Anammox System Research Articles

Response of nitrogen removal and microbial community to high concentration of humic acid in the anammox biofilm system

The anaerobic ammonium oxidation (anammox) process is highly effective to remove nitrogen from the wastewater with high ammonia concentration, such as landfill leachate and anaerobic digestion. This kind of wastewater generally contains high content of humic acid, and its effect on anammox is not clear. Therefore, this study investigated the effect of humic acid with high concentration (100–1000 mg/L) on the anammox biofilm system. The nitrogen degradation rates were greatly decreased at the high concentration of humic acid and the reaction time was prolonged by 4 h compared with that lacking humic acid. In the anammox biofilm system, the relative abundance of anammox bacteria Candidatus_Brocadia and Candidatus_Kuenenia decreased from 2.1 % and 15.01 % to 0.6 % and 8.32 %, respectively, while the denitrifying bacteria Thauera increased from zero to 8.86 %. Overall, the high humic acid concentration did not obviously inhibit nitrogen removal performance of anammox system, but affected anammox bacteria activity and microbial community structure.

The rapid start-up of CANON process through adding partial nitration sludge to ANAMMOX system

This study aimed to start up the completely autotrophic nitrogen removal over nitrite (CANON) process after adding partial nitration (PN) sludge to the ANAMMOX reactor, so as to help the rapid start-up and stable operation of the CANON process in practical engineering applications. There were three steps in the research: cultivating the PN sludge, building a reliable ANAMMMOX system, and finally starting and running the CANON process. The PN sludge was successfully cultivated in less than 45 days with around 90% nitrite accumulation rate. The ANAMMOX reactor enriched a significant quantity of red granular sludge within 70 days, achieving the maximum nitrogen removal rate of 1.74 kg/(m3·d). Eventually, the CANON reactor was started up successfully, which achieved 95.08% of average ammonium removal efficiency and 84.51% of average total nitrogen removal efficiency in 60 days. The residual recalcitrant nitrite-oxidizing bacteria in the CANON process was successfully inhibited by intermittent aeration and 12 mg/L free ammonia in UASB reactor. Besides, Candidatus Kuenenia, Candidatus Brocadia and Nitrosomonas were the main functional microorganisms involved in the CANON process.

Relationship between denitrification and anammox rates and N2 production with substrate consumption and pH in a riparian zone

ABSTRACT Denitrification and anaerobic ammonium oxidation (anammox) are the key processes to quantitatively remove nitrate (NO3 −) and balance the nitrogen (N) budget of the ecosystem. In this paper, a slurry-based 15N tracer approach was used to study the correlation and quantitative relation of substrate consumption and pH with rates of denitrification and anammox in a riparian zone. The results showed that the fastest rates of 0.93 µg N h−1 and 0.32 µg N h−1 for denitrification (Denitrif-N2) and anammox (Denitrif-N2), respectively. N2 produced by denitrification occupied 74.04% and produced by anammox occupied 25.96% of the total N2, proving denitrification is the dominant process to remove NO3 −. The substrate content (NO3 −, NH4 + and TOC) and pH varied during incubation and were significantly correlated with Dentrif-N2 and Anammox-N2. Nitrate and TOC as the substrates of denitrification demonstrated a significant correlation with Anammox-N2, which was associated with the products of denitrification involved in the anammox process. This proved a coupling of denitrification and anammox. A quantitative relationship was observed between Dentrif-N2 and Anammox-N2 in the range of 2.75–2.90 when TOC, NH4 + and NO3 − consumption per unit mass or pH changed per unit. Nitrogen mass balance analysis showed that 1 mg N substrate (NO3 −+NH4 +) consumption in the denitrification and anammox can produce 1.05 mg N2 with a good linear relationship (r 2 = 0.9334). This could be related to other processes that produced extra N2 in denitrification and anammox system.

