Post-consumer textile thermochemical recycling to fuels and biocarbon: A critical review.

This study aims to look at waste-to-energy (tertiary recycling) of post-consumer textile waste, based on a literature review. Because textiles are mostly made of cotton and polyester, which are carbon and energy sources, they can potentially be converted thermochemically into fuels and biocarbon. The critical parameters determining thermal recycling are summarized and discussed with a focus on pyrolysis, gasification, and torrefaction. For cotton and polyester mixtures, torrefaction presents a low environmental impact and an energy-dense fuel that can be used in cogeneration systems, reducing the energy requirements of these processes by 50-85%. Catalytic pyrolysis of cotton textile waste yields to a high conversion (90 wt%), a liquid fuel of high yields (35-65 wt%), and biocarbon (10-18 wt%), providing carbon and energy closure loops. However, pyrolysis is energy-intensive (T > 500 °C) and produces hazardous chemicals from the conversion of PET, nylon, and polyacrylonitrile. Gasification can handle many types of textile waste, but it needs continuous monitoring of the emissions. More research is needed to overcome existing limitations, LCA and sustainability assessment are required for the thermal recycling processes in order to estimate their future-proofing and sustainability. For the transition to a circular economy, consumers' awareness of resources limits and sustainable use is pivotal to change purchasing behavior and achieve a recycling thinking.

Organizational, societal, knowledge and skills capacity for a low carbon energy transition in a Circular Waste Bioeconomy (CWBE): Observational evidence of the Thessaly region in Greece.

Advancing a Circular Waste Bioeconomy (CWBE) should be a priority over business-as-usual, entailing sustainable resource use in early and late stages of industrialization processes. The present paper is both descriptive and prescriptive. Firstly, it aims to explore the main barriers, challenges, opportunities, and the context within agro-biomass and agro-industrial waste valorization can accelerate a low carbon economy, in the Thessaly region of Greece, where agricultural production and agro-industrial business are the prevailing economic sectors. Secondly, organizational, societal, knowledge and skills capacity actions are suggested as the most likely to change the business-as usual scenarios. A SWOT analysis performed to draw useful conclusions about the extent to which CWBE principles can be integrated into the economic, social, and environmental life of the Thessaly region, and recommendations made of what it is needed. One of the key insights is how to leverage emerging low carbon circular economy for regional regenerative future. The results showed that waste is managed inefficiently in the region and there is a lack of synergies and collaborations between different stakeholders. The milestones of accelerating a low carbon CWBE for regional development, and employment are a) the territorial cohesion and regional symbiosis, b) increasing the financial market opportunities for small and critical projects, c) promoting awareness, public knowledge, skills, and the responsibility of young scientists and citizens.

Experimental and feasibility study of spent coffee grounds upscaling via pyrolysis towards proposing an eco-social innovation circular economy solution.

There is a need for eco-social business models in the food waste sector that are more cascading and circular-based, while having economic, environmental and social benefits. The aim of this study is to bring insights and data of spent coffee grounds large-scale slow pyrolysis, to seize new opportunities for eco-innovative solutions in the circular economy, by identifying upcycling opportunities for resource recovery of this waste. First, an experimental study was conducted, and a set of pyrolysis experiments were carried out at a temperature range from 450 to 750 °C, with a heating rate of 50°/s, under helium atmosphere, to explore the products' yields and the best process' conditions. Second, an economic study was conducted for a standalone pyrolysis plant fueled with the spent coffee grounds streams from coffee shops of a city with 150,000 inhabitants, in central Greece, aiming at the cost and the profitability of the endeavor estimation. The calculations were based on the features of a slow pyrolysis rotary kiln technology designed at Aristotle University, and co-developed with an Irish company, under the funding of an EU LIFE+ project. For an estimated capacity of 2566 t/yr of SCG, the revenue of the endeavor was calculated at 47€/t of SCG. The economic indicators ROI and POT (ROI = 0.24, POT = 2.6), are very positive, suggesting pyrolysis of SCG as an efficient circular economy management solution, providing an eco-social innovation business in the coffee shop industry, engaging also consumers in the circular economy.

Simultaneous detoxification and bioethanol fermentation of furans-rich synthetic hydrolysate by digestate-based pyrochar.

