Life Cycle Assessment of Bioethanol Production: A Review of Feedstock, Technology and Methodology

Life cycle environmental benefits of recycling waste liquor and chemicals in production of lignocellulosic bioethanol

In recent decades, numerous bioconversion processes and techniques have been developed to utilize lignocellulosic biomass as feedstock in the production of bio-based fuels and materials. However, waste treatment, an important sub-system, is seldom considered in the life cycle assessment of lignocellulose derived products. This study comprehensively investigated the environmental impacts of bioethanol and electricity cogeneration from sugarcane bagasse, with a focus on recycling techniques adopted in waste treatment. A life cycle assessment indicated that high recycle rate of black liquor, acid and waste washing water can substantially reduce the consumption of fresh water, related chemicals and energy by 70-80%. Environmental impacts relating to global warming, acidification potential and primary energy demand can be decreased by 5-10 times or even entirely eliminated. These study outcomes demonstrate significant environmental benefits of integrating waste recycling techniques into lignocellulose biorefinery process, providing a solid foundation for future industrial development.

Process design and life cycle assessment of furfural and glucose co-production derived from palm oil empty fruit bunches

In light of environmental issues, lignocellulosic empty fruit bunch (EFB) biomass is promoted as a carbon-neutral, environmentally friendly, and renewable alternative feedstock. A comprehensive environmental assessment of EFB biorefineries is critical for determining their sustainability in parallel with the bioeconomy policy. Nonetheless, no life cycle assessment (LCA) has been performed on co-producing food and biochemicals (furfural and glucose) derived from EFB biomass. This research is the first to evaluate the environmental performance of the furfural and glucose co-production processes from EFB biomass. Environmental analysis is conducted using a prospective gate-to-gate LCA for four impact categories, including global warming potential (GWP), acidification (ADP), eutrophication (EP), and human toxicity (HT). Aspen Plus is used to simulate the co-production process of furfural and glucose as well as generate mass and energy balances for LCA inventory data usage. The findings suggest that the environmental footprint in respect of GWP, ADP, EP, and HT is 4846.85 kg CO2 equivalent per ton EFB, 7.24 kg SO2 equivalent per ton EFB, 1.52 kg PO4 equivalent per ton EFB, and 2.62E-05 kg 1,4-DB equivalent per ton EFB, respectively. The normalized overall impact scores for GWP, ADP, EP, and HT are 1.16E-10, 2.28E-11, 6.12E-10, and 2.18E-17 years/ton of EFB, respectively. In summary, the proposed integrated plant is not only economically profitable but also environmentally sustainable. In the attempt to enhance the Malaysian economic sector based on the EFB, this study has the potential to serve as an indicator of the environmental sustainability of the palm oil industry.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s10668-022-02633-8.

Screening for New Efficient and Sustainable-by-Design Solvents to Assist the Extractive Fermentation of Glucose to Bioethanol Fuels

The production of bioethanol fuels using extractive fermentation increases the efficiency of the bioconversion reaction by reducing the toxic product inhibition. The choice of appropriate solvents to remove the bioethanol product without inhibiting the fermentation is important to enable industrial scale application. This work applies computer-aided molecular design technologies to systematically screen a wide variety of candidate solvents to enhance the separation, also considering the microorganisms that perform the fermentation. The performance of the candidates was evaluated using a rigorous process simulator for extractive fermentation, assisted by functional group-contribution (QSPR/QSAR) models for the prediction of various solvent properties, including toxicity and life cycle impacts. The solvent designs generated through this approach can provide powerful insights on the kind of molecular structures and functionalities that satisfy the process objectives and constraints, as well the desired sustainability features.

Combinatorial use of environmental stresses and genetic engineering to increase ethanol titres in cyanobacteria

Current industrial bioethanol production by yeast through fermentation generates carbon dioxide. Carbon neutral bioethanol production by cyanobacteria uses biological fixation (photosynthesis) of carbon dioxide or other waste inorganic carbon sources, whilst being sustainable and renewable. The first ethanologenic cyanobacterial process was developed over two decades ago using Synechococcus elongatus PCC 7942, by incorporating the recombinant pdc and adh genes from Zymomonas mobilis. Further engineering has increased bioethanol titres 24-fold, yet current levels are far below what is required for industrial application. At the heart of the problem is that the rate of carbon fixation cannot be drastically accelerated and carbon partitioning towards bioethanol production impacts on cell fitness. Key progress has been achieved by increasing the precursor pyruvate levels intracellularly, upregulating synthetic genes and knocking out pathways competing for pyruvate. Studies have shown that cyanobacteria accumulate high proportions of carbon reserves that are mobilised under specific environmental stresses or through pathway engineering to increase ethanol production. When used in conjunction with specific genetic knockouts, they supply significantly more carbon for ethanol production. This review will discuss the progress in generating ethanologenic cyanobacteria through chassis engineering, and exploring the impact of environmental stresses on increasing carbon flux towards ethanol production.

