Sawdust, a versatile, inexpensive, readily available bio-waste: From mother earth to valuable materials for sustainable remediation technologies

Isolation, characterization and response surface method optimization of cellulose from hybridized agricultural wastes

This study explores the utilization of eight readily available agricultural waste varieties in Nigeria-sugarcane bagasse, corn husk, corn cob, wheat husk, melina, acacia, mahogany, and ironwood sawdust-as potential sources of cellulose. Gravimetric analysis was employed to assess the cellulose content of these wastes, following which two selected wastes were combined based on their cellulose content and abundance to serve as the raw material for the extraction process. Response Surface Methodology, including Box-Behnken design, was applied to enhance control over variables, establish an optimal starting point, and determine the most favorable reaction conditions. The cellulose extracted under various conditions was comprehensively examined for content, structure, extent of crystallinity, and morphological properties. Characterization techniques such as X-ray Diffraction, Scanning Electron Microscopy, and Fourier Transform Infrared Spectroscopy were employed for detailed analysis. Compositional analysis revealed sugarcane bagasse and corn cob to possess the highest cellulose content, at 41 ± 0.41% and 40 ± 0.32% respectively, with FTIR analysis confirming relatively low C=C bond intensity in these samples. RSM optimization indicated a potential 46% isolated yield from a hybrid composition of sugarcane bagasse and corn cob at NaOH concentration of 2%, temperature of 45 °C, and 10 ml of 38% H2O2. However, FTIR analyses revealed the persistence of non-cellulosic materials in this sample. Further analysis demonstrated that cellulose isolated at NaOH concentration of 10%, temperature of 70 °C, and 20 ml of 38% H2O2 was of high purity, with a yield of 42%. Numerical optimization within this extraction condition range predicted a yield of 45.6% at NaOH concentration of 5%, temperature of 45 °C, and 20 ml of 38% H2O2. Model validation confirmed an actual yield of 43.9% at this condition, aligning closely with the predicted value. These findings underscore the significant potential of combinning and utilizing agricultural wastes as a valuable source of cellulose, paving the way for sustainable and resource-efficient practices in various industrial applications.

Optimization of organic solid waste composting process through iron-related additives: A systematic review

Composting is an environmentally friendly method that facilitates the biodegradation of organic solid waste, ultimately transforming it into stable end-products suitable for various applications. The element iron (Fe) exhibits flexibility in form and valence. The typical Fe-related additives include zero-valent-iron, iron oxides, ferric and ferrous ion salts, which can be targeted to drive composting process through different mechanisms and are of keen interest to academics. Therefore, this review integrated relevant literature from recent years to provide more comprehensive overview about the influence and mechanisms of various Fe-related additives on composting process, including organic components conversion, humus formation and sequestration, changes in biological factors, stability and safety of composting end-products. Meanwhile, it was recommended that further research be conducted on the deep action mechanisms, biochemical pathways, budget balance analysis, products stability and application during organic solid waste composting with Fe-related additives. This review provided guidance for the subsequent targeted application of Fe-related additives in compost, thereby facilitating cost reduction and promoting circular economy objectives.

Chitosan-based magnetic bioadsorbent beads from eucalyptus sawdust waste for the Direct Violet-51 dye remediation: Eco-friendly strategy and statistical optimization

In the present study, a new application was proposed for the eucalyptus sawdust waste, which is an environmental passive. Three adsorbent materials composed of chitosan (CS), sawdust (CSW), and magnetic beads (CSWF) were developed and used for the Direct Violet-51 remediation. The adsorption testes were optimized based on the variation of the adsorption parameters: (i) pH (2-12), (ii) contact time (5-60 min), (iii) initial dye concentration (10-60 mg L-1), (iv) adsorbent mass (10-100 mg) in 10 mL. The optimized conditions of the adsorption essays showed that the three synthesized adsorbents completely removed the dye from the aqueous medium, but under different experimental conditions. As the main findings in this study, we can highlight the excellent performance of CSW adsorbent material, which promoted maximum removal efficiency of Direct Violet-51 at neutral pH, which is of great importance for the industrial processes. On the other hand, CS and CSWF adsorbent materials exhibited a maximum adsorption efficiency at pH 2. Furthermore, the adsorbent materials were applied in the dye remediation in environmental water samples from the tap water, Marcela dam, and Poxim River, they did not suffer any major matrix interference, whose removal efficiency values varied between 99.8 and 100, 70.7-100, and 98.8-99.5 % for the CS, CSW, and CSWF, respectively. Finally, besides being materials produced from the waste, they can be reused more times, fitting into the concept of circular economy.

