Waste and Biomass Valorization

This study investigated the conversion of corn stalk to bio-oil by solvothermal liquefaction using ethanol as a solvent. Effect of reaction temperature, time and solvent to biomass ratio on the yield and the properties of bio-oil and biochar was studied. Analysis of corn stalk and bio-oil were done to determine the surface functional groups, existing bonds and molecular structure of specified compounds. Investigations were done to identify different compounds in bio-oil, the thermal stability, and weight loss kinetics of biochar. Study shows that percentage yield of bio-oil increases with increase in temperature and time, up to a specific level, and then starts declining. Further, the heating value, carbon content, and fixed carbon content of both bio-oil and biochar increased to 30.52, 22.8 MJ/kg, and 66.42 and 61.25%, 26.10 and 27.97% respectively from those (19.55 MJ/kg, 51.12 and 6.36%) of the corn stalk. This study suggests that the bio-oil contained mostly phenolic compounds and its derivatives. Two major DTG peaks were observed at 380 and 620 °C indicating the improvement in thermal stability of the biochar after solvolysis liquefaction process. Investigation results can be very useful in optimizing process parameters for solvothermal liquefaction.

Citrus waste is an attractive feedstock for second generation bioethanol due to its richness in carbohydrates. For the production of bioethanol, removal of lignin through pretreatment to liberate more cellulose with minimal loss is essential. In the present work, the removal of lignin from musambi (Citrus limetta) peel by acid-catalyzed steam pretreatment and the characterization of musambi peel before and after pretreatment was studied. A Taguchi design was used to optimize solid loading, sulphuric acid concentration and time, for steam pretreatment with delignification as the response. The optimum conditions of process variables were 17% (w/v) for solid loading, 0.25% (v/v) for acid concentration with a time of exposure of 60 min with maximum delignification of 65%. The decrease in peak intensity in FTIR spectra and increase in the crystallinity index of pretreated peel indicated the reduction in pectin, hemicellulose, and lignin. The scanning electron micrographs of pretreated peel clearly showed the delignified microfibrils of cellulose. Enzymatic saccharification of pretreated musambi peel and the effect of peel loading, temperature, time, pH and the loading of cellulase, beta-glucosidase, and pectinase on reducing sugar were also investigated. The maximum reducing sugar obtained after the enzymatic hydrolysis was 386 mg/g for steam pretreated musambi peel at the optimum conditions whereas it was only 258 mg/g for the raw musambi peel. Thus, steam pretreatment of musambi peel resulted in better hydrolysis than untreated musambi peel. The yield of bioethanol production at the end of 48 h of fermentation was 85.97%.

Anaerobic digestion is a beneficial organic waste management technology that, in addition to biogas used for energy production, produces a by-product called anaerobic digestate, which can be used as a fertilizer or as an amendment as long as it has no harmful effects on the environment. The objective of the research described in this article was to assess one of these possible harmful effects, associated with the release of greenhouse gas emissions (GHG). Four anaerobic digestates were subjected to phase separation, and some of them also to composting, drying or reverse osmosis. Carbon dioxide (CO2) and nitrous oxide (N2O) emissions were measured during incubations of soil-digestate mixtures under controlled conditions. The mineralization of organic carbon reached 28–58 % of digestate organic carbon after 3 months in the presence of the solid digestates, and was lower (18–42 %) for the liquid digestates. The raw digestates had intermediate intensity of organic carbon mineralization to CO2. Drying and composting reduced CO2 emissions by stabilizing the digestate organic matter. N2O emission factors varied between 0.11 and 2.10 % of total digestate N depending on the origin and state of the digestates (raw, solid, liquid, composted). The highest emissions were measured with the raw digestates, and the lowest generally with the liquid ones. The study showed that in addition to phase separation, composting also reduced GHG emissions whereas drying and reverse osmosis considerably increased these emissions. Composted and dried digestates can be used as organic amendment leading to potential carbon storage larger than GHG emission, while for raw digestates, the GHG emissions always exceeded potential C storage.

