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Article

Effects of Calcium Peroxide Dosage on Physicochemical Parameters, Organic Matter Degradation, Humification, and Microbial Community Succession During Food Waste Composting

by
Kun Hu
,
Guoning Zhou
,
Jia Chen
,
Nalume Gerald Wafula
and
Guangming Li
*
State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
*
Author to whom correspondence should be addressed.
Waste 2025, 3(1), 3; https://doi.org/10.3390/waste3010003
Submission received: 2 November 2024 / Revised: 31 December 2024 / Accepted: 1 January 2025 / Published: 4 January 2025
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Abstract

:
To verify the possible roles of calcium peroxide (CaO2) in addressing the key challenges of aerobic composting of food waste, including long composting duration, poor compost product quality, and gas emissions during composting, this study conducted a 38-day composting experiment using artificially blended food waste. Five containers were employed for investigating the effects of five doses of CaO2 (0%, 5%, 10%, 15%, and 20%, w/w) on physicochemical parameters, organic matter (OM) degradation, and humification during composting. Additionally, more evidence from a microbial perspective was provided by analyzing the effects of CaO2 additions on microbial community succession. The results indicated that CaO2 additions increased the relative abundance of mineralization bacteria, accelerated the temperature increase of compost in the early composting stage, and elevated the peak temperature. It also facilitated the decomposition of OM and enhanced the synthesis of humic acid during the early composting stage. However, the addition of CaO2, especially at relatively high doses, impacted the humification process. Compared with the control, only the 5% CaO2 treatment had a significantly greater humification coefficient, reaching 1.73 ± 0.11. Moreover, adding CaO2 reduced the total ammonia emissions from composting by 17.1% to 59.7%. Overall, CaO2 is an effective additive for ameliorating key issues in food waste composting.

Graphical Abstract

1. Introduction

Food waste production has been increasing with the development of the social economy and the improvement of people’s living standards. China has an annual output of approximately 60 million tons of food waste, with an annual growth rate of around 5.34%. China’s food waste production is expected to exceed 100 million tons by 2030 [1]. Food waste has both pollution and resource attributes. On the one hand, mishandled food waste may become a potential source of soil and groundwater pollution while also releasing pollutant gases that pose risks to human and environmental health. On the other hand, food waste is rich in organic matter (OM), such as starch, oil, protein, and cellulose, as well as various plant nutrients, which makes it valuable for recycling. Aerobic composting is an effective treatment method to reduce and maximize the resource utilization of food waste. However, several key challenges prevent its widespread application. Firstly, the slow start-up of composting results in a long composting duration [2,3]. Secondly, the insufficient decomposition of OM during composting hinders the synthesis of humic substances (HS), resulting in poor-quality composting products [4,5]. Lastly, emissions of odors and greenhouse gases during the composting process can lead to nutrient loss and environmental impacts [6,7].
Various measures, such as adjusting pH levels [8,9], carbon-to-nitrogen (C/N) ratios [10], and the use of readily degradable carbon sources [11] and adsorbent materials (e.g., zeolites) [12], have been explored to address these issues. However, the adjustment of feedstock and process parameters is relatively limited in practical composting scenarios. The application of additives is generally considered an efficient and manageable strategy to improve the composting process [13]. Calcium peroxide (CaO2), an inorganic chemical additive, was initially developed and utilized in the anaerobic digestion field. Li et al. [14] discovered that it could promote the removal of refractory organic contaminants during activated sludge anaerobic digestion. Bao et al. [15] subsequently introduced CaO2 into the field of aerobic composting and found that CaO2 can accelerate the decomposition of recalcitrant OM, such as lignocellulose, within the composting of sewage sludge. Lu et al. [16] reported that CaO2 enhanced the synthesis of humus in straw and dairy manure composting. However, to our knowledge, there is still a lack of comprehensive research on the effects of CaO2 on the aerobic composting of food waste.
On the basis of existing studies on CaO2 being utilized in the composting of other organic solid wastes, it is possible that CaO2 may play potential roles in accelerating the temperature increase of compost during food waste composting, thus promoting the degradation of OM, and accelerating the maturation of compost. To test these hypotheses, we have investigated the effects of different CaO2 additions on physicochemical parameters, OM decomposition, and humification during food waste composting. Moreover, we analyzed microbial community succession in different treatments to provide more evidence of the effects of CaO2 additions from a microbial perspective.

