Life cycle assessment of advanced bioethanol production from pulp and paper sludge

Synergistic cell-free enzyme cocktails for enhanced fiber matrix development: improving dewatering, strength, and decarbonization in the paper industry

BACKGROUND

The pulp and paper industry is under increasing pressure to adopt sustainable solutions that address its substantial energy consumption and environmental impact. One of the most energy-intensive operations is the thermal drying, which presents significant opportunities for efficiency improvements. This study evaluates a cell-free mild enzyme pretreatment, utilizing a cocktail of cellulases and xylanases, combined with cationic starch, to enhance dewatering efficiency and improve paper strength utilizing bleached hardwood pulp fibers. Life cycle and economic analysis were also conducted to quantify the environmental impact and economic benefits, with a particular focus on direct greenhouse gas emissions. Enhanced water removal during pressing can significantly reduce energy consumption during thermal drying, facilitating the decarbonization of the paper industry.

RESULTS

The cell-free enzyme pretreatment, applied with mild refining and cationic starch, achieved significant improvements in dewatering efficiency and paper strength. The treatment led to an 11% point increase in solids and a 25% improvement in tensile strength. Morphological analyses revealed no changes in fiber length and width; however, reductions in kink and curl indexes indicated enhanced fiber flexibility and bonding potential. Furthermore, the enzyme-starch combination decreased water retention value by 27%, including substantial reductions in bound and hard-to-remove water content. Environmental assessments estimated a 12% reduction in global warming potential (GWP), with the technology yielding net savings of $11.29 per air-dried ton of paper through reduced natural gas consumption.

CONCLUSIONS

This study demonstrates the technical feasibility and economic viability of incorporating enzyme and cationic starch treatments into papermaking. The treatment improves paper quality while reducing energy consumption, costs, and carbon emissions. These findings support the broader adoption of enzyme-based innovations for sustainable manufacturing, aligning with decarbonization goals and industry demands for greater efficiency. The results highlight a promising avenue for achieving significant environmental and economic benefits in the pulp and paper sector.

Life cycle of bioethanol production from blends of different food waste

Food waste offers a potential source for bioethanol production, but productivity depends on the chemical composition of the raw materials and the processes involved. However, assessment of the environmental sustainability of these processes is often absent and can be carried out using the Life Cycle Assessment (LCA) methodology. This study aimed to perform an LCA on bioethanol production from mixtures of different wastes, including tubers, fruits, and processed foods, focusing on the gate-to-gate phase. The inventory included a standard scenario and an optimized scenario, which eliminated drying and replaced the phosphate buffer with citric acid. To assess impacts and damages, the Ecoinvent 3.4 database and the ReCiPe 2016 method were used, while uncertainty analysis was carried out using Monte Carlo simulation with the aid of SimaPro software version 8.5.0.0. Results indicate that processed food blends generate the greatest environmental impacts in all scenarios evaluated. The fermentation stage is the largest contributor to environmental impacts and damage when energy consumption is considered. Without energy consumption, pretreatment and enzymatic hydrolysis become more significant. The most notable categories of environmental impacts and damages are Global Warming Potential (GWP) and Resources. The optimized scenario showed a lower environmental impact compared to the standard scenario, highlighting its potential for more sustainable bioethanol production.

Pulp-paper industry sludge waste biorefinery for sustainable energy and value-added products development: A systematic valorization towards waste management

The pulp-paper industry is one of the main industrial sectors that produce massive amounts of residual sludge, constituting an enormous environmental burden for the industries. Traditional sludge management practices, such as landfilling and incineration, are restricted due to mounting environmental pressures, complex regulatory frameworks, land availability, high costs, and public opinion. Valorization of pulp-paper industry sludge (PPS) to produce high-value products is a promising substitute for traditional sludge management practices, promoting their reuse and recycling. Valorization of PPIS for biorefinery beneficiation includes biomethane, biohydrogen, bioethanol, biobutanol, and biodiesel production for renewable energy generation. Additionally, the various thermo-chemical technologies can be utilized to synthesize bio-oil, hydrochar, biochar, adsorbent, and activated carbon, signifying potential for value-added generation. Moreover, PPIS can be recycled as a byproduct by incorporating it into nanocomposites, cardboard, and construction materials development. This paper aims to deliver a comprehensive overview of PPIS management approaches and thermo-chemical technologies utilized for the development of platform chemicals in industry. Substitute uses of PPIS, such as making building materials, developing supercapacitors, and making cardboard, are also discussed. In addition, this article deeply discusses recent developments in biotechnologies for valorizing PPIS to yield an array of valuable products, such as biofuels, lactic acids, cellulose, nanocellulose, and so on. This review serves as a roadmap for future research endeavors in the effective handling of PPIS.