Effect of salinity stress on nitrogen and sulfur removal performance of short-cut sulfur autotrophic denitrification and anammox coupling system

The effects of salinity on anaerobic nitrogen and sulfide removal were investigated in a coupled anammox and short-cut sulfur autotrophic denitrification (SSADN) system. The results revealed that salinity had significant nonlinear effects on the nitrogen and sulfur transformations in the coupled system. When the salinity was <2 %, the anammox and SSADN activities increased with increasing salinity, and the total nitrogen removal rate, S0 production rate, and nitrite production rate were 0.41 kg/(m3·d), 0.37 kg/(m3·d), and 0.28 kg/(m3·d), respectively. With continuous increase of salinity, the performances of the anammox and SSADN gradually decreased, and the three indicators decreased to 0.14 kg/(m3·d), 0.22 kg/(m3·d), and 0.14 kg/(m3·d) at 5 % salinity, respectively. When the salinity reached 5 %, the nitrogen removal contribution of anammox decreased to 68.4 %, while the contribution of the sulfur autotrophic denitrification increased to 31.6 %. The coupled system recovered in a short time after alleviation of the salinity stress, and the SSADN activity recovery was faster than anammox. The microbial community structure and functional microbial abundance in the coupled system changed significantly with increasing salinity, and the functional microbial abundance after recovery was considerably different from the initial state.

Molecular insights into enhanced nitrogen removal induced by trace fluoroquinolone antibiotics in an anammox system

It has been widely reported that fluoroquinolones (FQs) can affect the anaerobic ammonium oxidization (anammox) microorganisms, which interferes with the performance of nitrogen removal from wastewater. However, the metabolic mechanism of anammox microorganisms responding to FQs has rarely been explored. In this study, it was found that 20 μg/L FQs promoted the nitrogen removal performance of anammox microorganisms in batch exposure assays, and 36–51% of FQs were removed simultaneously. Combined metabolomics and genome-resolved metagenomic analysis revealed up-regulated carbon fixation in anammox bacteria (AnAOB), while purine and pyrimidine metabolism, protein generation and transmembrane transport were enhanced in AnAOB and symbiotic bacteria by 20 μg/L FQs. Consequently, hydrazine dehydrogenation, nitrite reduction, and ammonium assimilation were bolstered, improving the nitrogen removal efficiency of the anammox system. These results revealed the potential roles of specific microorganisms in response to emerging FQs and provided further information for practical application of anammox technology in wastewater treatment.

Insights to Fe(II) on the fate of humic acid and humic acid Fe complex with biogeobattery effect in simultaneous partial nitritation, anammox and denitrification (SNAD) system

The role of Fe(II) on the humic acid (HA) transformation and the effects of humic acid Fe (HA-Fe) on simultaneous partial nitrification, anammox and denitrification (SNAD) system were investigated. After adding Fe(II), the HA content decreased and the HA inhibition on the SNAD system was released. Results showed that Fe(II) and HA formed the lower water-soluble HA-Fe, promoting the HA removal. HA-Fe with stronger electron transfer capacity constituted the interface with microorganisms to forming the biogeobattery effect. This accelerated the microbial electron transfer, as well as improved the key enzymes and ATP, indicating that HA-Fe stimulated the microbial activity of the SNAD system. Microbial community and quorum sensing analysis further demonstrated that HA-Fe enhanced the mutual symbiosis between electroactive and nitrogen removal bacteria, to ensure the stability of the SNAD system. The study provided references for efficient HA removal and revealed the biogeobattery effect of HA-Fe in the SNAD system.

