Simultaneous nitrification-denitrification by phosphate accumulating microorganisms

Advanced nitrogen and phosphorus removal in pilot-scale anaerobic/aerobic/anoxic system for municipal wastewater in Northern China

Removing nitrogen and phosphorus from low ratio of chemical oxygen demand to total nitrogen and temperature municipal wastewater stays a challenge. In this study, a pilot-scale anaerobic/aerobic/anoxic sequencing batch reactor (A/O/A-SBR) system first treated 15 m3/d actual municipal wastewater at 8.1-26.4 °C for 224 days. At the temperature of 15.7 °C, total nitrogen in influent and effluent were 45.5 and 10.9 mg/L, and phosphorus in influent and effluent were 3.9 and 0.1 mg/L. 16 s RNA sequencing results showed the relative abundance of Competibacter and Tetrasphaera raised to 1.25 % and 1.52 %. The strategy of excessive, no and normal sludge discharge enriched and balanced the functional bacteria, achieving an endogenous denitrification ratio more than 43.3 %. Sludge reduction and short aerobic time were beneficial to energy saving contrast with a Beijing municipal wastewater treatment. This study has significant implications for the practical application of the AOA-SBR process.

A review of the phosphorus removal of polyphosphate-accumulating organisms in natural and engineered systems

Increasing eutrophication has led to a continuous deterioration of many aquatic ecosystems. Polyphosphate-accumulating organisms (PAOs) can provide insight into the human response to this challenge, as they initiate enhanced biological phosphorus removal (EBPR) through cyclical anaerobic phosphorus release and aerobic phosphorus uptake. Although the limiting environmental factors for PAO growth and phosphorus removal have been widely discussed, there remains a gap in the knowledge surrounding the differences in the type and phosphorus removal efficiencies of natural and engineered PAO systems. Furthermore, due to the limitations of PAOs in conventional wastewater treatment environments, there is an urgent need to find functional PAOs in extreme environments for better wastewater treatment. Therefore, it is necessary to explore the effects of extreme conditions on the phosphorus removal efficiency of PAOs as well as the types, sources, and characteristics of PAOs. In this paper, we summarize the response mechanisms of PAOs, denitrifying polyphosphate-accumulating organisms (D-PAOs), aerobic denitrifying polyphosphate-accumulating organisms (AD-PAOs), and sulfur-related PAOs (S-PAOs). The mechanism of nitrogen and phosphorus removal in PAOs is related to the coupling cycles of carbon, nitrogen, phosphorus, and sulfur. The genera of PAOs differ in natural and engineered systems, but PAOs have more diversity in aquatic environments and soils. Recent studies on the impact of several parameters (e.g., temperature, carbon source, pH, and dissolved oxygen) and extracellular polymer substances on the phosphorus removal efficiency of PAOs in natural and engineered systems are further discussed. Most of the PAOs screened under extreme conditions still had high phosphorus removal efficiencies (>80.0 %). These results provide a reference for searching for PAOs with different adaptations to achieve better wastewater treatment.

Simultaneous aerobic nitrogen and phosphate removal capability of novel salt-tolerant strain, Pseudomonas mendocina A4: Characterization, mechanism and application potential

A salt-tolerant strain, Pseudomonas mendocina A4, was isolated from brackish-water ponds showing simultaneous heterotrophic nitrification-aerobic denitrification and phosphorus removal capability. The optimal conditions for nitrogen and phosphate removal of strain A4 were pH 7-8, carbon/nitrogen ratio 10, phosphorus/nitrogen ratio 0.2, temperature 30 °C, and salinity range of 0-5 % using sodium succinate as the carbon source. The nitrogen and phosphate removal efficiencies were 96-100 % and 88-96 % within 24 h, respectively. The nitrogen and phosphate removal processes were matched with the modified Gompertz model, and the underlying mechanisms were confirmed by the activities of key metabolic enzymes. Under 10 % salinity, the immobilization technology was employed to enhance the nitrogen and phosphate removal efficiencies of strain A4, achieving 87 % and 76 %, respectively. These findings highlight the potential application of strain A4 in both freshwater and marine culture wastewater treatment.

Isolation of a marine-derived yeast with potential applications in industrial nitrite utilizing

The nitrite efficient utilization microorganism Wickerhamomyces anomalus RZWP01 was identified. Using nitrite and ammonium as the sole nitrogen source, the nitrogen removal rate of W. anomalus RZWP01 was 97.4% and 87.1%, respectively. W. anomalus RZWP01 grew well in the nitrite medium with glucose or xylose as the only carbon source. However, the W. anomalus RZWP01 cannot live on the nitrite medium with lactose, citric acid, and methanol as the only carbon source. The maximal cell concentration occurred in the nitrite medium with glucose as the only carbon source at a C/N ratio of 20 for 48 h, reaching 8.92 × 108 cell mL-1. W. anomalus RZWP01 was the first reported yeast that can efficiently utilize nitrite. The isolation and identification of W. anomalus RZWP01 enriched the microbial resources of nitrite-degrading microorganisms and provided functional microorganisms for the water treatment of sustainable aquaculture.

