R.R.C. Bakker

Efficient hydrogen production from the lignocellulosic energy crop Miscanthus by the extreme thermophilic bacteria Caldicellulosiruptor saccharolyticus and Thermotoga neapolitana.

BackgroundThe production of hydrogen from biomass by fermentation is one of the routes that can contribute to a future sustainable hydrogen economy. Lignocellulosic biomass is an attractive feedstock because of its abundance, low production costs and high polysaccharide content.ResultsBatch cultures of Caldicellulosiruptor saccharolyticus and Thermotoga neapolitana produced hydrogen, carbon dioxide and acetic acid as the main products from soluble saccharides in Miscanthus hydrolysate. The presence of fermentation inhibitors, such as furfural and 5-hydroxylmethyl furfural, in this lignocellulosic hydrolysate was avoided by the mild alkaline-pretreatment conditions at a low temperature of 75°C. Both microorganisms simultaneously and completely utilized all pentoses, hexoses and oligomeric saccharides up to a total concentration of 17 g l-1 in pH-controlled batch cultures. T. neapolitana showed a preference for glucose over xylose, which are the main sugars in the hydrolysate. Hydrogen yields of 2.9 to 3.4 mol H2 per mol of hexose, corresponding to 74 to 85% of the theoretical yield, were obtained in these batch fermentations. The yields were higher with cultures of C. saccharolyticus compared to T. neapolitana. In contrast, the rate of substrate consumption and hydrogen production was higher with T. neapolitana. At substrate concentrations exceeding 30 g l-1, sugar consumption was incomplete, and lower hydrogen yields of 2.0 to 2.4 mol per mol of consumed hexose were obtained.ConclusionEfficient hydrogen production in combination with simultaneous and complete utilization of all saccharides has been obtained during the growth of thermophilic bacteria on hydrolysate of the lignocellulosic feedstock Miscanthus. The use of thermophilic bacteria will therefore significantly contribute to the energy efficiency of a bioprocess for hydrogen production from biomass.

Production of acetone, butanol, and ethanol from biomass of the green seaweed Ulva lactuca

Green seaweed Ulva lactuca harvested from the North Sea near Zeeland (The Netherlands) was characterized as feedstock for acetone, ethanol and ethanol fermentation. Solubilization of over 90% of sugars was achieved by hot-water treatment followed by hydrolysis using commercial cellulases. A hydrolysate was used for the production of acetone, butanol and ethanol (ABE) by Clostridium acetobutylicum and Clostridium beijerinckii. Hydrolysate-based media were fermentable without nutrient supplementation. C. beijerinckii utilized all sugars in the hydrolysate and produced ABE at high yields (0.35 g ABE/g sugar consumed), while C. acetobutylicum produced mostly organic acids (acetic and butyric acids). These results demonstrate the great potential of U. lactuca as feedstock for fermentation. Interestingly, in control cultures of C. beijerinckii on rhamnose and glucose, 1,2 propanediol was the main fermentation product (9.7 g/L).

Bioenergy by-products as soil amendments? Implications for carbon sequestration and greenhouse gas emissions

An important but little understood aspect of bioenergy production is its overall impact on soil carbon (C) and nitrogen (N) cycling. Increased energy production from biomass will inevitably lead to higher input of its by‐products to the soil as amendments or fertilizers. However, it is still unclear how these by‐products will influence microbial transformation processes in soil, and thereby its greenhouse gas (GHG) balance and organic C stocks. In this study, we assess C and N dynamics and GHG emissions following application of different bioenergy by‐products to soil. Ten by‐products were selected from different bioenergy chains: anaerobic digestion (manure digestates), first generation biofuel by‐products (rapeseed meal, distilled dried grains with solubles), second‐generation biofuel by‐products (nonfermentables from hydrolysis of different lignocellulosic materials) and pyrolysis (biochars). These by‐products were added at a constant N rate (150 kg N ha−1) to a sandy soil and incubated at 20 °C. After 60 days, >80% of applied C had been emitted as CO2 in the first‐generation biofuel residue treatments. For second‐generation biofuel residues this was approximately 60%, and for digestates 40%. Biochars were the most stable residues with the lowest CO2 loss (between 0.5% and 5.8% of total added C). Regarding N2O emissions, addition of first‐generation biofuel residues led to the highest total N2O emissions (between 2.5% and 6.0% of applied N). Second‐generation biofuel residues emitted between 1.0% and 2.0% of applied N, with the original feedstock material resulting in similar N2O emissions and higher C mineralization rates. Anaerobic digestates resulted in emissions <1% of applied N. The two biochars used in this study decreased N2O emissions below background values. We conclude that GHG dynamics of by‐products after soil amendment cannot be ignored and should be part of the lifecycle analysis of the various bioenergy production chains.