2. Materials and Methods

2.1. Composting Feedstock and Experimental Design

The composting experiment was conducted in the laboratory of the Mingjing Building, which is located in Yangpu District, Shanghai (31.2842° N, 121.4972° E). Five treatments with different CaO2 addition ratios (0% “CP0”, 5% “CP5”, 10% “CP10”, 15% “CP15”, and 20% “CP20” of wet weight) were set up in this experiment. This experiment used artificially blended food waste as the composting feedstock, which consisted of 40% staple food (rice and noodles), 35% vegetables, 20% fruits, and 5% meat (wet weight). All raw materials were sourced from local supermarkets. The detailed composition and properties of the raw materials are provided in Table 1. Moreover, 0.5% microbial agent (wet weight) and 15% sawdust (wet weight) were added to each treatment to adjust the C/N ratio and moisture content of the composting materials, thereby ensuring a smooth composting process. The CaO2 additive (active ingredient content ≥ 60%) was obtained from Jiangmen Haiju Biotechnology Co., Ltd. (Guangdong, China), the microbial agent (mainly concentrated compound microbial species developed by special technology from Bacillus, Actinobacteria, Pseudomonas, Aspergillus, Apiotrichum, Cladosporium, and other beneficial microorganisms) was provided by Ecoacell Co., Ltd. (Shanghai, China), and the sawdust was sourced from a wood processing plant (Henan, China). All the composting materials were crushed into 0.8–1.0 cm particles via a shredder and then mixed according to the raw material ratio. The corresponding proportions of the composting additives were then added and mixed thoroughly with a mixer to create the composting feedstock.
Five aerobic fermentation tanks with an effective volume of 15 L each were used in the composting experiment, as shown in Figure 1. Initially, the mixed composting feedstock of each treatment was filled into each experimental container. An aerator was used to introduce air into each system at an aeration rate of 0.56 L/min through the inlet. The air was directed into a ventilation ring located at the bottom of each device for even distribution, ensuring aerobic conditions throughout the composting process. Exhaust gases were released through the outlet at the top of each device. The temperature changes during composting were monitored in real time via temperature sensors. Leachate generated during composting was temporarily stored in each leachate storage chamber through porous filter plates and was collected daily. Each experimental setup was wrapped with a 5 cm thick polyurethane insulation layer to reduce heat loss during the composting process.
Sample collection occurred on days 0, 3, 6, 9, 12, 15, 18, 24, 30, and 38, covering all stages of composting, including the mesophilic, thermophilic, cooling, and mature phases. Before each sampling, the containers were turned, and samples were uniformly collected via the five-point sampling method and then thoroughly mixed [17]. Three bags of the mixed compost samples were collected to represent three replicates. All the samples were divided into two parts and stored in refrigerators at 4 °C and −80 °C for subsequent analysis.

2.2. Measurement of Experimental Parameters During Composting

2.2.1. Basic Physiochemical Properties

The composting temperature was measured at 2 p.m. daily via temperature sensors (SBWZ-2460, Shanghai Hongtian Co., Ltd., Shanghai, China). The ammonia (NH3) content in each device was determined at 2 p.m. daily via the outlet using a portable ammonia detector (S316, Henan Zhong’an Electronic Detection Technology Co., Ltd., Zhengzhou, China). Based on the method of Qiao [18], water extracts of fresh compost samples were prepared at a ratio of 1:10 (w/v). The samples were shaken at 180 r/min for 1 h and then centrifuged at 10,000 r/min for 10 min. Each supernatant was filtered through a 0.45 μm filter membrane. The pH of the extracts was measured via a pH electrode (PHS-3C, INESA Scientific Instrument Co., Ltd., Shanghai, China). The germination index (GI) was determined according to the Chinese Standard of Organic Fertilizer NY/T 525-2021 [19].