Valorization is the conversion of waste and biomass to energy, fuels and other useful materials, with particular focus on environmental indicators and sustainability goals. It is part of the larger endeavor of loop-closing. This topic is the object of cooperation between a large number of actors from various fields of engineering sciences, health and safety. In this paper, the relevance and the interest in this topic is discussed and supported with examples. The two examples proposed concern biomass and plastic films. Biomass has gained a tremendous interest during the ten last years and will be a subject for significant research progress in the future. The evolution of research in the production of biofuels from first, second and third generation biomass is discussed using thermal process. The second example concerns plastic films; valorization of plastics has been investigated for two decades already with relevant progress. However, this paper shows that there are still a number of issues to tackle and overcome for an efficient and effective valorization of plastic films. To improve and reach a significant valorization, integrated processes for proper separation, detection and classification of plastic film from industrial and commercial packaging waste are discussed. The paper also highlights the bottlenecks, barriers and challenging issues such as the emission of pollutants and greenhouse gases, energy efficiency, modeling, characterization, regulation and policy that will drive the development of this field in the future.

To adapt hydrotalcite-based sorbents (also known as layered double hydroxides—LDHs) to high-temperature CO2 sorption compatible with tar steam reforming, the addition of CaO was investigated, maintaining the LHDs porosity and accessibility but mostly assuring the CO2 sorption stability during sorption/desorption cycles. In co-precipitation synthesis, the investigated parameters are (i) various interlayer anions with different sizes and valences (carbonate, oxalate, and stearate); (ii) various pH values; (iii) different Mg/Ca molar ratios. The characterization of these modified LDHs by TGA, XRD, N2 adsorption, SEM, sorption capacity, and sorption/desorption stability (cyclic TGA) allowed understanding the effect of the various synthesis parameters and highlighted the effect of oxalate use as the interlayer anion. After calcination of sorbent with Mg/Ca/Al ratio = 1/2/1, typical LDH sand roses were formed both with carbonate and oxalate anions: this former exhibited the highest sorption capacity and accessibility of CaO sites at 600 °C, higher than pure CaO. However, the best stability during cycles was obtained with the sorbent from oxalate and Mg/Ca/Al ratio = 1.5/1.5/1 at pH 10 for which comparable sorption results are reached. For these two samples, the observed macro-porosity was associated with the highest specific surface area and pore volume.

This paper provides an overview of waste generation and treatment operations in the European Union (EU) and other European countries and an analysis of the possibilities for the use of municipal solid waste (MSW) for energy production. A geographic information system based methodology was developed to investigate the spatial distribution of MSW and to identify the optimal location for new potential waste-to-energy in Europe. In 2016, there were 512 plants in Europe, with 251 combined heat and power plants, 161 electricity-only and 94 heat-only plants, which provide a total incineration capacity of 93 million tonnes. The suitability analysis showed that there is a potential to implement around 248 new waste to energy plants in the EU and 330 in all Europe, with a total capacity of 37 and 50 million tonnes, respectively. This represents an additional primary energy production of 260 PJ (6.2 Mtoe) in the EU, in comparison to 406 PJ (9.7 Mtoe) already produced in 2015, and about 352 PJ (8.4 Mtoe) in all European countries considered in this analysis.

The current study investigated to which extent phenol could be replaced by lignins to produce lignin phenol formaldehyde (LPF) resins, utilising soda lignin and sodium lignosulphonate as by-products from the South African pulping industry. The lignins were characterised and soda lignin indicated the highest reactivity. It was therefore utilised to produce LPF resins at 60%, 80%, and 100% phenol substitution, using central composite designs to maximise the adhesive strength. A one-pot method allowing direct transition from phenolation to resin synthesis was used for the first time with a pulping lignin at 60% and 80% substitution. Plywood made with LPF60, LPF80, and LPF100 resins attained their highest shear strengths of 0.786, 1.09, and 0.987 MPa, respectively, which adhered to the GB/T 14,732–2013 standard (≥ 0.7 MPa). A substitution level of 68% produced the highest shear strength of 1.11 MPa. High-density particleboard made with this LPF68 resin gave a MOR and MOE of 40 and 3209 MPa, respectively, adhering to the ANSI A208.1 requirements. Thickness swelling and water absorption was 13.5% and 37.2%, respectively. The soda-lignin isolated by precipitation from sugarcane bagasse pulping liquor is the first industrial lignin shown to produce LPF100 resins adhering to standard requirements, without modification or additives.