Thermal Pretreatment Methods Research Articles

Designing Efficient Processes for Sustainable Bioethanol and Bio-Hydrogen Production from Grass Lawn Waste.

The effect of thermal, acid and alkali pretreatment methods on biological hydrogen (BHP) and bioethanol production (BP) from grass lawn (GL) waste was investigated, under different process schemes. BHP from the whole pretreatment slurry of GL was performed through mixed microbial cultures in simultaneous saccharification and fermentation (SSF) mode, while BP was carried out through the C5yeast Pichia stipitis, in SSF mode. From these experiments, the best pretreatment conditions were determined and the efficiencies for each process were assessed and compared, when using either the whole pretreatment slurry or the separated fractions (solid and liquid), the separate hydrolysis and fermentation (SHF) or SSF mode, and especially for BP, the use of other yeasts such as Pachysolen tannophilus or Saccharomyces cerevisiae. The experimental results showed that pretreatment with 10 gH2SO4/100 g total solids (TS) was the optimum for both BHP and BP. Separation of solid and liquid pretreated fractions led to the highest BHP (270.1 mL H2/g TS, corresponding to 3.4 MJ/kg TS) and also BP (108.8 mg ethanol/g TS, corresponding to 2.9 MJ/kg TS) yields. The latter was achieved by using P. stipitis for the fermentation of the hydrolysate and S. serevisiae for the solid fraction fermentation, at SSF.

Impact of hydrothermal pretreatment on anaerobic digestion efficiency for lignocellulosic biomass: Influence of pretreatment temperature on the formation of biomass-degrading byproducts

Anaerobic digestion (AD) of lignocellulosic biomass is appealing because of the abundance and ease of obtaining the biomass locally. However, the recalcitrance of lignocellulosic biomass presents an obstacle in the hydrolysis step of AD and lowers the process efficiency. In this study, sunflower, which is a model lignocellulosic biomass, was pretreated by thermal (hydrothermal pretreatment, HTP) and non-thermal (milling) methods; the methane yield and biodegradability of the pretreated biomass were determined using a series of batch tests. The thermal pretreatment method showed a significantly higher methane yield (213.87–289.47 mL g−1 VS) and biodegradability (43–63%) than those of the non-thermally pretreated biomass, and the optimum pretreatment effect was observed at an HTP temperature of 180 °C. However, at an HTP temperature exceeding 200 °C, the induced formation of 5-hydroxymethylfurfural and furfural significantly lowered the methane yield and biodegradability. This study revealed that the HTP temperature is closely related to the formation of lignocellulosic biomass-degrading byproducts, which potentially hinder the methanogenesis step in AD; severe HTP conditions may have the opposite effect on the AD performance of lignocellulosic biomass.

Thermal, ultrasonic and electrochemical pretreatment methods to enhance the solubilization of organic substance and methane generation in food waste

Food waste accounts for the largest fraction of municipal solid waste, and one-third of the food produced goes to waste. According to experts, the total food waste generation is expected to increase by 44%, by 2025. In this research, thermal, ultrasonic, and electrochemical pretreatments were used to enhance the solubilization and methane generation using food waste as the substrate. Different pretreatment conditions were examined to determine the optimum conditions for each pretreatment. The highest solubilization was observed at 20 V for 40 min with electrochemical pretreatment. Compared to the control, this was a 40–47% increase. For thermal pretreatment, 80 °C for 90 min, was selected as best conditions. The 2 W/mL for 30 min and 20 V for 40 min pretreatments were selected as the optimum conditions for ultrasonication and electrochemical pretreatments, respectively. The optimum buffer concentration was selected as 300 mg per g VS (volatile solids). The thermal pretreatment had the highest cumulative methane yield of 113.19 mL per g VS, which was an 11% increase compared to the control. This study shows the potential use of pretreatments on food waste to increase the solubilization and enhance methane production.