2.2.2. Parameters Related to Organic Matter Degradation

The OM content was determined by dry combustion at 550 °C for 8 h [20]. Dissolved organic carbon (DOC) was obtained as described by Wei et al. [21]. The dried compost samples were extracted with deionized water at a ratio of 1:10 (w/v). After shaking at 180 r/min for 24 h, the samples were centrifuged at 10,000 r/min for 10 min, and each supernatant was filtered through a 0.45 μm filter membrane. The DOC content of the extracts was determined via a total organic carbon analyzer (TOC-VCPN, Shimadzu, Kyoto, Japan). The Van Soest method [22] was employed to determine the content of the lignin component. On the basis of the method of Law [23], adenosine triphosphate (ATP) release during composting was determined via liquid chromatography (U3000, Thermo Fisher Scientific, Waltham, MA, USA).

2.2.3. Humus Dynamics

Based on the method of Xu [24], an extraction solution of 0.1 mol/L Na4P2O7 and 0.1 mol/L NaOH was prepared. The dried compost samples were extracted with this solution at a ratio of 1:20 (w/v). After shaking at 150 r/min for 24 h at room temperature, each supernatant was centrifuged at 10,000 r/min for 20 min and then filtered through a 0.45 μm filter membrane. The resulting precipitate was re-extracted using the same procedures, and the two supernatants were combined. The combined extract supernatant was diluted to determine the HS content of the extract via a total organic carbon analyzer (TOC-VCPN, Shimadzu, Japan). The pH of the combined extract supernatant was adjusted to 1.0–1.5 with 1:1 hydrochloric acid. The mixture was left to stand at room temperature for 12 h and then centrifuged at 10,000 r/min for 20 min. Each supernatant was filtered through a 0.45 μm filter membrane. The fulvic acid (FA) content of the extracts was measured via a total organic carbon analyzer (TOC-VCPN, Shimadzu, Japan). The humic acid (HA) content was calculated as the difference between the HS and FA contents.

2.2.4. High-Throughput Sequencing

For high-throughput sequencing, compost samples collected at days 0, 3, 15, 24, and 38 were selected to represent different stages of composting. Total DNA was extracted and purified using the proteinase K-CTAB method and isopropanol precipitation method. The concentration and purity of the DNA were assessed via a UV-vis spectrophotometer (NanoDrop 2000, Thermo Fisher Scientific, USA), and the quality of the extracted DNA was verified by 1% agarose gel electrophoresis. The bacterial 16S rRNA V3-V4 region sequences were amplified by polymerase chain reaction (PCR) using the universal bacterial primers 338F (5′-ACTCCTACGGGAGGCAGCA-3′) and 806R (5′-GGACTACHVGGGTWTCTAAT-3′) [25]. The fungal 18S rRNA V3-V4 region sequences were amplified by PCR using the universal fungal primers SSU0817F (5′-TTAGCATGGAATAATRRAATAGGA-3′) and 1196R (5′-TCTGGACCTGGTGAGTTTCC-3′) [26]. Finally, the PCR amplicons that passed quality control were sequenced via the Illumina MiSeq PE300 platform. After de-duplicating sequencing data using DADA2, Amplicon Sequence Variants (ASVs) were obtained to represent the sequence and abundance information for taxonomic analysis of the species and community diversity analysis. The raw data files corresponding to bacteria and fungi have been successfully submitted and deposited into the National Center for Biotechnology Information (NCBI) database, accompanied by accession number PRJNA1125162.

2.3. Data Processing and Statistical Analysis

The data were recorded and reported as the mean values with standard deviations. Data visualization was performed via OriginPro 2024 (OriginLab, Northampton, MA, USA). SPSS 26 software (IBM, Armonk, NY, USA) was employed to describe the significant differences and correlations between indicators. The differences in the experimental parameters were detected using Tukey’s honestly significant difference test. The correlations among environmental factors, OM degradation, humification, and the microbial community were analyzed using Pearson’s correlation coefficient. The variance in the microbial community during composting was characterized through principal coordinate analysis (PCoA) on the basis of weighted Unifrac distance.

