Application of multi-criteria decision-making tools for assessing biogas plants: a case study in Reykjavik, Iceland

The European Union is planning a new program to achieve climate neutrality by 2050. In this context, the Icelandic government plans to ban new registrations of fossil fuel cars after 2030 as one of the strategies to make Iceland a carbon-neutral country by 2040. Upgraded biogas can be directly used in vehicles with CNG engines, reducing CO2 emissions by 80%. In this paper, several alternatives of biogas plants, simulated in previous research, were evaluated by considering techno-economic and environmental criteria through the application of multi-criteria decision-making tools. Twelve alternatives were analyzed using the Definite 3.1 software. A weighted summation algorithm, which transforms all criteria into the same scale by multiplying them by weights and then summing them to obtain the results, was used in the analysis. The multi-criteria analysis of the twelve proposed alternatives included eleven criteria (three technical, five economic, and three environmental) whose weights were changed in a total of eleven scenarios. From a global perspective, when all criteria were considered (9.1% weight) the best alternative with a score of 0.58 was the single-stage biogas plant working with municipal solid waste. Sensitivity and uncertainty analyses also demonstrated that the multi-criteria results obtained were robust and reliable.The APC was paid by the COST Action CA17133 Circular City (“Implementing naturebased solutions for creating a resourceful circular city”, http://www.circular-city.eu, duration 22 October 2018–21 October 2022)

The effect of rotor geometry on particle size characteristics for knife-milled wheat straw

The paper aimed to experimentally identify the effect of rotor blade geometry on particle size characteristics for the knife-milled wheat straw of 12.5 wt % moisture content. Biomass was systematically reduced in size using two-blade rotor geometries (linear and screw), varying the following conditions: rotor speeds of 10.2 - 20.4 m s - 1 and screen sieve sizes of 0.75 - 10 mm. It was identified that rotor blade geometry affected particle size. The higher the rotational rotor speed and the screen sieve size, the higher the difference in particle size characteristics. The original empiric model was derived and calibrated by studying the mutual relationships among process variables. The model allows predicting characteristic particle size D50 for individual rotor blade geometries, knowing rotor speed and screen sieve size. The accuracies of R2=0.94 for linear- and R2=0.92 for screw-blade rotor geometry were reached for particle size estimation using the derived model.This research was supported by the Ministry of Education, Youth and Sports of the Czech Republic under OP RDE grant number CZ.02.1.01/0.0/0.0/16_019/0000753 "Research centre for low-carbon energy technologies

Sustainable management strategy for solidification/stabilization of zinc plant residues (ZPR) by fly ash/clay-based geopolymers

ABSTRACT: Solidification/stabilization (S/S) of acid waste using Ordinary Portland Cement (OPC) is widely implemented, but, due to the impact on climate change, alternative methods are being investigated. In this work, first, the feasibility of using coal fly-ash/clay-based geopolymers for the S/S of Zn plant residues (ZPR), Cadmium Sponge (CS), and Anode Mud (AM) is proposed as a treatment prior to disposal in landfills. Different variables, such as the type of processing, molding (as-received waste), and pressing (dried waste), and activators, a commercial and an alternative residual sodium carbonate, have been studied. The technical and environmental assessments of the S/S process by means of compressive strength and the leaching of critical pollutants have been monitored. Immobilization efficiencies of Cd and Zn higher than 99% have been obtained by dosing 50% of the acid waste, 6 M NaOH solution (20 min contact time), cured at 75 °C (48 h) and at room temperature (28 days), achieving in the leachates pH values of 7 to 10 and [Cd] and [Zn] < 1 and 2.5 mg/kg, respectively. However, alkaline activation increases As leaching, mainly associated with the clay. Secondly, removing clay from the geopolymer formulation, the optimization of geopolymer parameters, acid waste/geopolymer ratio, liquid/solid ratio, and NaOH molar concentration enables obtaining a significant reduction in the release of As and Cd, and Zn is kept at acceptable values that meet the non-hazardous waste landfill disposal limits for the S/S of both acid wastes.This work has been partially supported by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund by means of the research project RTI2018-097612-B-C22

Slow pyrolysis of specialty coffee residues towards the circular economy in rural areas

