Fungal pretreatment of lignocellulosic biomass

Pretreatment is a crucial step in the conversion of lignocellulosic biomass to fermentable sugars and biofuels. Compared to thermal/chemical pretreatment, fungal pretreatment reduces the recalcitrance of lignocellulosic biomass by lignin-degrading microorganisms and thus potentially provides an environmentally-friendly and energy-efficient pretreatment technology for biofuel production. This paper provides an overview of the current state of fungal pretreatment by white rot fungi for biofuel production. The specific topics discussed are: 1) enzymes involved in biodegradation during the fungal pretreatment; 2) operating parameters governing performance of the fungal pretreatment; 3) the effect of fungal pretreatment on enzymatic hydrolysis and ethanol production; 4) efforts for improving enzymatic hydrolysis and ethanol production through combinations of fungal pretreatment and physical/chemical pretreatment; 5) the treatment of lignocellulosic biomass with lignin-degrading enzymes isolated from fungal pretreatment, with a comparison to fungal pretreatment; 6) modeling, reactor design, and scale-up of solid state fungal pretreatment; and 7) the limitations and future perspective of this technology.     

Pretreatment of woody biomass for biofuel production: energy efficiency, technologies, and recalcitrance

This mini review discusses several key technical issues associated with cellulosic ethanol production from woody biomass: energy consumption for woody biomass pretreatment, pretreatment energy efficiency, woody biomass pretreatment technologies, and quantification of woody biomass recalcitrance. Both total sugar yield and pretreatment energy efficiency, defined as the total sugar recovery divided by total energy consumption for pretreatment, should be used to evaluate the performance of a pretreatment process. A post-chemical pretreatment wood size-reduction approach was proposed to significantly reduce energy consumption. The review also emphasizes using a low liquid-to-wood ratio (L/W) to reduce thermal energy consumption for any thermochemical/physical pretreatment in addition to reducing pretreatment temperature.     

Pretreatment of rapeseed straw by soaking in aqueous ammonia

Pretreatment of lignocellulosic biomass has gained attention for production of biofuels. In this study, pretreatment by soaking in aqueous ammonia was adopted for pretreatment of biomass for ethanol production. A central composite design of response surface methodology was used for optimization of the pretreatment condition of rapeseed straw, with respect to catalyst concentration, pretreatment time, and pretreatment temperature. The most optimal condition for pretreatment of rapeseed straw by soaking in aqueous ammonia was 19.8% of ammonia water, 14.2 h of pretreatment time, and a pretreatment temperature of 69.0 °C. Using these optimal factor values under experimental conditions, 60.7% of theoretical glucose was obtained, and this value was well within the range predicted by the model. SEM results showed that SAA pretreatment of rapeseed straw resulted in increased surface area and pore size, as well as enhanced enzymatic digestibility.     

Comparison of some new pretreatment methods for second generation bioethanol production from wheat straw and water hyacinth

Pretreatment of lignocellulosic residues like water hyacinth (WH) and wheat straw (WS) using crude glycerol (CG) and ionic liquids (IL) pretreatment was evaluated and compared with conventional dilute acid pretreatment (DAT) in terms of enzymatic hydrolysis yield and fermentation yield of pretreated samples. In the case of WS, 1-butyl-3-methylimidazolium acetate pretreatment was found to be the best method. The hydrolysis yields of glucose and total reducing sugars were 2.1 and 3.3 times respectively higher by IL pretreatment than DAT, while it was 1.4 and 1.9 times respectively higher with CG pretreatment. For WH sample, CG pretreatment was as effective as DAT and more effective than IL pretreatment regarding hydrolysis yield. The fermentation inhibition was not noticeable with both types of pretreatment methods and feedstocks. Besides, CG pretreatment was found as effective as pure glycerol pretreatment for both feedstocks. This opens up an attractive economic route for the utilization of CG.     

