Co-hydrothermal Carbonization Research Articles

Co-hydrothermal carbonization of rape straw and industrial sewage sludge – Applications of hydrochar for N and P adsorptions and for agricultural/horticultural purposes

Reuse of agricultural and industrial wastes simultaneously to prepare hydrochars (HCs) for removal of NH4+ and PO43− in practical sewage without additional wastes produced is still a challenge. Herein, HCs were fabricated by combination of rape straw and industrial sewage sludge to remove NH4+ and PO43− from hoggery effluent. Synthesis conditions were firstly optimized and optimized HC (OPT-HC) was further applied to adsorb NH4+ and PO43−. Monolayer and Pseudo-first-order as well as Pseudo-second-orders were confirmed via adsorption kinetic and isothermal adsorption studies. Morphologies and surface areas of the OPT-HC did not show any transformations before and after adsorption of NH4+ and PO43−. The OPT-HC after adsorption of NH4+ and PO43− (OPT–HC–N/P) was further applied as fertilizer for planting Ping-pong Chrysanthemum. Results indicate that the OPT–HC–N/P can improve comprehensive qualities of the Ping-pong Chrysanthemum such as plant height, fresh, Vitamin C, Chlorophyll, soluble protein and sugar because the OPT–HC–N/P can provide extra N and P elements and also promote to release available K in soil. OPT–HC–N/P treated Ping-pong Chrysanthemum open flowers in advance. Thus, two kinds of wastes were re-utilized to remove N and P in real-life effluent.

Structure evolution characteristic of hydrochar and nitrogen transformation mechanism during co-hydrothermal carbonization process of microalgae and biomass

Co-hydrothermal carbonization (co-HTC) of microalgae and lignocellulosic biomass has high potential for producing nitrogen-rich carbon materials (hydrochar) with relatively high yield. The synergistic effect, hydrochar structure evolution and nitrogen transformation mechanism during the co-HTC process were depicted in depth. The results of the co-HTC process showed that the positive synergy between biomass and microalgae could improve the hydrochar yield and facilitate incorporation of nitrogen into the hydrochar aromatic heterocycles structures. Moderate reaction conditions were beneficial for co-HTC hydrochar nitrogen enrichment and porosity increment, and the optimal nitrogen content and specific surface area reached 3.50% and 5.91 m2/g in co-HTC hydrochars at 240 °C and 1 h. Severe reaction conditions could enhance the formation of stable heterocyclic nitrogen species (reaching 54% at 300 °C). The hydrochar structure evolution and nitrogen transformation mechanism during co-HTC process could be generally divided into two stages. The first stage took place from 180 to 260 °C, and the nitrogen-rich secondary chars could be formed by the interaction of the hydrolysis intermediates. The second stage occurred from 260 to 300 °C, and the previously formed secondary char would be gradually decomposed. This study provides theoretical guidance for regulating the co-HTC process to produce nitrogen-rich carbon materials.

Stabilization of heavy metals in sewage sludge by co-hydrothermal carbonization with biomass bottom ash

Stabilization of heavy metals in sewage sludge by co-hydrothermal carbonization with biomass bottom ash

Co-hydrothermal carbonization of styrofoam and sawdust: fuel properties evaluation and effect of water recirculation on hydrochar properties

Co-hydrothermal carbonization of styrofoam and sawdust: fuel properties evaluation and effect of water recirculation on hydrochar properties

Co-hydrothermal carbonization of polystyrene waste and maize stover combined with KOH activation to develop nanoporous carbon as catalyst support for catalytic hydrotreating of palm oil

Plastic waste is massively generated daily from households, mainly as packaging material, causing serious surrounding ecological problems. The development of plastic waste for higher value-added applications instead of landfilling and incineration has received consideration interest in bioenergy and material science research. Herein, a nanoporous carbon support of nickel phosphide catalyst for palm oil hydrotreating was developed from blended polystyrene waste and maize stover via the Co-hydrothermal carbonization (HTC) coupled with the KOH activation process. The Co-HTC parameters, such as temperature, reaction time, and PS percentage, were studied on the properties of co-hydrochar feedstocks for further activation using the Box behnken design. From the comprehensive characterization results, response surface methodology (RSM) results showed that the rising polystyrene proportion significantly exhibited the higher production yield and fixed carbon of co-hydrochar products, an essential characteristic for porous carbon manufacturing. After activation step, the final nanoporous carbon derived from the co-hydrochar (PMPC) exhibited the highest specific surface area of 1033.58 m2/g with total pore volume of 0.45 cm3/g. Moreover, the PCMC-supported nickel phosphide catalysts were successfully synthesized and tested for the catalytic hydrotreating of palm oil as alternative catalyst. The NiP-PMPC catalyst represents an impressive liquid hydrocarbon yield of 74.68 % with a high green diesel selectivity of 85.92 % at 100 % palm oil conversion. The findings of this study might help develop and utilize blended plastic waste and agricultural waste as an alternate catalytic support for various processes in biofuel and biochemical synthesis.

