Comprehensive kinetic modeling and product distribution for pyrolysis of pulp and paper mill sludge

Pyrolysis holds immense potential for clean treatment of pulp and paper mill sludge (PPMS), enabling efficient energy and chemical recovery. However, current understanding of PPMS pyrolysis kinetics and product characteristics remains incomplete. This study conducted detailed modeling of pyrolysis kinetics for two typical PPMSs from a wastepaper pulp and paper mill, namely, deinking sludge (PPMS-DS) and sewage sludge (PPMS-SS), and analyzed comprehensively pyrolysis products. The results show that apparent activation energy of PPMS-DS (169.25-226.82 kJ/mol) and PPMS-SS (189.29-411.21 kJ/mol) pyrolysis undergoes significant change, with numerous parallel reactions present. A distributed activation energy model with dual logistic distributions proves to be suitable for modeling thermal decomposition kinetics of both PPMS-DS and PPMS-SS, with coefficient of determination >0.999 and relative root mean square error <1.99 %. High temperature promotes decomposition of solid organic materials in PPMS, and maximum tar yield for both PPMS-DS (53.90 wt%, daf) and PPMS-SS (56.48 wt%, daf) is achieved at around 500 °C. Higher levels of styrene (24.45 % for PPMS-DS and 14.71 % for PPMS-SS) and ethylbenzene (8.61 % for PPMS-DS and 8.33 % for PPMS-SS) are detected in tar and could be used as chemicals. This work shows great potential to propel development of PPMS pyrolysis technology, enabling green and sustainable production in pulp and paper industry.

Synergistic catalytic mechanism of red mud in the co-gasification of spirit-based distillers' grains and sewage sludge

Experiments of co-gasification of spirit-based distillers' grains (SDG) and sewage sludge (SS) were carried out with red mud (RM) by using a self-designed fixed-bed gasifier. The effects of RM addition, gasification reaction temperature, SS and SDG blending ratio and other factors on the gasification reaction characteristics and synergism were investigated. The results are as follow: RM had catalytic effect on SS and SDG co-gasification, which can enhance the gasification reaction and H2 yield; increasing the temperature can enhance the gasification reaction and reduce the syngas H2/CO; with the increase of SDG, the H2 yield gradually grew; with the rise of SS, the gasification reaction gradually augmented. The catalytic mechanism was mainly due to the redox cycle of Fe2O3 in RM, which can promote the water transfer reaction. At the same time, the eutectic mixture of K, Na, Ca, Fe and other metal elements at high temperatures was the main reason for the synergistic effect.

New trends in modelling of breakthrough curves to remove pollutants using adsorption on advanced monoliths geometries

This work proposes a rigorous mathematical model capable of reproducing the adsorption process in dynamic regime on advanced monoliths geometries. For this, four bed geometries with axisymmetric distribution of channels and similar solid mass were proposed. In each geometry a different distribution of channels was suggested, maintaining constant the bed dimensions of 15 cm high and 5 cm radius. The mathematical modeling includes mass and momentum transfer phenomena, and it was solved with the COMSOL Multiphysics software using mass transfer parameters published in the literature. The overall performance of the column was evaluated in terms of breakthrough (CA/CA0 = 0.1) and saturation times (CA/CA0 = 0.9). The mass and velocity distributions obtained from the proposed model show good physical consistency with what is expected in real systems. In addition, the model proved to be easy to solve given the short convergence times required (2-4 h). Modifications were made to the bed geometry to achieve a better use of the adsorbent material which reached up to 80%. The proposed bed geometries allow obtaining different mixing distributions, in such a way that inside the bed a thinning of the boundary layer is caused, thus reducing diffusive effects at the adsorbent solid-fluid interface, given dissipation rates of about 323 × 10-11 m2/s3. The bed geometry composed of intersecting rings deployed the best performance in terms of usage of the material adsorbent, and acceptable hydrodynamical behavior inside the channels (maximum fluid velocity = 35.4 × 10-5 m/s and drop pressure = 0.19 Pa). Based on these results, it was found that it is possible to reduce diffusional effects and delimit the mass transfer zone inside the monoliths, thus increasing the efficiency of adsorbent fixed beds.

Ivermectin adsorption by commercial charcoal in batch and fixed-bed operations

Emerging contaminants were used during the COVID-19 pandemic, including ivermectin. Studies that limit the optimal adsorption parameters of ivermectin are scarce in the literature. In this study, we analyzed the adsorption of ivermectin with a high surface area and porosity charcoal. Isotherms were better fitted to the Koble-Corrigan model. The maximum capacity was 203 μg g-1 at 328 K. Thermodynamics indicated a spontaneous and endothermic behavior. The equilibrium was quickly reached within the first few minutes regardless of the ivermectin concentration. The linear driving force (LDF) model fitted the kinetic data (qexp = 164.8 μg g-1; qpred = 148.1 μg g-1) at 100 μg L-1 of ivermectin. The model coefficient (KLDF) and diffusivity (Ds) increased with increasing drug concentration. Two sloped curves were obtained in the column experiments, with a breakthrough time of 415 min and 970 min. The capacity of the column (qeq) was 76 μg g-1. The length of the mass transfer zone was 9.04 and 14.13 cm. Therefore, it can be concluded that the adsorption of ivermectin is highly sensitive to changes in pH, being favored in conditions close to neutrality. Commercial activated charcoal was highly efficient in removing the studied compound showing high affinity with very fast kinetics and a good performance in continuous operation mode.

