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Article

A Performance Comparison of Three Amino Acid Additives in the Process of Photo-Fermentative Biohydrogen Production with Corn Straw

by
Chenxi Xia
1,2,
Danping Jiang
1,
Xueting Zhang
1,2,
Ning Xie
2,
Chaoyang Lu
1 and
Quanguo Zhang
1,2,*
1
Key Laboratory of New Materials and Facilities for Rural Renewable Energy (MOA of China), Henan Agricultural University, Zhengzhou 450002, China
2
Institute of Agricultural Engineering, Huanghe S & T University, Zhengzhou 450006, China
*
Author to whom correspondence should be addressed.
Fermentation 2025, 11(3), 108; https://doi.org/10.3390/fermentation11030108
Submission received: 13 December 2024 / Revised: 9 February 2025 / Accepted: 14 February 2025 / Published: 24 February 2025
(This article belongs to the Special Issue Bioconversion of Biomass for Effective Production of Biofuels as Well as Biobased Chemicals and Materials)
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Abstract

:
The growth and metabolism of photosynthetic bacteria play a significant role in the efficiency of substrate and energy conversion in photo-fermentation biohydrogen production (PFHP). In this paper, the influence of different concentrations of L-alanine (0.3–1.2 g/L), L-leucine (0.6–1.5 g/L), and L-serine (1–2.5 g/L) on the PFHP and microbial metabolism were investigated. The results showed that sole additions of L-alanine at 0.6 g/L, L-leucine at 0.9 g/L, and L-serine at 1.5 g/L to the PFHP could enhance the cumulative biohydrogen production to 260 ± 4.01 mL (39.04% increase), 267 ± 4.27 mL (42.78% increase), and 248 ± 3.97 mL (32.62% increase), respectively. An analysis of the scatter matrix plots indicated that three amino acid additives play a key role in increasing hydrogen production. This study helps to further explore the effect of amino acid-based additives on PFHP.