Comparative genomic analysis of two Arctic Pseudomonas strains reveals insights into the aerobic denitrification in cold environments

BACKGROUND

Biological denitrification has been commonly adopted for the removal of nitrogen from sewage effluents. However, due to the low temperature during winter, microorganisms in the wastewater biological treatment unit usually encounter problems such as slow cell growth and low enzymatic efficiency. Hence, the isolation and screening of cold-tolerant aerobic denitrifying bacteria (ADB) have recently drawn attention. In our previous study, two Pseudomonas strains PMCC200344 and PMCC200367 isolated from Arctic soil demonstrated strong denitrification ability at low temperatures. The two Arctic strains show potential for biological nitrogen removal from sewage in cold environments. However, the genome sequences of these two organisms have not been reported thus far.

RESULTS

Here, the basic characteristics and genetic diversity of strains PMCC200344 and PMCC200367 were described, together with the complete genomes and comparative genomic results. The genome of Pseudomonas sp. PMCC200344 was composed of a circular chromosome of 6,478,166 bp with a G + C content of 58.60% and contained a total of 5,853 genes. The genome of Pseudomonas sp. PMCC200367 was composed of a circular chromosome of 6,360,061 bp with a G + C content of 58.68% and contained 5,801 genes. Not only prophages but also genomic islands were identified in the two Pseudomonas strains. No plasmids were observed. All genes of a complete set of denitrification pathways as well as various putative cold adaptation and heavy metal resistance genes in the genomes were identified and analyzed. These genes were usually detected on genomic islands in bacterial genomes.

CONCLUSIONS

These analytical results provide insights into the genomic basis of microbial denitrification in cold environments, indicating the potential of Arctic Pseudomonas strains in nitrogen removal from sewage effluents at low temperatures.

Simultaneous nitrification, denitrification and phosphorus removal: What have we done so far and how do we need to do in the future?

Nitrogen and phosphorus contamination in wastewater is a serious environmental concern and poses a global threat to sustainable development. In this paper, a comprehensive review of the studies on simultaneous nitrogen and phosphorus removal (SNPR) during 1986-2022 (538 publications) was conducted using bibliometrics, which showed that simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) is the most promising process. To better understand SNDPR, the dissolved oxygen, carbon to nitrogen ratio, carbon source type, sludge retention time, Cu²⁺ and Fe³⁺, pH, salinity, electron acceptor type of denitrifying phosphorus-accumulating organisms (DPAOs), temperature, and other influencing factors were analyzed. Currently, SNDPR has been successfully implemented in activated sludge systems, aerobic granular sludge systems, biofilm systems, and constructed wetlands; sequential batch mode of operation is a common means to achieve this process. SNDPR exhibits a significant potential for phosphorus recovery. Future research needs to focus on: (1) balancing the competitiveness between denitrifying glycogen-accumulating organisms (DGAOs) and DPAOs, and countermeasures to deal with the effects of adverse conditions on SNDPR performance; (2) achieving SNDPR in continuous flow operation; and (3) maximizing the recovery of P during SNDPR to achieve resource sustainability. Overall, this study provides systematic and valuable information for deeper insights into SNDPR, which can help in further research.

A mechanistic review on aerobic denitrification for nitrogen removal in water treatment

The traditional biological nitrogen removal technology consists of two steps: nitrification by autotrophs in aerobic circumstances and denitrification by heterotrophs in anaerobic situations; however, this technology requires a huge area and stringent environmental conditions. Researchers reached the conclusion that the denitrification process could also be carried out in aerobic circumstances with the discovery of aerobic denitrification. The aerobic denitrification process is carried out by aerobic denitrifying bacteria (ADB), most of which are heterotrophic bacteria that can metabolize various forms of nitrogen compounds under aerobic conditions and directly convert ammonia nitrogen to N₂ for discharge from the system. Despite the fact that there is no universal agreement on the mechanism of aerobic denitrification, this article reviewed four current explanations for the denitrification mechanism of ADB, including the microenvironment theory, theory of enzyme, electron transport bottlenecks theory, and omics study, and summarized the parameters affecting the denitrification efficiency of ADB in terms of carbon source, temperature, dissolved oxygen (DO), and pH. It also discussed the current status of the application of aerobic denitrification in practical processes. Following the review, the difficulties of present aerobic denitrification technology are outlined and future research options are highlighted. This review may help to improve the design of current wastewater treatment facilities by utilizing ADB for effective nitrogen removal and provide the engineers with relevant references.

