Olive pomace-derived biochar mitigates gaseous emissions and enhances compost quality during thermophilic phase of composting

Abstract

Introduction:

The application of biochar (BC) has gained increasing attention as an effective strategy for reducing gaseous emissions and improving compost quality. This study evaluated the effects of olive pomace (OP)-derived BC produced at two pyrolysis temperatures (300 °C and 600 °C) and applied at two rates (5% and 10%) on gaseous emissions and compost physicochemical properties during the thermophilic phase of OP composting.

Methods:

Five treatments were evaluated, including a control without BC and four BC-amended treatments, each conducted in triplicate using three pilot-scale bioreactors operated sequentially under identical conditions. Emissions of ammonia (NH₃), nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) were continuously monitored over the 9-day thermophilic phase. Data were analyzed using two-way repeated-measures ANOVA to assess the effects of treatment, sampling day, and their interaction, followed by the LSD test at P ≤ 0.05.

Results:

BC addition significantly reduced cumulative NH₃, N₂O, CH₄, and CO₂ emissions by 56-78%, 62-93%, 43-55%, and 79-85%, respectively, compared with the control. The greatest mitigation was achieved with BC produced at 600 °C and applied at 10%. These reductions were associated with improved aeration and enhanced retention of nitrogen and labile carbon. BC also improved compost quality by increasing total nitrogen (up to 1.41%), phosphorus, potassium, and micronutrient contents, while decreasing ammonium concentration, electrical conductivity, bulk density, and the C ratio (18.2), indicating enhanced compost maturity.

Discussion:

OP-derived BC, particularly when produced at 600 °C and applied at 10%, effectively mitigated greenhouse gas and NH₃ while improving compost physicochemical properties and maturity during the thermophilic phase. These findings support the use of BC as a sustainable amendment for enhancing compost quality and reducing the environmental impacts of organic waste management.

Graphical Abstract

1 Introduction

The sustainable management of OP, a major by-product of the olive oil industry in Mediterranean and Middle Eastern regions, is critical due to its high organic load, phenolic compounds, and potential phytotoxicity that can harm soil and water quality. Compared with many other compost feedstocks, OP is characterized by a high lignocellulosic fraction, elevated concentrations of phenolic compounds, and a relatively low nitrogen content. These characteristics slow microbial degradation, delay compost stabilization, and may increase nutrient losses and gaseous emissions unless suitable amendments are incorporated during composting. Composting is an effective method to transform OP into stable, nutrient-rich soil amendments; however, it often results in emissions of greenhouse gases (GHGs) such as CO₂, CH₄, N₂O, and NH₃, which contribute to climate change and air pollution. Industrial-scale studies reveal that the type of nitrogen source used in co-composting mixtures significantly affects GHG emissions, with poultry manure causing the highest global warming potential due to elevated NO and CH₄ emissions, while bulking agents like urban pruning residues enhance mineralization without increasing GHG emissions (García-Rández et al., 2025). The addition of urea or easily degradable carbon sources can increase N₂O emissions by boosting mineral nitrogen availability during composting (Sánchez-Monedero et al., 2010). Storage duration of OP before composting influences organic matter (OM) degradation and reduces gaseous emissions by altering microbial community dynamics (Ruiz-Castilla et al., 2025). Mitigation strategies such as BC addition reduce nitrogen losses via GHGs and improve compost quality, whereas geotextile covers have limited effectiveness and cost-efficiency (Mira-Urios et al., 2025). Overall, optimizing feedstock composition, storage conditions, and composting management is essential to minimize environmental impacts while producing high-quality organic amendments from OP (Nasini et al., 2016; Pereira et al., 2024; Castellani et al., 2019).

NH₃ volatilization is a major nitrogen loss pathway during composting, reducing the fertilizer value of the final product and causing environmental issues such as odor and atmospheric pollution. N₂O, a potent greenhouse gas with a global warming potential about 298 times that of CO₂, is mainly produced through nitrification and denitrification under low-oxygen conditions. CH₄ emissions, although generally low in well-aerated composting systems, can occur due to anaerobic microsites within the compost matrix. CO₂ emissions reflect microbial respiration and OM mineralization but also represent significant carbon losses that reduce compost stability. Recent meta-analyses show that additives such as chemical salts (e.g., phosphate and magnesium salts) and physical amendments like BC can significantly reduce NH₃volatilization by up to 62% and greenhouse gas emissions including N₂O and CH₄ by over 40%, depending on feedstock properties and moisture content (MC) (Cao et al., 2019; Liu et al., 2023). Additionally, mature compost additions improve aeration and pH balance, reducing methane and N₂O emissions by about 20%, while promoting carbon sequestration through microbial humification (Zhang et al., 2025). Effective pile management, aeration control, moisture regulation, and optimized additive use remain key strategies to enhance composting efficiency while minimizing gaseous emissions (Nordahl et al., 2023; Ba et al., 2020).

BC, a carbon-rich material produced by pyrolysis of biomass, has gained attention for improving composting by reducing gaseous emissions and enhancing compost quality. Its high surface area, porosity, and diverse functional groups enable nutrient adsorption, improved aeration, and modulation of microbial activity. BC addition can significantly reduce NH₃ volatilization by retaining NH₄⁺ through cation exchange and surface adsorption mechanisms. It also decreases N₂O emissions by promoting oxygen diffusion and facilitating complete denitrification to nitrogen gas (N₂), while its porous structure suppresses CH₄ formation by limiting anaerobic microsites and stimulating methanotrophic bacteria. The effectiveness of BC depends on factors such as feedstock type, pyrolysis temperature, particle size, and application rate; for example, BC from crop residues or woody biomass at about 10% (w/w) dosage can reduce greenhouse gas emissions substantially (Yin et al., 2021; Nguyen et al., 2022). Different BC’s influence microbial communities and functional genes related to GHG emissions differently, with cornstalk BC showing superior reductions in CH₄, N₂O, NH₃, and H₂S during poultry manure composting (Dang et al., 2024). Overall, BC amendments improve compost maturity and reduce environmental impacts by altering the compost microenvironment and microbial dynamics (Geng et al., 2024).

