Optimizing on-farm pretreatment of perennial grasses for fuel ethanol production

Biotechnological advances in biomass pretreatment for bio-renewable production through nanotechnological intervention

Globally, the fossil fuel reserves are depleting rapidly and the escalating fuel prices as well as plethora of the pollutants released from the emission of burning fossil fuels cause global warming that massively disturb the ecological balance. Moreover, the unnecessary utilization of non-renewable energy sources is a genuine hazard to nature and economic stability, which demands an alternative renewable source of energy. The lignocellulosic biomass is the pillar of renewable sources of energy. Different conventional pretreatment methods of lignocellulosic feedstocks have employed for biofuel production. However, these pretreatments are associated with disadvantages such as high cost of chemical substances, high load of organic catalysts or mechanical equipment, time consuming, and production of toxic inhibitors causing the environmental pollution. Nanotechnology has shown the promised biorefinery results by overcoming the disadvantages associated with the conventional pretreatments. Recyclability of nanomaterials offers cost effective and economically viable biorefineries processes. Lignolytic and saccharolytic enzymes have immobilized onto/into the nanomaterials for the higher biocatalyst loading due to their inherent properties of high surface area to volume ratios. Nanobiocatalyst enhance the hydrolyzing process of pretreated biomass by their high penetration into the cell wall to disintegrate the complex carbohydrates for the release of high amounts of sugars towards biofuel and various by-products production. Different nanotechnological routes provide cost-effective bioenergy production from the rich repertoires of the forest and agricultural-based lignocellulosic biomass. In this article, a critical survey of diverse biomass pretreatment methods and the nanotechnological interventions for opening up the biomass structure has been carried out.

Mechanism of improved cellulosic bio-ethanol production from alfalfa stems via ambient-temperature acid pretreatment

Model compounds and recalcitrant biomass were studied to elucidate the mechanism of ambient-temperature acid pretreatment of cellulosic biomass for bio-ethanol production. Pure cellulose, a pure hemicellulose and alfalfa stems were pretreated with sulfuric acid under ambient temperature with varied acid loading and time. Changes in water-soluble carbohydrates (WSCs) and chemical components of substrates were determined, and ethanol production via simultaneous saccharification and fermentation (SSF) was studied. The results showed significant amount of WSCs formed, and the WSCs increased with increasing acid loading and pretreatment time. The ethanol yields from pure cellulose were primarily affected by the added ash. Acid loading showed significant positive effect on ethanol production from alfalfa stems, whereas pretreatment time showed much weaker positive effect. However, non-significant amounts of WSCs were removed by washing of dried substrates. It was hypothesized to be because the WSCs adsorbed onto bulk substrates during the freeze-drying step, as supported by experimental results.

Chemical Pretreatment Methods for the Production of Cellulosic Ethanol: Technologies and Innovations

Pretreatment of lignocellulose has received considerable research globally due to its influence on the technical, economic and environmental sustainability of cellulosic ethanol production. Some of the most promising pretreatment methods require the application of chemicals such as acids, alkali, salts, oxidants, and solvents. Thus, advances in research have enabled the development and integration of chemical-based pretreatment into proprietary ethanol production technologies in several pilot and demonstration plants globally, with potential to scale-up to commercial levels. This paper reviews known and emerging chemical pretreatment methods, highlighting recent findings and process innovations developed to offset inherent challenges via a range of interventions, notably, the combination of chemical pretreatment with other methods to improve carbohydrate preservation, reduce formation of degradation products, achieve high sugar yields at mild reaction conditions, reduce solvent loads and enzyme dose, reduce waste generation, and improve recovery of biomass components in pure forms. The use of chemicals such as ionic liquids, NMMO, and sulphite are promising once challenges in solvent recovery are overcome. For developing countries, alkali-based methods are relatively easy to deploy in decentralized, low-tech systems owing to advantages such as the requirement of simple reactors and the ease of operation.

