Constructing bimetal, alloy, and compound-modified nitrogen-doped biomass-derived carbon from coconut shell as accelerants for boosting methane production in bioenergy system
Abstract
Accelerants can enhance methane production in biomass energy systems. Single-component accelerants cannot satisfy the demands of anaerobic co-digestion (AcoD) to maximize overall performance. In this work, nitrogen-doped bio-based carbon derived from coconut shells, containing bimetallic Ni/Fe nanoparticles, FeNi3 alloys, and compounds (Fe2O3, FeN, and Fe3O4), was constructed as hybrid accelerants (Ni-N-C, Fe-N-C, and Fe/Ni-N-C) to boost CH4 production and CO2 reduction. The cumulative biogas yield (553.65, 509.65, and 587.76 mL/g volatile solids), methane content (63.58%, 57.90%, and 67.39%), and total chemical oxygen demand degradation rate (60.15%, 54.92%, and 65.38%) of AcoD with Ni-N-C (2.625 g/L), Fe-N-C (3.500 g/L), and Fe/Ni-N-C
Keywords
INTRODUCTION
With the rapid growth of cattle farming, cow dung (CD) pollution has become a significant problem. Accumulation of CD leads to the proliferation of a variety of bacteria and pathogens that can seriously affect animal husbandry and human health[1,2]. Therefore, the development of a safe and pollution-free method for handling CD is crucial for environmental protection. Anaerobic digestion (AD) technology is the process of forming combustible mixed biogas and digestate from diverse organic wastes under anaerobic conditions through the decomposition of various microorganisms. However, CD is not suitable as a digestive substrate alone because of its high nitrogen content[3], and the co-digestion of different natural plant wastes and cattle manure has been explored. Aloe is rich in carbon and, as a substrate, can balance C/N of the digestion system[2,4,5]. However, anaerobic co-digestion (AcoD) has drawbacks, including low biogas yield, poor stability, weak growth ability of microorganisms, difficult degradation of stubborn organic matter, and long process cycles[1,6,7]. These problems can be alleviated by applying magnetic fields[3,6], electric fields[8,9], and accelerants[10,11]. Among these methods, adding exogenous accelerants is a practical way to enhance AD performance.
The introduction of metals in AD facilitated the growth of methane-producing bacteria, enhanced degradation of stubborn substrates, and increased biogas yield and yield potential. Córdova-Lizama et al. found that Co nanoparticles and zero-valent iron stimulated enzyme activity, promoted the degradation of stubborn substrates, and maintained sufficient stability[12]. Abdelsalam et al. reported that zero-valent iron increased biogas and methane production, shortened the lag stage, and stimulated microbial growth[13].
The biochar has been widely applied in AD owing to its simple processing, low cost, and excellent physical and chemical properties[4,9,17]. Chen et al. found that biochar could boost the conversion of ethanol to methane, possibly due to the stimulation of DIET in co-cultures of Geobacter metallireducens with Geobacter sulfurreducens or Methanosarcina barkeri[18]. Wang et al. indicated biochar extracted from sawdust can promote methane production and volatile fatty acid (VFA) degradation, confirming that biochar can assist the DIET process[19]. They explored that the biochar prepared from corn straw enhanced the AD performance of kitchen waste, which contributed to enhanced DIET using biochar as an electronic mediator or shuttle[20]. These works proved that biochar can stimulate DIET and promote digestion performance. However, the pristine biochar had a limited effect on CH4 production and CO2 reduction.
Because the size of the N atom is equivalent to that of the C atom, N is typically introduced into the carbon matrix to alter its electron distribution[21-26]. Among them, the source of bio-based carbon or biomass-derived carbon included coconut shells, aloe peel, acorn shell, corn cob, sawdust, and walnut shell, and these biomass-derived carbon promoted AD performance[2-6,8,27-30]. Coconut shells, as a widely distributed biomass waste with high carbon content and low ash content, contain high lignin content (30-49 wt.%) and carbon content (53-64 wt.%) and low H/C ratio and O/C ratio, which is very suitable as a carbon source to synthesize the biomass-derived carbon. However, the low stability of N-doped biochar hinders its practical application in real life. Coupling N-doped biochar with metals possesses the potential to enhance its performance. Therefore, many researchers have prepared metal- and N-co-doped biochar; however, most studies have applied these materials in the field of batteries. Little research has been conducted on degradation of organic contaminants. Xu et al. produced Fe/N co-doped biochar extracted from sawdust, which showed excellent oxidative reducibility and high stability owing to its high specific surface area and abundant defects and the synergistic effect between Fe and N doping while achieving efficient degradation of organic pollutants[31]. Li et al. studied high stability, reusability, and adaptability of Fe/N co-doped biochar for degradation of various pollutants, thereby increasing its potential for practical applications[32]. Owing to their excellent oxidative reducibility, stability, and degradation properties, metal- and N-co-doped biochar is expected to be used as accelerants in AcoD systems.
Aside from metals and biochar, transition metal compounds promote microbial growth and accelerate electron transfer[33-36]. Li et al. found that transition metal carbides increased biogas yield, total chemical oxygen demand (TCOD) degradation rate, and total Kjeldahl nitrogen (TKN) concentration[10]. Jia et al. reported that titanium nitride and titanium oxide as electron carriers accelerated electron transfer[6]. Li et al. investigated that zero-valent iron nanoparticles stimulated the secretion of proteins and humus in extracellular polymers and promoted the DIET process in AD systems[34]. Wang et al. researched W2N and W18O49 as mediators of electron transfer and established an efficient interspecific electrical connection, thus alleviating acidification and enhancing the fermentation performance[37]. However, the reaction conditions of transition-metal compounds are difficult to control, and the reaction sites are limited; the product structure is complex, and the compounds easily aggregate[38]. This suggests that transition metal compounds play a crucial role in promoting digestion performance.