BC improves compost quality by enhancing nutrient retention, increasing total nitrogen, phosphorus, and potassium contents, and reducing nutrient leaching during composting. It accelerates compost maturity by lowering the carbon-to-nitrogen (C:N) ratio and stabilizing OM through organo-mineral complex formation. The nutrient retention mechanisms involve BC pores adsorbing dissolved nutrients and forming nutrient-rich organomineral layers during composting, which improve nutrient availability in the final product. BC produced at higher pyrolysis temperatures generally has greater surface area, aromaticity, and adsorption capacity, making it more effective in improving compost characteristics and controlling emissions. Nano-scale BC’s further enhance nutrient retention and microbial community diversity, leading to better compost maturity and reduced nitrogen loss. Additionally, combining BC with other amendments like gypsum can synergistically improve compost quality by promoting microbial enzyme activities and nutrient cycling (Joseph et al., 2018; Chang et al., 2025).

Despite the growing body of research on BC-amended composting, most studies have focused on manure, food waste, crop residues, or mixed organic wastes, whereas OP has received comparatively little attention despite being one of the major agro-industrial residues generated by the olive oil industry. The high lignocellulosic content, elevated concentrations of phenolic compounds, and low biodegradability of OP present unique challenges for composting and necessitate tailored management strategies. Furthermore, previous studies have generally evaluated BC as an externally sourced compost amendment, whereas the potential of an integrated pyrolysis composting system, in which OP is first converted into BC and subsequently reused as a composting amendment for fresh OP, remains largely unexplored. Although pyrolysis temperature and BC application rate are recognized as critical factors governing BC physicochemical properties and performance, their interactive effects on greenhouse gas emissions and compost quality during OP composting have not been systematically investigated. This knowledge gap limits the development of optimized BC production and application strategies for sustainable OP valorization within circular bioeconomy systems.

Therefore, this study evaluated the effects of OP-derived BC produced at two pyrolysis temperatures (300 °C and 600 °C) and applied at two rates (5% and 10%) on NH₃, N₂O, CH₄, and CO₂ emissions, as well as on the physicochemical characteristics of compost during the thermophilic phase, the period characterized by the greatest microbial activity and greenhouse gas emissions. We hypothesized that the interaction between BC pyrolysis temperature and application rate would regulate composting performance by modifying BC physicochemical properties, thereby differentially influencing gaseous emissions and compost quality. Specifically, we expected that BC produced at a higher pyrolysis temperature (600 °C), particularly when applied at an appropriate rate, would provide greater environmental and agronomic benefits owing to its higher porosity, greater specific surface area, enhanced adsorption capacity, and improved structural stability.

2 Materials and methods

2.1 Preparation and characterization of BC

OP was sourced from private olive-processing facilities in the Aljouf region. The material was first air-dried and mechanically reduced to particles of approximately 5 mm. Pyrolysis was conducted under oxygen-limited conditions using a sealed stainless-steel chamber placed inside a digital muffle furnace (FH-12, Dahan Scientific, Republic of Korea).

Two thermal regimes were applied: 300 °C and 600 °C, representing low- and high temperature pyrolysis conditions, respectively. These contrasting temperatures were selected to generate BC’s with distinct physicochemical properties, following approaches widely adopted in previous studies (e.g., (Yin et al., 2021; Keiluweit et al., 2010). After thermal treatment, the resulting BC was allowed to cool to ambient temperature, then ground and sieved to obtain a uniform particle size of 2 mm prior to use.

The physicochemical properties of the OP-derived BCs used in this study are summarized in Table 1 and served as the basis for evaluating the effects of pyrolysis temperature and application rate on composting performance. Increasing the pyrolysis temperature notably altered BC characteristics, including an increase in alkalinity (pH) and EC, indicating enrichment in ash and mineral constituents. Total carbon content increased slightly, whereas nitrogen content declined, likely due to volatilization losses during high temperature treatment. Phosphorus content showed a moderate increase. Additionally, a clear enhancement in specific surface area was observed, reflecting greater porosity development at higher temperatures. These changes suggest that BC produced at elevated temperatures possesses improved structural stability and adsorption capacity, which may enhance its performance during composting.

2.2 Compost feedstock preparation

The same OP feedstock was further processed into 1–2 cm particles using a mechanical shredder (FYS-76, Yongkang, China) to improve homogeneity and aeration during composting. Compost mixtures were formulated by blending OP with chicken manure (CM), which served as a nitrogen-rich amendment to adjust the carbon-to-nitrogen (C:N) ratio. BC was incorporated into the mixtures at two application rates: 5% and 10% (w/w), while a treatment without BC served as the control. The addition of CM was essential to counterbalance the high carbon content of OP, thereby creating favorable conditions for microbial degradation.

MC and C:N ratio were adjusted to approximately 60% and 30:1, respectively, following standard composting guidelines. These parameters were calculated based on the properties and proportions of individual components using established Equations 1, 2 (Haug, 2018):where MC, Q, C, and N are the MC (%), mass (kg), carbon content (%), and nitrogen content (%) of the CM (subscript c), and OP (subscript r), respectively, (Table 2). The prepared mixtures were then homogenized thoroughly before being transferred into the composting units.

2.3 Composting system and experiment setup

The composting process was carried out using three identical pilot-scale rotating bioreactors developed by environmental engineering unit at the Agricultural Engineering Department facilities, College of Food and Agricultural Sciences, King Saud University (Figures 1A,B). Each bioreactor had a total volume of 0.2 m³ and was designed to accommodate approximately 50 kg of wet compost mixture, with additional headspace to facilitate aeration (Alkoaik et al., 2019; Abdelfadeel et al., 2025).

FIGURE 1

Alkoaik et al., 2019), of the rotary drum bioreactor system: (A) overall design with dimensions (cm); (B) cross-sectional illustration showing the locations of aeration inlet and outlet ports and the positioning of thermocouple sensors.

The cylindrical bioreactors were constructed from steel and thermally insulated with a 25 mm layer of glass wool to minimize heat loss and maintain thermophilic conditions. Continuous mixing was achieved through rotation at 3 rpm along a central axis, while aeration was provided through perforations along the internal tube to ensure adequate oxygen supply throughout the compost mass.

Five composting treatments were evaluated: control without BC addition (T0R0), BC produced at 300 °C and applied at 5% (T1R1), BC produced at 300 °C and applied at 10% (T1R2), BC produced at 600 °C and applied at 5% (T2R1), and BC produced at 600 °C and applied at 10% (T2R2). Each treatment was independently replicated using the three identical bioreactors (n = 3). Because only three pilot-scale bioreactors were available, the treatments were conducted sequentially. Each treatment was composted in the three bioreactors for the 9-day thermophilic phase, after which the bioreactors were emptied, cleaned, and reused for the next treatment under the same operating conditions. After thermophilic phase, the compost was moved out of the bioreactor and set in piles and composting will continue in piles until reaching maturity.

