Gasification of sewage sludge: Mathematical modelling of an updraft gasifier

In this paper, a one-dimensional unsteady state mathematical model for the simulation of a small scale fixed-bed updraft gasifier is presented. The model is based on a set of differential equations which couples heat and mass transport in the solid and gas phases with sewage sludge drying and devolatilization, char gasification and combustion of both char and gaseous species. The model was used to simulate the behavior of sewage sludge with 20 % moisture in an updraft fixed-bed gasifier (2 m height, 0.165 m i.d.) of a pilot-scale plant operating at atmospheric pressure. Good agreement was achieved between predictions and experimental measurements for the dynamic axial temperature profiles and the steady state composition of the producer gas

Lithium silicate pellets for CO2 capture at high temperature

In this study, lithium orthosilicate-based pellets were developed and characterized as potential regenarable high-temperature CO2 sorbents. A mechanical method was used for pelletization of the powdered materials, namely K2CO3-doped lithium silicate (Li4SiO4) with cellulose fibres. Different amounts of cellulose fibres (20, 30 and 40 wt%) were added to powered doped-sorbent in order to identify the optimal amount to ensure an adequate porosity to the produced pellets. The CO2 sorption properties of the produced pellets were investigated at high temperature (500 - 600 °C) by using a thermal gravimetric analyzer (TGA) at low CO2 partial pressure with repeated calcination/carbonation cycles. Compared to the pure K2CO3-doped lithium silicate pellets, the sorbents prepared using cellulose fibres showed greater CO2 capture capabilities, which were ascribed to the higher porosity developed as a result of thermal degradation of cellulose. At 580 °C and a CO2 partial pressure of 0.04 atm, the uptake of CO2 in pellets prepared with 20 % of cellulose fibres reached about 20 wt% within 120 min corresponding to a Li4SiO4-conversion of 57 %. During multiple sorption/desorption cycles, a decay of the sorption capacity of the pellets was observed due to a partial sintering of the materials. This suggested that an appropriate binder should be added in order to improve the cyclic stability and the strength of the produced pellets

Leather manufacturing by using treated municipal wastewaters

Leather processing requires copious amounts of freshwater, approximately between 15 and 20 L per kg of raw hide. The possibility of reusing reclaimed municipal wastewaters in the leather production assumes a great significance, proving a sustainable solution to the conservation of the groundwater reserves. In the present work, a combination of a membrane bioreactor (MBR) and nanofiltration (NF) membrane processes was investigated for the municipal wastewater reclamation, and their performances were evaluated and designed to meet water quality criteria required by the wet stages of tanning process. The results showed that the municipal wastewaters treated by combing MBR and NF met the required quality criteria in terms of total/permanent hardness, Fe, Mn and ammonium contents. The quality of the leathers produced both on pilot and industrial scale using treated water did not show any significant difference in terms of physical and technical properties, and satisfied fully the tannery specifications

Life cycle assessment of remediation alternatives for dredged sediments

The Life Cycle Assessment (LCA) is an ISO standardized and widely used methodology for environmental assessment of products, processes and services, by identifying, quantifying and evaluating all the resources consumed and all the emissions and wastes released. The LCA methodology enables adequate comparison between different remediation options and can be used as a decision-making tool for the authorities. In this study, LCA was used to compare, in terms of their associated environmental burdens, two scenarios for managing the contaminated dredged sediments of the seabed of the Livorno Port area. The compared options were: (i) confined longshore disposal, i.e. placement of dredged material in a confined disposal facility; (ii) phytoremediation treatment, by an association of salt-tolerant shrub and grass species, aimed at turning the polluted sediment an agronomic substrate (techno-soil). The results of the life cycle impact assessment underline that the potential impacts of the two compared options involve different environmental problems. Indeed, for phytoremediation the most significant impacts are related to energy and resources consumption, while for the confined disposal are related to loads in the marine ecotoxicity categories. Therefore, phytoremediation can be considered a promising alternative solution for the management and valorization of contaminated dredged sediments

