Formation mechanisms and assembly patterns of anammox biofilm induced by carrier type: Novel insights based on low-strength wastewater treatment

Characterization of nitrogen transformation and microbial interactions of floc sludge and biofilms in single-stage gas-lift partial nitritation/anammox reactor with hollow cylindrical carriers

Floc sludge and biofilms are common biomass types used in the partial nitritation/anaerobic ammonium oxidation (anammox) (PN/A) process to treat ammonium wastewater; however, the interactions between these coexisting biomass types for stable nitrogen removal have not yet been well characterized. This study employed single-stage PN/A reactor with hollow cylindrical polypropylene carriers to investigate nitrogen transformation and microbial interactions in floc sludge and biofilms during long-term stable nitrogen removal. Floc sludge primarily drove ammonia oxidation, demonstrating 11.6-fold higher efficiency than biofilms, whereas biofilms mediated the anammox reaction, 3.6-fold more efficiently than floc sludge. Floc sludge and biofilms contributed 18.4 % and 65.9 % to nitrogen removal, respectively. Ammonia-oxidizing bacteria dominated the floc sludge (Nitrosomonas) and cooperated with anammox biofilms (Candidatus Kuenenia) to enable stable nitrogen removal. These findings deepen understanding of nitrogen transformation and microbial interactions across different biomass types and facilitate the optimization of PN/A efficiency through flexible control strategies.

Start-up of Anammox-HAP in IC reactors: Revelation of sludge characteristics and microbial community structure

The scarcity of seed sludge poses a significant barrier to the advancement of anaerobic ammonia oxidation (anammox) process. In this investigation, two alternative sludge (anaerobic granular sludge (AGS) and activated flocculent sludge (AFS)) were employed to start up the anammox process in internal circulation (IC) reactors with the hydroxyapatite (HAP) strategy. Both reactors achieved rapid start-up on days 83 and 53, respectively. Subsequently, a nitrogen removal rate (NRR) of 1.34 gN/L/d was attained at a nitrogen loading rate (NLR) of 1.39 gN/L/d on days 107 and 81 correspondingly. The analysis of granular properties revealed that the anammox granular sludge (AMXGS) transformed from AGS exhibited superior granular size distribution and settling performance. Furthermore, the assessment of microbial community structure demonstrated that inoculating AFS was capable of enriching anammox bacteria (AnAOB) in a shorter time. Last but most importantly, this study provides a comprehensive analysis of the distinct granulation routes of AGS and AFS. AGS predominantly underwent a "broken-adsorption-granulation" process, whereas AFS exhibited not only a typical "adsorption-granulation" process but also a "biofilm growth-granulation" cycle process. The findings of this study offer a novel approach for quickly initiating anammox process when inoculating alternative sludge.

Use of embedding immobilized biofillers to improve hydrolysis acidification efficiency in domestic wastewater treatment

This study evaluated the effectiveness of embedding immobilization technology in wastewater treatment and its capacity to enhance the hydrolysis acidification process. Based on this technology, a stable anaerobic environment has been maintained. Results showed that the rates of dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) conversion both exceeded 98 % under short hydraulic retention time (HRT = 2h) and ambient temperature. Notably, acetic acid and propionic acid comprised up to 90.9 % of the total volatile fatty acids in the effluent, providing suitable carbon sources for downstream denitrification. 16S rRNA gene sequencing indicated that biofillers effectively enriched and retained functional bacteria, causing norank_Anaerolineaceae (11.6 %-29.7 %) and norank_Bacteroidetes_vadinHA17 (10.8 %-14.9 %) as the dominant genera in the reactor, which were crucial for refractory organic matter degradation. Immobilized biofillers effectively improved wastewater biodegradability, supporting a stable microbial community with high DON and DOP conversion rates as well as increased VFA accumulation.