A novel strategy for a reinforced anammox process with iron-modified Enteromorpha prolifera biochar

Modified biochar with higher electron transport and adsorption capabilities could significantly improve the performance of anaerobic ammonia oxidation (anammox). However, there are few related investigations on the reinforcement of anammox through iron-modified Enteromorpha prolifera biochar (IMEPB). In this study, with the addition of the IMEPB in the anammox system, the enhancing process of anammox performance was studied, the improving feasibility of anammox was evaluated, and the reinforcing mechanism of anammox was elucidated. The results showed that the optimal iron−charcoal ratio (Fe:C) and IMEPB dosage were 1:10 and 10 g L−1, respectively. Under the optimal conditions, when the nitrogen loading rate gradually increased to 0.557 (kg m−3 day−1), the nitrogen removal efficiency and nitrogen removal rate of the anammox process supplemented with IMEPB increased by 11%, and the specific anammox activity increased by 23.8%. Compared with the control, the secretion of extracellular polymeric substances (EPS) of anammox bacteria supplemented IMEPB increased by 24.4%, greatly improving the stability of the anammox system. Meanwhile, EPS secretion further promoted the microbial activity of anammox bacteria, achieving a 19% increase in the abundance of Candidatus Brocadia. These findings demonstrate the potential mechanism of IMEPB in improving anammox, provide new insights into recycling E. prolifera, and provide a novel reinforcement strategy for anammox. In the future, adding IMEPB may be a vital measure for the practical application of anammox in coastal areas.Graphical

Fe(OH)3 induced the Anammox system to perform extracellular electron transfer for enhancement of NH4+ removal

It is widely found that the ratio of nitrite consumption to ammonia consumption (ΔNO2--N/ΔNH4+-N) in Anammox systems is lower than its stoichiometry of 1.32, but the reason is unclear. In this study, ΔNO2--N/ΔNH4+-N of an Anammox system decreased to 0.80 with the addition of Fe(OH)3, which was significantly lower than a control system without the addition of Fe(OH)3. The lower ratio or more NH4+ removal was likely related to the reduction of Fe(OH)3 that served as extracellular electron acceptor to anaerobically oxidize NH4+, namely Feammox. Chemical or biological oxidation of the produced Fe2+ formed the Fe(III)/Fe(II) cycle to likely cause the continuous Feammox in the Anammox system. Isotopic analysis verified that the Anammox sludge collected from the Fe(OH)3-added reactor produced more 30N2 by Feammox. Raman analysis showed that the outer membrane cytochrome c of Fe(OH)3-added Anammox sludge could participate in the extracellular electron transfer during Feammox. Metagenomic analysis further confirmed that the gene encoding redox enzymes of cytochrome c of Candidatus Brocadia were enriched with adding Fe(OH)3. The results suggested that the Fe(OH)3 induced Anammox bacteria to perform extracellular electron transfer, allowing the Anammox system to effectively remove NH4+ via the Feammox pathway.

Quantification of enhanced nitrogen removal pathways of pyrite interaction with anammox sludge system

Fe and S could improve the anammox performance by coupling with the N cycle. However, the coexistence of Fe and S complicates the metabolic process, troubling the quantification of nitrogen removal pathways. Herein, the nitrogen removal pathways were quantificationally analyzed by 15N stable isotope tracing and elaborate batch tests, and the enhancing mechanism was illuminated by physiological and metatranscriptome analyses in pyrite (FeS2)-amended anammox system. We found that anammox, denitrification and Feammox (NH4+ oxidation coupled with Fe(III) reduction) contributed to 80.22 %, 19.53 % and 0.25 % nitrogen removal in this process. With pyrite addition, Fe, S release and the extracellular polymeric substances secretion were responsible for the enhancement of nitrite and nitrate removal via chemical, autotrophic and heterotrophic denitrification, improving nitrogen removal by 14 % and 19 %. The network analyses further confirmed that the multiple nitrogen removal pathways (i.e., anammox, Feammox and denitrification) contribute to pyrite-induced nitrogen removal enhancement in the anammox system. This work enables the in-depth understanding, future design and optimization of the pyrite-amended anammox system, providing a fundamental basis for developing Fe- and S-based anammox enhancement technologies.