Co-hydrothermal carbonization of pomelo peel and gasifier coke for production of fuel pellets: Complementarity of feedstocks and synergistic effects

The production of nitrogen fertilizer in China generates a substantial quantity of gasifier coke (GFC) as an industrial by-product, posing challenges for its effective recycling. In this study, a combination of co-hydrothermal carbonization (co-HTC) and pelleting technology was employed to convert pomelo peel (PP) and GFC into fuel pellets. Notably, these two feedstocks, characterized by significantly distinct physicochemical properties, exhibited beneficial complementarity, mitigating the limitations of using a single feedstock for fuel preparation. The severe caking and non-uniformity of PP hydrochar resulted in significant flaws in the pellets prepared through direct blending with GFC. The co-HTC technology significantly alleviated the poor processability of PP hydrochar and the low energy density of PP hydrochar pellet while greatly improving the flammability of GFC and the mechanical strength of GFC pellet. The results demonstrated a significant enhancement in uniformity of hydrochar after co-HTC, leading to a reduction in compression energy consumption to 6.16–7.62 J/g and an increase in pellet energy density to 30.60–35.08 GJ/m3. The ignition temperature and the activation energy of GFC were significantly reduced. The co-HTC technology effectively addressed the challenge of GFC pelletizing by achieving fuel pellets with a compressive strength of 11.89 MPa and a drop resistance of 99.8 %. Interestingly, the co-HTC process showed significant synergistic effects, increasing the energy yield of PP hydrochar to 73.38–92.9 % and effectively reducing the ash and sulfur content in GFC to 4.99–11.92 % and 0.35–0.55 %, respectively. The most pronounced synergistic effects were observed when blending PP and GFC in a 5:5 ratio. The complementarity of feedstocks and the synergistic effects of co-HTC converge to facilitate the conversion of biomass and industrial waste into high-performance fuel pellets.

Co-hydrothermal carbonization with process water recirculation as a valuable strategy to enhance hydrochar recovery with high energy efficiency

This study aims at valorizing the residual aqueous phase from hydrothermal carbonization (HTC) of Sicilian agro-wastes in order to enhance the hydrochar recovery, positively affecting the process energy balance. Process waters (PW) obtained from HTC and co-HTC using orange peel waste and fennel plant residues were used as recycled solvent in experiments carried out at the temperatures of 180 and 230 °C. The results showed that an additional hydrochar formation was promoted during recirculation of solvent, leading to average increments of solid mass yield of 10.5 wt% for tests conducted at 180 °C and 3.9 wt% for 230 °C. After five consecutive recirculation phases in co-HTC runs, the hydrochar yield increased up to 18.2 wt%. The low H/C and O/C atomic ratios values, found after recirculation, indicate that organic acids, accumulated in the PW, may catalyze the process and promote the biomass deoxygenation by boosting dehydration and decarboxylation. The recovered PWs from conversion steps with deionized water were also carbonized in absence of the solid feedstock in order to quantify their contribution in hydrochar formation during recirculation and thus the synergistic interactions. After recirculation, energy recovery averagely augmented by more than threefold, showing that the proposed strategy could significantly improve the sustainability of HTC.

Co-hydrothermal carbonization of pretreated sludge and polyethylene terephthalate for the preparation of low-nitrogen clean solid fuels.

