Nitrogen-rich Wastewater Research Articles

Inhibition effect of Cu(II) on nitrogen removal in anammox-denitrification couple system

Due to the wide application in industries, copper can be detected in some nitrogen-rich wastewater. In this research, short-term and long-term experiments were conducted to explore the effects of Cu(II) on the anammox-denitrification couple system. It concluded that the half inhibition concentration (IC50) of Cu(II) was 35.54 mg/L. The system in reactor could tolerate low concentrations of Cu(II) (≤5 mg/L), while the total nitrogen removal efficiency decreased from 93 % to 33 % under 10 mg/L of Cu(II). After 45 days exposure to Cu(II) (1–10 mg/L), 14.54 mg/g SS copper accumulated in the sludge, which largely inhibited the microbial activity. More extracellular polymeric substances (EPS) were secreted to defend against copper toxicity. Proteobacteria (19.18 %–44.04 %) was the dominant phylum and showed excellent tolerance and adaptability to Cu(II). The dominant anammox bacteria, Candidatus_Brocadia, was slightly enhanced under low concentrations of Cu(II), but was highly inhibited under 10 mg/L of Cu(II). PICRUSt2 results showed that some metabolic activities were suppressed under the exposure of copper while defensive responses were also induced. Metabolic disorders eventually led to the death of some microbes, resulting in unrecoverable deterioration in microbial activity. Overall, this study explores the effect of Cu(II) on the anammox-denitrification process and provides a possible inhibition mechanism.

Engineering low-valent molybdenum sites in CoMoO4 nanosheets to boost electrochemical nitrogen-rich wastewater treatment

Electrochemical coupling nitrate-to-ammonia (NO3–-to-NH3) with urea oxidation reaction (UOR) is attractive for both energy-saving ammonia synthesis and comprehensive nitrogen-rich wastewater treatment. However, developing the efficient electrocatalyst that simultaneously promotes hydrogenation of NO3– and UOR is still challenging. Here, we engineered the porous CoMoO4 nanosheets with rich low-valent Mo sites (Mo(L)-CoMoO4-x) as a difunctional electrocatalyst for both NO3–-to-NH3 and UOR. The Mo(L)-CoMoO4-x displayed high Faradaic efficiency (93.33%) and selectivity (91.16%) for NO3–-to-NH3 and low potential (1.31 V vs. RHE) at 100 mA cm−2 toward UOR. Impressively, a low cell voltage of 1.83 V was needed for coupling UOR with NO3–-to-NH3 in two-electrode system. Mechanism study revealed that the introduction of low-valent Mo sites in CoMoO4 nanosheets accelerated the activation kinetics and multistep hydrogenation of NO3–, and also promoted the reconstruction of active CoOOH species for UOR, resulting the difunctional catalytic property for NO3–-to-NH3 and UOR.

Irons differently modulate bacterial guilds for leading to varied efficiencies in simultaneous nitrification and denitrification (SND) within four aerobic bioreactors

As a novel biological wastewater nitrogen removal technology, simultaneous nitrification and denitrification (SND) has gained increasing attention. Iron, serving as a viable material, has been shown to influence nitrogen removal. However, the precise impact of iron on the SND process and microbiome remains unclear. In this study, bioreactors amended with iron of varying valences were evaluated for total nitrogen (TN) removal efficiencies under aerobic conditions. The acclimated control reactor without iron addition (NCR) exhibited high ammonia nitrogen (AN) removal efficiency (98.9%), but relatively low TN removal (78.6%) due to limited denitrification. The reactor containing zero-valent iron (Fe0R) demonstrated the highest SND rate of 92.3% with enhanced aerobic denitrification, albeit with lower AN removal (84.1%). Significantly lower SND efficiencies were observed in reactors with ferrous (Fe2R, 66.3%) and ferric (Fe3R, 58.2%) iron. Distinct bacterial communities involved in nitrogen metabolisms were detected in these bioreactors. The presence of complete ammonium oxidation (comammox) genus Nitrospira and anammox bacteria Candidatus Brocadia characterized efficient AN removal in NCR. The relatively low abundance of aerobic denitrifiers in NCR hindered denitrification. Fe0R exhibited highly abundant but low-efficiency methanotrophic ammonium oxidizers, Methylomonas and Methyloparacoccus, along with diverse aerobic denitrifiers, resulting in lower AN removal but an efficient SND process. Conversely, the presence of Fe2+/Fe3+ constrained the denitrifying community, contributing to lower TN removal efficiency via inefficient denitrification. Therefore, different valent irons modulated the strength of nitrification and denitrification through the assembly of key microbial communities, providing insight for microbiome modulation in nitrogen-rich wastewater treatment.

