Highlights A lignin-based hydrogel was synthesized and shown to possess a swelling ratio of 2013%. The hydrogel contained important hydrophilic hydroxyl groups and macropores for water retention. The hydrogel improved soil water retention in silt loam soil at high matric potentials and in the dry soil range. Increasing hydrogel concentration increased water retention in a loamy fine sand soil at high and low matric potentials. Abstract. Superabsorbent polymers (hydrogels) have been proposed as soil amendments to increase the amount of plant-available water in the soil. Synthetic hydrogels have been widely investigated for use in agriculture. Due to increasing environmental concerns related to synthetic hydrogels, naturally sourced hydrogels are of interest because of their potential for increased biodegradability and biocompatibility. A lignin-based hydrogel was synthesized for this study, and its swelling properties and water absorption capacity were determined. The hydrogel was characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and gas pycnometry. A hanging water column, pressure plate apparatus, and dew point potentiometer were used to measure the soil water retention curve from saturation to oven-dryness for silt loam and loamy fine sand soils after amendment with the lignin-based hydrogel. Results showed a maximum swelling ratio in deionized water of 2013% of the hydrogel’s original mass, 1092% in tap water, and 825% in a 0.9% NaCl solution. The FTIR spectra of the hydrogel showed the presence of O-H bonds from the lignin structure, which renders the hydrogel reactive to a crosslinker and forms insoluble bonds, thereby allowing the hydrogel to swell when exposed to water. SEM images of the lignin hydrogels indicate large macropores, which allowed for water absorption. Applying hydrogels significantly increased the soil's water-holding capacity at 0.3% (w/w) treatment. Hydrogel treatment significantly increased water retention at saturation or near saturation by 0.12 cm3 cm-3 and at field capacity by 0.08 cm3 cm-3 for silt loam soil at 1% (w/w) treatment compared to the control treatment with no added lignin hydrogel. Hydrogel application increased water retention over the range of the soil water retention curve from -3 to -15,000 cm for the loamy fine sand soil at 1% (w/w) treatment. However, the application of lignin-based hydrogel did not affect plant available water capacity (PAWC) in either soil tested. These results serve as preliminary evidence upon which further lignin-based hydrogel amendment studies could be built by testing higher concentrations of hydrogel in the soil. Keywords: Lignin, Soil water retention curve, Super absorbent polymers, Swelling capacity, Water retention.

Highlights In this study, six machine learning (ML) models were developed using a large database of soils to predict saturated hydraulic conductivity of these soils using easily measured soil characteristics. Tree-based regression models outperformed all other ML models tested. Neural networks were not suitable for predicting saturated hydraulic conductivity. Clay content, followed by bulk density, explained the highest amount of variation in the data of the predictors examined. Abstract. One of the most important soil hydraulic properties for modeling water transport in the vadose zone is saturated hydraulic conductivity. However, it is challenging to measure it in the field. Pedotransfer Functions (PTFs) are mathematical models that can predict saturated hydraulic conductivity (Ks) from easily measured soil characteristics. Though the development of PTFs for predicting Ks is not new, the tools and methods used to predict Ks are continuously evolving. Model performance depends on choosing soil features that explain the largest amount of Ks variance with the fewest input variables. In addition, the lack of interpretability in most “black box” machine learning models makes it difficult to extract practical knowledge as the machine learning process obfuscates the relationship between inputs and outputs in the PTF models. The objective of this study was to develop a set of new PTFs for predicting Ks using machine learning algorithms and a large database of over 8000 soil samples (the Florida Soil Characterization Database) while incorporating statistical methods to inform predictor selection for the model inputs. Of the machine learning (ML) models tested, random forest regression (RF) and gradient-boosted regression (GB) gave the best performances, with R2 = 0.71 and RMSE = 0.47 cm h-1 on the test data for both. Using the permutation feature importance technique, the GB and RF regression models showed similar results, where clay content described the most variation in the data, followed by bulk density. The implication of this study is that, when predicting Ks using the Florida Soil Characterization Database, priority should be given to obtaining quality data on clay content and bulk density as they are the most influential predictors for estimating Ks. Keywords: Deep learning, Gradient boosted regression, Pedotransfer functions, Random forest regression, Soil database, Soil properties.