1. Introduction

Hydrogen energy, with a high calorific value and clean and pollution-free characteristics, is considered one of the ideal alternative energies in the future [1]. Biohydrogen production is a method that utilizes the metabolism of microorganisms to convert the energy that is stored in organic matter into hydrogen energy [2]. In this way, the reaction of biohydrogen production is carried out under mild conditions of ambient temperature, atmospheric pressure, and near neutrality due to the involvement of microorganisms. In addition, the feedstocks for biohydrogen production are mainly biomass, municipal waste, and organic wastewater [3]. These raw materials have huge reserves and are inexpensive, while the production process has the advantages of low energy consumption, no pollution, and no consumption of fossil energy [4,5]. Biohydrogen production technology not only achieves the reasonable disposal of waste but also produces clean energy, which has become a major development direction of hydrogen production technology at home and abroad [6]. Among them, PFHP is the method in which microorganisms produce hydrogen gas through the decomposition of substrates by photosynthesis [7]. It can utilize a wide range of small-molecule organics and has the advantages of high photoconversion efficiency and the ability to utilize solar energy [4]. In a long-term perspective, PFHP is one of the most promising pathways for hydrogen production [8,9].
PFHP is a complex biochemical reaction involving the metabolism of microorganisms and the conversion of organic matter [10]. Different additives have been proven to have a significant effect on the culture of photosynthetic bacteria and the operation of biodigestion [11]. Most of the additives, such as yeast extract, peptone, and a series of ammonium salts, have been used in fermentations for yield enhancement. Amongst these, nitrogen plays an important role in affecting the outcome of fermentation, which can be divided into organic nitrogen sources and inorganic nitrogen sources [12]. As organic nitrogen, amino acid additives will provide a nitrogen source for biohydrogen production. Because the metabolism of various substances within the cell requires the participation of amino acid additives, the osmotic pressure of the cell can be regulated to the appropriate range for the cell [13]. It has been found that when E. coli and Enterobacteriaceae are used as hydrogen-producing bacteria, amino acid additives can increase hydrogen production [14]. The addition of moderate amounts of L-arginine during anaerobic fermentation resulted in the highest methane yield, as well as a significant promotion of yeast growth and an increase in the viable cell rate [15,16]. In addition, it has been noted that appropriate L-cysteine addition greatly promotes cell growth and metabolism in Enterobacteriaceae and increases hydrogen production [17].
Microorganisms are susceptible to changes in the fermentation environment, and the amino acid additives and other nutrients in the fermentation broth are essential for their reproduction and hydrogen production [18,19]. Hence, the setting of the fermentation environment is very important in the process of biological fermentation. Only the right amount of nitrogen can increase the production of biogas: too high and too low are not conducive to the fermentation reaction [20]. Li et al. investigated the effects of the addition of amino acids and Fe3O4 on the potential for hydrogen production and showed that the additions not only enhanced microbial aggregation but also increased the activity of nitrogen-fixing enzymes, which ultimately contributed to hydrogen production [21]. Jiang et al. used glycerol as a co-substrate for hydrogen production by photo-fermentation and showed that the highest hydrogen production was obtained when giant reed and glycerol were mixed at a ratio of 1:1 (carbon-to-nitrogen ratio of 25:1), with a production level that was 294% higher than that of single-giant-reed fermentation [22]. Yuan et al. investigated the effect of amino acids on the anaerobic fermentation process of sucrose, and the results showed that the maximum hydrogen production increased by 70% relative to the blank group at an amino acid addition of 0.6 mmol, while the amino acid injection promoted the accumulation of acetic acid and butyric acid [23]. Xie et al. investigated the promotion of L-cysteine on anaerobic fermentation biohydrogen production and determined the most suitable concentration of added L-cysteine, and the experimental results found that, considering the effects of L-cysteine on microbial hydrogen production and growth, the concentration of L-cysteine added was selected to be optimal at 0.8–1.5 g/L. Amino acids are the main components that make up proteins, and a large number of scholarly studies have demonstrated that amino acids have a huge impact on the process of anaerobic fermentation [24]. Current research has focused on the incorporation of amino acid additives in dark fermentation biohydrogen production experiments, while less research has been conducted on PFHP [25]. Therefore, in order to improve the effectiveness of photosynthetic biohydrogen production, it is necessary to study the relationship between the types of amino acids and their additions and PFHP [26,27]. The aim was to develop new methods to improve the efficiency of PFHP based on amino acid additives [28].
The amino acid additives (L-alanine, L-leucine, and L-serine) are able to participate in protein synthesis during anaerobic fermentation. They can all be utilized by microorganisms as carbon or nitrogen sources. In addition, they participate in the metabolism of large molecular substances such as polysaccharides and lipids. Therefore, the objective of this study was to investigate the effects of three amino acids on biological hydrogen production by photosynthetic bacteria with corn straw. Moreover, the hydrogen yield, hydrogen production rate, and energy conversion efficiency were analyzed for optimizing the concentration of amino acids that are suitable for PFHP.

2. Materials and Methods

2.1. Experimental Materials

The corn straw was air-dried first and then was grounded to particles with a size of around 300 μm. The corn straw powder was stored in an air-tight bag before use [29].
The microorganism that was used for PFHP was the laboratory photosynthetic bacterium HAU-M1, which has long been used in PFHP experiments.
The amino acid additives, viz., L-alanine, L-leucine, and L-serine, were purchased from Shanghai Macklin Biochemical Co., Ltd., Shanghai, China.

2.2. Experimental Procedures

Experiments were carried out using conical flasks with a volume of 150 mL, using 5 g of maize straw at a time. First, we added 100 mL of sodium citrate buffer, hydrogen-producing culture medium, and 150 mg/g of cellulase concentrate from dry maize stover. The pH was initially adjusted to 7, and then, HAU-M1 was added with 30% inoculum (v/v) and an amino acid additive. Based on the reports of related studies and a series of pre-tests, the concentration range of L-alanine was set to 0.3, 0.6, 0.9, and 1.2 g/L; the L-leucine was set to 0.6, 0.9, 1.2, and 1.5 g/L; and the L-serine was set to 1.0, 1.5, 2.0, and 2.5 g/L. Amino acids were weighed using a standard analytical balance (accuracy 0.0001 g) prior to each experiment, the and accuracy was verified by three independent repeat tests. A sample without any amino acid additive was set as the control group. The reactors were incubated in a thermostatic light incubator (light intensity of 3000 Lux at 30 °C). The pH of the reaction solution was measured every 12 h, and the gases produced were extracted and analyzed for their composition (gas chromatography, 6820 GC-14B, Agilent Technologies, Santa Clara, CA, USA). At the end of the experiment, the content of volatile fatty acids was measured (gas chromatography, 7890B, Agilent Technologies, USA). All test groups were repeated three times at the same time, and the results of the measured data were averaged.

