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Article

Optimization of Fermentation Parameters for the Sustainable Production of Effective Carbon Sources from Kitchen Waste to Enhance Nutrient Removal in Sewage

by
Xuwei Gui
1,2,3,
Ling Wang
4 and
Zhenlun Li
2,*
1
Chongqing Key Laboratory of Chemical Process for Clean Energy and Resource Utilization, College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, China
2
Chongqing Key Laboratory of Interface Process and Soil Health, College of Resources and Environment, Southwest University, Chongqing 400716, China
3
Chongqing Water & Environment Holdings Group Ltd., Chongqing 400042, China
4
Hanhong College, Southwest University, Chongqing 400716, China
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(17), 8079; https://doi.org/10.3390/su17178079
Submission received: 5 August 2025 / Revised: 29 August 2025 / Accepted: 3 September 2025 / Published: 8 September 2025
(This article belongs to the Topic Advances in Organic Solid Waste and Wastewater Management)
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Abstract

In this study, we optimize the kitchen waste fermentation process by adjusting the fermentation time and temperature to prepare high-efficiency carbon sources to enhance nitrogen and phosphorus removal during sewage treatment. Simulated kitchen waste fermentation experiments were performed, and the impact on the pollutant removal efficiencies was analyzed using a sequence batch reactor (SBR). The results showed that the volatile fatty acid (VFA) concentration peak occurred on the first day of fermentation, the maximum increment was 543.19 mg/L, and the maximum soluble chemical oxygen demand/total nitrogen (COD/TN) ratio was 40.49. However, the highest total nitrogen (TN) removal efficiency was 70.42% on the second day of fermentation. An increase in temperature promoted organic matter release, with the highest soluble COD concentration of 22.69 g/L observed at 45 °C. Further, the maximum VFAs production (935.08–985.13 mg/L) occurred from 25 to 35 °C. In addition, the fermentation products in this temperature range also showed the optimal removal efficiencies for total phosphorus (TP) and TN at 91.50% and 79.63%, respectively. Although 15 °C and 45 °C were beneficial for COD reduction, they were not conducive to nitrogen and phosphorus removal. The energy consumption and the synergistic pollutant removal showed that the optimal fermentation conditions were 2 days at 35 °C. Under these conditions, the kitchen waste-derived carbon source achieved efficient TN and TP removal, as well as COD reduction. Therefore, these conditions provide a feasible solution for the “reduction and sustainability” of kitchen waste.

1. Introduction

Kitchen waste production continues to rise during the urbanization process. A conservative estimation is that kitchen waste accounts for 55% of domestic waste, and the 2023 production reached 1.397 × 108 tons [1,2]. This not only represents a loss of resources, but it also poses significant environmental challenges. In response, the government has proposed the guiding principles of “reduction, harmlessness, and resource utilization” to deal with these problems and promote sustainable development. Bio-transformation technology can reduce kitchen waste, and fermentation products can be effectively used in sewage treatment to achieve the environmental protection goal of “treating waste with waste.” [3]. This process helps to raise public awareness about waste management and resource recycling, and promotes societal understanding and support for sustainable development. The high carbon–nitrogen ratio (C/N) in kitchen waste hydrolysis helps improve the overall efficiency of sewage treatment systems. However, Zhang et al. [3] did not explore the product differences brought about by the fermentation environment and the differences in pollutant removal efficiency caused by the product differences.
Fermentation time and temperature are key parameters that significantly affect degradation efficiency and product characteristics [4]. Fermentation time determines the contact duration between the substrate and microorganisms, directly influencing the hydrolysis efficiency of the substrate and the overall reactor performance. A prolonged fermentation time will increase the degradation efficiency of kitchen waste, but exceeding a reasonable range will lead to an accumulation of acidic substances that will cause serious negative effects on degradation and acidogenic bacteria, thereby reducing the degradation efficiency of organic solids [5,6]. Temperature profoundly impacts metabolic activity and population dynamics of microbial communities, thus affecting hydrolysis kinetics and intermediate product solubility [7,8], and leading to product differences. Sudiartha et al. [9] further pointed out that temperature fluctuations can change competition between acidogenic and methanogenic bacteria, thereby affecting the accumulation of volatile fatty acids (VFAs). However, existing studies often focus broadly on VFAs production or general anaerobic digestion dynamics, without systematically evaluating the synergistic effects of time and temperature on both carbon source production and subsequent nutrient removal efficiency in biological wastewater treatment.
Therefore, the aim of this study is to quantify the direct impact of fermentation time and temperature on the resulting carbon source’s efficacy in achieving synergistic, high-efficiency TN and TP removal, addressing the need for precise process control highlighted in their work. The findings are expected to provide a sustainable and resource-efficient solution to kitchen waste while addressing challenges in wastewater treatment.

