BioLogicTool : A Simple Visual Tool for Assisting in the Logical Selection of Pathways from Biomass to Products

The current chemical industry has been heavily optimized for the use of petroleum-derived base chemicals as its primary source of building blocks. However, incorporation of heteroatoms, absent in the base chemicals, is necessary to meet the different property requirements in the plethora of products the industry makes such as plastics, cosmetics, and pharmaceuticals. As global oil reserves deplete, a shift toward renewable bioderived building blocks, so-called platform molecules, will become a necessity. Bioderived platform molecules are typically rich in heteroatoms as a result of their biomass feedstock also being heteroatom rich, and it would therefore seem logical to carry these heteroatoms through to the aforementioned products. A tool was herein developed to assess the rationality of a synthetic route from feedstock to product, designed specifically to give a visual representation of the pathways and options available. BioLogicTool plots (%heteroatom by mass vs M) are an alternative to the conventional van Krevelen diagram, and are designed to better consider the diversity in heteroatom content encountered in biobased chemicals. The tool can rapidly help its user to design more logical multistep synthetic routes and enhance the mass efficiency of pathways. Several examples were selected to demonstrate the power and limitations of the BioLogicTool, but it was clear from these examples that removing heteroatoms from platform molecules to reincorporate them later in the final product is, in most cases, not logical in a mass efficiency sense

Biohydrogen production from lignocellulosic biomass: Technology and sustainability

Among the various renewable energy sources, biohydrogen is gaining a lot of traction as it has very high efficiency of conversion to usable power with less pollutant generation. The various technologies available for the production of biohydrogen from lignocellulosic biomass such as direct biophotolysis, indirect biophotolysis, photo, and dark fermentations have some drawbacks (e.g., low yield and slower production rate, etc.), which limits their practical application. Among these, metabolic engineering is presently the most promising for the production of biohydrogen as it overcomes most of the limitations in other technologies. Microbial electrolysis is another recent technology that is progressing very rapidly. However, it is the dark fermentation approach, followed by photo fermentation, which seem closer to commercialization. Biohydrogen production from lignocellulosic biomass is particularly suitable for relatively small and decentralized systems and it can be considered as an important sustainable and renewable energy source. The comprehensive life cycle assessment (LCA) of biohydrogen production from lignocellulosic biomass and its comparison with other biofuels can be a tool for policy decisions. In this paper, we discuss the various possible approaches for producing biohydrogen from lignocellulosic biomass which is an globally available abundant resource. The main technological challenges are discussed in detail, followed by potential solutions

Hydrodynamic characterisation of a groundwater - surface water system and evaluation of BTEX, PAHs decay and heavy metals fate