In this work, polyethylene terephthalate (PET) and sewage sludge (SS) were co-hydrothermally carbonized to produce low-nitrogen solid fuels. To minimize the effect of nitrogen, this work introduces a co-hydrothermal carbonization method involving alkali (A), ultrasonic cell disruptor (UCC), and sodium dodecyl sulfate (SDS) for both individual and combined pretreatment of SS and PET. Comparative analysis of the products shows that the combined pretreatment with sodium dodecyl sulfate (SDS) and alkali (A) effectively disrupts the SS cell structure, leading to the loosening of stable extracellular polymeric substances (EPS). This condition is conducive to the release and hydrolysis of proteins during hydrothermal carbonization. Moreover, under conditions where PET serves both as an acid producer and a carbon source, and through parameter optimization at a temperature of 240 °C, reaction time of 2 h, PET addition of 20 wt%, and water addition of 0.6 g cm-3, a high-quality, low-nitrogen clean solid fuel was produced (N: 0.51 wt%, C: 19.10 wt%).

Cohydrothermal carbonization of defatted microalgae and glucose for the production of supercapacitor carbon material

Most research on the utilization of microalgae resources is the preparation of biodiesel, but this method will produce a large amount of defatted microalgae waste. This paper mainly studies the resource utilization of defatted microalgae waste, that is, through the cohydrothermal carbonization (C-HTC) of defatted Chlorella pyrenoidosa (DFCP) and glucose (G), to prepare nitrogen-containing carbon materials for the preparation of supercapacitor electrodes. The effects of feedstock, temperature, time, and G:DFCP mass ratio on the yield and properties of the hydrochar produced from the C-HTC of G and DFCP were examined. The hydrochar yield produced from the C-HTC of G and DFCP was 43 wt%, which is much higher than that of the HTC of G (34.0 wt%) and DFCP (25.5 wt%) alone due to the promotion of Maillard reactions between the derivatives produced from G and DFCP. The specific area and micropore volume played important roles in the specific capacitances of the activated hydrochars rather than the effect of heteroatomic doping. At a current density of 1 A/g, the activated hydrochar produced from the C-HTC of G and DFCP at 200 °C for 5 h (AHC-DFCP+G-200-5) achieved a specific capacity of 220.95 F/g. After 20,000 cycles at a charge density of 2 A/g, this kind of activated hydrochar still maintained an outstanding coulomb efficiency of 100 % and a good capacitance retention of 98.26 %. This study provides a new solution to the high-value-added utilization of defatted microalgae waste and the improvement of the economics of microalgae biorefinery.

Evolution characteristics and mechanism of carbon structure during co-hydrothermal carbonization of sewage sludge and sub-bituminous coal

Co-hydrothermal carbonization (Co-HTC) is a promising method for the conversion of organic solid waste with high moisture content into high-value-added products (hydrochar). Herein, the Co-HTC of sewage sludge (SS) and sub-bituminous coal (SC) was studied, and the structural evolution at different blending ratios and hydrothermal temperatures during Co-HTC was further investigated. The physicochemical structure of the hydrochar was characterized using SEM-EDS, Raman spectroscopy, XPS, FTIR, and 13C NMR. The results indicated that with the blending ratio of SC increasing, the oxygen-containing functional groups and aliphatic content of co-hydrochar decreased, whereas the aromatic structure content and apparent aromaticity increased. Additionally, the numbers of aliphatic branches and aromatic substituents decreased during Co-HTC. Furthermore, the interaction between the SS and SC promoted the expansion of aromatics and removed the oxygen-containing functional groups from the co-hydrochars during Co-HTC. In addition, a potential mechanism for the interaction of SS and SC on the hydrochar carbon structure during Co-HTC was proposed. The small aromatic rings could be linked to other rings by bridges of short-chain aliphatics in SS, which may be the key step in the interaction. The results may contribute to the better understanding of the structural characteristics of hydrochar from SS and SC, and provide a theoretical basis for the resource utilization of solid waste.

Adsorption and reduction of Cr(VI) by N, S co-doped porous carbon from sewage sludge and low-rank coal: Combining experiments and theoretical calculations