Removal of CO2 from flue gas at high temperature using novel porous solids

Since the CO2 separation is the first and most energy intensive step of carbon capture and storage (CCS) technology, many research have targeted at improving the current technologies or developing new approaches of CO2 separation and capture. In this study, lithium orthosilicate-based pellets were developed and characterized as potential regenarable high-temperature CO2 sorbents. A mechanical method was used for pelletization of the powdered materials, namely K2CO3-doped lithium silicate (Li4SiO4). For increasing the performance of the pellets over multiple cycles an activation strategy was applied: the powdered sorbents were pelletized with a binder for enhancing their porosity by applying a thermal activation before adsorption process. Different amounts of binders (layered graphite and carbon nanotubes) were added to powered doped-sorbent in order to identify the optimal amount to ensure an adequate porosity into the pellets. The CO2 sorption properties of the obtained pellets were investigated by using a thermal gravimetric analyzer (TGA) in a controlled gas flow environment at low CO2 partial pressure (0.04 atm). Compared to the pure K2CO3-doped lithium silicate pellets, the sorbents prepared using layered graphite showed greater CO2 capture capabilities, which were ascribed to the higher porosity developed as a result of the activation. At 580 °C and a CO2 partial pressure of 0.04 atm, the uptake of CO2 in pellets prepared with 20 % of graphite reached about 200 mg CO2/g sorbent within 120 minutes corresponding to a Li4SiO4-conversion of 72.1 %. During multiple sorption/desorption cycles, a decay of the sorption capacity of the pellets was observed due to a partial sintering of the materials

Use of Biochar as inexpensive lubricant filler in poly(butylene succinate-co-adipate) biocomposites

This study focused on the development of a novel bio-composite material formed by a thermoplastic biodegradable polyester, poly(butylene succinate-co-adipate) (PBSA), and a carbonaceous filler as biochar (BC) derived by the pyrolysis of woody biomass waste. Composites with various BC contents (5, 10, 15, and 20 wt.%, PBSA5, PBSA10, PBSA15, and PBSA20, respectively) were obtained by melt extrusion and investigated in terms of their processability, thermal, rheological, and mechanical properties. BC lowered melt viscosity in all the composites, behaving as a lubricant, and enhancing composite extrudability and injection molding at high temperatures up to 20 wt.% of biochar. While the use of biochar did not significantly change composite thermal stability, it increased its stiffness (Young modulus). Differential scanning calorimeter (DSC) revealed the presence of a second crystal phase induced by the filler addition. Furthermore, results suggest that biochar may form a particle network that hinders polymer chain disentanglement, reducing polymer flexibility. A biochar content of 10 weight % was selected as the best trade-off concentration to improve the composite processability and cost competitiveness without compromising excessively the tensile properties. The findings support the use of biochar as a sustainable renewable filler and pigment for PBSA. Biochar is a suitable candidate to replace more traditional carbon black pigments for agricultural applications

Absorption of n-butyl acetate from tannery air emissions by waste vegetable oil/water emulsions

Tanning industries emit a huge quantity of Volatile Organic Compounds (VOCs), including hydrophilic and hydrophobic solvents. In this study, vegetable oil/water emulsions with 2 and 5 vol% of corn oil (O) or waste cooking oil (WCO) were prepared. Their potential as absorbents of n-butyl acetate (BA), in place of water, was investigated to increase the efficiency of tannery wet scrubbers. BA was selected as a representative component of hydrophobic VOC emissions derived from leather finishing processes. Static and dynamic absorption tests were performed with a BA concentration of 500 ppmv (2.6 g/m3 ) and a flowrate of 3.0 L/min to evaluate Henry’s law constant, absorption efficiency, absorption capacity, and saturation time of the various investigated absorbents. The feasibility of the absorbent regeneration was also studied by hot stripping with nitrogen. The results showed that Henry’s constant of BA in oil/surfactant/water or oil/water emulsions (5 vol% oil), regardless of the oil used, were significantly lower than those in water (3.6 versus 15.9 atm), and BA absorption capacity (0.84 g/L) was four times higher than the value in water. The presence of the surfactant (0.2–0.8 vol%) contributed to improving the oil/water emulsions stability without having a significant effect on BA absorption capacity. Almost complete BA desorption from the saturated emulsions was obtained by flowing hot N2 at 80◦C, demonstrating the absorbent regeneration’s feasibility followed by recovery and reuse. Therefore, the oil/water emulsions containing 5 vol% of WCO are efficient and sustainable absorbents of BA, with potential use in VOC emission treatment systems

