Char Types Research Articles

A char removal protocol to visualize fiber cross‐sections of carbon/epoxy composites subjected to flame

AbstractPost‐crash fires obscure or destroy critical fracture surfaces needed to determine the origin of aircraft structural failures. Our goal is to eliminate combustion residue from carbon fiber‐reinforced polymer composites to enable fractographic examination during aviation accident investigations. In this work, combustion residues were removed from burned Hexcel SGP370‐8H/8552 woven‐fabric carbon/epoxy specimens by nitric/sulfuric acid oxidations. Scanning electron microscopy identified various types of char obscuring the fiber ends. For char removal, the burned specimens were immersed in a nitric acid/sulfuric acid/water solution (0.18 wt.%, 96.25 wt.%, 3.57 wt.%) at elevated temperatures (75–150°C). Higher temperatures enhanced nitric acid decomposition in this highly acidic, low‐water environment, accelerating char oxidation and progressively enhancing the extent of char removal. At lower temperatures (T < 100°C), char deposits were partially oxidized after 60 mins. At 125 and 150°C, the char was removed within 30 mins of immersion. The epoxy matrix both chemically decomposed and oxidized and the char oxidized during these oxidation treatments. Gas evolution and soluble products dissolved in the HNO3/H2SO4 media. The damage morphology created by the sawing action on the fiber ends, created before flame exposure, remained clearly visible after the acid oxidations. This occurs because oxidation rates at the carbon fiber ends are much slower than the char oxidation in these acid treatments. If the acid treatment temperature raised above 185°C, then this sawing‐induced fiber damage morphology will also be destroyed. This preliminary understanding can be applied to develop a comprehensive forensic analysis procedure for post‐crash fire investigations.Highlights Flame exposure of sawed specimen cross‐sections leads to char formation, obscuring fiber damage morphologies. HNO3/H2SO4 oxidations at elevated temperatures (75–150°C) resulted in char removal from fiber ends. Higher temperatures (T = 125 and 150°C) accelerated char oxidation. The sawing of carbon/epoxy composites caused extensive fiber damage and ply delamination. Residual decomposed resin matrix and char oxidized faster than the carbon fibers and the fiber sawing‐induced fiber damage morphologies created before flame exposure and were preserved after char removal.

Environmental impacts estimation by life cycle assessment of bioanodes fabricated from devilfish bone chars and their application in microbial fuel cells to produce bioenergy

ABSTRACT This study estimated the environmental impacts by life cycle assessment (LCA) of bioanodes fabricated from devilfish bone chars and their application in microbial fuel cells (MFC). Two types of devilfish bone chars were obtained by calcination using nitrogen (BCN) and air (BCA) as purge gases. Two bioanodes were fabricated with BCN and BCA and applied independently in MFC to produce bioenergy from ibuprofen and carbamazepine biodegradation. LCA was performed using the methodology ISO 14,040. 1 kg of fabricated bioanode and 1 kWh of produced bioenergy were the established functional units, integrating a detailed inventory of the materials’ fabrication and application in MFC. The impact assessment was made with SimaPro 9.2 software and the ReCiPe 2016 Midpoint (I) method, considering 18 impact categories. Results showed that the bioanode fabricated with BCN has less environmental impacts (1.09 times) than BCA, finding the highest impact in the categories of human carcinogenic toxicity (1.04 kg 1,4-DCB) and human non-carcinogenic toxicity (13.60 kg 1,4-DCB). The environmental impacts in MFC-Ibuprofen were 3.1 times higher than MFC-Carbamazepine in the same impact categories, with 12.76 kg 1,4-DCB and 168.34 kg 1,4-DCB, respectively. Therefore, it is recommended to use BCN to fabricate the bioanode and to apply it in MFC to produce bioenergy from carbamazepine biodegradation. Although the LCA was performed with data obtained at a laboratory level, the results provide information on the environmental impacts that could be generated if both processes are transferred on a large scale, identifying opportunities for improvement to reduce these impacts.