Temperature-resilient superior performances by coupling partial nitritation/anammox and iron-based denitrification with granular formation

Partial nitritation-anammox (PN/A), an energy-neutral process, is widely employed in the treatment of nitrogen-rich wastewater. However, the intrinsic nitrate accumulation limits the total nitrogen (TN) removal, and the practical application of PN/A continues to face a significant challenge at low temperatures (<15 °C). Here, an integrated partial nitritation-anammox and iron-based denitrification (PNAID) system was developed to address the concern. Two up-flow bioreactors were set up and operated for 400 days, with one as the control group and the other as the experiment group with the addition of Fe0. In comparison to the control group, the experiment group with the Fe0 supplement showed better nitrogen removal during the entire course of the experiment at different temperature levels. Specifically, the TN removal efficiency of the control group decreased from 82.9 % to 53.9 % when the temperature decreased from 30 to 12 °C, while in stark contrast, the experiment group consistently achieved 80 % of TN removal in the same condition. Apart from the enhanced nitrogen removal, the experiment group also exhibited better phosphorus removal (10.6 % versus 74.1 %) and organics removal (49.5 % versus 65.1 %). The enhanced and resilient nutrient removal performance of the proposed integrated process under low temperatures appeared to be attributed to the compact structure of granules and the increased microbial metabolism with Fe0 supplement, elucidated by a comprehensive analysis including microbial-specific activity, apparent activation energy, characteristics of granular sludge, and metagenomic sequencing. These results clearly confirmed that Fe0 supplement not only improved nitrogen removal of PN/A process, but also conferred a certain degree of robustness to the system in the face of temperature fluctuations.

Advances in Nitrogen-Rich Wastewater Treatment: A Comprehensive Review of Modern Technologies

Nitrogen-rich wastewater is a major environmental issue that requires proper treatment before disposal. This comprehensive overview covers biological, physical, and chemical nitrogen removal methods. Simultaneous nitrification–denitrification (SND) is most effective in saline water when utilizing both aerobic and anoxic conditions with diverse microbial populations for nitrogen removal. Coupling anammox with denitrification could increase removal rates and reduce energy demand. Suspended growth bioreactors effectively treated diverse COD/N ratios and demonstrated resilience to low C/N ratios. Moving biofilm bioreactors exhibit reduced mortality rates, enhanced sludge–liquid separation, increased treatment efficiency, and stronger biological structures. SND studies show ≥90% total nitrogen removal efficiency (%RETN) in diverse setups, with Defluviicoccus, Nitrosomonas, and Nitrospira as the main microbial communities, while anammox–denitrification achieved a %RETN of 77%. Systems using polyvinyl alcohol/sodium alginate as a growth medium showed a %RETN ≥ 75%. Air-lift reflux configurations exhibited high %RETN and %RENH4, reducing costs and minimizing sludge formation. Microwave pretreatment and high-frequency electric fields could be used to improve the %RENH4. Adsorption/ion exchange, membrane distillation, ultrafiltration, and nanofiltration exhibit promise in industrial wastewater treatment. AOPs and sulfate-based oxidants effectively eliminate nitrogen compounds from industrial wastewater. Tailoring proposed treatments for cost-effective nitrogen removal, optimizing microbial interactions, and analyzing the techno-economics of emerging technologies are crucial.