Catalytic performance of activated lignite chars on biomass tar cracking

The tar problems are the major obstacle to developing the biomass pyrolysis technology. The coal chars derived from in situ pyrolysis and/or partially gasification are a promising alternative tar cracking catalyst with great industrial application potential because of its cheap and easily available characteristics. This work investigated the application of lignite chars as catalysts for biomass tar decomposition. Raw lignite char was further gasified with CO₂ for 5 min (GC5) and 15 min (GC15) and used as tar cracking catalysts. Effects of pyrolysis temperature, char/biomass mass ratio, and pore structure of char on the pyrolysis tar removal were studied. The results showed that increasing pyrolysis temperature and char/biomass mass ratio would promote tar decomposition. When using GC15 as catalyst, tar yield was as low as 0.10 wt% at the temperature of 850 °C and the mass ratio of 2. Gasification treatment increased the specific surface area of raw char from 284.1 to 342.7 m²/g (GC5) and 435.6 m²/g (GC15). Comparing the catalytic activity of lignite chars with commercial activated carbon demonstrated that mesopores were more influential than micropores in tar removal. In addition, water produced during biomass pyrolysis could in situ contribute to tar reforming and char gasification reactions. The results obtained in this study suggested that a cheaper coal char-based catalyst with excellent performance for biomass tar cracking could be achieved by combining with a coal gasification process and optimizing gasification conditions.

Effect of modified CeO2 on the performance of PdCu/Ce1-xTixO2 catalyst for methanol purification

In this paper, we prepared a series of Ce_1-xTi_xO₂ (x = 0-0.20) nanorods by hydrothermal method, which were used to construct the PdCu/Ce_1-xTi_xO₂ catalysts. The Ce_1-xTi_xO₂ and PdCu/Ce_1-xTi_xO₂ samples were characterized by transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption, X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometer (ICP-OES), etc. Catalytic activity, stability, and repeatability of the catalysts for methanol oxidation were investigated. The results show that doping a proper amount of titanium could strengthen the interaction between Ce_1-xTi_xO₂ support and PdCu nanoalloy, thus increasing the oxygen vacancy concentration and promoting Pd species with a higher oxidation state. These modified properties are beneficial for the deep oxidation of methanol. The light-off temperature (T₅₀) and full-conversion temperature (T₉₀) of methanol over the PdCu/CeO₂ catalyst are 108 °C and 159 °C, respectively. The greatest activity improvement is found for PdCu/Ce_0.9Ti_0.1O₂, which shows the lowest T₅₀ of 88 °C and T₉₀ of 138 °C. Furthermore, neither PdCu/CeO₂ nor the modified PdCu/CeO₂ catalyst produces by-products and exhibit excellent stability and repeatability throughout the whole test period. This study provides a reference for in-depth understanding and designing of efficient and stable CeO₂-based oxidation catalysts.

Construction of metal-organic framework/polymer beads for efficient lead ions removal from water: Experiment studies and full-scale performance prediction

Metal-organic frameworks (MOFs) show great promise in heavy metal removal; however, their applications are restricted by the poor separability and water instability. Herein, granular Zr-based MOF-polymer composite beads (MPCB(Zr)) (mean diameter ∼ 1.74 mm) were synthesized using a facile dropping method, and applied on efficient lead ions (Pb(II)) removal. The as-prepared MPCB(Zr) demonstrated deep Pb(II) removal capability by reducing its concentration to ∼ 0.002 mg L^-1 after adsorption equilibrium at 360 min. The distribution coefficient for Pb(II) reached 8.0 × 10⁶ mL g^-1, and the theoretical adsorption capacity for Pb(II) was 144.5 mg g^-1 (0.70 mmol g^-1, 30 °C). The resulting MPCB(Zr) was highly selective for Pb(II), with the selectivity coefficient up to ∼ 1.0-3.6 × 10³ for the background cations (Na(I), K(I), Ca(II), and Mg(II)). Moreover, the MPCB(Zr) exhibited a broad working pH range (3.0-6.0) and satisfactory anti-interference to dissolved organic matters (humic acid and fuvic acid). Notably, the MPCB(Zr) also demonstrated excellent reusability with the Pb(II) removal efficiency over 99.0% after 20 cycles. Combined physicochemical characterizations unveiled that the thiol and oxygen-containing groups (e.g., hydroxyl, carboxylate) were responsible for the effective Pb(II) removal. To provide guidance for engineering application, the full-scale performance of the MPCB(Zr) under varying operation conditions was systematically evaluated via the validated pore surface diffusion model. This work provides an effective methodology to construct macroscopic MOF-polymer beads for effective Pb(II) removal, and promote the actual application of MOFs in water treatment.

