RT-CaCCO process: an improved CaCCO process for rice straw by its incorporation with a step of lime pretreatment at room temperature

Evaluation of the Enzymatic Saccharification Efficiency of an Energy Crop, Erianthus arundinaceus, Pretreated with Ca(OH)2 Using both Countercurrent Washing System and pH Adjustment by Nonpressurized CO2

Erianthus arundinaceus (ER) is greatly appreciated among domestic energy crops in Japan for the production of fermentable sugars from lignocellulosic polysaccharides. In this study, we developed an efficient Ca(OH)₂-based pretreatment of both stems and leaves of ER at ambient temperature with the addition of a washing step for enzymatic saccharification. The recoveries of glucans and xylans in the pretreated ER after four countercurrent washing cycles were 91 and 76 %, respectively, the former being considerably higher than that of rice straw (RS) (72 %). Their saccharification ratios in the washed sample under the pressure of 1 atm CO₂ were 80 and 92.5 %, respectively. The application of this simple sugar production process from ER would further support the domestic bioprocess development. ER is also foreseen to provide the additional feedstock favorable for harvesting from winter to spring in Japan, preventing a risk for feedstock shortage generated by single harvesting such as RS.

Use of activated carbons for detoxification of a lignocellulosic hydrolysate: Statistical optimisation

In order to improve bioethanol production from hydrolysates from olive tree pruning residues the present study assessed a detoxification method using the same waste material. The objective was to develop optimal removal without diminishing fermentable sugars. A statistical optimisation study was performed for the production of activated carbons using the same olive tree pruning residue as raw material. The effect of the impregnation ratio, activation temperature and the time needed for maximum removal of the phenolic compounds was assayed. The conditions for maximum adsorption were as follows: 799.18 °C, IR 4.88 and 101.38 min of activation, removing 55%, 64% and 41% of total phenolic compounds, HMF and furfural, respectively. The activated carbon obtained under optimum conditions (Aop) was submitted to adsorption kinetics and equilibrium assays. Experimental kinetic data were well represented by a pseudo-first order kinetic and intraparticle diffusion model, which helped explain the adsorption mechanism. Experimental isotherms were analysed with Langmuir, Freundlich and Temkin models, and Langmuir best fitted the experimental data. Hydrolysate from olive tree pruning residues, detoxified with the optimum activated carbon, was fermented with a commercial Saccharomyces cerevisiae yeast, obtaining a 100% theoretical maximum ethanol yield and a 56% bioconversion of fermentable sugars.

The RURAL (reciprocal upgrading for recycling of ash and lignocellulosics) process: A simple conversion of agricultural resources to strategic primary products for the rural bioeconomy

Rice straw (RS), an agricultural resource for lignocellulosic biorefineries, can deteriorate when sun-drying is ineffective. Poultry litter ash (PLA) has been considered as a renewable phosphorus source for crops but is highly alkaline. Here, a simple process was developed for their reciprocal upgrading. RS, PLA, and water were mixed for wet storage and alkali pretreatment of the RS at 25 °C for 14 d, and solid-solid separation was performed to obtain PLA-treated RS (PT-RS) and RS-treated PLA (RT-PLA). PT-RS was susceptible to enzymatic saccharification, and 65.5-68.6% of total sugar residues in PT-RS was converted to lactic acid by its nonsterile application for simultaneous saccharification and fermentation using Bacillus coagulans. RT-PLA exhibited 1.8-points lower pH and a more sensitive response of phosphorus solubilization to acid than those of PLA. This process could thus provide a breakthrough for the rural bioeconomy by manufacturing two strategic primary products for various commercial bioproducts.