Process and economic analysis of pretreatment technologies

Five pretreatment processes (dilute acid, hot water, ammonia fiber explosion (AFEX), ammonia recycle percolation (ARP), and lime) for the liberation of sugars from corn stover are compared on a consistent basis. Each pretreatment process model was embedded in a full bioethanol facility model so that systematic effects for variations in pretreatment were accounted in the overall process. Economic drivers influenced by pretreatment are yield of both five and six carbon sugars, solids concentration, enzyme loading and hemicellulase activity. All of the designs considered were projected to be capital intensive. Low cost pretreatment reactors in some pretreatment processes are often counterbalanced by higher costs associated with pretreatment catalyst recovery or higher costs for ethanol product recovery. The result is little differentiation between the projected economic performances of the pretreatment options. Additional process performance data, especially involving the identification of optimal enzyme blends for each pretreatment approach and conditioning requirements of hydrolyzates at process-relevant sugar concentrations resulting from each pretreatment may lead to greater differentiation in projected process economics.     

Effects of Mannitol Pretreatment on Androgenesis of Barley (Hordeum vulgare L.)

The effects of mannitol pretreatment on androgenesis of barley were systematically studied in comparison with that of cold pretreatment and control. The results showed that mannitol pretreatment could significantly increase the frequency of pollen survival reaching 19.0% on the eighth day, while in cold pretreatment and control they were 8.4% and 6.6 %, respectively. Mannitol pretreatment could also improve the quality of pollen and inhibit starch production from microspore, which were quite advantageous to microspore division and development. The developing period was shortened 2--3 days as compared with cold pretreatment and control. The major developmental pathways of androgenesis after mannitol pretreatment were the equal division (B pathway). In addition, the majority of microspore nuclei were diploids. On the contrary, the major microspores pretreated with low temperature had fewer chromosomes than with mannitol pretreatment, the microspore nuclei were haploids.     

Effect of washing on yield in one- and two-step steam pretreatment of softwood for production of ethanol

Two-step steam pretreatment of softwood on laboratory scale has previously been shown to result in higher yields than one-step steam pretreatment. In this study, these results are verified on a larger scale. In an industrial process filtration and washing of the material between the two pretreatment steps are difficult without release of pressure. A worst case without filtration or washing was thus investigated to determine the influence of poor washing on the yield of sugars and the formation of byproducts. Steam pretreatment with SO(2) impregnation was investigated using three different procedures. One-step steam pretreatment was performed at 215 degrees C for 5 min. Two different kinds of two-step steam pretreatment were performed at 190 degrees C for 2 min in the first step and at 210 degrees C for 5 min in the second step. In one case the slurry obtained after the first pretreatment step was separated into a liquid and a solid phase, where the water-insoluble solid material was washed with water and then used for pretreatment in the second step. In the other case of two-step steam pretreatment, neither separation nor washing was performed. The pretreated material was evaluated using both enzymatic hydrolysis and fed-batch simultaneous saccharification and fermentation. Both two-step steam pretreatment process configurations investigated resulted in higher yields of ethanol (300 L/ton) than one-step steam pretreatment (227 L/ton). Separation and washing of the material between the pretreatment steps in the two-step steam pretreatment process did not improve the overall sugar yield, although the formation of sugar degradation products was reduced.     

Comparison of various pretreatment methods for biohydrogen production from cornstalk

To establish high-efficiency pretreatments of cornstalk (CS) for hydrogen fermentative production, various pretreatment strategies have been investigated and contrasted in this work. Five pretreatment methods, including acid-soaking pretreatment, base-soaking pretreatment, high-temperature-assisted acid pretreatment, high-temperature-assisted base pretreatment and ultrasonic-assisted acid pretreatment (UAP), were performed on CS. The results showed that UAP significantly promoted the hydrogen production by CS compared with other pretreatments. The optimum UAP process, pretreating substrate with ultrasonication in 2.0% sulfuric acid solution for 1.5 h at the liquid-solid ratio of 20:1, obtained the maximum specific hydrogen accumulation of 142.59 mL g(-1)-CS and an average hydrogen production rate of 17.03 mL g(-1)-CS h(-1). Furthermore, the scanning electron microscope analysis of CS samples supports the hydrogen production results as well. The present work demonstrates that UAP is an efficient and practical CS pretreatment for hydrogen production from agricultural waste straws.     