Coffee, as one of the most consumed beverages, generates a wide variety of waste materials that can be used as biofuels and bio-products. Conventional pyrolysis can be used in rural areas, improving the circular bioeconomy of these places. In this work, the characterization and slow pyrolysis of specialty coffee residues, coffee silverskin (CSS), and spent coffee (SC) were conducted at temperatures from 300 to 600 °C. Physico-chemical and thermal analysis were carried out. In addition, the quantification of individual compounds as acetic, formic, and levulinic acids, caffeine, and other minor compounds was performed. The results indicate the differences between both waste materials in the obtained pyrolysis fractions. The biochar fraction for SC is lower at all temperatures and the liquid fraction higher, reaching maximum values of 62 wt.% in the liquid at 600 °C compared to 47% in CSS. The higher yield in the liquid fraction of SC corresponds to the higher contents of hemicellulose and extractives and the lower ash content. The calculated calorific value for the pyrolysis solid fractions reaches 21.93 MJ/kg in CSS and 26.45 MJ/kg in SC. Finally, biorefinery options of major components of the liquid fraction were also presented.This research was funded by EUROPEAN COMMISSION, Marie Sklodowska-Curie Actions—RISE, grant number 101007733 (CELISE project), by Solvay, under projects 3399 and 3824, and the European LignoCOST Action, number CA17128 (https://lignocost.eu/, accessed on 1 February 2023)

Technical and environmental improvement of the bleaching sequence of dissolving pulp for fibre production

Reactivity of dissolving pulp is one of the main parameters to determine its availability to be transformed into viscose. It is related to the use of carbon disulphide (CS2). An industrial sequential totally chlorine free bleaching process is used as case study. It is carried out in two stages: (1) Alkaline extraction (EOP) and (2) peroxide bleaching (PO). In order to assess how to decrease the use of carbon disulphide, several experiments were performed at laboratory scale for the two stages mentioned before by modifying the operating conditions: NaOH and H2O2 dosages, time and temperature. Reactivity using a modified Fock’s method and pentosan content was analysed along with quality pulp parameters: α-cellulose, viscosity and lignin content (kappa number). Results showed that reactivity increases through the bleaching process and varies with the chemical dosage in both stages. Pulp obtained at the best conditions had the following characteristics: reactivity, 95.3%; α-cellulose 91.17%; intrinsic viscosity, 448 mL/g; kappa number, 1.81 and pentosan content 2.86%, and as a result, CS2 usage was reduced by 11.88%. At the best conditions obtained in this work, NaOH dosage in PO stage was reduced to zero and temperature was slightly lower, when compared with industrial operating conditions

Hidrólisis y separación de biomasa lignocelulósica en un proceso al sulfito con el objeto de valorizar las principales fracciones dentro del concepto de bio-refinería

ABSTRACT: Physico-chemical and biological processes can be used to transform different pulp and paper industries through integrated forest biorefineries in order to valorise all of the main fractions of the lignocellulosic biomass (cellulose, hemicellulose and lignin). In this work, hydrolysis and fractionation processes have been studied in a sulphite pulp mill to obtain not only dissolving pulp from the cellulose but also lignosulphonates from the lignin and fermentation products from the hemicellulose. Delignification and hydrolysis experiments have been carried out at laboratory scale in order to increase the valorization opportunities and trying to decrease the inhibitors in the final by-product. In addition, detoxification or separation treatments have been developed in order to separate the lignosulphonates and other inhibitors from the sugar substrate.RESUMEN:Diferentes procesos físico-químico y biológicos se pueden utilizar para transformar la industria de la pasta y celulosa en bio-refinerías forestales integradas, con el objetivo de valorizar las principales fracciones de la biomasa lignocelulósica (celulosa, hemicelulosa y lignina). En este trabajo se han utilizado diferentes procesos de hidrólisis y fraccionamiento en una industria de pasta celulósica con el fin de obtener no solo la pasta dissolving sino también lignosulfonatos procedentes de la lignina y productos de fermentación de la hemicelulosa. Se han llevado a cabo diferentes experimentos de hidrólisis y deslignificación a escala laboratorio para aumentar las oportunidades de valorización y tratando de disminuirla producción de inhibidores en los sub-productos. Además, se han desarrollado diferentes procesos de detoxificación o separación con el objeto de separarlos lignosulfonatos y otros inhibidores del sustrato de azúcar.Los autores desean agradecer la ayuda de este trabajo al proyecto Europeo KBBE-2012-6-311935 bajo el séptimo programa marco de la Unión Europea. www.brigit-project.eu

Multi-criteria analysis of detoxification alternatives: techno-economic and socio-environmental assessment