Pyrolysis is a sustainable pathway to transform renewable biomasses into both biofuels and advanced carbonaceous materials (i.e. pyrochar) which can be used as adsorbent of furan compounds. In particular, the aim of this study was to: i) evaluate the effect of vibro-ball milling on physical characteristics of pyrochar and its consequent performance on solely detoxification of a synthetic medium, containing furans and soluble sugars; ii) study the simultaneous detoxification and bioethanol fermentation, by adding activated pyrochar into fermentation medium. Results demonstrated that, compared to untreated pyrochar, the use of milled pyrochar increased by 52% furfural removal from the synthetic medium. Furfural removal rate was also increased (adsorption kinetic constant increased from 0.015 min-1 up to 0.215 min-1), at a pyrochar loading of 40 g L-1. Although, the simultaneous addition of pyrochar into the fermentation medium did not improve the bioethanol yield of the synthetic medium, it has significantly increased the bioethanol production rate.

Pyrochars from bioenergy residue as novel bio-adsorbents for lignocellulosic hydrolysate detoxification.

The robust supramolecular structure of biomass often requires severe pretreatments conditions to produce soluble sugars. Nonetheless, these processes generate some inhibitory compounds (i.e. furans compounds and aliphatic acids) deriving mainly from sugars degradation. To avoid the inhibition of the biological process and to obtain satisfactory sugars conversion level into biofuels, a detoxification step is required. This study investigates the use of two pyrochars derived from solid anaerobic digestates for the detoxification of lignocellulosic hydrolysates. At a pyrochar concentration of 40gL(-1), more than 94% of 5-HMF and 99% of furfural were removed in the synthetic medium after 24h of contact time, whereas sugars concentration remained unchanged. Furfural was adsorbed faster than 5-HMF by both pyrochars and totally removed after 3h of contact. Finally, the two pyrochars were found efficient in the detoxification of corn stalks and Douglas fir wood chips hydrolysates without affecting the soluble sugars concentrations.

Cascade approach of red macroalgae Gracilaria gracilis sustainable valorization by extraction of phycobiliproteins and pyrolysis of residue.

Phycobiliproteins extraction (primary refining) from Gracilaria gracilis seaweed, harvested in Lesina Lagoon (Italy) and further valorization of the residual algal via pyrolysis (secondary refining), were investigated with a cascade biorefinery approach. R-phycoerythrin (7 mg/g d.w.), allophycocyanin (3.5 mg/g d.w.) and phycocyanin (2 mg/g d.w.) were the main phycobiliproteins extracted. Pyrolysis of G.gracilis residue followed, aiming to investigate the production of bio-oil and biochar within a pyrolysis temperature range of 400-600 °C. Results showed that the bio-oil yield is high (∼65 wt%) at pyrolysis temperature ∼500 °C, but its high content in nitrogenous compounds prevents its use as a biofuel, unless some further de-nitrogenation takes place. Biochar yield ranged between 33 wt% (400 °C) and 26.5 wt% (600 °C). Interestingly, inorganic nutrients including P, K, Ca, Fe and Mg were detected in biochar, suggesting its potential use as recovering system of natural mineral resources from the oceanic reservoir.

Analysis of good practices, barriers and drivers for ELTs pyrolysis industrial application.

Boosting of eco-innovative solutions for End of Life Tyres (ELTs) management, under the principles of the EU Resource Efficiency Roadmap and the Waste Framework Directive, can not only diminish the environmental hazards and the consequent societal cost, but also result to the establishment of a novel perception regarding ELTs; thus, a valuable stock of resources that can be exploited. Despite the extensive scientific research of the previous years on ELTs depolymerisation via pyrolysis highlighting its eco-innovative characteristics, the use of pyrolysis to process scrap tyres has not yet achieved a broad commercial success, with economic viability and product standardization to constitute the primary impediments. More specifically, pyrolysis was not applied to an extensive industrial scale so far, due to deficient market analysis, legislative barriers, economic instability and sometimes public acceptance. All the above issues are addressed by the present study. Modifications on current EU legislation can prevent or reduce delays or derailment of efforts on pyrolysis, through its differentiation from incineration. The attainment of economic viability could be realized through the valorization of the pyrolytic char towards activated carbon production for environmental depollution applications; needless to say, the penetration on niche and well-organised markets is more than essential.

Comparative assessment of municipal sewage sludge incineration, gasification and pyrolysis for a sustainable sludge-to-energy management in Greece.