膜前助滤预处理对高藻水微滤膜污染的影响研究

研究采用添加硅藻土、植物棉、活性炭等3种不同预处理手段来过滤铜绿微囊藻,并考察未预处理及预处理后的藻液过滤过程中的过滤特性、有机物分布及膜污染特性。结果表明, 3种预处理手段对过滤通量均有所提高并减缓膜污染。其中,硅藻土预处理提高平均过滤通量达915%,明显优于其他助滤手段。活性炭预处理能够有效吸附芳香族蛋白质类荧光污染物,显著降低污染膜的不可逆化学污染阻力。通过OCT及SEM分析可知未预处理的高藻水直接过滤造成的膜污染最严重,饼层结构的粗糙度最低并且厚度也最小,而硅藻土通过优化饼层结构以达到缓解膜污染的效果。最后基于XDLVO理论结果也进一步证实硅藻土预处理手段对改善膜污染效果最好。研究结果对未来蓝藻水华膜处理技术的预处理手段研发具有指导意义。     

木质纤维素预处理及高值化技术研究进展

木质纤维素生物质是地球上最丰富的可再生生物资源.随着化石能源的消耗及环境的污染,以取代石化燃料为目标的由生物质向生物燃料的转化受到了广泛的关注.木质纤维素有很强的天然抗降解屏障,需先通过物理、化学及微生物等手段进行预处理,进而以更低的成本和更高的效率转化为生物燃料及其他高附加值产品.本文在总结酸碱等传统预处理方法优缺点...     

Low Temperature and Long Residence Time AFEX Pretreatment of Corn Stover

Low temperature and long residence time pretreatments have been proposed as an alternative to conventional pretreatments within a centralized biorefinery, allowing for a decentralized pretreatment without high energy costs. Ammonia fiber expansion (AFEX?) pretreatment may be uniquely suitable for decentralized pretreatment, and this study considers the possibility of decreasing the temperature in AFEX pretreatment of corn stover. AFEX pretreatment at 40°C and 8?h produced comparable sugar and ethanol yields as conventional AFEX pretreatment at high temperatures and short residence time during subsequent hydrolysis and fermentation. Increasing the ammonia loading at these temperatures tends to increase digestibility, although the moisture content of the reaction has little effect. This study suggests a greater flexibility in AFEX pretreatment conditions than previously thought, allowing for an alternative approach for decentralized facilities if the economic conditions are appropriate.     

Reducing acid in dilute acid pretreatment and the impact on enzymatic saccharification

Dilute acid pretreatment is a leading pretreatment technology for biomass to ethanol conversion due to the comparatively low chemical cost and effective hemicellulose solubilization. The conventional dilute acid pretreatment processes use relatively large quantities of sulfuric acid and require alkali for pH adjustment afterwards. Significant amounts of sulfate salts are generated as by-products, which have to be properly treated before disposal. Wastewater treatment is an expensive, yet indispensable part of commercial level biomass-to-ethanol plants. Therefore, reducing acid use to the lowest level possible would be of great interest to the emerging biomass-to-ethanol industry. In this study, a dilute acid pretreatment process was developed for the pretreatment of corn stover. The pretreatment was conducted at lower acid levels than the conventional process reported in the literature while using longer residence times. The study indicates that a 50% reduction in acid consumption can be achieved without compromising pretreatment efficiency when the pretreatment time was extended from 1–5 min to 15–20 min. To avoid undesirable sugar degradation and inhibitor generation, temperatures should be controlled below 170°C. When the sulfuric acid-to-lignocellulosic biomass ratio was kept at 0.025 g acid/g dry biomass, a cellulose-to-glucose conversion of 72.7% can be achieved at an enzyme loading of 0.016 g/g corn stover. It was also found that acid loading based on total solids (g acid/g dry biomass) governs the pretreatment efficiency rather than the acid concentration (g acid/g pretreatment liquid). While the acid loading on lignocellulosic biomass may be achieved through various combinations of solids loading and acid concentration in the pretreatment step, this work shows that it is unlikely to reduce acid use without undermining pretreatment efficiency simply by increasing the solid content in pretreatment reactors, therefore acid loading on biomass is indicated to be the key factor in effective dilute acid pretreatment.     

Effect of lime pretreatment of brown midrib sorghums

The effect of lime pretreatment of brown midrib sorghums on enzymatic saccharification was investigated. Under most of the pretreatment conditions, the saccharification yields of bmrs were higher than those of the normal counterparts. This result suggests that bmr is useful to reduce pretreatment costs, because the amount of lime necessary for the pretreatment of biomass can reduced by using bmr mutants.     