2. Materials and Methods

2.1. Test Materials and Microbial Samples

To ensure the stability of kitchen waste composition analysis, the sampling point is fixed at a university canteen in Chongqing, China, from 12:40 to 13:00 daily, for a total of 30 times. The long-term monitoring is designed to validate the feasibility of utilizing it as a sustainable carbon source. When optimizing fermentation parameters, the simulated kitchen waste was used to ensure consistency of the raw materials, facilitating direct comparisons of KWH application in sewage treatment., The raw materials included 25 wt% meat, 25 wt% vegetables, and 50 wt% rice.
The kitchen waste degradation bacteria were screened in the laboratory and stored in the China General Microbiological Culture Collection Center (CGMCC) with the preservation numbers BS-P21 (protein-degrading bacteria, CGMCC No. 20541), BS-S7 (starch-degrading bacteria, CGMCC No. 20543), MI-A13 (fat-degrading bacteria, CGMCC No. 20545), and MI-C4 (cellulose-degrading bacteria, CGMCC No. 20542), respectively [10].
Sewage and sludge are collected from the inlet and sludge return tanks of the Beibei Wastewater Treatment Plant in Chongqing, China. The properties of the sewage are shown in Table 1. The sludge is produced during the long-term operation of the sewage treatment process, and has good microbial activity and community stability.

2.2. Reactor Setup and Operating Conditions

This study used three sets of six-unit reactors for synchronous experiments, with 3 biological repetitions, and a single sewage treatment unit is shown in Figure S1. The reactor has an effective volume of 3L, a reaction volume of 2L, and a drainage ratio of 0.5. The operating conditions of the reactor were 23 ± 1 °C, 150 r/min, the aeration rate was 1 L/min, and the initial sludge concentration was 3000 mg/L. The reactor operation cycle was 6 h, including 15 min of influent, 30 min of stirring, 250 min of aeration, 50 min of sedimentation and 15 min of effluent. All reactors are in triple.

2.3. Experimental Design

2.3.1. Primary Component Analysis of the Kitchen Waste

Based on the pretreatment experience of kitchen waste treatment plants, impurities and excess oil were removed from the kitchen waste through manual sorting and three brief rinses with boiling water (at 100 °C) for 5–10 s each. The physical and chemical properties of kitchen waste were measured, including total solids (TS), volatile solids (VS), moisture content (MC), fat, protein, total sugars and soluble nutrients.