Interaction of reed litter and biochar presences on performances of constructed wetlands

Constructed wetlands (CWs) are frequently used for effective biological treatment of nitrogen-rich wastewater with external carbon source addition; however, these approaches often neglect the interaction between plant litter and biochar in biochar-amended CW environments. To address this, we conducted a comprehensive study to assess the impacts of single or combined addition of common reed litter and reed biochar (pyrolyzed at 300 and 500 °C) on nitrogen removal, greenhouse gas emission, dissolved organic matter (DOM) dynamics, and microbial activity. The results showed that combined addition of reed litter and biochar to CWs significantly improved nitrate and total nitrogen removal compared with biochar addition alone. Compared to those without reed litter addition, CWs with reed litter addition had more low-molecular-weight and less aromatic DOM and more protein-like fluorescent DOM, which favored the enrichment of bacteria associated with denitrification. The improved nitrogen removal could be attributed to increases in denitrifying microbes and the relative abundance of functional denitrification genes with litter addition. Moreover, the combined addition of reed litter and 300 °C-heated biochar significantly decreased nitrous oxide (30.7 %) and methane (43.9 %) compared to reed litter addition alone, while the combined addition of reed litter and 500 °C-heated biochar did not. This study demonstrated that the presences of reed litter and biochar in CWs could achieve both high microbial nitrogen removal and relatively low greenhouse gas emissions.

Nitrogen removal intensification of biofilm through bioaugmentation with Methylobacterium gregans DC-1 during wastewater treatment

The increasing concern for environmental remediation has led to a search for effective methods to remove eutrophic nutrients. In this study, Methylobacterium gregans DC-1 was utilized to improve nitrogen removal in a sequencing batch biofilm reactor (SBBR) via aerobic denitrification. This bacterium has the extraordinary characteristics of strong auto-aggregation and a high ability to remove nitrogen efficiently, making it an ideal candidate for enhanced treatment of nitrogen-rich wastewater. This strain was used for the bioassessment of a test reactor (SBBRbio), which showed a shorter biofilm formation time compared to a control reactor (SBBRcon) without this strain inoculation. Moreover, the enhanced biofilm was enriched in TB-EPS and had a wider variety of protein secondary structures than SBBRcon. During the stabilization phase of SBBRbio, the EPS molecules showed the highest proportion of intermolecular hydrogen bonding. It is possible that bioaugmentation with this strain positively affects the structural stability of biofilm. At influent ammonia loadings of 100 and 150 mg. L−1, the average reduction of ammonia and nitrate-nitrogen was higher in the experimental system compared to the control system. Additionally, nitrite-N accumulation was lower and N2O production decreased compared to the control. Analysis of the microbial community structure demonstrated successful colonization in the bioreactor by a highly nitrogen-tolerant strain that efficiently removed inorganic nitrogen. These results illustrate the great potential of this type of denitrifying bacteria in the application of bioaugmentation systems.

Deciphering performance and microbial characterization of marine anammox bacteria-based consortia treating nitrogen-laden hypersaline wastewater: Inhibiting threshold of salinity

Hypersaline wastewater posed a challenge to microbial nitrogen removal processes. Herein, halophilic marine anammox bacteria (MAB) were applied to treat nitrogen-rich wastewater with 35–90 g/L salts for the first time. It was found that MAB, with low relative abundance (2.3–6.9 %), still exhibited good nitrogen removal efficiency (>90 %) under 35–70 g/L salts. The specific anammox activity peaked at 180.16 mg N/(g·VSS·d) at 65 g/L salts. MAB secreted more extracellular polymeric substances to resist the adverse effects of hypersaline stress. Nevertheless, the nitrogen removal deteriorated at 75 g/L salts, and further collapsed as the salinity increased. At 90 g/L salts, total nitrogen removal rate decreased by 74 % compared with that of 35 g/L salts. Besides, SBR1031 increased from 12.0 % (35 g/L salts) to 17.4 % (90 g/L salts) and became the dominant bacterial genus in the reactor. This work shed light on the treatment of hypersaline wastewater through MAB.