Most contaminated sites related to past industrial activities in Europe are adjacent to rivers and urbanized areas. These sites pose a major problem for water authorities and policy makers in terms of contaminants mobility, natural attenuation (or degradation) and risk assessment for environment and humans. Natural attenuation in groundwater is only effective if hydrogeochemical conditions of the system are favourable and contaminant degrading microorganisms are present. To evaluate this effectiveness, many site specific factors have to be considered, among which the dynamics of groundwater fluxes and groundwater – surface water interactions and biogeochemical processes. The site of concern in this study is a brownfield located in the north bank of the Meuse River, upstream of the city of Liège, Belgium. The soil, the unsaturated zone and the gravel aquifer are heavily contaminated by organic pollutants (BTEX and PAHs) and metals due to past industrial activities of coke production in the XXth Century. Various point sources of contaminants were delineated in the site. Benzene and Toluene concentrations in groundwater were found up to 50.000 μg l-1 and 23.000 μg l-1 respectively in source areas, while pollution due to metals was less important, with presence of Fe (> 6400 μg l-1), Zn (40 μg l-1), Co (18 μg l-1), Cu (>9 μg l-1), Pb (>100 μg l-1) and Cr (2 μg l-1) mainly with higher concentrations in some hot spots. The Meuse River level is established at around 59.5 meters a.s.l. by dams. However, river water levels fluctuate continuously with amplitude varying between a few centimetres up to 2 meters during winter and spring seasons. The main objectives of the research investigations were 1) to evaluate whether an interaction exists, at the level of the mentioned brownfield, between groundwater and the neighbouring river; 2) to assess the dynamics of such interactions and to quantify groundwater fluxes as the main potential vector of mobility of contaminants offsite; 3) to determine the potential of bacterial degradation of organic compounds and fate of metals contaminants in the specific environment of the site; and 4) to integrate groundwater – surface water dynamics with potential degradation of contaminants in order to evaluate further evolutions of contaminants in the aquifer. A detailed monitoring of groundwater and surface water levels, together with a series of field tests like pumping and tracer tests, contributed to a good knowledge in hydrodynamics of the contaminated aquifer. Groundwater and surface water monitoring datasets were analyzed in order to characterize hydraulic dynamics of the groundwater – surface water system. Groundwater heads observed were strongly influenced by Meuse River stages, and groundwater flow in the transition zone (seepage) was oriented in the direction going from the aquifer to the river under normal conditions. The use of an analytical model, however, pointed out that small changes on water river level were enough for a groundwater flow inversion, so seepage going from the Meuse River into the aquifer. Organic compounds (mainly benzene and low weight PAHs) have been studied with respect to their intrinsic bacterial degradation potential. Two independent stable isotope-based approaches (laboratory and field) were used to determine in situ biodegradation rates for benzene, and for the two- and three-ring aromatic hydrocarbons naphthalene and acenaphthene. In the laboratory, microcosms were set up with 13C-labeled substrates as well as with groundwater and with sediments from the site. The increase in 13C-CO2 over time was monitored by GC-IRMS analysis and used to calculate biodegradation rates. Benzene, naphthalene and acenaphthene were found to be biodegradable by the intrinsic microbial community under in situ-like conditions. The respective biodegradation rates decreased with increasing number of aromatic rings and were significantly lower under anoxic conditions. Apart from the microcosm study, in situ-biodegradation rates could be retrieved in a field study from 13C/12C signatures of residual groundwater contaminants using first-order kinetics. Biodegradation rates of lab- and field-based approaches were found to be in good agreement. Batch tests revealed that the heavy metals could be precipitated under sulphate (present at the site) reducing conditions. This in situ bioprecipitation process can be induced by the presence of electron donors and plays an important role in the natural attenuation process. Other conditions as aerobic or nitrate reducing conditions, did not lead to heavy metal immobilization. This gives specific indications about future site management and land use. It was also proved that the present heavy metal concentration did not influence the PAH biodegradation. However, PAH biodegradation under aerobic conditions is very slow. Further investigations will be necessary to evaluate the effect of aerobic biodegradation (addition of air) on the mobilization of the heavy metals, bound to the aquifer. The continuous changes of the groundwater flow direction observed in the studied site, lead to surface water flowing into the aquifer. This is likely to be an additional source of oxygen for the aquifer. This influx of oxygen-saturate water could enhance the degradation of BTEX and PAHs in the regions of the aquifer which are affected. Further investigations are needed to come to a qualitative evaluation to what extent oxygen from river water contributes to the removal of BTEX and PAHs at the site

Electrosynthesis of Biobased Chemicals Using Carbohydrates as a Feedstock

The current climate awareness coupled with increased focus on renewable energy and biobased chemicals have led to an increased demand for such biomass derived products. Electrosynthesis is a relatively new approach that allows a shift from conventional fossil-based chemistry towards a new model of a real sustainable chemistry that allows to use the excess renewable electricity to convert biobased feedstock into base and commodity chemicals. The electrosynthesis approach is expected to increase the production efficiency and minimize negative health for the workers and environmental impact all along the value chain. In this review, we discuss the various electrosynthesis approaches that have been applied on carbohydrate biomass specifically to produce valuable chemicals. The studies on the electro-oxidation of saccharides have mostly targeted the oxidation of the primary alcohol groups to form the corresponding uronic acids, with Au or TEMPO as the active electrocatalysts. The investigations on electroreduction of saccharides focused on the reduction of the aldehyde groups to the corresponding alcohols, using a variety of metal electrodes. Both oxidation and reduction pathways are elaborated here with most recent examples. Further recommendations have been made about the research needs, choice of electrocatalyst and electrolyte as well as upscaling the technology