Effect of pretreatment techniques on enzymatic hydrolysis of food waste

Food waste could be acknowledged as an auspicious feedstock for bioethanol production, given its high organic and polysaccharides’ content. In an effort to render enzymatic hydrolysis of food waste more efficient and maximize sugar release, six different thermal, sono-electrochemical, and chemical pretreatment methods were examined. In all cases, starch was solubilized from 26.8 to 42.8% releasing from 1.38 to 2.14 g glucose per 100 g food waste. After 6 h of enzymatic saccharification, the glucose yield was higher than the respective value of the control trial (no pretreatment) for all the experiments, apart from the hydrolysates from thermal autoclaving, implying the presence of possible inhibitory compounds. Saccharification yields ranging 16.43–17.31 g glucose per 100 g raw material after sono-electrochemical pretreatments were not significantly improved and thus if other techno-economic factors are also taken into account, their application may not stand as a viable option. The highest glucose concentrations were observed in food waste hydrolysates that had been subjected to oil extraction with hexane, with 21.66 g glucose per 100 g raw material and 90.30% and 53.75% starch and cellulose degradations, respectively. Thus, oil extraction was qualified as an appropriate pretreatment for food waste, as high glucose yield and starch and cellulose degradations were obtained after enzymatic hydrolysis.

Reverse flotation separation of talc from molybdenite without addition of depressant: Effect of surface oxidation by thermal pre-treatment

The excellent inherent floatability of talc and molybdenite makes them very difficult to be separated in the flotation process. To conquer the problem, for the first time, an attempt was made to separate molybdenite and talc by calcining the ores under the air condition before flotation separation. Micro-flotation test results showed that the natural floatability of molybdenite vanished after thermal pretreatment at above 400 °C. In contrast, for that of talc, it barely changes. A satisfying flotation separation effect of molybdenite and talc in either mixed minerals or molybdenite-talc bulk concentrate was achieved through the thermal pretreatment method. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis indicated that the surface of molybdenite underwent dramatical oxidation after thermal treatment at 400 °C. The formation of MoO3 and reduction in sulfur content on the surface of molybdenite were proposed to result in the poor floatability of molybdenite after thermal treatment.

Comparative study of different thermal pretreatment techniques for accelerated methane production from rice straw

This study emphasizes the use of different thermal pretreatment methods (i.e., hot air oven, hot water bath, autoclave and microwave) on pretreatment of rice straw prior to anaerobic degradation. These pretreatment methods resulted in reasonably high solubilization of recalcitrant biomass. Maximum solublisation was attained by microwave (190 °C; exposure time-4 min) (66.6%) followed by autoclave, hot air oven and hot water bath methods. Accelerated cumulative methane yield of microwave pretreated sample achieved was 367.71 mL/g-VSadded, which was 160.68 mL/g-VSadded higher than the control. Combining this high temperature conditions with lesser exposure time also improved the energy balance of the process. The physicochemical characteristics of pretreated rice straw were investigated by Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), FESEM analysis showed the increased porosity of the rice straw, FTIR analysis showed the omission of hemicellulose from the matrix and with XRD analysis reduced value of crystallinity index supports the destruction of the crystalline matrix.

Selective flotation separation of molybdenite and chalcopyrite by thermal pretreatment under air atmosphere

The flotation separation of molybdenite and chalcopyrite is very difficultly due to their excellent natural floatability. Thermally pretreat minerals under 250 °C before flotation was investigated as a potential approach for the flotation separation of molybdenite and chalcopyrite. The bench-scale flotation tests of single mineral were carried out and showed that chalcopyrite lost its floatability in flotation process. Whereas for molybdenite, it maintained good floatability.Based on the thermal pretreatment method, the flotation separation of molybdenite and chalcopyrite was realized for both mixed binary minerals and Cu-Mo bulk concentrates without addition of depressant. The XPS analysis results showed that the oxidation degree of chalcopyrite was much higher than that of molybdenite. For chalcopyrite, the oxidation products were hydrophilic species, which made it cannot be recovered in the flotation process. For molybdenite, despite slight surface oxidation, the little changes of surface S species made it still can be easily recovered in the flotation process. According to these findings, the thermal treatment method can be potentially applied as an effective route to separate Cu-Mo sulfide ore.