2.3.2. Preparation of a High Nitrogen and Phosphorus Removal Carbon Source from Kitchen Waste

Simulated kitchen waste was fermented in a fermentation tank, and the basic fermentation conditions were as follows: a fermentation cycle of 48 h, a fermentation temperature of 35 °C, a stirring speed of 180 r/min, and uncontrolled pH. The fermentation time and temperature were adjusted according to the test requirements, with fermentation times of 0 days, 1 day, 2 days, 3 days, and 4 days; 0 days means undergo the same processing steps as other treatments but without fermentation. The fermentation temperatures used in the experiments were 15 °C, 25 °C, 35 °C, and 45 °C. The degradation rate of kitchen waste, the TS and vs. of hydrolysate, and the content of TN, COD and VFAs in the liquid were measured. To ensure the standardization of the initial carbon source quality and minimize its impact on pollutant removal efficiency in biological replicates during the backend sewage treatment, fermentation experiments were conducted in a technical replicate manner.
After sludge inoculation, the kitchen waste hydrolysate (KWH) was added to the SBR reactor, and the initial COD/TN was set to 9. The reactor operated for 3 days, and the concentrations of TN, NH4+, NO3−, TP and COD in the influent and effluent were measured during the last operating cycle. Also, the dynamic changes of TN, NH4+ and NO3− were measured by sampling every 1 h.

2.4. Analytical Methods

2.4.1. Kitchen Waste Detection and Analysis

Kitchen waste samples were dried to a constant weight at 105 °C to determine the TS and MC contents. The samples were then heated in a muffle furnace at 550 °C for 3 h to determine the ash and vs. contents, with vs. = TS—ash [11]. The total polysaccharide content was determined using the Anthrone method, with glucose as the standard [12]. The protein and fat contents in the kitchen waste were determined according to the current national standards of China [13,14]. The concentration of VFAs (acetic acid, propionic acid, butyric acid, and valeric acid) was measured by a gas chromatograph (GC, Agilent 7890B, Agilent Technologies, Inc., Santa Clara, California, USA) equipped with a FID detector, nitrogen as the carrier gas, and a column temperature of 80 °C. Sample preparation: KWH was centrifuged at 4 °C, 7500 r/min for 15 min. Supernatant was filtered through a 0.45 μm filter membrane and mixed with 3% phosphoric acid solution in equal volume, to be tested [15].

2.4.2. Sewage Detection and Analysis

Liquid samples were filtered through filter paper, and the filtered liquid was analyzed for water quality indicators according to the Standard Methods for Water and Wastewater Testing [16]. The pH of the liquid was measured using a pH meter (pHS-3D, Shanghai Precision Scientific Instrument Co., Ltd., Shanghai, China). NH4+, nitrite nitrogen (NO2−), nitrate nitrogen (NO3−), and total nitrogen (TN) were analyzed using the salicylic acid-hypochlorite method, the N-(1-naphthyl)-ethylenediamine photometric method, the ultraviolet spectrophotometric screening method, and the alkaline potassium persulfate oxidation-ultraviolet spectrophotometric method, respectively. The total phosphorus (TP) was measured using the molybdenum antimony spectrophotometric method. The chemical oxygen demand (COD) was detected using the rapid closed catalytic digestion method. Mixed liquor suspended solids (MLSS) in the sewage were analyzed using the gravimetric method. Dissolved oxygen (DO) was measured online using a portable DO meter (JPB-607A, INASE Scientific Instrument Co., Ltd., Shanghai, China).

2.5. Statistical Analyses

The sample was measured in triplicate, and the results were expressed as mean ± standard error. A p-value of <0.05 was considered to be statistically significant. Data integration was conducted in Excel 2016. One-way analysis of variance (ANOVA) was conducted in SPSS Statistics 19 to identify differences between two groups. Plotting was conducted in Origin Pro 9.

