A pilot study of situ sludge fermentation-driven multiple biological nitrogen removal pathways (SFBNR): Revealing microbial synergy mechanism based on co-occurrence network analysis

Enhanced nitrogen removal from low C/N municipal wastewater in a step-feed integrated fixed-film activated sludge system: Synergizing anammox and partial denitrification with sludge fermentation liquid supplementation

The scarcity of rapidly biodegradable organics, which serve as essential electron donors for the partial denitrification (PD) process, significantly hinders the combined application of PD coupled with anammox (PDA) in municipal wastewater treatment plants. This study innovatively applied, for the first time, a step-feed strategy combined with the use of sludge fermentation liquid (SFL) as an external carbon source in an integrated fixed-film activated sludge (IFAS) system, successfully driving full nitrification and PDA to achieve advanced nitrogen removal from low C/N real municipal wastewater. Moreover, the associated nitrogen removal mechanism of this system was systematically analyzed. By employing second-step SFL feed as a supplementary carbon source, the nitrogen removal efficiency reached 92.26 ± 2.77 % and the effluent total inorganic nitrogen was 6.43 ± 2.23 mg/L, with anammox contributing approximately 70 % to total inorganic nitrogen removal. 16S rRNA gene sequencing and fluorescence in situ hybridization analysis unveiled the extensive cooperation and synergistic interactions among anammox bacteria, denitrifying bacteria, and nitrifying bacteria, with Candidatus Brocadia being highly enriched in biofilms with a relative abundance of 2.21 %. Metagenomic sequencing confirmed that the relative abundance of the narGHI gene was greater than that of the nirS gene, providing stable nitrite accumulation conditions for the anammox process. Overall, this study proposes an innovative synergistic treatment scheme that utilizes a step-feed full nitrification-PDA process driven by SFL to achieve advanced nitrogen removal in municipal wastewater treatment plants. This approach is characterized by low energy consumption, low operational costs and a high nitrogen removal efficiency.

Pilot-scale partial nitrification and anaerobic ammonium oxidation system for nitrogen removal from municipal wastewater

Partial nitrification has the advantages of saving energy and reducing the need for carbon sources in municipal wastewater treatment. However, for municipal wastewater with low ammonia, start-up and maintenance of partial nitrification is a worldwide challenge. Here we developed a pilot-scale double sludge system consisting of two sequencing batch reactors for partial nitrification (12 m2) and denitrification/anaerobic ammonium oxidation (denitrification/anammox, 8.4 m2) to treat municipal wastewater. Partial nitrification was maintained at no ammonium remaining with a nitrite accumulation rate of 87.7%. This study found that partial nitrification system effluent chemical oxygen demand increased from 24.8 mg L-1 to 64.9 mg L-1 accompanied by transformation from complete nitrification to partial nitrification. In the denitrification/anammox system, the reduction of nitrite to nitrogen required about 40% less carbon consumption than nitrate. High nitrogen removal was achieved with effluent total inorganic nitrogen of 2.7 mg L-1 without carbon addition. This work provided a pilot-scale demonstration of low-carbon high-nitrogen removal.

Impact of carbon/nitrogen ratio on sequencing batch biofilm reactors initiated with different seed sludges for treating actual mariculture effluents

The impact of carbon/nitrogen (C/N) ratio on sequencing batch biofilm reactor (SBBR) initiated with different seed sludges for treating actual mariculture effluent was explored. Increasing the C/N ratio significantly enhanced the nitrogen removal efficiency, achieving average removal efficiency of 95% for ammonia nitrogen and 73% for total nitrogen at ratio of 30, while the impact of seed sludge was minimal. High C/N ratio promoted the secretion of tightly bound extracellular polymeric substances (TB-EPS), which showed significant correlation with nitrogen removal. Interactions between bacteria and archaea were enhanced and conditionally rare or abundant taxa were the keystone taxa. High C/N ratio inhibited the relative abundance of ammonia-oxidizing archaea (Candidatus_Nitrosopumilus) and bacteria (Nitrosomonas), but promoted the heterotrophic nitrification-aerobic denitrification bacteria (Halomonas). The expression of nitrogen removal functional genes significantly correlated with functional genera. This study emphasized the crucial role of high C/N ratios in biological nitrogen removal from actual mariculture effluent.

Optimizing roof-harvested rainwater storage: Impact of dissolved oxygen regime on self-purification and quality dynamics

Roof-harvested rainwater presents a promising, unconventional, and sustainable water resource for both potable and non-potable uses. However, there is a significant gap in understanding the quality evolution of stored rainwater under varying dissolved oxygen conditions and its suitability for various applications. This study investigated the evolution of rainwater quality under three distinct storage conditions: aerated, open, and sealed. Additionally, the microbial community and metabolic functions were analyzed to systematically evaluate the self-purification performance over long-term storage durations. The results indicate that aerated storage enhances microbial carbon metabolism, leading to a degradation rate of 54.4 %. Sealed and open storage conditions exhibited primary organic matter degradation during the early and late stages, respectively. Roof-rainwater harvesting (RRWH) systems showed limited denitrification activity across all three dissolved oxygen conditions. The maximum accumulation of NO3-N during the storage period reached 5.23 mg/L. In contrast, sealed storage demonstrated robust self-purification performance, evidenced by a comprehensive coefficient of 15.83 calculated by Streeter-Phelps model. These findings provide valuable insights into the mechanisms governing rainwater quality changes under various storage conditions, emphasizing the necessity for developing effective management strategies for the storage and utilization of roof-harvested rainwater.