The Effect of Flue Gas Contaminants on CO2 Capture at High Temperature by Li4SiO4-based Sorbents

In this study, high-temperature CO2 capture by solid sorbent based on lithium orthosilicate (Li4SiO4) was investigated in the presence of gas contaminants, such as NO and SO2. Simulated flue gas containingCO2 (4 vol%), SO2 (up to 2,000 ppm), and NO (up to 1,000 ppm) was used during the CO2 capture process. The CO2 sorption properties of the sorbent were investigated at high temperature (580 °C) by a thermal gravimetric analyzer (TGA). The tested sorbent showed high CO2 sorption capacity (210 mg CO2/g sorbent) along with high absorption rates, and lower regeneration temperature than other solids such as calcium oxide. The results also showed that the solid sorbent is inert with respect to NO. Instead, the presence of SO2 resulted in a negatively effect on the sorption capacity of the sorbent, due to an irreversible reaction with the adsorbent. Thus, industrial application would require desulfurization of flue gas prior to contacting the sorbent

Depoxo process: technical and environmental study of hide oxidative unhairing

As an alternative to the traditional process based on the use of sulfides, an unhairing process in drum by hydrogen peroxide, named DEPOXO, was developed for the production of high-quality bovine upper leather. A preliminary investigation at laboratory scale has allowed to set out the optimal process conditions, in terms of H2O2 dosage (9 %) and pH (12.5), in order to achieve an effective unhairing and a compatible swelling of hides. The following pilot-scaled runs have assessed the industrial feasibility of the process that allows the production of a versatile base for different final applications of the leather (either chrome or vegetable tanned), and appear practical to implement. The crust leather obtained by the oxidative unhairing process showed good physical-mechanical and technical properties comparable with those obtained by the traditional one, and the leather was technically assessed as satisfactory and suitable according to the market request. The actual reduction of the environmental impact of the novel process, in relation with the traditional one, was evaluated performing a Life Cycle Assesment (LCA) using SimaPro 7.3, one of the most used software for LCA analysis. The results of the life cycle impact assessment underline that damages on main impact categories are greatly reduced through the adoption or the oxidative unhairing. Therefore, the DEPOXO process appears a feasible process, either from the environmental or from the technical point of view, to produce high quality bovine upper leather

Beyond water: Physical and heat transfer properties of phase change slurries for thermal energy storage

Thermal energy storage is a key technology for decarbonization. In this context, phase change slurries (PCSs) retain the heat storage advantages of phase change materials (PCMs) while relying on fluidity to overcome heat transfer inefficiencies caused by the poor thermal conductivity of bulk PCMs. PCSs can replace water in conventional low-temperature storage tanks, offering numerous advantages. Despite their potential, there is a lack of research in this area, especially regarding natural convection heat transfer. Furthermore, addressing the complex thermo-physical and rheological properties of slurries is essential. This review focuses on the characterization, measurement, and modeling of physical properties of micro/nanoPCSs and their heat transfer performance under natural convection. The state-of-the-art in the field is presented, research gaps are identified, and directions for future research are proposed. Filling the above gaps will support the choice of PCSs as future and sound enhanced fluids for low-temperature heat storage