In summary, metal particles, N-doped biochar, and transition metal compounds can boost AD performance by facilitating electron transfer and microbial metabolism in the AD process, whereas an individual accelerant cannot maximize its potential to improve AD performance owing to intrinsic physicochemical shortcomings, including the biotoxicity of excess metal particles and the ready agglomeration of transition metal compounds. Therefore, the objective of this work was to exploit a hybrid accelerant containing metals, carbon, and compounds to explore its synergistic effect on AcoD performance. The effects of the hybrid accelerant on the AcoD were evaluated from biogas production, CH4 yield, CO2 reduction, TCOD degradation rate, total solids (TS), volatile solids (VS), thermal stability, and the fertility of the digestate. In addition, mediated electrochemistry was employed to analyze the reduction and oxidation capacity of accelerants. Based on synergistic effects of different components of hybrid accelerants, an understanding of boosted methanogenesis for AcoD systems is illustrated.
EXPERIMENTAL SECTION
Substrate and inoculum
Anaerobic sludge from a wastewater treatment plant in Xi’an was used as the inoculum. The CD was gathered from a breeding farm in Lantian, China, and aloe peel waste was from a beverage processing plant in Yangling, China. The wet weight ratio of 1:3 is based on fresh CD and aloe peel waste as a substrate[2]. Before digestion, fresh CD was domesticated for a week at room temperature. Aloe peel waste was disposed of in water to remove surface dirt, sliced into 1 cm × 1 cm pieces, soaked in 2 M NaOH solution to degrade lignocellulose[4], and then rinsed with water until pH = 7. The detailed characteristics of CD, aloe peel waste, and anaerobic sludge are listed in Table 1.
Characteristics of cow dung, aloe peel waste, and anaerobic sludge
| Parameters | Cow dung | Aloe peel waste | Anaerobic sludge |
| Total solids (TS, % Fresh matter) | 15.74 ± 0.62 | 12.23 ± 0.64 | 4.37 ± 0.10 |
| Volatile solids (VS, % Fresh matter) | 12.65 ± 0.42 | 8.01 ± 0.14 | 3.70 ± 0.12 |
| VS/TS (%) | 80.30 ± 0.49 | 65.49 ± 0.46 | 84.67 ± 1.21 |
| Total chemical oxygen demand (TCOD, mg/g Fresh matter) | 91.17 ± 0.06 | 38.20 ± 0.24 | 43.00 ± 0.62 |
| pH | 7.17 ± 0.03 | 5.79 ± 0.33 | 7.34 ± 0.41 |
| C (% TS) | 52.74 ± 0.39 | 60.21 ± 0.11 | 17.43 ± 0.16 |
| H (% TS) | 5.46 ± 0.09 | 11.05 ± 0.36 | 3.44 ± 0.47 |
| N (% TS) | 4.64 ± 0.04 | 1.77 ± 0.45 | 2.03 ± 0.07 |
| C/N | 11.36 ± 0.37 | 34.02 ± 0.94 | 8.59 ± 0.20 |
Preparation of the hybrid accelerant
A N-doped biomass-derived carbon hybrid accelerant was prepared by a simple pyrolysis process, as shown in Figure 1. First, the coconut shell is crushed into a powder of nearly 2 mm in an electric mixer. Then, in a Fe/Ni-N-C synthesis process (red line), 11.16 g Fe(NO3)3·9H2O (2.0 mmol, Aladdin, 99.99%),
Figure 1. Illustration for the preparation process of Ni-N-C, Fe-N-C, and Fe/Ni-N-C (Blue line: synthesis path of Ni-N-C; Green line: synthesis path of Fe-N-C; Red line: synthesis path of Fe/Ni-N-C).
Experimental set-up
Batch experiments were tested in glass bottles with an effective volume of 400 mL in a constant temperature water bath at 37 °C for 35 days. Previous work has reported an optimal substrate-to-inoculum ratio of 3:7[2,39]. Ni-N-C, Fe-N-C, and Fe/Ni-N-C as accelerants were added in digesters, where the dosage of each accelerant in the reactors was 0.875, 1.750, 2.625, and 3.500 g/L, respectively. No accelerants were added to the control group. To ensure the veracity of the experiment, all batches were repeated twice. Kinetic analysis of biogas production can be found in the Supplementary Material.
Statistical analysis
SPSS software was used to perform statistical analysis. The differences in experimental data are evaluated by using one-way analysis of variance (ANOVA), and a P value lower than 0.05 (P < 0.05) was considered as a significant difference.
RESULTS AND DISCUSSION
Characteristics of materials
The X-ray powder diffractometer (XRD) results are shown in Figure 2A-C. Ni-N-C, Fe-N-C, and Fe/Ni-N-C exhibit a peak at 26°, representing the (002) plane of graphitic carbon. The diffraction of carbon support in the accelerant does not show clearly in the XRD data, which may be due to the strong peaks of Ni, Fe, FeNi3, and other metal compounds covering the diffraction of carbon. Similar situations have been reported in the previous literature[25,31]. Ni-N-C has three peaks (JCPDS: 70-1849) at 45°, 52°, and 76°, responding to the (111), (200) and (220) lattice planes of Ni, respectively. The two distinct characteristic peaks occurring at 45° and 65° of Fe-N-C are attributed to (110) and (200) lattice planes of Fe (JCPDS: 87-0722), respectively. The characteristic peaks appear at 44°, 51° and 76° in Fe/Ni-N-C, matching with the (111), (200), and (220) lattice surfaces of the FeNi3 alloy (JCPDS: 88-1715), respectively. Due to the different diameters of Fe and Ni atoms, the strain in the crystal lattice increased the surface energy and, thus, enhanced redox properties and electron mobility of the FeNi3 alloy[25,40]. The remaining impurity characteristic peaks pattern of Fe-N-C originate from Fe2O3 (JCPDS: 73-0603) and FeN (JCPDS: 75-2127). In addition, Fe3O4 (JCPDS: 75-1609) of Fe/Ni-N-C accelerants may be due to the redox reaction between the pyrolysis and biological carbon[31,41,42]. As expected, bimetal, alloy, and compound-modified nitrogen-doped biomass-derived carbon was successfully constructed.
