Improvement in nitrogen removal and changes in community structure in a sequencing batch reactor bioaugmented with P. stutzeri strain XL-2

Enhancing sequencing batch reactors for efficient wastewater treatment across diverse applications: A comprehensive review

This review explores recent progress in sequencing batch reactors (SBRs) and hybrid systems for wastewater treatment, emphasizing their adaptability and effectiveness in managing diverse wastewater compositions. Through extensive literature analysis from 1985 to 2024, the integration of advanced technologies like photocatalysis within hybrid systems is highlighted, showing promise for improved pollutant removal efficiencies. Insights into operational parameters, reactor design, and microbial communities influencing SBR performance are discussed. Sequencing batch biofilm reactors (SBBRs) demonstrate exceptional efficiency in Chemical Oxygen Demand, nitrogen, and phosphorus removal, while innovative anaerobic-aerobic-anoxic sequencing batch reactors (AOA-SBRs) offer effective nutrient removal strategies. Hybrid systems, particularly photocatalytic sequencing batch reactors (PSBRs), show potential for removing persistent pollutants like antibiotics and phenols, underscoring the significance of advanced oxidation processes. However, research gaps persist, including the need for comparative studies between different SBR types and comprehensive evaluations of long-term performance, environmental variability, and economic viability. Addressing these gaps will be vital for the practical deployment of SBRs and hybrid systems. Further exploration of synergies, economic considerations, and reactor stability will enhance the sustainability and scalability of these technologies for efficient and eco-friendly wastewater treatment.

Nitrogen removal intensification of biofilm through bioaugmentation with Methylobacterium gregans DC-1 during wastewater treatment

The increasing concern for environmental remediation has led to a search for effective methods to remove eutrophic nutrients. In this study, Methylobacterium gregans DC-1 was utilized to improve nitrogen removal in a sequencing batch biofilm reactor (SBBR) via aerobic denitrification. This bacterium has the extraordinary characteristics of strong auto-aggregation and a high ability to remove nitrogen efficiently, making it an ideal candidate for enhanced treatment of nitrogen-rich wastewater. This strain was used for the bioassessment of a test reactor (SBBRbio), which showed a shorter biofilm formation time compared to a control reactor (SBBRcon) without this strain inoculation. Moreover, the enhanced biofilm was enriched in TB-EPS and had a wider variety of protein secondary structures than SBBRcon. During the stabilization phase of SBBRbio, the EPS molecules showed the highest proportion of intermolecular hydrogen bonding. It is possible that bioaugmentation with this strain positively affects the structural stability of biofilm. At influent ammonia loadings of 100 and 150 mg. L-1, the average reduction of ammonia and nitrate-nitrogen was higher in the experimental system compared to the control system. Additionally, nitrite-N accumulation was lower and N2O production decreased compared to the control. Analysis of the microbial community structure demonstrated successful colonization in the bioreactor by a highly nitrogen-tolerant strain that efficiently removed inorganic nitrogen. These results illustrate the great potential of this type of denitrifying bacteria in the application of bioaugmentation systems.

The acceleration of aerobic sludge granulation by alternating organic loading rate: Performance and mechanism

As a highly promising treatment technology for wastewater, long start-up time is one of the bottlenecks hindering the widespread application of aerobic granular sludge (AGS). This study focused on exploring the possibility of alternating organic loading rate (OLR) in promoting AGS granulation. Under alternating OLR (3.6-14.4 kgCOD/m3·d), AGS granulation was significantly accelerated. The mean granule size under alternating load reached 234.6 μm at 17 d, while under constant OLR (7.2 kgCOD/m3·d), the mean granule size was only 179.2 μm. Moreover, the granule size maintained continuous growth even when the alternating OLR was changed to constant OLR. Alternating load significantly increased the content of extracellular polymeric substances (EPS), especially proteins (PN) in tightly bound EPS (TB-EPS), which was likely the main reason for accelerating AGS granulation. Moreover, alternating load reduced the hydrophilicity of EPS and promoted the content of proteins secondary structures that favored aggregation in TB-EPS, which were also beneficial for granulation. Microbial community results showed that alternating load might promote the enrichment of EPS producing bacteria, such as Thauera, Brevundimonas and Shinella. Meanwhile, the content of enzymes that regulated amino acids metabolism also increased under alternating load, which might be related to the increase of PN in EPS. These results further demonstrated that alternating load promoted granulation through EPS.