3. Results and Discussion

3.1. Composition Analysis of Kitchen Waste

Figure 1 shows that the moisture contents of kitchen waste at the sampling sites were high, at approximately 80.49–84.85%. The TS and vs. contents varied due to the instability of the kitchen waste, and they ranged from 15.15 to 19.51% and 14.46 to 19.11%, respectively. The VS/TS ratio ranged from 95.01 to 98.49%. This result indicated that organic matter in the kitchen waste occupied a dominant position, and the kitchen waste possessed a good fermentation potential. There was no significant difference compared with Zhang’s [17] one-year monitoring of food waste in a university canteen in Xi’an. This result was likely due to simpler meal types and a more consistent dining population in the campus canteen compared to the social source. Carbohydrates were the primary food waste components, and the total sugar content was in the range of 5.62–8.74 g/100 g. In addition, a large number of carbohydrates can be converted into pyruvate through the glycolysis pathway and then to acetic acid, propionic acid, and butyric acid, which provide a good resource recovery potential [6,18]. The fat and protein contents were only 1.15 g/100 g and 0.67 g/100 g, respectively. This result is closely related to the eating habits of Chinese people who have a higher proportion of cereals and vegetables in their diet and a relatively small intake of soy products [19]. In addition, the fat content was further reduced after oil–water separation pretreatment.
The contents of carbon, nitrogen, phosphorus, and other nutrients are of great significance to the fermentation process and resource utilization of kitchen waste. The distribution of soluble nutrients in kitchen waste was analyzed (Figure 2), and the soluble TN, TP, and COD contents ranged from 112.57 mg/L to 384.76 mg/L, 16.70 mg/L to 64.27 mg/L, and 6.64 g/L to 14.79 g/L, respectively. The primary purpose of the kitchen waste application in a sewage treatment system is to increase the carbon source of low-carbon sewage to enhance the sewage pollutant removal efficiency. Therefore, the COD content has important significance for efficient sewage treatment [20]. In addition, the sum of NH4+, NO3−, and NO2− accounted for only 12.39% of the TN. It was concluded that the dissolved TN in kitchen waste primarily existed in the form of organic nitrogen. Organic nitrogen needs to be converted into other nitrogen sources through microbial action to provide nutrients for nitrifying and denitrifying microorganisms. However, a high organic nitrogen content may slow down the start-up rate of the reactor [21]. The optimal C/N ratio for kitchen waste fermentation is typically between 20 and 30, and this ratio is considered a key parameter for enhancing microbial metabolic activity during fermentation to effectively facilitate the degradation of proteins and carbohydrates and increase VFA production [22]. The soluble COD/TN ratio of the kitchen waste in this study was 36.82 to 76.85, indicating the need to adjust other fermentation processes to optimize fermentation.

3.2. Preparation of High-Efficiency Kitchen Waste Carbon Sources Using Fermentation Process Control

3.2.1. Fermentation Product Differences Due to Fermentation Times

Kitchen waste hydrolysate composition and properties vary with fermentation conditions, which will affect its denitrification performance as an external carbon source during wastewater treatment [23]. The fermentation product differences under different fermentation times are shown in Figure 3a. The pH in the fermentation tank decreased as the fermentation time increased, and the pH ranged from 4.30 to 4.71. At this point, both acidogens and methanogens are inhibited. There was no significant difference in the degradation efficiency after 1–4 days of fermentation. In addition, only 40.18–54.42% was likely due to the acidic environment of free fermentation, which weakens the activity of degrading bacteria. The TS and vs. contents that corresponded to the degradation rate decreased with increasing fermentation times. There was no significant change in the TS, but the VS/TS ratio decreased significantly after three days of fermentation. This result indicated that the proportion of organic solids in the fermentation tank was significantly reduced, and the degradation effect was enhanced.
Both the TN and COD in the hydrolysate increased with increasing fermentation time. In addition, the TN increased from 489.37 mg/L to 998.89 mg/L, and the COD increased from 20.03 g/L to 26.92 g/L. The dissolved TN and COD were significantly greater after three days of fermentation than at other fermentation times (Figure 3b). Further analysis of the product changes during fermentation revealed the presence of acetic acid and propionic acid in the hydrolysate, and acetic acid was the dominant component (Figure 3c). Compared with the unfermented samples, the VFA concentration increased by 333.27 mg/L–543.19 mg/L, 54.82–66.41%, and the highest VFA concentration was produced after one day of fermentation. Several studies have shown that short-term fermentation is beneficial for the hydrolysis process and inhibits methanogen activity, thereby maximizing VFA accumulation [24]. On the other hand, long-term fermentation leads to a decrease in VFA concentration because the metabolic activities of the microbial community gradually become weakened, and VFA may be further metabolized into other products, such as methane. Additionally, the composition of the microbial community may also change, and the relative abundance of some VFA-producing bacteria may decrease [25]. VFAs are high-quality carbon sources that enhance microbial denitrification, and there is a need to minimize nitrogen introduction when using hydrolysate as a carbon source in sewage treatment. In our study, the C/N ratio of the hydrolysis products reached its highest values of 36.28 to 40.49 after 1–2 days of fermentation. This optimal C/N ratio not only maximized the carbon source available for nitrogen and phosphorus removal but also minimized nitrogen introduction. At this point, the TN removal efficiency reached the highest level of 70.42%. Similarly, Chen et al. [26] effectively removed nitrogen and phosphorus from wastewater by increasing the C/N ratio through the addition of a plant fermentation carbon source. In addition, Law et al. [27] found that VFA production doubled after 1.5 days of fermentation, reaching 0.77 gVFAs/g COD; their findings are consistent with the results of this study.