Control of pH by CO 2 Pressurization for Enzymatic Saccharification of Ca(OH) 2 -Pretreated Rice Straw in the Presence of CaCO 3

The aim of this study was to investigate the effect of pH control by CO ₂ pressurization on the enzymatic hydrolysis of herbaceous feedstock in the calcium capturing by carbonation (CaCCO) process for fermentable sugar production. The pH of the slurry of 5 % (w/w) Ca(OH) ₂ -pretreated/CO ₂ -neutralized rice straw could be controlled between 5.70 and 6.38 at 50 °C by changing the CO ₂ partial pressure ( p CO ₂ ) from 0.1 to 1.0 MPa. A mixture of fungal enzyme preparations, namely, Trichoderma reesei cellulases/hemicellulases and Aspergillus niger β-glucosidase, indicated that pH 5.5-6.0 is optimal for solubilizing sugars from Ca(OH) ₂ -pretreated rice straw. Enzymatic saccharification of pretreated rice straw under various p CO ₂ conditions revealed that the highest soluble sugar yields were obtained at p CO ₂ 0.4 MPa and over, which is consistent with the expected pH at the p CO ₂ without enzymes and demonstrates the effectiveness of pH control by CO ₂ pressurization.

Washing Lime-Pretreated Rice Straw with Carbonated Water Facilitates Calcium Removal and Sugar Recovery in Subsequent Enzymatic Saccharification

Generally, Ca(OH)₂ pretreatment of lignocellulosics for fermentable sugar recovery requires a subsequent washing step for calcium removal and pH control for optimized saccharification. However, washing Ca(OH)₂-pretreated feedstock with water is considered problematic because of the low solubility of Ca(OH)₂ and its adsorption to biomass. In this study, we estimated the availability of carbonated water for calcium removal from the slurry of Ca(OH)₂-pretreated rice straw (RS). We tested two kinds of countercurrent washing sequences, four washings exclusively with water (W4) and two washings with water and subsequent two washings with carbonated water (W2C2). The ratios of calcium removal from pretreatment slurry after washing were 64.2 % for the W4 process and 92.1 % for the W2C2 process. In the W2C2 process, 49 % of the initially added calcium was recovered as CaO by calcination. In enzymatic saccharification tests under a CO₂ atmosphere at 1.5 atm, in terms of recovery of both glucose and xylose, pretreated, feedstock washed through the W2C2 process surpassed that washed through the W4 process, which could be attributed to the pH difference during saccharification: 5.6 in the W2C2 process versus 6.3 in the W4 process. Additionally, under an unpressurized CO₂ atmosphere at 1 atm, the feedstock washed through the W2C2 process released 78.5 % of total glucose residues and 90.0 % of total xylose residues. Thus, efficient removal of calcium from pretreatment slurry would lead to not only the recovery of added calcium but also the proposal of a new, simple saccharification system to be used under an unpressurized CO₂ atmosphere condition.

Evaluation of Two Sets of Sorghum Bagasse Samples as the Feedstock for Fermentable Sugar Recovery via the Calcium Capturing by Carbonation (CaCCO) Process

Sorghum bagasse samples from two sets (n6 and bmr6; n18 and bmr18) of wild-type and corresponding "brown midrib" (bmr) mutant strains of sweet sorghum were evaluated as the feedstock for fermentable sugar recovery via the calcium capturing by carbonation (CaCCO) process, which involves Ca(OH)₂ pretreatment of bagasse with subsequent neutralization with CO₂ for enzymatic saccharification. Saccharification tests under various pretreatment conditions of the CaCCO process at different Ca(OH)₂ concentrations, temperatures or residence periods indicated that bmr strains are more sensitive to the pretreatment than their counterparts are. It is expected that variant bmr6 is more suitable for glucose recovery than its wild-type counterpart because of the higher glucan content and better glucose recovery with less severe pretreatment. Meanwhile, bmr18showed higher scores of glucose recovery than its counterpart did, only at low pretreatment severity, and did not yield higher sugar recovery under the more severe conditions. The trend was similar to that of xylose recovery data from the two bmr strains. The advantages of bmr strains were also proven by means of simultaneous saccharification and fermentation of CaCCO-pretreated bagasse samples by pentose-fermenting yeast strain Candida shehatae Cs 4R. The amounts needed for production of 1 L of ethanol from n6, bmr6, n18, and bmr18samples were estimated as 4.11, 3.46, 4.03, and 3.95 kg, respectively. The bmr strains seem to have excellent compatibility with the CaCCO process for ethanol production, and it is expected that integrated research from the feedstock to bioprocess may result in breakthroughs for commercialization.

