Modular Open-Source Design of Pyrolysis Reactor Monitoring and Control Electronics

Industrial pilot projects often rely on proprietary and expensive electronic hardware to control and monitor experiments. This raises costs and retards innovation. Open-source hardware tools exist for implementing these processes individually; however, they are not easily integrated with other designs. The Broadly Reconfigurable and Expandable Automation Device (BREAD) is a framework that provides many open-source devices which can be connected to create more complex data acquisition and control systems. This article explores the feasibility of using BREAD plug-and-play open hardware to quickly design and test monitoring and control electronics for an industrial materials processing prototype pyrolysis reactor. Generally, pilot-scale pyrolysis plants are expensive custom designed systems. The plug-and-play prototype approach was first tested by connecting it to the pyrolysis reactor and ensuring that it can measure temperature and actuate heaters and a stirring motor. Next, a single circuit board system was created and tested using the designs from the BREAD prototype to reduce the number of microcontrollers required. Both open-source control systems were capable of reliably running the pyrolysis reactor continuously, achieving equivalent performance to a state-of-the-art commercial controller with a ten-fold reduction in the overall cost of control. Open-source, plug-and-play hardware provides a reliable avenue for researchers to quickly develop data acquisition and control electronics for industrial-scale experiments

A high solids field-to-fuel research pipeline to identify interactions between feedstocks and biofuel production

Background: Environmental factors, such as weather extremes, have the potential to cause adverse effects on plant biomass quality and quantity. Beyond adversely affecting feedstock yield and composition, which have been extensively studied, environmental factors can have detrimental effects on saccharification and fermentation processes in biofuel production. Only a few studies have evaluated the effect of these factors on biomass deconstruction into biofuel and resulting fuel yields. This field-to-fuel evaluation of various feedstocks requires rigorous coordination of pretreatment, enzymatic hydrolysis, and fermentation experiments. A large number of biomass samples, often in limited quantity, are needed to thoroughly understand the effect of environmental conditions on biofuel production. This requires greater processing and analytical throughput of industrially relevant, high solids loading hydrolysates for fermentation, and led to the need for a laboratory-scale high solids experimentation platform. Results: A field-to-fuel platform was developed to provide sufficient volumes of high solids loading enzymatic hydrolysate for fermentation. AFEX pretreatment was conducted in custom pretreatment reactors, followed by high solids enzymatic hydrolysis. To accommodate enzymatic hydrolysis of multiple samples, roller bottles were used to overcome the bottlenecks of mixing and reduced sugar yields at high solids loading, while allowing greater sample throughput than possible in bioreactors. The roller bottle method provided 42–47% greater liquefaction compared to the batch shake flask method for the same solids loading. In fermentation experiments, hydrolysates from roller bottles were fermented more rapidly, with greater xylose consumption, but lower final ethanol yields and CO2 production than hydrolysates generated with shake flasks. The entire platform was tested and was able to replicate patterns of fermentation inhibition previously observed for experiments conducted in larger-scale reactors and bioreactors, showing divergent fermentation patterns for drought and normal year switchgrass hydrolysates. Conclusion: A pipeline of small-scale AFEX pretreatment and roller bottle enzymatic hydrolysis was able to provide adequate quantities of hydrolysate for respirometer fermentation experiments and was able to overcome hydrolysis bottlenecks at high solids loading by obtaining greater liquefaction compared to batch shake flask hydrolysis. Thus, the roller bottle method can be effectively utilized to compare divergent feedstocks and diverse process conditions

Ammonia fiber expansion (AFEX) pretreatment of lignocellulosic biomass

Lignocellulosic materials are plant-derived feedstocks, such as crop residues (e.g., corn stover, rice straw, and sugar cane bagasse) and purpose-grown energy crops (e.g., miscanthus, and switchgrass) that are available in large quantities to produce biofuels, biochemicals, and animal feed. Plant polysaccharides (i.e., cellulose, hemicellulose, and pectin) embedded within cell walls are highly recalcitrant towards conversion into useful products. Ammonia fiber expansion (AFEX) is a thermochemical pretreatment that increases accessibility of polysaccharides to enzymes for hydrolysis into fermentable sugars. These released sugars can be converted into fuels and chemicals in a biorefinery. Here, we describe a laboratory-scale batch AFEX process to produce pretreated biomass on the gram-scale without any ammonia recycling. The laboratory-scale process can be used to identify optimal pretreatment conditions (e.g., ammonia loading, water loading, biomass loading, temperature, pressure, residence time, etc.) and generates sufficient quantities of pretreated samples for detailed physicochemical characterization and enzymatic/microbial analysis. The yield of fermentable sugars from enzymatic hydrolysis of corn stover pretreated using the laboratory-scale AFEX process is comparable to pilot-scale AFEX process under similar pretreatment conditions. This paper is intended to provide a detailed standard operating procedure for the safe and consistent operation of laboratory-scale reactors for performing AFEX pretreatment of lignocellulosic biomass

