Search

Most pretreatment methods for lignocellulosic biomass use strong chemicals, such as sulphuric acid and ammonia, to open up the cellular structure of plant biomass. However, those chemicals are not environmentally friendly and their use leads to safety risks. As a result, different chemical-free pretreatment methods have been developed, which focus on the usage of pressure, high or low temperatures and mild chemicals. Freezing pretreatment and explosive decompression pretreatments, using different operating gases, such as nitrogen and steam, are compared in the context of glucose, ethanol and methane yield in this review. For the methane production, the stillage from bioethanol production is used. The usage of this waste improves the overall valorisation of lignocellulosic biomass. The review also investigates, whether the nitrogen explosive decompression pretreatment is suitable for the treatment of softwoods, hardwoods and herbaceous materials. In the comparison of different chemical-free pretreatment methods, it is concluded that heat and water are the most influential parameters for opening up the lignocellulosic biomass structure. The operating gas and pressure in the pretreatment reactor are less relevant. Steam explosion, nitrogen explosive decompression pretreatment and autohydrolysis pretreatment are the most suitable chemical-free pretreatment methods for lignocellulosic biomass.

Received: February 19th, 2022 ; Accepted: April 24th, 2022 ; Published: April 29th, 2022 ; Correspondence: jasola@unilorin.edu.ng Xylitol is a natural polyol with broad applications in the food and pharmaceutical industries. However, its large-scale production through chemical means is still an expensive and not environmentally friendly process. Therefore, great attention has been paid to low-cost and renewable substrates like corn cobs (CC), which can be utilized to improve the economic outlook of xylitol production. In this study, CC were used as a feedstock for xylitol production, with the help of yeasts and filamentous fungi. The results obtained in this study showed that the amount of xylitol produced from CC hydrolysate was similar to the amount of xylitol obtained on xylose substrate. Overall, yeast produced higher amounts of xylitol than filamentous fungi. Pachysolen tannophilus had the highest xylitol production at pH 5.0, 72 h fermentation time, substrate concentration 15%, and inoculum size 1.5×108 cfu mL-1 , while Pichia kudriavzevii performed better at pH 5.0, with a 72 h fermentation time, substrate concentration of 20%, and inoculum size of 2.5×108 cfu mL-1 . When comparing the combined optimal parameters with and without supplementation, supplementation with 1.5% methanol, has increased the xylitol production of P. tannophilus and P. kudriavzevii by 31% and 18.6%, respectively. These findings demonstrate the robustness of these yeast strains for sustainable and cost-effective xylitol production from CC waste.

Soil compaction has detrimental effects on the physical, mechanical and hydraulic properties of soils, and affects important soil processes and function, and crop productivity. This work was conducted to investigate soil compaction impacts in integrated arable croppinglivestock systems managed under conventional tillage (CT) and no-tillage (NT). The work examined the combined effects of cattle trampling and farm machinery traffic on: soil strength, soil deformation, and water infiltration into soil. The following treatments were applied to soil (Entic Haplustoll, 60% sand) managed under CT and NT: three traffic intensities (1, 5, 7 passes) performed with light (2WD, 53 kN) and heavy (4WD, 100.4 kN) tractors, and two stocking densities (400 and 700 kg ha-1 ), respectively. Controls were also used to represent the condition of the soil without any effect of livestock or field traffic. In both tillage systems, soil penetration resistance (strength) increased and water infiltration into soil decreased as traffic intensities or stocking rates applied increased. There was a significant traffic intensity × stocking rate interaction, which influenced the depth and extent of soil compaction at depth. Despite these results, stubble grazing during fallow should not be discouraged as this practice offers mixed farming systems several agronomic and financial benefits. If stubble was to be grazed, the system would need to be carefully managed: (1) avoid ‘random’ traffic using permanent or semipermanent traffic paths to minimise the field wheeled area, (2) vacate livestock from the field, or confine it to a sacrificial area, when the soil water content exceeds a critical level above which soil damage is likely, and (3) maintain more than 60%–70% ground cover. Tillage repair treatments can be targeted to those sacrificial or ‘hot-spots’ areas so that localised, as supposed to widespread, compaction problems are rectified before the next crop is established.