Electro-flocculation of aquaculture wastewater microalgal communities reduces nutrient loading

Land-based aquaculture provides dietary protein to the world’s population in a sustainable way, but issues related to release of nitrogen rich wastewater limits its expansion. Sedimentation of naturally occurring microalgae that assimilate excess nitrogen, is slow and land intensive. Electro-flocculation, used in wastewater treatment processes, is a potential alternative for aquaculture. Trials of different electro-flocculation configurations applied to three prawn farm pondwater samples containing varying microalgal assemblages are reported. In 64 % of trials, electro-flocculation reduced total nitrogen (TN) and dissolved inorganic nitrogen (DIN) loads within regulatory limits.TN was reduced up to 83.2 % (10.93 to 1.83 mg.L−1) within 20 mins in stationary water, and DIN to 90.6 % (3.19 to 0.30 mg.L−1) in 102 mins trials in flowing water. Bellerochea andGloeocapsa spp. were dominant in wastewater. The role of microalgal community composition on flocculation is discussed, including evidence Bellerocheapromotes flocculation. This study confirmed electro-flocculation quickly reduces TN and DIN.

Advances in the Efficient Enrichment of Anammox Bacteria

Anaerobic ammonia oxidation (anammox) process is known as a low-energy and environmentally friendly process for treating nitrogen-rich wastewater. Anammox bacteria are the key microorganisms to achieve this biological process. However, the efficient enrichment of anammox bacteria has been a bottleneck for its practical application because of their slow growth and high sensitivity, and no pure culture has been found. Therefore, the development of efficient anammox bacterial enrichment techniques is of great theoretical and application value. Solving the problem of anammox bacterial activity and improving the process denitrification performance is one of the current research hotspots. In this paper, three aspects of anammox bacteria are described in terms of their physiological properties, environmental influencing factors, and short-term starvation tolerance; a systematic review of the latest research progress in accelerating the activity of anammox bacteria using enrichment strategies for process regulation, the construction of granulation models, suspended sludge biomass management, and strain preservation. Finally, the future frontier development of anammox bacteria was discussed and foreseen.

A zero energy-input nitrogen removal reactor based on a short-circuited microfluidic fuel cell.

Excessive discharge of ammonia nitrogen would deteriorate water quality. In this work, we designed an innovative microfluidic electrochemical nitrogen-removal reactor (MENR) based on a short-circuited ammonia-air microfluidic fuel cell (MFC). The MENR utilizes the laminar characteristics of two flows (an anolyte containing nitrogen-rich wastewater and a catholyte of acid electrolyte solution) in a microchannel to establish an efficient reactor system. At anode, ammonia was catalyzed by a NiCu/C modified electrode to N2, while O2 in the air was reduced at cathode. In essence, the MENR reactor is a short-circuited MFC. Maximum discharge currents were achieved accompanied with strong ammonia oxidation reaction. Factors indicating electrolyte flow rate, initial nitrogen concentration, electrolyte concentration, and electrode geometry have various effects on the nitrogen removal performance of the MENR. Results indicate that the MENR showed efficient nitrogen removal properties. This work proposes an energy-saving process by using the MENR to remove nitrogen from ammonia-rich wastewater.

