Advances in Studies on Microbiota Involved in Nitrogen Removal Processes and Their Applications in Wastewater Treatment

Insights into current bio-processes and future perspectives of carbon-neutral treatment of industrial organic wastewater: A critical review

With the rise of the concept of carbon neutrality, the current wastewater treatment process of industrial organic wastewater is moving towards the goal of energy conservation and carbon emission reduction. The advantages of anaerobic digestion (AD) processes in industrial organic wastewater treatment for bio-energy recovery, which is in line with the concept of carbon neutrality. This study summarized the significance and advantages of the state-of-the-art AD processes were reviewed in detail. The application of expanded granular sludge bed (EGSB) reactors and anaerobic membrane bioreactor (AnMBR) were particularly introduced for the effective treatment of industrial organic wastewater treatment due to its remarkable prospect of engineering application for the high-strength wastewater. This study also looks forward to the optimization of the AD processes through the enhancement strategies of micro-aeration pretreatment, acidic-alkaline pretreatment, co-digestion, and biochar addition to improve the stability of the AD system and energy recovery from of industrial organic wastewater. The integration of anaerobic ammonia oxidation (Anammox) with the AD processes for the post-treatment of nitrogenous pollutants for the industrial organic wastewater is also introduced as a feasible carbon-neutral process. The combination of AnMBR and Anammox is highly recommended as a promising carbon-neutral process for the removal of both organic and inorganic pollutants from the industrial organic wastewater for future perspective. It is also suggested that the AD processes combined with biological hydrogen production, microalgae culture, bioelectrochemical technology and other bio-processes are suitable for the low-carbon treatment of industrial organic wastewater with the concept of carbon neutrality in future.

Microbiota composition and correlations with environmental factors in grass carp (Ctenopharyngodon idella) culture ponds in South China

To maintain the health of aquaculture fish, it is critical to understand the composition of microorganisms in aquaculture water and sediment and the factors affecting them. This study examined the water and sediment microbiota compositions of four different types of ponds in South China that were used to culture grass carp (Ctenopharyngodon idella) of different sizes through high-throughput sequencing of the 16S rRNA gene, and analyzed their correlations with environmental factors. The results showed that ponds with cultured grass carp of different sizes exhibited significant differences in terms of water physicochemical properties and composition of water and sediment microbiota. Furthermore, the exchange of microorganisms between water and sediment microbiota was lowest in ponds with the smallest grass carp and highest in ponds with the largest grass carp. All detected environmental factors except water temperature were significantly correlated with the water microbiota, and all detected environmental factors in the sediment were correlated with sediment microbiota. Moreover, Aeromonas hydrophila and Vibrio were significantly increased in the water microbiota, especially in ponds with small juvenile grass carp, implying an increased risk of A. hydrophila and Vibrio infections in these environments. Our results provide useful information for the management of grass carp aquaculture ponds.

Enhanced nitrogen removal in low-carbon saline wastewater by adding functional bacteria into Sesuvium portulacastrum constructed wetlands

Functional bacterial communities (FBC) have members of different taxonomic biochemical groups, such as N2-fixation, nitrification and denitrification. This study explored the mechanism of the FBC from an upflow three-dimensional biofilm electrode reactor on enhancing the nitrogen removal efficiencies in a Sesuvium potulacastum (S. potulacastum) constructed wetland. There were high abundances of denitrifying bacteria detected in the FBC, and they had potential metabolic processes for nitrogen reduction. In the constructed wetland, cellular nitrogen compounds of S. potulacastum were enriched by overexpressed differentially expressed genes (DEGs), and the napA, narG, nirK, nirS, qnorB, and NosZ genes related to the denitrification process had more copies under FBC treatment. Nitrogen metabolism in root bacterial communities (RBCs) was activated in the FBC group compared with the control group without FBC. Finally, these FBCs improved the removal efficiencies of DTN (dissolved total nitrogen), NO3¯-N, NO2¯-N, and NH4+-N by 84.37 %, 87.42 %, 67.51 %, and 92.57 %, respectively, and their final concentrations met the emission standards of China. These findings indicate that adding FBC into S. potulacastum-constructed wetlands would result in high nitrogen removal efficiencies from wastewater and have large potential applications in further water treatment technology.