2.3. Analysis Methods

A modified Gompertz equation was used to analysis the hydrogen production, as shown in Equation (1):
P t = P m a x exp − exp r m e P m a x λ − t + 1
where P(t) is the hydrogen production (mL), P m a x is the maximum hydrogen production potential (mL/g), r m is the maximum hydrogen production rate (mL/L/h), λ is the lag period (h), and e is 2.72.

2.4. Energy Conversion Efficiency Calculation

The energy conversion efficiency was calculated based on Equation (2).
E = V H 2 × Q H 2 Q c × m × 100 %
where V H 2 denotes the volume of hydrogen produced by the experiment (mL); Q H 2 denotes the calorific value of hydrogen; Q c denotes the calorific value of corn straw; m denotes the mass of corn stover used in the experiment (g); and E denotes the energy conversion efficiency (%).

3. Results

3.1. Effect of Amino Acid Additives on PFHP

The effects of different amino acid additives on hydrogen production are shown in Figure 1a. Although different amino acid additives were added, hydrogen production is essentially the same over time. In the first 12 h of photo-fermentation, because photosynthetic bacteria need to adapt to the environment in the reaction solution, the hydrogen production increased very slowly, and the average hydrogen production per gram of corn straw was kept below 10 mL at 12 h. During the period of 12–60 h, the photo-fermentation entered the peak period, and the photosynthetic bacteria gradually adapted to the fermentation environment. Corn straw was hydrolyzed to a volatile fatty acid by cellulase. Then, a large amount of hydrogen was produced, and the hydrogen production increased rapidly. In the late phase of PFHP, many photosynthetic bacteria began to decline, and the volatile fatty acids were gradually used up. The photosynthetic bacteria stopped producing hydrogen [30,31]. The hydrogen production remained constant as the L-alanine concentration increased, and the hydrogen production first increased and then decreased. The hydrogen production in the control group was 187 ± 4.61 mL. When the L-alanine concentration was 0.3, 0.6, and 0.9 g/L, the amount of hydrogen produced was greater than that of the control group. When the L-alanine concentration was 0.6 g/L, the maximum hydrogen production was 260 ± 4.01 mL, which was a 39.04% improvement over the control group. However, when the concentration of L-alanine was too high at 1.2 g/L, the hydrogen production decreased instead. When the concentration of L-leucine was 0.6, 0.9, 1.2, and 1.5 g/L, the hydrogen production was 208 ± 3.63 mL, 267 ± 4.27 mL, 193 ± 3.82 mL, and 170 ± 3.65 mL, respectively. When the concentration of L-serine was 1, 1.5, 2, and 2.5 g/L, the hydrogen production was 193 ± 3.71 mL, 248 ± 3.97 mL, 163 ± 4.82 mL, and 159 ± 3.23 mL, respectively. The most suitable concentrations for adding L-leucine and L-serine to photo-fermentation were 0.9 g/L and 1.5 g/L, respectively. In general, L-Alanine, L-leucine, and L-serine at appropriate concentrations can improve hydrogen production. Amino acids can be used as nitrogen and carbon sources in PFHP to directly support the growth and reproduction of photosynthetic bacteria, thus further enhancing the metabolic activity of microorganisms. Amino acids also produce reducing forces that help maintain the redox balance within the cell. This is essential for promoting anaerobic fermentation [32]. In addition, pyruvate produced from the breakdown of amino acids can serve as a substrate for hydrogenase or other key enzymes. It can directly or indirectly affect the enzyme activity and promote enzyme-catalyzed reactions [33]. Different amino acid additives have different molecular structures, so their effect on the hydrogen production of photo-fermentation will be different [34]. It was found that L-leucine had the best promoting effect on the hydrogen production among the three amino acid additives [35]. However, when the concentration was over a certain level, the hydrogen production of photo-fermentation was inhibited.
The delay time of PFHP was the shortest when the three amino acids were at optimum concentrations of 3.34, 3.67, and 4.51 h, respectively (Table 1). Only when L-serine was added was the delay time longer than in the control group (3.52 h). This may be due to the fact that the largest amount of L-serine was added, which resulted in the deposition of by-products such as NH3 and H2S, and the microorganisms took longer to start their growth metabolism.
The hydrogen production rate is also an essential indicator in the evaluation of the PFHP. The higher the rate is, the more the hydrogen production will increase. It was possible to determine through experimentation that different concentrations of amino acid additives could vary the rate of hydrogen production, and the trend in rate was basically the same as that of the control group (Figure 1b). In the initial phase of PFHP, the rate increased rapidly and reached the peak value in 24 h. At this time, the rate was the fastest, and the rate of hydrogen production was the highest. After 72 h, the rate decreased to less than 10 mL/(L*h), and the photosynthetic bacteria basically stopped hydrogen production, resulting in a cease of hydrogen production at 96 h. The amino acid additive did not change the hydrogen production pattern of PFHP, but it affected the metabolic capacity of the microorganisms. When the L-alanine concentration was 0.3, 0.6, 0.9, and 1.2 g/L, the maximum rate was 39 ± 0.23 mL/(L*h), 45 ± 0.33 mL/(L*h), 37 ± 0.23 mL/(L*h), and 26 ± 0.25 mL/(L*h), respectively. When the concentration of L-leucine was 0.6, 0.9, 1.2, and 1.5 g/L, the maximum rate was 34 ± 0.21 mL/(L*h), 45 ± 0.32 mL/(L*h), 29 ± 0.26 mL/(L*h), and 30 ± 0.35 mL/(L*h), respectively. When the L-serine concentration was 1, 1.5, 2, and 2.5 g/L, the maximum rate was 32 ± 0.23 mL/(L*h), 42 ± 0.35 mL/(L*h), 26 ± 0.31 mL/(L*h), and 24 ± 0.28 mL/(L*h), respectively. When L-leucine and L-serine were added, the maximum rates of other concentrations were slower than the rate for the control group, except for the concentration with the highest hydrogen production. In summary, amino acid additives can alter the rate of hydrogen production from PFHP and thus affect the amount of hydrogen that is produced (Figure 2). However, only at the right concentration will it have a boosting effect.