Biomass Potential for Producing Power via Green Hydrogen

Hydrogen (H2) has become an important energy vector for mitigating the effects of climate change since it can be obtained from renewable sources and can be fed to fuel cells for producing power. Bioethanol can become a green H2 source via Ethanol Steam Reforming (ESR) but several variables influence the power production in the fuel cell. Herein, we explored and optimized the main variables that affect this power production. The process includes biomass fermentation, bioethanol purification, H2 production via ESR, syngas cleaning by a CO-removal reactor, and power production in a high temperature proton exchange membrane fuel cell (HT-PEMFC). Among the explored variables, the steam-to-ethanol molar ratio (S/E) employed in the ESR has the strongest influence on power production, process efficiency, and energy consumption. This effect is followed by other variables such as the inlet ethanol concentration and the ESR temperature. Although the CO-removal reactor did not show a significant effect on power production, it is key to increase the voltage on the fuel cell and consequently the power production. Optimization was carried out by the response surface methodology (RSM) and showed a maximum power of 0.07 kWh kg−1 of bioethanol with an efficiency of 17%, when ESR temperature is 700 °C. These values can be reached from different bioethanol sources as the S/E and CO-removal temperature are changed accordingly with the inlet ethanol concentration. Because there is a linear correlation between S/E and ethanol concentration, it is possible to select a proper S/E and CO-removal temperature to maximize the power generation in the HT-PEMFC via ESR. This study serves as a starting point to diversify the sources for producing H2 and moving towards a H2-economy.

Conversion of Lignocellulose for Bioethanol Production, Applied in Bio-Polyethylene Terephthalate

The increasing demand for petroleum-based polyethylene terephthalate (PET) grows population impacts daily. A greener and more sustainable raw material, lignocellulose, is a promising replacement of petroleum-based raw materials to convert into bio-PET. This paper reviews the recent development of lignocellulose conversion into bio-PET through bioethanol reaction pathways. This review addresses lignocellulose properties, bioethanol production processes, separation processes of bioethanol, and the production of bio-terephthalic acid and bio-polyethylene terephthalate. The article also discusses the current industries that manufacture alcohol-based raw materials for bio-PET or bio-PET products. In the future, the production of bio-PET from biomass will increase due to the scarcity of petroleum-based raw materials.

Hydrogen Production through Autothermal Reforming of Ethanol: Enhancement of Ni Catalyst Performance via Promotion

Autothermal reforming of bioethanol (ATR of C2H5OH) over promoted Ni/Ce0.8La0.2O1.9 catalysts was studied to develop carbon-neutral technologies for hydrogen production. The regulation of the functional properties of the catalysts was attained by adjusting their nanostructure and reducibility by introducing various types and content of M promoters (M = Pt, Pd, Rh, Re; molar ratio M/Ni = 0.003–0.012). The composition–characteristics–activity correlation was determined using catalyst testing in ATR of C2H5OH, thermal analysis, N2 adsorption, X-ray diffraction, transmission electron microscopy, and EDX analysis. It was shown that the type and content of the promoter, as well as the preparation mode (combined or sequential impregnation methods), determine the redox properties of catalysts and influence the textural and structural characteristics of the samples. The reducibility of catalysts improves in the following sequence of promoters: Re < Rh < Pd < Pt, with an increase in their content, and when using the co-impregnation method. It was found that in ATR of C2H5OH over bimetallic Ni-M/Ce0.8La0.2O1.9 catalysts at 600 °C, the hydrogen yield increased in the following row of promoters: Pt < Rh < Pd < Re at 100% conversion of ethanol. The introduction of M leads to the formation of a NiM alloy under reaction conditions and affects the resistance of the catalyst to oxidation, sintering, and coking. It was found that for enhancing Ni catalyst performance in H2 production through ATR of C2H5OH, the most effective promotion is with Re: at 600 °C over the optimum 10Ni-0.4Re/Ce0.8La0.2O1.9 catalyst the highest hydrogen yield 65% was observed.

Environmental Impact Evaluation of Current Municipal Solid Waste Treatments in India Using Life Cycle Assessment

An environmental life cycle assessment was conducted to compare proposed municipal solid waste treatment systems with the existing system in Visakhapatnam, India. Five waste alternative treatment systems, including open dumping of municipal solid waste (S1), landfill without gas recovery [LFWGR] (S2), landfill with gas recovery (S3), anaerobic digestion + LFWGR (S4), and incineration + LFWGR (S5). EASETECHTM was considered for assessment using ReCiPE Midpoint (Heuristic) world environmental impact assessment method. Global warming potential (GWP), terrestrial acidification (TA), freshwater eutrophication (FEW), marine water eutrophication (ME), human toxicity (HTP), terrestrial ecotoxicity (TE), freshwater ecotoxicity (FWT), and marine ecotoxicity (MET) impacts were determined for each option. The existing MSW disposal practice in Visakhapatnam city (baseline scenario, S1) has the highest GWP (1107 kg CO2 eq.), which can potentially be reduced to 68.2%, 81.5%, 98.2%, and 94.5% by alternative waste management scenarios S2, S3, S4 and S5, respectively. Scenario S4, involving the use of anaerobic digestion of food waste and residues dumped in engineered landfill without energy recovery was found to be the option with the highest mitigation potential of most of the impacts, and it contributes to significant environmental benefits in terms of ecological footprints in a low-income country such as India. Sensitivity analysis was conducted to confirm the reasonable legitimacy of data used for the determination of the impacts.