Impact of dissolved carbon dioxide concentration on the process parameters during its conversion to acetate through microbial electrosynthesis

© 2018 The Royal Society of Chemistry. The reduction of carbon dioxide (CO2) released from industry can help to reduce the emissions of greenhouse gases (GHGs) to the atmosphere while at the same time producing value-added chemicals and contributing to carbon fixation. Microbial electrosynthesis (MES) is a recently developed process which accomplishes this idea by using cathodic bacteria at the expense of only minimum energy. In this study, enriched mixed homoacetogenic bacteria as cathodic biocatalysts for the reduction of CO2 with five different concentrations were evaluated to produce acetate at a constant potential. Increasing the carbon concentration showed an improved acetate production rate and carbon conversion efficiency. A maximum acetate production rate of 142.2 mg L per day and a maximum carbon conversion efficiency of 84% were achieved, respectively, at 4.0 and 2.5 g HCO3- L-1. The changes in pH due to interactive reactions between the bicarbonate (substrate) and acetate (products) were able to create a buffering nature in the catholyte controlling the operating parameters of the MES process, such as pH and substrate specificity. A higher acetate production shifted the catholyte pH toward acidic conditions, which further triggered favorable conditions for the bioelectrochemical reduction of acetate to ethanol.G. Mohanakrishna gratefully acknowledges the Marie-Curie Intra-European Fellowship (IEF) supported project BIO-ELECTRO-ETHYLENE (Grant No: 626959) from the European Commission

Microbial electrosynthesis feasibility evaluation at high bicarbonate concentrations with enriched homoacetogenic biocathode

An enrichment methodology was developed for a homoacetogenic biocathode that is able to function at high concentrations of bicarbonates for the microbial electrosynthesis (MES) of acetate from carbon dioxide. The study was performed in two stages; enrichment of consortia in serum bottles and the development of a biocathode in MES. A homoacetogenic consortium was sequentially grown under increasing concentrations of bicarbonate, in serum bottles, at room temperature. The acetate production rate was found to increase with the increase in the bicarbonate concentration and evidenced a maximum production rate of 260 mg/L d−1 (15 g HCO3−/L). On the contrary, carbon conversion efficiency decreased with the increase in the bicarbonate concentration, which evidenced a maximum at 2.5 g HCO3−/L (90.16%). Following a further increase in the bicarbonate concentration up to 20 g HCO3−/L, a visible inhibition was registered with respect to the acetate production rate and the carbon conversion efficiency. Well adapted biomass from 15 g HCO3−/L was used to develop biocathodic catalyst for MES. An effective biocathode was developed after 4 cycles of operation, during which acetate production was improved gradually, evidencing a maximum production rate of 24.53 mg acetate L−1 d−1 (carbon conversion efficiency, 47.72%). Compared to the enrichment stage, the carbon conversion efficiency and the rate of acetate production in MES were found to be low. The production of acetate induced a change in the catholyte pH, from neutral conditions towards acidic conditions

Bioelectrochemical conversion of CO2 to chemicals : CO2 as a next generation feedstock for electricity-driven bioproduction in batch and continuous modes