Life cycle assessment of ethanol derived from sawdust

The life cycle of ethanol derived from sawdust by enzymatic hydrolysis process is evaluated to determine if environmentally preferable and economically viable ethanol can be produced. Two scenarios are considered to estimate net energy consumption, greenhouse gas (GHG) emission and production costs. The estimated net energy consumption, GHG emission and production costs are 12.29-13.37 MJ/L, 0.75-0.92 kg CO2 e/L and about $0.98-$1.04/L, respectively depending on the scenarios of this study. The result confirmed that environmental benefit can be gained with present technologies; however, economic viability remains doubtful unless Feed-in Tariff (FiT) is considered. The production cost of ethanol reduces to $0.5/L, if FiT is considered to be $0.025/MJ. This study indicates that the implementation of FiT program for ethanol industry not only helps Ontario mitigate GHG emissions, but may also attract more investment and create rural employment opportunities.

Integration of a phenolic-acid recovery step in the CaCCO process for efficient fermentable-sugar recovery from rice straw

An advanced sugar-platform bioprocess for lignocellulosic feedstocks by adding a phenolic-acid (PA: p-coumaric acid and ferulic acid) recovery step to the CaCCO process was designed. For efficient PA extraction, pretreatment was 95°C for 2h, producing a yield of 7.30 g/kg-dry rice straw (65.2% of total ester-linked PAs) with insignificant effects on saccharification. PAs were readily recovered in solution during the repeated washings of solids, and the glucose yield, after 72-h saccharification of the washed solids, was significantly improved from 65.9% to 70.3-72.7%, suggesting the removal of potential enzyme inhibitors. The promotion of xylose yield was insignificant, probably due to 13.1-17.8% loss of xylose residues after washing(s). This new bioprocess, termed the SRB (simultaneous recovery of by-products)-CaCCO process, would effectively produce fermentable sugars and other valuables from feedstocks, strengthening the platform in both economic and environmental terms.

Sulfite-formaldehyde pretreatment on rice straw for the improvement of enzymatic saccharification

Rice straw is one of the most abundant agricultural residues in China. It is considered as a promising raw material for bioethanol production. In this work, rice straw was pretreated by sodium sulfite-formaldehyde (SF) for improving enzymatic saccharification. The SF pretreatment, using proven technology and industrialized equipment, showed efficient delignification selectivity and high carbohydrates retention in pretreated solid. The highest sugar yields of 79.0%, 88.8% and 71.1% for total sugar, glucan and xylan, respectively were obtained at an enzyme loading of 40 FPU/g-substrate after the raw material pretreated with 12% sodium sulfite at 160°C. About 75% of lignin was dissolved in pretreatment spent liquor and 78% of silica was retained in the residue of enzymatic hydrolysis. The results proved sulfite-formaldehyde as a promising pretreatment for the production of bioethanol as well as potential high value added by-products of silica nanoparticles and lignosulfonate.

Sequential incubation of Candida shehatae and ethanol-tolerant yeast cells for efficient ethanol production from a mixture of glucose, xylose and cellobiose

A mixture of 5% (w/v) glucose, 4% (w/v) xylose and 5% (w/v) cellobiose was fermented into ethanol using non-recombinant yeasts. Two series of experiments were carried out: (1) sequential fermentation with Candida shehatae D45-6 and Saccharomyces cerevisiae (Cs-Sc), and (2) sequential fermentation with C. shehatae D45-6 and Brettanomyces bruxellensis (Cs-Bb). C. shehatae D45-6 was initially used for glucose and xylose fermentation before adding highly ethanol-tolerant yeasts, either S. cerevisiae or B. bruxellensis, for cellobiose fermentation. For the sequential fermentation using S. cerevisiae, β-glucosidase was also included in the second step. In these two experiments, ethanol concentration reached 5.6-5.8% (w/v) and 99% sugar was consumed. Our results suggest that restricted glucose production from cellulose by saccharification could allow D45-6 to complete monosaccharide fermentation before the ethanol concentration exceeded its tolerance level.