3.2.2. Differences in Fermentation Products Due to Fermentation Temperature

Temperature significantly affects microbial activity in the fermentation tank and is an important condition for controlling the preparation of carbon sources from kitchen waste. Figure 4a shows that the hydrolysate pH decreased with an increase in fermentation temperature, and the kitchen waste degradation rate continued to increase. The degradation rate at 25–45 °C was significantly higher than that at a low temperature (15 °C), and the TS content showed the opposite trend. These results indicated that low temperatures inhibited microorganism activities and reduced their ability to degrade organic matter. Cha et al. [28] found that when the temperature decreased from 30 °C to 15 °C, the substrate degradation rate decreased from 92% to 25%.
An analysis of the soluble nutrient changes (Figure 4b) showed that there was a significant difference in the soluble COD concentration under different fermentation temperatures. The highest value of 22.69 g/L was at 45 °C, indicating the importance of temperature for organic nutrient release. The soluble COD/TN ratio of the hydrolysate increased with an increase in temperature, with a significant difference at 45 °C. However, Xiong [29] found that as fermentation time increased (>4 days), the soluble COD concentration in the hydrolysate gradually became lower than at 25–35 °C. This result suggested that short-term high-temperature fermentation is beneficial for organic matter hydrolysis in kitchen waste.
The VFAs concentration results (Figure 4c) showed that the highest VFAs were produced at 25–35 °C, and these were 935.08 mg/L and 985.13 mg/L, respectively. It has been reported that the optimal temperature of acid-producing bacteria is approximately 35 °C, at which acetic acid fermentation dominates. Additionally, the microbial community structure is relatively stable under mesophilic conditions, maintaining a relatively stable VFA production [30]. The acid-producing efficiency will be reduced by 50% or more [31,32] when the temperature is less than 20 °C, and this study showed similar results. This is because low temperature inhibits the activity of microorganisms' growth rate, and slows down the decomposition rate of organic matter and the production of metabolic products [33]. It has been found that VFA production after 6 days of fermentation at 24 °C is equivalent to that after 14 days of fermentation at 14 °C [34]. Although high temperature can increase the hydrolysis rate of organic matter and promote VFA production to a certain extent, the changes in microbial community structure under high-temperature conditions may be more intense, which may lead to fluctuations in VFA production [30]. In addition, Zhang et al. [35] pointed out that VFAs can provide sufficient metabolic demand for denitrifying bacteria to exhibit higher denitrification efficiency in the presence of VFAs. This finding is consistent with the results of this study, as the TN removal efficiency of the 35 °C fermentation products was the highest (79.63%).