Defense mechanism of Fe(III)-assisted anammox under salt stress: Performance and microbial community dynamics

Anammox process has attracted attention due to its excellent nitrogen removal properties in nitrogen-rich wastewater treatment. However, there were some obstacles for the application of anammox to treat high saline wastewater due to its sensitivity to salinity. In this study, Fe(III) addition strategy was developed to assist anammox to adapt high saline surroundings, with the defense mechanism involved in Fe(III)-assisted anammox emphasized. Nitrogen removal performance of anammox was deteriorated at 3.5% salinity, with the average total nitrogen removal rate of 0.85 kg/(m3·d) observed. The continuous addition of Fe(III) could significantly assist anammox to resist high salinity through facilitating the enrichment of anammox species. Candidatus Kuenenia was the main anammox species and outcompeted Candidatus Brocadia under high saline surrounding. The relative abundance of Candidatus Kuenenia increased with increased salinity and reached 41.04% under 3.5% salinity. The synthesis of key enzymes of anammox species were improved through Fe(III) addition and then facilitated the energy metabolism of anammox bacteria under 3.5% salinity. This study provides a new thought in Fe(III)-assisted anammox enhancement technologies and deepens the insight of anammox in high saline wastewater treatment.

Whey permeate as a phosphorus source for algal cultivation.

Microalgal cultivation for biodiesel and feed requires recycled nutrient resources for a sustainable long-term operation. Whey permeate (WP) from dairy processing contain high organic load (lactose, oils, proteins) and nitrogen (recourses tested for microalgal cultivation) and organic phosphorus (P) that has not yet been tested as a P source for microalgal cultivation. We explored the potential of green algae strains (brackish) and polyculture (freshwater) in exploiting P from WP added to a medium based on either seawater (7 psu) or landfill leachate. Both strains showed a capacity of using organic P in WP with equal growth rates (0.94-1.12 d-1 ) compared to chemical phosphate treatments (0.88-1.07 d-1 ). The polyculture had comparable growth rate (0.25-0.57 d-1 ) and biomass yield (152.1-357.5 mg L-1 ), and similar or higher nutrient removal rate in the leachate-WP medium (1.3-6.4 mg L-1 day-1 nitrogen, 0.2-1.1 mg L-1 day-1 P) compared to the leachate-chemical phosphate medium (1.2-4.7 mg L-1 day-1 nitrogen, 0.3-1.4 mg L-1 day-1 P). This study showed that WP is a suitable P source for microalgal cultivation over a range of salinities. To date, this is the first study demonstrating that raw WP can replace mineral P fertilizer for algal cultivation.

Treatment of nitrogen-rich wastewater by mixed aeration combined with bioaugmentation in a sequencing batch biofilm reactor: Biofilm formation and nitrogen-removal capacity analysis

The mixed aerated and bioaugmented sequencing batch biofilm reactor (SBBR) was developed to improve the efficiency of nitrogen-rich wastewater treatment, and the mechanism of biofilm formation and nitrogen removal was analyzed. The results showed that the addition of aerobic denitrifiers could shorten the start-up time and significantly improve the biofilm formation ability of SBBRs. The presence of nanobubbles could make the biofilm more compact and secrete more EPS, which promoted the activity and stability of the biofilm. During the stable operation stage, the bioaugmented SBBR under mixed aeration mode showed the best nitrogen removal performance and the removal rates of NH4+-N (95.65) and TN (94.88%） were increased by 19.86% and 14.36% compared with the control group, respectively. Microbial community structure and nitrogen metabolism pathway analysis revealed that strain ZS1 colonized the reactor. Hyphomonas, Defluviicoccus and Hydrogenophaga played important roles in N removal in the mixed aerated and bioaugmented SBBR. Meanwhile, the suitable oxidative environment created by mixed aeration made autotrophic nitrifiers（mainly Nitrospira and Nitrosomonas）and aerobic denitrifiers (mainly Hydrogenophaga, Hyphomonas and Pseudofulvimonas) coexist successfully, increasing the relative abundance of the key functional genes (amoABC, hao, napAB genes) in nitrification and denitrification processes to improve the N removal performance. Furthermore, mixed aeration combined with bioaugmented stimulated the nirA, gltBD and GLUD genes, thus promoting the process of nitrogen assimilation and providing a pathway of the direct removal of NH4+-N.