Impacts of exogenous quorum sensing signal molecule-acylated homoserine lactones (AHLs) with different addition modes on Anammox process

Anammox was proved having the quorum sensing ability, and several acylated homoserine lactones (AHLs) signal molecules were detected in the system. In this study, the impact of exogenous N-dodecanoyl homoserine lactone (C12-HSL) with different addition modes on the nitrogen removal, key enzymes’ activity, and microbial revolution were investigated in Anammox system. Results showed that once-addition of C12-HSL had no obvious impact on Anammox. Daily-addition with 40 nM slightly improved the TN removal from 71.1 % to 74.5 %, while 80 and 200 nM significantly decreased it to 62.7 % and 61.8 %, respectively. The enzyme activity of ammonia monooxygenase increased from 0.015 to 0.068, nitrite reductase increased from 0.25 to 1.23, and nitrate reductase increased from 0.05 to 0.11 μg NO2–-N mg−1 Protein min−1. Arenimonas abundance showed positive correlation with TN removal while Candidatus Kuenenia was continuously suppressed. C12-HSL was beneficial for partial nitrification, and it could be adopted for regulating the nitrite production.

Decoding the carbon and nitrogen metabolism mechanism in anammox system treating pharmaceutical wastewater with varying COD/N ratios through metagenomic analysis

In current study, the underlying mechanism of coupling dissimilatory nitrate reduction to ammonium (DNRA) pathway with anaerobic ammonium oxidation (anammox) process was explored through metagenomics sequencing analysis in an anammox granular system treating pharmaceutical wastewater under varying COD/N ratios. It was found that average NH4+-N and NO2--N concentration in effluent was stabled around 2.89 ± 2.53 and 14.23 ± 9.23 mg L-1 with nitrogen removal efficiency (NRE) increase to 85.3% when influent COD/N ratio was around 0.63. Besides, metagenomics sequencing analysis revealed that different COD/N ratios significantly influenced the abundances of functional nitrogen and carbon metabolic genes and microbial community succession. The low COD/N ratio strengthened DNRA pathway in Ca. Kuenenia_stuttgartiensis, as well as the abundance of functional gene nrf. The abundance of the genes encoding acetate degradation, for example, AMP-acs, ADP-acs and AckA increased, suggesting the acetate could stimulate the multiple carbon metabolic potentials of AnAOB. On the contrary, the genes encoding for propionate metabolism were enriched in denitrification bacteria. Our findings revealed the new insight into the mixotrophic characteristic of AnAOB which might help widen engineering application of anammox proocess in various industrial wastewater.

Alleviation of substrate inhibition in an anaerobic ammonia oxidation reactor: Recovery process performance and microbial community

Substrate inhibition is one of the key factors that threatens the stability of anaerobic ammonia oxidation (anammox) reactors. Most of the current studies have focused on the inhibition of anammox by substrates; however, little attention has been given to the recovery process and microbial community changes in anammox reactors after inhibition. To remediate the damage substrate inhibition can do to anammox systems, the study investigated the recovery process of an anammox reactor that was inhibited by high substrate concentrations. The results showed that a reduction in the ratio of influent NO2−-N to NH4+-N from the theoretical stoichiometric ratio of 1.32 to 0.5 was conducive to the rapid recovery of anammox system performance. The analysis of the microbial community structure indicated that the relative abundance of the primary anammox bacteria on the biofilm carriers and mixed sludge was 19.51 % and 9.92 %, respectively, after reactor recovery. Biofilms played an important role in resisting reactor destabilization.

