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Article

Food Waste Fermentation Liquid as a Supplementary Carbon Source for Enhanced Biological Nitrogen Removal from Rural Wastewater

by
Yanju Zhang
1,
Yu Su
1,
Feng Wang
1,*,
Leiyu Feng
1,2,*,
Xiaojuan Wang
3 and
Ahmed M. Mustafa
1,4
1
State Key Laboratory of Pollution Control and Resources Reuse, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
2
Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China
3
Natural History Research Center, Shanghai Natural History Museum, Shanghai Science & Technology Museum, 510 West Beijing Road, Jingan District, Shanghai 200041, China
4
Department of Agricultural Engineering, Faculty of Agriculture, Suez Canal University, Ismailia 41522, Egypt
*
Authors to whom correspondence should be addressed.
Water 2024, 16(22), 3191; https://doi.org/10.3390/w16223191
Submission received: 24 September 2024 / Revised: 16 October 2024 / Accepted: 29 October 2024 / Published: 7 November 2024
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Abstract

Large variations in water quality and quantity are the main characteristics of rural wastewater in China, and the biggest impact caused by this is the lack of carbon sources. In this study, an anoxic–oxic (A/O) biological contact oxidation (BCO) reactor was used to explore the feasibility of using food waste fermentation liquid as the supplementary carbon source for enhanced nitrogen removal from rural wastewater. After using the carbon source supplements, the removal performance of the A/O BCO system was improved, with the removal efficiencies of COD, NH4+–N, and TN at 92.4%, 97.8%, and 67.6%, respectively. Mechanism studies showed that the activities of key denitrifying enzymes (NAR, NIR, NOR, and NOS) for nitrogen removal were improved, with NIR activity increasing by 36.9%. Microbial community analysis revealed that food waste fermentation liquid increased the diversity of denitrifying microbial populations. Notably, insights from metagenomics showed that the relative abundances of two key genes (nirS and nirK), which are vital indicators of the denitrification process, were significantly improved with the addition of food waste fermentation liquid as a supplemental carbon source, resulting in the enhancement of nitrogen removal from rural wastewater.

1. Introduction

The development of rural living standards in China and the continuous advancement of urbanization have led to increased levels of domestic sewage in rural Chinese regions [1]. However, the sanitation infrastructure in rural areas, including sewer systems and wastewater treatment facilities, remains relatively underdeveloped [2,3]. The discharge and incomplete treatment of rural wastewater pose a serious risk of contamination to the surrounding water environment, increasingly threatening the health of local residents. Rural areas generally face significant economic constraints that limit their ability to construct, operate, and maintain costly wastewater treatment infrastructure. Moreover, there is often a shortage of adequately trained personnel to manage such systems. By contrast, biological treatment is a promising approach in rural wastewater treatment because it is highly efficient and cost-effective and only requires simple operation and management.
Conventional biological wastewater treatment processes like anoxic/oxic (A/O) treatment have matured in recent years, consequently gaining popularity in many countries [4]. Considering the lack of expertise and smart controls in rural areas, A/O treatment technology has become a common method for rural wastewater treatment because of its low required investment, small equipment footprint, and convenient operation and management [5]. And the traditional A/O treatment technology was further developed into the A/O BCO reactor, which was widely recognized as having a strong anti-shock loading capability [6,7]. For example, Zheng et al. investigated the utilization of the A/O BCO process in rural areas and found that the process was effective in improving nitrogen removal and reducing sludge production [8]. Accordingly, wastewater treatment based on the A/O BCO method has been widely used in rural China and is a representative treatment process.
However, some problems remain in the practical application of A/O BCO reactors. Due to the variability of rural wastewater in China, especially in summer and winter, the lack of carbon sources has become a common problem. Without enough carbon sources, biological denitrification is inhibited, and the biological treatment process is prone to problems like sludge loss and biomass reduction [9]. Consequently, external carbon sources need to be added to enhance biological denitrification. Traditional external carbon sources comprise single compounds and exhibit some shortcomings. For example, methanol and ethanol are flammable as well as dangerous to transport and store [10,11]. Acetate and glucose, despite a higher denitrification rate, incur a substantial economic burden on wastewater treatment plants due to their higher cost [12]. Therefore, it is necessary to find an economical and efficient carbon source. China has begun to implement measures to classify dry and wet waste in recent years, and the amount of generated food waste is considerable. Food waste mainly comprises oil, starch, and protein while featuring high organic matter content. After pretreatment of food waste, including oil-separation and high-temperature cooking, acidification in an anaerobic environment is used to obtain a food waste fermentation liquid that contains both small molecular organic acids and macromolecules like soluble carbohydrates that can act as slow-release carbon sources, and it can completely meet carbon source production needs [13,14,15]. Therefore, using food waste fermentation liquid as an external carbon source is an economically viable and feasible approach, which can alleviate food waste pollution and promote waste recycling. However, during biological wastewater treatment, information about denitrification performance and mechanisms, particularly regarding the key enzymes and genes, when using food waste fermentation liquid as a supplementary carbon source, is currently limited.
The objective of this study was to evaluate the feasibility of using food waste fermentation liquid as a supplementary carbon source in an A/O BCO reactor for enhanced biological nitrogen removal. For this purpose, the effect of food waste fermentation liquid as a carbon source on the removal of COD, NH4+–N, and TN in rural wastewater was investigated. Then, the mechanisms for the enhanced denitrification of food waste fermentation liquid were also explored via microbial community and metagenomic analysis. This work provides a feasible direction for rural wastewater treatment to choose external carbon sources while also revealing the key mechanisms for using food waste fermentation liquid to enhance nitrogen removal.