For a sustainable municipal sewage sludge management, not only the available technology, but also other parameters, such as policy regulations and socio-economic issues should be taken in account. In this study, the current status of both European and Greek Legislation on waste management, with a special insight in municipal sewage sludge, is presented. A SWOT analysis was further developed for comparison of pyrolysis with incineration and gasification and results are presented. Pyrolysis seems to be the optimal thermochemical treatment option compared to incineration and gasification. Sewage sludge pyrolysis is favorable for energy savings, material recovery and high added materials production, providing a 'zero waste' solution. Finally, identification of challenges and barriers for sewage sludge pyrolysis deployment in Greece was investigated.

Thermal degradation studies and kinetic modeling of cardoon (Cynara cardunculus) pyrolysis using thermogravimetric analysis (TGA).

A key element in the design of sustainable pyrolysis processes is the thermal degradation kinetics of biomass. In this work, pyrolysis tests for cardoon (Cynara carduculus) stems and leaves were performed in a non-isothermal thermogravimetric analyzer (TGA) in order to determine the thermal degradation behavior of both stems and leaves. The kinetic parameters of the process were evaluated using three different kinetic models, the independent parallel reaction model, KAS and OFW iso-conversional model. Good agreement with the experimental TGA data was observed for all models, the best being with the independent parallel reaction model. A variance in the activation energy with conversion was observed when the KAS and OFW models were employed, which reveals that the pyrolysis of cardoon progresses through more complex and multi-step kinetics.

Bioenergy production for CO2-mitigation and rural development via valorisation of low value crop residues and their upgrade into energy carriers: a challenge for sunflower and soya residues.

The present study concerns the energetic valorization of sunflower and soya residues by air fixed-bed gasification. The main process parameters that have been investigated were the temperature and air equivalence ratio. Experimental results indicated that the high temperature and air had a positive effect in gas yield for both residues by ensuring mild oxidative conditions. Gasification gas composition showed different trends of H(2)/CO ratio for the two residues at low equivalence ratios. The LHV of the produced gas from both residues varied from 6.84 to 12 MJ/Nm(3). The energy recovery achieved via gasification could reach 0.07 and 0.02 per acre of cultivated area for the sunflower and soya residues, respectively, in terms of tons of oil equivalent. Sunflower shown higher oil production and energy recovery than soya did. The results of the present study indicate the viability of alternative energy production from agricultural biomass by gasification. Such residues could comprise an attractive renewable source of energy for covering additional energy demands in agricultural regions through exploitation in small gasification systems.

Sustainable valorization of plastic wastes for energy with environmental safety via High-Temperature Pyrolysis (HTP) and High-Temperature Steam Gasification (HTSG).

In the present study the energetic valorization of electric cable shredder residues (mixed plastics) has been investigated. Thermochemical conversion by means of High-Temperature Steam Gasification (HTSG) and High-Temperature Pyrolysis (HTP) was studied. The effects of temperature and reaction time--process parameters--were investigated. Comparison of the results showed that HTSG seems a more suitable process in terms of produced syngas quality (64%, v/v and 13MJ/Nm(3)) than HTP because of higher H(2) yield and lower tar content.

Process characteristics and products of olive kernel high temperature steam gasification (HTSG).

Exploitation of olive kernel for bioenergy production, with respect to the green house gases (GHGs) mitigation, is the main aim of this work. In this study, olive kernels were used as a solid biofuel, and high temperature steam gasification (HTSG) was investigated, in the fixed bed unit at KTH Sweden, with regard to hydrogen maximization in the produced gasification gas. Experiments were carried out in a temperature range of 750-1050 degrees C, with steam as the gasifying agent. The behaviour of olive kernels, under residence times from 120 up to 960 s, has been studied. At 1050 degrees C, a medium to high calorific value gas was obtained (LHVgas=13.62 MJ/Nm3), while an acquired H2/CO molar ratio equal to four proved that olive kernel HTSG gasification could be an effective technology for a hydrogen-rich gas production (approximately 40%vv H2 in the produced gasification gas at 1050 degrees C). The produced char contained 79%ww of fixed carbon, low chlorine and sulphur content, which enables it for further re-use for energetic purposes. Tar content in the produced gas at 750 degrees C was 124.07 g/Nm3, while a 1050 degrees C at 79.64% reduction was observed and reached the value of 25.26 g/Nm3.