The recent concept of microbial electrosynthesis (MES) has evolved as an electricity-driven production technology for chemicals from low-value carbon dioxide (CO2) using micro-organisms as biocatalysts. MES from CO2 comprises bioelectrochemical reduction of CO2 to multi-carbon organic compounds using the reducing equivalents produced at the electrically-polarized cathode. The use of CO2 as a feedstock for chemicals is gaining much attention, since CO2 is abundantly available and its use is independent of the food supply chain. MES based on CO2 reduction produces acetate as a primary product. In order to elucidate the performance of the bioelectrochemical CO2 reduction process using different operation modes (batch vs. continuous), an investigation was carried out using a MES system with a flow-through biocathode supplied with 20:80 (v/v) or 80:20 (v/v) CO2:N2 gas. The highest acetate production rate of 149 mg L−1 d−1 was observed with a 3.1 V applied cell-voltage under batch mode. While running in continuous mode, high acetate production was achieved with a maximum rate of 100 mg L−1 d−1. In the continuous mode, the acetate production was not sustained over long-term operation, likely due to insufficient microbial biocatalyst retention within the biocathode compartment (i.e. suspended micro-organisms were washed out of the system). Restarting batch mode operations resulted in a renewed production of acetate. This showed an apparent domination of suspended biocatalysts over the attached (biofilm forming) biocatalysts. Long term CO2 reduction at the biocathode resulted in the accumulation of acetate, and more reduced compounds like ethanol and butyrate were also formed. Improvements in the production rate and different biomass retention strategies (e.g. selecting for biofilm forming micro-organisms) should be investigated to enable continuous biochemical production from CO2 using MES. Certainly, other process optimizations will be required to establish MES as an innovative sustainable technology for manufacturing biochemicals from CO2 as a next generation feedstock

Application of gas diffusion biocathode in microbial electrosynthesis from carbon dioxide

Microbial catalysis of carbon dioxide (CO2) reduction to multi-carbon compounds at the cathode is a highly attractive application of microbial electrosynthesis (MES). The microbes reduce CO2 by either taking the electrons or reducing the equivalents produced at the cathode. While using gaseous CO2 as the carbon source, the biological reduction process depends on the dissolution and mass transfer of CO2 in the electrolyte. In order to deal with this issue, a gas diffusion electrode (GDE) was investigated by feeding CO2 through the GDE into the MES reactor for its reduction at the biocathode. A combination of the catalyst layer (porous activated carbon and Teflon binder) and the hydrophobic gas diffusion layer (GDL) creates a three-phase interface at the electrode. So, CO2 and reducing equivalents will be available to the biocatalyst on the cathode surface. An enriched inoculum consisting of acetogenic bacteria, prepared from an anaerobic sludge, was used as a biocatalyst. The cathode potential was maintained at −1.1 V vs Ag/AgCl to facilitate direct and/or hydrogen-mediated CO2 reduction. Bioelectrochemical CO2 reduction mainly produced acetate but also extended the products to ethanol and butyrate. Average acetate production rates of 32 and 61 mg/L/day, respectively, with 20 and 80 % CO2 gas mixture feed were achieved with 10 cm2 of GDE. The maximum acetate production rate remained 238 mg/L/day for 20 % CO2 gas mixture. In conclusion, a gas diffusion biocathode supported bioelectrochemical CO2 reduction with enhanced mass transfer rate at continuous supply of gaseous CO2. [Figure not available: see fulltext.

Strategies for the Removal of Polysaccharides from Biorefinery Lignins: Process Optimization and Techno Economic Evaluation

The utilization of biorefinery lignins as a renewable resource for the production of bio-based chemicals and materials remain a challenge because of the high polysaccharide content of this variety of lignins. This study provides two simple methods; (i) the alkaline hydrolysis-acid precipitation method and (ii) the acid hydrolysis method for the removal of polysaccharides from polymeric biorefinery lignin samples. Both purification strategies are optimized for two different hardwood hydrolysis lignins, HL1 and HL2, containing 15.1% and 10.1% of polysaccharides, respectively. The treated lignins are characterized by polysaccharide content, molecular weight, hydroxyl content, and Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR). Preliminary techno-economic calculations are also carried out for both purification processes to assess the economic potential of these technologies. The results indicate that both protocols could be used for the purification of HL1 and HL2 hydrolysis lignins because of the minimal polysaccharide content obtained in the treated lignins. Nevertheless, from an industrial and economic perspective the acid hydrolysis technology using low acid concentrations and high temperatures is favored over the alkaline hydrolysis-acid precipitation strategy