The role of physicochemical marble processing wastewater treatment sludge in the production of new generation pyrolysis char from waste polypropylene

ABSTRACT The effects of marble processing wastewater physicochemical treatment sludge (K1) on polypropylene (PP) waste pyrolysis were investigated by lab-scale batch pyrolysis system. PP-K1 proportions and pyrolysis temperature were studied as variables and both were found to have influences onto pyrolysis char, oil/tar, gas fractions distribution, as well as pyrolysis char characteristics (determined via SEM, EDX, FTIR, TGA and XRD analyses). The influence of K1 could be related to its high mineral composition (CaCO3, CaMg(CO3)2 and (Mg0.03Ca0.97)(CO3)) which also detected in the char products. K1 acts as catalyst and remained unchanged in thermochemical reactions below 700°C. The main thermal degradation of PP occurs around 400–470°C, although it starts at about 300–350°C, whereas, K1 resulted in more thermal degradation at 300°C pyrolysis. As K1 dose increased, pyrolysis chars became more thermally stable with the pyrolysis temperature. Diverse types of chars in terms of porosity, thermal strength and chemical structure were produced with PP + K1 as compared to the PP chars. For example, with 10%–20% K1 doses, the chars are in aromatic structure while chars become aliphatic when K1 dosage increased to 30% or above. The structural diversity made these chars new products that can be used as raw material for subsequent purposes. This study provided a basis for the chars’ physical and chemical properties which are needed for further research to develop new generation evaluation areas for them. Therefore, a new symbiotic upcycling approach has been presented for PP wastes and marble processing wastewater treatment sludge.

How the physio-chemical properties of char from the pyrolysis of Automotive Shredder Residue (ASR) influences its future uses

Abstract Pyrolysis of ASR is an emerging technology which may increase circularity in End-of-Life Vehicle (ELV) waste recycling. To scale up from the current pilot scale, physiochemical characterisation of the by-products is required to determine their utilisation. This paper explored how the physiochemical properties of char from different pyrolysis fractions influence secondary uses. ASR was pyrolysed in a pilot-scale unit capable of processing 100 kg h−1 at 900 °C, producing 480 kg of char from which samples were taken for analysis. Three types of pyrolysis char were identified: (i) coarse char (CC) (ii) medium char (MC) and (iii) fine char (FC). Physical (particle size, moisture content and surface analysis) and chemical (calorific value, organic and inorganic elemental analysis) analysis was conducted. Physical and chemical differences were determined between char fractions: CC had the highest particle size (800 µm; mean 353.5 µm) calorific value (14,544 kcal g−1) and metal concentration; the relationship was CC > MC > FC. Organic elemental analysis indicated %C was highest under FC (80.29 %) and %S was highest in CC (1.04 %). Findings from this experiment provided initial insight into the differences in properties of char fractions from ASR pyrolysis. Potential future uses in char commercial markets were evaluated, with upgrading recommendations provided.

The effect of Na/K on the NO adsorption behavior and heterogeneous reduction of internal nitrogen-containing char: A DFT study

Sodium and potassium in high alkali coal have an effect on the heterogeneous reduction of NO with char. The microscopic mechanisms of the effect of Na and K on the adsorption behavior and heterogeneous reduction roads of NO on the surface of internal nitrogen-containing char were investigated at the GGA-PBE level using DFT. The adsorption energy of NO on the surface of nitrogen-containing char doped with Na and K was calculated using zigzag, armchair and saturated structures, and the reaction path of Z-N-2 with NO was also calculated. The results showed that the adsorption effects of the three types of nitrogen-containing char on NO ranked from strong to weak were: Z-N > A-N > G-N. The addition of Na and K both promoted the adsorption of NO with char structure. The highest energy barrier for the reaction of the Z-N-2 structure with NO was 232.80 kJ/mol, which decreased to 180.52 kJ/mol when Na doped and 176.04 kJ/mol when K doped. The exotherm of the reaction increases from 378.59 to 1245.26 kJ/mol, it appears that the addition of sodium and potassium facilitates the reaction. The study will provide a theoretical pavement for the continued study of the heterogeneous reduction process, which is of great significance for the clean use of high alkali coals.