2. Materials and Methods

2.1. Experimental Setup and Operation

A lab-scaled plug-flow-integrated A/O BCO reactor was used, comprising anoxic and oxic zones (Vanoxic:Voxic = 1:2). The influent flowed sequentially through the anoxic and oxic zones. The oxic zone was aerated by an air pump, and the aeration strength was adjusted by rotameters. The reactor incorporated an elastic three-dimensional filler, and its primary material was a high-molecular-weight polymer that exhibits a long service life, agglomeration resistance, resistance to blocking, and rapid biofilm replacement.
The working volume of the A/O BCO reactor was 14 L, the water residence time was 12 h, and the influent flow rate was 1.17 L/h. The dissolved oxygen (DO) concentration in the oxic zone was 3.5 mg/L and the temperature was maintained at 25 °C. The nitrification solution in the oxic zone was returned to the anoxic zone by internal reflux to achieve denitrification. The internal reflux ratio was set to 200%.
The experiment comprised three phases. Sodium acetate and glucose were used as the normal carbon source. In phase A (the normal carbon source phase), the values of influent COD, NH4+–N, and TN were about 250, 15, and 30 mg/L, respectively. In phase B (with a high flow rate and a low carbon concentration), the influent flow was increased by 50%, and the COD concentration was reduced by 50% compared to phase A, with other conditions remaining the same. Through variable control experiments, it was found that the effect of changing the flow rate was almost negligible compared to changing the carbon source. Therefore, in phase C, the remaining experimental conditions were the same as in phase A, with only 50% of the carbon source being supplemented by food waste fermentation liquid. The stable operation time of the abovementioned stages was about 30 days, with operating conditions shown in Table 1.
The influent of phases A and B was synthetic wastewater, and phase C comprised synthetic wastewater combined with food waste fermentation liquid. The food waste fermentation liquid was obtained from Guoxin Biotechnology Co., Ltd. (Anhui, Huainan, China) and was prepared through pretreatment, including oil separation, high-temperature cooking, and acidification in an anaerobic environment. The primary components are shown in Table 2.