3.2. Effect of Amino Acid Additives on pH

The pH value is a key factor in determining the PFHP environment [36]. An increase or decrease in pH value changes the composition and concentration of the gases that are produced, as well as the type of small-molecule acid, ultimately changing the hydrogen production [37]. The changing trend of the pH value was similar under the conditions of different amino acid additives (Figure 3). In the whole process of PFHP, the pH value first dropped sharply from 7.5 to between 4.5 and 5, then rose slowly, and finally remained stable at about 6. For the photosynthetic bacteria, their growth and reproduction are the results of a series of enzymatic reactions in the cell, which need to be carried out in the appropriate pH range [38]. The change in pH value will directly affect the activity of the enzyme. If the pH is much different from 7, it will inhibit the activity of the enzyme and the metabolism of microorganisms. In the extreme acid–base environment, photosynthetic bacteria may be inactivated or dead, and the PFHP could end prematurely [39]. Therefore, changes in pH value during the PFHP process should be explored, which is very important for improving hydrogen production. In the early phase of PFHP, the substrate (corn straw) was degraded by cellulase to sugars, and sugars will be further decomposed into volatile fatty acids so that the pH value will be greatly reduced [40]. With the development of PFHP, microbial growth and metabolism and hydrogen production consume volatile fatty acids, which will make the pH value rise to a certain extent [41]. In the later stage of photo-fermentation, the corn straw was completely enzymolyzed, and the photosynthetic bacteria gradually died, and they did not use volatile fatty acid, resulting in the pH value being basic until the end of the photo-fermentation [42]. The pH value of the reaction solution with amino acid additives was reduced in all cases, which indicated more effective enzymolysis and more volatile fatty acid accumulation. The increase in volatile fatty acids can help photosynthetic bacteria produce more hydrogen [43]. However, when amino acid additions exceed a certain amount, the acidic environment affects the growth and reproduction of photosynthetic bacteria, which in turn inhibits the production of hydrogen.
The addition of all three amino acids affects the pH value of the fermentation broth. The pH of each group was minimized when the concentration of L-alanine was 0.6 g/L and L-leucine was 0.9 g/L. The pH decreased with increasing L-serine concentrations. At 24 h, when the L-serine concentration was 2.5 g/L, the pH value could be reduced to 4.5. This phenomenon may be because the amount of L-serine that was added was too large, causing the pH of the reaction solution to be significantly lower than that of the other experimental groups. In general, L-Alanine, L-leucine, and L-serine can change the pH of a reaction solution to different degrees. Appropriate concentrations can create an acid–base environment that is suitable for microbial growth and reproduction, further promoting the operation of PFHP. However, excessive amino acid additives will destroy the acid–base balance of the reaction solution, which is not conducive to photo-fermentation.