Experimental analysis on products distribution and characterization of medical waste pyrolysis with a focus on liquid yield quantity and quality

The massive generation of medical waste (MW) poses a serious risk to the natural environment and human health. The pyrolysis technique is proposed as a potential treatment for MW to tackle the associated environmental issues and produce value-added products. In this work, medical waste pyrolysis has been conducted at various temperatures using a fixed bed reactor with a 20 °C·min^-1 heating rate and nitrogen was used as a career gas with a flow rate of 100 ml·min^-1. In addition, the effect of temperature on products yield and chemical composition of MW pyrolysis have been investigated. The maximum yield of 57.1% for liquid oil was observed from the mixed MW pyrolysis at 500 °C. The gas and char yield were found between 26.5-37.3% and 24.2-12.4%, respectively, for the pyrolysis temperature of 450 °C to 600 °C. According to GC analysis, the concentration of the main gaseous products such as CH₄, H₂, and C₂H₄ was increased with increasing temperature, while CO and CO₂ experienced a decreasing trend. The results of GC-MS analysis revealed that the main components of MW pyrolysis oil were aromatic hydrocarbons, cyclic hydrocarbons, aliphatic hydrocarbons, alcohol, carboxylic acids, and their derivatives. The aromatic and cyclic hydrocarbons content increased up to 38.2% at a pyrolysis temperature of 600 °C. As pyrolysis oil tends to have more long-chain hydrocarbons therefore carbon distributions from C₇ to C₃₅ were observed. The ultimate analysis of oil and char revealed that the increased temperature enhanced the carbon content up to 78.6% and 68.0%, respectively. Furthermore, the higher heat values of 41.8, 24.4, and 52.7 MJ·kg^-1 were reported for oil, char, and gas, respectively.

Biodegradation of the petroleum hydrocarbons using an anoxic packed-bed biofilm reactor with in-situ biosurfactant-producing bacteria

The present study employed an anoxic packed bed biofilm reactor (AnPBR) inoculated with in-situ biosurfactant-producing bacteria for the biodegradation of petroleum wastewater. Highly acclimated biomass decreased the start-up phase period and with increasing the initial total petroleum hydrocarbon (TPH) concentration from 1.5 to 4 g/L was accompanied by TPH and chemical oxygen demand (COD) removal efficiencies of above 99% and 96%, respectively. Decreasing hydraulic retention time (HRT) from 24 to 6 h caused an increase in the specific hydrocarbon utilization rate value from 0.45 to 1.66 gTPH/g_biomass.d. Moreover, dehydrogenase activity, surfactin, and rhamnolipid reached 31.8 μgTF/g_biomass.d, 95.1, and 27.1 mg/L, respectively. The biodegradation kinetic coefficients such as K, K_s, K_d, Y and µ_max were 0.784 (d^-1), 0.005 (g/L), 0.138 (d^-1), 0.569 (gVSS/gCOD), and 0.446 (d^-1), respectively. Dropping of bioreactor performance, especially TPH removal efficiency from 99% to 37.6% in the absence of nitrate after 10 days, indicates anoxic metabolism has been the dominant biodegradation pathway. The effluent chromatogram of gas chromatography/flame ionization detector (GC/FID) showed aliphatic, cyclic aliphatic, and aromatic hydrocarbons efficiently degraded. According to the high degradation rate of AnPBR in different operational parameters, it can be recommended for the treatment of oil-contaminated wastewater.

Insight into the role of the zeolitization process in enhancing the adsorption performance of kaolinite/diatomite geopolymer for effective retention of Sr (II) ions; batch and column studies

Diatomite/kaolinite-based geopolymer (GP) was synthesized and incorporated in zeolitization process (Z/GP) to investigate the role of the zeolite phases in inducing its retention capacity of the dissolved Sr (II) ions in water. The retention of Sr (II) ions using Z/GP in comparison with GP was evaluated based on both batch and fixed-bed column studies. In the batch study, the zeolitized geopolymer (Z/GP) shows enhancement in the Sr (II) retention capacity (193.7 mg/g) as compared to the normal geopolymer (102 mg/g). Moreover, the recyclability studies demonstrate higher stability for Z/GP than GP with a retention percentage higher than 90% for five reusing runs. The kinetic and the equilibrium properties of the occurred Sr (II) retention reactions follow the assumption of the Pseudo-Second order model (R² > 0.96) and Langmuir model (R² > 0.97), respectively. The Gaussian energies (15.4 kJ/mol (GP) and 11.47 kJ/mol (Z/GP)) related to retention mechanism of chemical type and within the suggested range for the zeolitic ion exchange processes. The Sr (II) retention reactions by GP and Z/GP are of spontaneous and exothermic properties which qualifies the products to be used at low-temperature conditions (20 °C). The column studies also declared higher performance for the Z/GP fixed bed as compared to the normal GP bed considering the total Sr (II) retention percentage (72.9%), treated volume (8 L), saturation time (1620 min), and a maximum capacity of Z/GP particles in the bed (567.6 mg/g).