2.2. Analytical Methods

2.2.1. Enzyme Assay

Samples used to investigate key enzymes and functional genes involved in denitrification were taken from the anoxic zone, while samples for investigating key enzymes and functional genes used to study nitrification were taken from the oxic zone.
Sludge samples (15 mL) were rinsed three times with 10 mL of a 100 mM sodium phosphate (Na3PO4) solution (pH 4.0–11.0) and resuspended. The mixtures were sonicated in an ice-water bath (20 kHz) for 30 min to disrupt microbial cell walls and then centrifuged at 10,000 rpm and 4 °C for 30 min. The precipitate was then discarded, followed by a collection of the extract and storage at 4 °C for subsequent analysis.
The activities of key nitrification enzymes (AMO and HAO) and denitrification enzymes (NAR, NIR, NOR, and N2OR) were spectrophotometrically determined using an enzyme activity kit obtained from Shanghai Enzyme-linked Biotechnology Co., Ltd. (Shanghai, China).

2.2.2. DNA Extractions

DNA for metagenomics analysis was extracted from 0.5 g of biofilm samples using a FastDNA Kit (MP Biomedicals, Thomas Irvine, CA, USA) according to the manufacturer’s protocols. The DNA concentrations and purity were quantified using a NanoDrop 2000 spectrophotometer (Thermo Fisher Scientific Inc., Waltham, MA, USA). DNA quality was then examined with 1% agarose gel electrophoresis.
16S rRNA gene high-throughput sequencing was used to characterize the microbial communities of the samples. DNA was extracted from the biofilm samples, and 16S rRNA genes were amplified using the universal primers CCTACGGRRBGCASCAGKVRVGAAT and GGACTACNVGGGTWTCTAATCC. Amplification success was validated, followed by sequencing on the Hiseq2500 Illumina platform (Shanghai, China). Sequences were then clustered to evaluate bacterial community composition. Quantitative real-time polymerase chain reaction (qPCR) amplifications were also used to detect the abundances of microbial nitrogen-removal functional genes in the biofilms.

2.2.3. Metagenomic Sequencing

Metagenomic sequencing was conducted with paired-end sequencing on an Illumina NovaSeq Reagent Kits/HiSeq platform (Illumina Inc., San Diego, CA, USA). Raw sequence reads were trimmed using Seqprep, followed by the selection of paired- and single-end reads using Sickle. The quality-filtered sequences were assembled using the MEGAHIT software (version 1.0) program. MetaGene was used to predict open reading frames (ORFs). Redundancy of ORFs was reduced with CD-HIT using bacterial and fungal redundant coding sequence catalogs. Taxonomic classification was conducted using the BLASTP search algorithm.