3.3. Effect of Amino Acid Additives on Oxidation–Reduction Potential and Reducing Sugar

The oxidation–reduction potential (ORP) is an important parameter that represents the changes in the fermentation system, as it indicates the electron transfer during the growth and metabolism of microorganisms [44]. Figure 4a shows the graphs of the changes in the ORP of PFHP after adding different concentrations of L-alanine, L-leucine, and L-serine. It can be seen that the addition of different amino acids leads to basically the same trend of ORP change with time. Due to the ability of amino acid metabolism to generate reducing power, the ORPs of the fermentation broth with added amino acids were lower than those of the control. This facilitates microbial growth and enzyme-catalyzed reactions to take place. Since photosynthetic bacteria in the 0–12 h stage need to adapt to the new fermentation environment, and they are in the late logarithmic growth stage at this time, the growth and metabolism of photosynthetic bacteria consume significant amounts of oxidative power, and the redox potential will rapidly drop to the lowest point. During the 12–96 h stage, anaerobic fermentation consumes a large amount of energy and uses cellular reducing power to produce hydrogen, while the capacity of the system to generate oxidative power decreases, resulting in a gradual increase in redox potential. In the late stage of PFHP, with the depletion of the fermentation substrate and high concentration of metabolites, the photosynthetic bacteria gradually enter the decay phase, and cell growth metabolism basically stops, causing the ORP to continue to rebound slowly. The addition of amino acids made the ORP values lower than the control group throughout the fermentation process, and it can be concluded that L-alanine, L-leucine, and L-serine can reduce the ORP values of the reaction solution within a certain range as a way to create a more suitable environment for the growth and metabolism of photosynthetic bacteria. Most microorganisms require a suitable oxidation–reduction potential environment for growth and fermentation, and some dehydrogenase systems and iron–oxygen-reducing proteins of anaerobic microorganisms, such as photosynthetic bacteria, can remain active in a lower-ORP environment. Therefore, maintaining a low oxidation–reduction potential range during PFHP is necessary for the growth and metabolism of photosynthetic bacterial microorganisms. In general, it is important to investigate the effect of amino acids on the redox potential values of photo-fermentation biohydrogen production. It was concluded from the experiments that appropriate concentrations of L-alanine, L-leucine, and L-serine were able to reduce the redox potential of the fermentation system, thus increasing the gas production of photosynthetic biogenic hydrogen production.
In the process of photo-fermentation biohydrogen production, corn straw is hydrolyzed into sugars by the action of cellulase, and the sugars are further decomposed into small-molecule acids for hydrogen production by photosynthetic bacteria [45]. Hence, the content of reducing sugars in the fermentation system plays an important role in hydrogen production. Figure 4b shows the graphs of the effect of adding different concentrations of L-alanine, L-leucine, and L-serine on the content of photosynthetic biogenic hydrogen-reducing sugars. When different types and concentrations of amino acids were added, the trend of reducing sugar content showed a sharp decrease first and then a gradual and slow decrease with time, until it finally remained basically stable. When the concentrations of L-alanine, L-leucine, and L-serine were 1.2, 1.5, and 2.5 g/L, respectively, the initial reducing sugar content of the fermentation broth was basically the same as that of the control group. However, the reducing sugar content of each experimental group was higher than that of the control group at other concentrations [46]. It can be concluded that the addition of suitable concentrations of L-alanine, L-leucine, and L-serine improved the efficiency of substrate decomposition and increased the reducing sugar content in the fermentation system, and the amino acid concentration had less effect on the reducing sugar content when it was too high. As the photosynthetic biogenesis of hydrogen proceeded, the reducing sugar content gradually decreased, accompanied by a large amount of hydrogen gas production. At 96 h, the reducing sugar content of the fermentation broth with each concentration of L-alanine, L-leucine, and L-serine added separately was basically not significantly different from that of the control group. In general, the addition of appropriate concentrations of L-alanine, L-leucine, and L-serine can increase the reducing sugar content while affecting the hydrogen production of the photosynthetic fermentation system.