Functional stability correlates with dynamic microbial networks in anammox process

Understanding the relationship between dynamic microbial networks and functional stability is critical for the stable operation of anammox systems. Here, by operating an anammox reactor under constant condition over 250 days, it was found that the relative abundance of Planctomycetota gradually decreased while Chloroflexi and Proteobacteria increased, with stochasticity predominating the bacterial assembly as the reactor operation. Network analysis revealed a successional dynamic pattern of microbial interaction despite stable performance. The variation of subnetworks indicated Chloroflexi and Proteobacteria alternately played important role in anammox microbial network, and the negative relationship between anammox bacteria and heterotrophs could achieve a balance to keep functional stability under long-term operation. Furthermore, the identified keystone species mainly belonged to heterotrophs that were critical in maintaining network structure and system function. The results of this study revealed clear changing patterns of microbial community and network succession, which could provide valuable reference for other stably operated bioreactors.

Highly efficient transformation of slowly-biodegradable organic matter into endogenous polymers during hydrolytic fermentation for achieving effective nitrite production by endogenous partial denitrification

The utilization of slowly-biodegradable organic matter (SBOM) to provide nitrite efficiently for anaerobic ammonia oxidation (anammox) process is an essential topic. High nitrite concentration without inhibition of exogenous organic matter is optimal condition for anammox process. In this study, hydrolytic fermentation (HF) of SBOM was applied to drive an endogenous partial denitrification (EPD) process (nitrate to nitrite) during an anaerobic-anoxic operation in a starch-fed system. With a limited production of exogenous organic matter (22.3 ± 4.9 mg COD/L), 79.0% of SBOM was transformed into poly-hydroxyalkanoates (PHA) through a pathway of simultaneous HF-absorption and endogenous polymer synthesis, corresponding to a hydrolytic fermentation ratio of 86.0%. A high nitrate to nitrite transformation ratio of 85.4% was achieved under an influent carbon to nitrogen ratio of 4.8. Denitrifying glycogen-accumulating organisms (DGAOs) was enriched from 0.6% to 10.9%, with an increase from 0.7 to 1.0 of nitrate reductase genes to nitrite reductase genes ratio. Subsequently, nitrate reduction rate was 5.6-fold higher than the nitrate reduction rate. A prominent migration of exogenous complete denitrification to EPD was accomplished. Furthermore, the starch-fed system exhibited performance with significant adaptability and stability in the presence of different SBOMs (dissolved protein and primary sludge). Therefore, the HF-EPD system achieved efficient nitrite production through EPD with the addition of various SBOMs, providing a potential alternative to anammox systems for the treatment of SBOM-rich wastewater.

Use of iron-loaded biochar to alleviate anammox performance inhibition under PFOA stress conditions: Integrated analysis of sludge characteristics and metagenomics

The negative effects of perfluorooctanoic acid (PFOA) on biological nitrogen removal performance in wastewater treatment plants, are receiving increasing attention due to the widespread reporting of this issue. In this study, pomelo peel iron-loaded biochar (Fe-PBC) was added to an anammox bioreactor to alleviate the negative effects of PFOA. Results showed that the addition of Fe-PBC increased the ammonia and nitrite removal efficiencies from 77.7 ± 9.6 % and 79.5 ± 5.6 % to 94.45 ± 5.1 % and 95.9 ± 5.0 %, respectively. In addition, Fe-PBC promoted the removal of PFOA from wastewater, increasing the PFOA removal efficiency from 5.2 % to 29.2 ± 4.3 % from 100 to 200 days. The introduction of iron-loaded biochar into the anammox bioreactor increased the CO ratio by 13.64 % by 150 days. In addition, a CO fitting peak was detected in the Fe-PBC, indicating that the Fe-PBC was loaded with microorganisms. Microbial community analysis showed a decrease in the relative abundances of Proteobacteria and Nitrospirae from 31 % and 3.4 % to 16.8 % and 0.9 %, respectively, while the relative abundance of Planctomycetes increased from 26.8 % to 44.1 %. Metagenomic analysis found that the functional genes hzsB and hdh increased from 98,666 ± 11,400 and 3190 ± 460 to 119,333 ± 15,534 and 138,650 ± 11,233 copy numbers/MLSS. The increase in anammox biomass may be attributed to the presence of iron, an essential element for the synthesis of key anammox enzyme. Furthermore, iron was also associated with the enhanced extracellular electron transfer in the anammox system induced by Fe-PBC.