Figure 2. (A-C) XRD patterns of Ni-N-C, Fe-N-C, and Fe/Ni-N-C, (D) Raman spectra, (E-G) fitted curves of Raman spectra, and (H) the ratio of ID/IG of Ni-N-C, Fe-N-C, and Fe/Ni-N-C.
The Raman spectra of three accelerants exhibit the D-band at 1,340-1,360 cm-1 and the G-band at
The microstructure of hybrid accelerants was determined by field emission scanning electron microscope (FESEM), which has an obvious stacking layer and wrinkle morphology, as depicted in Figure 3A-C. The transmission electron microscope (TEM) and high resolution TEM (HRTEM) of Ni-N-C, Fe-N-C, and
Figure 3. (A-C) SEM images. (D and E) TEM and HRTEM images of Ni-N-C. (F and G) TEM and HRTEM images of Fe-N-C. (H and I) TEM and HRTEM images of Fe/Ni-N-C. (J) HRTEM images for the (111) planes of Ni of Ni-N-C, HRTEM images for (110), (111), and (110) planes of Fe, FeN, and Fe2O3 of Fe-N-C, HRTEM images for (111) and (103) planes of FeNi3 and Fe3O4 of Fe/Ni-N-C. (K) EDS mapping images of Fe/Ni-N-C.
Furthermore, the relevant components of hybrid accelerants are further verified through X-ray photoelectron spectroscope (XPS) measurement. Ni, Fe, C, N, and O can be identified from the full spectrum of XPS [Figure 4A]. The Fe 2p spectrum of Fe-N-C and Fe/Ni-N-C shows two obvious asymmetric bands, namely the low energy (Fe 2p1/2) band and high energy (Fe 2p3/2) band in
Figure 4. (A) XPS measurement spectra, (B and C) Fe 2p XPS spectra of Fe-N-C and Fe/Ni-N-C, (D and E) Ni 2p XPS spectra of Ni-N-C and Fe/Ni-N-C, (F-H) N 1s XPS spectra of Ni-N-C, Fe-N-C, and Fe/Ni-N-C, and (I) schematic diagram of different N types.
The N 1s spectrum of Ni-N-C, Fe-N-C, and Fe/Ni-N-C in Figure 4F-H was fitted to five sub-peaks, namely pyridinic-N (~398.5 eV), pyrrolic-N (~400.9 eV), graphitic-N (~401.8 eV), oxidized-N (~403.2 eV), and
AcoD performance
Biogas production, CH4 and CO2 content
The daily biogas yield obtained by adding different concentrations of accelerants in AcoD systems is shown in Figure 5A-C. Throughout the digestion process, there are two representative peaks; the first peak represents the decomposition of hydrocarbons, and the second peak represents the consuming decomposition of complex crude proteins, as proved in the previous works[5,29,37]. The first peak occurred on days 9-12, days 7-12, and days 10-14, and the second peak occurred on days 21-22, days 14-19, and days
Figure 5. (A-C) Daily biogas yield, (D-F) measured and fitted cumulative biogas production, and (G) cumulative biogas yield of AcoD systems with Ni-N-C, Fe-N-C, and Fe/Ni-N-C.
The results of the cumulative biogas yield experiments were fitted using modified Gompertz models
Furthermore, CH4 and CO2 contents were measured for the experimental group supplemented with
Figure 6. Average CH4 and CO2 contents of the AcoD systems with Ni-N-C, Fe-N-C, and Fe/Ni-N-C accelerants.
pH values, TCOD degradation rate, TS, and VS reduction
The change in pH value is presented in Figure 7A-C. All digestion systems showed similar trends. The initial pH values of different experimental groups varied between 7.12 and 7.34. In the first five days of digestion, pH is reduced, which may be caused by the decomposition and acidification of readily degradable organic matter[10,11,61]. Subsequently, pH began to rise in all the digesters. During the whole co-digestion process, all pH values varied between 6.27-7.59, which was within the appropriate range of 5.5-8.2 for the acetogenesis and methanogenesis[39,62,63]. However, the pH of digesters with accelerants was higher than the control on days 5-10, possibly because the buffer capacity of the non-accelerant system is weak. TCOD degradation rates (41.19%-54.92% for Ni-N-C, 36.39%-60.15% for Fe-N-C, and 49.69%-65.38% for
Figure 7. (A-C) pH values variation and (D-F) TCOD degradation rate of AcoD systems after adding Ni-N-C, Fe-N-C, and Fe/Ni-N-C.
As shown in Figure 8, the initial TS and VS of digestate before digestion were 73.60 and 39.01 g/kg, respectively. TS and VS contents decreased as organic matter began to degrade. At the end of digestion, TS and VS contents remained stable. Then, TS and VS contents were monitored to calculate their reduction. TS and VS reductions were 34.64%-38.48% and 42.51%-51.59% for Ni-N-C, 38.06%-45.60% and
Figure 8. (A-C) TS reduction and (D-F) VS reduction of AcoD systems after adding Ni-N-C, Fe-N-C, and Fe/Ni-N-C.
According to the economic analysis in the previous literature[1,64], by comparing the cost of these accelerants to the income generated from the increased biogas production, these accelerants are not cost-effective. However, this analysis did not take into account the overall benefits as a whole system. For example, these accelerants can reduce COD and solids content, resulting in lower costs for storage and transport of digestate in the industrial-scale biogas plant. The digestate can act as one component of a compound fertilizer, offering an option to reduce the cost of accelerants. In large-scale biogas plants, utilizing the biogas generated for cogeneration can result in additional economic and environmental benefits. Furthermore, to develop renewable energy and combat environmental pollution, the government is introducing policies to reduce the cost and tax burden of large biogas plants.