Temperature dynamics within each bioreactor were continuously monitored throughout the thermophilic phase. Three type-T (copper-constantan) thermocouples were installed at different locations inside the bioreactor to capture spatial variation. Data were recorded at 30-min intervals using a portable data logger (Testo 177-T4, Germany), and the mean temperature was calculated from the three sensors.

2.4 Measurement of headspace gas emissions

Gas emissions of CO₂, CH₄, N₂O, and NH₃ in the bioreactor were measured daily using a Fourier-transform infrared (FTIR) gas analyzer (Gasmet DX4015, Finland) coupled with Calcmet software (Figure 2). Gas concentrations were recorded and reported as parts per million (ppm). The Gasmet DX4015 has been widely validated for monitoring gaseous compounds in agricultural and environmental applications. The analyzer detects gases based on their characteristic infrared absorption spectra (Heimsch, 2024; Brummell, 2015).

FIGURE 2

Prior to sampling, the bioreactor outlets were sealed for 1 hour to allow gases to accumulate in the bioreactor headspace. Daily headspace gas concentrations were used as comparative indicators of gaseous release among treatments. For each measurement, three consecutive readings were obtained and averaged to improve analytical precision and reproducibility.

Cumulative greenhouse gas concentrations were calculated using the direct summation method by summing the daily measured values throughout the 9-day thermophilic composting period as indicated in Equation 3:where CE is the cumulative greenhouse gas emission, Ei is the measured value on sampling day i, and n is the total number of sampling days.

2.5 Compost sampling and physiochemical analysis

Greenhouse gas emissions were monitored during the 9-day thermophilic phase of composting, which represents the period of maximum microbial activity and gaseous emissions. At the end of the thermophilic stage (day 9), compost samples were collected from multiple points within each pile (left, center, and right) to ensure representativeness. The subsamples were combined and homogenized to produce three composite samples. A total of three composite samples from each pile (three piles per treatment) were taken as three replicates. The physicochemical analyses presented in this study therefore reflect compost characteristics at the end of the thermophilic phase rather than those of fully matured compost. All the physiochemical analysis were conducted according to the Test Methods for the Examination of Composting and Compost (TMECC) (Council and Thompson, 2002). The analyzed parameters included, pH, EC, OM, total carbon (C) and nitrogen (N), and C:N ratio. Macro and micronutrients (P, K, Ca, Mg, Na, Fe, Zn, and Cu) were determined following acid digestion using inductively coupled plasma optical emission spectrometry (ICP-OES). All measurements were performed in triplicate, and the results are presented as mean ± standard error (SE).

2.6 Statistical analysis

Gas emission data were analyzed using two-way repeated measures ANOVA where the effects of treatments, days of gas analysis and their interactions on emitted gases values were tested. Treatment means were compared using the least significant difference (LSD) test at P ≤ 0.05. Results are presented as mean ± standard error (SE) based on three independent bioreactor replicates. All statistical analyses were performed using OriginPro (Version 2025).

3 Results

3.1 Temperature dynamics

Figure 3 illustrates the temperature evolution of OP composting under different BC treatments during the 9-day thermophilic phase. All treatments exhibited a rapid transition from mesophilic to thermophilic conditions, confirming active microbial decomposition of organic substrates. Initial temperatures on Day 1 ranged from 25.4 °C to 30.4 °C, with BC-amended treatments generally showing slightly higher temperatures than the control.

FIGURE 3

A sharp increase in temperature occurred during the first few days of composting. The thermophilic phase was reached rapidly in all BC treatments, with temperatures increasing to 50.5 °C–58.5 °C by Days 3–7. The highest temperatures were consistently observed in the BC-amended treatments, particularly T2R2, which reached 63.5 °C on Day 7, followed by T1R2 and T2R1 with maximum temperatures of 58.5 °C and 59.5 °C, respectively.

In contrast, the control treatment (T0R0) showed comparatively lower temperatures, with a maximum of 54.5 °C recorded on Day 8. BC addition accelerated the onset and prolongation of the thermophilic phase compared with the control. Treatments amended with BC produced at 600 °C, especially at the 10% application rate (T2R2), maintained elevated temperatures for longer periods. Following the thermophilic peak, temperatures gradually declined toward the end of the composting period, reaching 39.8 °C–47.8 °C on Day 9.

Overall, the results demonstrate that BC amendment, particularly BC produced at 600 °C and applied at 10%, enhanced composting performance by stimulating microbial activity, increasing thermophilic intensity, and promoting more efficient OM degradation. The two-way ANOVA confirmed that temperature was significantly influenced by treatment, composting time, and their interactions (P < 0.0001).

3.2 Greenhouse gases and NH₃ emissions

3.2.1 NH₃ emissions

BC addition reduced NH₃ emissions throughout the thermophilic composting period compared with the control treatment (P < 0.001) (Figure 4). The control treatment exhibited the highest NH₃ emissions, with a peak occurring during the early thermophilic stage (81.28 ppm on Day 2), followed by a gradual decline toward the end of thermophilic period of composting.

FIGURE 4

The incorporation of BC suppressed NH₃ emissions compared with the control, with the reduction becoming more pronounced at higher BC application rates and pyrolysis temperatures. At 300 °C, the 5% BC treatment (T1R1) reduced NH₃ emissions from 67.82 ppm on Day 1–6.49 ppm by Day 9, while the 10% BC treatment (T1R2) showed substantially lower emissions throughout the composting period, declining from 32.55 to only 0.28 ppm by the end of the thermophilic phase. Similarly, BC produced at 600 °C further decreased NH₃ emissions. The 5% treatment (T2R1) decreased from 30.48 ppm on Day 1 to 0.30 ppm on Day 9, whereas the 10% treatment (T2R2) exhibited the lowest NH₃ emissions among all treatments, declining from 26.68 ppm initially to 0.22 ppm at the end of the experiment. Cumulative NH₃ emissions were 484 ppm in the control, compared to 211, 140, 119, and 104 ppm for T1R1, T1R2, T2R1, and T2R2, respectively. This corresponds to reductions of 56%, 71%, 75%, and 78%, respectively.