3. Results and Discussion

3.1. Removal Efficiency of A/O BCO Reactor

The COD, NH4+–N, TN, and NO3−–N removal efficiencies in the A/O BCO reactor were evaluated across different operating phases (Figure 1). The COD removal efficiency in phase A was 92.2% (Figure 1a). However, the COD removal efficiency in phase B decreased significantly to 87.4%, which could be attributed to the decreased microbial activity caused by the lack of carbon sources. After carbon source supplementation, the COD removal efficiency in phase C regained stability and recovered to 92.4%, which was even higher than that under steady-state conditions. The food waste fermentation liquid can serve as a suitable carbon source for microbial metabolism due to the fact that its main components are volatile fatty acids (VFAs) [16].
The NH4+–N removal efficiency in phases A (98.3%), B (99.4%), and C (97.8%) was high and stable (Figure 1b). The DO concentration and temperature in oxic zones played critical roles in nitrification. During reactor operation, the DO concentration was 3.5 mg/L, and the temperature was maintained at 25 °C, which was stable and consequently led to high NH4+–N removal efficiency.
The TN removal efficiency reached 70.1% in phase A but significantly decreased to 42.5% under the conditions of low carbon concentrations and high flow rate (Figure 1c). The removal efficiency of TN is primarily affected by the C/N ratios and the internal reflux ratios. A sufficient organic carbon supply can provide a large number of electron donors for the reduction of nitrate and nitrite to gaseous nitrogen, thus leading to an efficient denitrification process [17]. If the carbon sources in the anoxic zone are insufficient (phase B), denitrifying microorganisms will lack electron donors to perform denitrification reactions, thereby reducing denitrification capacity. And after supplementing food waste fermentation liquid as the carbon source, the TN removal efficiency reached 67.6%, which was close to that achieved under steady-state conditions. The added food waste fermentation liquid contained not only small-molecule organic compounds, such as acetic acid which can be directly utilized by denitrifying microorganisms, but also large-molecule organic compounds, such as polysaccharides which can be biodegraded [18]. The macromolecular organics could be degraded into smaller ones by microorganisms, thereby ensuring carbon source supplies for denitrifying microorganisms in the anoxic zone.
In the A/O BCO reactor, the influent NO3−–N in the anoxic zone was primarily derived from the reflux of nitrification liquid in the oxic zone. The removal efficiency of NO3−–N in the anoxic zone was evaluated across different phases (Figure 1d). The removal efficiency of NO3−–N in phases A, B, and C was 47.3%, 33.6%, and 48.3%, respectively. The sharp decrease in available carbon sources in phase B led to significant reductions in the denitrification capacity of microorganisms in the anoxic zone, resulting in a poor removal efficiency of NO3−–N and TN. In phase C, after carbon source supplementation, the removal efficiency of NO3−–N was significantly improved, and the removal effect was stable.

3.2. Key Functional Enzymes

In the A/O BCO reactor, nitrification is controlled by key functional enzymes like ammonia monooxygenase (AMO) and hydroxylamine oxidase (HAO), and denitrification is controlled by enzymes like nitrate reductase (NAR), nitrite reductase (NIR), nitric oxide reductase (NOR), and nitrous oxide reductase (NOS) [19,20,21]. As shown in Figure 2, the enzymatic activities of AMO and HAO in phase A were 5.08 and 22.39 U/mL, respectively. When carbon sources were deficient (phase B), their activities increased by 32.3% and 20.1%, respectively. After carbon source supplementation (phase C), AMO and HAO activities both decreased, with HAO activity being very close to that in phase A and AMO activity being slightly higher than that in phase A. AMO and HAO are the main enzymes responsible for nitrification, which are mainly derived from autotrophic microorganisms such as ammonia-oxidizing bacteria [22]. However, autotrophic nitrifying bacteria are susceptible to competitive inhibition by other heterotrophic microorganisms at high organic compound concentrations. Therefore, the key enzyme activities related to nitrification increased in the absence of carbon sources and decreased after the supplementation of food waste fermentation liquid.
In phase A, the activities of NAR and NIR, which are closely related to denitrification in the anoxic zone, were 10.17 and 4.46 U/mL, respectively. High activities of NAR and NIR contributed to the conversion of NO3− and NO2− to N2. The activities of key denitrification enzymes were significantly decreased in phase B due to the lack of available carbon sources. The activities of key denitrification enzymes increased after carbon source supplementation, with NIR activity increasing by 36.9%, exceeding that in phase A. The small-molecule organic compounds in the food waste fermentation liquid can promote the growth and reproduction of denitrifying microorganisms. Also, macromolecular organic compounds such as carbohydrates can be continuously degraded into smaller ones by microorganisms, providing a continuous supply of energy substances. Therefore, the activities of NAR and NIR reached high levels after supplementation of the food waste fermentation liquid, which effectively improved denitrification.