Digestate performance
Digestate stability
After the digestion, based on excellent biogas production and co-substrate degradation, the digestates with hybrid accelerants of the optimal concentration (2.625 g/L Ni-N-C, 3.500 g/L Fe-N-C, and
Figure 9. (A) TG, (B) Mass loss, (C) DTG, and (D) DSC profiles for the digestate in AcoD systems with accelerants of Ni-N-C, Fe-N-C, and Fe/Ni-N-C.
Nutrient content of the digestate
Fertility was evaluated by measuring TK, TP, and TN contents in 2.625 g/L Ni-N-C, 3.500 g/L Fe- N-C, and 2.625 g/L Fe/Ni-N-C digestate [Table 2]. The total nutrient contents of Ni-N-C, Fe-N-C, and Fe/Ni-N-C digestate were 4.46%, 4.61%, and 4.43%, respectively, which were higher than that of soil. In addition, according to the NY525-2021 standard of the Ministry of Agriculture of the People’s Republic of China, the total nutrient mass fraction (on a dry basis) of organic compound fertilizers must be 4% and above[65,66], which makes the addition of hybridization enhancers as digestate for organic fertilizers promising. In addition, as summarized in Table 2, the total nutrient contents of Ni-N-C, Fe-N-C, and Fe/Ni-N-C digestate were also higher than those (3.54%-3.64%) of the digestate without accelerants[8,9]. The effect of bimetallic accelerants and monometallic accelerants makes no big difference, which may be due to the fact that the substrate in AD systems is the same, and the NPK content in the bimetallic accelerant and monometallic accelerant is not significantly different. In general, digestate can be used as a compound fertilizer to improve soil fertility, improve crop quality, and maintain soil fertility. According to the Chinese risk control standard for soil contamination of agriculture land (GB15618-2018) and the organic fertilizer standard (NY525-2021, China), heavy metal pollutants mainly include Hg, Cr, Pb, Cu, As, and Cd, and most listed heavy metals have the upper limit of higher than 15 mg/kg in soil except for Cd and Hg. Fe and Ni elements are not listed in the risk control standard, and their concentration would also not exceed the risk control standard. Therefore, the digestates with residual nitrogen-doped biomass-derived carbon would not cause environmental risks[3]. Actually, addition of carbon-based byproducts in soil is gaining popularity as a plant growth stimulator, soil quality enhancer, and fostering green land vegetation[67,68]. Therefore, the utilization of digestate as a carbon-based fertilizer can further enhance its added value.
The effect of Ni-N-C, Fe-N-C, and Fe/Ni-N-C accelerants on fertility of digestate
| Experiments | TN (g/kg) | TK (g/kg) | TP (g/kg) | Total nutrient content (%) | Ref. |
| Soil | 0.15-0.20 | 0.06-0.10 | 0.10-0.15 | 0.31-0.45 | [10] |
| Bioorganic fertilizer | 17.10 | 25.40 | 18.00 | 6.05 | [39] |
| NY525-2021 | - | - | - | 4.00 | Chinese agricultural standard |
| Digestate (CK) | - | - | - | 3.64 | [8] |
| Digestate (CK) | 17.07 ± 0.12 | 6.48 ± 0.36 | 11.80 ± 0.08 | 3.54 ± 0.21 | [9] |
| Digestate (BC) | 15.60 ± 0.15 | 11.62 ± 0.21 | 6.45 ± 0.22 | 3.37 ± 0.58 | [4] |
| Digestate (TiMF) | 20.80 ± 0.22 | 6.51 ± 0.04 | 14.86 ± 0.21 | 4.21 ± 0.40 | [3] |
| Digestate (Ni-N-C) | 21.31 ± 0.11 | 13.06 ± 0.18 | 10.23 ± 0.21 | 4.46 ± 0.50 | This work |
| Digestate (Fe-N-C) | 21.66 ± 1.67 | 11.57 ± 0.06 | 12.86 ± 0.21 | 4.61 ± 0.18 | This work |
| Digestate (Fe/Ni-N-C) | 21.22 ± 0.13 | 12.41 ± 0.19 | 10.74 ± 0.21 | 4.43 ± 0.53 | This work |
Mediated electrochemical analysis
Figure 10A-C showed the reduction and oxidation current peaks of Ni-N-C, Fe-N-C, and Fe/Ni-N-C in mediated electrochemical reduction (MER) and oxidation (MEO), respectively. The number of transferred electrons (Q) and the mass of the accelerants are highly correlated (R2 > 0.95) [Figure 10D-F]. Fe/Ni-N-C exhibited the highest electronic exchange capacity (EEC = electron accepting capacity (EAC) + electron donating capacity (EDC), 1.09 μmol e-/g), followed by
Figure 10. (A-C) Electron exchange capacity and (D-F) transferred electron number of Ni-N-C, Fe-N-C, and Fe/Ni-N-C accelerants.
Understanding of enhanced methanogenesis pathway in AcoD systems
This work herein briefly introduced the AcoD process. AcoD is involved in the nutrient metabolism in various bacteria[69]. In the hydrolysis stage, recalcitrant substances are broken down into soluble monomers; in the acidification stage, acetogens metabolize hydrolytic products to acetic acid, hydrogen, and carbohydrates; in the methanogenesis stage, acidification products are converted to CH4 by methanogens. To understand the role of the hybrid accelerant in AcoD systems, a possible strategy was proposed [Figure 11]. Depending on the metabolism of methanogens, methanogenesis can be divided into acetate-dependent CH4 production (Route I: CH3COO- + H+ → CH4 + CO2), H2-dependent CH4 production
Figure 11. Schematic for understanding enhanced CH4 production and CO2 reduction in AcoD systems without and with accelerants.