Readily-milled fraction of wet sugarcane bagasse as an advanced feedstock for monosaccharide production via the RT-CaCCO process

The RT-CaCCO process for enzymatic saccharification was applied to readily-milled fractions of wet sugarcane bagasse. Wet bagasse immediately after juice extraction was crushed with shark-mill blades to prepare two fractions referred to as readily-milled (RF) and hardly-milled fraction (HF). Monosaccharide recoveries from RFs via the RT-CaCCO process were 1.03-1.21 times higher than those from HFs. Moreover, when the wet weight ratio of RF/HF was adjusted to 2/8, the hexose recovery from RF was 90.9%, which was 1.3 times higher than that of the wet bagasse before fractionation. The results show that this process can be used for efficient monosaccharide recovery from RF of wet bagasse. In addition, the process can be adapted to more fibrous HF for multiple uses such as fuel for boilers and fibers for particleboards.

Evaluation of the life cycle of bioethanol produced from rice straws

This study evaluated the life cycle of bioethanol produced by enzymatic hydrolysis of rice straw. Net energy consumption, CO(2) emission and production costs were estimated to determine whether environmentally preferable and economically viable bioethanol can be produced from rice straws. Two varieties of rice straw (Koshihikari and Leafstar), three energy scenarios (F-E-RH: Fuel-Electricity-Residues used for Heat; F-E-RE: Fuel-Electricity-Residues used to generate Electricity; F-RE: Fuel-Residues used to generate Electricity) and three types of primary energy (heavy oil; LNG: liquefied natural gas; agri-residues) were considered. The net energy consumption, CO(2) emission and production costs were estimated to be 10.0-17.6MJ/L, -0.5 to 1.6kg/L and 84.9-144.3¥/L (1 US$≈100¥), respectively, depending on the feedstock and scenarios of this study. A shift in energy scenarios or in the type of primary energy (heavy oil to LNG or agri-residues) not only reduces emissions and production costs of bioethanol from rice straw, but may also reduce the fluctuation in production cost over time and risk on investment, which would encourage more investment in this sector.

Combination of hot compressed water treatment and wet disk milling for high sugar recovery yield in enzymatic hydrolysis of rice straw

Rice straw has attracted significant interest in Japan as a potential raw material for biorefineries. Combination of hot-compressed water treatment (HCWT) and wet disk milling (WDM) was investigated to improve the enzymatic digestibility of rice straw and enhance sugar recovery yield. Rice straw, cut to <3 mm, was autoclaved at 121, 135, and 150 °C for 60 min, and subsequently treated by wet disk milling. WDM with HCWT at 135 °C for 60 min produced maximum xylose and glucose yields of 79% and 90%, respectively, at 10 FPU/g-substrate cellulase loading. Autoclaving at 150 °C leaked a 35% arabinose effluence in the liquid phase. Hydrolysis via WDM with HCWT required a lower enzyme loading (5 FPU/g-substrate) than either pretreatment process in isolation for >70% xylose and 80% glucose yield. Economical analysis indicate that enzymes cost for ethanol production is reduced by 19-67% by WDM with HCWT.

DiSC (direct saccharification of culms) process for bioethanol production from rice straw

A simple process (the direct-saccharification-of-culms (DiSC) process) to produce ethanol from rice straw culms, accumulating significant amounts of soft carbohydrates (SCs: glucose, fructose, sucrose, starch and β-1,3-1,4-glucan) was developed. This study focused on fully mature culms of cv. Leafstar, containing 69.2% (w/w of dried culms) hexoses from SCs and cellulose. Commercially-available wind-separation equipment successfully prepared a culm-rich fraction with a SC recovery of 83.1% (w/w) from rice straw flakes (54.1% of total weight of rice straw). The fraction was suspended in water (20%, w/w) for starch liquefaction, and the suspension was subjected to a simultaneous saccharification and fermentation with yeast, yielding 5.6% (w/v) ethanol (86% of the theoretical yield from whole hexoses in the fraction) after 24h fermentation. Thus, the DiSC process produced highly-concentrated ethanol from rice straw in a one vat process without any harsh thermo-chemical pretreatments.