3.3. Impact of Product Differences on Pollutant Removal in Sewage

3.3.1. Effect of Products Under Different Fermentation Times on Sewage Treatment

Figure 5 shows the impact of the kitchen waste hydrolysate on pollutant removal under different fermentation times. The results demonstrate that the products from 2 to 3 days of fermentation significantly improved the TN removal compared to other treatments. The TN removal efficiency increased and then decreased, peaking at 70.42% after 2 days of fermentation, which was consistent with the trend of soluble COD. However, compared to the properties of the hydrolysate, the VFA content after 2 days of fermentation was less than that at 1 day, but the pH was lower. This result suggested that other organic acid types were present in the hydrolysate. These organic acids not only effectively promoted nitrogen removal, but they also lowered the pH due to their low pKa [36].
The DO concentration under constant aeration conditions was lower after 2–3 days of fermentation, according to an analysis of the DO changes (Figure S2). This suggested that more organic nitrogen consumed oxygen; hence, the low DO accelerated the denitrification process in the reactor. This may have also been one of the factors that led to the higher TN removal efficiency from the fermentation products at 2–3 days. Xu et al. [37] demonstrated that low DO levels significantly enhance the denitrification effect. A higher nitrogen removal rate was achieved due to simultaneous nitrification–denitrification and anoxic denitrification. Observations of the NH4+ and NO3− transformations (Figure 6) showed that the amount of NH4+ converted exceeded the amount of NO3− generated during the reaction cycle. This result, combined with the DO, NO2− (Figure S3), and NH2OH (Figure S4) results, allowed us to conclude that NO3− was immediately consumed after generation. This led to reduced detection levels. In addition, simultaneous nitrification and denitrification occurred within the same reactor, and this could have resulted in a greater reduction in NH4+ than the net generation of NO3−.
The COD removal efficiency ranged from 84.17 to 87.26%, with no significant variation or strong pattern observed for the COD and TP removal under different fermentation durations (Figure 5). However, these rates were still higher than those of the CK. It is speculated that the high addition of KWH may have led to a carbon source saturation state for the microorganisms, thereby limiting the utilization of COD. In summary, short-term fermentation is more conducive to reducing energy consumption and balancing the removal of pollutants. The two-day fermentation hydrolysate was considered the optimal duration for the preparation of carbon sources.

3.3.2. Effect of Products Under Different Fermentation Temperatures on Wastewater Treatment

Based on the premise that the addition of kitchen waste hydrolysate effectively reduces pollutant concentrations in sewage, the products generated under different fermentation temperatures on the effect of sewage pollutants removal were explored. Figure 7 shows that with an increase in fermentation temperature, the TN concentration in the reactor effluent first decreased and then increased. The TN concentrations in the effluent at 25 °C and 35 °C were significantly less than those at 15 °C and 45 °C, and the removal efficiencies were 70.87% and 79.63%, respectively. This result was similar to the results of the fermentation product types. Therefore, the denitrifying bacteria preferred acetic acid, which has been confirmed in many studies [36,38]. The concentration trends of the NH4+ and NO3− effluent in the reactor were similar to that of TN, with 1.45 mg/L–5.37 mg/L for NH4+ and 2.96 mg/L–7.82 mg/L for NO3− in the effluent. The high TN content in the effluent may have been due to the high initial organic nitrogen content (7.45 mg/L–21.76 mg/L) in the reactor wastewater. The conversion of organic nitrogen to NH4+ is a common phenomenon under such conditions. The subsequent accumulation of NH4+ slows down the denitrification process and poses a challenge to effective denitrification [39].
The TP removal efficiency at 25 °C was the highest at 91.50%, and the effluent concentration was significantly less than that at 45 °C. As shown in Figure 4, KWH at 45 °C exhibited high COD values coupled with low VFAs content. The weaker competition for VFAs and less diverse carbon source uptake by polyphosphate-accumulating bacteria compared to denitrifying bacteria may account for the reduced TP removal of KWH at higher temperatures [40]. The COD removal rates between each treatment showed significant differences with increases in the fermentation temperatures, first increasing and then decreasing. In addition, the COD removal efficiency was between 73.12% and 91.69%. The 15 °C and 45 °C treatments were significantly higher than those at 35 °C and 25 °C, but the removal effects of TN and TP were not satisfactory. It is speculated that the low VFAs content limits the carbon source supply for microbial denitrification and biological phosphorus removal. Due to the TN, TP, and COD removal efficiency results and the potential energy consumption during fermentation, it was concluded that 35 °C could be used as the optimal fermentation temperature for carbon source preparation. Li et al. [41] analyzed the energy consumption of fermentation systems under different temperatures, and the energy consumption under high and medium temperature heating was 441 kJ and 189 kJ, respectively. This result further supported the feasibility of fermentation temperature optimization in engineering applications.