Somatostatin pretreatment facilitates GRF-induced GH release and increase in free calcium in pituitary cells

Somatostatin pretreatment sensitizes rat anterior pituitary to hGRF stimulation in vitro. The pretreatment (1 nM for 10 min) facilitated GH release response of dispersed rat anterior pituitary cells to hGRF (1 nM for 3 min) 2.04-fold in a perifusion system. The effect lasted even 20 min after the pretreatment. SRIF pretreatment decreased cAMP content in the cells after hGRF stimulation to 61% of the control value. When hGRF was replaced by 1 mM DBcAMP and 15 mM KCl, the pretreatment increased GH secretion 1.69- and 1.67-fold respectively. SRIF pretreatment (1 nM for 10 min) caused a larger increase in (Ca2+)i by hGRF than that of control. The effect of SRIF pretreatment facilitates GRF-induced increase in GH secretion probably through the stimulation of increase in (Ca2+)i.     

FAHP ranking and selection of pretreatment module for membrane separation processes in textile cluster

Recent development in membrane manufacturing and extensive application of membranes in effluent treatment has opened up a new water resource. The effluent pretreatment module plays a critical role in membrane performance. Appropriate selection of conventional and advanced pretreatment modules in membrane separation processes (MSP) is significant to the success of zero effluent discharge (ZED). This study addresses performance assessment of eight conventional and advanced pretreatment modules implemented for wastewater management in a textile cluster in South India. The comparative pollutant reduction, capital, operation and maintenance (OM) cost of pretreatment modules are discussed. The ranking and interdependence of the pretreatment modules were analyzed through fuzzy analytical hierarchy process (FAHP) with MATLAB software.The pretreatment module IV ranked third with a composite weight of 15.46%. The integrated study of performance assessment and FAHP resulted in an optimum pretreatment module IV comprising the sequence of chemical precipitation, bio-oxidation processes (activated sludge processes) followed by chemical precipitation, to achieve the ZED. This study provides a techno-economically feasible solution for selection of an effective pretreatment module for MSP in the textile cluster.     

The Role of Abscisic Acid in Induction of Androgenesis: A Comparative Study Between Hordeum vulgare L. Cvs. Igri and Digger

Under the same mannitol pretreatment and culture conditions, regeneration efficiency in the barley cultivar (cv.) Igri was about 10 times higher than in the cv. Digger, a difference only partially reflected by a difference in viable microspores after anther pretreatment. Therefore, a comparative study between cvs. Igri and Digger was carried out under various pretreatment conditions. For both cultivars, under water, CPW buffer and mannitol pretreatment conditions, there was a positive correlation between microspore viability and regeneration efficiency in that mannitol > CPW buffer >> water. Mannitol pretreatment of cv. Igri produced a much higher endogenous abscisic acid (ABA) level than as to Digger. Addition of ABA stimulated both percentages of viability and regeneration efficiency except in the case of mannitol pretreatment. Under CPW buffer pretreatment conditions, addition of ABA significantly stimulated regeneration efficiency and was ABA concentration dependent. However, cv. Digger was less responsive to ABA than cv. Igri. In both cultivars, under less optimal pretreatment conditions (e.g., water and CPW buffer), the effect of ABA was to stimulate increased percentages of viability and/or to reduce the number of binucleate microspores. Moreover, in cv. Igri, direct culture of anthers for 4 days without pretreatment caused an increased number of binucleate microspores compared with microspores with pretreatment for 4 days. These binucleate microspores showed DNA degradation in the nuclei. However, with mannitol pretreatment binucleate microspores and DNA fragmentation in the nuclei of microspores was rarely observed. On the basis of our observations, we suggest that the difference in regeneration efficiency in cv. Igri and cv. Digger is related to the differences in endogenous ABA production levels under mannitol pretreatment and responsiveness to ABA. One of the effects of ABA is likely due to an inhibition of cell death. Received May 21, 1999; accepted October 5, 1999     

Effect of various pretreatment methods on anaerobic mixed microflora to enhance biohydrogen production utilizing dairy wastewater as substrate

