Modeling alkali consumption and digestibility improvement from alkaline treatment of wheat straw

The alkali consumption during alkaline treatment of wheat straw at ambient temperature was measured as a function of time, solids concentration, and alkali concentration. The maximum measured alkali consumption was 5.5 g NaOH/100 g TS over a period of 30 days of treatment. Chemical functional groups (e.g., acyl and carboxyl groups) were measured and compared with the observed alkali consumption. The kinetics of alkali consumption were studied and a model was developed which predicts alkali consumption reasonably well. Use of this model was made to predict biodegradability of alkali-treated wheat straw, since a strong correlation was found to exist between alkali consumption and observed biodegradability. The method of bioconversion used was anaerobic digestion for methane production.     

Evaluation of chemical pretreatment for enzymatic solubilization of rice straw

Summary Rice straw was treated with NaOH, peracetic acid (PA), and sodium chlorite (NaClO₂). Quantitative changes in the composition of the treated straw, crystallinity of the treated straw and extracted cellulose, and susceptibility of the treated straw to Trichoderma reesei cellulase were studied. The alkali treatment resulted in a remarkable decrease in hemicellulose as well as lignin. Consequently, the recovery of residual straw after NaOH treatment was lowest among the three chemical reagents evaluated. The treatment with PA or NaCIO₂ resulted in a slight loss in hemicellulose and cellulose in the straw. The three chemical treatments caused little or no breakdown of the crystalline structure of cellulose in the straw. The treated straw was solubilized with the culture filtrate of T. reesei. The degree of enzymatic solubilization relative to the amount of residual straw was 69% after treatment with 0.25 N NaOH, 42% after treatment with 20% PA, and 50% after treatments with NaClO₂ (twice). The degree of enzymatic solubilization relative to the amount of the untreated straw, however, was 30% after treatment with 0.25 N NaOH, 32% after treatment with 20% PA, and 37% after treatments with NaClO₂ (twice).     

Using FTIR spectroscopy to model alkaline pretreatment and enzymatic saccharification of six lignocellulosic biomasses

Fourier transform infrared, attenuated total reflectance (FTIR-ATR) spectroscopy, combined with partial least squares (PLS) regression, accurately predicted solubilization of plant cell wall constituents and NaOH consumption through pretreatment, and overall sugar productions from combined pretreatment and enzymatic hydrolysis. PLS regression models were constructed by correlating FTIR spectra of six raw biomasses (two switchgrass cultivars, big bluestem grass, a low-impact, high-diversity mixture of prairie biomasses, mixed hardwood, and corn stover), plus alkali loading in pretreatment, to nine dependent variables: glucose, xylose, lignin, and total solids solubilized in pretreatment; NaOH consumed in pretreatment; and overall glucose and xylose conversions and yields from combined pretreatment and enzymatic hydrolysis. PLS models predicted the dependent variables with the following values of coefficient of determination for cross-validation (Q2): 0.86 for glucose, 0.90 for xylose, 0.79 for lignin, and 0.85 for total solids solubilized in pretreatment; 0.83 for alkali consumption; 0.93 for glucose conversion, 0.94 for xylose conversion, and 0.88 for glucose and xylose yields. The sugar yield models are noteworthy for their ability to predict overall saccharification through combined pretreatment and enzymatic hydrolysis per mass dry untreated solids without a priori knowledge of the composition of solids. All wavenumbers with significant variable-important-for-projection (VIP) scores have been attributed to chemical features of lignocellulose, demonstrating the models were based on real chemical information. These models suggest that PLS regression can be applied to FTIR-ATR spectra of raw biomasses to rapidly predict effects of pretreatment on solids and on subsequent enzymatic hydrolysis.     

