Occurrence and Roles of Comammox Bacteria in Water and Wastewater Treatment Systems:A Critical Review

Nitrogen removal is a critical process in water treatment plants(WIPs)and wastewater treatment plants(WWTPs).The recent discovery of a novel bacterial process,complete ammonia oxidation(comammox,CMX),has refuted a century-long perception of the two-step conversion of NH3to NO3-.Compared with canonical nitrifiers,CMX bacteria offer undeniable advantages,such as a high growth yield propensity and adaptability to nutrient-and growth-limiting conditions,which collectively draw attention to validate the aptness of CMX bacteria to wastewater treatment.As there has been no comprehensive review on the relevance of CMX bacteria for sustainable water and wastewater treatment,this review is intended to discuss the roles and applications of CMX in the removal of nitrogen and pollutants from water and wastewater.We took into account insights into the metabolic versatilities of CMX bacteria at the clade and subclade levels.We focused on the distribution of CMX bacteria in engineered systems,niche differentiation,co-occurrence and interactions with cano nical nitrifiers for a better understanding of CMX bacteria in terms of their ecophysiology.Conceptualized details on the reactor adaptability and stress response of CMX bacteria are provided.The potential of CMX bacteria to degrade micropollutants either directly or co-metabolically was evaluated,and these insights would be an indispensable advantage in opening the doors for wider applications of CMX bacteria in WWTPs.Finally,we summarized future directions of research that are imperative in improving the understanding of CMX biology.

Genome-resolved metagenomic analysis reveals different functional potentials of multiple Candidatus Brocadia species in a full-scale swine wastewater treatment system

The increasing application of anammox processes suggests their enormous potential for nitrogen removal in wastewater treatment facilities.However,the functional potentials and ecological differentiation of cooccurring anammox species in complex ecosystems have not been well elucidated.Herein,by utilizing functional reconstruction and comparative genome analysis,we deciphered the cooccurring mechanisms of four Candidatus Brocadia species that were spontaneously enriched in a full-scale swine wastewater treatment system.Phylogenetic analysis indicated that species SW172 and SW745 were closely related to Ca.Brocadia caroliniensis and Ca.Brocadia sapporoensis,respectively,whereas the dominant species SW510 and SW773,with a total average abundance of 34.1%,were classified as novel species of the genus Ca.Brocadia.Functional reconstruction revealed that the novel species SW510 can encode both cytochrome cd1-type nitrite reductase and hydroxylamine oxidase for nitrite reduction.In contrast,the detected respiratory pentaheme cytochrome c nitrite reductase and acetate kinase genes suggested that SW773 likely reduced nitrite to ammonium with acetate as a carbon source.Intriguingly,the presence of genes encoding urease and cyanase indicated that both novel species can use diverse organic nitrogen compounds in addition to ammonia and nitrite as substrates.Taken together,the recovery and comparative analysis of these anammox genomes expand our understanding of the functional differentiation and cooccurrence of the genus Ca.Brocadia in wastewater treatment systems.

“Gray Carbon”in Sewage Treatment Plants:A Neglected Carbon Sink

This study introduces the concept of“gray carbon,”emphasizing its critical role in carbon sequestration in sewage treatment.By focusing on recalcitrant dissolved organic carbon(RDOC)in sewage effluents and its subsequent transformation in marine environments,we underscore the significant impact of sewage-derived organic carbon on the efficiency of carbon sequestration.Through analysis of carboxylic-rich alicyclic molecules,this study illuminates the convergence in the molecular compositions of RDOC across various aquatic systems.Dark-culture experiments reveal marked variations in the microbial community structures of the aforementioned molecules,indicating that these changes may play an important role in the degradation and subsequent transformation of organic matter in marine environments.These insights lay the groundwork for advancing technologies designed to enhance wastewater alkalinity,which will improve the sustainability of wastewater treatment and preserve marine ecosystems.Enhancing sewage alkalinity can influence microbial processes and chemical equilibria,potentially affecting the formation and accumulation of gray carbon.Further investigation is necessary to understand the potential effect of alkalinity enhancement on the microbial communities and biochemical pathways involved in gray carbon formation.Our findings support the integration of gray carbon strategies into broader carbon neutrality initiatives,providing a scientific and technological blueprint for enhancing global carbon management and mitigating climate change.