Bioethanol from Lignocellulosic Biomass: Current Findings Determine Research Priorities

“Second generation” bioethanol, with lignocellulose material as feedstock, is a promising alternative for first generation bioethanol. This paper provides an overview of the current status and reveals the bottlenecks that hamper its implementation. The current literature specifies a conversion of biomass to bioethanol of 30 to ~50% only. Novel processes increase the conversion yield to about 92% of the theoretical yield. New combined processes reduce both the number of operational steps and the production of inhibitors. Recent advances in genetically engineered microorganisms are promising for higher alcohol tolerance and conversion efficiency. By combining advanced systems and by intensive additional research to eliminate current bottlenecks, second generation bioethanol could surpass the traditional first generation processes

A walnut shell biochar-nano zero-valent iron composite membrane for the degradation of carbamazepine via persulfate activation

In this study, novel walnut shell biochar-nano zero-valent iron nanocomposites (WSBC-nZVI) were synthesized using a combined pyrolysis/reduction process. WSBC-nZVI displayed a high removal efficiency (86 %) for carbamazepine (CBZ) compared with walnut shell biochar (70 %) and nano zero-valent iron (76 %) in the presence of persulfate (PS) (0.5 g/L catalyst, 10 mg/L CBZ, 1 mM persulfate). Subsequently, WSBC-nZVI was applied for the fabrication of the membrane using a phase inversion method. The membrane demonstrated an excellent removal efficiency of 91 % for CBZ in a dead-end system (2 mg/L CBZ, 1 mM persulfate). In addition, the effect of various operating conditions on the degradation efficiency in the membrane/persulfate system was investigated. The optimum pH was close to neutral, and an increase in CBZ concentration from 1 mg/L to 10 mg/L led to a drop in removal efficiency from 100 % to 24 %. The degradation mechanisms indicated that oxidative species, including 1O2, ·OH, SO4·−, and O2·−, all contribute to the degradation of CBZ, while the role of 1O2 is highlighted. The CBZ degradation products were also investigated, and the possible pathways and the predicted toxicity of intermediates were proposed. Furthermore, the practical use of the membrane was validated by the treatment of real wastewater

Reviewing the thermo-chemical recycling of waste polyurethane foam

The worldwide production of polymeric foam materials is growing due to their advantageous properties of light weight, high thermal insulation, good strength, resistance and rigidity. Society creates ever increasing amounts of poly-urethane (PU) waste. A major part of this waste can be recycled or recovered in order to be put into further use. The PU industry is committed to assist and play its part in the process. The recycling and recovery of PU foam cover a range of mechanical, physical, chemical and thermo-chemical processes. In addition to the well- documented mechanical and chemical processing options, thermo-chemical treatments are important either as ultimate disposal (incineration) or towards feedstock recovery, leading to different products according to the thermal conditions of the treatment. The review focuses on these thermo-chemical and thermal processes. As far as pyrolysis is concerned, TDI and mostly polyol can be recovered. The highest recovery yields of TDI and polyols occur at low temperatures (150–200 ◦C). It is however clear from literature that pure feedstock will not be produced, and that a further upgrading of the condensate will be needed, together with a thermal or alternative treatment of the non-condensables. Gasification towards syngas has been studied on a larger and industrial scale. Its application would need the location of the PU treatment plant close to a chemical plant, if the syngas is to be valorized or considered in conjunction with a gas-fired CHP plant. Incineration has been studied mostly in a co- firing scheme. Potentially toxic emissions from PU combustion can be catered for by the common flue gas cleaning behind the incineration itself, making this solution less evident as a stand-alone option: the combination with other wastes (such as municipal solid waste) in MSWI′s seems the indicated route to go