Biomethanation of rice and wheat straw

When rice or wheat straw was added to cattle dung slurry and digested anaerobically, daily gas production increased from 176 to 331 l/kg total solids with 100% rice straw and to 194 l/kg total solids with 40% wheat straw. Not only was methane production enhanced by adding chopped crop residues but a greater biodegradability of organic matter in the straws was achieved.The authors are with the Microbiology and Molecular Genetics Unit, Tata Energy Research Institute, 158 Jor Bagh, New Delhi 110 003, India     

Liquid hot water and alkaline pretreatment of soybean straw for improving cellulose digestibility

Soybean straw was pretreated with either liquid hot water (LHW) (170-210 °C for 3-10 min) or alkaline soaking (4-40 g NaOH/100 g dry straw) at room temperature to evaluate the effects on cellulose digestibility. Nearly 100% cellulose was recovered in pretreated solids for both pretreatment methods. For LHW pretreatment, xylan dissolution from the raw material increased with pretreatment temperature and time. Cellulose digestibility was correlated with xylan dissolution. A maximal glucose yield of 70.76%, corresponding to 80% xylan removal, was obtained with soybean straw pretreated at 210 °C for 10 min. NaOH soaking at ambient conditions removed xylan up to 46.37% and the subsequent glucose yield of pretreated solids reached up to 64.55%. Our results indicated LHW pretreatment was more effective than NaOH soaking for improving cellulose digestibility of soybean straw.     

Utilization of alkali-treated and neutralized wheat straw-based rations for growing goat kids

Six groups of six goat kids were fed individually for 168 days with wheat straw given various treatments: (1) control; (2) 33 g NaOH/kg straw; (3) 80 g NaOH/kg, partly neutralized with mineral acids; (4) mineral control for 80 g NaOH/kg; (5) 120 g NaOH/kg, partly neutralized with mineral acids, and (6) mineral control for 120 g NaOH/kg straw. The average weight gain was significantly superior (P< 0.05) and the efficiency of dry matter (DM) and energy utilization was the highest with the 80 g NaOH/kg straw treatment. This treatment also gave significantly higher (P<0.05) digestibility of DM, organic matter (OM), neutral detergent fibre (NDF), acid detergent fibre (ADF), nitrogen-free extract (NFE) and hemicellulose than the control and 33 g NaOH/kg straw treatments. Increasing levels of alkali decreased (P<0.05) the digestibility of crude protein (CP) and ether extract (EE). Digestible energy and nitrogen-corrected metabolisable energy (ME_n) (as a percentage of gross energy (GE)) were maximal with 80 g NaOH/kg. The pH value of rumen liquor was the same for the control and the 33 g NaOH/kg and 80 g NaOH/kg treatments, but significantly increased (P<0.05) with the 120 g NaOH/kg straw treatment. The mean values for rumen ammonia nitrogen (NH₃ -N) were the same for the control, the 33 g NaOH/kg, and mineral controls for 80 and 120 g NaOH/kg treatments, but 80 g NaOH and 120 g NaOH/kg straw gave significantly lower values. It is suggested that by partially neutralizing the residual alkali, 80 g NaOH/kg straw can give higher efficiency of energy utilization for growth and digestibility of nutrients compared with 33 g NaOH/kg or the untreated control group, and the extensive use of treated straw in the diets of animals of which a rapid rate of production is not demanded, may be advantageous.     

Ensiled alkali-treated straw. I. Effect of level and type of alkali on the composition and digestibility in vitro of ensiled barley straw

In three experiments barley straw chopped to 5 cm nominal particle length was ensiled in laboratory silos for 90 days after treatment with alkali. In the first two experiments, NaOH was added at 0, 1.05, 2.10, 3.15 or 4.20 g per 100 g straw dry matter (DM) (Experiment 1) or at 0, 2.5, 5.0, 7.5 and 10.0 g per 100 g straw DM (Experiment 2) in solutions at either 60 ml or 120 ml solution per 100 g straw DM. Digestibility in vitro of organic matter (OM) and digestible OM in DM (DOMD) increased with increasing level of NaOH. The effect of volume of solution on digestibility was small. The pH of the straws decreased during storage. The content of neutral detergent fibre decreased as the level of NaOH increased, but there was relatively little change in the contents of acid detergent fibre or acid detergent lignin. Lactate and acetate were detected in all silages, and butyrate was present in silages made from straws treated with less than 5 g NaOH per 100 g straw DM. On opening the silos little moulding was seen and the temperature of the straws remained close to ambient in both experiments throughout 16 days of subsequent exposure to air.In the third experiment, the comparative effects of Ca(OH)₂ and KOH were studied alone and in combination ($\text{50}\text{50}$ by weight) with NaOH. KOH mixed with NaOH gave levels of DOMD in vitro similar to those obtained with NaOH alone. Ca(OH)₂, whilst improving DOMD, was slightly less effective than the other alkalis.The optimum level of alkali for the treatment of barley straw prior to ensiling appeared to be 7.5 g/100 g straw DM. At this level of addition, DOMD in vitro would be expected to be about 65%. Ca(OH)₂ is worth further attention as an alternative to NaOH.     