Water-soluble saponins accumulate in drought-stressed switchgrass and may inhibit yeast growth during bioethanol production

Background: Developing economically viable pathways to produce renewable energy has become an important research theme in recent years. Lignocellulosic biomass is a promising feedstock that can be converted into second-generation biofuels and bioproducts. Global warming has adversely affected climate change causing many environmental changes that have impacted earth surface temperature and rainfall patterns. Recent research has shown that environmental growth conditions altered the composition of drought-stressed switchgrass and directly influenced the extent of biomass conversion to fuels by completely inhibiting yeast growth during fermentation. Our goal in this project was to find a way to overcome the microbial inhibition and characterize specific compounds that led to this inhibition. Additionally, we also determined if these microbial inhibitors were plant-generated compounds, by-products of the pretreatment process, or a combination of both. Results: Switchgrass harvested in drought (2012) and non-drought (2010) years were pretreated using Ammonia Fiber Expansion (AFEX). Untreated and AFEX processed samples were then extracted using solvents (i.e., water, ethanol, and ethyl acetate) to selectively remove potential inhibitory compounds and determine whether pretreatment affects the inhibition. High solids loading enzymatic hydrolysis was performed on all samples, followed by fermentation using engineered Saccharomyces cerevisiae. Fermentation rate, cell growth, sugar consumption, and ethanol production were used to evaluate fermentation performance. We found that water extraction of drought-year switchgrass before AFEX pretreatment reduced the inhibition of yeast fermentation. The extracts were analyzed using liquid chromatography–mass spectrometry (LC–MS) to detect compounds enriched in the extracted fractions. Saponins, a class of plant-generated triterpene or steroidal glycosides, were found to be significantly more abundant in the water extracts from drought-year (inhibitory) switchgrass. The inhibitory nature of the saponins in switchgrass hydrolysate was validated by spiking commercially available saponin standard (protodioscin) in non-inhibitory switchgrass hydrolysate harvested in normal year. Conclusions: Adding a water extraction step prior to AFEX-pretreatment of drought-stressed switchgrass effectively overcame inhibition of yeast growth during bioethanol production. Saponins appear to be generated by the plant as a response to drought as they were significantly more abundant in the drought-stressed switchgrass water extracts and may contribute toward yeast inhibition in drought-stressed switchgrass hydrolysates

High temperatures and low soil moisture synergistically reduce switchgrass yields from marginal field sites and inhibit fermentation

‘Marginal lands’ are low productivity sites abandoned from agriculture for reasons such as low or high soil water content, challenging topography, or nutrient deficiency. To avoid competition with crop production, cellulosic bioenergy crops have been proposed for cultivation on marginal lands, however on these sites they may be more strongly affected by environmental stresses such as low soil water content. In this study we used rainout shelters to induce low soil moisture on marginal lands and determine the effect of soil water stress on switchgrass growth and the subsequent production of bioethanol. Five marginal land sites that span a latitudinal gradient in Michigan and Wisconsin were planted to switchgrass in 2013 and during the 2018–2021 growing seasons were exposed to reduced precipitation under rainout shelters in comparison to ambient precipitation. The effect of reduced precipitation was related to the environmental conditions at each site and biofuel production metrics (switchgrass biomass yields and composition and ethanol production). During the first year (2018), the rainout shelters were designed with 60% rain exclusion, which did not affect biomass yields compared to ambient conditions at any of the field sites, but decreased switchgrass fermentability at the Wisconsin Central–Hancock site. In subsequent years, the shelters were redesigned to fully exclude rainfall, which led to reduced biomass yields and inhibited fermentation for three sites. When switchgrass was grown in soils with large reductions in moisture and increases in temperature, the potential for biofuel production was significantly reduced, exposing some of the challenges associated with producing biofuels from lignocellulosic biomass grown under drought conditions