Promoting performance of Anammox by iron loaded sludge biochar with hydrothermal carbonization (HTC-Fe-BC) addition

Anaerobic ammonia oxidation (Anammox) treatment cannot always achieve optimal efficiency due to its sensitivity to environmental conditions. The nitrogen removal efficiency of Anammox reactors with different iron loaded sludge biochar modified by hydrothermal carbonization (HTC-Fe-BC) addition dose of 0, 2.5 and 5.0 g/L (named BC0, BC1 and BC2) were analyzed. The effects of adding HTC-Fe-BC on the performance of Anammox reactor, extracellular polymeric substances (EPS), microbial community and functional genes were investigated. The results showed that the addition of HTC-Fe-BC could reduce the environmental sensitivity of Anammox reactor, the removal efficiency of total nitrogen increased from 51.20 (BC0) to 70.83 % (BC2), and the activity of Anammox sludge improved by 49.58 %. HTC-Fe-BC increased the activity of Anammox sludge by promoting the secretion of protein, humic acids and cytochrome c in EPS and alleviated the inhibitory effect by mediating the Anammox electron transfer process. After EPS removal and enzymatic hydrolysis, the activity of Anammox sludge in BC2 decreased by 61.38% and 79.80 %, respectively, significantly higher than the reduced values of BC0. Further, the relative abundance of Candidatus_Brocadia in Anammox reactors supplemented with HTC-Fe-BC was increased by 35.56–55.56 % compared to the control group, as were the relative abundances of the key functional genes connected to N transformation. These results deepened the understanding of the potential mechanism by which HTC-Fe-BC improved the efficiency of Anammox system.

Establishment of anammox coupled with sulfide-depending autotrophic denitrification process and its efficient pollutants removal performance

Nitrogen and sulfur pollutants coexist in many industrial wastewaters, which may cause serious water pollution issues. In this study, Anammox coupled with sulfide-depending autotrophic denitrification process (coupling process) was established by adding sulfide to an Anammox system in a membrane bioreactor. Variations in nitrogen and sulfur removal performance, extracellular polymeric substances (EPS), key enzyme activities, and microbial components were analyzed. The sulfide in 25.0 mg L−1 successfully induced denitrification, and then helped establish the coupling process. This process achieved 96.1% TN removal and complete sulfide removal when the sulfide was increased to 100.0 mg L−1. The protein and polysaccharide in EPS gradually increased to 2.0 and 4.9 mg g−1 SS, respectively. The hydroxylamine oxidoreductase activity, Heme-c content, nitrite reductase activity, and nitrate reductase activity slightly decreased to 19.1 EU g−1 SS, 0.001 mmol g−1 SS, 0.002 μg min−1 mg−1 protein, and 0.005 μg min−1 mg−1 protein, respectively, indicating the slight suppression of sulfide in high concentration on the coupling process. However, after acclimatization, the Anammox and denitrifying bacteria interacted and cooperatively contributed to the simultaneous nitrogen and sulfur removal, with relative abundances of Thiobacillus-denitrifying bacteria and Candidatus Kuenenia-Anammox bacteria of 31.7% and 9.0%, respectively. The establishing strategy was proposed and then verified in another Anammox system, in which the coupling process was also established, with TN removal increasing from 73.4% to 82.5%.