Structure and saccharification of rice straw pretreated with sulfur trioxide micro-thermal explosion collaborative dilutes alkali

In this paper, a sulfur trioxide collaborative dilutes alkali method has been developed to pre-treat rice straw and it has been studied that the pre-treated rice straw structure affected the saccharification of the rice straw hydrolyzed by cellulose enzymatic hydrolysis. The results show that the reaction of the sulfur trioxide with rice straw resulted in the internal micro-thermal explosion, and the saccharification rate was 91% based on the pretreated rice straw with sulfur trioxide for 4h following 1% w/v NaOH treatment for 7h at 50°C.     

Review article: The alkali treatment of straws

The Beckmann method of alkali treatment consists of soaking straw in dilute alkali solutions for 24 hours and then washing it with clean water. Straw digestibility is increased from about 40 to about 70%. While this process has been known for 50 years, it has not been much used because treatment costs are too high. Also, it cannot be industrialised. The spray process, in which the straw is wetted with an alkali solution (Wilson and Pigden, 1964) is an improvement from both points of view, but poses nutritional problems since straw is not washed after treatment. So great is the potential, however, that within the last seven years nearly 100 research reports have been published on the production and use of spray-treated straw. These reports are reviewed in this article.Straws are poorly digested by ruminants because of their high cell-wall content. Alkali treatment disrupts the cell-wall by dissolving hemicellulose, lignin and silica, by hydrolysing uronic and acetic acid esters and by swelling cellulose. Digestibility in vitro increases from about 40 to about 80% with $\text{10}\text{g NaOH}\text{100}\text{g straw}$. Equally large increases are not, however, obtained in vivo because of unreacted alkali and/or high sodium concentration. Several hypotheses concerning the depression of digestibility in vivo are reviewed. In general $\text{3–6}\text{g NaOH}\text{100}\text{g straw}$ is the optimum. For maximum effectiveness the volume of the alkali solution must be between 50 and $\text{200}\text{ml}\text{100}\text{g straw}$. The usefulness of neutralising unreacted alkali has not yet been determined. Crop and industrial residues with lower initial digestibility than straw (e.g. paddy hulls, bagasse and some types of sawdust) are usually still too poor after treatment (digestibility 30–50%) to be useful feeds. Pressure and temperature increase the effectiveness of alkali, but add to the cost of treatment. The pelleting of treated straws probably increases the effectiveness of alkali treatment. The length of time treated straw is allowed to “cure” before being fed does not affect its digestibility. Chemicals other than NaOH, like chlorine, ammonia and peroxides, are also effective in treating straws but are more expensive and/or more difficult to apply.Animal feeding experiments with sprayed straw have shown its utility for livestock normally fed poor straw diets, in high concentrate diets for growing, finishing and milking stock, and as an extender of silage. The factors affecting the degree of improvement to be expected in digestibility, growth and production from the treatment of straw need to be identified and studied.In spite of its high pH and Na content, sprayed straw has not been found to cause any health problems in livestock when treatment is in the range of 3–8 g NaOH/100 g straw. The extra sodium is excreted in the urine. Water intake and urine volume increase. Milk composition is unaffected.Several factories producing alkali spray-treated straw-based diets in pelleted form are already in operation in Europe. The process is briefly described.     