Effective decontamination of Ca2+ and Mg2+ hardness from groundwater using innovative muscovite based sodalite in batch and fixed-bed column studies; dynamic and equilibrium studies

A novel form of sodalite was synthesized from muscovite (M.SD) as low-cost softening material for both Ca²⁺ and Mg²⁺ ions from real groundwater in batch and column studies. The sodalite sample showed significant surface area (105 m²/g) and ion exchange capacity (87.3 meq/100 g) which qualifies it strong for softening applications. The incorporation of the M.SD as a fixed bed in column system at a fixed thickness of 4 cm and flow rates of 5 mL/min resulted in removal percentages of 90.5% and 92.2% for Ca²⁺ and Mg²⁺, respectively at pH 7.6. Considering the real concentrations of the ions (Ca²⁺ (233 mg/L) and Mg²⁺ (114 mg/L)), the M.SD bed has the ability to reduce their concentrations according to the recommended limits (75 mg/L for Ca²⁺ and 50 mg/L for Mg²⁺). These conditions resulted in purification of about 8.1 L and 8.7 L with breakthrough intervals of 1380 min and 1440 min; and saturation interval more than 1620 min for Ca²⁺ and Mg²⁺, respectively. The M.SD columns' performances were described considering the assumption of the Thomas model, Adams-Bohart model, and Yoon-Nelson model. The batch studies demonstrate the uptake of both Ca²⁺ and Mg²⁺ ions according to the Pseudo-First order kinetics and Langmuir equilibrium behaviour. Considering the values of Gaussian energies (0.77 KJ/mol (Ca²⁺) and 1.36 KJ/mol (Mg²⁺)), the uptake of these ions occurred by homogenous reactions of monolayer form and physical nature. The thermodynamic studies declared the spontaneous properties of the reactions and their exothermic properties.

Development of intensified flat-plate packed-bed solar reactors for heterogeneous photocatalysis

Solar-driven photocatalysis is a promising water-cleaning and energy-producing technology that addresses some of the most urgent engineering problems of the twenty-first century: universal access to potable water, use of renewable energy, and mitigation of CO₂ emissions. In this work, we aim at improving the efficiency of solar-driven photocatalysis by studying a novel reactor design based on microfluidic principles using 3D-printable geometries. The printed reactors had a dimensional accuracy of 97%, at a cost of less than $1 per piece. They were packed with 1.0-mm glass and steel beads coated with ZnO synthesised by a sol-gel routine, resulting in a bed with 46.6% void fraction (reaction volume of ca. 840 μL and equivalent flow diameter of 580 μm) and a specific surface area of 3200 m² m^-3. Photocatalytic experiments, under sunlight-level UV-A irradiation, showed that reactors packed with steel supports had apparent reaction rates ca. 75% higher than those packed with glass supports for the degradation of an aqueous solution of acetaminophen; however, they were strongly deactivated after the first use suggesting poor fixation. Glass supports showed no measurable deactivation after three consecutive uses. The apparent first-order reaction rate constants were between 1.9 and 9.5 × 10^-4 s^-1, ca. ten times faster than observed for conventional slurry reactors. The mass transfer was shown to be efficient (Sh > 7.7) despite the catalyst being immobilised onto fixed substrates. Finally, the proposed reactor design has the merit of a straightforward scaling out by sizing the irradiation window according to design specifications, as exemplified in the paper.

Chitosan-coated sand and its application in a fixed-bed column to remove dyes in simple, binary, and real systems

Adsorption of tartrazine yellow food dye, in a fixed-bed column, was carried out using a single system, a binary system (in the presence of sunset yellow food dye), and in a real effluent provides from an ice cream industry. Chitosan was used to coat sand particles by the dip-coating technique, and these particles were applied in fixed-bed adsorption. The assays were performed in flow rates of 3 mL min^-1 and 5 mL min^-1. The best performance was reached at 3 mL min^-1. In this flow rate, for single and binary systems, the breakthrough time was 95 min and 65 min, and the maximum capacity of the column was around 595 mg g^-1 and 497 mg g^-1, respectively. In the assay conducted with the real effluent, the breakthrough time was 10 min, and the maximum adsorption capacity of the column was reduced to 191 mg g^-1 for tartrazine dye. The dynamic models of Thomas and Yoon-Nelson were used, and both were suitable to represent the breakthrough curves.

Comment on ″Exponential and logistic functions: The two faces of the Bohart-Adams model″

The Bohart-Adams model has been one of the most widely used breakthrough models for the modeling of dynamic adsorption behaviors of water pollutants in a fixed-bed column. However, the fitting quality was often questioned by many researchers when the Bohart-Adams model was correlated with the experimental data. Recently, Chu (2020) discussed the two simplified forms of the Bohart-Adams model and tested their applicability. In fact, in our previous study (Hu et al., 2019), it has been proved that the two forms represented the logistic and exponential functions in mathematical nature, respectively. The fitting quality depended on whether the experimental data approached the shape of the model curve. Besides, the curve characteristics and fitting ability of the original Bohart-Adams model were not revealed, and how to analyze asymmetrical breakthrough curve remained to be solved. This comment tried to expound the Bohart-Adams model completely. The authors hope that this work will be helpful for readers who are interested in the adsorption studies.