Surface functional groups and degree of carbonization of selected chars from different processes and feedstock.

The knowledge of the structural and chemical properties of biochars is decisive for their application as technical products. For this reason, methods for the characterization of biochars that are generally applicable and allow quality control are highly desired. Several methods that have shown potential in other studies were used to investigate two activated carbons and seven biochars from different processes and feedstock. The chars were chosen to cover a wide range of chemical composition and structural properties as a hardness test for the analytical methods used in this study. Specific problems connected with the pretreatment of samples and drawbacks of some methods for some types of chars could be identified in an integrated consideration of the results from different methods. None of the spectroscopic methods was found to be suitable for the quality control of all types of chars. The most valuable results were obtained by chemical analysis that, however, required the complete determination of the main elements, including that of oxygen, and of inorganic components for adequate results. The combination of X-ray photoelectron spectroscopy (XPS) and FT-IR spectroscopy allows a rough characterization of surface functional groups, but cannot discriminate aliphatic and aromatic OH groups. FT-IR might be a suitable method for the quality control of biochars made at lower temperature. The results of Raman spectroscopy did not well correlate with the amount of sp2 hybridized carbon determined by XPS. A better correlation of XPS data was found with the electrical polarization determined by the method of spectral induced polarization that was used for the first time in conjunction with extensive analytical characterization.

Intrinsic combustion kinetics of rapid-pyrolysis Zhundong coal char

Driven by the demand for accurate intrinsic kinetics for the prediction of the combustion rate of purely fired Zhundong coal (ZDC) in a slag tapping boiler, the surface activation function (SAF) and intrinsic kinetic parameters of two types of rapid-pyrolysis ZDC chars were revealed via the isothermal and nonisothermal thermogravimetric analysis methods. The isothermal kinetic results show that the activation energy (E), reaction order and SAF of these two chars were the same, at 146 kJ/mol, 0.78 and X0.44 (1 – X)−0.48, respectively. Therefore, the difference in the intrinsic reaction rate between these two chars was caused only by the different pre-exponential factors, which are mainly influenced by the specific surface area and catalytic elements in char ash. Nonisothermal kinetic parameters were obtained via the isothermal model-fitting method (ISOM), thereby using the isothermal SAF to fit the nonisothermal data at different heating rates (βs). The results indicate that the E values of the two chars were 148.95 ± 3.12 kJ/mol and 146.16 ± 1.66 kJ/mol, indicating that β has little influence on E. These measured values are consistent with the isothermal E values, so the ISOM is suitable for the determination of the nonisothermal kinetics of rapid-pyrolysis char combustion.

Application of Taguchi optimization for evaluating the capability of hydrochar, biochar, and activated carbon prepared from different wastes in multi-elements bioadsorption

Adsorption processes play important roles in the removal of metals from wastewaters. A laboratory experiment was conducted to find out effective factors in improving biosorption removal of heavy metals (HMs) using three char types (hydrochar (HC), biochar (BC), and activated carbon (AC)) prepared from different wastes (coffee, tomato, & sesame wastes) using Taguchi optimization. Metals adsorption was investigated at initial concentrations of 50,100, & 200 mg L−1 under three different temperatures (15, 25, & 35 °C). Results of ANOVA regarding metal adsorbtion efficiency (qe) showed that the first rank among the tested factors belonged to the initial concentration. According to the results, the level of 200 mg L−1 had the highest qe for the four metals studied, which was in the range of 1746–1992 mg g−1. The second rank for Cd and Pb was related to the char types, but for Zn and Ni was related to the temperature. HC was selected as the optimal bioadsorbent for Cd, Pb, & Zn. The signal to noise ratio (SNR) value for Ni was in the range of 59.21–69.84 while for the other HMs it was in the range of 53.85–65.99. Based on the SNR main effects, the optimal levels in the adsorption of studied HMs were HC, coffee or tomato waste, 200 mg L−1, 25 or 35 C for char type, source, initial concentration, and temperature, respectively. The results related to FTIR showed that the highest number of functional groups was related to HC and the coffee and tomato chars. According to SEM images, the number of pores in the AC and BC obtained from coffee and tomato wastes was more than in the sesame waste. Results of present study revealed high capability of HC prepared from coffee and tomato wastes in bioadsorption removal of HMs.