As shown in Figure 11, CH4 production depends on Route I and Route II in the AD system without accelerants. After adding accelerants, in addition to enhancing Route I and Route II, Route III is proposed. The enhanced methanogenesis was attributed to the enhanced DIET process. Conductive materials can create a bioelectric link between acetogens and methanogens. On the one hand, electron carriers facilitate e- transfer between acetogen and methanogens (Route II); on the other hand, conductive materials enhance the transfer of H+ and e- (Route III), as has been demonstrated previously[3,6,7,72,73].
In this work, N-doped biomass-derived carbon, bimetallic Ni/Fe nanoparticles, and FeNi3 alloys are conductive materials. N-doped biomass-derived carbon containing bimetallic Ni/Fe nanoparticles and FeNi3 alloys as accelerants enhanced methanogenesis. On the other hand, the hybrid accelerant has a high degree of graphitization [Figure 2] and forms many Fe-Nx and Ni-Nx active sites on the surface [Figure 4], which may promote electron transfer between microorganisms. On the other hand, pyridinic-N and pyrrolic-N can promote EDC, and C=O can promote charge transfer between microorganisms and matter in the substrate, enhancing EAC[4,53,56]. Therefore, hybrid accelerants have strong EEC (1.05-1.09 μmol e-/g), which can reduce CO2 to CH4, which is confirmed by CH4 content analysis (hybrid accelerants: 57%-68%, control: 40.13%). For the hybrid accelerants constructed, N species (pyridinic-N, pyrrolic-N, and
In addition, compounds (Fe2O3, FeN, and Fe3O4) in the hybrid accelerant can release Fe2+ and Fe3+ to break down the chemical bonds of recalcitrant organic matter into simpler organic molecules, providing more substrates for methanogens; simultaneously, the released metal ions promote metal enzymes activity, providing necessary nutrients for microorganisms to promote their growth and metabolism, further promoting methane production, which has been verified in previous studies[3,4].
Based on the above analysis, the improvement of AcoD performance by biomass-derived carbon hybrid accelerant is due to the synergistic effect of different components of bimetallic Ni/Fe nanoparticles, FeNi3 alloys, and compounds (Fe2O3, FeN, and Fe3O4). In the future, more experiments will be carried out to study the synergistic effect of accelerants and microorganisms by using sludge + peel waste and also model chemicals such as CH3COOH, CH4, and CO2.
CONCLUSIONS
Nitrogen-doped biomass-derived carbon hybrid accelerants (Ni-N-C, Fe-N-C, and Fe/Ni-N-C) were prepared by simple pyrolysis. The accelerants contain bimetallic Ni/Fe nanoparticles, FeNi3 alloys, and compounds (Fe2O3, FeN, and Fe3O4). These components exhibit a high degree of graphitization, high pyridine-N and pyrrole-N contents, good stacking and wrinkled structures, and Ni-NX or Fe-NX active sites, resulting in enhanced electron transfer. The digesters with accelerants increased cumulative biogas production (402.95-587.76 mL/g VS) and TCOD degradation rates (36.39%-65.38%). The digestate of hybrid accelerants exhibited remarkable thermal stability (22.97%-32.75%) and fertility (4.43%-4.61%). The designed hybrid accelerants exhibited superior EEC (1.05-1.09 μmol e-/g). The enhanced methanogenesis in AcoD systems is attributable to the synergistic effects of different components (Fe and Ni metal nanoparticles, nitrides, oxides, and nitrogen-doped carbon) of hybrid accelerants.
DECLARATIONS
Authors’ contributions
Investigation, formal analysis, data curation, writing-original draft: Ke T
Conceptualization, supervision, methodology, resources, visualization, funding acquisition, project administration, writing-review & editing: Yun S
Methodology, formal analysis: Wang K, Xing T, Dang J, Zhang Y, Sun M
Methodology: An J, Liu L, Liu J
Availability of data and materials
Not applicable.
Financial support and sponsorship
The financial support from the National Key R&D Program of China (2018YFB1502900), Key Program for International S&T Cooperation Projects of Shaanxi Province (2019KWZ-03), Key Science and Technology Innovation Team of Shaanxi Province (2022TD-34), Open Foundation Project of Qinghai Building and Materials Research Co., Ltd, and Key Lab of Plateau Building and Eco-community in Qinghai (KLKF-2019-002) is greatly acknowledged.
Conflicts of interest
All authors declared that there are no conflicts of interest.
Ethical approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Copyright
© The Author(s) 2024.
Supplementary Materials
REFERENCES
1. Wang K, Yun S, Ke T, et al. Use of bag-filter gas dust in anaerobic digestion of cattle manure for boosting the methane yield and digestate utilization. Bioresour Technol 2022;348:126729.
2. Huang X, Yun S, Zhu J, Du T, Zhang C, Li X. Mesophilic anaerobic co-digestion of aloe peel waste with dairy manure in the batch digester: focusing on mixing ratios and digestate stability. Bioresour Technol 2016;218:62-8.
3. Ke T, Yun S, Wang K, An J, Liu L, Liu J. Enhanced anaerobic co-digestion performance by using surface-annealed titanium spheres at different atmospheres. Bioresour Technol 2022;347:126341.
4. Li B, Yun S, Xing T, Wang K, Ke T, An J. A strategy for understanding the enhanced anaerobic co-digestion via dual-heteroatom doped bio-based carbon and its functional groups. Chem Eng J 2021;425:130473.
5. Xu H, Yun S, Wang C, et al. Improving performance and phosphorus content of anaerobic co-digestion of dairy manure with aloe peel waste using vermiculite. Bioresour Technol 2020;301:122753.
6. Jia B, Yun S, Shi J, et al. Enhanced anaerobic mono- and co-digestion under mesophilic condition: Focusing on the magnetic field and Ti-sphere core-shell structured additives. Bioresour Technol 2020;310:123450.
7. Wu Y, Wang S, Liang D, Li N. Conductive materials in anaerobic digestion: from mechanism to application. Bioresour Technol 2020;298:122403.