3.3. Microbial Community

Investigating changes in the microbial community structures can be helpful for understanding their relationship to pollutant removal. Moreover, such information is useful for maintaining the stable and long-term operation of reactors. Thus, to comprehensively understand the responses of microbial communities after carbon source supplementation, it is necessary to analyze the microbial communities within each zone of the reactor. Here, anoxic biofilms (QY1) and oxic biofilms (HY1) in phase A; anoxic biofilms (QY2) and oxic biofilms (HY2) in phase B; and anoxic biofilms (QY3) and oxic biofilms (HY3) in phase C were extracted and analyzed with high-throughput sequencing.
The composition classified by phylum for each zone of the A/O BCO reactor is shown in Figure 3. Proteobacteria were the most present in the reactor and are frequently observed in biological denitrification processes since most are associated with denitrification [23]. In QY2 and HY2, the microbial community changed significantly due to the lack of carbon sources. After supplementation with carbon sources, the microbial community not only restabilized but also increased the diversity of denitrifying species. For example, Ignavibacteriae utilize extracellular peptides to reduce nitrate to nitrite, thereby improving nitrogen removal efficiency [24]. Additionally, the addition of food waste fermentation liquid may cause acidification and lower pH of wastewater, which may be the reason for the increase in the relative abundance of Acidobacteria and Firmicutes.
The genus composition for each zone of the A/O BCO reactor is shown in Figure 4. The relative abundance of Gemmatimonadetes was the highest in HY1 (4.69%), followed by Deltaproteobacteria and Betaproteobacteria, with relative abundances of 4.09% and 3.39%, respectively. In HY2, the relative abundances of Gemmatimonadetes, Deltaproteobacteria, and Proteobacteria significantly decreased relative to HY1. However, Nitrosomonas was unique to the HY2 community, with a relative abundance of 7.54%. Studies have shown that ammonia-oxidizing bacteria Nitrosomonas are autotrophic, and phylogenetic analysis of the ammonia-oxidizing bacteria AMO enzyme showed that Nitrosomonas are chiefly responsible for catalyzing ammonia oxidation [25]. Thus, Nitrosomonas dominate in environments with insufficient carbon sources, consistent with the key enzyme activity results. Additional dominant genera in HY2 included Alphaproteobacteria, Parvularcula, and Planctomycetes. After the supplementation of the carbon sources, heterotrophic microorganisms dominated in competition with autotrophic microorganisms, resulting in almost no detection of Nitrosomonas and Nitrospira in HY3. And the microbial community composition was more complex compared with HY1 and HY2, which may be due to the richness of organic compounds in food waste fermentation liquid.
The dominant genera in QY1 were Gemmatimonadetes, Betaproteobacteria, and Acidobacteria, with relative abundances of 5.12%, 4.14%, and 3.38%, respectively. The dominant genera in QY2 significantly changed due to carbon source deficiency, and the highest increase in relative abundance was observed for Rhodospirillaceae and Chloroflexi, with relative abundances of 4.75% and 4.58%, respectively. Chloroflexi plays a key role in organic compound degradation and nitrogen removal. Therefore, the biological activity of Chloroflexi increases in order to rapidly reduce large carbon compounds when the small-molecule carbon sources are quickly consumed [26]. In QY3, the relative abundances of dominant genera were similar to QY2, while unique genera like Parvularcula and Rhodocyclales were also present. Facultative or heterotrophic metabolisms have been reported for Acidovorax, Thermomonas, Bradyrhizobiaceae, and Dongia strains, which can also conduct denitrification [27,28,29,30]. This suggests that the addition of food waste fermentation liquid increased the diversity of denitrifying bacteria species during nitrogen removal.
In this study, alteration of carbon sources and hydraulic retention times led to significant replacement of the dominant bacterial species in each zone. After the addition of the food waste fermentation liquid, there were still some bacterial species that could not be determined, but what could be determined was that the number of denitrifying bacterial species increased in all zones of the system.