A thesis for applying for the degree of Doctor of Philosophy in Engineering Sciences. Due to the increase of the energy production mainly from non–renewable energy sources, there is a need for alternative sources of energy. Second–generation biofuel production, using lignocellulosic biomass as a feedstock, is emerging as an important liquid biofuel for the transportation sector. However, its production is still very costly, and inefficient mainly due to the large quantity of sidestreams that are generated. Sidestreams from bioethanol production process bring environmental, economic and energetic constraints. a. Environment From the environmental point of view, sidestreams from bioethanol production are highly pollutant. There are several handling options for these residues and it includes: discharge; marine outfall; agricultural fields; sewage treatment; lagoon treatment; anaerobic digestion; incineration; and drying. From all these solutions, anaerobic digestion can be used to reduce the pollution potential of the production waste, and to reduce CO2 and other greenhouse gas (GHG) emissions. b. Economics From the economic point of view, the high costs of bioethanol production require additional valorisation of its stillage to create new revenue streams. Pretreatment and enzymatic hydrolysis are the two most costly parts of the production process. Anaerobic digestion of bioethanol stillage is a prospective solution to offset the costs of bioethanol production and add value to the production chain. c. Energetics Finally, stillage has a high energetic value and can be used to produce energy in the form of methane. Its utilization can give higher net energy outputs and improve the efficiency of the production chain. In addition, ethanol from biomass has an energy return on energy invested (ERoEI) lower than for fossil fuels. Thus, stillage and bioethanol sidestreams can be used for processing energy, through anaerobic digestion to add value to the production chain and improve the energy balance. To sum up, there is a continuous search for strategies that make use of the high energy content of bioethanol sidestreams. Anaerobic digestion to produce energy in the form of methane has been reported as an effective strategy to increase the energy output from the biomass, help to balance the costs of bioethanol production and as an environmental solution to this highly pollutant residues. Vajadus alternatiivsete energia allikate järele kasvab pidevalt kuna üldine energia tarbimine kasvab ning see vajadus rahuldatakse fossiilsete allikate arvelt. Lignotselluoossel biomassil põhinevad teise põlvkonna biokütused on esile kerkinud kui võimalik lahendus transpordi sektori vajaduse katmiseks. Siiski on biokütuste tootmine lignotselluloossest biomassist võrreldes fossiilsete kütustega endiselt väga kulukas. Lisaks tekib nende tootmisel kõrvalvoogusid, mis hetkel ei ole kasutust leidnud ning vajavad eraldi tähelepanu, et vältida nende keskkonna, majanduslikke ja energeetilisi mõjusid. a. Keskkond Keskkonnamõjult on bioetanooli tootmisel tekkivad kõrvalvood kõrge reostuspotentsiaaliga. Nende neutraliseerimiseks on mitmeid strateegiaid. Näiteks: bioloogiline puhastamine, laguunpuhastamine, põletamine, merre pumpamine, kuivatamine, anaeroobne kääritamine jne. Neist käitlemisvõimalustest anaeroobne kääritamine võimaldab samaaegselt vähendada nii kõrvalvoogude reostuspotentsiaali, kui süsihappegaasi ja teiste kasvuhoonegaaside emissioone. b. Majandus Majanduslikust vaatepunktist lähtudes on vajadus väärindada bioetanooli tootmise kõrvalvoogusid, et parandada selle üldist tasuvust ja tekitada lisaväärtust. Eeltöötlus ja ensümaatiline hüdrolüüs on kaks kõige kulukamat protsessi nii bioetanooli kui ka biogaasi tootmises. Bioetanooli tootmise kõrvalvoogude anaeroobne kääritamine võimaldab vähese lisakuluga tekitada lisaväärtus, mis parandab ka bioetanooli tootmisprotsessi tasuvust. c. Energeetika Bioetanooli tootmise kõrvalvoogude kõrge energeetiline väärtus võimaldab neid kasutada anaeroobses kääritamises biometaani tootmiseks. Kõrvalvoogude kasutamine biokütuse tootmiseks võimaldab efektiivsemalt ära kasutada kogu biomassis sisalduvat energiat, tõsta kogu tootmisahela efektiivsust ning parandada energia väljundit sisendenergia suhtes (ERoEI) sedavõrd, et see oleks võimeline konkureerima fossiilsete kütustega. Seega on võimalik bioetanooli tootmisprotsessi energeetilist tasakaalu parandada tootmise kõrvalvoogude kasutamisega anaeroobses kääritamises. Kokkuvõtteks võib öelda, et teadus otsib üha uusi strateegiaid ja lahendusi kuidas parandada bioetanooli tootmisprotsessi efektiivsust kõigist kolmest vaatepunktist lähtuvalt. Tootmise kõrvalvoogude kasutamine biometaani tootmiseks anaeroobses kääritusprotsessis on välja toodud kui üks võimalikest strateegiatest, mis parandaks bioetanooli tootmise energeetilist ja majanduslikku efektiivsust ning vähendaks selle mõju keskkonnale. The publication of this thesis is supported by the Estonian University of Life Sciences. It had the financial support of the European Regional Development Fund via the Mobilitas Pluss (project MOBERA1) of the Estonian Research Council and the base financed projects of EULS P170025 TIPT and PM180260 TIPT; Smart Specialization scholarship for PhD students, funded by the European Regional Development Fund and Estonian government; Dora Plus programme provided by the European Regional Development Fund and Estonian Government; and the Doctoral School of Energy and Geotechnology III, (Estonian University of Life Sciences ASTRA project „Value-chain based bio-economy“).