3.2.2 N₂O emissions

The application of BC amendments revealed significant improvement in N₂O emissions during the thermophilic stage of composting (P < 0.0001) (Figure 5). N₂O emissions followed a clear decreasing trend in all BC-amended treatments relative to the control, indicating the strong mitigation potential of BC during the thermophilic stage of composting.

FIGURE 5

The control treatment (T0R0) exhibited the highest N₂O emissions throughout the experiment. Emissions increased during the initial days of composting, rising from 7.04 ppm on Day 1 to a maximum of 8.60 ppm on Day 3, after which emissions progressively declined and reached 1.10 ppm by Day 9.

The addition of BC produced at 300 °C substantially lowered N₂O release. In the 5% BC treatment (T1R1), emissions decreased sharply over time, from 5.63 ppm at the beginning of composting to nearly negligible levels (0.0067 ppm at the end of the thermophilic phase. A stronger suppression effect was observed in the 10% BC treatment (T1R2), where emissions remained consistently lower than those recorded in T1R1 throughout the experiment and declined to 0.0033 ppm by Day 9.

A further reduction in N₂O emissions was achieved with BC produced at 600 °C. The T2R1 treatment maintained relatively low emissions during the entire composting period, decreasing from 1.87 to 0.09 ppm between Days 1 and 9. Among all treatments, T2R2 showed the greatest mitigation effect, with emissions remaining below 1.0 ppm from the start of composting and steadily decreasing to 0.03 ppm by the final day.

The cumulative emission data supported these observations. Total N₂O emissions reached 43.2 ppm in the control, whereas BC-amended treatments significantly reduced cumulative losses to 16.5, 8.6, 5.3, and 2.9 ppm for T1R1, T1R2, T2R1, and T2R2, respectively. Relative to the control, these reductions corresponded to 62%, 80%, 88%, and 93%, demonstrating that higher BC application rates and elevated pyrolysis temperatures were highly effective in mitigating N₂O emissions during thermophilic composting.

3.2.3 CH₄ emissions

CH₄ emissions were significantly influenced by BC amendment, composting time, and their interaction (P < 0.0001). As shown in Figure 6, CH₄ emissions remained relatively low throughout the thermophilic phase, while the control treatment (T0R0) generally exhibiting higher emissions than all BC-amended treatments. In the control, CH₄ emissions increased from 12.40 ppm on Day 1–22.27 ppm on Day 3, followed by fluctuations during the remaining composting period, reaching a maximum of 57.33 ppm on Day 6 before declining to 10.97 ppm by Day 9.

FIGURE 6

BC amendment reduced CH₄ emissions across all treatments, although the extent of reduction depended on the BC application rate and pyrolysis temperature. At 300 °C, the 5% BC treatment (T1R1) exhibited lower CH₄ emissions than the control during most of the composting period, with emissions ranging from 1.85 ppm on Day 1–5.43 ppm on Day 9. The 10% BC treatment (T1R2) provided greater CH₄ mitigation, maintaining relatively low emissions throughout the thermophilic phase and decreasing from 1.62 ppm on Day 1–4.05 ppm on Day 9.

BC produced at 600 °C also effectively suppressed CH₄ emissions. In T2R1, emissions remained consistently lower than the control, ranging from 1.05 ppm on Day 1–3.60 ppm on Day 9. The T2R2 treatment recorded the lowest initial CH₄ emissions (0.72 ppm) and maintained relatively low values throughout most of the thermophilic phase, although a temporary increase was observed on Day 6 (42.59 ppm), before declining to 7.20 ppm by the end of composting.

The cumulative CH₄ concentrations further demonstrated the effectiveness of BC in mitigating CH₄ accumulation during composting. The control treatment recorded the highest cumulative CH₄ emission (172.72 ppm), whereas cumulative emissions decreased to 98.27, 79.04, 77.36, and 92.63 ppm in T1R1, T1R2, T2R1, and T2R2, respectively. These reductions corresponded to decreases of 43%, 54%, 55%, and 46% relative to the control.

3.2.4 CO₂ emissions

The result revealed that BC amendment, composting time, and their interaction had highly significant effects on the CO₂ emissions (P < 0.0001). As illustrated in Figure 7, CO₂ emissions were markedly higher in the control treatment during the thermophilic phase, particularly in the initial stages of composting, whereas all BC-amended treatments substantially suppressed CO₂ release in the bioreactor headspace. In the control (T0R0), CO₂ concentrations increased from 96847 ppm on Day 1–114737 ppm on Day 2, and reached 126612 ppm on Day 3. Emissions then peaked at 163544 ppm on Day 4 before declining sharply during the remainder of the composting period, reaching 4833 ppm and 30192 ppm by Day 9.

FIGURE 7

The addition of BC considerably reduced CO₂ emissions compared with the control. At 300 °C, the 5% BC treatment (T1R1) maintained substantially lower emissions throughout the thermophilic phase, ranging from 12753 to 35253 ppm during the early composting period before decreasing to only 189 ppm on Day 9. Likewise, the 10% BC treatment (T1R2) exhibited lower emissions than the control across all sampling days, with values ranging from 15198 ppm to 44051 ppm during the initial stages and declining to 162 ppm at the end of composting.

BC produced at 600 °C also effectively suppressed CO₂ emissions. In T2R1, emissions remained substantially lower than those of the control, varying between 10171 and 32176 ppm before decreasing to 163 ppm on Day 9. Among all treatments, T2R2 recorded the lowest cumulative CO₂ emissions, with values remaining consistently below the control throughout the thermophilic phase, decreasing from 10860 ppm on Day 1–198 ppm by the end of composting. The cumulative CO₂ emissions further demonstrated the effectiveness of BC in mitigating carbon losses during composting. The control treatment recorded the highest cumulative emission (604685 ppm), whereas cumulative emissions were reduced to 124742, 125480, 109504, and 89865 ppm in T1R1, T1R2, T2R1, and T2R2, respectively. These reductions corresponded to decreases of approximately 79%, 79%, 82%, and 85% respectively, relative to the control.