Herein, a novel N, S co-doped porous carbon (S5C5-AC) for Cr(VI) removal was prepared by co-hydrothermal carbonization (HTC) of sewage sludge (SS) and low-rank coal (LC) combining with KOH modification. The results showed that S5C5-AC had excellent adsorption performance on Cr(VI), and lower pH value, higher initial concentration and longer contact time were beneficial for Cr(VI) adsorption. The adsorption kinetics and isotherms revealed that Cr(VI) adsorption by S5C5-AC was homogeneous and dominated by chemisorption. The adsorption isotherm showed that the maximum equilibrium adsorption capacity of S5C5-AC for Cr(VI) was 382.04 mg/g at 25 °C. Furthermore, the results showed that the main mechanisms for Cr(VI) removal were the pore filling, electrostatic interaction and reduction. Moreover, the electron transfer mechanism during the adsorption and reduction process was further explored at the molecular and electronic levels by density functional theory (DFT) and front orbital theory (FOT) simulations. The analysis of DFT and FOT indicated that the synergistic effect between S and N functional groups was exhibited during the Cr(VI) removal process. Considering the existence of synergistic effects between N and S functional groups during adsorption, the S and N content and form were modified collaboratively. Increasing the relative content of pyrrolic N may be the most effective pathway for improving removal performance. Besides that, S5C5-AC exhibited excellent adsorption capacity over a high coexisting ion concentration range and various actual water bodies and regeneration performance, which indicated that S5C5-AC had promising potential for the remediation of wastewater in industrial applications.

Clean solid fuel production through co-hydrothermal carbonization of polyvinyl chloride mat and wheat straw with acid assistance: Conversion mechanism and combustion performance

Hydrothermal carbonization (HTC) of polyvinyl chloride (PVC) to produce high-value-added hydrochars as a solid fuel alternative can play a pivotal role in carbon sequestration and energy supply. However, there is unclear for the interaction mechanism and combustion performance of co-hydrochars derived from PVC waste and biomass. In this study, waste PVC mats (PVCM) mixed with wheat straw (WS) were as feedstocks to prepare the co-hydrochars by the acid-catalyzed co-HTC at different hydrothermal temperatures and mass ratios. The presence of WS enhanced the PVCM substitution and prevented the condensation of the PVCM-derived hydrochar aggregation. In turn, PVCM played a stimulative role in the WS decomposition. Meanwhile, the interactions were improved sufficiently in the acidic mediums. The fuel properties and combustion behavior of co-hydrochars were elevated by valid interactions between PVCM and WS. The co-hydrochar obtained using co-HTC at a mass ratio of 1:1 under 240 °C (HC-240–1:1) exhibited the optimal higher heating value (32.72 MJ/kg), splendid dechlorination efficiency (97.41%) as well as worthy fuel ratio (0.89). The combustion process of HC-240–1:1 was more facile and consistent as a result of the elevated ignition and burnout temperatures along with reduced activation energies. Furthermore, the liquid phase products were recycled to assess the reusability. The process water expedited the process of co-HTC, which was confirmed by the improved HHV (32.72 MJ/kg to 39.71 MJ/kg) and mass yield (30.73% to 32.44%). The strategy of PVC waste mixed with biomass through the acid-catalyzed co-HTC was considered a promising way to produce environmentally friendly solid fuels, providing some theoretical basis for the commercialization of co-HTC.

Preparation of carbon materials for supercapacitors in energy storage by direct hydrothermal carbonization of cellulose and pyrazine

In this study, cohydrothermal carbonization (co-HTC) of cellulose and pyrazine for the production of supercapacitor carbon was investigated at heating of 240 °C for 1 h. The effect of pyrazine loading on the yield of the resulting solid product (hydrochar, HC) and the properties of the activated hydrochar (AHC) were studied. The HC yield increased from 54.3 wt% to 67.2 wt% as the pyrazine loading increased from 4 wt% to 20 wt%. Further increasing the pyrazine loading had little effect on the HC yield. Adding acrylic acid (AA) to the reaction co-HTC system further increased the yield of HC, and the higher the amount of AA added, the higher the yield of hydrochar was. The results also showed that the presence of pyrazine improved the physical properties of the HC by increasing the proportion of functional groups and the specific surface area and promoting the pore-forming process of micropores. At 20 wt% pyrazine loading, the activated hydrochar (AHC) by KOH showed a specific capacitance of 195.8 F/g at a current density of 1 A/g. At a current density of 5 A/g, after 20,000 charge–discharge cycles, the capacity retention remained at 99.96 %. After addition of AA, the proportion of functional groups and the specific surface area of the resulting HC were further improved; however, the specific capacitance of the AHC decreased.