Pollution control of swine manure and straw by conversion to Chaetomium cellulolyticum SCP feed

Swine manure has a very high pollution potential and obnoxious odor. Large farms particularly are confronted with a manure disposal problem since environmentally acceptable solutions are now required by government regulations. Swine manure was found to be a good source of supplementary nutrients to ferment wheat straw into single-cell protein (SCP) with Chaetomium cellulolyticum when 0.13g (NH₄)₂SO₄/g solid was used as an additional source of N. In batch fermentations, inhibitory effects, possibly due to soluble released from the straw during alkali or acid pretreatment, were overcome by starting the fermentation at about pH 7.0 and then reducing it to 5.0 during growth. An overall protein productivity of up to 66 mg/L h was obtained from a slurry mixture of 1% w/v solids of manure and straw. This compares favorably with 99 mg/L h when manure was fermented with glucose instead of straw as the main carbon source. A high protein productivity of 200 mg/L h was obtained from a slurry mixture containing anaerobically prefermented swine manure liquor and 1.5% w/v solids from straw. The final products of the manure and straw fermentations contained 25–30% DW crude protein and 6–20% DW cellulose and the materials were free of the original obnoxious odor and undesirable microbial contamination.     

Bioconversion of wheat straw to ethanol: Chemical modification,enzymatic hydrolysis,and fermentation

Native wheat straw (WS) was pretreated with various concentrations of H₂SO₄ and NaOH followed by secondary treatments with ethylene diamine (EDA) and NH₄OH prior to enzymatic saccharification. Conversion of the cellulosic component to sugar varied with the chemical modification steps. Treatment solely with alkali yield 51–75% conversion, depending on temperature. Acid treatment at elevated tempeatures showed a substantial decrease in the hemicellulose component, whereas EDA-treated WS (acid pretreated) showed a 69–75% decrease in the lignin component. Acid-pretreated EDA-treated straw yielded a 98% conversion rate, followed by 83% for alkali–NH₄OH treated straws. In other experiments, WS was pretreated with varying concentration of H₂SO₄ or NaOh followed by NH₄OH treatment prior to enzymatic hydrolysis. Pretreatment of straw with 2% NaOH for 4 h coupled to enzymatic hydrolysis yield a 76% conversion of the cellulosic component. Acid–base combination pretreatment yielded only 43% conversions. A reactor column was subsequently used to measure modification–saccharification–fermentation for wheat straw conversion on a larger scale. Thirty percent conversions of wheat straw cellulosics to sugar were observed with subsequent fermentation to alcohol. The crude cellulase preparation yielded considerable quantities of xylose in addition to the glucose. Saccharified materials were fermented directly with actively proliferating proliferating yeast cells without concentration of the sugars.     

稀酸和稀碱预处理对四种不同生物质资源制备还原糖的影响

本论文探讨了不同浓度的稀H_2SO_4和稀NaOH预处理对大豆秸秆、水稻秸秆、象草和狼尾草四种不同生物质酶解制备还原糖的影响。结果表明,大豆秸秆、水稻秸秆、象草和狼尾草具有较高的纤维素和半纤维素含量,是制备还原糖的理想原料。与稀H_2SO_4预处理相比,经稀NaOH预处理后的样品表现出较好的酶解性能。通过使用4%的NaOH对大豆秸秆和狼尾草进行预处理,还原糖产量分别为145.8 mg/mL和319.2 mg/mL。此外,以1%NaOH预处理后的水稻秸秆和象草为原料,可以分别获得385.2 mg/mL和231.6 mg/mL还原糖产量。     

Enzymatic hydrolysis of cellulosic materials by Sclerotium rolfsii culture filtrate for sugar production.