3.3 Temporal dynamics and hierarchical clustering of nitrogen and carbon gas emissions under BC amendments

The heatmaps demonstrate that adding BC (T1 and T2) significantly mitigates the loss of nitrogen and carbon compared to the control (T0R0) during the critical 9-day thermophilic phase (Figure 8). In the control group, intense red clusters for NH₃-N (Figure 8A) and N₂O-N (Figure 8B) during the first 3 days indicate rapid nitrogen volatilization, whereas the BC-amended treatments remain predominantly blue, suggesting that the BC effectively adsorbs ammonium and inhibits gaseous emissions. This cooling effect is similarly visible in the CO₂-C (Figure 8C) and CH₄-C (Figure 8D) plots, where the control exhibits high-intensity spikes-likely due to unchecked microbial decomposition and localized anaerobic conditions-while the BC treatments maintain low, stable levels, acting as a structural bulking agent that improves aeration and carbon sequestration.

FIGURE 8

Statistically, the hierarchical clustering highlights that the presence of BC is a more dominant factor in emission reduction than the specific pyrolysis temperature (R1 vs. R2) or application rate. While T0R0 branches off as a distinct outlier due to its high emission profile, the T1 and T2 subgroups cluster closely together, showing that even at different pyrolysis temperatures, the BC provides a consistent buffering capacity. The temporal clustering further reveals that the BC’s primary impact occurs in the early stages (Days 1–4), where it successfully prevents the massive flushing of nutrients and gases typically seen at the onset of high-temperature composting.

3.4 Influence of BC addition on compost physicochemical characteristics and nutrient content

Table 3 showed that the application of BC amendment significantly enhanced the physicochemical and nutrient properties of compost compared to the control. Dry matter (DM) and OM contents increased in all BC treatments, with the highest values observed in T1R2 (69.5% and 57.8%, respectively). BD decreased in BC treatments (0.57–0.61 g cm^-3) compared to the control (0.649 g cm^-3), indicating improved compost structure and porosity. The pH remained within an optimal range (7.95–8.20), while EC decreased in BC-amended treatments, particularly in T2R2 (11.00 dS m^-1).

Compost maturity was improved with BC addition, as indicated by a decrease in the C:N ratio from 22:1 in the control to 18.2–20.5 in treated composts, with the lowest value recorded in T2R2. This was accompanied by a substantial reduction in NH₄⁺-N (613 mg kg^-1 in control vs. 220–280 mg kg^-1 in treatments) and a corresponding increase in NO₃⁻-N (up to 18.5 mg kg^-1).

Nutrient enrichment was evident across all BC treatments. Total nitrogen (TN) increased to 1.41% in T2R2 compared to 1.19% in the control. Similarly, total phosphorus (TP) and potassium (TK) increased significantly, with the highest values observed in T1R2 and T2R2 (0.52%–0.55% for P and up to 2.40% for K). Ca, Mg, and S and micronutrients (Fe, Cu, Zn, Mn, and B) were consistently higher in BC-amended treatments, particularly at the higher application rate (10%) and higher pyrolysis temperature (600 °C). For instance, Fe increased from 2083 mg kg^-1 in the control to 5400 mg kg^-1 in T2R2, while Zn and Mn reached 125.8 mg kg^-1 and 155.4 ppm, respectively.

4 Discussion

BC application significantly mitigated gaseous emissions during thermophilic composting while improving nutrient retention and compost quality. The observed reduction in NH₃ emissions may be attributed to the strong adsorption capacity of BC for NH₄⁺ and NH₃ owing to its porous structure, high surface area, and elevated cation exchange capacity (CEC). These physiochemical properties likely enhanced nitrogen retention and reduced transformation of NH₄⁺ into volatile NH₃. In addition, BC may have improved aeration and moderated localized alkaline conditions within the compost matrix, thereby reducing NH₃ volatilization. The stronger mitigation observed at higher BC application rates and pyrolysis temperatures is consistent with the greater pore development and aromaticity generally reported for high-temperature BCs.

Nguyen et al. (2023), reported that applying a BC amendment during food waste co-composting minimizes NH₃ emissions due to nitrogen retention driven by its highly porous micro-structure and large specific surface area. Among the tested trials, the 20% BC treatment achieved the maximum reduction, yielding the lowest NH₃ emission of 2 ppm on day 16 and completely stopping the emission by day 1. Shin et al. (2024), reported that low-temperature BC rich in oxygen-containing functional groups effectively buffered compost pH and enhanced nitrification. Although microbial processes were not directly assessed in the present study, the observed reduction in NH₃ emissions is consistent with these previously reported mechanisms. Similarly, Yin et al. (2021), demonstrated that BC amendments reduces cumulative compost NH₃ emissions by an average of 35.9%–51.42% by trapping ammonium in its pores, while chemical modification can suppress emissions by an additional 47.8%.

The significant decline in N₂O emissions following BC addition may be explained by improved oxygen diffusion and modified nitrogen transformation processes within the compost matrix. The porous structure of BC likely reduced anaerobic microsites, thereby limiting conditions favorable for incomplete denitrification, a major source of N₂O production. BC can facilitate electron transfer through redox-active surface groups and promote microbial pathways involved in the reduction of N₂O to N₂. Wang et al. (2022), reported that biogas residue amendments promoted N₂O release, whereas adding BC significantly decreased N₂O emissions by 33.6% by enhancing the abundance of the nosZ gene to accelerate the conversion of N₂O into harmless nitrogen gas, while Wang et al. (2023), demonstrated that the application of BC-carried microbial agent decreased gaseous losses during sheep manure composting, reducing emissions of N₂O by 68.64%. Yang et al. (2023), showed that adding 10% BC decreased compost N₂O emissions by 26.5% by downregulating N₂O producing genes and upregulating N₂O reducing genes. These literature-supported mechanisms are consistent with greater N₂O reductions observed in the present study, particularly for the 600 °C BC treatments. Yin et al. (2021), also found that BC produced at higher pyrolysis temperatures improved N₂O mitigation efficiency.

CH₄ emissions were also reduced following BC amendment, which may be attributed to improved aeration and oxygen penetration within the compost matrix. The porous structure of BC likely enhanced gas diffusivity and reduced anaerobic conditions that favor methanogenic microorganisms. In addition, BC may have promoted conditions favorable for CH₄ oxidation while improving moisture distribution and reducing the formation of anaerobic microsites. These mechanisms are proposed based on previous studies, as microbial communities were not directly evaluated in the present work. Dang et al. (2024), investigated that the addition of 10%–20% BC to poultry manure compost decreased cumulative CH₄ emissions by 53.7% by improving pile aeration and shifting the evolution of associated methane-metabolizing functional genes. Similarly, Harrison et al. (2024), found that BC at (5%) improved compost structure and oxygen availability, resulting in reduced CH₄ emissions by 58%. Gu et al. (2025), further revealed that amending compost with BC at different stages significantly suppressed carbon losses, reducing cumulative CH₄ emissions by 17.4%–44.6%. These mechanisms explain the greater CH₄ reductions observed at higher BC application rates in the present study.