3.4. Metabolic Pathway

Four primary metabolic pathways involved in nitrogen metabolism were identified in the metagenomes of the A/O BCO reactor (Figure S1, including those involved in denitrification (narG, napA, nirS, nirK, norB, and nosZ), nitrification (amoA and hao), assimilatory nitrate reduction (nasA and narB), and dissimilatory nitrate reduction (nrfA) (Figure 5). In phase B, the relative abundances of key genes involved in nitrification (hao and amoA) were much higher than in phase A, with the relative abundances dramatically increasing from 0.16% and 0.04% to 1.75% and 0.37%, respectively. After carbon source supplementation (phase C), the relative abundances of key nitrification genes were significantly decreased again. Among them, the relative abundance of hao decreased to 0.37% and the relative abundance of amoA decreased to 0.08%, following the same trend as the key enzyme activities during nitrification.
Denitrification includes NO3− reduction, NO2− reduction, NO reduction, and N2O reduction while involving key functional genes including narG and napA; nirS and nirK; and norB and nosZ, respectively [31,32,33]. The relative abundances of narG, napA, nirS, nirK, and norB in phase A were 9.4%, 2.5%, 3.8%, 1.2%, and 3.5%, respectively. Due to the insufficient carbon sources, the denitrification process was inhibited and the relative abundances of the key functional genes in phase B were decreased to 6.1%, 1.2%, 3.1%, 0.8%, and 3.0%, respectively. During phase C, their relative abundances were considerably higher. The relative abundances of narG and napA increased from 6.1% and 1.2% to 8.2% and 1.7%, respectively. Moreover, the relative abundances of nirS, nirK, and norB increased from 3.1%, 0.8%, and 3.0% to 4.8%, 2.6%, and 3.6%, respectively, even exceeding the relative abundances observed in phase A. The rate-limiting step in denitrification is NO2− reduction, and nirS and nirK are specific genes for the denitrification process, so the abundance of these genes is usually used as a common index to reflect the denitrification process [34,35,36]. This further demonstrates that food waste fermentation liquid as a supplementary carbon source can effectively stabilize and improve nitrogen removal.
Evaluation of the nitrifying and denitrifying metabolic pathways confirmed that carbon source deficiency suppressed the bioactivity of heterotrophic bacteria and enhanced the bioactivity of nitrifying bacteria [37]. However, the bioactivity of autotrophic nitrifying bacteria and heterotrophic bacteria was rebalanced after carbon source supplementation, with denitrification levels being essentially restored. However, in real situations, the impact of other metabolic pathways on nitrogen metabolism cannot be ignored, such as carbon and phosphorus. Therefore, further analysis of metagenomic data should be conducted to explore regulating strategies for promoting biological denitrification of rural wastewater using food waste fermentation liquid.

4. Conclusions

The results of this study reveal that the use of food waste fermentation liquid as a supplementary carbon source can strengthen rural wastewater treatment with an A/O BCO reactor. Although nitrogen removal was suppressed in the carbon source deficient phase, excellent COD, NH4+–N, and TN removal efficiencies (92.4%, 97.8%, and 67.6%, respectively) of the A/O BCO reactor were achieved after carbon source supplementation, and these were close to those achieved during the normal carbon source phase. The activities of key nitrification enzymes (AMO and HAO) and denitrification enzymes (NAR, NIR, NOR, and NOS) exhibited similar trends as the nitrogen removal efficiency of the A/O BCO reactor. Changes in the relative abundances of genes associated with nitrogen removal also exhibited similar trends. The relative abundances of nirS and nirK, which are specific genes for the denitrification process, even exceeded those observed in the normal carbon source phase. The abundant organic compounds in the food waste fermentation liquid induced complex structural changes in functional microbial compositions at the genus level. In future work, it will be necessary to further verify whether the obtained regulation strategies are still applicable in pilot tests or real engineering settings and to optimize them accordingly.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/w16223191/s1, Figure S1: Metabolic pathway of nitrogen.

Author Contributions

Conceptualization, Y.S., F.W., L.F., X.W. and A.M.M.; Methodology, Y.Z. and Y.S.; Validation, X.W.; Formal analysis, Y.Z.; Data curation, Y.Z. and A.M.M.; Writing—original draft, Y.Z.; Writing—review & editing, L.F.; Supervision, L.F.; Project administration, F.W. All authors have read and agreed to the published version of the manuscript.