4. Conclusions

The effects of different fermentation times and temperatures on kitchen waste hydrolysis characteristics and their application effects in sewage treatment were compared in this study. The results indicated the key role of fermentation parameters in the preparation of efficient carbon sources from kitchen waste fermentation. Fermentation at 35 °C for 2 days offers advantages in energy consumption and pollutant removal efficiency, and was considered feasible for engineering implementation, making it an ideal parameter for the resourceful utilization of kitchen waste as a carbon source. This research provides a scientific basis for the “reduction and sustainability” of kitchen waste, and it also provides an efficient, low-cost carbon source solution for the sewage treatment field. Future studies should further explore the succession of microbial communities during fermentation and their impact on the pollutant removal mechanisms to further optimize the kitchen waste fermentation process and sewage treatment efficacy.

Supplementary Materials

https://www.mdpi.com/article/10.3390/su17178079/s1, Figure S1: Test device diagram; Figure S2: Dynamic change of DO concentration under different fermentation time; Figure S3: ynamic change of NO2− concentration under different fermentation time; Figure S4: Dynamic change of NO2OH concentration under different fermentation time.

Author Contributions

Conceptualization, Z.L. and X.G.; methodology, X.G.; software, X.G.; validation, X.G., Z.L. and L.W.; formal analysis, X.G.; investigation, X.G. and L.W.; resources, Z.L.; data curation, X.G.; writing—original draft preparation, X.G.; writing—review and editing, Z.L.; visualization, Z.L.; supervision, Z.L.; project administration, Z.L.; funding acquisition, Z.L. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the National Natural Science Foundation of China (No. 42077217) and the National Training Program of Innovation and Entrepreneurship for Undergraduates (No. 202210635048).

Data Availability Statement

Xuwei Gui (2025), “The influence of different fermentation conditions on the preparation of carbon sources from kitchen waste to enhance the removal of pollutants in sewage”, Mendeley Data, V2, doi: 10.17632/dtpppbwz2d.2.