3.4. Effect of Amino Acid Additives on Volatile Fatty Acid Generation

In the process of PFHP, VFAs will be produced with the degradation of corn straw. The volatile fatty acids that are produced at different concentrations of amino acid additives will also be different [47]. The volatile fatty acids that are produced by photo-fermentation mainly include acetate, propionate, and butyrate (Figure 5). In addition, acetate and butyrate were the main components. In the absence of added amino acids, the contents of acetate, propionate, and butyrate were 0.97 ± 0.03, 0.48 ± 0.04, and 1.08 ± 0.04 g/L, respectively. As the concentration of L-alanine increased, there were peaks in acetate, propionate, and butyrate. During the PFHP process, the concentration of L-alanine had the greatest influence on the acetate. When the L-alanine was 0.6 g/L, the maximum acetate content was 1.68 ± 0.02 g/L. The acetate content first increased and then decreased with the added L-leucine concentration. When the L-leucine concentration was 0.9 g/L, the acetate content in the reaction solution was the highest (1.2 ± 0.04 g/L). The changes in acetate, propionate, and butyrate contents in L-serine-added groups were tiny. The levels of acetate, propionate, and butyrate showed peaks with increasing concentrations of L-serine. When the concentration of L-serine was 1.5 g/L, the yields of acetate, propionate, and butyrate in the fermentation broth were the highest, at 1.63 ± 0.02, 0.59 ± 0.02, and 1.11 ± 0.04 g/L, respectively. From the data obtained from the experiment, it can be determined that adding L-alanine, L-leucine, and L-serine can make different changes in the content of volatile fatty acids that are produced by photo-fermentation biohydrogen production.

3.5. Correlation of Fermentation Broth Features

The correlations among the three different amino acid (L-alanine, L-leucine, and L-serine) concentrations and the impacts on PFHP (sugar yield, hydrogen yield, VFAs) were analyzed using scatter matrix plots, as shown in Figure 6. The sugar yield and hydrogen yield were positively correlated with a positive Pearson’s r value (0.75). This suggests that the increased saccharification of corn straw results in more reducing sugars that can participate in the PFHP process and be further converted to hydrogen. The hydrogen yield was negatively correlated with VFAs. The reason for this might be that the main substances used in the metabolism of photosynthetic bacteria to produce hydrogen were small-molecule acids. The higher the hydrogen production was, the fewer VFAs remained in the fermentation broth at the end. For the three different amino acids, which were analyzed separately, there was a high correlation between the amino acid concentration and hydrogen yield but a lower correlation between the amino acid type and some parameters such as the hydrogen yield. The reason may be because most amino acids can increase the efficiency of hydrogen production by promoting the metabolism of the substance. However, the highest yield can only be achieved at the appropriate concentration, and too high or too low a concentration can have an inhibitory effect instead [22]. This further illustrates the importance of the three amino acid additions in the PFHP process.

4. Conclusions

The addition of appropriate concentrations of three amino acids (L-alanine, L-leucine, and L-serine) had a positive effect on the growth and metabolism of the strains, substrate degradation, and conversion. Optimized concentrations of L-alanine, L-leucine, and L-serine significantly enhanced the biohydrogen yield by 39.04%, 42.78%, and 32.62%, respectively. The maximum hydrogen yield of 267 ± 4.27 mL was achieved from l-leucine addition at a concentration of 0.9 g/L. An analysis of the scatter matrix plots showed that the amino acid concentration plays a key role in increasing hydrogen production. In addition, amino acid additives are closely related to the concentrations of sugars and volatile fatty acids in biohydrogen production systems. This study provides a new reference for enhancing photo-fermentation biohydrogen production using amino acids.