The superiority of hydrophilic polyurethane in comammox-dominant ammonia oxidation during low-strength wastewater treatment

Carriers have been extensively employed to enhance nitrification performance during low-strength wastewater treatment by retaining slow-growing ammonia oxidizing microorganisms (AOMs). Still, there is a dearth of systematic understanding of biofilm properties and microbial community structure formed on different carriers. In this study, hydrophilic polyurethane foam (PUF) carriers were prepared and compared with five widely used commercial carriers, namely Kaldness 3, Biochip, activated carbon, volcanic rock, and zeolite. The results indicated that the biofilms formed on carriers enhanced microbial ammonia oxidation activity. Additionally, the biofilm developed on the PUF demonstrated the most superior performance among all selected carriers, not only exhibiting the highest abundant and the most active AOMs, with amoA gene abundance of 1.41 × 1013 copies/m3 and specific ammonia oxidation rate of 9.84 g NH4+-N/(m3 × h), but also possessing a compact structure, with 3.41 kg VSS/m3 and 46.83 mg extracellular polymeric substances/g VSS. The high-throughput sequencing analysis revealed that the comammox (CMX) Nitrospira dominated on biofilm due to the intrinsically low apparent half-saturation constant for substrate. A unique ecological community structure was established on PUF, characterized by low species diversity and high homogeneity in alignment with community characteristics of CMX. The biofilms on PUF contributed to the proliferation of CMX Nitrospira dominated by Nitrospira nitrosa, achieving the highest proportion among colonial three AOMs at 86.58 %. The appropriate average pore size, superior hydrophilicity, and large specific surface area of PUF carriers provided a robust foundation for the exceptional ammonia oxidation performance of the formed biofilms.

Comparison of treatment performance and microbial community evolution of typical dye wastewater by different combined processes

The degradation of typical dye wastewater is a focus of research in the printing and dyeing industry. In this study, a combined micro-electrolysis and microbial treatment method was established to treat refractory dye wastewater, and the pivotal factors in the microbial treatment were optimized. In the series and coupled modes, the removal rates of chroma reached 98.75% and 92.50%, and the removal rates of chemical oxygen demand (COD) reached 96.17% and 82.29%, respectively. The high-throughput sequencing results showed that the microbial communities in the microbial system varied at different treatment stages. From the culture stage to the domestication stage, the dominant phylum was Proteobacteria; however, the community abundance of microorganisms decreased. A combination of micro-electrolysis and biological methods can alter the characteristics of the microbial community, increase the number of dominant phyla, and increase the abundance of microorganisms. The degradation effect of the series mode and the overall strengthening effect of micro-electrolysis on the microorganisms were better than those of the coupled mode. In actual wastewater, the maximum removal rates of chroma, COD, total nitrogen (TN), ammonia nitrogen (NH3-N), and total phosphorus (TP) are 97.50%, 98.90%, 94.35%, 93.95%, and 91.17%, respectively. Three-dimensional fluorescence spectrum analysis showed that microbial processes could significantly degrade fluorescent components in wastewater, and methanogenic active enzymes in anaerobic processes could continue to react. The combined process can realize the efficient treatment of toxic dye wastewater by reducing the toxicity of wastewater and efficiently degrading organic matter, which has important guiding significance for the treatment of refractory dye wastewater.

Mechanism of gel immobilization driving efficient anammox in mainstream partial nitritation/anammox process: Structural characterization and multi-perspective microbial analysis

Here, the mechanism of encapsulated anammox bacteria (AnAOB) driving efficient nitrogen removal in the mainstream partial nitritation/anammox process is revealed. The results show that a high nitrogen removal rate (1.21±0.02 kgN·(m3·d)-1) was achieved due to the abundant micropore structure inside the anammox immobilized filler, ensuring good connectivity, and a stable aggregation capacity, reducing dependence on extracellular polymeric substances. AnAOB were uniformly distributed throughout all regions of the immobilized filler, and their abundance was higher than that of the control anammox granular sludge (AnGS). Conversely, cracks appeared on the surface of the AnGS, and hollows formed inside. The metagenome analysis revealed that the immobilized filler supported the coexistence of multiple AnAOB, and the appropriate niche enhanced coordination between the AnAOB and dominant companion microorganisms. In contrast, AnGS exhibited stronger NH4+-N and NO2--N loops, potentially reducing the total nitrogen removal efficiency. This study promotes the mainstream application of anammox.