Reviewing the potential of bio-hydrogen production by fermentation

Hydrogen is a common reactant in the petro-chemical industry and moreover recognized as a potential fuel within the next 20 years. The production of hydrogen from biomass and carbohydrate feedstock, though undoubtedly desirable and favored, is still at the level of laboratory or pilot scale. The present work reviews the current researched pathways. Different types of carbohydrates, and waste biomass are identified as feedstock for the fermentative bio-hydrogen production. Although all techniques suffer from drawbacks of a low H2 yield and the production of a liquid waste stream rich in VFAs that needs further treatment, the technical advances foster the commercial utilization. Bacterial strains capable of high hydrogen yield are assessed, together with advanced techniques of co-culture fermentation and metabolic engineering. Residual VFAs can be converted. The review provides an insight on how fermentation can be conducted for a wide spectrum of feedstock and how fermentation effluent can be valorized by integrating fermentation with other systems, leading to an improved industrial potential of the technique. To boost the fermentation potential, additional research should firstly target its demonstration on pilot or industrial scale to prove the process efficiency, production costs and method reliability. It should secondly focus on optimizing the micro-organism functionality, and should finally develop and demonstrate a viable valorization of the residual VFA-rich waste streams

11CO2 positron emission imaging reveals the in-situ gas concentration profile as function of time and position in opaque gas-solid contacting systems

The in situ analysis of industrial processes, mostly conducted in opaque equipment is difficult. Whereas previously the positron emission technique was successfully applied to study the flow and mixing in gas-solid and liquid-solid systems using radio-active tracer particles, research on imaging a radio- active tracer gas is scarce. The present paper demonstrates the use of a fully three-dimensional (3D) Positron Emission Tomography (PET) in imaging the adsorption of 11CO2 tracer gas, while validating the measurement by conventional exit gas analysis. It will be demonstrated that PET can be used to measure the kinetics of high-pressure CO2 adsorption in situ, including the essential breakthrough and mass transfer zone characteristics. Such high-pressure operation is characteristic of pre-combustion CO2 capturing processes. It is expected that this work will foster further studies of gas-solid systems of adsorption, gas-solid catalysis, gas-solid hydrodynamics, and processes where the gas-solid interaction is of primary importance

Requirements for measurement and validation of biochemical methane potential (BMP).

This document presents the minimal requirements for measurement and validation of biochemical methane potential (also called biomethane potential) (BMP) in batch tests. It represents the consensus of more than 50 biogas researchers. The list of requirements is the same as in the open-access commentary by Holliger et al. [2021]. For details on development of these requirements see the open-access papers Holliger et al. [2016] and Hafner et al. [2020c]

Anaerobic digestion as a key technology in bio-energy production: Current achievements and challenges

Anaerobic digestion has been applied for many decades for the treatment of organic wastes like manure, wastewater sludge and crop residues. Whereas these streams were considered as a nuisance in the past, nowadays, emphasis lies on resource recovery. These wastes are, indeed, providing an important source of renewable energy. Therefore, there is a renewed interest in anaerobic digestion as a technology for sustainable renewable energy production. Also, anaerobic digestion plays a central role in a biorefinery concept. All over Europe, the application of anaerobic digestion is steadily growing, although there are major differences between individual countries on the adaptation of this technology. Because of the high complexity of the degradation mechanisms occurring, digesters are currently still treated as black box systems, and are mainly designed by rules of thumb. Much research is carried out to gain additional insight to be used for process optimisation. Some major research topics include (i) reducing the long retention times in the digester, (ii) increasing the (limited) biogas production efficiency (currently merely ca. 50% of the organic matter in the waste stream is converted to biogas), (iii) increasing the methane content in the biogas (hereby increasing its heating value), (iv) opening the way to include lignocellulosic materials as feedstock for digestion and (v) adapting the digestion process to cope with inhibition by recalcitrant LCFA (for high lipid containing feeds) and ammonia (for high nitrogen containing feeds). The aim of this paper is to provide an overview of the current status on anaerobic digestion research. First, an overview on the application of the technology in European countries will be provided, and it potential will be highlighted. Next, the main trends in anaerobic digestion research will be critically discussed. Highly innovative research topics in anaerobic digestion include (i) stimulation of the anaerobic micro-organisms by process technological innovations (e.g. application of microwaves and ultrasonic fields), (ii) integration of knowledge on microbial community composition and development in steering anaerobic digestion and (iii) advanced mathematical modelling for simulation and control of the digestion. Current achievements will be highlighted and future opportunities will be identified. The main aspects will be illustrated by some examples of state-of-the-art research in the respective domains.status: publishe

