Newly designed high-coverage degenerate primers for nitrogen removal mechanism analysis in a partial nitrification-anammox (PN/A) process

Influence of high-load shocks on achieving mainstream partial nitrification: Microbial community succession

Driving microbial community succession through the regulation of operational strategies is crucial for achieving partial nitrification (PN) in municipal wastewater. However, at present, there is a decoupling between the strategic regulation of PN systems and the succession characteristics of the microbial community. This study examined the correlation between microbial community succession and PN performance under two high-load shocks (HLS1 and HLS2) treating actual sewage. During HLS1, the influent organic loading rate (OLR) and nitrogen loading rate (NLR) increased from 116.7 ± 37.7 to 219.7 ± 24.7 mg COD/(g VSS·d) and 0.21±0.02 to 0.33±0.02 kg N/m3/d respectively, with the nitrite concentration and nitrite accumulation ratio only reaching 11.7 ± 2.7 mg/L and 49.3 ± 13.9 %, respectively. During HLS2, the influent OLR and NLR increased from 123.5 ± 17.2 to 300.3 ± 49.2 mg COD/(g VSS·d) and 0.19±0.03 to 0.32±0.03 kg N/m3/d respectively, resulting in a nitrite accumulation ratio of 89.4 ± 10.7 %. The system achieved efficient PN performance and sustained for 124 days. High-throughput sequencing results showed that community diversity remained consistently high, and the community composition returned to its initial state following a minor succession during HLS1. During HLS2, the high-load shock reduced the richness and evenness of the microbial community. The community underwent succession in a new direction, leading to community composition and function changes. The results indicate that the realization, stabilization, and disruption of PN are influenced not only by operational parameters but also by microbial community structure.

Segregation of effect between granules and flocs in PN/A system treating acrylic fiber wastewater: Performance and mechanism

Nitrogen removal of petrochemical wastewater through partial nitritation/anammox (PN/A) is appealing, but its feasibility and stability under toxic inhibition remain unclear. This study started a PN/A granular sludge system in a membrane bioreactor and fed it with diluted acrylic fiber wastewater. During long-term operation, the nitritation and anammox performance remained stable at a 30% volume ratio, and declined with increasing volume ratio, resulting in deteriorated nitrogen removal. Meanwhile, the short-term inhibition batch tests further showed that ammonia oxidation bacteria (AOB) in the flocs were suppressed while anammox bacteria (AnAOB) in the granules were not affected. Further analysis indicated suppression of AnAOB over the long-term operation, which was mainly caused by the disintegration of granules as demonstrated by sludge morphology. This selective inhibition is associated with variational sludge morphology, and the distribution of functional bacteria plays an important role in the feasibility and stability of PN/A treating acrylic fiber wastewater. As above, this study demonstrated the feasibility of PN/A for acrylic fiber wastewater treatment, but wastewater dilution or pre-treatment is still required for efficient nitrogen removal.

Fixed nitrogen removal mechanisms associated with sulfur cycling in tropical wetlands

Wetland ecosystems play an important role in nitrogen cycling, yet the role of anaerobic ammonium oxidation (anammox) in tropical wetlands remains unclear. In the current study the anammox process accounted for 29.8 ~ 57.3% of nitrogen loss in ex situ activity batch tests of microcosms established from anoxic sediments of different tropical wetlands, with the highest activity being 17.95±0.51 nmol-N/g dry sediment/h. This activity was most likely driven by sulfide oxidation with dissimilatory nitrate reduction to ammonium (sulfide-driven DNRA). Microbial community analyses revealed a variety of anammox bacteria related to several known lineages, including Candidatus Anammoximicrobium, Candidatus Brocadia and Candidatus Kuenenia, at different wetlands. Metagenome predictions, batch tests, and isotope-tracing suggested that the high level of anammox activity was due to sulfide-driven DNRA. This was corroborated by a strong correlation (through Pearson's analysis) between the abundance of anammox bacteria and the nrfA (a dissimilatory nitrate reduction to ammonium gene) and dsrA (a sulfate reductase gene) genes, as well as sulfate, ammonium and nitrate concentrations. These correlations suggest syntrophic interactions among sulfate-reducing, sulfide-driven DNRA, and anammox bacterial populations. A better understanding of the role of sulfur in nitrogen loss via the anammox reaction in natural systems could inform development of a viable wastewater treatment strategy that utilizes sulfate to minimize the activity of denitrifying bacteria and thus to reduce nitrous oxide emissions from wastewater treatment plants.

Sustained organic loading disturbance favors nitrite accumulation in bioreactors with variable resistance, recovery and resilience of nitrification and nitrifiers

Sustained disturbances are relevant for environmental biotechnology as they can lead to alternative stable states in a system that may not be reversible. Here, we tested the effect of a sustained organic loading alteration (food-to-biomass ratio, F:M, and carbon-to-nitrogen ratio, C:N) on activated sludge bioreactors, focusing on the stability of nitrification and nitrifiers. Two sets of replicate 5-L sequencing batch reactors were operated at different, low and high, F:M (0.19–0.36 mg COD/mg TSS/d) and C:N (3.5–6.3 mg COD/mg TKN) conditions for a period of 74 days, following 53 days of sludge acclimation. Recovery and resilience were tested during the last 14 days by operating all reactors at low F:M and C:N (henceforth termed F:M–C:N). Stable nitrite accumulation (77%) was achieved through high F:M–C:N loading with a concurrent reduction in the abundance of Nitrospira. Subsequently, only two of the three reactors experiencing a switch back from high to low F:M–C:N recovered the nitrite oxidation function, with an increase in Nitrobacter as the predominant NOB, without a recovery of Nitrospira. The AOB community was more diverse, resistant and resilient than the NOB community. We showed that functional recovery and resilience can vary across replicate reactors, and that nitrification recovery need not coincide with a return to the initial nitrifying community structure.