Conflicts of Interest

Author Xuwei Gui was employed by Chongqing Water & Environment Holdings Group Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Analysis of solid content and composition of kitchen waste. Data are presented as the means ± standard error, n = 3.
Figure 1. Analysis of solid content and composition of kitchen waste. Data are presented as the means ± standard error, n = 3.
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Figure 2. Distribution of soluble substances in kitchen waste. (a) soluble nitrogen content; (b) soluble phosphorus content; (c) soluble COD content; (d) soluble COD/TN. Data are presented as the means ± standard error, n = 3.
Figure 2. Distribution of soluble substances in kitchen waste. (a) soluble nitrogen content; (b) soluble phosphorus content; (c) soluble COD content; (d) soluble COD/TN. Data are presented as the means ± standard error, n = 3.
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Figure 3. Effect of fermentation time on product type. (a) fermentation product; (b) soluble nitrogen, COD content and soluble COD/TN; (c) VFAs content. Note: Data are presented as the means ± standard error, n = 3, n is a technical replicate. Different letters indicate significant differences (Tukey HSD, p < 0.05). In the figure comparing VFA concentrations, the letters in the top row indicate significant differences in propionic acid, and letters in the bottom row indicate significant differences in acetic acid. Same as below.
Figure 3. Effect of fermentation time on product type. (a) fermentation product; (b) soluble nitrogen, COD content and soluble COD/TN; (c) VFAs content. Note: Data are presented as the means ± standard error, n = 3, n is a technical replicate. Different letters indicate significant differences (Tukey HSD, p < 0.05). In the figure comparing VFA concentrations, the letters in the top row indicate significant differences in propionic acid, and letters in the bottom row indicate significant differences in acetic acid. Same as below.
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Figure 4. Effect of fermentation temperature on product type. (a) fermentation product; (b) soluble nitrogen, COD content and soluble COD/TN; (c) VFAs content. Data are presented as the means ± standard error, n = 3, n is a technical replicate.
Figure 4. Effect of fermentation temperature on product type. (a) fermentation product; (b) soluble nitrogen, COD content and soluble COD/TN; (c) VFAs content. Data are presented as the means ± standard error, n = 3, n is a technical replicate.
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Figure 5. Influence of different fermentation time products on pollutant removal in sewage. “CK” is raw sewage without added KWH. Data are presented as the means ± standard error, n = 3, n is biological replicates. Note: Only indicators with significant differences are labeled, and different letters indicate significant differences (Tukey HSD, p < 0.05). RE is the removal efficiency, Effl. is the effluent, and Infl. is the influent. Same as below.
Figure 5. Influence of different fermentation time products on pollutant removal in sewage. “CK” is raw sewage without added KWH. Data are presented as the means ± standard error, n = 3, n is biological replicates. Note: Only indicators with significant differences are labeled, and different letters indicate significant differences (Tukey HSD, p < 0.05). RE is the removal efficiency, Effl. is the effluent, and Infl. is the influent. Same as below.
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Figure 6. Nitrogen removal from sewage is affected by fermentation conditions. Data are presented as the means ± standard error, n = 3.
Figure 6. Nitrogen removal from sewage is affected by fermentation conditions. Data are presented as the means ± standard error, n = 3.
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Figure 7. Influence of different fermentation temperature products on pollutant removal in sewage. Data are presented as the means ± standard error, n = 3. Note: Only indicators with significant differences are labeled, and different letters indicate significant differences (Tukey HSD, p < 0.05). RE is the removal efficiency, Effl. is the effluent, and Infl. is the influent.
Figure 7. Influence of different fermentation temperature products on pollutant removal in sewage. Data are presented as the means ± standard error, n = 3. Note: Only indicators with significant differences are labeled, and different letters indicate significant differences (Tukey HSD, p < 0.05). RE is the removal efficiency, Effl. is the effluent, and Infl. is the influent.
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Table 1. The properties of the sewage are used in process optimization.
Table 1. The properties of the sewage are used in process optimization.
TestTN
(mg/L)		COD
(mg/L)		TP
(mg/L)		pHCOD/TN
Fermentation time test24.1370.480.657.543.11
Fermentation temperature test27.13117.730.947.664.34
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Gui, X.; Wang, L.; Li, Z. Optimization of Fermentation Parameters for the Sustainable Production of Effective Carbon Sources from Kitchen Waste to Enhance Nutrient Removal in Sewage. Sustainability 2025, 17, 8079. https://doi.org/10.3390/su17178079

AMA Style

Gui X, Wang L, Li Z. Optimization of Fermentation Parameters for the Sustainable Production of Effective Carbon Sources from Kitchen Waste to Enhance Nutrient Removal in Sewage. Sustainability. 2025; 17(17):8079. https://doi.org/10.3390/su17178079

Chicago/Turabian Style

Gui, Xuwei, Ling Wang, and Zhenlun Li. 2025. "Optimization of Fermentation Parameters for the Sustainable Production of Effective Carbon Sources from Kitchen Waste to Enhance Nutrient Removal in Sewage" Sustainability 17, no. 17: 8079. https://doi.org/10.3390/su17178079

APA Style

Gui, X., Wang, L., & Li, Z. (2025). Optimization of Fermentation Parameters for the Sustainable Production of Effective Carbon Sources from Kitchen Waste to Enhance Nutrient Removal in Sewage. Sustainability, 17(17), 8079. https://doi.org/10.3390/su17178079

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