Microbial dynamics reveal the adaptation strategies of ecological niche in distinct anammox consortia under mainstream conditions

Community assembly and succession of the functional membrane biofilm in the anammox dynamic membrane bioreactor: Deterministic assembly of anammox bacteria

The anammox dynamic membrane bioreactor (DMBR) exhibits potential for efficient nitrogen removal via anammox processes. The functional membrane biofilm in the anammox DMBR significantly enhances nitrogen removal, ensuring robust operation. Nevertheless, ecological mechanisms underpinning the nitrogen removal function of the membrane biofilm remain unclear. We investigated the community succession and assembly of the membrane biofilm communities in two anammox DMBRs utilizing distinct inoculated anammox sludges. Anammox bacteria displayed niche differentiation in both DMBRs. Anammox bacteria Candidatus Kuenenia was selectively enriched to 8.5% abundance in the membrane biofilm communities, contributing to 5.2-7.2% of the nitrogen removal load. Membrane biofilm communities were primarily assembled through deterministic processes. Specifically, the selective enrichment of Candidatus Kuenenia on the membrane biofilms was primarily governed by homogenous selection process, explaining 9.67-9.82% of the variance. The deterministic assemblies of anammox bacteria were mainly influenced by the high substrate affinity of Candidatus Kuenenia and the limited availability of substrates (NH4+ and NO2-) in the membrane biofilms. Furthermore, the relatively weak permeate drag force during the DMBR filtration facilitated the preferential colonization of microbes from the anammox sludge to the membrane biofilm, resulting in the deterministic formation of the membrane biofilm communities with nitrogen removal function. Our findings offer insights into the ecological mechanisms driving the deterministic assembly of the functional membrane biofilm communities in the anammox DMBRs, informing the precise regulation of membrane biofilms for improved nitrogen removal in anammox applications of wastewater treatment.

Comprehensive performance of a new-type hybrid membrane bioreactor applied to mainstream anammox process

The new-type submerged granular sludge membrane bioreactor (S-GSMBR) was constructed by installing a membrane module inside an upflow anaerobic sludge blanket. S-GSMBR achieved the fast start-up (47 d) and long-term stable operation (133 d) of mainstream Anammox process as well as the effective control of membrane fouling. The maximum nitrogen removal rate and efficiency were 0.52 kg N m-3 d-1 and 88.32%. The flow field analysis indicated that the turbulent effects were found around the membrane module and benefited for alleviating the membrane fouling at the special axial flow velocity at the central section of the membrane module (4.89 × 10-7 m s-1 to 1.30 × 10-6 m s-1). On day 133, S-GSMBR achieved sludge granulation with 68.63% of particles larger than 200 μm. Meanwhile, Candidatus Brocadia and Candidatus Kuenenia were typical Anammox bacteria in mature Anammox granular sludge. The relative abundance of Candidatus Brocadia and Candidatus Kuenenia was 21.22% and 0.36%, indicating that Candidatus Brocadia occupied the main niche under mainstream Anammox conditions. The feasibility of application of S-GSMBR in mainstream Anammox process was confirmed and moreover S-GSMBR was proven to be a robust mainstream Anammox reactor. This study lays the important theoretical foundation and technical support for the engineering application of the mainstream Anammox process.

Insight into the responses of the anammox granular sludge system to tetramethylammonium hydroxide (TMAH) during chip wastewater treatment

Tetramethylammonium hydroxide (TMAH), an extensively utilized photoresist developer, is frequently present in ammonium-rich wastewater from semiconductor manufacturing, and its substantial ecotoxicity should not be underestimated. This study systematically investigated the effects of TMAH on the anammox granular sludge (AnGS) system and elucidated its inhibitory mechanisms. The results demonstrated that the median inhibitory concentration of TMAH for anammox was 84.85 mg/L. The nitrogen removal performance of the system was significantly decreased after long-term exposure to TMAH (0-200 mg/L) for 30 days (p < 0.05), but it showed adaptability to certain concentrations (≤50 mg/L). Concurrently, the stability of the granules decreased dramatically, resulting in the breakdown of AnGS. Further investigations indicated that TMAH exposure increased the secretion of extracellular polymeric substances but weakened their defense function. The increase in reactive oxygen species resulted in damage to the cell membrane. Reduced activity of anammox bacteria, impeded electron transfer, and changes in enzyme activity suggested that TMAH affected the metabolic activity. Microbiological analysis revealed that TMAH caused a decrease in the abundance of anammox bacteria and a weakening of symbiotic interactions within the microbial community. These results provide valuable guidance for the AnGS system application in chip wastewater treatment.