Microbial Biofilms: Applications, Clinical Consequences, and Alternative Therapies

Biofilms are complex communities of microorganisms that grow on surfaces and are embedded in a matrix of extracellular polymeric substances. These are prevalent in various natural and man-made environments, ranging from industrial settings to medical devices, where they can have both positive and negative impacts. This review explores the diverse applications of microbial biofilms, their clinical consequences, and alternative therapies targeting these resilient structures. We have discussed beneficial applications of microbial biofilms, including their role in wastewater treatment, bioremediation, food industries, agriculture, and biotechnology. Additionally, we have highlighted the mechanisms of biofilm formation and clinical consequences of biofilms in the context of human health. We have also focused on the association of biofilms with antibiotic resistance, chronic infections, and medical device-related infections. To overcome these challenges, alternative therapeutic strategies are explored. The review examines the potential of various antimicrobial agents, such as antimicrobial peptides, quorum-sensing inhibitors, phytoextracts, and nanoparticles, in targeting biofilms. Furthermore, we highlight the future directions for research in this area and the potential of phytotherapy for the prevention and treatment of biofilm-related infections in clinical settings.

Selection, Identification and Functional Performance of Ammonia-Degrading Microbial Communities from an Activated Sludge for Landfill Leachate Treatment

The increasing amounts of municipal solid waste and their management in landfills caused an increase in the production of leachate, a liquid formed by the percolation of rainwater through the waste. Leachate creates serious problems to municipal wastewater treatment plants; indeed, its high levels of ammonia are toxic for bacterial cells and drastically reduce the biological removal of nitrogen by activated sludge. In the present work, we studied, using a metagenomic approach based on next-generation sequencing (NGS), the microbial composition of sludge in the municipal wastewater treatment plant of Porto Sant'Elpidio (Italy). Through activated sludge enrichment experiments based on the Repetitive Re-Inoculum Assay, we were able to select and identify a minimal bacterial community capable of degrading high concentrations of ammonium (NH₄⁺-N ≅ 350 mg/L) present in a leachate-based medium. The analysis of NGS data suggests that seven families of bacteria (Alcaligenaceae, Nitrosomonadaceae, Caulobacteraceae, Xanthomonadaceae, Rhodanobacteraceae, Comamonadaceae and Chitinophagaceae) are mainly responsible for ammonia oxidation. Furthermore, we isolated from the enriched sludge three genera (Klebsiella sp., Castellaniella sp. and Acinetobacter sp.) capable of heterotrophic nitrification coupled with aerobic denitrification. These bacteria released a trace amount of both nitrite and nitrate possibly transforming ammonia into gaseous nitrogen. Our findings represent the starting point to produce an optimized microorganisms's mixture for the biological removal of ammonia contained in leachate.

Charting the landscape of the environmental exposome

The exposome depicts the total exposures in the lifetime of an organism. Human exposome comprises exposures from environmental and humanistic sources. Biological, chemical, and physical environmental exposures pose potential health threats, especially to susceptible populations. Although still in its nascent stage, we are beginning to recognize the vast and dynamic nature of the exposome. In this review, we systematically summarize the biological and chemical environmental exposomes in three broad environmental matrices-air, soil, and water; each contains several distinct subcategories, along with a brief introduction to the physical exposome. Disease-related environmental exposures are highlighted, and humans are also a major source of disease-related biological exposures. We further discuss the interactions between biological, chemical, and physical exposomes. Finally, we propose a list of outstanding challenges under the exposome research framework that need to be addressed to move the field forward. Taken together, we present a detailed landscape of environmental exposome to prime researchers to join this exciting new field.

Coupled process of in-situ sludge fermentation and riboflavin-mediated nitrogen removal for low carbon wastewater treatment

Volatile fatty acid recovery from waste activated sludge (WAS) was highly suggested to supplement carbon source for nitrogen removal. However, it was not easy to separate them from the metabolites under the ex-situ fermentation. In this study, in-situ WAS fermentation combined in the denitrification system was established to treat low carbon wastewater (COD/TN = 4), and riboflavin was employed as a redox mediator. This coupled process could simultaneously enhance the WAS fermentation and nitrogen removal, and riboflavin could significantly enrich the fermentative bacteria (Firmicutes phylum), denitrifying bacteria (Denitratisoma genus) and related functional genes (narGHJI, napABC, nirKS, nosZ, norBC), generating more available carbon sources for efficient nitrogen removal. This resulted in the effluent TN (<15 mg/L) satisfying the required discharge standard in China. This study provided new insights into the efficient nitrogen removal from low carbon wastewater, realizing the carbon-neutral operation of new concept wastewater treatment plant in China.