Author Contributions

C.X.: Writing—original draft, software, methodology, investigation, data curation, and conceptualization. D.J.: Writing—review and editing, data curation, and conceptualization. X.Z.: Writing—review and editing, formal analysis, and conceptualization. N.X.: Writing—review and editing and conceptualization. C.L.: Writing—review and editing and conceptualization. Q.Z.: Writing—review and editing, supervision, project administration, funding acquisition, and conceptualization. All authors have read and agreed to the published version of the manuscript.

Funding

The authors are grateful for the support of the National Natural Science Foundation of China (52076068) and the Natural Science Foundation of Henan (242300421251).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors have no relevant financial or non-financial interests to disclose.

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Fermentation 11 00108 g001
Figure 1. Effect of three amino acid additives on cumulative hydrogen production (a) and hydrogen production rate (b) via PFHP.
Figure 1. Effect of three amino acid additives on cumulative hydrogen production (a) and hydrogen production rate (b) via PFHP.
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Figure 2. Gompertz fitting of three amino acid additives.
Figure 2. Gompertz fitting of three amino acid additives.
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Figure 3. Effect of three amino acid additives on the pH of PFHP.
Figure 3. Effect of three amino acid additives on the pH of PFHP.
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Figure 4. Effect of three amino acid additives on the ORP (a) and reducing sugar content (b) of PFHP.
Figure 4. Effect of three amino acid additives on the ORP (a) and reducing sugar content (b) of PFHP.
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Figure 5. Effect of three amino acid additives on the VFAs of PFHP.
Figure 5. Effect of three amino acid additives on the VFAs of PFHP.
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Figure 6. Scatter matrix analysis of the correlation among amino acid additives, sugar yield, hydrogen yield, and VFAs.
Figure 6. Scatter matrix analysis of the correlation among amino acid additives, sugar yield, hydrogen yield, and VFAs.
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Table 1. Kinetic parameters at different amino acid concentrations.
Table 1. Kinetic parameters at different amino acid concentrations.
Amino Acid Conc. (g/L)Gompertz Kinetics
Pmax (mL)rm (mL/(L*h))λ (h)R2
Control (0)192.2037.163.520.9953
L-alanine
0.3196.1538.214.340.9997
0.6266.1046.583.340.9984
0.9205.4536.846.130.9993
1.2137.5525.716.140.9991
L-leucine
0.6214.9533.866.490.9984
0.9279.3546.963.470.9985
1.2207.4531.734.630.9986
1.5175.1028.685.930.9985
L-serine
1207.7530.785.710.9987
1.5253.8045.914.510.9986
2168.7527.685.150.9996
2.5164.5524.675.680.9978
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Xia, C.; Jiang, D.; Zhang, X.; Xie, N.; Lu, C.; Zhang, Q. A Performance Comparison of Three Amino Acid Additives in the Process of Photo-Fermentative Biohydrogen Production with Corn Straw. Fermentation 2025, 11, 108. https://doi.org/10.3390/fermentation11030108

AMA Style

Xia C, Jiang D, Zhang X, Xie N, Lu C, Zhang Q. A Performance Comparison of Three Amino Acid Additives in the Process of Photo-Fermentative Biohydrogen Production with Corn Straw. Fermentation. 2025; 11(3):108. https://doi.org/10.3390/fermentation11030108

Chicago/Turabian Style

Xia, Chenxi, Danping Jiang, Xueting Zhang, Ning Xie, Chaoyang Lu, and Quanguo Zhang. 2025. "A Performance Comparison of Three Amino Acid Additives in the Process of Photo-Fermentative Biohydrogen Production with Corn Straw" Fermentation 11, no. 3: 108. https://doi.org/10.3390/fermentation11030108

APA Style

Xia, C., Jiang, D., Zhang, X., Xie, N., Lu, C., & Zhang, Q. (2025). A Performance Comparison of Three Amino Acid Additives in the Process of Photo-Fermentative Biohydrogen Production with Corn Straw. Fermentation, 11(3), 108. https://doi.org/10.3390/fermentation11030108

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