3. Results and Discussion

3.1. Physicochemical Parameters

As shown in Figure 2a, all the treatments underwent the mesophilic, thermophilic, and cooling phases and entered the mature phase after day 15. Compared with the control (CP0), the CaO2 treatments (CP5, CP10, CP15, and CP20) showed a faster increase in compost temperature and entered the thermophilic phase earlier. The peak temperatures of the treatments reached 71.9 °C (CP0, day 7), 72.9 °C (CP5, day 3), 73.3 °C (CP10, day 3), 73.7 °C (CP15, day 4) and 73.9 °C (CP20, day 3), respectively. These may be due to the heat released from CaO2 hydrolysis, as well as from the enhanced mineralization of OM by CaO2 additions [15].
Figure 2b shows the pH variations in each treatment. The pH of the CaO2 treatments changed similarly, following a general increasing trend. Compared with the CaO2 treatments, the control had a significantly lower pH on days 3 and 12. These decreases in the control were likely attributed to the organic acids generated by OM decomposition during the two high-temperature periods, whereas the calcium hydroxide derived from the CaO2 hydrolysis in the CaO2 treatments played a cushioning role. Thereafter, with the consumption of organic acids and the ammonification of organic nitrogen caused by microbial metabolic activities [27], the pH began to gradually increase in CP0.
Unlike most studies that reported that NH3 emissions were concentrated mainly in the thermophilic phase [28,29], the NH3 emissions in this experiment occurred primarily during the mature phase (Figure 2c). The lower pH in the early composting stage may have contributed to the delayed NH3 emissions [30]. By the end of composting, the accumulative NH3 emissions of each treatment amounted to 25.8 (CP0), 21.4 (CP5), 15.1 (CP10), 13.0 (CP15), and 10.4 (CP20) grams per kilogram of initial dry matter (DM) (Figure 2d). This indicated that CaO2 additions achieved a 17.1–59.7% reduction in NH3 emissions during composting, which may be due to the more sufficient decomposition of nitrogenous OM in the early composting stage by the addition of CaO2.

3.2. Organic Matter Degradation

Figure 3a,b show the variations in the OM content and its residual rate in each treatment. There was a significant difference in the initial OM content among the treatments due to the addition of CaO2. After composting started, the OM residual rate of the CaO2 treatments decreased faster than that of the control during the mesophilic and thermophilic phases, which indicated that the CaO2 treatments had higher mineralization rates in the initial stage of composting, in agreement with the study of Bao et al. [15]. From day 12 onward, there was no significant difference in the OM residual rates between CP5 and CP0, while those of CP10, CP15, and CP20 were significantly lower than CP0 throughout the composting process. This suggested that the addition of CaO2 promoted OM mineralization, which was probably attributed to its oxidizing capacity.
Changes in the lignin content and its residual rate in each treatment during composting are shown in Figure 3c,d. The observed increase in lignin content on day 6 across all the treatments was attributed to the decomposition of readily degradable OM, which led to a reduction in total weight and, consequently, a relative increase in lignin content. Lignin degradation in all the treatments occurred primarily after day 15, which corresponds to the mature phase of composting, which is in agreement with the findings of Qiao et al. [18]. This was attributed mainly to the specific temperature requirements of lignin-degrading microorganisms, which thrive better at lower temperatures [31]. At the end of composting, the lignin residue rate was significantly lower in the CaO2 treatments than in the control, indicating that the addition of CaO2 promoted the degradation of lignin. This could be due to the fact that the hydroxyl radical generated by CaO2 hydrolysis can oxidize and attack the resistant structure of lignocellulose, thus increasing the efficiency of lignin degradation [32]. This was one of the reasons for the higher OM degradation rates observed in the treatments with CaO2 additions, especially at relatively high doses.
Figure 3e,f illustrate the variations in the contents and residual rates of DOC, which can be utilized directly by microbes [33]. On day 3, the DOC content of CP5, CP10, and CP15 increased, with residual rates significantly higher than that of CP0. This suggested that CaO2 additions promoted the decomposition of macromolecular OM, probably by disrupting the structure of macromolecular OM and causing a faster temperature rise to increase the activity of hydrolytic enzymes. There was no significant difference in the residual DOC rate between CP20 and CP0, possibly because CP20 had the highest OM mineralization rate among all the treatments during the initial stage of composting. After day 3, the DOC decreased rapidly in all the treatments. On day 15, the DOC content in all the treatments decreased to 23.8–45.3% of the initial DOC content. After that, the DOC content in each treatment fluctuated, accompanied by the decomposition of recalcitrant OM and the utilization of DOC by HS synthesis. By the end of composting, the DOC residual rates of CP10, CP15, and CP20 were significantly higher than those of CP0 and CP5. This may be attributed to the combined effects of the promoted decomposition of recalcitrant OM and the inhibited humification process due to the addition of relatively high doses of CaO2.
Figure 4 shows the amount of ATP released in each treatment on days 3 and 6 to further explain the impact of CaO2 additions on OM decomposition in the initial stage of composting. On day 3, the ATP content in CP0 was significantly lower than that in CP5, CP10, and CP15. This may be due to the significantly lower pH of the control on day 3, which affected the microbial activity. On day 6, no significant difference in pH was observed between the control and the CaO2 treatments, while the ATP content in CP0 was significantly higher than that in the other treatments. These findings indicated that CaO2 additions reduced microbial activity. In addition, although the CaO2 treatments showed significantly lower microbial activity on day 3 than on day 6, the mineralization rate was still high on day 3. This further confirmed the role of CaO2 in promoting OM mineralization.