The marked reduction in CO₂ emissions indicated that BC influenced carbon transformation during composting. BC contains recalcitrant carbon fractions that resist microbial degradation and can adsorb labile organic compounds, reducing their accessibility for microbial mineralization. Consequently, the observed reduction in CO₂ concentrations likely reflects a combination of enhanced carbon retention and altered carbon transformation pathways rather than carbon stabilization alone. Because microbial activity was not directly measured in this study, it cannot be concluded that the lower CO₂ concentrations resulted exclusively from enhanced carbon sequestration or reduced microbial respiration. Moreover, the formation of organo-mineral complexes between BC and compost OM may have contributed to improved carbon retention during composting.

Awasthi et al. (2020), reported that the addition of 10% bamboo BC (by dry weight) to poultry manure compost effectively mitigated carbon loss, reducing cumulative CO₂ emissions by 72.6% (from 542.3 mg kg^-1 in the control to 148.8 mg kg^-1 Likewise, Lin et al. (2022), reported that the combined amendment of BC and biogas residue significantly mitigated carbon losses during straw composting by suppressing coenzyme activities and upregulating the acsB gene to drive CO₂ assimilation, successfully counteracting the sharp increases in CO₂ (13.07%) caused by adding biogas residue alone. Nguyen et al. (2022), further demonstrated that high-temperature BC was more effective in stabilizing organic carbon due to its condensed aromatic structure and chemical recalcitrance. The present findings are consistent with these studies and suggest that BC reduced CO₂ concentrations while maintaining effective thermophilic composting, as evidenced by the temperature profiles. However, the relative contributions of microbial activity, carbon stabilization, and adsorption processes require further investigation through direct microbial and biochemical analyses.

The enhanced temperature dynamics observed in BC-amended composts suggest that BC did not inhibit the thermophilic composting process and may have promoted more efficient decomposition of readily biodegradable substrates. However, because microbial biomass, enzyme activities, and microbial community composition were not measured, enhanced microbial activity is proposed as a plausible explanation rather than a direct finding of this study. Huang et al. (2022), reported that adding 10% of BC enhanced microbial diversity and enzyme activity associated with OM decomposition, leading to higher thermophilic temperatures and faster compost stabilization. Tahsini et al. (2025), further demonstrated that microbial-inoculated BC accelerated compost maturation and improved metabolic activity during composting. Similarly, Zhou et al. (2019), observed increased abundance of Actinobacteria and functional pathways related to carbohydrate and amino acid metabolism in BC-amended composts. The faster decline in temperature following the thermophilic peak may indicate more efficient degradation of readily biodegradable substrates and a faster transition toward the subsequent composting stages.

In addition to reducing gaseous losses, BC may substantially improve compost quality and nutrient conservation. The increase in nutrient concentrations, including total N, P, K, and micronutrients, can be attributed to reduced nutrient leaching and volatilization through adsorption onto BC surfaces. BC also improved compost quality by lowering the C:N ratio and enhancing OM stabilization, both of which are widely recognized indicators of compost maturation. Abban-Baidoo et al. (2024), reported that amending compost with 5%–10% BC increases total carbon by 24.7%–37.6% and total nitrogen by 1.8%–2.4%, while keeping the Germination Index above 60% to ensure safe, non-phytotoxic agricultural use. While, Zhou et al. (2022), evaluated the effect of BC addition through a global meta-analysis which shows that adding 10%–15% straw-derived BC drastically improves compost quality and reduces environmental risks, notably cutting NH₃ (35.9%), CH4 (53.7%), and N₂O (49.8%) emissions while boosting the Germination Index by 26.6% and nitrate nitrogen by 56.6%.

Although the 10% BC application rate consistently produced the greatest reductions in greenhouse gas emissions and the largest improvements in compost quality, its practical implementation at commercial scale should consider BC production costs, feedstock availability, and operational feasibility. Higher BC application rates require greater quantities of BC, which may increase production and transportation costs depending on the feedstock source and pyrolysis process. Nevertheless, the 5% BC treatments also provided substantial reductions in gaseous emissions while improving compost quality, suggesting that lower application rates may represent a more economically feasible option for large-scale composting. Future studies should include techno-economic and life-cycle assessments to determine the optimal BC application rate for sustainable commercial implementation.

5 Conclusion

The present study demonstrated that BC amendment is an effective approach for enhancing thermophilic composting of OP while mitigating gaseous emissions and improving compost quality. BC application significantly reduced cumulative NH₃, N₂O, CH₄, and CO₂ emissions, indicating improved nitrogen conservation and enhanced carbon retention and stabilization during composting. The observed reductions may be attributed to the adsorption capacity, porous structure, and improved aeration provided by BC, which likely influenced nitrogen and carbon transformation processes during the thermophilic phase.

In addition to mitigating gaseous emission, BC improved the physicochemical properties of the compost during this thermophilic phase by increasing nutrient retention and availability, lowering the C:N ratio and EC, and improving BD and OM stabilization. The effects were more pronounced at higher BC application rates and pyrolysis temperatures, with BC produced at 600 °C and applied at 10% showing the greatest overall performance in terms of gaseous emission reduction and compost quality enhancement.

Overall, the findings demonstrate the strong potential of BC as a sustainable composting amendment for improving compost quality while mitigating greenhouse gas emissions during the thermophilic phase. Among the tested treatments, BC produced at 600 °C and applied at 10% exhibited the greatest technical effectiveness. Although this application rate may appear challenging under conventional BC use, the proposed approach is based on an integrated biomass valorization system, in which OP generated at olive mills is converted into BC and subsequently reused as a composting amendment within the same production cycle. This closed-loop strategy enhances the practical feasibility of BC application by reducing dependence on externally sourced BC while promoting circular agricultural waste management. It should be noted that the present study specifically focused on the thermophilic phase, as this stage is characterized by the highest microbial activity and the greatest greenhouse gas emissions, making it the most critical period for evaluating the environmental benefits of BC addition. The composting experiment is ongoing, and after completion of the thermophilic phase, the compost piles were removed from the bioreactors and are continuing through the curing and maturation stages under conventional composting conditions. Therefore, the effects of BC during the later stages of compost stabilization will be reported separately. Future work will integrate the results from the complete composting process with microbial community analyses, functional gene characterization, and techno-economic and life-cycle assessments to further optimize integrated pyrolysis composting systems for sustainable compost production.