Experimental study on no heterogeneous reduction by char

The NO heterogeneous reduction by char is one of the most prominent options to control NOx emissions from coal-fired power plants. Experiments on the char-NO heterogeneous reaction were carried out in an electrically heated fixed-bed reac-tor to investigate the effect of temperature, type of char, pretreatment method, additives and reaction atmosphere on the NO reduction capacity of char. The re-sults showed that temperature plays a crucial role in the NO reduction by differ-ent char. The kinetic analysis showed that char-NO heterogeneous reaction is controlled by chemical kinetic below Tt and by diffusion kinetic above Tt. The value of transition temperature Tt depends on the types of char and ranges from 600?C to 800?C. The synergistic effect of specific surface area, mineral abun-dance and reactivity combine to result in the reduction efficiencies of different char. Oxygen has a promoting effect on the char-NO heterogeneous reaction, and the oxygen content of the promoting peak moves to low oxygen content with in-creasing temperature. At 1050 ?C, the denitrification efficiency at 0.25% O2 con-tent is 12.7% higher than that under oxygen-free conditions. At high tempera-tures, the promotion of the char-NO heterogeneous reaction by CO and the inhi-bition of the reaction by CH4 were more obvious.

Evaluation of Fluoride Adsorption Mechanism and Capacity of Different Types of Bone Char.

The fluoride adsorption capacity of three types of bone char (BC), including cow BC (CBC), chicken BC (CKBC), and pig BC (PBC), was examined. At the optimum charring conditions (temperature and time), PBC had the highest hydroxyapatite (HAP) content (0.928 g-HAP/g-BC), while CBC had the highest specific surface area (103.11 m2/g-BC). CBC also had the maximum fluoride adsorption capacity (0.788 mg-F/g-HAP), suggesting that fluoride adsorption capacity depends more on the specific surface area of the BC than the HAP content. The adsorption data of CBC, CKBC, and PBC fit well with the pseudo-second-order model and the Langmuir isotherm. The maximum fluoride adsorption capacity of BC reached the maximum value when the solution had a pH of approximately 6.0. Lastly, the highest fluoride desorption occurred when the BCs were soaked in solutions with a pH higher than 11.0.

Experimental study of char gasification characteristics with high temperature flue gas

To explore the feasibility of converting oxy-fuel combustion flue gas into valuable syngas through char gasification process, the reactivity of three types of char (bituminous coal char, biochar, and waste char) were experimentally studied under atmospheric pressure in a fixed-bed reactor. The effects of flue gas flow rate and temperature, CO2/H2O/O2 ratio, char types on the char gasification characteristics were mainly investigated. It was found that when the flue gas temperature is 1200 °C or even higher, no matter which char is used, >90% CO2 conversion rate can be reached in line with the Boudouard equilibrium. The reactivity of biochar-H2O is relatively higher than that of waste char-H2O. Besides, 5% oxygen ratio in CO2/H2O mixture is preferred to promote the gasification reaction to some degree. It is important to balance the fixed carbon conversion rate and CO/H2 yield in syngas to decide the optimum residence time of char. Overall, it is a novel way of CO2 reduction and waste resources utilization.