Optimization of Hydrogen Yield from the Anaerobic Digestion of Crude Glycerol and Swine Manure

Crude glycerol and swine manure are residues with exponential production in Mexico, nonetheless, they have the potential to generate hydrogen from the fermentation process. For this reason, this study has evaluated the optimization of hydrogen yield from crude glycerol and swine manure, using the response surface methodology. The response surface methodology helps in the compression of the mixture of crude glycerol/ swine manure, with the production of hydrogen as a result, which improves the yields of the process, reducing variability and time of development. A central composite design was employed with two factors, six axial points and four central points. The two factors evaluated were crude glycerol and swine manure concentrations, which were examined over a range of 4 to 10 g L−1 and 5 to 15 g L−1, respectively. This study demonstrated that the thermal pretreatment method is still the most suitable method to be applied, mainly in the preparation of hydrogen-producing inoculum. The maximum hydrogen yield was 142.46 mL per gram of volatile solid added. It used up 21.56% of the crude glycerol (2.75 g L−1) and 78.44% (10 g L−1) of the swine manure, maintaining a carbon/nitrogen ratio of 18.06, with a fermentation time of 21 days. The response surface methodology was employed to maximize the hydrogen production of crude glycerol/swine manure ratios by the optimization of factors with few assays and less operational cost.

Process simulation of an integrated biomass torrefaction and pelletization (iBTP) plant to produce solid biofuels

Abstract Torrefaction is an important thermal pretreatment method to produce solid biofuels from lignocellulosic biomass to replace coal for sustainable heat and power generation. In this study, a thermodynamic-based process simulation model was developed for an integrated biomass torrefaction and pelletization (iBTP) plant to conduct mass and energy balances and to determine equipment size and design parameters using an Aspen Plus simulation tool. The key unit operations of an iBTP plant consisted of a biomass drying, fuel combustion, torrefaction, grinding, pelletizing, and cooling operations. A solid convective rotary dryer was simulated to study the temperature profiles and moisture content of hot gas and solid biomass along the dryer length. A rotary kiln torrefaction reactor was modeled through pre-defined reactor modules to investigate the main thermal and electrical energy requirements. The reactor output parameters such as mass and energy yield, HHV, and torgas compositions were validated for a torrefaction temperature range of 230–290 °C. The other main unit operations including combustion, grinding, pelletization, and cooling were also simulated to conduct detailed thermodynamic mass and energy balances at an industrial scale (pellet production capacity of 100,000 Mg yr−1) from pine wood chip feedstock. When wood bark is used as an auxiliary fuel over natural gas (base case), a separate solid fuel burner unit was simulated. The total thermal energy consumption for the production of torrefied pellets were ranged from 5.2 to 14.1 MJ kg−1 with the torgas energy contributions of 30–90% for the torrefaction temperature range of 250–290 °C. For the base case torrefaction temperature of 270 °C, the overall thermal and electrical energy consumptions were 7.2 and 0.9, respectively for the Mg of torrefied pellets produced. The developed model can be used to conduct process economics and safety assessments of a commercial scale plant.

Torrefaction after pelletization (TAP): Analysis of torrefied pellet quality and co-products

Torrefaction is a thermal pretreatment method to increase the energy density and to decrease the grinding energy of biomass. In this study, the torrefaction of two types of commercially available wood pellets was carried out in the temperature range of 230–290 °C for 30 min residence time. Torrefaction produces both the solid fuel known as torrefied pellets and the volatile stream known as torgas. The torgas was further separated into condensable liquids, known as tor-liquid and non-condensable gases. The products yield, its compositions and fuel properties at various torrefaction temperatures were also determined. The increase in temperature reduced the torrefied pellet yield from 89 to 52%, while increased the condensable liquid yield from 5 to 23% within the torrefaction study condition. The heating value (24 MJ kg−1) and the volumetric energy density (12.5 GJ m−3) of torrefied pellets at 270 °C were comparable to that of coal for biopower. The increase in torrefaction temperature improved the hydrophobicity (resistance to water uptake), but adversely reduced the pellet density, hardness, and durability of torrefied pellets causing high susceptibility to breakage and fine generation during handling, transport, and storage. Further research is required to improve the quality of torrefied pellets for safe handling and storage. The non-condensable fraction of torgas was mainly composed of carbon dioxide, carbon monoxide, and traces of methane. The condensable liquid was rich in organic acids, ketones, furfural, and levoglucosan, which could be potentially transformed into high-value chemicals and other commercially viable products.

Comparison of Different Electricity-Based Thermal Pretreatment Methods for Enhanced Bioenergy Production from Municipal Sludge.