8. An J, Yun S, Wang W, et al. Enhanced methane production in anaerobic co-digestion systems with modified black phosphorus. Bioresour Technol 2023;368:128311.
9. Xing T, Yun S, Li B, et al. Coconut-shell-derived bio-based carbon enhanced microbial electrolysis cells for upgrading anaerobic co-digestion of cow manure and aloe peel waste. Bioresour Technol 2021;338:125520.
10. Li X, Yun S, Zhang C, Fang W, Huang X, Du T. Application of nano-scale transition metal carbides as accelerants in anaerobic digestion. Int J Hydrog Energy 2018;43:1926-36.
11. Zhang T, Yun S, Li X, et al. Fabrication of niobium-based oxides/oxynitrides/nitrides and their applications in dye-sensitized solar cells and anaerobic digestion. J Power Sources 2017;340:325-36.
12. Córdova-lizama A, Carrera-figueiras C, Palacios A, Castro-olivera P, Ruiz-espinoza J. Improving hydrogen production from the anaerobic digestion of waste activated sludge: effects of cobalt and iron zero valent nanoparticles. Int J Hydrog Energy 2022;47:30074-84.
13. Abdelsalam E, Samer M, Attia Y, Abdel-hadi M, Hassan H, Badr Y. Influence of zero valent iron nanoparticles and magnetic iron oxide nanoparticles on biogas and methane production from anaerobic digestion of manure. Energy 2017;120:842-53.
14. Zhang W, Zhang L, Li A. Enhanced anaerobic digestion of food waste by trace metal elements supplementation and reduced metals dosage by green chelating agent [S, S]-EDDS via improving metals bioavailability. Water Res 2015;84:266-77.
15. Huang W, Yang F, Huang W, Wang D, Lei Z, Zhang Z. Weak magnetic field significantly enhances methane production from a digester supplemented with zero valent iron. Bioresour Technol 2019;282:202-10.
16. Cubero-Cardoso J, Maluf Braga AF, Trujillo-Reyes Á, et al. Effect of metals on mesophilic anaerobic digestion of strawberry extrudate in batch mode. J Environ Manag 2023;326:116783.
17. Abbas Y, Yun S, Wang Z, Zhang Y, Zhang X, Wang K. Recent advances in bio-based carbon materials for anaerobic digestion: a review. Renew Sustain Energy Reviews 2021;135:110378.
18. Chen S, Rotaru AE, Shrestha PM, et al. Promoting interspecies electron transfer with biochar. Sci Rep 2014;4:5019.
19. Wang G, Li Q, Gao X, Wang XC. Synergetic promotion of syntrophic methane production from anaerobic digestion of complex organic wastes by biochar: performance and associated mechanisms. Bioresour Technol 2018;250:812-20.
20. Wang J, Zhao Z, Zhang Y. Enhancing anaerobic digestion of kitchen wastes with biochar: Link between different properties and critical mechanisms of promoting interspecies electron transfer. Renew Energy 2021;167:791-9.
21. Chen M, Shao L, Lv X, et al. In situ growth of Ni-encapsulated and N-doped carbon nanotubes on N-doped ordered mesoporous carbon for high-efficiency triiodide reduction in dye-sensitized solar cells. Chem Eng J 2020;390:124633.
22. Dai Y, Chan Y, Jiang B, et al. Bifunctional Ag/Fe/N/C catalysts for enhancing oxygen reduction via cathodic biofilm inhibition in microbial fuel cells. ACS Appl Mater Interfaces 2016;8:6992-7002.
23. Lai Y, Wang Q, Wang M, Li J, Fang J, Zhang Z. Facile synthesis of mesoporous Fe-N-C electrocatalyst for high performance alkaline aluminum-air battery. J Electroanal Chem 2017;801:72-6.
24. Lu Z, Liu B, Dai W, Ouyang L, Ye J. Carbon network framework derived iron-nitrogen co-doped carbon nanotubes for enhanced oxygen reduction reaction through metal salt-assisted polymer blowing strategy. Appl Surf Sci 2019;463:767-74.
25. Yun S, Zhang Y, Zhang L, Liu Z, Deng Y. Ni and Fe nanoparticles, alloy and Ni/Fe-Nx coordination co-boost the catalytic activity of the carbon-based catalyst for triiodide reduction and hydrogen evolution reaction. J Colloid Interface Sci 2022;615:501-16.
26. Pei X, Peng X, Jia X, Wong PK. N-doped biochar from sewage sludge for catalytic peroxydisulfate activation toward sulfadiazine: efficiency, mechanism, and stability. J Hazard Mater 2021;419:126446.
27. Abbas Y, Yun S, Mehmood A, et al. Co-digestion of cow manure and food waste for biogas enhancement and nutrients revival in bio-circular economy. Chemosphere 2023;311:137018.
28. Abbas Y, Yun S, Wang K, Ali Shah F, Xing T, Li B. Static-magnetic-field coupled with fly-ash accelerant: a powerful strategy to significantly enhance the mesophilic anaerobic-co-digestion. Bioresour Technol 2021;327:124793.
29. Wang Z, Yun S, Xu H, et al. Mesophilic anaerobic co-digestion of acorn slag waste with dairy manure in a batch digester: focusing on mixing ratios and bio-based carbon accelerants. Bioresour Technol 2019;286:121394.
30. Yun S, Fang W, Du T, et al. Use of bio-based carbon materials for improving biogas yield and digestate stability. Energy 2018;164:898-909.
31. Xu L, Fu B, Sun Y, et al. Degradation of organic pollutants by Fe/N co-doped biochar via peroxymonosulfate activation: synthesis, performance, mechanism and its potential for practical application. Chem Eng J 2020;400:125870.
32. Li X, Jia Y, Zhou M, Su X, Sun J. High-efficiency degradation of organic pollutants with Fe, N co-doped biochar catalysts via persulfate activation. J Hazard Mater 2020;397:122764.
