation to limit microbial degradation, has been demonstrated to successfully stabilize algae biomass (20% solids) and algae-lignocellulosic blends (40% algae-60% lignocellulosic biomass, dry basis) for over 6 months, resulting in fuel production cost savings with fewer emissions. Preservation of algae as blends could be beneficial to biorefineries that utilize thermochemical approaches to fuel production as co-processing of algae and lignocellulosic biomass has been observed to enhance biocrude yield and improve oil quality. This study conducts a resource assessment of biomass residues in the southern United States to identify materials available during peak algae productivity and in sufficient quantity to meet the algae storage needs of an algae biofuel industry. Eight feedstocks met the quantity threshold but only three, distillers grains, haylage, and yard waste, were also available in season. Storage experiments utilizing both freshwater and marine strains of microalgae-Scenedesmus acutus, Chlorella vulgaris, Chlorella zofingiensis, Nannochloropsis gaditana, and Porphyridium purpureum-and yard waste were conducted for 30 days. Storage losses were less than 10% in all but one case, and the pH of all but one blend was reduced to less than 4.7, indicating that yard waste is a suitable feedstock for blending with algae prior to storage. To better understand whether the benefits to conversion realized by processing blends might be affected by storage, elemental analysis and bomb calorimetry of pre-and post-storage algae-yard waste

Effects of Inoculation with Lactic Acid Bacteria on the Preservation of Nannochloropsis Gaditana Biomass in Wet Anaerobic Storage and Its Impact on Biomass Quality

“…of the algae samples were higher and the oxygen contents (20 -23%, d.b.) were lower than the ones reported for lignocellulosic biomass feedstocks such as Miscanthus, Switchgrass, and Arundo [27,28], pinewood and pine bark [29], yard wastes [16], and forest residues [30,31].…”

“…The high ash contents reported in this study can be attributed to the cultivation conditions of N. gaditana, which as a marine strain higher ash content compared to freshwater strains is expected due to the much higher dissolved solid content of seawater. [16] It is imperative to note that high ash content in algal biomass, or in any biomass, is an undesirable property. Elevated ash content can adversely impact conversion operations to produce biofuels by reducing fuel yield, requiring greater throughput due to unconvertible material and can have an adverse effect on equipment operation (e.g., wear, slagging, scaling, etc.…”

“…The effectiveness of wet anaerobic storage in preserving biochemical composition and dry matter content of algal biomass can be fully evaluated when this storage approach is utilized for various algae strains and the results are consistent. Previous work by the authors have focused on wet anaerobic storage of freshwater algae strains (S. obliquus, S. acutus), algae blended with yard waste and corn stover [1,2,15,16]. However, this study is investigating the wet anaerobic storage of a saline algae strain and the results from this study will contribute to the development of a holistic understanding of the effectiveness of wet anaerobic storage in preserving algal biomass feedstocks.…”

Sustainable resource production for manufacturing bioactives from micro‐ and macroalgae: Examples from harvesting and cultivation in the Nordic region

“…The results showed lower yields and oxidative effects on carotenoids and other lipids (Safafar et al, 2017). Ensiling is currently being investigated as a promising and simple conservation method for both micro‐ (Wahlen et al, 2020) and macroalgae (Gallagher et al, 2017; Wu et al, 2018). Ensiling is a commonly used method for the preservation of biomass for feed purposes, both from terrestrial (e.g., hay and grass) and marine origin (e.g., fish by‐products).…”

Optimization of Biochar Production by Co-Torrefaction of Microalgae and Lignocellulosic Biomass Using Response Surface Methodology

“…A possible alternative is the decantation of the sedimented biomass, in the form of an algal sludge that can be further dried or mixed with other biomass feedstocks to be used in energy or material applications. For example, mixing wet algal biomass (80% moisture) with yard waste has been proposed as a stabilization technique to preserve the algal biomass and avoid or facilitate the drying step [11].…”