Response of biofilm-based systems for antibiotics removal from wastewater: Resource efficiency and process resiliency

Biofilm-based systems have efficient stability to cope-up influent shock loading with protective and abundant microbial assemblage, which are extensively exploited for biodegradation of recalcitrant antibiotics from wastewater. The system performance is subject to biofilm types, chemical composition, growth and thickness maintenance. The present study elaborates discussion on different type of biofilms and their formation mechanism involving extracellular polymeric substances secreted by microbes when exposed to antibiotics-laden wastewater. The biofilm models applied for estimation/prediction of biofilm-based systems performance are explored to classify the application feasibility. Further, the critical review of antibiotics removal efficiency, design and operation of different biofilm-based systems (e.g. rotating biological contactor, membrane biofilm bioreactor etc.) is performed. Extending the information on effect of various process parameters (e.g. hydraulic retention time, pH, biocarrier filling ratio etc.), the microbial community dynamics responsible of antibiotics biodegradation in biofilms, the technological problems, related prospective and key future research directions are demonstrated. The biofilm-based system with biocarriers filling ratio of ∼50-70% and predominantly enriched with bacterial species of phylum Proteobacteria protected under biofilm thickness of ∼1600 μm is effectively utilized for antibiotic biodegradation (>90%) when operated at DO concentration ≥3 mg/L. The C/N ratio ≥1 is best suitable condition to eliminate antibiotic pollution from biofilm-based systems. Considering the significance of biofilm-based systems, this review study could be beneficial for the researchers targeting to develop sustainable biofilm-based technologies with feasible regulatory strategies for treatment of mixed antibiotics-laden real wastewater.

A critical review of improving mainstream anammox systems: Based on macroscopic process regulation and microscopic enhancement mechanisms

Full-scale anaerobic ammonium oxidation (anammox) engineering applications are vastly limited by the sensitivity of anammox bacteria to the complex mainstream ambience factors. Therefore, it is of great necessity to comprehensively summarize and overcome performance-related challenges in mainstream anammox process at the macro/micro level, including the macroscopic process variable regulation and microscopic biological metabolic enhancement. This article systematically reviewed the recent important advances in the enrichment and retention of anammox bacteria and main factors affecting metabolic regulation under mainstream conditions, and proposed key strategies for the related performance optimization. The characteristics and behavior mechanism of anammox consortia in response to mainstream environment were then discussed in details, and we revealed that the synergistic nitrogen metabolism of multi-functional bacterial genera based on anammox microbiome was conducive to mainstream anammox nitrogen removal processes. Finally, the critical outcomes of anammox extracellular electron transfer (EET) at the micro level were well presented, carbon-based conductive materials or exogenous electron shuttles can stimulate and mediate anammox EET in mainstream environments to optimize system performance from a micro perspective. Overall, this review advances the extensive implementation of mainstream anammox practice in future as well as shedding new light on the related EET and microbial mechanisms.

Rapid start-up and long-term stable operation of the anammox reactor based on biofilm process: Status, challenges, and perspectives

Anammox-biofilm processes have great potential for wastewater nitrogen removal, as it overcomes the slow growth and easy loss of AnAOB (anaerobic ammonium oxidation bacteria). Biofilm carrier is the core part of the Anammox-biofilm reactor and plays a key role in the start-up and long-term operation of the process. Therefore, the research on the biofilm carrier of Anammox-based process was summarized and discussed in terms of configurations and types. In the Anammox-biofilm process, fixed bed biofilm reactor is a relatively mature biofilm carrier configuration and has advantages in terms of nitrogen removal and long-term operational stability, while moving bed biofilm reactor has advantages in terms of start-up time. Although the long-term operational stability of fluidized bed biofilm reactor is good, its nitrogen removal performance needs to be improved. Among the different biofilm carrier categories, the inorganic biofilm carrier has an advantage in start-up time, due to the enhancement of the growth and metabolic of AnAOB by inorganic materials (such as carbon and iron). Anammox-based reactors using organic biofilm carriers, especially suspension carriers, are well-established and more stable in long-term operation. Composite biofilm carriers combine the advantages of several materials, but their complex preparation procedures lead to high costs. In addition, possible research directions for accelerating the start-up and keeping the long-term stable operation of Anammox reactor by biofilm process were highlighted. It is hoped to provide a possible pathway for the rapid start-up of Anammox-based process, and references for the optimization and promotion of process.