The hydrolysis of purified celluloses (cotton, Avicel, Cellulose-123, Solka Floc SW40) and cellulosic wastes (rice straw, sugarcane bagasse, wood powders, paper factory effluents) by Sclerotium rolfsii CPC 142 culture filtrate was studied. Factors which effect saccharification such as pH, temperature, enzyme concentration, substrate concentration, produce inhibition, adsorption, and inactivation of enzyme and particle size were studied. Virtually no inhibition (less than 3%) of cellulose hydrolysis by the culture filtrate was observed by cellobiose and glucose up to 100 mg/mL. Filter paper degrading enzyme(s) (but neither carboxymethylcellulase nor beta-glucosidase) was adsorbed on cellulose. The n value in the S. rolfsii system was calculated to be 0.32 for Avicel P.H. 101 and 0.53 for alkali-treated (AT) rice straw indicating penetration of cellulase into AT rice straw. In batch experiments at 10% substrate level, solutions containing 6 to 7%, 3.8 to 4.7%, 4.0 to 5.1%, and 4.2 to 4.9% reducing sugars were produced in 24 to 48 from AT rice straw. AT bagasse, alkali - peracetic acid treated mesta wood and paper factory sedimented sludge effluent, respectively. The main constituent in the hydrolysate from cellulose was glucose with little or no cellobiose, probably due to the high cellobiase content in the culture filtrate.     

Alkaline pre-treatment of oilseed rape straw for bioethanol production: evaluation of glucose yield and pre-treatment energy consumption

The objective of the research was to investigate the effect of biomass loading, alkali (NaOH) concentration and pre-treatment time on the yield of glucose obtained following alkaline pre-treatment and enzymatic hydrolysis of oilseed rape (OSR) straw. A maximum glucose yield of (440.6 ± 14.9) g glucose kg⁻¹ biomass was obtained when OSR straw was pre-treated at a biomass loading of 50 g kg⁻¹ and an alkali concentration of 0.63 mol dm⁻³ NaOH for 30 min. The energy efficiency of glucose extraction (0.39 kg glucose MJ⁻¹ consumed) was highest when OSR straw was pre-treated at a biomass loading of 50 g kg⁻¹ and an alkali concentration of 0.63 or 0.75 mol dm⁻³ for 30 min. The study demonstrated alkaline pre-treatment of OSR straw is superior to acid pre-treatment in terms of glucose yield and energy efficiency.     

Different pretreatments for increasing the anaerobic biodegradability in swine manure

The effect of three methods (mechanical, chemical, and thermal pretreatment) were tested to improve methane production and anaerobic biodegradability of swine wastes. The first experiment was designed to determine the biodegradability enhancement through the separation of liquid and solid matrix by using a 0.25mm pore size screen (mechanical pretreatment). The second approach was the treatment of swine waste by the addition of a flocculant agent and strong chemicals such as acid (HCl) and alkali (NaOH). The third pretreatment studied was thermal application (170 degrees C provided by vapor). The soluble COD was increased by 57% and 32% during the pretreatment period with alkali and thermal application, respectively. In addition, these two pretreatments gave the highest enhancement on methane production with regard to the untreated sample. Meanwhile, the addition of a flocculant improved the methane production of the liquid fraction but not the solid one. On the other hand, mechanical pretreatment did not show any important enhancement. Biodegradability percentage followed the same trend as methane productivity.     

Effect of time of storage and method of drying on the digestibility in vitro of alkali-treated barley straw

Samples of barley straw, chopped to 5 cm nominal particle length, were treated with 7.5 g NaOH in 120 ml solution per 100 g dry matter (DM) and either dried immediately after treatment or stored at ?15°C for 24 days prior to drying. The samples were either dried at 100°C in a forced-draught oven, or were freeze-dried. For the samples dried immediately after treatment, incubation in vitro commenced 40 h after treatment. Digestibility in vitro was higher for oven-dried than for freeze-dried samples, particularly when the samples were incubated 40 h after treatment with alkali. Digestibility was also higher for samples which were stored prior to being dried than for those dried directly after treatment with alkali. This suggests that the reaction of alkali with straw continued during the storage of undried material at ?15°C.     