Multi-omics analysis reveals the collaboration and metabolisms of the anammox consortia driven by soluble/non-soluble Fe(III) as the sole iron element

Iron is recognized as a physiological requirement for anammox bacteria (AnAOB), with Fe(II) considered to be the most effective form. However, Fe(III), instead of Fe(II) is the common iron form in natural and artificial ecosystems. In this study, the nitrogen removal performance and metabolic mechanisms in anammox consortia with soluble and non-soluble Fe(III) as the sole iron element were investigated. After the 150-day operation, the soluble (FeCl3) and insoluble (Fe2O3) Fe(III)-fed anammox systems reached nitrogen removal rates of 71.84 ± 0.80% and 50.20 ± 0.98%, respectively. AnAOB could survive with soluble (FeCl3) or insoluble (Fe2O3) Fe(III) as the sole iron element, reaching relative abundances of 18.49% and 13.16%, respectively. The results show that the formation of anammox core consortia can enable AnAOB's survival to adverse external conditions of Fe(II) deficiency. Metagenomic and metatranscriptomic analysis reveal that Ca. Kuenenia can only uptake Fe(II) into the cell for metabolisms either independently through the extracellular electron transfer or with the cross-feeding of symbiotic microbes. This study provides insight into the utilization and metabolic mechanisms of Fe(III) in Ca. Kuenenia-dominated consortia, and deepens the understanding of anammox core consortia in the nitrogen, carbon, and iron cycling, further promoting the practical applications of anammox processes.

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.

Elucidating prioritized factor for mainstream partial nitritation between C/N ratio and dissolved oxygen: Response surface methodology and microbial community shifts

Recently, C/N ratio is suggested as a promising control factor with dissolved oxygen (DO) achieving mainstream partial nitritation (PN); however, their combined effects on mainstream PN are still limited. This study evaluated the mainstream PN with respect to the combined factors, and investigated the prioritized factor affecting the community of aerobic functional microbes competing with NOB. Response surface methodology was performed to assess the combined effects of C/N ratio and DO on the activity of functional microbes. Aerobic heterotrophic bacteria (AHB) played the greatest role in oxygen competition among functional microbes, which resulted in relative inhibition of nitrite-oxidizing bacteria (NOB). The combination of high C/N ratio and low DO had a positive role in the relative inhibition of NOB. In bioreactor operation, the PN was successfully achieved at ≥ 1.5 of C/N ratio for 0.5-2.0 mg/L DO conditions. Interestingly, aerobic functional microbes outcompeting NOB were shifted with C/N ratio rather than DO, suggesting C/N ratio is more prioritized factor achieving mainstream PN. These findings will provide insights into how combined aerobic conditions contribute to achieve mainstream PN.

Succession of microbial communities reveals the inevitability of anammox core in the development of anammox processes

The lack of anammox seeds is regarded as the bottleneck of anammox-based processes. Although the interactions in anammox consortia have attracted increasing attention, little is known about the influence of inoculated sludge populations on the growth of anammox bacteria. In this study, four sludge of distinct communities mixed with anammox sludge (the relative abundance of Ca. Kuenenia was 1.96 %) were used as the seeds, respectively for the start-up of anammox processes. Notably, all these mixed microbial communities tend to form a similar microbial community, defined as the anammox core, containing anammox-bacteria (22.9 ± 5.9 %), ammonia-oxidizing-bacteria (0.8 ± 0.7 %), nitrite-oxidizing-bacteria (0.2 ± 0.2 %), Chloroflexi-bacteria (0.7 ± 0.4 %), and heterotrophic-denitrification-bacteria (0.3 ± 0.2 %). It also elucidated that the communities of Nitrosomonas-dominated sludge were the closest to the anammox core, and achieved the highest nitrogen-removal rate of 0.73 kg-N m^-3 d^-1. This study sheds light on the solution to the shortage of anammox seeds in the full-scale wastewater treatment application.