Catalytic steam gasification of food waste using Ni-loaded rice husk derived biochar for hydrogen production

The disposal of food waste (FW) is a major cause of environmental contamination. This study reports an environmentally friendly FW disposal method in the form of catalytic steam gasification using various types of Ni-loaded chars (untreated char, steam-treated char, and ZnCl2-treated char). The results were also compared with the gasification results from the Ni catalysts supported on commercial α-alumina (Ni/α-Al2O3). The Ni/steam-treated char showed the maximum hydrogen generation (0.471 mol/(g feedstock•g cat)) because of the high reducibility, high nickel dispersion, large amount of inherent K and Ca, and moderate surface area. The overall gas and H2 yield were observed in the following order: Ni/steam-treated char > Ni/ZnCl2 treated char > Ni/untreated char > Ni/α-Al2O3. Brunauer-Emmett-Teller analysis of various catalysts showed that the treated chars have a mesoporous structure, and the X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy – energy dispersive spectroscopy showed that the presence of silica in the chars providing the stable support for the Ni loading and prevented coke formation. The chars obtained from biomass pretreatment could be a potential solution for preventing coke formation at high temperatures, thereby increasing the gas yield and enhancing hydrogen generation.

An Intensification of Biomass and Waste Char Gasification in a Gasifier

Gasification is considered a clean and effective way to convert low quality biomass to higher value gas and solve various waste utilization problems as well. However, only 80% of biomass is converted through thermal processes. The remaining part is char, which requires more time for conversion and in that case reduces the efficiency of gasifier. Seeking to optimize the process of gasification, this work focuses on the intensification of residual char gasification in a gasifier. For this purpose, three different types of char prepared from wood, sewage sludge and tire were examined under different conditions in a lab-scale gasification setup. Results showed that the air flux increase from 0.11 kg/(m2s) to 0.32 kg/(m2s) intensified the gasification process and the gasification rate increased from 0.8 to 2.61 g/min with the decrease of duration of wood char gasification by 72%. An additional introduction of pyrolysis gas into the char gasifier led to decreased bed temperatures, but the gasification rate increased from 0.8 to 1.25 g/min and from 2.61 g/min to 2.83 g/min, respectively, for the wood char and the sewage sludge char. Moreover, the use of pyrolysis gas coupled with air as the gasifying agent enhanced the composition of produced gas from char, and the CO2 concentration decreased by 1.68 vol% while the H2 concentration increased by 2.8 vol%.

Char derived from sewage sludge of hydrothermal carbonization and supercritical water gasification: Comparison of the properties of two chars

Supercritical water gasification (SCWG) is considered a promising technology for sewage sludge (SS) treatment and utilization; however, char produced by a side reaction has become a bottleneck in SCWG. In this study, SS and its model compound (10% humic acid) were treated in an autoclave by SCWG at 400 °C for 30 min and by hydrothermal carbonization (HTC) at 250 °C for 300 min. The char yield was 15.4% in SCWG and 41.3% in HTC. The chars were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller (BET) analysis, and elemental analysis. By comparing the properties the char produced by SCWG and the hydrochar produced by HTC, which has been considered a valuable product, the feasibility of using char as an additional product in SCWG was explored. Compared with the char produced by HTC, the char generated in SCWG exhibits a lower BET specific surface area (8.257 and 15.782 m2/g) and combustion activity, a higher proportion of small pores (with pore sizes of 1–2 nm), and greater thermal stability. The formation pathway of the two types of chars is related to both dehydration and aromatization; decarboxylation also occurs in char formation during SCWG. Humus was proved to be related to char formation during the SCWG of SS based on experimental results obtained with the model compound. This work provides insights needed to guide follow-up treatments or utilization of the char produced during the SCWG of SS.

Lead(II) adsorption on microwave-pyrolyzed biochars and hydrochars depends on feedstock type and production temperature