This paper presents results for a comprehensive study that compares the performance of three electricity-based thermal pretreatment methods for improving the effectiveness of anaerobic digestion (AD) to process municipal wastewater sludge. The study compares thermal pretreatment using conventional heating (CH), microwave (MW), and radio frequency (RF) heating techniques. The effectiveness of the pretreatment methods was assessed in terms of chemical oxygen demand (COD) and biopolymers solubilization, AD bioenergy production, input electrical energy, and overall net energy production of the sequential pretreatment/AD process. The heating applicators for the bench-scale testing consisted of a custom-built pressure-sealed heating vessel for CH experiments, an off-the-shelf programmable MW oven operating at a frequency of 2.45 GHz for MW heating experiments, and a newly developed 1 kW RF heating system operating at a frequency of 13.56 MHz for RF heating experiments. Under identical thermal profiles, all three thermal pretreatment methods achieved similar sludge disintegration in terms of COD and biopolymer solubilization as well as AD bioenergy production (p-value > 0.05). According to the energy assessment results, the application of CH and MW pretreatments resulted in overall negative energy production, while positive net energy production was obtained through the sequential pretreatment/AD process utilizing RF pretreatment.

Simple Thermal Pretreatment Strategy to Tune Mechanical and Antifouling Properties of Zwitterionic Hydrogels.

Zwitterionic hydrogels are promising biomaterials because of their high water content, three-dimensional network structure, and antifouling property. However, it still remains unclear about how mechanical properties of zwitterionic hydrogels affect their antifouling property. In this work, we propose a simple, thermal-pretreatment method to fabricate poly(sulfobetaine methacrylate) (pSBMA) hydrogels with varied mechanical properties that can be readily tuned by thermal pretreatment time and cross-linker density, as well as to correlate their mechanical property with antifouling property. The resulting thermal-treated pSBMA hydrogels show significantly enhanced mechanical properties with tunable compressive modulus and elastic modulus as compared to the untreated hydrogels. A combination of ELISA investigations and short-term cell adhesion assays also confirm that pSBMA hydrogels exhibit superior antifouling properties to resist protein adsorption and cell adhesion. Further analysis shows a linear inversion correlation between elastic modulus and protein adsorption of pSBMA hydrogels, i.e., the hydrogel with the higher elastic modulus exhibits the lower protein adsorption (the better antifouling property). This work not only provides a simple thermal-pretreatment strategy for fabricating pSBMA hydrogels, but also demonstrates multifunctional properties of the pSBMA hydrogels, which possess a great potential to fulfill some biomedical applications.

Enhancement of biogas production from sewage sludge in a wastewater treatment plant: Evaluation of pretreatment techniques and co-digestion under mesophilic and thermophilic conditions

Boosting biomethane production makes it possible to offset the required energy in a wastewater treatment plant. In this research, using batch biomethane potential assays, various techniques including pretreatment, co-digestion, and digestion temperature rise were evaluated to increase the methane productivity of municipal sewage sludge (SS). Between thermal and sonication pretreatment methods, thermal pretreatment was shown to be more efficient and there was no need to pretreat SS for more than 0.5 h. Thermophilic digestion of SS led to 160.8% rise in the methane productivity, compared to mesophilic digestion. The most suitable co-substrate for co-digestion with SS was food waste (FW). FW and SS had little negative synergistic effect, however higher FW concentration caused to higher specific methane yield. Thermal pretreatment was not effective on FW. To evaluate the techniques, a combined cooling, heat and power plant was suggested. The energy recovery balance was positive for all the techniques, but co-digestion was not successful to reduce the levelized cost of energy (LCOE). Unlike co-digestion, thermal pretreatment and digestion temperature rise decreased the LCOE. The thermophilic digestion of SS, pretreated at 90 °C for 0.5 h, resulted in the lowest amount of LCOE by 43.70% reduction, compared to the mesophilic single digestion of non-treated SS.

Influence of Different Pretreatment Methods on Biomass Gasification and Production of Fischer-Tropsch Crude Integrated with a Pulp and Paper Mill