Treatment of greywater using waste biomass derived activated carbons and integrated sand column

Utilization of greywater can reduce water stress if, it is used as an alternative source of water for non-potable use, but it requires careful treatment to remove the contaminants including micropollutants associated with the use of a large number of personal care products. The present paper deals with the batch as well as continuous adsorption study for the treatment of greywater using activated carbons prepared from sawdust, sugarcane bagasse and pine needles. Characterization of adsorbents were done through sophisticated instruments such as FE-SEM, FTIR and BET. The optimum conditions in batch mode for the removal of contaminants are found as pH 7, contact time 240 min. and adsorbent dose 8 g/L with initial COD of greywater as 554 mg/L and BOD as 120 mg/L. For isotherms study, models such as Langmuir, Freundlich and Temkin were used whereas for kinetic study pseudo-first-order, pseudo-second-order and Elovich models were investigated to validate the experimental data. The column adsorption study has been performed to carry out breakthrough analysis of the column bed with respect to COD and BOD removal. To understand the behaviour of breakthrough curves three models viz. Bohart-Adams, Yoon-Nelson and Thomas models have been tested. Out of these adsorbents, the sawdust activated carbon is found to be more efficient. To maintain the concentration of pollutants in treated water below the permissible limit as per CPCB (Central pollution control board), India, a coupled unit of sand and the adsorbent column was investigated in continuous mode. The present investigation appears to be highly competitive to the published literature.

Chitosan-coated different particles in spouted bed and their use in dye continuous adsorption system

In this work, three polymer suspensions were used for coating glass beads (GB), porcelain beads (PB), and polyethylene pellets (PP) in spouted bed. Subsequently, the continuous adsorption assays of the food dye Brilliant Blue FCF in a fixed bed column were performed, which was packed with the covered particles. Also, the static adsorption assays were carried out. The adsorption equilibrium isotherms were fitted by Freundlich, Langmuir, and Temkin models, being that the Temkin model was the most suitable to represent the equilibrium data. The particle coating in the spouted bed showed promising results due to the high efficiency of the process. The PB, GB, and PP obtained coating efficiency values in the range to 92-96% when using the suspension of chitosan and hydroxyethyl cellulose. However, only the polyethylene particles coated with the chitosan suspension maintained its coating efficiency (95%). The maximum adsorption capacities at equilibrium of the coated particles of PP and GB were achieved with the chitosan suspension, being the values of around 800 mg g^-1. Thus, the chitosan-coated polyethylene particles showed to be a promising adsorbent for fixed bed column. Graphical abstract.

Potential of Cedrella fissilis bark as an adsorbent for the removal of red 97 dye from aqueous effluents

Cedar bark (Cedrella fissilis), a waste from wood processing, was evaluated as an adsorbent for the removal of red 97 dye from effluents. The material exhibited an amorphous structure, irregular surface, and was mainly composed of lignin and holocellulose. The adsorption was favored at pH 2.0. The general order model was most suitable for describing the experimental kinetic data, being the equilibrium reached in around 30 min. The isotherm experiments were better described by the Langmuir model. The maximum adsorption capacity was 422.87 mg g^-1 at 328 K. The values of standard Gibbs free energy change (ΔG⁰) were from - 21 to - 26 kJ mol^-1, indicating a spontaneous and favorable process. The enthalpy change (ΔH⁰) was 18.98 kJ mol^-1, indicating an endothermic process. From the fixed bed adsorption experiment, an inclined breakthrough curve was found, with a mass transfer zone of 5.36 cm and a breakthrough time of 329 min. Cedar bark was able to treat a simulated effluent attaining color removal of 86.6%. These findings indicated that cedar bark has the potential to be applied as a low-cost adsorbent for the treatment of colored effluents in batch and continuous adsorption systems.

Modeling and economic analysis of waste tire gasification in fluidized and fixed bed gasifiers

Waste tires have an organic-matter composition of more than 90% and have been proposed as an excellent calorific fuel material. The objective of this study is to find an economic and efficient pathway for producing syngas by waste tires gasification. To achieve this goal, two most commonly used gasifier types of fluidized bed and fixed bed have been simulated and compared by using a semi-empirical model and a one-dimensional kinetics model, respectively. Moreover, economic analysis of the levelized cost of syngas is used to compare economic indicators of different gasifiers. Results show that the lower heating value of the tire-syngas product is 2.5-7.4 MJ/Nm³, moreover, equivalence ratio and tire mixture ratio have negative impacts on syngas heating value and syngas efficiency. Furthermore, the levelized cost of syngas of tire gasification is 0.33-0.60 ¢/kWh that is lower than the market price of natural gas at 0.68 ¢/kW, which indicates tire gasification is a potential technology for syngas production. Finally, compared with the fluidized bed tire gasification, the fixed bed tire gasification has worse performance but better economic indicators, indicating that fixed bed gasification is an economic pathway for the syngas product.

Upscaling fixed bed adsorption behaviors towards emerging micropollutants in treated natural waters with aging activated carbon: Model development and validation

A scale-up procedure was assessed in this study to predict the fixed bed adsorption behaviors with aging granular activated carbon (GAC) for various micropollutants (pesticides, pharmaceuticals). Two assumptions of this upscaling methodology (i.e., involving equal adsorption capacities and surface diffusivities between the batch test and the fixed bed) were studied for the first time to investigate the aging effect on the adsorption capacity and kinetics of carbon at full scale. This study was conducted in natural waters (the Seine River) treated by Veolia Eau d'Ile de France in Choisy-Le-Roi, a division of Syndicat des Eaux d'Ile de France, aiming to monitor real industrial conditions. The isotherms showed that the adsorption capacity for most compounds was significantly affected by aging. For the mass transfer coefficients (i.e., as determined by the homogeneous surface diffusion model (HSDM)), different patterns of adsorbate/adsorbent behaviors were observed, suggesting different competition mechanisms. The model predictions (i.e., HSDM) performed with all parameters obtained during the batch tests tended to overestimate the full-scale pilot adsorption performance. This overestimation could be compensated for by applying a scaling factor. Finally, an empirical pseudo-first order function was used to model the impact of the GAC service time on the characteristic adsorption parameters. Thus, our scale-up procedure may enable the prediction of long-term fixed bed adsorption behaviors and increase the model efficiency for practical implementation.

