Denitrification for acidic wastewater treatment: Long-term performance, microbial communities, and nitrous oxide emissions

Sulfur cycle-mediated biological nitrogen removal and greenhouse gas abatement processes: Micro-oxygen regulation tells the story

Sulfur-mediated autotrophic biological nitrogen removal (BNR) processes favor the reduction of greenhouse gas (GHG) emissions compared to heterotrophic BNR processes. Micro-oxygen environments are widely prevalent in practical BNR systems, and the mechanisms of GHG emissions mediated by multi-elements, including nitrogen (N), sulfur (S), and oxygen (O), remain to be systematically summarized. This review reveals the functional microorganisms involved in sulfur-mediated BNR processes under micro-oxygen regulation, elucidating their metabolic mechanisms and interactions. The GHG abatement potential of sulfur-mediated BNR processes under micro-oxygen regulation is highlighted, along with recent advances in multi-scenario applications. The fate of GHG in wastewater treatment systems is explored and insights into future multi-scale GHG regulatory strategies are provided. Overall, the application of sulfur-mediated BNR processes under micro-oxygen regulation exhibits great potential. This review can act as a guide for the effective implementation of strategies to mitigate the environmental impacts of GHG emissions from wastewater treatment processes.

Dynamics, diversity, and roles of bacterial transmission modes during the first asexual life stages of the freshwater sponge Spongilla lacustris

BACKGROUND

Sponge-associated bacteria play important roles in the physiology of their host, whose recruitment processes are crucial to maintain symbiotic associations. However, the acquisition of bacterial communities within freshwater sponges is still under explored. Spongilla lacustris is a model sponge widely distributed in European rivers and lakes, producing dormant cysts (named gemmules) for their asexual reproduction, before winter. Through an in vitro experiment, this study aims to describe the dynamics of bacterial communities and their transmission modes following the hatching of these gemmules.

RESULTS

An overall change of bacterial β-diversity was observed through the ontology of the juvenile sponges. These temporal differences were potentially linked, first to the osculum acquisition and the development of a canal system, and then, the increasing colonization of the Chlorella-like photosymbionts. Gemmules hatching with a sterilized surface were found to have a more dispersed and less diverse microbiome, revealing the importance of gemmule epibacteria for the whole holobiont stability. These epibacteria were suggested to be vertically transmitted from the maternal tissues to the gemmule surface. Vertical transmission through the incorporation of bacterial communities inside of the gemmule, was also found as a dominant transmission mode, especially with the nitrogen fixers Terasakiellaceae. Finally, we showed that almost no ASVs were shared between the free-living community and the juveniles, suggesting that horizontal recruitment is unlikely to happen during the first stages of development. However, the free-living bacteria filtered are probably used as a source of nutrients, allowing an enrichment of copiotrophic bacteria already present within its microbiome.

CONCLUSIONS

This study brings new insight for a better understanding of the microbiome acquisition during the first stages of freshwater sponge development. We showed the importance of epibacterial communities on gemmules for the whole holobiont stability, and demonstrated the near absence of recruitment of free-living bacteria during the first stages.

Sunlight-Driven Nitrate-to-Ammonia Reduction with Water by Iron Oxyhydroxide Photocatalysts

The photocatalytic reduction of harmful nitrates (NO3-) in strongly acidic wastewater to ammonia (NH3) under sunlight is crucial for the recycling of limited nitrogen resources. This study reports that a naturally occurring Cl--containing iron oxyhydroxide (akaganeite) powder with surface oxygen vacancies (β-FeOOH(Cl)-OVs) facilitates this transformation. Ultraviolet light irradiation of the catalyst suspended in a Cl--containing solution promoted quantitative NO3--to-NH3 reduction with water under ambient conditions. The photogenerated conduction band electrons promoted the reduction of NO3--to-NH3 over the OVs. The valence band holes promoted self-oxidation of Cl- as the direct electron donor and eliminated Cl- was compensated from the solution. Photodecomposition of the generated hypochlorous acid (HClO) produced O2, facilitating catalytic reduction of NO3--to-NH3 with water as the electron donor in the entire system. Simulated sunlight irradiation of the catalyst in a strongly acidic nitric acid (HNO3) solution (pH ∼ 1) containing Cl- stably generated NH3 with a solar-to-chemical conversion efficiency of ∼0.025%. This strategy paves the way for sustainable NH3 production from wastewater.

Effects of regular zooplankton supplement on the bacterial communities and process performance of biofilm for wastewater treatment

Biofilm processing technologies were widely used for wastewater treatment due to its advantages of low cost and easy management. However, the aging biofilms inevitably decrease the purification efficiency and increase the sludge production, which limited the widely application of biofilms technologies in rural area. In this study, we proposed a novel strategy by introducing high-trophic organisms to prey on low-trophic organisms, and reduce the aged biofilms and enhance treatment efficiencies in rural wastewater treatment. The effect of three typical zooplankton (Paramecium, Daphnia, and Rotifer) supplement on the purification efficiency and biofilm properties in the contact oxidation process were investigated, and the reaction conditions were optimized by an orthogonal experiment. Under optimal conditions, the biofilms weight decreased 67.6%, the oxygen consumption rate of biofilms increased 9.4%, and wastewater treatment efficiency was obviously increased after zooplankton supplement. Microbial sequencing results demonstrated that the zooplankton optimize the contact oxidation process by altering the bacterial genera mainly Diaphorobacter, Thermomonas, Alicycliphilus and Comamonas. This research provides insight into mechanism of the zooplankton supplement in biological contact oxidation process and provides a feasible strategy for improving the rural sewage treatment technology.