Fermentative hydrogen production from pretreated biomass: A comparative study

The aim of this work was to evaluate the potential of employing biomass resources from different origin as feedstocks for fermentative hydrogen production. Mild-acid pretreated and hydrolysed barley straw (BS) and corn stalk (CS), hydrolysed barley grains (BG) and corn grains (CG), and sugar beet extract (SB) were comparatively evaluated for fermentative hydrogen production. Pretreatments and/or enzymatic hydrolysis led to 27, 37, 56, 74 and 45 g soluble sugars/100 g dry BS, CS, BG, CG and SB, respectively. A rapid test was applied to evaluate the fermentability of the hydrolysates and SB extract. The thermophilic bacterium Caldicellulosiruptor saccharolyticus showed high hydrogen production on hydrolysates of mild-acid pretreated BS, hydrolysates of BG and CG, and SB extract. Mild-acid pretreated CS showed limited fermentability, which was partially due to inhibitory products released in the hydrolysates, implying the need for the employment of a milder pretreatment method. The difference in the fermentability of BS and CS is in strong contrast to the similarity of the composition of these two feedstocks. The importance of performing fermentability tests to determine the suitability of a feedstock for hydrogen production was confirmed.

Feasibility of collecting naturally leached rice straw for thermal conversion

Abstract The practical application of field or natural leaching to rice straw was evaluated with the goal of improving biomass fuel value. Observations on three rice farms in the Sacramento Valley, California indicated that potassium, chlorine and total ash are leached from rice straw by rainfall regardless of rice variety, grain harvest method, straw arrangement, or stubble length. Leaching of sulfur by natural precipitation was not clearly established. In selected field plots leached straw was successfully collected in spring, even though biomass yields were variable (2.2– 3.4 Mg ha −1 ) and equipment had to operate in difficult conditions. Total costs for collecting leached straw on an area basis (

Integration of first and second generation biofuels: Fermentative hydrogen production from wheat grain and straw

77.07 ha −1 ) are 31% higher compared to collecting crude straw in the fall (

Biodiesel and biohydrogen production from cotton-seed cake in a biorefinery concept

58.67 ha −1 ) , due to reduced performance of machinery and addition of field curing operations. Analysis of historical rainfall data for the Sacramento Valley revealed that there is an 85% probability of receiving sufficient rainfall ( 250 mm or more) for substantial natural leaching of straw during the winter period. The available period for mechanized collection of rice straw after the winter period ranges from 0 to 45 days, depending on drying time needed to accomplish favorable field conditions, and planting date of the next crop. The feasibility of spring collection of rice straw could be improved if straw collection equipment were better equipped to operate under wet field conditions. The commercial implementation of natural leaching of rice straw as a strategy to improve fuel quality depends on a combination of factors that include grain harvest and straw collection practices, rainfall intensity and distribution, and field-specific factors.

Polysaccharide-Acting Enzymes and Their Applications

Integrating of lignocellulose-based and starch-rich biomass-based hydrogen production was investigated by mixing wheat straw hydrolysate with a wheat grain hydrolysate for improved fermentation. Enzymatic pretreatment and hydrolysis of wheat grains led to a hydrolysate with a sugar concentration of 93.4 g/L, while dilute-acid pretreatment and enzymatic hydrolysis of wheat straw led to a hydrolysate with sugar concentration 23.0 g/L. Wheat grain hydrolysate was not suitable for hydrogen production by the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus at glucose concentrations of 10 g/L or higher, and wheat straw hydrolysate showed good fermentability at total sugar concentrations of up to 10 g/L. The mixed hydrolysates showed good fermentability at the highest tested sugar concentration of 20 g/L, with a hydrogen production of 82-97% of that of the control with pure sugars. Mixing wheat grain hydrolysate with wheat straw hydrolysate would be beneficial for fermentative hydrogen production in a biorefinery.

Release of inorganic constituents from leached biomass during thermal conversion

Biodiesel production from cotton-seed cake (CSC) and the pretreatment of the remaining biomass for dark fermentative hydrogen production was investigated. The direct conversion to biodiesel with alkali free fatty acids neutralization pretreatment and alkali transesterification resulted in a biodiesel with high esters content and physicochemical properties fulfilling the EN-standards. Blends of cotton-seed oil methyl esters (CME) and diesel showed an improvement in lubricity and cetane number. Moreover, CME showed good compatibility with commercial biodiesel additives. On the basis of conversion of the remaining CSC to sugars fermentable towards hydrogen, the optimal conditions included removal of the oil of CSC and pretreatment at 10% NaOH (w/w dry matter). The extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus showed good hydrogen production, 84-112% of the control, from NaOH-pretreated CSC and low hydrogen production, 15-20% of the control, from the oil-rich and not chemically pretreated CSC, and from Ca(OH)2-pretreated CSC.

Lactic acid production from lime-treated wheat straw by Bacillus coagulans: neutralization of acid by fed-batch addition of alkaline substrate.

Biobased economy is expected to grow substantially in Europe within the coming 20 years. An important part of the bioeconomy is biorefineries in which biomass is processed in a sustainable manner to various exploitable products and energy. Bioeconomy can be seen as an expansion of the biorefinery concept as it also includes the exploitation of biotechnology in processing of non-biological raw materials or production of non-bio products exploiting certain biological principles.