In this paper, the influence on the system performance of different biomass pretreatment methods before gasification and subsequent production of Fischer-Tropsch crude is considered. Entrained flow gasification at high pressure is a well proven technology for coal as feedstock with the benefit of producing a practically tar free raw gas with a close to complete carbon conversion. The short residence time in this type of gasifier requires a fuel, which is relatively dry and has a small particle size, to be pressurized from ambient conditions up to 20-50 bar. The small particle size can be acquired by grinding but this is highly energy intensive and feeding is challenging. Torrefaction is a thermal pretreatment method carried out at around 300 °C which makes the biomass easier to grind, thus requiring less electricity, and makes the material less fibrous, while on the other hand requiring heat for the process. Pyrolysis is a process carried out at around 500 °C which lets the biomass decompose into a gaseous, a liquid and a solid part. The solid part can be grinded and fed into the gasifier together with the liquid and gaseous phases. This will further facilitate the feeding but with a further increased heat demand compared to torrefaction. The different pretreatment methods and their impact on the overall biorefinery energy system have been studied and evaluated using process integration methodology. The results show that the excess heat from an FT process with a biomass input of 300 MW(HHV) can replace the solid fuel boiler in a large chemical pulp and paper mill. With the preconditions given for this study, thermal pretreatment of the biomass can be beneficial in terms of system thermal efficiency.

An integrated microbial electrolysis-anaerobic digestion process combined with pretreatment of wastewater solids to improve hydrogen production

This paper explores an integrated anaerobic digestion/microbial electrolysis cell process (ADMEC) with alkaline or thermal hydrolysis pretreatment methods to improve COD conversion to hydrogen gas.

Influence of torrefaction pretreatment on the pyrolysis of Eucalyptus clone: A study on kinetics, reaction mechanism and heat flow

The adverse nature of biomass requires specific pretreatment processes to better utilize it in bioenergy applications, and torrefaction is one of the most recognized thermal pretreatment methods. In this regard, we studied the effect of torrefaction pretreatment on kinetics, reaction mechanism and heat flow during the pyrolysis of biomass by making a comparative analysis between the pyrolysis of dried and torrefied Eucalyptus wood. Torrefied biomass was produced at three temperatures, namely 250, 275 and 300°C. Pyrolysis was performed at 700°C. The char yield during pyrolysis increased from 22.39 percent to 36.34 percent when the torrefaction temperature was increased from 250 to 300°C. Kinetic analysis showed that torrefied biomass has higher activation energy values than dried biomass. The reported activation energy values for dried biomass were within the range of 165–185kJ/mol, and for the biomass torrefied at 300°C they were within the range of 180–245kJ/mol. We used two different approaches, namely master plots and kinetic compensation parameters, to identify the reaction mechanism. The results showed that torrefaction treatment had an effect on the reaction mechanism of the biomass pyrolysis. The reason could be the degradation of hemicellulose during torrefaction, and thereby the formation of smaller molecules during the pyrolysis of torrefied biomass. The heat flow data from differential scanning calorimetry (DSC) showed that pyrolysis started with exothermic reactions for dried samples, and endothermic reactions for torrefied samples. The results presented provide valuable insights into increasing the understanding of the pyrolysis of torrefied biomass.

Lignite ash: Waste material or potential resource - Investigation of metal recovery and utilization options

Ashes from lignite combustion for power generation contain strategic metals, metalloids and rare earth elements (REE) and may thus be a potential source of industrially demanded metals. The presented project focused on the assessment and utilization of this potential raw material. Lignite ash assessment showed that the largest ash amounts for a potential utilization in Germany are available in the Lusatia region and that these ashes have a high value potential. A stabilized ash taken from the landscape building “Spreyer Höhe”, Lusatia, served as the main sample. For enrichment, separation and mobilization of valuable substances from the lignite ashes mechanical and thermal pre-treatment methods as well as chemical and biological leaching approaches were applied. Mechanical ash pre-treatment provided enriched fractions by different methods but still suffered from low yields of enriched fractions. Thermal ash processing showed multiple significant phase changes compared to original ash. Digestion with sc-CO2 and chemical leaching using HClaq of untreated and thermally treated ash provided high extraction for the metals Al, Ca, Fe, Mg, with the highest values achieved for thermally treated ash. Alternatively, bioleaching was applied using acidophilic Fe/S-metabolizing microorganisms (MO) as well as heterotrophic MO. The results indicated likewise high and partly specific metal mobilizations, e.g. for the elements Al, Ca, Fe, Mg, Mn, V, Zn, Zr and for some REE. A potential utilization was investigated for the original stabilized ash (not treated otherwise) as well as for ash fractions and leaching residues. Two potential utilization routes were identified i) partial substitution of the original resource by original stabilized ash or ash fractions in the production of Al-Fe-solutions applicable for water treatment and ii) usage of original stabilized ash or residues from ash leaching as (reactive) supplement in cement, concrete and mortar production.