On the ‘bio-way’ to sustainability: Novel fermentation pathways to produce fuels and chemicals

The search for novel technologies to generate renewable chemicals and fuels has attracted large attention in recent years, mainly because of the necessity to develop sustainable alternatives for fossil fuel based processes. The conversion of biomass and organic wastes by fermentation processes is of growing importance. Whereas in the past microbial conversions were limited to ‘simple molecules’ like bio-ethanol, methane (via anaerobic digestion) or hydrogen production, the application of microbial resource management paves the way towards the fermentative production of more complex and value added organic molecules, which can be used as a feedstock in chemical processes or as liquid fuel. In both cases, they can replace fossil fuels. Microbial resource management aims to control and steer the capabilities of complex communities by operating the bioreactors in such a way to promote the development of a microbial community that accommodates the desired functional process. The application of molecular biology and the advent of culture-independent molecular techniques like high throughput DNA sequencing methods has caused a revolution in the capabilities to practice microbial resource management, opening the door to engineer communities with superior functions. Currently, bioreactors exploiting natural microbial communities for bioenergy production are commonly operated based on bulk parameters and empirical expert knowledge. The composition of the fermentation mixture in the bioreactor often remains a black box. The ability of current molecular and cell based methods to derive structurefunction-relationships, that is, correlations between the microbial community structure and dynamics, and the reactor performance, are considered as key-criteria for the future development of biofuel production. This paper will review the current state-of-the art in fermentation technology and will analyse the current trends in microbial resource management. Examples of applications will be presented with a focus on integration with process measurements to improve system performance.status: publishe

Simultaneous conversion of C5 and C6 lignocellulosic polysaccharides to platform chemicals through microwave-assisted hydrolysis

Lignocellulosic biomass consists for ca. 70% of polysaccharides (cellulose microfibrils and hemicellulose) and ca. 30% lignin. Therefore, it is a valuable source for platform chemical production from polysaccharides. Even though biomass is relatively cheap and readily available, it is still a major challenge to break down the energy rich polysaccharides into platform chemicals that can be used in further processes. In this research, the possibility of microwave-assisted acid hydrolysis to convert lignocellulosic polysaccharides into platform chemicals (i.e. HMF and furfural) was investigated. A biphasic reaction system is applied to prevent the rapid rehydration of hydroxymethylfurfural (HMF) to levulinic acid and avoid polymerization to disperse polymers, the so-called humins. The biphasic reaction system consists of an acidified water phase (where the acid functions as the catalyst) and an organic solvent phase. The system has been heated by microwave radiation, which allows a quicker heating process and is said to have direct positive effects on the production of HMF. These advantages of a microwave heated biphasic reaction system contribute to the increase of the yields of the platform chemicals. In a first stage, the process parameters (temperature, acid concentration and reaction time) for the conversion of cellulose to HMF were optimized using response surface methodology (i.e., Box Behnken design). Then, under these optimized parameters, the simultaneous conversion of C5 and C6 polysaccharides (using xylan and cellulose as model components) to furfural and HMF was investigated. From the results it is clear that no humins are formed during the microwave treatment and that it is possible to convert C5 and C6 sugars into furfural and HMF respectively. A maximal HMF yield is found to be 32,98 w%(± 1,11w%). Furfural yields were within the same range. Previously named results were obtained using xylan and cellulose as model compounds for lignocellulosic polysaccharides. However, the lignocellulosic matrix itself (including lignin) can have a significant influence on the conversion pathways to the desired platform chemicals. Therefore the effect of the lignocellulosic matrix has also been investigated. In this research bamboo was applied as lignocellulosic biomass. In advance the cellulose and hemicellulose content of bamboo was determined using the Van Soest analysis. Also in this case C5 and C6 polysaccharides were simultaneous converted to furfural and HMF, while lignin remained after reaction.status: publishe