Simultaneous denitrification and phosphorus removal: A review on the functional strains and activated sludge processes

Eutrophication has attracted extensive attention owing to its harmful effects to the organisms and aquatic environment. Studies on the functional microorganisms with the ability of simultaneously nitrogen (N) and phosphorus (P) removal is of great significance for alleviating eutrophication. Thus far, several strains from various genera have been reported to accomplish simultaneous N and P removal, which is primarily observed in Bacillus, Pseudomonas, Paracoccus, and Arthrobacter. The mechanism of N and P removal by denitrifying P accumulating organisms (DPAOs) is different from the traditional biological N and P removal. The denitrifying P removal (DPR) technology based on the metabolic function of DPAOs can overcome the problem of carbon source competition and sludge age contradiction in traditional biological N and P removal processes and can be applied to the treatment of urban sewage with low C/N ratio. This paper reviews the mechanism of N and P removal by DPAOs from the aspect of the metabolic pathways and enzymatic processes. The research progress on DPR processes is also summarized and elucidated. Further research should focus on the efficient removal of N and P by improving the performance of functional microorganisms and development of new coupling processes. This review can serve as a basis for screening DPAOs with high N and P removal efficiency and developing new DPR processes in the future.

Phosphorus removal and recovery: state of the science and challenges

Phosphorus is one of the main nutrients required for all life. Phosphorus as phosphate form plays an important role in different cellular processes. Entrance of phosphorus in the environment leads to serious ecological problems including water quality problems and soil pollution. Furthermore, it may cause eutrophication as well as harmful algae blooms (HABs) in aquatic environments. Several physical, chemical, and biological methods have been presented for phosphorus removal and recovery. In this review, there is an overview of phosphorus role in nature provided, available removal processes are discussed, and each of them is explained in detail. Chemical precipitation, ion exchange, membrane separation, and adsorption can be listed as the most used methods. Identifying advantages of these technologies will allow the performance of phosphorus removal systems to be updated, optimized, evaluate the treatment cost and benefits, and support select directions for further action. Two main applications of biochar and nanoscale materials are recommended.

Enriched microbial communities for ammonium and nitrite removal from recirculating aquaculture systems

The aim of this study was the enrichment of high-performance microbial communities in biofilters for removal of ammonium and nitrite from aquaculture water. Ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were enriched from different environmental water samples. The microbial communities with higher ammonium and nitrite removal activity were selected and adapted to different temperatures [9 °C, 15 °C, room temperature (25 °C), and 30 °C]. The expression of genes involved in nitrification including ammonia monooxygenase (AMO) and nitrite oxidoreductase (NXR) were measured in temperature-adapted AOB and NOB microbiomes. The microbial species present in the selected microbiomes were identified via 16s rRNA sequencing. The microbial communities containing Nitrosomonas oligotropha and Nitrobacter winogradskyi showed the highest ammonium and nitrite removal activity at all temperatures used for adaptation. Furthermore, the microbial communities do not contain any pathogenic bacteria. They also exhibited the highest expression of AMO and NXR genes. Using the enriched microbial communities, we achieved a 288% and 181% improvement in ammonium and nitrite removal over the commonly used communities in biofilters at 9 °C, respectively. These results suggest that the selected microbiomes allowed for a significant improvement of water quality in a recirculating aquaculture system (RAS).

Remediation of algal cells, PO43-, and NO3- from eutrophic wastewater using Echinodorus cordifolius in zigzag-horizontal subsurface constructed wetlands

The pollutant removal efficiency of traditionally constructed wetlands (CWs) is often limited due to low interaction time between wastewater and the CW matrix (plants, microbes, and substrates). A zigzag-horizontal subsurface flow constructed wetland with effluent recirculation (Z-HSSF + ER) was developed to improve removal efficiency. Echinodorus cordifolius plants were used in this study. The efficiency of the systems was evaluated using eutrophic wastewater. The results showed that the developed systems exhibited the high removal efficiency of algal cells, PO₄^3-, and NO₃^- (97%, 70%, and 100%, respectively), within 5 days. Algal cells were removed by the interception mechanism of gravel and zigzag baffles. PO₄^3- and NO₃^- in the eutrophic wastewater was mainly removed by E. cordifolius including rhizobacteria and other microorganisms. The long flow pathway created by the installation of zigzag baffles combined with effluent recirculation provides high dissolved oxygen (DO) in the systems and increases the interaction time between wastewater and the CW matrix, thus improving the pollutant removal efficiency of CWs.