Inhibition and recovery of ANAMMOX with Na2SO3: From performance to microbial community analysis

In this study, three concentrations of Na2SO3 solution were used to remove dissolved oxygen in the influent water and enter the up-flow anaerobic sludge bed reactor (UASB). This study investigated the effects of three concentrations of Na2SO3 on the inhibition and performance recovery of the ANAMMOX system and the structure of the microbial community. The results showed that although Na2SO3 had a deoxidizing function, the ANAMMOX system underwent a sulfate reduction reaction after adding Na2SO3, and the reduction product was mainly H2S, which caused the AnAOB to be inhibited by sulfide. The denitrification performance was less than 1/2 of that under normal conditions. The ANAMMOX system was restored by immediately removing Na2SO3 and reducing nitrogen load. After 11, 20, and 34 days, the performance of the ANAMMOX system returned to normal, but low concentrations(45 mg/L) required a long recovery time. High-throughput sequencing analysis showed that the community of the ANAMMOX system changed significantly. Before and after the experiment, the relative abundance of ANAMMOX functional bacteria Candidatus Brocadia decreased from 32.66% to 21.4%, and Candidatus Kuenenia decreased from 7.3% to 4.06%. However, the relative abundances of Armatimonadetes and Ignavibacteriae increased from below 2% to about 20%. At the same time, Thiobacillus and Desulfuromonadales were observed. This paper explores and summarizes the cause of Na2SO3's inhibition of AnAOB, highlights the recovery of AnAOB after inhibition for the stable operation and deepens the understanding of the environmental conditions regulating the ANAMMOX process.

Dosing with pyrite significantly increases anammox performance: Its role in the electron transfer enhancement and the functions of the Fe-N-S cycle

Anaerobic ammonium oxidation (anammox) represents an energy-efficient process for biological nitrogen removal from ammonium-rich wastewater. However, there are mechanistic issues unsolved regarding the low microbial electron transfer and undesired accumulation of nitrate in treated water, limiting its widespread engineering applications. We found that the addition of pyrite (1 g L−1 reactor), an earth-abundant iron-bearing sulfide mineral, to the anammox system significantly improved the nitrogen removal rate by 52% in long-term operation at a high substrate shock loading (3.86 kg N m−3 d−1). Two lines of evidence were presented to unravel the underlying mechanisms of the pyrite-induced enhancement. Physiochemical evidence indicated that an increase of cytochromes c and Fe-S protein was responsible for the accelerated electron transfer among metabolic enzymes. Multi-omics evidence showed that the depletion of nitrate was attributed to the Fe-N-S cycle driven by nitrate-dependent Fe(II) oxidation and S-based denitrification. This study deepens our understanding of the roles of electron transfer and the Fe-N-S cycle in anammox systems, providing a fundamental basis for the development of mediators in the anammox process for practical implications.

Nitrogen and phosphorus removal by coupling Anaerobic ammonia oxidation reaction with algal-bacterial symbiotic system

The pig farm wastewater after anaerobic digestion has attracted much attention due to its difficulty to be biochemically treated. This paper evaluated the potential of the combined anaerobic-aerobic process to treat digested wastewater from synthetic pig farms in terms of nitrogen, phosphorus, and organic compound removal. The experimental results showed that despite the low COD/TN(C/N) ratio of digested wastewater from pig farms, the removal efficiency of ammonium, total phosphorus (TP), and organic compound could reach 100%, 85%, and 87% respectively after reaching a steady-state by the combined anaerobic-aerobic process with an average hydraulic retention time of 3 days. The Anammox and Algae-Bacteria Symbiosis (An-ABS) system was significantly more effective than the Algae-Bacteria Symbiosis (ABS) system for nitrogen and phosphorus removal. When anaerobic ammonia-oxidizing granular sludge was introduced, the sedimentation performance of the algae-bacterial synergistic symbiotic system was significantly improved. The addition of anaerobic ammonia-oxidized granular sludge not only reduced the sludge diversity but also changed the sludge community structure. In addition, the suspended growth of Chlorella vulgaris protected ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) from Optical damage. This study would provide some new insights into the combined anaerobic-aerobic process system for treating digested wastewater from synthetic pig farms, which would contribute to the development of low-energy wastewater treatment processes. Data availabilityAll data generated and/or analyzed during this study are included in this published article and its supplementary files.