A review on the lignocellulosic derived biochar-based catalyst in wastewater remediation: Advanced treatment technologies and machine learning tools

Wastewater disposal in the ecosystem affects aquatic and human life, which necessitates the removal of the contaminants. Eliminating wastewater contaminants using biochar produced through the thermal decomposition of lignocellulosic biomass (LCB) is sustainable. Due to its high specific surface area, porous structure, oxygen functional groups, and low cost, biochar has emerged as an alternate contender in catalysis. Various innovative advanced technologies were combined with biochar for effective wastewater treatment. This review examines the use of LCB for the synthesis of biochar along with its activation methods. It also elaborates on using advanced biochar-based technologies in wastewater treatment and the mechanism for forming oxidizing species. The research also highlights the use of machine learning in pollutant removal and identifies the obstacles of biochar-based catalysts in both real-time and cutting-edge technologies. Probable and restrictions for further exploration are discussed.

Brilliant blue FCF dye adsorption using magnetic activated carbon from Sapelli wood sawdust

Sapelli wood sawdust-derived magnetic activated carbon (SWSMAC) was produced by single-step pyrolysis using KOH and NiCl₂ as activating and magnetization agents. SWSMAC was characterized by several techniques (SEM/EDS, N₂ adsorption/desorption isotherms, FTIR, XRD, VSM, and pH_PZC) and applied in the brilliant blue FCF dye adsorption from an aqueous medium. The obtained SWSMAC was a mesoporous material and showed good textural properties. Metallic nanostructured Ni particles were observed. Also, SWSMAC exhibited ferromagnetic properties. In the adsorption experiments, adequate conditions were an adsorbent dosage of 0.75 g L^-1 and a solution pH of 4. The adsorption was fast, and the pseudo-second-order demonstrated greater suitability to the kinetic data. The Sips model fitted the equilibrium data well, and the maximum adsorption capacity predicted by this model was 105.88 mg g^-1 (at 55 °C). The thermodynamic study revealed that the adsorption was spontaneous, favorable, and endothermic. Besides, the mechanistic elucidation suggested that electrostatic interactions, hydrogen bonding, π-π interactions, and n-π interactions were involved in the brilliant blue FCF dye adsorption onto SWSMAC. In summary, an advanced adsorbent material was developed from waste by single-step pyrolysis, and this material effectively adsorbs brilliant blue FCF dye.

Comparative study for removal of cationic and anionic dyes using alginate-based hydrogels filled with citric acid-sawdust/UiO-66-NH2 hybrid

Nowadays, a big challenge is developing a sustainable and effective method for removing contaminants like dyes from aqueous solutions. In this regard, Zr-based metal-organic framework (UiO-66-NH₂) and sawdust as the ideal adsorbents were used. Due to their low separation in adsorption processes, embedding into alginate and obtaining composite beads are suggested as a suitable strategy. The achieved Ca-alginate/citric acid (CA)-sawdust/UiO-66-NH₂ hydrogel beads were used to compare cationic and anionic dyes removal. This sorbent indicated an excellent selectivity for removing methylene blue versus methyl orange in a binary system. pH = 6, adsorbent amount = 80 mg, methylene blue concentration = 10 mg/L, and contact time = 420 min were achieved as optimal parameters on methylene blue adsorption with an adsorption capacity of about 26 mg/g. The removal process of methylene blue followed linear Freundlich isotherm and nonlinear pseudo-2nd-order kinetic models. The regeneration test demonstrated methylene blue removal efficiency higher than about 89 % after 9 cycles. According to the outcomes, methylene blue could be attached to the adsorbent surface through the electrostatic, hydrogen bonding, and π-π interactions of the aromatic rings. These results confirm the potential of Ca-alginate/CA-sawdust/UiO-66-NH₂ hydrogel beads as a selective bio-sorbent for cationic dye removal.