33. Li L, Liu H, Chen Y, et al. Effect of magnet-Fe3O4 composite structure on methane production during anaerobic sludge digestion: establishment of direct interspecies electron transfer. Renew Energy 2022;188:52-60.
34. Li S, Cao Y, Zhao Z, Zhang Y. Regulating secretion of extracellular polymeric substances through dosing magnetite and zerovalent iron nanoparticles to affect anaerobic digestion mode. ACS Sustain Chem Eng 2019;7:9655-62.
35. Wang T, Zhang D, Dai L, Dong B, Dai X. Magnetite triggering enhanced direct interspecies electron transfer: a scavenger for the blockage of electron transfer in anaerobic digestion of high-solids sewage sludge. Environ Sci Technol 2018;52:7160-9.
36. Yang L, Chen J, Park S, Wang H. Recent progress on metal-organic framework derived carbon and their composites as anode materials for potassium-ion batteries. Energy Mater 2023;3:300042.
37. Wang Z, Yun S, Shi J, et al. Critical evidence for direct interspecies electron transfer with tungsten-based accelerants: an experimental and theoretical investigation. Bioresour Technol 2020;311:123519.
38. Zhao J, Bao J, Yang S, et al. Exsolution-dissolution of supported metals on high-entropy Co3MnNiCuZnOx: toward sintering-resistant catalysis. ACS Catal 2021;11:12247-57.
39. Zhang C, Yun S, Li X, Wang Z, Xu H, Du T. Low-cost composited accelerants for anaerobic digestion of dairy manure: focusing on methane yield, digestate utilization and energy evaluation. Bioresour Technol 2018;263:517-24.
40. Liang S, Guo F, Du S, et al. Synthesis of Sargassum char-supported Ni-Fe nanoparticles and its application in tar cracking during biomass pyrolysis. Fuel 2020;275:117923.
41. Xu L, Wu C, Liu P, et al. Peroxymonosulfate activation by nitrogen-doped biochar from sawdust for the efficient degradation of organic pollutants. Chem Eng J 2020;387:124065.
42. Chen Y, Gokhale R, Serov A, Artyushkova K, Atanassov P. Novel highly active and selective Fe-N-C oxygen reduction electrocatalysts derived from in-situ polymerization pyrolysis. Nano Energy 2017;38:201-9.
43. Yang C, Yun S, Shi J, et al. Tailoring the supercapacitive behaviors of Co/Zn-ZIF derived nanoporous carbon via incorporating transition metal species: a hybrid experimental-computational exploration. Chem Eng J 2021;419:129636.
44. Zhang Y, Yun S, Sun M, et al. Implanted metal-nitrogen active sites enhance the electrocatalytic activity of zeolitic imidazolate zinc framework-derived porous carbon for the hydrogen evolution reaction in acidic and alkaline media. J Colloid Interface Sci 2021;604:441-57.
45. Chen X, Qin R, Li Z, Shan S, Liu Y, Yang C. One-pot synthesis of Fe/Cu/N-doped carbon materials derived from shale oil for efficient oxygen reduction reaction. Mol Catal 2021;500:111330.
46. Sun M, Yun S, Shi J, et al. Designing and understanding the outstanding tri-iodide reduction of N-coordinated magnetic metal modified defect-rich carbon dodecahedrons in photovoltaics. Small 2021;17:e2102300.
47. Cai H, Fu L, Pan H, Yan Z, Chen T, Zhao T. Pore engineering of ultramicroporous carbon from an N-doped polymer for CO2 adsorption and conversion. Mol Catal 2023;550:113557.
48. Cheng H, Ji R, Bian Y, Jiang X, Song Y. From macroalgae to porous graphitized nitrogen-doped biochars - using aquatic biota to treat polycyclic aromatic hydrocarbons-contaminated water. Bioresour Technol 2020;303:122947.
49. Choi CH, Park SH, Woo SI. N-doped carbon prepared by pyrolysis of dicyandiamide with various MeCl2·xH2O (Me = Co, Fe, and Ni) composites: effect of type and amount of metal seed on oxygen reduction reactions. Appl Catal B Environ 2012;119-20:123-31.
50. Luo B, Zhou L, Tian Z, He Y, Shu R. Hydrogenolysis of cornstalk lignin in supercritical ethanol over N-doped micro-mesoporous biochar supported Ru catalyst. Fuel Process Technol 2022;231:107218.
51. Wang X, Yun S, Zhang Y, et al. Boosting catalytic activity of niobium/tantalum-nitrogen active-sites for triiodide reduction in photovoltaics. J Colloid Interface Sci 2021;603:651-65.
52. Huang Z, Zhou H, Yang W, Fu C, Chen L, Kuang Y. Three-dimensional hierarchical porous nitrogen and sulfur-codoped graphene nanosheets for oxygen reduction in both alkaline and acidic media. ChemCatChem 2017;9:987-96.
53. Chan Y, Dai Y, Li R, Zou J, Tian G, Fu H. Low-temperature synthesized nitrogen-doped iron/iron carbide/partly-graphitized carbon as stable cathode catalysts for enhancing bioelectricity generation. Carbon 2015;89:8-19.
54. Masa J, Sinev I, Mistry H, et al. Ultrathin high surface area nickel boride (NixB) nanosheets as highly efficient electrocatalyst for oxygen evolution. Adv Energy Mater 2017;7:1700381.
55. Chen B, Wang D, Zhang B, et al. Engineering the active sites of graphene catalyst: from CO2 activation to activate Li-CO2 batteries. ACS Nano 2021;15:9841-50.
56. Xiong Y, Li H, Liu C, et al. Single-atom Fe catalysts for fenton-like reactions: roles of different N species. Adv Mater 2022;34:e2110653.
