Production of Methane, Hydrogen and Ethanol from Secale cereale L. Straw Pretreated with Sulfuric Acid.

The study describes sulfuric acid pretreatment of straw from Secale cereale L. (rye straw) to evaluate the effect of acid concentration and treatment time on the efficiency of biofuel production. The highest ethanol yield occurred after the enzyme treatment at a dose of 15 filter paper unit (FPU) per gram of rye straw (subjected to chemical hydrolysis with 2% sulfuric acid (SA) at 121 °C for 1 h) during 120 h. Anaerobic digestion of rye straw treated with 10% SA at 121 °C during 1 h allowed to obtain 347.42 L methane/kg volatile solids (VS). Most hydrogen was released during dark fermentation of rye straw after pretreatment of 2% SA, 121 °C, 1 h and 1% SA, 121 °C, 2 h-131.99 and 134.71 L hydrogen/kg VS, respectively. If the rye straw produced in the European Union were processed into methane, hydrogen, ethanol, the annual electricity production in 2018 could reach 9.87 TWh (terawatt-hours), 1.16 TWh, and 0.60 TWh, respectively.

Biorefinery Concept Employing Bacillus coagulans: LX-Lignin and L-(+)-Lactic Acid from Lignocellulose.

A new biorefinery concept is proposed that integrates the novel LX-Pretreatment with the fermentative production of L-(+)-lactic acid. Lignocellulose was chosen as a substrate that does not compete with the provision of food or feed. Furthermore, it contains lignin, a promising new chemical building material which is the largest renewable source for aromatic compounds. Two substrates were investigated: rye straw (RS) as a residue from agriculture, as well as the fibrous digestate of an anaerobic biogas plant operated with energy corn (DCS). Besides the prior production of biogas from energy corn, chemically exploitable LX-Lignin was produced from both sources, creating a product with a low carbohydrate and ash content (90.3% and 88.2% of acid insoluble lignin). Regarding the cellulose fraction of the biomass, enzymatic hydrolysis and fermentation experiments were conducted, comparing a separate (SHF), simultaneous (SSF) and prehydrolyzed simultaneous saccharification and fermentation (PSSF) approach. For this purpose, thermophilic B. coagulans 14-300 was utilized, reaching 38.0 g L-1 LA in 32 h SSF from pretreated RS and 18.3 g L-1 LA in 30 h PSSF from pretreated DCS with optical purities of 99%.

Effect of dilute acid pretreatment on the saccharification and fermentation of rye straw.

This research shows the effect of dilute acid pretreatment with various sulfuric acid concentrations (0.5-2.0% [wt/vol]) on enzymatic saccharification and fermentation yield of rye straw. After pretreatment, solids of rye straw were suspended in Na citrate buffer or post-pretreatment liquids (prehydrolysates) containing sugars liberated after hemicellulose hydrolysis. Saccharification was conducted using enzymes dosage of 15 or 25 FPU/g cellulose. Cellulose saccharification rate after rye straw pretreatment was enhanced by performing enzymatic hydrolysis in sodium citrate buffer in comparison with hemicellulose prehydrolysate. The maximum cellulose saccharification rate (69%) was reached in sodium citrate buffer (biomass pretreated with 2.0% [wt/vol] H2 SO4 ). Lignocellulosic complex of rye straw after pretreatment was subjected to separate hydrolysis and fermentation (SHF) or separate hydrolysis and co-fermentation (SHCF). The SHF processes conducted in the sodium citrate buffer using monoculture of Saccharomyces cerevisiae (Ethanol Red) were more efficient compared to hemicellulose prehydrolysate in respect with ethanol yields. Maximum fermentation efficiency of SHF processes obtained after rye straw pretreatment at 1.5% [wt/vol] H2 SO4 and saccharification using enzymes dosage of 25 FPU/g in sodium citrate buffer, achieving 40.6% of theoretical yield. However, SHCF process using cocultures of pentose-fermenting yeast, after pretreatment of raw material at 1.5% [wt/vol] H2 SO4 and hydrolysis using enzymes dosage of 25 FPU/g, resulted in the highest ethanol yield among studied methods, achieving 9.4 g/L of ethanol, corresponding to 55% of theoretical yield.

Ozonolysis of straw from Secale cereale L. for anaerobic digestion.

The effect of different ozonation conditions on straw from Secale cereale (rye straw) pretreatment has been investigated. Using the Taguchi method, this study analyzed the optimum conditions for pretreatment of rye straw by ozonation. After 60min of rye straw ozonation the concentration of reducing sugars (RS) and volatile fatty acid (VFA), chemical oxygen demand (COD) were 7.4, 32.3 and 11.7 times higher, respectively compared to samples raw rye straw. The most effective rye straw ozonation occurred while using the highest amount of the rye straw (15g) treated with lower ozone dose (100gO3/m3) in the longest period of time (60min). For this variant of experiment the increment of methane production was 291.71dm3CH4/kgVS. Moreover, co-digestion of sewage sludge with addition of 20% ozonated rye straw allowed to obtain 269.1dm3CH4/kgVS. The positive effect of ozone on changes in the rye straw structure has been confirmed by SEM and FTIR analysis.