Superabsorbent polymers (SAPs), sometimes known as hydrogels, have been proposed as soil amendments to enhance soil water management. But the performance of SAPs as soil amendments depends on their stability in soil. Bio-based SAPs have been praised as environmentally sustainable due to their apparent fast biodegradation relative to synthetic SAPs. But the fast biodegradation of bio-based SAPs may come at a cost to their long-term performance for repeated absorption and release of water in the soil. The purpose of this review is to (i) concisely summarize the methods and mechanisms involved in the biodegradation of different bio-based and synthetic SAPs, (ii) critically review studies conducted on the biodegradability of bio-based and synthetic SAPs when used as soil amendments, and (iii) discuss the implications of the biodegradability of bio-based and synthetic SAPs on their physical properties and stability in soil and (iv) identify potential research directions. Understanding the biodegradability of synthetic compared to bio-based SAPs and their advantages and disadvantages as soil amendments is important to researchers and farmers when choosing a specific type of SAPs as an agricultural soil amendment.

Superabsorbent polymers (hydrogels) have been studied for their ability to influence soil hydraulic conductivity because they can store and release water due to their swelling properties. However, concerns related to the increased use of synthetic hydrogels necessitates a switch to bio-based hydrogels, which are renewable and more biodegradable in comparison to synthetic hydrogels. In this study, we synthesized a lignin-based hydrogel and amended a silt loam soil with it at concentrations of 0, 0.1, and 0.3% (w/w). A laboratory permeameter, double membrane tension infiltrometer, and evaporation method were used to measure the saturated (Ks), near saturated, and unsaturated hydraulic conductivity (K) of the samples, respectively. Saturated hydraulic conductivity was significantly decreased by the application of hydrogel at 0.1 and 0.3% (w/w) in comparison to the control treatment. The application of 0.3% (w/w) lignin-based hydrogel only significantly decreased hydraulic conductivity at −1 cm soil water pressure head. Hydraulic conductivity in the 0.1 and 0.3% (w/w) treatments increased along the K(θ) curve in the unsaturated zone (−750 cm < h < −10 cm) in comparison to the control treatment, which we hypothesized was due to bound water in the hydrogel being released and creating a wider path for the movement of water. The 0.1 and 0.3% hydrogel treatments also tended to store more water than the control treatment, especially after 24 h of evaporation. The implication of this study is that lignin-based hydrogels could swell and retain water in saturated soils and the bound water could be released to enhance the flow of soil water in unsaturated soil, thereby reducing the water stress of plants, which require less energy to move and absorb water.

Soil hydraulic properties are important for the movement and distribution of water in agricultural soils. The ability of plants to easily extract water from soil can be limited by the texture and structure of the soil, and types of soil amendments applied to the soil. Superabsorbent polymers (hydrogels) have been researched as potential soil amendments that could help improve soil hydraulic properties and make water more available to crops, especially in their critical growing stages. However, a lack of a comprehensive literature review on the impacts of hydrogels on soil hydraulic properties makes it difficult to recommend specific types of hydrogels that positively impact soil hydraulic properties. In addition, findings from previous research suggest contrasting effects of hydrogels on soil hydraulic properties. This review surveys the published literature from 2000 to 2020 and: (i) synthesizes the impacts of bio-based and synthetic hydrogels on soil hydraulic properties (i.e., water retention, soil hydraulic conductivity, soil water infiltration, and evaporation); (ii) critically discusses the link between the source of the bio-based and synthetic hydrogels and their impacts as soil amendments; and (iii) identifies potential research directions. Both synthetic and bio-based hydrogels increased water retention in soil compared to unamended soil with decreasing soil water pressure head. The application of bio-based and synthetic hydrogels both decreased saturated hydraulic conductivity, reduced infiltration, and decreased soil evaporation. Hybrid hydrogels (i.e., a blend of bio-based and synthetic backbone materials) may be needed to prolong the benefit of repeated water absorption in soil for the duration of the crop growing season.