57. Zhou Y, Li Y, Zhang L, et al. Fe-leaching induced surface reconstruction of Ni-Fe alloy on N-doped carbon to boost oxygen evolution reaction. Chem Eng J 2020;394:124977.
58. Deng Y, Yun S, Dang J, et al. A multi-dimensional hierarchical strategy building melamine sponge-derived tetrapod carbon supported cobalt-nickel tellurides 0D/3D nanohybrids for boosting hydrogen evolution and triiodide reduction reaction. J Colloid Interface Sci 2022;624:650-69.
59. Dang J, Yun S, Zhang Y, et al. Constructing double-shell structured N-C-in-Co/N-C electrocatalysts with nanorod- and rhombic dodecahedron-shaped hollow morphologies to boost electrocatalytic activity for hydrogen evolution and triiodide reduction reaction. Chem Eng J 2022;449:137854.
60. Shen Y, Linville JL, Urgun-demirtas M, Schoene RP, Snyder SW. Producing pipeline-quality biomethane via anaerobic digestion of sludge amended with corn stover biochar with in-situ CO2 removal. Appl Energy 2015;158:300-9.
61. Han F, Yun S, Zhang C, Xu H, Wang Z. Steel slag as accelerant in anaerobic digestion for nonhazardous treatment and digestate fertilizer utilization. Bioresour Technol 2019;282:331-8.
62. Liu L, Yun S, Ke T, Wang K, An J, Liu J. Dual utilization of aloe peel: aloe peel-derived carbon quantum dots enhanced anaerobic co-digestion of aloe peel. Waste Manag 2023;159:163-73.
63. Yun S, Xing T, Wang Y, et al. Mineral residue accelerant-enhanced anaerobic digestion of cow manure: an evaluation system of comprehensive performance. Sci Total Environ 2023;858:159840.
64. Yun S, Xing T, Han F, et al. Enhanced direct interspecies electron transfer with transition metal oxide accelerants in anaerobic digestion. Bioresour Technol 2021;320:124294.
65. Zhang W, Lang Q, Wu S, Li W, Bah H, Dong R. Anaerobic digestion characteristics of pig manures depending on various growth stages and initial substrate concentrations in a scaled pig farm in Southern China. Bioresour Technol 2014;156:63-9.
66. Xie S, Wickham R, Nghiem LD. Synergistic effect from anaerobic co-digestion of sewage sludge and organic wastes. Int Biodeter Biodegr 2017;116:191-7.
67. Kumar A, Singh E, Singh L, Kumar S, Kumar R. Carbon material as a sustainable alternative towards boosting properties of urban soil and foster plant growth. Sci Total Environ 2021;751:141659.
68. Zhang A, Bian R, Pan G, et al. Effects of biochar amendment on soil quality, crop yield and greenhouse gas emission in a Chinese rice paddy: a field study of 2 consecutive rice growing cycles. Field Crops Res 2012;127:153-60.
69. Li Y, Chen Y, Wu J. Enhancement of methane production in anaerobic digestion process: a review. Appl Energy 2019;240:120-37.
70. Lovley DR. Syntrophy goes electric: direct interspecies electron transfer. Ann Rev Microbiol 2017;71:643-64.
71. Yang Y, Zhang Y, Li Z, Zhao Z, Quan X, Zhao Z. Adding granular activated carbon into anaerobic sludge digestion to promote methane production and sludge decomposition. J Clean Prod 2017;149:1101-8.
72. Barua S, Dhar BR. Advances towards understanding and engineering direct interspecies electron transfer in anaerobic digestion. Bioresour Technol 2017;244:698-707.
73. Chen J, Yun S, Shi J, et al. Role of biomass-derived carbon-based composite accelerants in enhanced anaerobic digestion: focusing on biogas yield, fertilizer utilization, and density functional theory calculations. Bioresour Technol 2020;307:123204.
74. Liang M, Liu Y, Zhang J, et al. Understanding the role of metal and N species in M@NC catalysts for electrochemical CO2 reduction reaction. Appl Catal B Environ 2022;306:121115.
75. Wang J, Zhu W, Meng F, Bai G, Zhang Q, Lan X. Integrating dual-metal sites into covalent organic frameworks for enhanced photocatalytic CO2 reduction. ACS Catal 2023;13:4316-29.
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Ke T, Yun S, Wang K, Xing T, Dang J, Zhang Y, Sun M, An J, Liu L, Liu J. Constructing bimetal, alloy, and compound-modified nitrogen-doped biomass-derived carbon from coconut shell as accelerants for boosting methane production in bioenergy system. Energy Mater 2024;4:400011. http://dx.doi.org/10.20517/energymater.2023.62
AMA Style
Ke T, Yun S, Wang K, Xing T, Dang J, Zhang Y, Sun M, An J, Liu L, Liu J. Constructing bimetal, alloy, and compound-modified nitrogen-doped biomass-derived carbon from coconut shell as accelerants for boosting methane production in bioenergy system. Energy Materials. 2024; 4(1): 400011. http://dx.doi.org/10.20517/energymater.2023.62
Chicago/Turabian Style
Ke, Teng, Sining Yun, Kaijun Wang, Tian Xing, Jiaoe Dang, Yongwei Zhang, Menglong Sun, Jinhang An, Lijianan Liu, Jiayu Liu. 2024. "Constructing bimetal, alloy, and compound-modified nitrogen-doped biomass-derived carbon from coconut shell as accelerants for boosting methane production in bioenergy system" Energy Materials. 4, no.1: 400011. http://dx.doi.org/10.20517/energymater.2023.62
ACS Style
Ke, T.; Yun S.; Wang K.; Xing T.; Dang J.; Zhang Y.; Sun M.; An J.; Liu L.; Liu J. Constructing bimetal, alloy, and compound-modified nitrogen-doped biomass-derived carbon from coconut shell as accelerants for boosting methane production in bioenergy system. Energy Mater. 2024, 4, 400011. http://dx.doi.org/10.20517/energymater.2023.62
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