Adaptive regulation of activated sludge's core functional flora based on granular internal spatial microenvironment

A great deal of efforts has been put into studying the influence of the external macroenvironment for activated sludge to survive on microbial community succession, while granular internal spatial microenvironment should be given equal attention, because it is more directly involved in the information exchange and material transfer among microorganisms. This study systematically investigated the effects of granular microenvironment on spatial colonization and composition of sludge's core functional flora, and the corresponding difference of biological treatment performance. High content of extracellular-proteins (67.53 mg/gVSS) or extracellular-polysaccharide (65.02 mg/gVSS) stimulated the microbial flocculation and aggregation of 0.5-1.5 mm granules (GS) or 1.5-3.0 mm granules (GM), respectively, which was resulted from excellent cell hydrophobicity (59.26%) or viscosity (3.47 mPa s), therefore, constituted relatively dense porous frame. More hollow space existed in 3.0-5.0 mm granules (GL), which formed loose skeleton with 0.213 mL/g of total pore volume and 17.21 nm of average pore size. Combining scanning electron microscope images and fluorescent in-situ hybridization based microbiological analysis, aerobic nitrifiers were observed to wrap or surround anaerobic bacteria, or facultative/anaerobic bacteria were self-encapsulated, which created granule's unique microenvironment with alternating aerobic and anaerobic zones. GS has the most rich organic matter degrading bacteria and anaerobic heterotrophic denitrifiers, while GM and GL presented the greatest relative abundance of facultative and aerobic denitrifiers, respectively. The activity of dehydrogenase and nitrogen invertase of GM showed be 1.32-3.09 times higher than those of GS and GL, contributing to its higher carbon and nitrogen removal. These findings highlight the importance of granular microenvironment to adaptive regulation of activated sludge's core functional flora and corresponding pollutant removal performance.

Novel system design for high solid lignocellulosic biomass conversion

A novel system (Oregon State University High Solids Reactor; OSU-HSR) was designed and constructed for enzymatic hydrolysis at ultrahigh solids content (40%) by promoting better mixing using low energy consumption in a horizontal reactor with a new impeller design and a controllable feeding unit. System performance was evaluated using separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) methodologies. Using the dilute acid pretreated wheat straw as the substrate in the OSU-HSR system, the highest glucose (219.7 g/L) and ethanol (127.1 g/L) concentrations were achieved with the use of the SHF method while the highest ethanol concentration using SSF method was 134.5 g/L. The SSF method increased the return on investment to 12.21% with an estimated global warming potential of 54.5 g CO₂ eq/MJ Ethanol. The OSU-HSR successfully provided effective mixing and different fed-batch schemes, and can be used for efficient biochemical conversion of lignocellulosic biomass into bio-chemicals and biofuels.

Assessing the impact of industrial waste on environment and mitigation strategies: A comprehensive review

The increasing demand of rising population leads to the escalation of industrial sectors such as agro-, food-, paper and pulp industries. These industries generated hazardous waste which is primarily organic in nature thus is being dumped or processed in the environment. These waste leads to increasing contamination leading to increased mortality, physical and morphological changes in the organisms/animals in contact. Although the generated waste is hazardous yet it predominantly contains macromolecules and bioactive compounds thus can be efficiently utilized for the extraction and production of value added products. This article reviews the effect of these waste streams on terrestrial and aquatic ecosystems. Since these wastes abundantly contain proteins, lipids, carbohydrates and lignocelluloses thus recycling, reuse and valorization offers an effective strategy for their reduction while comforting the environment. The policies laid down by national and international agencies that directs these industries for reducing the generation of waste and increasing the recyclability and reuse of the generated waste is discussed and the gaps and bottlenecks for these is identified. This study essentially provides the state-of-art information on above aspects by identifying the gaps for future research directions and may contribute in policy development for mitigation strategies.