Cell immobilization in polymers have proven successful in protecting the nitrogen-fixing bacteria Rhizobium. This study evaluated the feasibility of using lignin to develop lignin-alginate beads with a starch additive to immobilize and release Rhizobial cells. A lignin-alginate hydrogel was synthesized and cultured at different concentrations with 1 ml inoculum of Rhizobium meliloti and Rhizobium leguminosarum to determine the hydrogel's compatibility with the Rhizobium spp. The Rhizobium cells (3 ml inoculum) were then entrapped into the lignin-alginate beads (ratio of 2 g lignin to 1 g alginate) with starch additive and their entrapment efficiency, cell release and surface morphology investigated. The results suggest concentration of the lignin-alginate hydrogel had no effect on the survival of Rhizobium cells with time. Dried lignin-alginate beads increased the survival of Rhizobium cells from 61% to 73% while dried lignin-alginate beads with starch additive increased the survival of Rhizobium cells from 61% to 84% compared to only alginate beads. Light microscopy suggests alginate beads lost their sphericity without lignin and starch additive while fixed SEM images highlighted Rhizobium cells attached to starch granules. Overall, the results indicate the potential applicability of lignin as a component for the manufacture of carrier materials for entrapping Rhizobial cells.

Cell immobilization provides a physical protection for viable Rhizobial cells in a confined carrier material allowing for the cells’ slow release into the environment. While several petroleum-based polymers have been tested for encapsulating microbes, they are often less biodegradable in the environment and may adversely affect viability of cells. One material that is biobased and has been underutilized for Rhizobium cell carriers is lignin. The present study was conducted to evaluate the feasibility of using lignin-alginate biopolymers with a starch additive to bioencapsulate and release Rhizobium cells.Rhizobium cells were bioencapsulated into the lignin-alginate starch beads and their efficiency i.e [(log of number of cells in wet beads/log of number of cells in solution matrix) x 100%] and release kinetics were determined. Light microscopy and scanning electron microscopy were also used to investigate the surface morphology of the beads. Our results show that all variations (alginate, lignin-alginate, and lignin-alginate with starch additive) of the wet bioencapsulated beads achieved a similar efficiency 97%. However, the presence of starch in the lignin-alginate beads increased the survival of Rhizobium cells after drying from 61 to 84% compared to only alginate encapsulation. These results imply that lignin, a readily available biopolymer is a potential component for the manufacture of carrier materials for encapsulating Rhizobium cells.

Lignin bio-oils with selective antimicrobial properties against lactic acid bacteria were prepared by depolymerizing corn stover lignin with peracetic acid. Bio-oil treatments significantly increased ethanol yields of contaminated fermentations.

Superabsorbent polymers (hydrogels) have been proposed as soil amendments to increase plant available water in soil. Synthetic hydrogels have been widely investigated for use in agriculture. Due to increasing environmental concerns related to synthetic hydrogels, hydrogels from natural sources which are more degradable and biocompatible compared to synthetic hydrogels are being developed. Here, a lignin-based hydrogel was synthesized. The swelling properties of the hydrogel were determined in different aqueous solutions and in soil. Fourier Transform Infrared (FTIR) spectroscopy was used to characterize the hydrogel. Using the hanging water column and the pressure plate method, the soil water retention curve was measured from a soil water pressure head range of -3 cm to the permanent wilting point i.e -15,000 cm for a silt loam soil. For this purpose, the soil was amended with the lignin-based hydrogel at rates of 0, 0.1 and 0.3% (w/w) concentration. Results of the swelling properties of the lignin-based hydrogel show a maximum swelling ratio of 2030% of the hydrogel‘s original mass in deionized water, 1092% in tap water, and 825% in the 0.9% NaCl solution. FTIR spectra of the hydrogel show the presence of O-H bonds which come from the lignin structure and render the hydrogel reactive to water molecules causing swelling as a result. Lignin hydrogel treatment significantly increased water retention near saturation compared to a control treatment of soil with no added lignin hydrogel.

