Efficient acetone-butanol-ethanol production by Clostridium beijerinckii from sugar beet pulp.

Sugar beet pulp (SBP) has been investigated as a promising feedstock for ABE fermentation by Clostridium beijerinckii. Although lignin content in SBP is low, a pretreatment is needed to enhance enzymatic hydrolysis and fermentation yields. Autohydrolysis at pH 4 has been selected as the best pretreatment for SBP in terms of sugars release and acetone and butanol production. The best overall sugars release yields from raw SBP ranged from 66.2% to 70.6% for this pretreatment. The highest ABE yield achieved was 0.4g/g (5.1g/L of acetone and 6.6g/L butanol) and 143.2g ABE/kg SBP (62.3g acetone and 80.9g butanol) were obtained when pretreated SBP was enzymatically hydrolyzed at 7.5% (w/w) solid loading. Higher solid loadings (10%) offered higher acetone and butanol titers (5.8g/L of acetone and 7.8g/L butanol). All the experiments were carried out under not-controlling pH conditions reaching about 5.3 in the final samples.

Acetone-butanol-ethanol (ABE) production by Clostridium beijerinckii from wheat straw hydrolysates: efficient use of penta and hexa carbohydrates.

ABE fermentation by Clostridium beijerinckii of steam-exploded and ozonated wheat straw hydrolysates was investigated. In steam-exploded hydrolysates, highest yields of 0.40 g/g ABE yield and 127.71 g ABE/kg wheat straw were achieved when the whole slurry from the pretreatment was used. In ozonated hydrolysates, 0.32 g/g ABE yield and 79.65 g ABE/kg wheat straw were obtained from washed ozonated wheat straw. Diverse effects were observed in steam explosion and ozonolysis of wheat straw which resulted in hemicellulose removal and acid insoluble lignin solubilization, respectively. SEM analysis showed structural differences in untreated and pretreated biomass. Depending on the operational strategy, after pretreatment and enzymatic hydrolysis, the glucose recovery ranged between 65.73-66.49% and 63.22-65.23% and the xylose recovery ranged between 45.19-61.00% and 34.54-40.91% in steam-exploded and ozonated hydrolysates, respectively. The effect of the main inhibitory compounds found in hydrolysates (oxalic acid, acetic acid, 5-hydroxymethylfurfural and furfural) was studied through ABE fermentation in model media.

Influence of aeration on bioethanol production from ozonized wheat straw hydrolysates using Pichia stipitis.

The influence of aeration on ethanol production by Pichia stipitis was studied in wheat straw hydrolysates subjected to ozone pretreatment for the first time. In a first stage, different aeration rates ranging from 0.03 to 0.50 L air/min, which corresponds to a volumetric oxygen transfer coefficient from 1.1 to 9.6 h(-1), were applied to model glucose/xylose substrates. The most promising value was found to be 3.3 h(-1) (0.1 L air/min) leading to better xylose utilization, an ethanol yield of 0.40 g ethanol/g sugars and complete depletion of sugars at 72 h. In a second stage, the effect of aeration was analyzed in ozonized wheat straw hydrolysates. Sugars were completely depleted at 96 h and ethanol yield reached a value of 0.41 g ethanol/g sugars. The addition of controlled oxygen (K(L)a=3.8 h(-1)) enhances the efficiency of the process causing an increase of 29.1% in ethanol production and a considerable reduction of 42.9% in fermentation time as compared to non-aerated hydrolysates.

An analysis of lignin removal in a fixed bed reactor by reaction of cereal straws with ozone.

The chemical pretreatment with ozone of rye and wheat straws was carried out in a fixed bed reactor. The effect of ozone pretreatment time on lignin removal was determined. Glucose and xylose concentrations in the hydrolysates were also measured after the subsequent enzymatic hydrolysis step. Acid insoluble lignin reacts with ozone within the first 90 min reaction. Insoluble lignin reduction was about 50%. The higher hydrolysis yields were obtained after 120 min ozonation: the glucose yield ranged from 40% to 50% for rye straw and from 34% to 39% for wheat straw, whereas xylose yields were about 30%, independently of the cereal straw. The glucose yields corresponding to the untreated raw straws were considerably lower, about 10%. Longer ozonation time sharply reduced the production of monosaccharides, probably due to the formation of side products. The kinetic model, with the reaction parameters estimated, predicted reasonably well the experimental data.

Effect of inhibitors formed during wheat straw pretreatment on ethanol fermentation by Pichia stipitis.

The inhibitory effect of the main inhibitors (acetic acid, furfural and 5-hydroxymethylfurfural) formed during steam explosion of wheat straw was studied through ethanol fermentations of model substrates and hydrolysates from wheat straw by Pichia stipitis. Experimental results showed that an increase in acetic acid concentration led to a reduction in ethanol productivity and complete inhibition was observed at 3.5 g/L. Furfural produced a delay on sugar consumption rates with increasing concentration and HMF did not exert a significant effect. Fermentations of the whole slurry from steam exploded wheat straw were completely inhibited by a synergistic effect due to the presence of 1.5 g/L acetic acid, 0.15 g/L furfural and 0.05 g/L HMF together with solid fraction. When using only the solid fraction from steam explosion, hydrolysates presented 0.5 g/L of acetic acid, whose fermentations have submitted promising results, providing an ethanol yield of 0.45 g ethanol/g sugars and the final ethanol concentration reached was 12.2 g/L (10.9 g ethanol/100 g DM).

Production of biomass by Spirulina maxima using sugar beet vinasse in growth media.

Cultivation of Spirulina maxima in media containing vinasse from beet molasses fermentation has been studied in both batch cultures and a photobioreactor. The results obtained in batch tests showed that S. maxima was able to grow in Schlösser media containing up to 5 g/L of vinasse or alkaline diluted vinasse (5 g/L). Biomass concentrations ranging from 3.5 and 4.8 g/L, productivities from 0.15 to 0.24 (g/L d) and specific growth rates about 0.1 d⁻¹ were found. Betaine, an organic nitrogenous compound present in vinasse, was completely consumed. The continuous operation in a tubular photobioreactor with Schlösser medium supplemented with 2g/L of vinasse led to S. maxima concentrations about 8 g/L and productivities of 0.7 g/L d for an hydraulic retention time of 11 d using a light intensity of 3000 lux, slightly higher than those achieved with Schlösser medium, showing that the addition of vinasse presents a positive effect on the growth of the microalgae.

Effect of ozonolysis pretreatment on enzymatic digestibility of wheat and rye straw.

Wheat and rye straws were pretreated with ozone to increase the enzymatic hydrolysis extent of potentially fermentable sugars. Through a 2(5-1) factorial design, this work studies the influence of five operating parameters (moisture content, particle size, ozone concentration, type of biomass and air/ozone flow rate) on ozonization pretreatment of straw in a fixed bed reactor under room conditions. The acid insoluble lignin content of the biomass was reduced in all experiments involving hemicellulose degradation. Near negligible losses of cellulose were observed. Enzymatic hydrolysis yields of up to 88.6% and 57% were obtained compared to 29% and 16% in non-ozonated wheat and rye straw respectively. Moisture content and type of biomass showed the most significant effects on ozonolysis. Additionally, ozonolysis experiments in basic medium with sodium hydroxide evidenced a reduction in solubilization and/or degradation of lignin and reliable cellulose and hemicellulose degradation.