Adsorption of lead(II) using carbon-rich chars is an environmentally sustainable approach to remediate lead(II) pollution in industrial wastewater. We studied mechanisms for lead(II) adsorption from synthetic wastewater by biochars produced by microwave-assisted pyrolysis and hydrochars by hydrothermal carbonization at three temperatures using four feedstocks. Lead(II) adsorption was highest (165 mg g−1) for canola straw biochar produced at 500 °C. Except for chars derived from sawdust, biochars outperformed hydrochars for lead(II) adsorption due to changes in solution pH driven by char pH. As char production temperature increased, lead(II) adsorption decreased in hydrochar mainly due to interaction with aromatic carbon but increased in biochar due to precipitation as hydrocerussite and lead oxide phosphate. Lead(II) adsorption also occurred via surface complexation and cation-ᴨ interaction, as the data fitted well to Freundlich, Langmuir and Temkin models, and the pseudo-first and pseudo-second order kinetic models, depending on feedstock type and production temperature. More than 80% of lead(II) adsorption occurred in the first 3 h for both types of chars; with a few exceptions, adsorption continued for almost 24 h. We conclude that production method, production temperature and feedstock type are crucial factors to consider in designing chars as adsorbents for removing lead(II) from wastewater.

Distribution and Mode of Occurrence of Co, Ni, Cu, Zn, As, Ag, Cd, Sb, Pb in the Feed Coal, Fly Ash, Slag, in the Topsoil and in the Roots of Trees and Undergrowth Downwind of Three Power Stations in Poland

It is supposed that the determination of the content and the mode of occurrence of ecotoxic elements (EE) in feed coal play the most significant role in forecasting distribution of EE in the soil and plants in the vicinity of power stations. Hence, the aim of the work was to analyze the properties of the feed coal, the combustion residues, and the topsoil which are reached by EE together with dust from power stations. The mineral and organic phases, which are the main hosts of EE, were identified by microscopy, X-ray powder diffraction, inductively coupled plasma atomic emission spectrometry, and scanning electron microscope with an energy dispersive X-ray methods. The highest content of elements was observed in the Oi and Oe subhorizons of the topsoil. Their hosts are various types of microspheres and char, emitted by power stations. In the areas of long-term industrial activity, there are also sharp-edged grains of magnetite emitted in the past by zinc, lead, and ironworks. The enrichment of the topsoil with these elements resulted in the increase in the content of EE, by between 0.2 times for Co; and 41.0 times for Cd in the roots of Scots pine, common oak and undergrowth, especially in the rhizodermis and the primary cortex and, more seldom, in the axle roller and cortex cells.

Investigations on NO reduction with biomass char: Char structural changes during the heat treatment in N2 and subsequent NO/O2 gasification

NO reduction with biomass char was studied from considering its structural properties. Raman, XPS and XRD were employed to characterize the char structure. Three types of biomass chars were used for NO reduction at a fixed bed reactor in NO/O2 at 900 ℃. The results showed that the heat treatment led to an obvious reordering of structures in all chars. There were significant differences between NO and O2 reaction in terms of the char structural changes in aromatic systems, surface groups and crystalline developments. New O-containing groups were formed and could be present as C-O and –COO groups in both the NO and O2 reactions. Two different pathways for char-NO and char-O2 reaction were given, respectively. It is proposed that the reaction channel of NO would be blocked as carbon molecular was firstly surrounded by O2 during NO/O2 reaction. The denitration performance of biomass char should be linked to the structural features of char-HT and the behaviors of char structural changes in the subsequent gasification in NO/O2.

Macro, colloidal and nanobiochar for oxytetracycline removal in synthetic hydrolyzed human urine

Macro (BC), colloidal (CBC) and nanobiochar (NBC) were examined for the particle size effect for adsorptive removal of oxytetracycline (OTC) and co-occurring nutrients, which are present in synthetic hydrolyzed human urine. The surface morphologies and functionality of biochars were characterized using Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface area and Fourier Transform Infra-Red (FTIR) Spectroscopy. Experiments for the removal of OTC were performed at the natural pH (pH 9.0) of hydrolyzed human urine using solid-solutions of 3 types of chars (1 g/L) with a contact time of 5 h, at initial OTC concentration of 50 mg/L where isotherm experiments were investigated with OTC concentrations from 25 to 1000 mg/L. The highest maximum adsorption capacity of 136.7 mg/g was reported for CBC, while BC reported slightly low value (129.34 mg/g). Interestingly, NBC demonstrated a two-step adsorption process with two adsorption capacities (16.9 and 113.2 mg/g). Colloidal biochar depicted the highest adsorption for NH4+, PO43−, and SO42− nutrients. All 3 types of chars showed strong retention with a poor desorption (6% in average) of OTC in synthetic hydrolyzed urine medium. CBC and NBC demonstrated both physisorption and chemisorption, whereas the OTC removal by BC was solely via physisorption. Nevertheless, CBC biochar demonstrated the best performance in adsorptive removal of OTC and nutrients in hydrolyzed human urine and its capability towards wastewater treatment. As the removal of nutrients were low, the treated urine can possibly be used as a safe fertilizer.