Useful fuels and chemicals can be produced from lignin by microwave-assisted pyrolysis, but a dearth of understanding of this process impedes its successful implementation. Continuous mass loss kinetics of the pyrolysis of Kraft lignin pellets were carried out in an innovative reactor system comprised of a high-Q cylindrical microwave resonant cavity and a specially designed quartz reactor, in the temperature range of 300-700 ?C. Multiphysics numerical simulations indicated that both absorbed power and resulting temperatures profiles are heavily dependent on position of the sample relative to the electric field. Kraft lignin degradation (5 g samples) was complete in about 40 s, which was much faster than conventionally heated reactors. Activation energies (5-22 kJ/mol) and pre-exponential factors (0.06-0.64 s-1) were indicative that the process is low in energy consumption. At higher temperatures, phenols and phenolics were the major constituents of the bio-oil. A reliable method of obtaining microwave-assisted mass loss kinetics continuously is established.

Poplar is considered a suitable resource for production of renewable fuels and chemicals due to its rapid growth and tolerance to environmental stresses. Switchgrass is also extensively studied for biofuel production due to its use as a resource-efficient low-input plant and ability to grow and thrive in diverse weather or soil conditions. In this study, fast pyrolysis of biomass obtained from various parts (main stem, secondary stems, branches) of eastern cottonwood (Populus deltoides) and switchgrass (Panicum virgatwn) was carried out in an inductively heated reactor. Devolatilization rates (ranging from 450 degrees C to 600 degrees C) were initially obtained to determine their decomposition kinetics and estimate process parameters (temperatures and times) suitable for their pyrolysis using this method of pyrolysis. The effect of temperature (450 degrees C, 500 degrees C, 550 degrees C) on pyrolysis product yields and composition was investigated. Results indicate that activation energies ranged from 9.2 to 13.5 kJ/mol, while pre-exponential constants ranged from 0.23 to 0.51 s(-1). The maximum quantity of bio-oil of 39.8% +/- 9.50 was obtained from poplar stem at 450 degrees C whereas the least amount of bio-oil obtained was 33% +/- 0.0085 from poplar branch at 550 degrees C. The highest amount of bio-oils from switchgrass (34% +/- 0.023) was obtained at 450 degrees C. Water content in the bio-oil obtained from switchgrass was significantly higher than that from poplar. The GC-MS results showed that bio-oil compositions are similar among the various parts of poplar trees, with phenols being the dominant chemical specie and acids and alcohols present in negligible amounts. As temperature increases, an increase in furans is observed. Bio-oil and char fractions derived from stems have higher HHV than those from switchgrass, with the average HHV of char and water-free bio-oils ranging between 20.2 and 25.6 MJ/kg and 13.2 and -16.4 MJ/kg, respectively. Overall process energy recovery from initial biomass reached a maximum of 80.1% in the case of cottonwood main stem pyrolyzed at 500 degrees C.

Process simulations of batch fermentations with in situ product separation traditionally decouple these interdependent steps by simulating a separate “steady state” continuous fermentation and separation units. In this study, an integrated batch fermentation and separation process was simulated for a model system of acetone–butanol–ethanol (ABE) fermentation with in situ gas stripping, such that the fermentation kinetics are linked in real-time to the gas stripping process. A time-dependent cell growth, substrate utilization, and product production is translated to an Aspen Plus batch reactor. This approach capitalizes on the phase equilibria calculations of Aspen Plus to predict the effect of stripping on the ABE fermentation kinetics. The product profiles of the integrated fermentation and separation are shown to be sensitive to gas flow rate, unlike separate steady state fermentation and separation simulations. This study demonstrates the importance of coupled fermentation and separation simulation approaches for the systematic analyses of unsteady state processes.