Modelling grate combustion of biomass and low rank fuels with CFD application

A reactor cascade model is used for the numerical simulation of the fixed bed combustion of biomass, municipal solid waste and other low rank fuels. Non-spherical particle geometries are accounted for via their plain specific surface. The model is able to reproduce key quantities like ignition delay time, ignition rate, reaction front velocity and mass conversion rate in close agreement with experimental data. This provides a basis to transfer the fixed bed results to the situation of continuous combustion on forward acting grates. A simplified numerical procedure is presented for this purpose. It allows to estimate the structure of a fuel bed moving on the grate as well as the overbed gas temperature and composition. These data serve as input for separate CFD applications which simulate the gas flow in small scale and in industrial scale power plants together with the associated heat transfer processes. Validation of the modelling is presented for lab scale and bench scale experiments as well as for an industrial municipal solid waste incinerator.

Defluoridation using novel chemically treated carbonized bone meal: batch and dynamic performance with scale-up studies

Novel defluoridating adsorbent was synthesized by chemical treatment of carbonized bone meal using aluminum sulfate and calcium oxide. Precursor for chemical treatment was prepared by partial carbonization of raw bone meal at 550 °C for 4 h. Maximum fluoride removal capacity was 150 mg/g when carbonized bone meal (100 g/L) was treated with aluminum sulfate (500 g/L) and calcium oxide (15 g/L). Morphological analysis revealed formation of a coating layer consisting of aluminum compounds on the precursor surface. This was verified by stretching frequency of aluminum hydroxide (602 cm^-1) in the infrared spectra. Presence of hydroxylapatite (2θ = 30° and 2θ = 24°) and aluminum mineral phases (2θ = 44°) in the adsorbent were identified from the X-ray diffractograms. Adsorption capacity decreased from 150 mg/g (30 °C) to 120 mg/g (50 °C) indicating exothermic adsorption. Adsorption experiments under batch kinetic mode were simulated using shrinking core model. Effective fluoride diffusivity in the adsorbent and the mass transfer coefficient were estimated as 5.8 × 10^-12 m²/s and 9 × 10^-4 m/s, respectively. Desorption was maximum at basic pH and desorption efficiency was decreased by 31% after third cycle. Dynamic filtration with artificially fluoride-spiked solution showed that the empty bed contact time for a packed column with equal weight of carbonized and chemically treated adsorbent was 4.7 min and number of bed volumes treated (till WHO limit of 1.5 mg/L) was 340 for a column of 3-cm diameter and 18-cm length. The system was successfully tested using contaminated groundwater from an affected area. Fixed-bed column experiments were simulated from the first principles using convective pore diffusion-adsorption model for both synthetic solution and contaminated groundwater. Axial dispersion coefficient was found to be one order of magnitude less than the pore diffusivity indicating dominance of fluoride diffusion within porous network of adsorbent. The developed adsorbent exhibited antibacterial property as well.

Removal of emerging pharmaceutical contaminants by adsorption in a fixed-bed column: A review

Pharmaceutical pollutants substantially affect the environment; thus, their treatments have been the focus of many studies. In this article, the fixed-bed adsorption of pharmaceuticals on various adsorbents was reviewed. The experimental breakthrough curves of these pollutants under various flow rates, inlet concentrations, and bed heights were examined. Fixed-bed data in terms of saturation uptakes, breakthrough time, and the length of the mass transfer zone were included. The three most popular breakthrough models, namely, Adams-Bohart, Thomas, and Yoon-Nelson, were also reviewed for the correlation of breakthrough curve data along with the evaluation of model parameters. Compared with the Adams-Bohart model, the Thomas and Yoon-Nelson more effectively predicted the breakthrough data for the studied pollutants.

Pyrolysis of agricultural biomass residues: Comparative study of corn cob, wheat straw, rice straw and rice husk

Pyrolysis studies on conventional biomass were carried out in fixed bed reactor at different temperatures 300, 350, 400 and 450°C. Agricultural residues such as corn cob, wheat straw, rice straw and rice husk showed that the optimum temperatures for these residues are 450, 400, 400 and 450°C respectively. The maximum bio-oil yield in case of corn cob, wheat straw, rice straw and rice husk are 47.3, 36.7, 28.4 and 38.1wt% respectively. The effects of pyrolysis temperature and biomass type on the yield and composition of pyrolysis products were investigated. All bio-oils contents were mainly composed of oxygenated hydrocarbons. The higher area percentages of phenolic compounds were observed in the corn cob bio-oil than other bio-oils. From FT-IR and ¹H NMR spectra showed a high percentage of aliphatic functional groups for all bio-oils and distribution of products is different due to differences in the composition of agricultural biomass.