Adsorption of chlorophenols on activated pine sawdust-activated carbon from solution in batch mode

In this work, a novel adsorbent, activated carbon (PSAC) developed by the activation of pine sawdust's pyrolytic carbon (PSPC), is applied to adsorb 2,4-dichlorophenol (2,4-DCP) and 4-chlorophenol (4-CP). The optimized preparation conditions of PSAC were presented. The results revealed that equilibrium adsorption capacity (q_e) of PSAC was notably enhanced up to threefold compared with PSPC. The adsorbents were characterized by a variety of techniques such as SEM, XRD, FT-IR, and elemental analysis. The key factors (such as adsorbent dosage, pH, salt concentration, temperature, and contact time) influencing the adsorption process were also studied. The adsorption quantities of PSAC for 2,4-DCP and 4-CP were 135.7 mg·g^-1 and 77.3 mg·g^-1, respectively. The equilibrium adsorption of 4-DCP and 4-CP was suitable to be predicted by the Freundlich and Koble-Corrigan models, while kinetic process was better described by the pseudo-second-order kinetic model and Elovich equation. The process was spontaneous. After repeated regeneration of PSAC with ethanol, the adsorption capacity of PSAC was not significantly reduced, indicating that PSAC can be recycled by regeneration after adsorption of 4-CP. This work provides a viable method to use activated carbon as an effective adsorbent for pollutant removal.

Adsorptive Features of Magnetic Activated Carbons Prepared by a One-Step Process towards Brilliant Blue Dye

Water pollution by dyes has been a major environmental problem to be tackled, and magnetic adsorbents appear as promising alternatives to solve it. Herein, magnetic activated carbons were prepared by the single-step method from Sapelli wood sawdust, properly characterized, and applied as adsorbents for brilliant blue dye removal. In particular, two magnetic activated carbons, MAC1105 and MAC111, were prepared using the proportion of biomass KOH of 1:1 and varying the proportion of NiCl₂ of 0.5 and 1. The characterization results demonstrated that the different proportions of NiCl₂ mainly influenced the textural characteristics of the adsorbents. An increase in the surface area from 260.0 to 331.5 m² g^-1 and in the total pore volume from 0.075 to 0.095 cm³ g^-1 was observed with the weight ratio of NiCl₂. Both adsorbents exhibit ferromagnetic properties and the presence of nanostructured Ni particles. The different properties of the materials influenced the adsorption kinetics and equilibrium of brilliant blue dye. MAC111 showed faster kinetics, reaching the equilibrium in around 10 min, while for MAC1105, it took 60 min for the equilibrium to be reached. In addition, based on the Sips isotherm, the maximum adsorption capacity was 98.12 mg g^-1 for MAC111, while for MAC1105, it was 60.73 mg g^-1. Furthermore, MAC111 presented the potential to be reused in more adsorption cycles than MAC1105, and the use of the adsorbents in the treatment of a simulated effluent exhibited high effectiveness, with removal efficiencies of up to 90%.

Using Waste Tire-Derived Particles to Remove Benzene and n-Hexane by Dynamic and Static Adsorption

Scrap tire rubber particles were used and evaluated to adsorb some gaseous volatile organic compounds (VOCs), such as benzene and n-hexane. The results present that the adsorption capacities were 0.18 and 0.072 mg/g for n-hexane and benzene, respectively, in the static adsorption mode; the effective adsorption may be attributed to the carbon black of the tire. The adsorption process is in accordance with the Freundlich isothermal model and Lagergren pseudo-first-order kinetic equation. Correspondingly, the adsorption process is multilayer adsorption analyzed by the intramolecular diffusion model. In the dynamic adsorption mode, the maximum adsorption efficiencies of n-hexane and benzene were 80.7 and 81%, respectively, at flow velocities of 0.1 L/min n-hexane and 0.2 L/min benzene.

Assessment of the impact of diluted and pretreated olive mill wastewater on the treatment efficiency by infiltration-percolation using natural bio-adsorbents

The current study was carried out to treat the olive mill wastewater (OMW) via infiltration percolation process, using low-cost natural adsorbents that could improve the ability of the system to enhance the disposal rate of elimination of pollutant from the OMW. The experimental pilot was composed of three PVC (polyvinyl chloride) columns with 10 cm in diameter and 110-cm height equipped with lateral air entries. Each column was filled with four layers of 10 cm of a mixture of sand (70%), charcoal (20%) and sawdust (10%) respectively. These layers were alternated by four permeable layers of 10 cm of Pouzzolane. To assess the effect of the pretreatment on the efficiency of the system, three types of OMW were used: raw OMW, diluted OMW with domestic wastewater at 1/1(v/v) ratio and OMW pretreated with lime. For the column feed with raw OMW, an average removal of total COD (41%), dissolved COD (54%), NH4-N (40.25%), NO₃^- (15.76%), total phosphorus (55.63%) and orthophosphate (50.84%) was recorded. The results showed that the column feed with diluted OMW with domestic wastewater was the most efficient one with a removal rate that reached 93.2% of total COD, 86.2% of dissolved COD, 92% of polyphenol, 92% of orthophosphate (OP), 97.2% of total phosphorus (TP) and 81% of NH4-N. The pretreatment of OMW with lime gave the lowest removal rate for all the parameters: total COD (34%), dissolved COD (50%), NH4-N (30%), NO₃^- (- 21%), total phosphorus (15.19%) and orthophosphate (9.04%). This study demonstrated that the dilution is a way to optimize the efficiency of the system of infiltration-percolation in treating the OMW.