Rice husk hydrochar prepared by hydrochloric acid assisted hydrothermal carbonization for levofloxacin removal in bioretention columns

Hydrochars are promising adsorbents in pollutant removal for water treatment. Herein, hydrochloric acid (HCl) co-hydrothermally treated hydrochars were prepared from rice husk biomass at 180 °C via a one-step hydrothermal method. Adsorption behaviors of levofloxacin (LVX) on hydrochars were evaluated. The specific surface area and pore volume of the hydrochar synthesized in 5 mol/L HCl (5H-HC) were almost 17 and 8 times of untreated hydrochar, respectively. The 5H-HC sample exhibited the highest LVX adsorption capability at room temperature (107 mg/g). Thermodynamic experimental results revealed that adsorption was a spontaneous endothermic process. Yan model provided the best description of the breakthrough behavior of LVX in bioretention column, indicating that the adsorption on the samples involved several rate-limiting factors including diffusion and mass transfer. The results show that facile HCl co-hydrothermal carbonization of waste biomass can produce novel hydrochars with high LVX adsorption ability.

The influence of biomass type on hydrothermal carbonization: Role of calcium oxalate in enhancing carbon sequestration of hydrochar

Addressing climate change through effective carbon sequestration strategies is critical. This study presents an investigation into the hydrothermal carbonization (HTC) and co-hydrothermal carbonization (Co-HTC) of invasive plants (IPs) to produce hydrochars to unveil the significant impact of biomass type and unique mineral on the stability of hydrochars. Nine hydrochars were produced from six IPs, utilizing both single and mixed biomass. A key finding is the observable that calcium oxalate forms as a surface mineral during HTC through different characterization techniques, the presence of which notably influenced the stability of hydrochars, resulting in enhanced thermal (highest R50 = 0.81) and chemical (lowest carbon loss rate = 4.02%) stability of hydrochars, possibly acting as a protective layer. Besides, a positive correlation was established between the yield of hydrochars and the lignin content of the original biomass. It is also observed that Co-HTC of plant materials rich in Ca2+ can enhance the formation of calcium oxalate minerals. This is likely due to their synergistic role in the HTC process, promoting the release of more C2O42− and Ca2+. Our results signify the crucial role of biomass composition in the HTC process and spotlight the potential of calcium oxalate in augmenting hydrochar stability. This study offers valuable insights that bolster the theoretical framework for employing hydrochar derived from IPs as a potent material for carbon sequestration.

Analysis of fuel properties of hydrochar derived from food waste and biomass: Evaluating varied mixing techniques pre/post-hydrothermal carbonization

To address the pressing need for reducing carbon emissions linked to fossil fuels, there is an urgent requirement to explore cleaner fuel options as substitutes for traditional fossil energy sources. This study introduces an innovative experimental comparative method where corn stover (CS) is used as an external additive to create three types of samples: mixed feedstocks, mixed-hydrochar (MHC), and co-hydrochar (CHC), in conjunction with food waste (FW). By comparing CHC with MHC, the influence of co-hydrothermal carbonization (co-HTC) synergy on their physicochemical properties and combustion performance has been confirmed. The research results indicate that CHC demonstrates superior attributes in terms of physical and chemical properties, energy output, and combustion behavior. Furthermore, dynamic parameters were determined using the Flynn-Wall-Ozawa (FWO) and Friedman methods. According to the FWO and Friedman calculations, the average activation energy for CHC is 128.5 kJ/mol and 114.3 kJ/mol, which is lower than that of mixed feedstocks and MHC. These research findings suggest that utilizing FW and biomass for the synthesis of CHC results in a lower activation energy, making it more suitable for energy applications. In summary, CHC derived from FW and biomass presents a promising approach for renewable energy production.

Hydrothermal carbonization of mixture waste Gingko leaf and wheat straw for solid biofuel production

Co-hydrothermal carbonization (co-HTC) of ginkgo leaf residues (GLR) and wheat straw (WS) were conducted to investigate the possibility for mutually benefitting the two residues as feedstock to produce solid biofuel pellets. The mass yield, proximate, and elemental analysis of the hydrochar were characterized. The energy consumption during pelletization, pellet density, pellet durability, water resistance ability, and pyrolysis characteristics of hydrochar pellets were evaluated. The results show that when WS blended with 50%, the energy density of pellet increased from to the highest of 26.7 GJ/m3. The ash content decreased from 7.7% to 6.3% when the WS blended with 30%− 70%, while HHV showed a opposite trend. As the WS blended ratio increased from to 30–70%, the high lignin content in WS helped to enhance the mechanical properties of pellet including pellet density, durability, and hardness. The hydrochar pellets from high ratio WS had high devolatilization index indicating increased devolatilization ability. These findings imply adding WS in co-HTC would potentially promote the GLR to manufacture high quality solid biofuel. Overall, the co-HTC of WS and GLR is a promising alternative to transfer solid wastes to renewable fuels.