The transformation of fermentable sugars provided from lignocellulosic wastes into biofuels or bioproducts is a key point at second-generation biorefineries. Spent sulfite liquor is a xylose-rich hydrolysate constituting the main residue of sulfite mills producing dissolving cellulose. Due to the presence of the inhibitors in the spent liquor, the most promising valorization options require detoxification before sugars bioconversion. In this work, a multi criteria analysis was implemented to select techno-economic and socio-environmental feasible detoxification alternatives that can be adapted to a wide variety of fermenting scenarios. Total inhibitors removal, phenolics removal, acetic acid removal, lignosulfonates removal, total sugar losses, fixed capital invested, manufacturing costs, waste toxicity, social acceptance, and employment were chosen as the most relevant criteria. The maximum allowable concentration of undesirable inhibitors cannot be established with a general character, and thereby decision-making tools result in feasible and efficient solutions. From a technical viewpoint best solution was anionic resins with a score of 0.68; the most economical alternative was the overliming with a score of 0.76; finally, from a socio-environmental perspective, overliming reached the highest score of 0.78. In addition, three spent liquor biorefinery models were proposed. Based on the multicriteria analysis and based on the inhibitor?s concentration affecting fermentation yields and productivity, the best detoxification alternatives were (1) anionic resins for polyhydroxyalkanoate production; (2) activated carbon for ethanol biorefinery; (3) overliming for xylitol biorefinery.The authors gratefully acknowledge the financial support by KBBE-2012-6-311935 BRIGIT research project www.brigit-project.e

Influence of unburned carbon on environmental-technical behaviour of coal fly ash fired clay bricks

ABSTRACT: The incorporation of coal fly ash (CFA) in fired clay bricks (FCBs), as a clay replacement, contributes toward cleaner production practices. CFA disposal is an important issue worldwide due to its huge volume and to its potential negative environmental impacts, and currently does not have a recovery route due to its high concentration in unburned materials. In this study, the impact of the incorporation of two CFA, with different content of unburned carbon, FAA (low LOI) and FAB (high LOI) in FCBs, from a technical and environmental point of view was conducted. Unburned carbon plays an important role on the final properties of FCBs. The thermal decomposition during the firing process promotes an increase of water absorption, decreasing the flexural strength as the porosity increases, although the technical and mechanical properties of samples containing up to 30% FAA and percentages of 20% FAB are acceptable. The leaching behaviour showed an immobilisation of Cr and Se in FCBs while Mo reduced its mobility to values below non-hazardous limits. Acid gas emission values do not exceed the reference emission value, except for SO2 emissions while the level of CO2 emissions must be estimated based on the total annual production of the ceramic factory.This work was presented at the workshop “Engineering and circular economy: the road to sustainability” funded as a part of the ECO-MET-AL Project (PID2019-109520RB-I00), “Can industrial and mining metalliferous wastes produce green lightweight aggregates" Applying the Circular Economy” funded by the Spanish Ministry of Science, Innovation, and Universities and ERDF funds, framed in the “Grants for “R&D&I Projects” in the framework of the State Programmes for the Generation of Knowledge and Scientific and Technological Strengthening of the R&D&I System and R&D&I oriented to the Challenges of Society, Call 2019”

Evolution of lignocellulosic macrocomponents in the wastewater streams of a sulfite pulp mill: a preliminary biorefining approach

The evolution of lignin, five-and six-carbon sugars, and other decomposition products derived from hemicelluloses and cellulose was monitored in a sulfite pulp mill. The wastewater streams were characterized and the mass balances throughout digestion and total chlorine free bleaching stages were determined. Summative analysis in conjunction with pulp parameters highlights some process guidelines and valorization alternatives towards the transformation of the traditional factory into a lignocellulosic biorefinery.The results showed a good separation of cellulose (99.64%) during wood digestion, with 87.23% of hemicellulose and 98.47% lignin dissolved into the waste streams. The following steps should be carried out to increase the sugar content into the waste streams: (i) optimization of the digestion conditions increasing hemicellulose depolymerization; (ii) improvement of the ozonation and peroxide bleaching stages, avoiding deconstruction of the cellulose chains but maintaining impurity removal; (iii) fractionation of the waste water streams, separating sugars fromthe rest of toxic inhibitors for 2nd generation biofuel production. A total of 0.173 L of second-generation ethanol can be obtained in the spent liquor per gramof dry wood.The proposed methodology can be usefully incorporated into other related industrial sectors.The authors wish to express their sincere gratitude to the Sniace personnel and the financial support of the European Union by the BRIGIT “new tailor-made biopolymers produced from lignocellulosic sugars waste for highly demanding fire-resistant applications” research project http://www .brigit-project.eu/