Removal of heavy metals from acid mine drainage using chicken eggshells in column mode

Chicken eggshells (ES) as alkaline sorbent were immobilized in a fixed bed to remove typical heavy metals from acid mine drainage (AMD). The obtained breakthrough curves showed that the breakthrough time increased with increasing bed height, but decreased with increasing flow rate and increasing particle size. The Thomas model and bed depth service time model could accurately predict the bed dynamic behavior. At a bed height of 10 cm, a flow rate of 10 mL/min, and with ES particle sizes of 0.18-0.425 mm, for a multi-component heavy metal solution containing Cd²⁺, Pb²⁺ and Cu²⁺, the ES capacities were found to be 1.57, 146.44 and 387.51 mg/g, respectively. The acidity of AMD effluent clearly decreased. The ES fixed-bed showed the highest removal efficiency for Pb with a better adsorption potential. Because of the high concentration in AMD and high removal efficiency in ES fixed-bed of iron ions, iron floccules (Fe₂(OH)₂CO₃) formed and obstructed the bed to develop the overall effectiveness. The removal process was dominated by precipitation under the alkaline reaction of ES, and the co-precipitation of heavy metals with iron ions. The findings of this work will aid in guiding and optimizing pilot-scale application of ES to AMD treatment.

Cow bones char as a green sorbent for fluorides removal from aqueous solutions: batch and fixed-bed studies

Cow bone char was investigated as sorbent for the defluoridation of aqueous solutions. The cow bone char was characterized in terms of its morphology, chemical composition, and functional groups present on the bone char surface using different analytical techniques: SEM, EDS, N₂-BET method, and FTIR. Batch equilibrium studies were performed for the bone chars prepared using different procedures. The highest sorption capacities for fluoride were obtained for the acid washed (q = 6.2 ± 0.5 mg/g) and Al-doped (q = 6.4 ± 0.3 mg/g) bone chars. Langmuir and Freundlich models fitted well the equilibrium sorption data. Fluoride removal rate in batch system is fast in the first 5 h, decreasing after this time until achieving equilibrium due to pore diffusion. The presence of carbonate and bicarbonate ions in the aqueous solution contributes to a decrease of the fluoride sorption capacity of the bone char by 79 and 31 %, respectively. Regeneration of the F-loaded bone char using 0.5 M NaOH solution leads to a sorption capacity for fluoride of 3.1 mg/g in the second loading cycle. Fluoride breakthrough curve obtained in a fixed-bed column presents an asymmetrical S-shaped form, with a slow approach of C/C ₀ → 1.0 due to pore diffusion phenomena. Considering the guideline value for drinking water of 1.5 mg F^-/L, as recommended by World Health Organization, the service cycle for fluoride removal was of 71.0 h ([F^-]_feed ∼ 9 mg/L; flow rate = 1 mL/min; m _sorbent = 12.6 g). A mass transfer model considering the pore diffusion was able to satisfactorily describe the experimental data obtained in batch and continuous systems.

Synthesis, characterization and evaluation of two crosslinked polymeric resins and their comparison with walnut shell in oil removal from water

The aim of this paper was to compare two kinds of adsorbents (walnut shell and polymeric resins) in terms of their efficiency to remove oil from water, since walnut shell losses weight during the process requiring interruption, while polymeric resins do not. Polymeric resins based on glycidyl methacrylate and divinylbenzene (GMA-DVB) and styrene and divinylbenzene (STY-DVB) were synthesized and characterized. All adsorbents were tested by continuous flow process, eluting 3,000 bed volumes of synthetic oily water, and the oil content was monitored by fluorescence spectroscopy. Although the walnut shell presented high efficiency (∼94%), STY-DVB was even better (∼100%) besides presenting better mechanical resistance. Moreover, polymeric resins, mainly when based on GMA, can be chemically modified to remove specific contaminants still remaining in water after conventional treatment.

Partial oxidation of sewage sludge briquettes in a updraft fixed bed

The fixed bed reaction of sewage sludge briquettes was investigated to evaluate the potential applications to gasification, combustion, or production of biochar as soil ameliorator. The reaction had two distinctive stages: ignition propagation and char oxidation. The ignition front of the sludge briquettes propagated at a lower speed, which significantly increased the stoichiometric ratio of overall combustion reaction and peak temperatures. The ignition front also had irregular shapes due to the channeling effects. During the char oxidation stage, the sludge ash agglomerated because of the slow reaction rate and increased CO2 formation. Because of low energy content in the product gas, the large briquettes were not favorable for syngas production. In addition, the low burning rates and ash agglomeration could cause problems in the operation of a grate-type furnace for combustion. However, the char accumulated above the ignition front had similar properties with that from pyrolysis under inert atmosphere. Therefore, the fixed bed reaction under partial oxidation conditions can be applied to produce biochar as soil ameliorator from the sludge briquettes without external heat supply.