The effect of torrefaction temperature and catalyst loading in Microwave-Assisted in-situ catalytic Co-Pyrolysis of torrefied biomass and plastic wastes

In the current study, the effect of torrefaction temperatures (125-175 °C) and catalyst quantity (5-15 g) on co-pyrolysis of torrefied sawdust (TSD) and polystyrene (PS) are investigated to obtain value-added products. The role of torrefaction in co-pyrolysis of TSD: PS was analyzed to understand the product yields, synergy, and energy consumption . As the torrefaction temperature increases, oil yield (48.3-59.6 wt%) and char yield (24.3-29 wt%) increase while gas yield (27.4-11.4 wt%) decreases. Catalytic co-pyrolysis showed a significant level of synergy when compared to non-catalytic co-pyrolysis. For the conversion (%), a positive synergy maximum (-2.6) exists at a torrefaction temperature of 175 °C and 15 g of KOH catalyst. To develop the model, polynomial regression-based machine learning was used to predict pyrolysisproduct yields and energy usage variables. The developed models showed significant prediction accuracy (R2 > 0.98), suggesting the experimental values and the predicted values matched well.

In-situ generation of H2O2 by zero valent iron to control depolymerization of lignocellulose in composting niche

Lignocellulosic degradation is a bottleneck of bioconversion during the composting process. In-situ generation of H₂O₂ in the composting system was an ideal method for efficiently promoting lignocellulase degradation, and zero valent iron (ZVI) was concerned because it can generate H₂O₂ by reducing dissolved oxygen. This study focused on the effects of ZVI treatment on lignocellulose degradation, microbial communities, and carbohydrate-active enzymes (CAZymes) genes during composting. Its results indicated that ZVI increased H₂O₂ content during composting, accompanied by the formation of •OH. The degradation rates of lignin, cellulose and hemicellulose in ZVI group (20.77%, 30.35% and 44.7%) were significantly higher than in CK group (17.01%, 26.12% and 38.5%). Metagenomic analysis showed that ZVI induced microbial growth that favored lignocellulose degradation, which increased the abundance of Actinobacteria and Firmicutes but reduced Proteobacteria. At the genus level, the abundance of Thermomonospora, Streptomyces, and Bacillus significantly increased. In addition, glycoside hydrolases and auxiliary activities were important CAZymes families of lignocellulose degradation, and their abundance was higher in the ZVI group. Redundancy analysis showed that the increased H₂O₂ and •OH content was a critical factor in improving lignocellulose degradation. Overall, H₂O₂ as a co-substrate enhanced the enzymatic efficiency, •OH unspecifically attacked lignocellulose, and the increase in functional microbial abundance was the main reason for promoting lignocellulose degradation in composting.

Combustion, Pyrolysis, and Gasification of Waste-Derived Fuel Slurries, Low-Grade Liquids, and High-Moisture Waste: Review

The article discusses the modern achievements in the field of thermal recovery of industrial and municipal waste. The average accumulation rate and calorific value of typical wastes were analyzed. The focus is on the opportunities to exploit the energy potential of high-moisture waste, low-grade liquid components, and fuel slurries. We consider the relevant results in the field of combustion, pyrolysis, and gasification of such fuels. The main attention is paid to synergistic effects, the influence of additives, and external conditions on the process performance. Vortex combustion chambers, boilers with burners, and nozzles for fuel injection, grate, and fluidized bed boilers can be used for the combustion of waste-derived liquid, high-moisture, and slurry fuels. The following difficulties are possible: long ignition delay, incomplete combustion, low combustion temperature and specific calorific value, high emissions (including particulate matter, polycyclic aromatic hydrocarbons), fast slagging, and difficult spraying. A successful solution to these problems is possible due to the use of auxiliary fuel; boiler modifications; oxy-fuel combustion; and the preparation of multi-component fuels, including the use of additives. An analysis of methods of waste recovery in the composition of slurries for fuel gas production showed that there are several main areas of research: pyrolysis and gasification of coal–water slurry with additives of oil waste; study of the influence of external conditions on the characteristics of final products; and the use of specialized additives and catalysts to improve the efficiency of the pyrolysis and gasification. The prospects for improving the characteristics of thermochemical conversion of such fuels are highlighted.