3.3. Humification

Figure 5a shows that the HS contents in CP0 and CP5 followed a similar trend of initial increase with subsequent decrease, which aligns with existing studies [16,34], whereas the HS contents in CP10, CP15, and CP20 fluctuated during the early composting stage and started to decrease from day 15 onward. The initial increase in CP0 and CP5 might be attributed to the formation of unstable humic-like substances from large amounts of unstable compounds such as fat and oil in food waste [35] in addition to the synthesis of HA, while the significantly lower initial OM contents in CP10, CP15, and CP20 might explain the absence of an initial increase exhibited in these treatments. The decrease in the HS contents in all the treatments could have occurred because the unstable FA was utilized by microorganisms as a substrate [36] or condensed to form a more stable HA [37], as shown in Figure 5b,c. Notably, the FA contents in CP0 and CP5 started to decrease after day 6, whereas those in CP10, CP15, and CP20 decreased from the beginning of composting. This indicated that the addition of CaO2, especially at relatively high doses, promoted the utilization of FA by microorganisms. This was one of the reasons for the significantly higher HA in CP10, CP15, and CP20 on day 6. At the end of composting, there was almost no significant difference in the FA contents among the treatments, suggesting that the unstable FA had been basically consumed during composting. The HA contents in CP0 and CP5 were significantly higher than those in CP10, CP15, and CP20 on day 38, indicating that higher doses of CaO2 inhibited the synthesis of HA during the mature phase. A possible explanation could be that higher CaO2 additions affected the utilization of HA precursors and contributed to the decomposition of relatively unstable HA.
Changes in the HS components directly affected each treatment’s HA/FA, i.e., the humification coefficient, which can reveal the humification process and maturity of the compost [34]. The humification coefficients of all the treatments showed a continuous increase along with composting (Figure 5d). Since the addition of CaO2 facilitated the conversion of FA to HA, the humification coefficients of all the CaO2 treatments were significantly higher than the control on day 9 and day 12. By the end of composting, the humification coefficient of CP5 was significantly higher than that of the other treatments, reaching 1.73 ± 0.11. There was no significant difference between the humification coefficients of CP0, CP10, and CP15, but all of them were significantly higher than that of CP20. There were two possible reasons for the significantly high humification coefficient of CP5. On the one hand, CaO2 additions promoted the decomposition of OM, providing more HA precursors, and on the other hand, the addition of CaO2 facilitated the conversion of FA to HA. The 5% CaO2 addition did not cause significant inhibition to the humification process compared with the addition of higher doses of CaO2. Therefore, a 5% added dosage on the basis of wet weight was suggested.