Soil amendment with sewage sludge‐derived chars increases C‐sequestration potential and provides N and P for plant growth during a second cropping period with Lolium perenne

AbstractHydrothermal carbonization and dry pyrolysis transform sewage sludge (SS) into nitrogen‐ (N) and phosphorus‐ (P) rich hydrochars (Hyd) and pyrochars (Py), respectively, which may act as slow‐release fertilizers with carbon (C) sequestration potential. Whereas this has been mostly studied with short‐term experiments, this study focused on the cycling of char‐derived N, P and C after ageing during a second grass cropping cycle. Lolium perenne was grown for 3 months in pots on soil mixed with 13C and 15N‐enriched SS, Hyd or Py and allowed to age during a first cropping period of 10‐month incubation. The δ15N of the plants confirmed that even during the second cropping, N derived from the amendments was plant accessible. Higher uptake of N from Hyd than from Py is explained by the lower biodegradability of the latter. Plant growth during the second cropping period was associated with a decrease of total P in all treatments, but only the soils with Hyd and Py evidenced an increase of Olsen P. Thus, during the second cropping, more insoluble P was mobilized from the carbonized residues than P needed for plant growth. Compared to control soils prepared with and without KNO3, higher biomass production was yielded with the amended soils. Hyd proved to have the highest longer‐term N mobilization potential. Following the change in δ13C of the soil, we observed that during the second incubation, independently of their aromaticity, all amendments and the native soil organic matter had comparable turnover rates, although the amount of organic matter with slower turnover added with the amendment increased with aromaticity. A rough estimation of the impact of thermal treatment of SS on its C‐sequestration potential revealed no major differences between char types. The higher fertilization capacity of Hyd, however, indicates that it is a good candidate for soil amendment as long‐term fertilization is combined with a long‐term increase of the SOC pool.Highlights Medium‐term fertilization and C‐sequestration potential of chars from sewage sludge were tested. Hydrochar (Hyd) and pyrochar (Py) provide N and P for plant growth during a second cropping period. Compared to soils with and without KNO3, Hyd and Py increase plant productivity of the second crop. On a long‐term scale, native SOM, amended SS, its aged Hyd and Py show comparable turnover rates.

Experimental study on co-pyrolysis of petroleum coke and coals: Synergy effects and co-gasification reactivity

In this work, the co-gasification reactions of petroleum coke and three Chinese coals were carried out using a thermogravimetric analyzer (TGA) to investigate the influences of blend ratio, coal rank, coal ash and coal char types (in situ formed char and preprepared char) on the synergy effects and co-gasification reactivities during co-gasification. Due to the difference of particle size distribution, petroleum coke particles were filtered from blended chars and tested using a Raman spectrometer and a scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDX). The results indicated that the gasification reaction rate of unreactive petroleum coke was enhanced through co-processing with low rank coals. For preprepared coal char, the catalytic effect of alkaline and alkaline earth metals (AAEMs) of coal ash was the main synergy effect. The in situ formed coal char presented a more significant synergy effect on the enhancement of reaction rate of petroleum coke, which was caused by the carbon structural changes of unreactive petroleum coke particles in co-pyrolysis process, such as less ordered carbon structure, lower graphitization degree, more amorphous carbon structure and more carbon active sites. Moreover, the SEM-EDX results also indicated that significant interactions existed during co-pyrolysis of petroleum coke char and in situ formed coal char.