Funding

The work is financially supported by the Shandong Provincial Key Research and Development Project (2022CXGC021001), the National Natural Science Foundation of China (21777121), the National Key Research and Development Program of China (2019YFD1100203), and the Foundation of the State Key Laboratory of Pollution Control and Resource Reuse (Tongji University) (No. 2022-4-YB-09).

Data Availability Statement

Data is contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

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Water 16 03191 g001
Figure 1. Removal efficiency of (a) COD, (b) NH4+–N, (c) TN, and (d) NO3−–N in different operating phases.
Figure 1. Removal efficiency of (a) COD, (b) NH4+–N, (c) TN, and (d) NO3−–N in different operating phases.
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Figure 2. Activities of key enzymes involved in nitrification (a) and denitrification (b) in different operating phases.
Figure 2. Activities of key enzymes involved in nitrification (a) and denitrification (b) in different operating phases.
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Figure 3. Comparison of the microbial community at the phylum level in each zone of the A/O biological contact oxidation reactor.
Figure 3. Comparison of the microbial community at the phylum level in each zone of the A/O biological contact oxidation reactor.
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Figure 4. Comparison of the microbial community at the genus level in each zone of the A/O biological contact oxidation reactor.
Figure 4. Comparison of the microbial community at the genus level in each zone of the A/O biological contact oxidation reactor.
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Figure 5. Relative abundance of genes associated with nitrogen removal (a) and genes in the denitrification process (b).
Figure 5. Relative abundance of genes associated with nitrogen removal (a) and genes in the denitrification process (b).
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Table 1. Characteristics of simulated rural wastewater in different operating phases.
Table 1. Characteristics of simulated rural wastewater in different operating phases.
Operational ConditionpHCOD (mg/L)NH4+–N (mg/L)TN (mg/L)
Phase A: steady-state6.8–7.8220–30013–1920–40
Phase B: low carbon concentration and high flow rate6.8–7.880–12010–1620–35
Phase C: After carbon source supplementation6.8–7.8250–30015–2020–38
Table 2. Composition of the food waste fermentation liquid.
Table 2. Composition of the food waste fermentation liquid.
CompositionConcentration (mg/L)
Total solid (g/L)54.7
Volatile solid (g/L)27
Acetic acid (mg COD/L)5739.9
Propionic acid (mg COD/L)933.8
Butyric acid (mg COD/L)1455.6
Total volatile fatty acids (mg COD/L)11,553.8
COD (mg/L)136,400
Dissolved COD (mg/L)74,200
NH4+–N (mg/L)301.5
TN (mg/L)2997.8
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Zhang, Y.; Su, Y.; Wang, F.; Feng, L.; Wang, X.; Mustafa, A.M. Food Waste Fermentation Liquid as a Supplementary Carbon Source for Enhanced Biological Nitrogen Removal from Rural Wastewater. Water 2024, 16, 3191. https://doi.org/10.3390/w16223191

AMA Style

Zhang Y, Su Y, Wang F, Feng L, Wang X, Mustafa AM. Food Waste Fermentation Liquid as a Supplementary Carbon Source for Enhanced Biological Nitrogen Removal from Rural Wastewater. Water. 2024; 16(22):3191. https://doi.org/10.3390/w16223191

Chicago/Turabian Style

Zhang, Yanju, Yu Su, Feng Wang, Leiyu Feng, Xiaojuan Wang, and Ahmed M. Mustafa. 2024. "Food Waste Fermentation Liquid as a Supplementary Carbon Source for Enhanced Biological Nitrogen Removal from Rural Wastewater" Water 16, no. 22: 3191. https://doi.org/10.3390/w16223191

APA Style

Zhang, Y., Su, Y., Wang, F., Feng, L., Wang, X., & Mustafa, A. M. (2024). Food Waste Fermentation Liquid as a Supplementary Carbon Source for Enhanced Biological Nitrogen Removal from Rural Wastewater. Water, 16(22), 3191. https://doi.org/10.3390/w16223191

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