Influence of different pretreatment methods applied on anaerobic mixed inoculum was evaluated for selectively enriching the hydrogen (H(2)) producing mixed culture using dairy wastewater as substrate. The experimental data showed the feasibility of molecular biohydrogen generation utilizing dairy wastewater as primary carbon source through metabolic participation. However, the efficiency of H(2) evolution and substrate removal efficiency were found to be dependent on the type of pretreatment procedure adopted on the parent inoculum. Among the studied pretreatment methods, chemical pretreatment (2-bromoethane sulphonic acid sodium salt (0.2 g/l); 24 h) procedure enabled higher H(2) yield along with concurrent substrate removal efficiency. On the contrary, heat-shock pretreatment (100 degrees C; 1 h) procedure resulted in relatively low H(2) yield. Compared to control experiments all the adopted pretreatment methods documented higher H(2) generation efficiency. In the case of combination experiments, integration of pH (pH 3; adjusted with ortho-phosphoric acid; 24 h) and chemical pretreatment evidenced higher H(2) production. Data envelopment analysis (DEA), a frontier analysis technique model was successfully applied to enumerate the relative efficiency of different pretreatment methods studied by considered pretreatment procedures as input and cumulative H(2) production rate and substrate degradation rate as corresponding two outputs.     

苏云金杆菌预处理小菜蛾对有机磷和氨基甲酸酯杀虫剂的增效作用

研究了小菜蛾Plutella xylostella幼虫经苏云金杆菌Bacillus thuringiensis预处理后,对有机磷和氨基甲酸酯杀虫剂敏感性的变化以及预处理对小菜蛾幼虫体内乙酰胆碱酯酶、羧酸酯酶、谷胱甘肽S-转移酶和谷胱甘肽的含量的影响。结果表明：苏云金杆菌预处理抗性小菜蛾幼虫后,其对甲胺磷、水胺硫磷和克百威的敏感性分别为未处理组的6.74、8.83和8.50倍;处理敏感小菜蛾幼虫后则分别为未处理组的2.96、1.69和3.88倍。苏云金杆菌预处理抗性小菜蛾,未处理组乙酰胆碱酯酶的K_m和V_max值分别为预处理组的1.86和1.56倍,所使用的6种杀虫剂对乙酰胆碱酯酶的K_I值,处理组为未处理组的1.80～2.66倍,苏云金杆菌预处理抗性小菜蛾对羧酸酯酶的K_m、K_I影响不大,但能显著地抑制羧酸酯酶和谷胱甘肽S-转移酶的活性并导致谷胱甘肽含量下降(对照分别为处理的2.02、1.76和1.66倍)。苏云金杆菌预处理敏感小菜蛾,对乙酰胆碱酯酶的K_m、V_max、K_I值和羧酸酯酶的K_m、K_I值以及谷胱甘肽含量影响不大,但能显著地抑制羧酸酯酶和谷胱甘肽S-转移酶的活性(对照分别为处理的1.54和1.64倍)。     

Ultrasonic pretreatment for thermophilic aerobic digestion in industrial waste activated sludge treatment

In order to enhance the degradation efficiency of waste activated sludge (WAS) by thermophilic aerobic digestion, an ultrasonic pretreatment was examined. It was observed that ultrasonic pretreatment increased the solubilization of organic matter in the WAS and that the solubilization ratio of the organics increased during the first 30 min but did not extensively increase thereafter. Therefore, a pretreatment time of 30 min was determined to be the economical pretreatment time from the experimental results. From the digestion experiments, which was conducted using the WAS collected from an oil refinery plant in Inchon, Korea, investigating the effects of an ultrasonic pretreatment on thermophilic aerobic digestion, it was confirmed that the proposed ultrasonic pretreatment was effective at enhancing the release of the cellular components in WAS and the degradation of released components in the thermophilic aerobic digestion.     

Organosolv pretreatment of lignocellulosic biomass for enzymatic hydrolysis

Production of ethanol by bioconversion of lignocellulosic biomass has attracted much interest in recent years. However, the pretreatment process for increasing the enzymatic digestibility of cellulose has become a key step in commercialized production of cellulosic ethanol. During the last decades, many pretreatment processes have been developed for decreasing the biomass recalcitrance, but only a few of them seem to be promising. From the point of view for integrated utilization of lignocellulosic biomass, organosolv pretreatment provides a pathway for biorefining of biomass. This review presents the progress of organosolv pretreatment of lignocellulosic biomass in recent decades, especially on alcohol, organic acid, organic peracid and acetone pretreatments, and corresponding action mechanisms. Evaluation and prospect of organosolv pretreatment were performed. Finally, some recommendations for future investigation of this pretreatment method were given.