3.4. Microbial Community Succession

3.4.1. Microbial Community Diversity

As shown in Figure 6a, 47.06% and 26.35% of the variance within the bacterial community was explained by PC1 and PC2, respectively. The bacterial community contained five aggregates throughout the composting process, indicating noticeable differences in the bacterial community at various composting stages. This suggested a good succession status of the bacterial community in all the treatments. Figure 6b illustrates the dynamics of the α-diversity of the bacterial community across all the treatments. The decline in the α-diversity of the bacterial community observed on day 3 across all treatments was primarily attributed to the dominance of thermophilic bacteria during the thermophilic phase, concurrent with the mortality or dormancy of bacteria that were not heat-resistant. The CaO2 treatments, especially CP10, CP15, and CP20, showed a greater decrease in α-diversity on day 3, probably due to their faster temperature increase of the compost. Thereafter, as the compost entered the cooling and mature phases, the α-diversity of the bacterial community in each treatment started to increase. Compared with the control, all the CaO2 treatments exhibited higher α-diversity of the bacterial community on day 15 and day 24, indicating that the addition of CaO2 accelerated the succession of the bacterial community [38].
Figure 6c illustrates the dynamics of the fungal community. PC1 and PC2 explained 76.24% and 13.16% of the variance in the fungal community, respectively. After composting started, the fungal community in each treatment at different composting stages was difficult to distinguish from each other, suggesting that the succession of the fungal community was affected in all the treatments. This can be further verified by the variations in the α-diversity of the fungal community. There was a general decreasing trend in the α-diversity of the fungal community in all the treatments, as shown in Figure 6d, indicating that bacteria adapted to changing environmental situations by rapidly biodegrading OM [39], whereas fungi were restricted within the composting process. Therefore, the following analysis focused mainly on the bacterial community.

3.4.2. Bacterial Community Structure and Dynamics

By analyzing the correlations among environmental factors, OM degradation, humification, and the bacterial community at the genus level (Figure 7a), genera associated with mineralization and humification within the bacterial community can be identified. For example, the abundance of Chelatococcus was negatively correlated with DOC (p < 0.01), HS (p < 0.05), and FA (p < 0.001) and positively correlated with HA (p < 0.001) and GI (p < 0.01). These findings suggested that Chelatococcus may utilize DOC, unstable HS, and FA to produce stable HA, thereby promoting composting maturation. The relative abundances of dominant mineralization and humification genera in the bacterial community are depicted in Figure 7b,c. The results demonstrated that the CaO2 treatments, especially CP10, CP15, and CP20, had a higher relative abundance of mineralization bacteria throughout the composting process. This may be due to the enhancement of OM biodegradability caused by CaO2 additions, which facilitated the growth and reproduction of mineralization bacteria. During the early composting stage, when bioavailable OM was abundant, the relative abundances of both mineralization and humification bacteria were higher in the CaO2 treatments than in the control. This explained the higher humification coefficients in the CaO2 treatments within the early composting stage. However, with limited bioavailable OM in the late composting stage, the competition between mineralization and humification bacteria became increasingly intense. A higher relative abundance of mineralization bacteria in CP10, CP15, and CP20 inevitably caused a greater impact on humification bacteria, thus affecting the humification process of these treatments during the late composting stage.

4. Conclusions

This study confirmed the hypotheses about the potential roles of CaO2 in food waste composting. The addition of CaO2 accelerated the temperature increase of compost and elevated the peak temperatures in the initial stage of composting. The CaO2 additions facilitated the degradation of OM, including refractory OM, and the synthesis of HA in the early composting stage. Moreover, the addition of CaO2 to food waste composting reduced NH3 emissions by 17.1–59.7%. These findings demonstrated the effects of CaO2 in ameliorating key issues in food waste composting. However, relatively high doses of added CaO2 could affect the humification process, thus affecting the synthesis of HA in the late composting stage. Based on these results, a 5% added dosage on the basis of wet weight was suggested to achieve better composting performance. This study provided a comprehensive overview of the effects of the CaO2 dosage on food waste composting, laying the groundwork for promoting the application of the CaO2 additive in aerobic composting of food waste.