Integrating biological and chemical CO2 sequestration using green microalgae for bioproducts generation

Microalgae cultivation is considered an attractive negative emission technology (NET) due to its ability to remove carbon dioxide (CO2) from the atmosphere as well as from flue gases. Moreover, some microalgae can uptake dissolved carbon in the form of bicarbonate (HCO3-) and grow well by removing nutrients from various wastewater effluents without competing with freshwater resources. Conventional carbon mineralization is another NET where carbon is fixed into carbonate minerals such as calcite (CaCO3), magnesite (MgCO3), nesquehonite (MgCO3-3H2O), and nahcolite (NaHCO3), which can be reused in various applications such as construction and cosmetics, and in this case, to supply carbon to microalgae. Previous initial laboratory studies demonstrated the possibility of using metastable carbonates as a source of carbon for biomass growth of the freshwater microalga Scenedesmus obliquus. In this study, we present results from an experimental and modeling work where 100 L open raceway reactors were used to grow an algae polyculture using industrial nitrogen-rich wastewater. In addition, carbonates such as MgCO3-3H2O and sodium carbonate (Na2CO3) were added to the ponds to primarily buffer the pH and maintain it within the acceptable algae physiological values and to provide extra carbon to the cultures. Cultures using BG-11 growth medium and without addition of carbonates were run as controls. Continuous online monitoring of pH, temperature, and dissolved oxygen was performed while nutrients content and dry weight of algae culture were measured offline daily. A mathematical model coupled with geochemistry was implemented to describe the overall process of algae growth, carbonate dissolution, and solution composition. Biomass harvested from the raceway reactors was concentrated and oil and fatty acid methyl esters (FAME) content were determined. Results showed that biomass and oil content obtained were comparable to controls, indicating a successful metabolic-based pH control by the addition of carbonates in the ammonium-based media. Furthermore, FAME analysis revealed different profiles depending on the source of carbon used. Overall, this study suggests that integrating both types of NET strategies can contribute to the reduction of carbon emissions while producing biomass that can be further processed to generate a variety of bioproducts.

Additional N Input May Alter the Species-Specific Blue Carbon Cycling Differently in Mangroves

Aquaculture is one of the fastest-growing economic activities in the world that results in a high amount of nitrogen-rich wastewater discharge into mangroves and affects the plant tissue’s decomposition. However, a comprehensive analysis of above- and belowground litter affected by the nitrogen (N) input is rare. This study investigated the responses of above- and belowground litter decomposition to the different levels of N input in decomposition rates, chemical components, and the release of chemical compounds. Exogenous N input had stimulating, retarding, or even no effect on plants’ litter decomposition and nutrient release in mangroves. The above- and belowground litter decompositions had different responses to anthropogenic N addition and varied among different mangrove species. The mechanism of the impacts of anthropogenic nitrogen input varies depending on species identity, litter composition, and additional N level. These results show that N enrichment in mangroves can be beneficial and detrimental to ecosystem function. For the native mangrove species, Kandelia obovata and Avicennia marina , the belowground tissues that had a direct correlation with carbon accumulation were significantly influenced by the additional N input. The worldwide problem of offshore aquaculture effluent discharge is a potential risk to the ecological function of mangroves in carbon storage.

Exploring denitrification and anammox processes in the saturated zone of passively operated vegetated biofiltration systems

Vegetated biofiltration systems (VBS) are common nature-based solutions (NBS) for urban water treatment, but their performance in treating nitrogen-rich wastewater is yet to be explored.

Phylogenomic analysis of Citrobacter sp. strain AAK_AS5 and its metabolic capabilities to support nitrogen removal behavior.