Technological innovations in silage production and utilization

Technology innovation is the process through which new technologies are developed. Silage research addresses the various agronomical, biochemical, microbiological, nutritional and engineering aspects of the process. Forage harvesters, additives (inoculants), and plastic films for sealing are important recent developments. The corn silage is the major source of energy in rations, but recently the use of other ensiled crops, such as sugarcane and legumes, has been increased. Two newer ensiling techniques are the pressed bag and the wrapped bale. Polyethylene film has been the most common method used to protect silage near the surface, but new plastic films are available or in the process of development. A co-extruded polyethylene-polyamide film and new polyvinyl alcohol film also have been used to seal corn silage. Various types of additives have been developed in order to improve the ensiling process. Lactobacillus buchneri, that is an obligate heterolactic acid bacterium, might improve the aerobic stability of silages and have been more effective in corn silage than in other silages. Energy production from silage has also attracted much interest in recent years, as perennial grasses that have been stored as biomass to produce biofuels in the United States, and silage as feedstock for biogas in Europe.

Comparison of alkaline- and fungi-assisted wet-storage of corn stover

Storage of lignocellulosic biomass is critical for a year-round supply of feedstock for a biorefinery. Compared with dry storage, wet storage is a promising alternative technology, providing several advantages including reduced dry matter loss and fire risk and improved feedstock digestibility after storage. This study investigated the concurrent pretreatment and wet-storage of corn stover with the assistance of NaOH or a lignin-degrading fungus, Ceriporiopsis subvermispora, during a 90-d period. Compared with ensilage, adding NaOH or inoculation with C. subvermispora significantly enhanced the enzymatic degradability of corn stover by 2-3-fold after 90-d wet storage. Lignin and xylan removal during NaOH pretreatment and wet-storage were influenced by NaOH loading and moisture. NaOH pretreatment retarded the production of organic acids during storage and the acetate release correlated with lignin and xylan removal. Further study is needed to reduce cellulose degradation during the late stage of fungal treatment.

Effect of reduced ferulate-mediated lignin/arabinoxylan cross-linking in corn silage on feed intake, digestibility, and milk production

Cross-linking of lignin to arabinoxylan by ferulates limits in vitro rumen digestibility of grass cell walls. The effect of ferulate cross-linking on dry matter intake (DMI), milk production, and in vivo digestibility was investigated in ad libitum and restricted-intake digestion trials with lambs, and in a dairy cow performance trial using the low-ferulate sfe corn mutant. Silages of 5 inbred corn lines were fed: W23, 2 W23sfe lines (M04-4 and M04-21), B73, and B73bm3. As expected, the W23sfe silages contained fewer ferulate ether cross-links and B73bm3 silage had a lower lignin concentration than the respective genetic controls. Silages were fed as the sole ingredient to 4 lambs per silage treatment. Lambs were confined to metabolism crates and fed ad libitum for a 12-d adaptation period followed by a 5-d collection period of feed refusals and feces. Immediately following the ad libitum feeding trial, silage offered was limited to 2% of body weight. After a 2-d adaptation to restricted feeding, feed refusals and feces were collected for 5 d. Seventy Holstein cows were blocked by lactation, days in milk, body weight, and milk production and assigned to total mixed ration diets based on the 5 corn silages. Diets were fed for 28 d and data were collected on weekly DMI and milk production and composition. Fecal grab samples were collected during the last week of the lactation trial for estimation of feed digestibility using acid-insoluble ash as a marker. Silage, total mixed ration, feed refusals, and fecal samples were analyzed for crude protein, starch, neutral detergent fiber (NDF), cell wall polysaccharides, and lignin. The W23sfe silages resulted in lower DMI in the ad libitum trial than the W23 silage, but DMI did not differ in the restricted trial. No differences were observed for NDF or cell wall polysaccharide digestibility by lambs with restricted feeding, but the amount of NDF digested daily increased for lambs fed the M04-21 W23sfe silage ad libitum. Lambs were less selective against NDF and lignin when offered W23sfe silages. The B73bm3 silage did not affect DMI or digestibility of cell walls at the restricted feeding level, but total daily NDF digested was greater at ad libitum intake. Intake, milk production, and cell wall digestibility were greater for cows fed diets containing W23sfe silages than for those fed W23 silage. Although milk production was greater for the B73bm3 diet, DMI and cell wall digestibility were not altered. Cows were less selective against cell wall material when fed both W23sfe and B73bm3 silages. Reduced ferulate cross-linking in sfe corn silage is a new genetic mechanism for improving milk production.