Author Contributions

K.H.: Conceptualization, methodology, formal analysis, investigation, data curation, software, writing—original draft. G.Z.: Methodology, resources, software, writing—review and editing, supervision. J.C.: Conceptualization, methodology, resources. N.G.W.: Resources, investigation. G.L.: Conceptualization, supervision, validation, writing—review and editing, project administration, funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Key Research and Development Project of China (2019YFC1906000).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data will be made available on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Schematic of the composting experimental setup.
Figure 1. Schematic of the composting experimental setup.
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Figure 2. Effects of CaO2 dosage on temperature (a) and pH (b) during composting (the letters “a” to “c” were used to demonstrate the significance of the differences, and different letters indicated significant differences among treatments (p < 0.05)). The daily NH3 emissions (c) and accumulative NH3 emissions (d) of the treatments with different CaO2 additions (the term “DM” referred to dry matter).
Figure 2. Effects of CaO2 dosage on temperature (a) and pH (b) during composting (the letters “a” to “c” were used to demonstrate the significance of the differences, and different letters indicated significant differences among treatments (p < 0.05)). The daily NH3 emissions (c) and accumulative NH3 emissions (d) of the treatments with different CaO2 additions (the term “DM” referred to dry matter).
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Figure 3. Changes in the content of organic matter (OM) (a) and its residual rate (b) during composting in each treatment with different CaO2 additions. Changes in the content of lignin (c) and its residual rate (d) during composting in each treatment with different CaO2 additions. Changes in the content of dissolved organic carbon (DOC) (e) and its residual rate (f) during composting in each treatment with different CaO2 additions. The term “DM” referred to dry matter. The letters “a” to “e” were used to demonstrate the significance of the differences, and different letters indicated significant differences among treatments (p < 0.05).
Figure 3. Changes in the content of organic matter (OM) (a) and its residual rate (b) during composting in each treatment with different CaO2 additions. Changes in the content of lignin (c) and its residual rate (d) during composting in each treatment with different CaO2 additions. Changes in the content of dissolved organic carbon (DOC) (e) and its residual rate (f) during composting in each treatment with different CaO2 additions. The term “DM” referred to dry matter. The letters “a” to “e” were used to demonstrate the significance of the differences, and different letters indicated significant differences among treatments (p < 0.05).
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Figure 4. The ATP content in each treatment with different CaO2 additions on day 3 (narrower, darker colored columns) and day 6 (wider, lighter colored columns). The letters “a” to “c” and “a′” to “d′” were used to demonstrate the significance of the differences, and different letters indicated significant differences among treatments (p < 0.05). The term “p < 0.001” indicated that the ATP contents of all the treatments were significantly different between day 3 and day 6 (p < 0.001).
Figure 4. The ATP content in each treatment with different CaO2 additions on day 3 (narrower, darker colored columns) and day 6 (wider, lighter colored columns). The letters “a” to “c” and “a′” to “d′” were used to demonstrate the significance of the differences, and different letters indicated significant differences among treatments (p < 0.05). The term “p < 0.001” indicated that the ATP contents of all the treatments were significantly different between day 3 and day 6 (p < 0.001).
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Figure 5. Dynamics of humic substances (HS) (a), fulvic acid (FA) (b), and humic acid (HA) (c) contents during composting affected by different CaO2 additions (the term “DM” referred to dry matter). (d) Changes in HA/FA in each treatment with different CaO2 additions. The letters “a” to “e” were used to demonstrate the significance of the differences, and different letters indicated significant differences among treatments (p < 0.05).