Numerical simulation of gas concentration and dioxin formation for MSW combustion in a fixed bed

A numerical model was employed to simulate the combustion process in a fixed porous bed of municipal solid waste (MSW). Mass, momentum, energy and species conservation equations of the waste bed were set up to describe the incineration process. The rate of moisture evaporation, volatile matter devolatilization, char combustion, NOx production, and reduction and dioxin formation were calculated and established according to the local thermal conditions and waste property characteristics. Changes in the bed volume during incineration were calculated according to the reaction rate of the process. The simulation results were compared with experimental data, which shows that the incineration process of waste in the fixed bed was reasonably simulated. The simulation results of weight loss and solid temperature in the bed agree with the experimental data, which shows that the waste combustion rate is nearly constant in the middle of the incineration process, and that moisture evaporation takes up most of the time for the overall incineration experiment. The emission of gas species from the bed surface is also agreeably simulated, with O2, CO2, and CO concentrations in flue gas agreeing with the experimental data. The simulation results benefit the understanding of the combustion process in the waste bed as well as the design of incinerator grates.

Process aspects in combustion and gasification Waste-to-Energy (WtE) units

The utilisation of energy in waste, Waste to Energy (WtE), has become increasingly important. Waste is a wide concept, and to focus, the feedstock dealt with here is mostly municipal solid waste. It is found that combustion in grate-fired furnaces is by far the most common mode of fuel conversion compared to fluidized beds and rotary furnaces. Combinations of pyrolysis in rotary furnace or gasification in fluidized or fixed bed with high-temperature combustion are applied particularly in Japan in systems whose purpose is to melt ashes and destroy dioxins. Recently, also in Japan more emphasis is put on WtE. In countries with high heat demand, WtE in the form of heat and power can be quite efficient even in simple grate-fired systems, whereas in warm regions only electricity is generated, and for this product the efficiency of boilers (the steam data) is limited by corrosion from the flue gas. However, combination of cleaned gas from gasification with combustion provides a means to enhance the efficiency of electricity production considerably. Finally, the impact of sorting on the properties of the waste to be fed to boilers or gasifiers is discussed. The description intends to be general, but examples are mostly taken from Europe.

Kinetics studies of uranium sorption by powdered corn cob in batch and fixed bed system

Sorption of uranium (VI) from aqueous solution onto powdered corn cob has been carried out using batch and fixed-bed technique. The experimental results in batch technique were fitted well with pseudo second-order kinetics model. In the fixed bed technique, Thomas and Bohart–Adams models were evaluated by linear regression analysis for U(VI) uptake in different flow rates, bed heights and initial concentrations. The column experimental data were fitted well with Thomas mode (r² = 0.999), but the Bohart–Adams model (r² = 0.911), predicted poor performance of fixed-bed column.

Co-pyrolysis of corn cob and waste cooking oil in a fixed bed

Corn cob (CC) and waste cooking oil (WCO) were co-pyrolyzed in a fixed bed. The effects of various temperatures of 500 °C, 550 °C, 600 °C and CC/WCO mass ratios of 1:0, 1:0.1, 1:0.5, 1:1 and 0:1 were investigated, respectively. Results show that co-pyrolysis of CC/WCO produce more liquid and less bio-char than pyrolysis of CC individually. Bio-oil and bio-char yields were found to be largely dependent on temperature and CC/WCO ratios. GC/MS of bio-oil show it consists of different classes and amounts of organic compounds other than that from CC pyrolysis. Temperature of 550 °C and CC/WCO ratio of 1:1 seem to be the optimum considering high bio-oil yields (68.6 wt.%) and good bio-oil properties (HHV of 32.78 MJ/kg). In this case, bio-char of 24.96 MJ/kg appears attractive as a renewable source, while gas with LHV of 16.06 MJ/Nm(3) can be directly used in boilers as fuel.

Pyrolysis decomposition of tamarind seed for alternative fuel

The conversion of tamarind seed into bio-oil by pyrolysis has been taken into consideration in the present work. The major components of the system were fixed bed fire-tube heating reactor, liquid condenser and collector. The crushed tamarind seed in particle form was pyrolyzed in an electrically heated fixed bed reactor. The products were liquid, char and gasses. The parameters varied were reactor temperature, running time, gas flow rate and feed particle size. The maximum liquid yield was 45 wt% at 400°C for a feed size of 3200 μm diameter at a gas flow rate of 6l/min with a running time of 30 min. The obtained pyrolysis liquid at these optimum process conditions were analyzed for physical and chemical properties to be used as an alternative fuel. The results show the potential of tamarind seed as an important source of alternative fuel and chemicals as well.

Comparison between a fixed bed hybrid membrane bioreactor and a conventional membrane bioreactor for municipal wastewater treatment: a pilot-scale study

A hybrid membrane bioreactor (HMBR) was developed, by adding biofilm support media into a conventional membrane bioreactor (CMBR), and operated in parallel with a CMBR. Results showed that effluent quality was significantly better with the HMBR. The removal efficiencies of COD, BOD5, NH4(+)-N and TN with the HMBR were 84%, 98%, 97% and 75%, respectively, as compared to 80%, 96%, 93% and 38% with the CMBR. There were no differences in phosphorus removal. The membrane fouling rate in the HMBR was on average only 57% of that in the CMBR. The lower concentration of colloidal biopolymer clusters in the HMBR sludge, probably due to their retention by the biofilm, could be partially responsible for this difference. Filterability and settleability of the sludge were also better in the HMBR. Consequently, it is concluded that the addition of fixed support media for biofilm growth can improve the performance of CMBRs.