References

• 1

  Abban-BaidooE.Manka’abusiD.ApuriL.MarschnerB.FrimpongK. A. (2024). Biochar addition influences C and N dynamics during biochar co-composting and the nutrient content of the biochar co-compost. Sci. Rep.14 (1), 23781. 10.1038/s41598-024-67884-z

  • CrossRef
  • Google Scholar
  • View reference in article

• 2

  AbdelfadeelI. A.AlotaibiK. D.AlkoiakF. N.AloudS. S.FullerosR. B. (2025). Effects of biochar addition on gaseous emissions during the thermophilic composting phase and subsequent changes in compost characteristics. Processes13 (10), 3210. 10.3390/pr13103210

  • CrossRef
  • Google Scholar
  • View reference in article

• 3

  AlkoaikF.Al-FarajA.Al-HelalI.FullerosR.IbrahimM.Abdel-GhanyAMJS (2019). Toward sustainability in rural areas: composting palm tree residues in rotating bioreactors. Sustainability12 (1), 201. 10.3390/su12010201

  • CrossRef
  • Google Scholar
  • View reference in article

• 4

  AwasthiM. K.DuanY.AwasthiS. K.LiuT.ZhangZ. (2020). Influence of bamboo biochar on mitigating greenhouse gas emissions and nitrogen loss during poultry manure composting. Bioresour. Technology303, 122952. 10.1016/j.biortech.2020.122952

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 5

  BaS.QuQ.ZhangK.GrootJ. C. (2020). Meta-analysis of greenhouse gas and ammonia emissions from dairy manure composting. Biosyst. Eng.193, 126–137. 10.1016/j.biosystemseng.2020.02.015

  • CrossRef
  • Google Scholar
  • View reference in article

• 6

  BrummellM. (2015). Greenhouse Gas Production and Consumption in Soils of the Canadian High Arctic Doctoral Dissertation. Saskatoon, SK: University of Saskatchewan.

  • Google Scholar
  • View reference in article

• 7

  CaoY.WangX.BaiZ.ChadwickD.MisselbrookT.SommerS. G.et al (2019). Mitigation of ammonia, nitrous oxide and methane emissions during solid waste composting with different additives: a meta-analysis. J. Clean. Prod.235, 626–635. 10.1016/j.jclepro.2019.06.288

  • CrossRef
  • Google Scholar

• 8

  CastellaniF.EspositoA.GeldermannJ.AltieriR. (2019). Life cycle assessment of passively aerated composting in gas-permeable bags of olive mill waste. Int. J. Life Cycle Assessmen24 (2), 281–296. 10.1007/s11367-018-1514-0

  • CrossRef
  • Google Scholar

• 9

  ChangY.ChenY.WeiY.MiaoN.KangZ.ZhangY.et al (2025). Multi-source biochar: effects on composting humification, soil properties and plant growth. J. Environ. Manag.392, 126667. 10.1016/j.jenvman.2025.126667

  • CrossRef
  • Google Scholar

• 10

  Council (2002). “UaUUSDoAaUSC,” in Test Methods for the Examination of Composting and Compost (TMECC). Editor ThompsonW. H. (Washington, DC: U.S. Government Printing Office).

  • Google Scholar
  • View reference in article

• 11

  DangR.CaiY.LiJ.KongY.JiangT.ChangJ.et al (2024). Biochar reduces gaseous emissions during poultry manure composting: evidence from the evolution of associated functional genes. J. Clean. Prod.452, 142060. 10.1016/j.jclepro.2024.142060

  • CrossRef
  • Google Scholar

• 12

  García-RándezA.OrdenL.MarksE. A.Andreu-RodríguezJ.Franco-LuesmaS.Martínez-SabaterE.et al (2025). Monitoring of greenhouse gas emissions and compost quality during olive mill waste co-composting at industrial scale: the effect of N and C sources. Waste Manag.193, 33–43. 10.1016/j.wasman.2024.11.039

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 13

  GengX.YangH.GaoW.YueJ.MuD.WeiZ. (2024). Greenhouse gas emission characteristics during kitchen waste composting with biochar and zeolite addition. Bioresour. Technol.399, 130575. 10.1016/j.biortech.2024.130575

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 14

  GuS.JiZ.LiX.QinH.LiM.ZhangL.et al (2025). Organic matter components rather than microbial enzymes and genes predominate CO2/CH4 emissions during composting amended with biochar at different stages. Environ. Pollut.373, 126129. 10.1016/j.envpol.2025.126129

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 15

  HarrisonB. P.MooZ.Perez-AgredanoE.GaoS.ZhangX.RyalsR. (2024). Biochar-composting substantially reduces methane and air pollutant emissions from dairy manure. Environ. Research Letters19 (1), 014081. 10.1088/1748-9326/ad1ad2

  • CrossRef
  • Google Scholar
  • View reference in article

• 16

  HaugR. (2018). The Practical Handbook of Compost Engineering. Boca Raton, FL:Routledge. 10.1201/9780203736234

  • CrossRef
  • Google Scholar
  • View reference in article

• 17

  HeimschL. (2024). Greenhouse Gas Fluxes and Carbon Balance in Finnish Agroecosystems that Utilise Regenerative Farming Practices.