Life cycle assessment of bio-based levoglucosan production from cotton straw through fast pyrolysis

This study aimed to evaluate the environmental impacts (i.e. global warming potential (GWP) and resource depletion (RD)) of the bio-based levoglucosan production process through fast pyrolysis of cotton straw via life cycle assessment (LCA). An LCA model consisting of feedstock transportation, biomass pretreatment, fast pyrolysis, bio-oil transportation, bio-oil recovery and levoglucosan extraction was developed. Results indicated that GWP and RD of bio-based levoglucosan production were approximately 2 and 32.5 times less than that of the petroleum-based counterpart. Sensitivity analysis showed that the GWP and RD of levoglucosan production were highly sensitive to plant size, hydrochloric acid usage, cooling energy, levoglucosan yield and bio-oil yield. The results of this research could provide a framework for robust decision making at an industrial level, which is useful for the commercial-scale production of levoglucosan.

Sustainable production of bio-based chemicals and polymers via integrated biomass refining and bioprocessing in a circular bioeconomy context

The sustainable production of bio-based chemicals and polymers is highly dependent on the development of viable biorefinery concepts using crude renewable resources for the production of diversified products. Within this concept, this critical review presents the availability of fractionated co-products and fermentable sugars that could be derived from major industrial and food supply chain side streams in EU countries. Fermentable sugars could be used for the production of bio-based chemicals and polymers. The implementation of biorefinery concepts in industry should depend on the evaluation of process efficiency and sustainability including techno-economic, environmental and social impact assessment following circular bioeconomy principles. Relevant sustainability indicators and End-of-Life scenarios have been presented. A case study on the techno-economic evaluation of bio-based succinic acid production from the organic fraction of municipal solid waste has been presented focusing on the evaluation of process profitability and feedstock requirements.

Life Cycle Assessment for Bioethanol Production from Oil Palm Frond Juice in an Oil Palm Based Biorefinery

A study was conducted to estimate the possible environmental impacts arising from the generation of bioethanol from oil palm frond sugar juice in a theoretical oil palm based biorefinery model. A life cycle assessment (LCA) with the gate-to-gate approach was performed with the aid of SimaPro version 8.0 whereby ten impact categories were evaluated. The scope included frond collection and transportation, frond sugar juice extraction, and bioethanol fermentation and purification. Evaluation on the processes involved indicated that fermentation contributed to the environmental problems the most, with a contribution range of 52% to 97% for all the impact categories. This was due to a substantial usage of nutrient during this process, which consumes high energy for its production thus contributing a significant burden to the surrounding. Nevertheless, the present system offers a great option for biofuel generation as it utilizes sugar juice from the readily available oil palm waste. Not only solving the issue of land utilization for feedstock cultivation, the enzymatic saccharification step, which commonly necessary for lignocellulosic sugar recovery could also be eliminated.

Second Generation Bioethanol Production: On the Use of Pulp and Paper Industry Wastes as Feedstock

Due to the health and environment impacts of fossil fuels utilization, biofuels have been investigated as a potential alternative renewable source of energy. Bioethanol is currently the most produced biofuel, mainly of first generation, resulting in food-fuel competition. Second generation bioethanol is produced from lignocellulosic biomass, but a costly and difficult pretreatment is required. The pulp and paper industry has the biggest income of biomass for non-food-chain production, and, simultaneously generates a high amount of residues. According to the circular economy model, these residues, rich in monosaccharides, or even in polysaccharides besides lignin, can be utilized as a proper feedstock for second generation bioethanol production. Biorefineries can be integrated in the existing pulp and paper industrial plants by exploiting the high level of technology and also the infrastructures and logistics that are required to fractionate and handle woody biomass. This would contribute to the diversification of products and the increase of profitability of pulp and paper industry with additional environmental benefits. This work reviews the literature supporting the feasibility of producing ethanol from Kraft pulp, spent sulfite liquor, and pulp and paper sludge, presenting and discussing the practical attempt of biorefineries implementation in pulp and paper mills for bioethanol production.