Are Wetlands as an Integrated Bioremediation System Applicable for the Treatment of Wastewater from Underground Coal Gasification Processes?

Underground coal gasification (UCG) can be considered as one of the clean coal technologies. During the process, the gas of industrial value is produced, which can be used to produce heat and electricity, liquid fuels or can replace natural gas in chemistry. However, UCG does carry some environmental risks, mainly related to potential negative impacts on surface and groundwater. Wastewater and sludge from UCG contain significant amounts of aliphatic and aromatic hydrocarbons, phenols, ammonia, cyanides and hazardous metals such as arsenic. This complicated matrix containing high concentrations of hazardous pollutants is similar to wastewater from the coke industry and, similarly to them, requires complex mechanical, chemical and biological treatment. The focus of the review is to explain how the wetlands systems, described as one of bioremediation methods, work and whether these systems are suitable for removing organic and inorganic contaminants from heavily contaminated industrial wastewater, of which underground coal gasification wastewater is a particularly challenging example. Wetlands appear to be suitable systems for the treatment of UCG wastewater and can provide the benefits of nature-based solutions. This review explains the principles of constructed wetlands (CWs) and provides examples of industrial wastewater treated by various wetland systems along with their operating principles. In addition, the physicochemical characteristics of the wastewater from different coal gasifications under various conditions, obtained from UCG’s own experiments, are presented.

Application of aerobic denitrifier for simultaneous removal of nitrogen, zinc, and bisphenol A from wastewater

High concentrations of heavy metals and other pollutants affect microbial activity in the wastewater treatment system and impede biological denitrification process. In this study, a novel Zn(II)-resistant aerobic denitrifier (Pseudomonas stutzeri KY-37) was isolated with potential in Bisphenol A (BPA) biodegradation and removal. The capability of this denitrifier in removing nitrogen, zinc, and BPA was tested. Using 56 mg/L nitrate as the sole nitrogen source, its removal efficiency achieved 98.5% in 12 h. This novel denitrifier had a strong auto-aggregation (maximum 65.8%), a high hydrophobicity rate (maximum 88.2%), and a massive amount (maximum 41.1 mg/g cell dry weight) of extracellular polymeric substances (EPS) production. Moreover, Zn(II) removal efficiency reached more than 95% with the initial high concentrations of 200 mg/L. The maximum BPA removal efficiency reached 88.8% with initial 10 mg/L. The removal mechanism of BPA was further explored in terms of microbial degradation, EPS adsorption, and intermediate degradation products.

Achieving Partial Nitrification-Anammox Process Dependent on Microalgal-Bacterial Consortia in a Photosequencing Batch Reactor

Partial nitrification coupled with anammox (PN/A) process is an energy-efficient approach for nitrogen removal from low C/N wastewater. In this study, PN/A was achieved with optimal oxygen supply from a green microalga, Chlorella sorokiniana. The PN process was first initiated within 35 days, and the following algae-intensified PN then reached the steady state within the next 32 days. The dissolved oxygen (DO) concentration was gradually maintained at 0.6 mg L-1 via adjusting the photoperiod to 6-h light/18-h dark cycles, when the accumulation ratio of NO2 --N and the removal ratio of NH4 +-N were both more than 90%. The nitrogen removal capability of anammox was acclimated via elevating the individual effluent NH4 +-N and NO2 --N levels from 100 to 200, to 300 mg L-1. After acclimation, the removal rates of NH4 +-N and total nitrogen (TN) reached more than 70 and 80%, respectively, and almost all the NO2 --N was removed. Then, the algae-intensified PN/A, algammox biofilm system, was successfully started up. When the NH4 +-N level increased from 100 to 300 mg L-1, the TN removal varied between 78 and 82%. In the photosequencing bioreactor, C. sorokiniana, ammonia-oxidizing bacteria (AOB), and anammox coexisted with an illumination of 200 μmol m-2 s-1 and a 6-h light/18-h dark cycles. The DO levels ranged between 0.4 and 0.5 mg L-1. In addition, the microbial community analysis by Illumina MiSeq sequencing showed that the dominant functional bacteria in the algae-intensified PN/A reactors included Nitrosomonas (AOB) and Candidatus Brocadia (anammox), while Nitrospira and Nitrobacter (nitrite oxidizing bacteria), together with Denitratisoma (denitrifier) were largely inhibited. Further studies are required to optimize the microalgal-bacterial consortia system to achieve superior nitrogen removal rates under controllable conditions.