  • Google Scholar
  • View reference in article

• 18

  HuangX.HeY.ZhangY.LuX.XieL. (2022). Independent and combined effects of biochar and microbial agents on physicochemical parameters and microbial community succession during food waste composting. Bioresour. Technology366, 128023. 10.1016/j.biortech.2022.128023

  • CrossRef
  • Google Scholar
  • View reference in article

• 19

  JosephS.KammannC. I.ShepherdJ. G.ConteP.SchmidtH.-P.HagemannN.et al (2018). Microstructural and associated chemical changes during the composting of a high temperature biochar: mechanisms for nitrate, phosphate and other nutrient retention and release. Sci. Total Environ.618, 1210–1223. 10.1016/j.scitotenv.2017.09.200

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 20

  KeiluweitM.NicoP. S.JohnsonM. G.KleberM. J. (2010). Dynamic molecular structure of plant biomass-derived Black carbon (biochar). Environ. Sci. Technol.44 (4), 1247–1253. 10.1021/es9031419

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 21

  LinX.WangN.LiF.YanB.PanJ.JiangS.et al (2022). Evaluation of the synergistic effects of biochar and biogas residue on CO2 and CH4 emission, functional genes, and enzyme activity during straw composting. Bioresour. Technol.360, 127608. 10.1016/j.biortech.2022.127608

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 22

  LiuY.TangR.LiL.ZhengG.WangJ.WangG.et al (2023). A global meta-analysis of greenhouse gas emissions and carbon and nitrogen losses during livestock manure composting: influencing factors and mitigation strategies. Sci. Total Environ.885, 163900. 10.1016/j.scitotenv.2023.163900

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 23

  Mira-UriosM. Á.SáezJ. A.OrdenL.Marhuenda-EgeaF. C.Andreu-RodríguezF. J.ToribioA. J.et al (2025). Composting of olive mill wastewater sludge using a combination of multiple strategies: assessment of improvement in biodegradability, GHG emissions, and characteristics of the end product. Agronomy15 (4), 808. 10.3390/agronomy15040808

  • CrossRef
  • Google Scholar
  • View reference in article

• 24

  NasiniL.De LucaG.RicciA.OrtolaniF.CaselliA.MassaccesiL.et al (2016). Gas emissions during olive mill waste composting under static pile conditions. Int. Biodeterior. Biodegrad.107, 70–76. 10.1016/j.ibiod.2015.11.001

  • CrossRef
  • Google Scholar
  • View reference in article

• 25

  NguyenM. K.LinC.HoangH. G.SandersonP.DangB. T.BuiX. T.et al (2022). Evaluate the role of biochar during the organic waste composting process: a critical review. Chemosphere299, 134488. 10.1016/j.chemosphere.2022.134488

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 26

  NguyenM. K.LinC.HoangH. G.BuiX. T.NgoH. H.LeV. G.et al (2023). Investigation of biochar amendments on odor reduction and their characteristics during food waste co-composting. Sci. Total Environ.865, 161128. 10.1016/j.scitotenv.2022.161128

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 27

  NordahlS. L.PrebleC. V.KirchstetterT. W.ScownC. D. (2023). Greenhouse gas and air pollutant emissions from composting. Environ. Science Technology57 (6), 2235–2247. 10.1021/acs.est.2c05846

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 28

  PereiraJ. L.CostaT.FigueiredoV.MarquesF.PerdigãoA.BrásI.et al (2024). Influence of different agro-food waste on ammonia and greenhouse gas emissions during composting. Agronomy14 (1), 220. 10.3390/agronomy14010220

  • CrossRef
  • Google Scholar
  • View reference in article

• 29

  Ruiz-CastillaF. J.Barbudo-LunarM.GutiérrezM. C.MichánC.MartínM. Á.AlhamaJ. (2025). Storage of alperujo influences composting performance: insights into gaseous emissions and functional metagenomics. J. Environ. Manag.393, 127015. 10.1016/j.jenvman.2025.127015

  • CrossRef
  • Google Scholar
  • View reference in article

• 30

  Sánchez-MonederoM. A.SerramiáN.CivantosC. G.-O.Fernández-HernándezA.RoigA. (2010). Greenhouse gas emissions during composting of two-phase olive mill wastes with different agroindustrial by-products. Chemosphere81 (1), 18–25. 10.1016/j.chemosphere.2010.07.022

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 31

  ShinY.IwabuchiK.ItohT. (2024). Low-temperature biochars are more effective in reducing ammonia emissions through various mechanisms during manure composting. J. Material Cycles Waste Management26 (1), 138–148. 10.1007/s10163-023-01808-3

  • CrossRef
  • Google Scholar
  • View reference in article

• 32

  TahsiniM. J.NikaeenM.MohammadiF.TaghipourA.TahmasebiM.NafezA. H. (2025). Composting of municipal solid waste with microbial-inoculated biochar amendment: impact on process and end-product quality. Biochar7 (1), 25. 10.1007/s42773-025-00426-6

  • CrossRef
  • Google Scholar
  • View reference in article

• 33

  WangN.AwasthiM. K.PanJ.JiangS.WanF.LinX.et al (2022). Effects of biochar and biogas residue amendments on N2O emission, enzyme activities and functional genes related with nitrification and denitrification during rice straw composting. Bioresour. Technol.357, 127359. 10.1016/j.biortech.2022.127359

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 34

  WangZ.XuY.YangT.LiuY.ZhengT.ZhengC. (2023). Effects of biochar carried microbial agent on compost quality, greenhouse gas emission and bacterial community during sheep manure composting. Biochar5 (1), 3. 10.1007/s42773-022-00202-w

  • CrossRef
  • Google Scholar
  • View reference in article

• 35

  YangX.DuanP.CaoY.WangK.LiD. (2023). Mechanisms of mitigating nitrous oxide emission during composting by biochar and calcium carbonate addition. Bioresour. Technol.388, 129772. 10.1016/j.biortech.2023.129772

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 36

  YinY.YangC.LiM.ZhengY.GeC.GuJ.et al (2021). Research progress and prospects for using biochar to mitigate greenhouse gas emissions during composting: a review. Sci. Total Environ.798, 149294.

  • Pubmed Abstract
  • Google Scholar
  • View reference in article

• 37

  ZhangL.FanR.LiW.LiG.LuoW.XuZ. (2025). Unravelling biotic and abiotic mechanisms of mature compost to alleviate gaseous emissions in kitchen waste composting by metagenomic analysis. Bioresour. Technology419, 132102. 10.1016/j.biortech.2025.132102

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 38

  ZhouG.XuX.QiuX.ZhangJ. (2019). Biochar influences the succession of microbial communities and the metabolic functions during rice straw composting with pig manure. Bioresour. Technology272, 10–18. 10.1016/j.biortech.2018.09.135

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 39

  ZhouS.KongF.LuL.WangP.JiangZ. (2022). Biochar—An effective additive for improving quality and reducing ecological risk of compost: a global meta-analysis. Sci. Total Environ.806, 151439. 10.1016/j.scitotenv.2021.151439

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article