Environmental performance of straw-based pulp making: A life cycle perspective

Agricultural straw-based pulp making plays a vital role in pulp and paper industry, especially in forest deficient countries such as China. However, the environmental performance of straw-based pulp has scarcely been studied. A life cycle assessment on wheat straw-based pulp making in China was conducted to fill of the gaps in comprehensive environmental assessments of agricultural straw-based pulp making. On average, the global warming potential (GWP), GWP excluding biogenic carbon, acidification potential and eutrophication potential of wheat straw based pulp making are 2299kg CO₂-eq, 4550kg CO₂-eq, 16.43kg SO₂-eq and 2.56kg Phosphate-eq respectively. The dominant factors contributing to environmental impacts are coal consumption, electricity consumption, and chemical (NaOH, ClO₂) input. Chemical input decrease and energy recovery increase reduce the total environmental impacts dramatically. Compared with wood-based and recycled pulp making, wheat straw-based pulp making has higher environmental impacts, which are mainly due to higher energy and chemical requirements. However, the environmental impacts of wheat straw-based pulp making are lower than hemp and flax based pulp making from previous studies. It is also noteworthy that biogenic carbon emission is significant in bio industries. If carbon sequestration is taken into account in pulp making industry, wheat straw-based pulp making is a net emitter rather than a net absorber of carbon dioxide. Since wheat straw-based pulp making provides an alternative for agricultural residue management, its evaluation framework should be expanded to further reveal its environmental benefits.

A multi-criteria decision analysis of management alternatives for anaerobically digested kraft pulp mill sludge

The Multi-Criteria Decision Analysis (MCDA) procedure was used to compare waste management options for kraft pulp mill sludge following its anaerobic digestion. Anaerobic digestion of sludge is advantageous because it produces biogas that may be used to generate electricity, heat and biofuels. However, adequate management of the digested sludge is essential. Landfill disposal is a non-sustainable waste management alternative. Kraft pulp mill digested sludge applied to land may pose risks to the environment and public health if the sludge has not been properly treated. This study is aimed to compare several recycling alternatives for anaerobically digested sludge from kraft pulp mills: land application, landfill disposal, composting, incineration, pyrolysis/gasification, and biofuel production by algae. The MCDA procedure considered nine criteria into three domains to compare digested sludge recycling alternatives in a kraft pulp mill: environmental (CO₂ emission, exposure to pathogens, risk of pollution, material and energy recovery), economic (overall costs, value of products) and technical (maintenance and operation, feasibility of implementation). The most suitable management options for digested sludge from kraft pulp mills were found to be composting and incineration (when the latter was coupled with recycling ash to the cement industry). Landfill disposal was the worst option, presenting low performance in feasibility of implementation, risk of pollution, material and energy recovery.

Life cycle environmental impacts of bioethanol production from sugarcane molasses in Iran

In recent years, bioethanol from sugarcane molasses has been produced on an industrial scale in Iran. The aim of this study was to evaluate molasses-based bioethanol production from an environmental point of view. Data were collected from Debel Khazai agro-industry situated in southern region of Iran by using face-to-face interviews and annual statistics of 2010 to 2016 (6-year life cycle of sugarcane cultivation). Ten impact categories including abiotic depletion (AD), acidification (AC), eutrophication (EP), global warming potential (GWP), ozone layer depletion (OLD), human toxicity (HT), freshwater aquatic ecotoxicity (FE), marine aquatic ecotoxicity (ME), terrestrial ecotoxicity (TE), and photochemical oxidation (PO) were selected based on CML methodology. Inventory data for production of the inputs were taken from Ecoinvent, BUWAL 250, and IDMAT 2001 databases. The results revealed that in sugarcane cultivation process, electricity and trash burning were the most important contributors to all impact categories except OLD and TE. In industrial phase, natural gas had the highest contribution to the most impact categories. Greenhouse gas (GHG) emission for production of 1000 L molasses-based bioethanol was 1322.78 kg CO₂ eq. By comparing total GHG emissions from 1000 L bioethanol to gasoline, the net avoided GHG emissions came out at 503.17 kg CO₂ eq. According to results, it is clear that with increasing irrigation efficiency and improving performance of heating systems in industrial phase, environmental burdens would be significantly reduced.

Environmental impact of an agro-waste based polygeneration without and with CO2 storage: Life cycle assessment approach

Life cycle assessment (LCA) is the most scientific tool to measure environmental sustainability. Poly-generation is a better option than single-utility generation due to its higher resource utilization efficiency and more flexibility. Also biomass based polygeneration with CO2 capture and storage may be useful being 'net negative' greenhouse gas emission option. But this 'negativity' should be studied and confirmed through LCA. In this paper, cradle-to-gate life cycle assessment of a straw based polygeneration without and with CO2 storage is studied. Results show that captured CO2 of this polygeneration should be stored to get a net negative energy system. However, biomass distribution density, ethanol production rate and CO2 transportation distance affect the net GHG emission. For this polygeneration system, exergy based allocation should be preferred.