Enhancing the solid-state anaerobic digestion of fallen leaves through simultaneous alkaline treatment

Previous studies have shown that alkali pretreatment prior to anaerobic digestion (AD) can increase the digestibility of lignocellulosic biomass and methane yield. In order to simplify the process and reduce the capital cost, simultaneous alkali treatment and anaerobic digestion was evaluated for methane production from fallen leaves. The highest methane yield of 82 L/kg volatile solids (VS) was obtained at NaOH loading of 3.5% and substrate-to-inoculum (S/I) ratio of 4.1. The greatest enhancement in methane yield was achieved at S/I ratio of 6.2 with NaOH loading of 3.5% which was 24-fold higher than that of the control (without NaOH addition). Reactors at S/I ratio of 8.2 resulted in failure of the AD process. In addition, increasing the total solid (TS) content from 20% to 26% reduced biogas yield by 35% at S/I ratio of 6.2 and NaOH loading of 3.5%. Cellulose and hemicellulose degradation and methane yields are highly related.     

A new algorithm to characterize biodegradability of biomass during anaerobic digestion: influence of lignin concentration on methane production potential

We examined the influence of fibrous fractions of biomass on biochemical methane potential (BMP) with the objective of developing an economical and easy-to-use statistical model to predict BMP, and hence the biodegradability of organic material (BD) for biogas production. The model was developed either for energy crops (grass, maize, and straw) or for animal manures, or as a combined model for these two biomass groups. It was found that lignin concentration in volatile solids (VS) was the strongest predictor of BMP for all the biomass samples. The square of the sample correlation coefficient (R(2)) from the BMP versus lignin was 0.908 (p<0.0001), 0.763 (p<0.001) and 0.883 (p<0.001) for animal manure, energy crops and the combined model, respectively. Validation of the combined model was carried out using 65 datasets from the literature.     

Effects of microwave and alkali induced pretreatment on sludge solubilization and subsequent aerobic digestion

Individual and combined effects of microwave (MW) and alkali pretreatments on sludge disintegration and subsequent aerobic digestion of waste activated sludge (WAS) were studied. Pretreatments with MW (600 W-85 °C-2 min), conventional heating (520 W-80 °C-12 min) and alkali (1.5 g NaOH/L - pH 12-30 min) achieved 8.5%, 7% and 18% COD solubilization, respectively. However, combined MW-alkali pretreatment synergistically enhanced sludge solubilization and achieved 46% COD solubilization, 20% greater than the additive value of MW alone and alkali alone (8.5 + 18% = 26.5%). Moreover, the results of the batch aerobic digestion study on MW-alkali pretreated sludge showed 93% and 63% reductions in SCOD and VSS concentrations, respectively, at 16 days of SRT. The VSS reduction was 20% higher than that of WAS without pretreatment.     

Effects of NaOH treatment on condensed tannin contents and gas production kinetics of tree leaves

Effects of NaOH treatment on the crude protein (CP), condensed tannin (CT) and in vitro gas production kinetics of leaves of Arbutus andrachne, Glycyrrhiza glabra L. and wheat straw were determined. Wheat straw, which is tannin-free, was used as the standard. The NaOH treatment was completed by pulverization of samples with 0, 20, 40, 60 and 80 g/L of NaOH solution in the proportion of 1 L of solution to 1 kg of sample. Gas production was determined at 3, 6, 12, 24, 48, 72 and 96 h of incubation. NaOH treatment linearly decreased (P<0.001) the CT contents of leaves of Arbutus andrachne and Glycyrrhiza glabra L. whereas NaOH treatment had no effect on the CP contents of Arbutus andrachne, Glycyrrhiza glabra L. and wheat straw. The 80 g/L NaOH treatment reduced the CT content of leaves of Arbutus andrachne and Glycyrrhiza glabra L. by 59.6% and 86.7%, respectively. NaOH treatment linearly decreased (P<0.01) gas production rate of Arbutus andrachne although it linearly increased (P<0.01) gas production rate of wheat straw. In contrast, NaOH treatment had no effect on gas production rate of leaves of Glycyrrhiza glabra L. NaOH treatment linearly decreased (P<0.001) potential gas production of leaves of Arbutus andrachne and Glycyrrhiza glabra L. whereas NaOH treatment linearly increased (P<0.001) potential gas production of wheat straw. Treatment with NaOH can be used to improve the nutritive value of tannin-free forages such as straw, but not for tannin-containing leaves.