Impact of extreme rainfall and flood events on harmful cyanobacterial communities and ecological safety in the Baiyangdian Lake Basin, China

Globally, climate change has intensified extreme rainfall events, leading to substantial hydrological changes in aquatic ecosystems. These changes, in turn, have increased the frequency of harmful algal blooms, particularly those of cyanobacteria. This study examines cyanobacterial community dynamics in the Baiyangdian Lake Basin, China, after heavy rainfall and flooding events. The aim was to clarify how such extreme hydrological events affect cyanobacterial populations in floodplain ecosystems and assess related ecological risks. The results demonstrated a significant increase in cyanobacterial diversity, exemplified by an increase of the Shannon diversity index from an average of 1.72 to 2.1 (p < 0.05). Following heavy rainfall and subsequent flooding, the average relative abundance of cyanobacteria in the microbial community increased from 7.59 % to 9.62 %, along a notable rise in the abundance of harmful cyanobacteria. The community structure exhibited notable differences after flooding, showing an increase in species richness, but a decrease in community tightness and clustering, as well as a reduction in niche overlap among harmful cyanobacteria. Environmental factors such as dissolved oxygen, water temperature, and pH were identified as crucial predictors of harmful cyanobacterial community differences and abundance variations resulting from flooding. These findings provide a critical framework for predicting ecological risks associated with the expansion of bloom-forming cyanobacteria in large shallow lake basins, particularly under intensified rainfall and flooding events. This insight is essential to anticipate potential ecological disruptions in sensitive aquatic ecosystems.

Achieving high nitrogen and antibiotics removal efficiency by nZVI-C in partial nitritation/anammox system with a single-stage membrane-aerated biofilm reactor

This study innovated constructed an activated carbon-loaded nano-zero-valent iron (nZVI-C) enhanced membrane aerated biofilm reactor (MABR) coupled partial nitritation/anammox (PN/A) system for optimizing nitrogen and antibiotics removal. Results showed that nitrogen and antibiotic removal efficiencies of 88.45 ± 0.14% and 89.90 ± 3.07% were obtained by nZVI-C, respectively. nZVI-C hastened Nitrosomonas enrichment (relative abundance raised from 2.85% to 12.28%) by increasing tryptophan content in EPS. Furthermore, nZVI-C proliferated amo gene by 3.92 times and directly generated electrons, stimulating Ammonia monooxygenase (AMO) co-metabolism activity. Concurrently, via antibiotic resistance genes (ARGs) horizontal transfer, Nitrosomonas synergized with Arenimonas and Comamonadaceae for efficient antibiotic removal. Moreover, nZVI-C mitigated antibiotics inhibition of electron transfer by proliferating genes for PN and anammox electron production (hao, hdh) and utilization (amo, hzs, nir). That facilitated electron transfer and synergistic substrate conversion between ammonia oxidizing bacteria (AOB) and anaerobic ammonia oxidizing bacteria (AnAOB). Finally, the high nitrogen removal efficiency of the MABR-PN/A system was achieved.

Effect of rainfall in shaping microbial community during Microcystis bloom in Nakdong River, Korea

Various environmental factors play a role in the formation and collapse of Microcystis blooms. This study investigates the impact of heavy rainfall on cyanobacterial abundance, microbial community composition, and functional dynamics in the Nakdong River, South Korea, during typical and exceptionally rainy years. The results reveal distinct responses to rainfall variations, particularly in cyanobacterial dominance and physicochemical characteristics. In 2020, characterized by unprecedented rainfall from mid-July to August, Microcystis blooms were interrupted significantly, exhibiting lower cell densities and decreased water temperature, compared to normal bloom patterns in 2019. Moreover, microbial community composition varied, with increases in Gammaproteobacteria and notably in genera of Limnohabitans and Fluviicola. These alterations in environmental conditions and bacterial community were similar to those of the post-bloom period in late September 2019. It shows that heavy rainfall during summer leads to changes in environmental factors, consequently causing shifts in bacterial communities akin to those observed during the autumn-specific post-bloom period in typical years. These changes also accompany shifts in bacterial functions, primarily involved in the degradation of organic matter such as amino acids, fatty acids, and terpenoids, which are assumed to have been released due to the significant collapse of cyanobacteria. Our results demonstrate that heavy rainfall in early summer induces changes in the environmental factors and subsequently microbial communities and their functions, similar to those of the post-bloom period in autumn, leading to the earlier breakdown of Microcystis blooms.