 Great attention has been paid to liquid biofuels produced from lignocellulosic biomass.  The production of liquid biofuels still has environmental, economic and energetic limitations: a) Large volume of sidestreams are produced c) High costs of pretreatment and enzymatic hydrolysis b) High energy inputs are required to produce the fuel  There is a continuous search for solutions to add value to the bioethanol production chain.  Anaerobic digestion has been proposed as a handling option for waste recovery from biodegradable waste and bioethanol sidestreams. European Regional Development Fund via the Mobilitas Pluss (project MOBERA1) of the Estonian Research Council and base financed projects number EULS P170025 TIPT and PM180260 TIPT. Estonian University of Life Science, the Archimedes Foundation, Estonian Research Council, the Estonian Goverment and the Ministry of Education of Estonian for financial support this research. Dora Plus programme, Smart Specialization scholarship for PhD students and the Doctoral School of Energy and Geotechnology III (Estonian University of Life Science ASTRA project „Valu-chain based bio-economy“). European Regional Development Fund via the Mobilitas Pluss (project MOBERA1) of the Estonian Research Council and base financed projects number EULS P170025 TIPT and PM180260 TIPT. Estonian University of Life Science, the Archimedes Foundation, Estonian Research Council, the Estonian Goverment and the Ministry of Education of Estonian for financial support this research. Dora Plus programme, Smart Specialization scholarship for PhD students and the Doctoral School of Energy and Geotechnology III (Estonian University of Life Science ASTRA project „Valu-chain based bio-economy“).

Controlled traffic farming (CTF) is a mechanisation system in which all load-bearing wheels are confined to the least possible area of permanent traffic lanes and where crops are grown in permanent, non-trafficked beds. In well-designed systems, the area affected by traffic represents less than 15% of the total field cropped area. The extent and distribution of soil compaction at locations laterally outboard of the permanent traffic lanes may explain the performance of the crop on the rows located either side of the wheeling. This compaction is due to lateral displacement of soil caused by repetitive wheeling, the effect of soil-tyre interaction and the soil conditions (strength) at the time of traffic. The impact of compaction on crop rows adjacent to permanent traffic lanes is also dependent on the seasonal effect of weather, because of changes in soil water availability. This work was conducted to model the spatial distribution of soil mechanical strength under increasing number of tractor passes to simulate the soil conditions that may be encountered in CTF systems at locations near-permanent traffic lanes. The study was conducted on a Typic Argiudoll (26% clay, 72% silt, 2% sand) with four traffic intensities (0, 6, 12 and 18 passes) using a 120 HP tractor (overall mass: 6.3 Mg). Traffic treatments were applied to experimental plots using a completely randomized block design with three replications per treatment. The spatial distribution of soil strength within wheeled and non-wheeled zones was determined using a cone penetrometer (depth range: 0–300 mm) and geostatistical techniques. In all treatments, cone index showed a quadratic response with depth, which explained between 67% and 88% of the variation in soil strength. The number of tractor passes had no effect on the range of spatial dependence of residuals. No differences were observed in the proportion of grid cells where penetration resistance was greater than 2 MPa (considered to be the soil strength limit for root growth of most arable crops) between-traffic treatments, or wheeled and non-wheeled zones, respectively. The overall mean proportion (± 95% confidence interval) of grid cells (4.9 ± 4.5%) suggested that this measure has a relatively high variability and therefore may not be a reliable parameter to be used in the design of future experimental work.