Valorization of cotton stalks by fast pyrolysis and fixed bed air gasification for syngas production as precursor of second generation biofuels and sustainable agriculture.

In the present study, the potential of cotton stalks utilization for H(2) and syngas production with respect to CO(2) mitigation, by means of thermochemical conversion (pyrolysis and gasification) was investigated. Pyrolysis was conducted at temperature range of 400-760 degrees C and the main parametric study concerned the effect of temperature on pyrolysis product distribution. Atmospheric pressure, air gasification at 750-950 degrees C for various lambda (0.02-0.07) was also studied. Experimental results showed that high temperature favors gas production in both processes; while low lambda gasification gave high gas yield. Syngas (CO and H(2)) was increased with temperature, while CO(2) followed an opposite trend. By pyrolysis, higher H(2) concentration in the produced gas (approximately 39% v/v) was achieved and at the same time lower amounts of CO(2) produced, compared to air gasification.

Soil contamination by heavy metals: measurements from a closed unlined landfill.

The aim of the present study was the characterization of soil samples of a closed unlined landfill located northwest of Thessaloniki, North Greece, in relation to heavy metals values. Samples were obtained by drilling in different depths (2.5-17.5m). Then they were analyzed by atomic absorption spectrophotometry for Cd, Cr, Cu, Ni, Pb and Zn investigation. The chemical analysis showed that the metal values varied over a wide range: from 0.50 to 18.75mg/kg for Cd, 3.88-171.88mg/kg for Cr, 8.13-356.25mg/kg for Cu, 5.63-63.75mg/kg for Ni, 2.50-92.50mg/kg for Pb and 6.38-343.75mg/kg for Zn. The highest values found in three of the six drillings, in depths over 2.5m. Although the area is heavily industrialized, the presented results indicated that local industries have not constituted an extensive metal pollution source for the site. Finally, after all necessary preparatory operations of site cleaning and flattening, surface planting selected and applied as a phytoremediation rehabilitation method of the site.

Sunflower shells utilization for energetic purposes in an integrated approach of energy crops: laboratory study pyrolysis and kinetics.

Sunflower is a traditional crop which can be used for the production of bioenergy and liquid biofuels. A study of the pyrolytic behaviour of sunflower residues at temperatures from 300 to 600 degrees C has been carried out. The experiments were performed in a captive sample reactor under atmospheric pressure and helium as sweeping gas. The yields of the derived pyrolysis products were determined in relation to temperature, with constant sweeping gas flow of 50 cm3 min(-1) and heating rate of 40 degrees Cs(-1). The maximum gas yield of around 53 wt.% was obtained at 500 degrees C, whereas maximum oil yield of about 21 wt.% was obtained at 400 degrees C. A simple first order kinetic model has been applied for the devolatilization of biomass. Kinetic constants have been estimated: E=78.15 kJ mol(-1); k(0)=1.03 x 10(3)s(-1).

Activated carbon from olive kernels in a two-stage process: industrial improvement.

Activated carbons have been prepared from olive kernels and their adsorptive characteristics were investigated. A two stage process of pyrolysis-activation has been tested in two scales: (a) laboratory scale pyrolysis and chemical activation with KOH and (b) pilot/bench scale pyrolysis and physical activation with H(2)O-CO(2). In the second case, olive kernels were first pyrolysed at 800 degrees C, during 45 min under an inert atmosphere in an industrial pyrolyser with a throughput of 1t/h (Compact Power Ltd., Bristol, UK). The resulting chars were subsequently activated with steam and carbon dioxide mixtures at 970 degrees C in a batch pilot monohearth reactor at NESA facility (Louvain-la Neuve, Belgium). The active carbons obtained from both scales were characterized by N(2) adsorption at 77 K, methyl-blue adsorption (MB adsorption) at room temperature and SEM analysis. Surface area and MB adsorption were found to increase with the degree of burn-off. The maximum BET surface area was found to be around 1000-1200 m(2)/g for active carbons produced at industrial scale with physical activation, and 3049 m(2)/g for active carbons produced at laboratory with KOH activation. The pores of the produced carbons were composed of micropores at the early stages of activation and both micropores and mesopores at the late stages. Methylene blue removal capacity appeared to be comparable to that of commercial carbons and even higher at high degrees of activation.