Effect of Deep Drying and Torrefaction Temperature on Proximate, Ultimate Composition, and Heating Value of 2-mm Lodgepole Pine (Pinus contorta) Grind.

Deep drying and torrefaction compose a thermal pretreatment method where biomass is heated in the temperature range of 150–300 °C in an inert or reduced environment. The process parameters, like torrefaction temperature and residence time, have a significant impact on the proximate, ultimate, and energy properties. In this study, torrefaction experiments were conducted on 2-mm ground lodgepole pine (Pinus contorta) using a thermogravimetric analyzer. Both deep drying and torrefaction temperature (160–270 °C) and time (15–120 min) were selected. Torrefied samples were analyzed for the proximate, ultimate, and higher heating value. The results indicate that moisture content decreases with increases in torrefaction temperature and time, where at 270 °C and 120 min, the moisture content is found to be 1.15% (w.b.). Volatile content in the lodgepole pine decreased from about 80% to about 45%, and ash content increased from 0.77% to about 1.91% at 270 °C and 120 min. The hydrogen, oxygen, and sulfur content decreased to 3%, 28.24%, and 0.01%, whereas the carbon content and higher heating value increased to 68.86% and 23.67 MJ/kg at 270 °C and 120 min. Elemental ratio of hydrogen to carbon and oxygen to carbon (H/C and O/C) calculated at 270 °C and a 120-min residence time were about 0.56 and 0.47. Based on this study, it can be concluded that higher torrefaction temperatures ≥230 °C and residence time ≥15 min influence the proximate, ultimate, and energy properties of ground lodgepole pine.

Improving methane production from digested manure biofibers by mechanical and thermal alkaline pretreatment

Animal manure digestion is associated with limited methane production, due to the high content in fibers, which are hardly degradable lignocellulosic compounds. In this study, different mechanical and thermal alkaline pretreatment methods were applied to partially degradable fibers, separated from the effluent stream of biogas reactors. Batch and continuous experiments were conducted to evaluate the efficiency of these pretreatments. In batch experiments, the mechanical pretreatment improved the degradability up to 45%. Even higher efficiency was shown by applying thermal alkaline pretreatments, enhancing fibers degradability by more than 4-fold. In continuous experiments, the thermal alkaline pretreatment, using 6% NaOH at 55°C was proven to be the most efficient pretreatment method as the methane production was increased by 26%. The findings demonstrated that the methane production of the biogas plants can be increased by further exploiting the fraction of the digested manure fibers which are discarded in the post-storage tank.

Fungal leaching of valuable metals from a power plant residual ash using Penicillium simplicissimum: Evaluation of thermal pretreatment and different bioleaching methods

Each year a tremendous volume of V-Ni rich ashes is produced by fuel oil consuming power plants throughout the world. Recovery of precious metals existing in these ashes is very important from both economic and environmental aspects. The present research was aimed at investigating bioleaching potential of Penicillium simplicissimum for the recovery of metals from power plant residual ash (PPR ash) using different bioleaching methods such as one-step, two-step, and spent-medium bioleaching at 1% (w/v) pulp density. Furthermore, the effects of thermal pretreatment on leaching of V, Ni, and Fe, as major elements present in PPR ash, were studied. Thermal pretreatment at various temperatures removed the carbonaceous and volatile fraction of the ash and affected the fungal growth and metal leachability. The highest extraction yields of V and Ni were achieved for the original PPR ash, using spent-medium bioleaching in which nearly 100% of V and 40% of Ni were extracted. The maximum extraction yield of Fe (48.3%) was obtained for the pretreated PPR ash at 400°C by spent-medium bioleaching. In addition, the fungal growth in pure culture was investigated through measurement of produced organic acids via high performance liquid chromatography (HPLC). Chemical leaching experiments were performed, using commercial organic acids at the same concentrations as those produced under optimum condition of fungal growth (5237ppm citric, 3666ppm gluconic, 1287ppm oxalic and 188ppm malic acid). It was found that in comparison to chemical leaching, bioleaching improved V and Ni recovery up to 19% and 12%, respectively. Moreover, changes in physical and chemical properties as well as morphology of the samples utilizing appropriate analytical methods such as XRF, XRD, FTIR, and FE-SEM were comprehensively investigated.