Session 2B Characterizing fungal inhibitors from drought-stressed switchgrass

Development of economically viable and greener pathways to synthesize renewable energy has been an important research theme in recent years. Previously it was reported that drought experienced during the growth of switchgrass led to complete inhibition of yeast growth during fermentation. In this project, we characterized specific compounds that led to this inhibition by extracting the samples using solvents (i.e., water, ethanol, and ethyl acetate) to selectively remove potential inhibitory compounds and determining whether pretreatment affects the inhibition. A key goal of the project was to determine whether the microbial-inhibitors are plant-generated compounds, by-products of the pretreatment process, or a combination of both

STUDYING EFFECT OF DROUGHT ON SWITCHGRASS AND IDENTIFYING ASSOCIATED MICROBIAL INHIBITORS

Recent research reports newer sustainable technologies for bioenergy generation that would serve as an alternative to conventional petroleum sources. There is abundant research reported on individual subsets of the study that has linked growth parameters to biomass yield, treatment conditions to bioethanol production or pretreatment conditions to microbial inhibitors. However, there is a lack of literature that undertakes the entire field-to-fuel process conditions in a single study. In this thesis, we focus on isolating and characterizing secondary metabolites provoked by drought in switchgrass, an upcoming bioenergy crop, during the mid-western drought of 2012. To characterize these inhibitors, switchgrass was separately solvent extracted before and after the pretreatment method followed by sequential hydrolysis and fermentation using yeast. Our analysis concluded that adding a water extraction step prior to AFEX-pretreatment overcame the inhibition, and saponins, a class of plant-generated triterpene glycosides, potentially ceased yeast growth in the drought-stressed switchgrass. Using non-targeted mass spectrometry (negative ESI/MS and positive ESI LC-MS), we identified many known and unknown compounds in relatively higher amounts in the drought-stressed switchgrass compared to control. A molecular networking mathematical calculation was performed using an R-based software, MFAssignR, for the detected compounds (abundance, m/z and retention time) to get a better insight on empirical formula, oxidation state and aromatic index. Further, we studied the effect of drought-like water-stress on switchgrass, simulated using rainout shelters, harvested on five “marginal lands” located across latitudinal gradient throughout Michigan and Wisconsin. In 2018, the 60% roof occlusion failed to induce water-stress on switchgrass under the shelters compared to ambient samples at the all sites except for the Hancock site. The water-stress imposed by the rainout shelters compounded with relatively low soil moisture holding capacity and high soil temperature due to sandy nature of the soil at the Hancock site resulted in reduced fermentability of switchgrass than ambient samples. However, there was no significant reduction in the biomass yield between the paired rainout and ambient samples. Hence, in the subsequent years the shelters were modified to 100% roof occlusion resulting in reduction of the biomass yield for the rainout samples compared to ambient samples

Lignin-propiconazole nanocapsules are an effective bio-based wood preservative

In the modern forest industry, the need for bio-based, renewable, and environmentally-benign wood preservatives is increasing. The world harvests approximately 1700 million m3 of wood annually for use in a variety of applications. Unfortunately, when exposed to moisture, wood products are at high risk of decay by wood degrading fungi. Preservatives are used to prevent or limit decay, and there has been an increasing interest in developing wood preservatives from renewable materials. For this work, the effectiveness of water-dispersible, double-shell, lignin nanocapsules encapsulating the fungicide propiconazole, as a sustainable wood preservative, was evaluated. The system was tested for its biocidal efficacy against brown rot decay by Gloeophyllum trabeum in southern yellow pine wood using both dip and pressure treatments. The preservative successfully penetrated the wood block during pressure treatment, and following 3 months of soil-jar incubation, only wood blocks pressure-treated with either the double-shelled-propiconazole nanocapsule system or the conventional exterior wood preservative, chromated copper arsenate (CCA), showed less weight loss (19.95 ± 2.05 and 16.40 ± 3.80%, respectively) compared to the control (41.58 ± 9.51%). Additionally, the novel preservative system exhibited enhanced antifungal resistance compared to its individual constituents, as confirmed with Kirby-Bauer disk diffusion tests. The double-shell lignin nanocapsule exhibited radical quenching activity against DPPH of 75.9 ± 4.2%, and this could have contributed to the enhanced antifungal activity of the double-shell lignin nanocapsule-propiconazole system. This novel preservative system can be considered as a potential bio-based antifungal wood preservative