Adsorption performance on tetracycline by novel magnetic adsorbent derived from hydrochar of low-rank coal and sewage sludge

Herein, a novel magnetic tetracycline (TC) adsorbent (S3C7-Fe) was prepared by co-hydrothermal carbonization (HTC) of sewage sludge (SS) and low-rank coal (LC) combining with K2FeO4 modification. The adsorption performance at different conditions, adsorption kinetics, isotherms and thermodynamics were investigated. The results showed that S3C7-Fe exhibited high TC removal efficiency over a wide pH range (2∼11) and a high coexisting ion concentration range (50∼200 mg/L), and the maximum equilibrium adsorption capacity could reach to 884.04 mg/g. TC adsorption process by S3C7-Fe fitted the Langmuir and pseudo-second-order models, and the adsorption process was homogeneous and dominated by chemisorption. The π-π EDA interaction between the S3C7-Fe and TC molecular was the main mechanism, and pore filling, hydrogen bonding and cation-π complexation also contributed to the adsorption. Besides that, the microscopic interface interaction mechanism between the adsorbent and TC was analyzed both at molecular and electronic levels through theoretical calculations by density functional theory and frontier orbital theory. Interestingly, the results indicated that the oxygen and nitrogen containing functional groups in the adsorbent surface facilitated TC adsorption, and increasing the relative content of COOH and pyrrolic N could be the most effective pathway for improving adsorption capacity.

Upgrading of Corn Stalk Residue and Tannery Waste into Sustainable Solid Biofuel via Conventional Hydrothermal Carbonization and Co-Hydrothermal Carbonization

Upgrading of Corn Stalk Residue and Tannery Waste into Sustainable Solid Biofuel via Conventional Hydrothermal Carbonization and Co-Hydrothermal Carbonization

Co-hydrothermally carbonized sewage sludge and lignocellulosic biomass: An efficiently renewable solid fuel

The objectives of this investigation were to elucidate the potential use of metal oxide-rich sewage sludge obtained from the treated brewery wastewater into a value-added solid fuel via co-hydrothermal carbonization process (co-HTC). Two residue biomass including spent coffee grounds and bagasse were supplied as co-combustion. The effects of sewage sludge and biomass addition on fuel properties were evaluated to optimize the best condition for biocoal-liked production. The chemical composition and mineral phase of solid product were further analyzed. Combustion kinetics analysis including activation energy (E) and pre-exponential factor (A) were derived from thermogravimetric analysis. It was found that the addition of coffee grounds and bagasse enhanced the fuel properties of the solid products, remarkably increasing high heating value (HHV) along with a low ash content, providing an increased fuel ratio of 0.34 – 1.01 and higher HHV as 14.29 – 22.19 MJ/kg. The highest rate of energy recovery was achieved when combining 75 wt% sewage sludge with 25 wt% spent coffee grounds. A substantial decrease of H/C and O/C atomic ratios was distinguished after bagasse addition compared to commercial lignite coal. It was also noticed that the relationship between the sewage sludge and biomass feedstocks during co-HTC is synergistic by increasing the amount of oxidative carbon during the char combustion stage and enhancing the degree of thermal stability. Moreover, it was also emphasized that during co-HTC some carbon and inorganic contents of sludge and lignocellulosic biomass were partially transferred into a liquid phase confirmed by TOC and ICP-OES analyses. A heavy metal leaching toxicity in a liquid product was also determined according to the USA-EPA standard. The combustion reactivity was improved, especially combustion reactivity of the biomass-sewage sludge-derived hydrochar. Interestingly, the hydrochar product was anticipated to possess enhanced safety and stability. Moreover, the co-combustion of hydrochar and coal improved the devolatilization properties and ignition of coal. This strategy revealed that co-hydrothermal process with biomass is a prospective approach to increase the value-added of sewage sludge feedstock as bicoal-like solid fuel.