OF THESIS FRACTIONATION OF LIGNIN DERIVED COMPOUNDS FROM THERMOCHEMICALLY PROCESSED LIGNIN TOWARDS ANTIMICROBIAL PROPERTIES The overuse of antibiotics in agriculture is an emerging concern, due to their potential detrimental impact to the environment. This study focuses on exploring antimicrobial properties of lignin derived compounds. Lignin is of interest as a feedstock to replacing some petroleum-based chemicals and products because it is the most abundant source of renewable aromatic compounds on the planet. Two lignin rich streams, residues from the enzymatic hydrolysis of dilute acid and alkaline pretreated corn stover, were decomposed via pyrolysis and hydrogenolysis, respectively. The resulting liquid oils were subjected to sequential extractions using a series of solvents with different polarities. Chemical compositions of the extracted fractions were characterized through HPLC and GC/MS. These extracted compounds were screened against Saccharomyces cerevisiae (S. cerevisiae), Escherichia coli, and Lactobacillus amylovorus for antimicrobial properties. Six lignin model monomers: guaiacol, vanillin, vanillic acid, syringaldehyde, 2,6-dimethoxyphenol, and syringic acid were compared to the oils and extracted fractions for antimicrobial properties. Development of ligninderived chemicals with antimicrobial properties could provide a novel use for this underutilized natural resource.

Pretreatment is considered a necessary step in the use of lignocellulosic biomass for biochemical conversion to higher value products. There are multiple choices of chemicals for pretreatment in industrial settings, however on-farm choices are constrained to those that function well at near ambient conditions with minimal specialized equipment, personnel training, and require limited waste disposal. This work presents a novel pretreatment system biomass using a recirculating, saturated calcium hydroxide (lime) solution in an up-flow, high solids (14-16% w/w) configuration at ambient conditions. In this system, lime solids were efficiently consumed, post-pretreatment washing of substrate was not required, and energy and resources were conserved. Pretreatment effectiveness was assessed by glucose yield comparisons for both switchgrass and corn stover. Based on mean glucose yields from 5 mm corn stover, lime pretreatment would require 350 kg of dry stover to produce 100 kg glucose at a chemical cost of $8.67 while NaOH pretreatment would require 300 kg of chemical at a cost of $22.38. (C) 2017 Elsevier B.V. All rights reserved.

Appears in: INTED2017 Proceedings Publication year: 2017Page: 7445 (abstract only)ISBN: 978-84-617-8491-2ISSN: 2340-1079doi: 10.21125/inted.2017.1723Conference name: 11th International Technology, Education and Development ConferenceDates: 6-8 March, 2017Location: Valencia, Spain

High-solids lignocellulosic pretreatment using NaOH followed by high-solids enzymatic hydrolysis was evaluated for an on-farm biochemical conversion process. Increasing the solids loadings for these processes has the potential for increasing glucose concentrations and downstream ethanol production; however, sequential processing at high-solids loading similar to an in-situ on-farm cellulose conversion system has not been studied. This research quantified the effects of high-solids pretreatment with NaOH and subsequent high-solids enzymatic hydrolysis on cellulose conversion. As expected, conversion efficiency was reduced; however, the highest glucose concentration (40.2 g L-1), and therefore the highest potential ethanol concentration, resulted from the high-solids combined pretreatment and hydrolysis. Increasing the enzyme dosage improved cellulose conversion from 9.6% to 36.8% when high-solids loadings were used in both unit operations; however, increasing NaOH loading and pretreatment time did not increase the conversion efficiency. The enzyme-to-substrate ratio had a larger impact on cellulose conversion than the NaOH pretreatment conditions studied, resulting in recommendations for an on-farm bioconversion system.

Phanerochaete chrysosporium treatment is less effective as a biological pretreatment on feedstock with larger particle sizes. We hypothesized that the improved effectiveness of the pretreatment when smaller particle sizes are used may be due to the inherently higher bulk density with smaller particle sizes. The effects of substrate bulk density and particle size on the efficacy of P. chrysosporium pretreatment of switchgrass (Panicum virgatum) was tested experimentally. Phanerochaete chrysosporium was grown on senesced switchgrass (2 different particle sizes) with various bulk densities. In all treatments, the fungal-pretreated samples released more glucose during enzymatic saccharification than the control sample. Substrate bulk density was a statistically significant factor in explaining the variation in the amount of glucose released per gram of substrate used. However, the particle size was not found to be a significant factor. On-farm switchgrass pretreatment may not require particle size reduction if the switchgrass is supplied in high-density bales.