Figure 5. Dynamics of humic substances (HS) (a), fulvic acid (FA) (b), and humic acid (HA) (c) contents during composting affected by different CaO2 additions (the term “DM” referred to dry matter). (d) Changes in HA/FA in each treatment with different CaO2 additions. The letters “a” to “e” were used to demonstrate the significance of the differences, and different letters indicated significant differences among treatments (p < 0.05).
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Figure 6. The β-diversity (indicated by PCoA based on weighted Unifrac distance) of the following: (a) The bacterial community; (c) The fungal community. The α-diversity (indicated by Chao richness and Shannon diversity) of the following: (b) The bacterial community; (d) The fungal community.
Figure 6. The β-diversity (indicated by PCoA based on weighted Unifrac distance) of the following: (a) The bacterial community; (c) The fungal community. The α-diversity (indicated by Chao richness and Shannon diversity) of the following: (b) The bacterial community; (d) The fungal community.
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Figure 7. (a) Primary bacterial community and correlations among environmental factors, OM degradation, humification, and the bacterial community at the genus level (top 15) (the marks “*”, “**”, and “***” were used to show the significance levels, in which the marker “*” referred to “p < 0.05”, “**” referred to “p < 0.01”, and “***” referred to “p < 0.001”); the relative abundances of dominant mineralization bacteria (b) and humification bacteria (c) in each treatment with different CaO2 additions.
Figure 7. (a) Primary bacterial community and correlations among environmental factors, OM degradation, humification, and the bacterial community at the genus level (top 15) (the marks “*”, “**”, and “***” were used to show the significance levels, in which the marker “*” referred to “p < 0.05”, “**” referred to “p < 0.01”, and “***” referred to “p < 0.001”); the relative abundances of dominant mineralization bacteria (b) and humification bacteria (c) in each treatment with different CaO2 additions.
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Table 1. Components and properties of the artificially blended food waste.
Table 1. Components and properties of the artificially blended food waste.
Food Waste Components (Wet Weight)Mass
(g)		Percentage
(%)		Moisture Content (%)C/N RatioOM
(%)
Cooked rice17502558.62 ± 0.0938.26 ± 0.2499.64 ± 0.09
Cooked noodles10501545.00 ± 0.1517.75 ± 0.3398.17 ± 0.12
Cooked chicken breast350568.17 ± 0.233.52 ± 0.3697.54 ± 0.11
Cabbage7001091.96 ± 0.1916.10 ± 0.2593.13 ± 0.21
Celery7001094.69 ± 0.1712.77 ± 0.2289.59 ± 0.13
Potato10501561.19 ± 0.1429.65 ± 0.3195.41 ± 0.14
Apple7001085.60 ± 0.1480.04 ± 0.2597.34 ± 0.09
Banana7001082.66 ± 0.2133.75 ± 0.2494.71 ± 0.12
TOTAL700010071.21 ± 0.7622.98 ± 1.1294.97 ± 0.82
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Hu, K.; Zhou, G.; Chen, J.; Wafula, N.G.; Li, G. Effects of Calcium Peroxide Dosage on Physicochemical Parameters, Organic Matter Degradation, Humification, and Microbial Community Succession During Food Waste Composting. Waste 2025, 3, 3. https://doi.org/10.3390/waste3010003

AMA Style

Hu K, Zhou G, Chen J, Wafula NG, Li G. Effects of Calcium Peroxide Dosage on Physicochemical Parameters, Organic Matter Degradation, Humification, and Microbial Community Succession During Food Waste Composting. Waste. 2025; 3(1):3. https://doi.org/10.3390/waste3010003

Chicago/Turabian Style

Hu, Kun, Guoning Zhou, Jia Chen, Nalume Gerald Wafula, and Guangming Li. 2025. "Effects of Calcium Peroxide Dosage on Physicochemical Parameters, Organic Matter Degradation, Humification, and Microbial Community Succession During Food Waste Composting" Waste 3, no. 1: 3. https://doi.org/10.3390/waste3010003

APA Style

Hu, K., Zhou, G., Chen, J., Wafula, N. G., & Li, G. (2025). Effects of Calcium Peroxide Dosage on Physicochemical Parameters, Organic Matter Degradation, Humification, and Microbial Community Succession During Food Waste Composting. Waste, 3(1), 3. https://doi.org/10.3390/waste3010003

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