Despite the ubiquity of the genus Citrobacter in clinical, industrial, and environmental scenarios, a large number of Citrobacter strains have not been explored at the genome-scale level. In this study, accurate taxonomic assignment of strain AAK_AS5 isolated from activated sludge was achieved by in-silico genomic comparison using Overall Genome-based Relatedness Indices (ANI(OAT): 97.55%, ANIb:97.28%, and ANIm: 97.83%) that indicated its closest identity to the related strain Citrobacter portucalensis A60T . Results were consistent with a digital DNA-DNA hybridization value of 80% with C. portucalensis A60T which was greater than the species boundary value >70% for delineating closely related bacterial species. Gene mining through Kyoto Encyclopedia of Genes and Genomes (KEGG), and annotation using rapid annotation subsystem technology (RAST) revealed the notable gene contents for nitrogen metabolism and other pathways associated with nitrate/nitrite ammonification (28 genes), ammonia assimilation (22 genes), and denitrification pathways (14 genes). Furthermore, the strain AAK_AS5 also exhibited a high soluble chemical oxygen demand (sCOD), NH4 + -N, and NO3 - -N removal efficiency of 91.4%, 90%, and 93.6%, respectively thus validating its genetic capability for utilizing both (NH4 )2 SO4 and KNO3 as the nitrogen source. The study provided deeper insights into the phylogenomics and the genetic potential of Citrobacter, sp. strain AAK AS5 associated with nitrogen metabolism thus signifying the potential application of the isolate for treating nitrogen-rich wastewaters.

Start-up of the combined anaerobic ammonium oxidation and solid phase denitrification process and microbial characterization analysis

To improve the nitrogen removal performance of anaerobic ammonia oxidation (anammox)-based processes, a modified anaerobic baffled reactor (ABR) equipped with a packed bed of poly-3-hydroxybutyrate-cohyroxyvelate (PHBV) was employed to start up the combined anammox and solid phase denitrification (SPD) process for the treatment of nitrogen-rich wastewater. Results showed that a stable removal of total inorganic nitrogen (TIN) of 98.5 % was achieved with a nitrogen loading rate of 0.46 kg·(m3·d)−1, decreasing the effluent TIN concentration to <2 mg·L−1. Throughout the operation period of 180 days, sludge granulation in three compartments of the ABR was promoted by a stepwise decrease in the hydraulic retention time. The anammox reaction and endogenous denitrification mainly occurred in the first two compartments with inorganic feeding and contributed >86 % of TIN removal. 16S rRNA gene amplicon sequencing showed that anammox communities, dominated by genera Candidatus Kuenenia and Candidatus Brocadiaceae, were enriched in granular sludges with symbiotic heterotrophic bacteria. Co-cultures of hydrolytic bacteria (Burkholderiales, Kapabacteriales, and Clostridium-sensu-stricto-7) and denitrifying bacteria (Comamonadaceae, Rhodocyclaceae, and Denitratisoma) were detected within the biofilm on the surface of PHBV particles. PHBV hydrolysate input effectively drove heterotrophic denitrification in the successive compartment and increased the complexity of microbial co-occurrence networks. These findings provide insight into the synergistic mechanisms between anammox and SPD and present a feasible combined process application for advanced biological nitrogen removal.

In-situ utilization of nitrogen-rich wastewater discharged from a biotrickling filter as a moisture conditioning agent for composting: Insights into nitrogen transformation behavior and microbial mechanism

An NH4+–NO2–-rich wastewater discharged from a composting-biotrickling filter coupled system can be reused as a composting moisture adjustment agent. To investigate the impact mechanism of reuse, NH4+–NO2–-rich wastewater, NH4+-rich wastewater, NO2–-rich wastewater, and distilled water were added into the composting (i.e., AMN, AAN, ANO2, and ADW groups). Results show that compost of all groups met the corresponding criteria for stabilization, humification, and non-phytotoxicity of mature compost. AMN increased organic-N and NO3–-N content and reduced NH3 emissions, like AAN or ANO2, and avoid stimulating N2O emission in AAN and ANO2. Furthermore, LEfSe analysis of microorganisms revealed that AMN reduced NH3 emissions and increase organic-N content probably due to the inhibition of Alphaproteobacteria by ammonium, and increased nitrate content probably due to the stimulation of Aquamicrobium by nitrite. The avoided N2O emission is probably due to a negative synergistic effect on the stimulation from ammonia and nitrite to denitrifying bacteria (eg., Sphingobacteriaceae).