Discovery of a heterotrophic aerobic denitrification Pseudomonas sp. G16 and its unconventional nitrogen metabolic pathway

From the aerobic pond of the farm, the Pseudomonas sp. G16 was screened and isolated, which was confirmed to exhibit heterotrophic nitrification and aerobic denitrification. The removal rates of Ammonia (100 mg/L), nitrate (120 mg/L), and nitrite (100 mg/L) by the strain were 94.13%, 92.62%, and 85.67%, and the nitrogen metabolism pathway of strain G16 was analyzed by whole genome sequencing combined with its nitrification-denitrification intermediate products, it was found that the strain had independent nitrification-denitrification ability and no nitrite accumulation. Under the conditions of carbon source of sodium succinate hexahydrate, C/N ratio of 15, pH of 7.5, temperature of 15 °C, and DO of 210 rpm, strain G16 showed excellent denitrification performance. Strain G16 was prepared into biochar-based immobilized bacterial particles, which successfully improved its nitrogen removal efficiency and stability. Therefore, the application of strain G16 in the field of real wastewater treatment has very necessary research value.

Static magnetic field increases aerobic nitrogen removal from hypersaline wastewater in activated sludge with coexistence of fungi and bacteria

Fungi have been found to exist in activated sludge treating saline wastewater, but their role in removing pollution has been neglected. This study explored the aerobic removal of total inorganic nitrogen (TIN) from saline wastewater under static magnetic fields (SMFs) with several strengths. Compared to the control, the aerobic removal of TIN was significantly increased by 1.47 times in 50 mT SMF, due to the increased dissimilation nitrogen removal by fungi and bacteria. Under SMF, fungal nitrogen dissimilation removal was significantly increased by 3.65 times. The fungal population size decreased, and its community composition changed significantly under SMF. In contrast, bacterial community composition and population remained relatively stable. Under SMFs, heterotrophic nitrification - aerobic denitrification bacteria Paracoccus and the fungi denitrifying Candida formed a synergistic interaction. This study elucidates the fungal role in aerobic TIN removal and provides an efficient solution to improve TIN removal from saline wastewater by SMF.

Impacts of nano-titanium dioxide toward Vallisneria natans and epiphytic microbes

In this study, Vallisneria natans plants were exposed to 5 and 20 nm of titanium dioxide nanoparticles (TiO₂ NPs) anatase and 600-1000 nm of bulk at 5 and 20 mg/L for 30 days. SEM images and EDX spectra revealed that epiphytic biofilms were more prone to TiO₂ NPs adhesion than bare plant leaves. TiO₂ NPs injured plant leaf cells, ruptured epiphytic diatoms membranes and increased the ratio of free-living microbes. The TN, NH₄⁺-N and NO₃--N concentrations significantly decreased, respectively, by 44.9%, 33.6%, and 23.6% compared to bulk treatments after 30 days due to macrophyte damage and a decline in diversity of epiphytic bacterial community and abundance of nitrogen cycle bacteria. TiO₂ NPs size-dependent decrease in bacterial relative abundance was detected, including phylum Cyanobacteria, Planctomycetes, and Verrucomicrobia. Although TiO₂ NPs increased eukaryotic diversity and abundance, abundances of Bacillariophyceae and Vampyrellidae classes and Gastrotricha and Phragmoplastophyta phylum decreased significantly under TiO₂ NPs exposure compared to bulk and control. TiO₂ NPs reduced intensities of interaction relationships among epiphytic microbial genera. This study shed new light on the potential effects of TiO₂ NPs toxicity toward aquatic plants and epiphytic microbial communities and its impacts on nitrogen species removal in wetlands.

Candida tropicalis prompted effectively simultaneous removal of carbon, nitrogen and phosphorus in activated sludge reactor: Microbial community succession and functional characteristics

A new Candida tropicalis that simultaneously remove nitrogen and phosphorus, and degrade organic matters was isolated. Three continuous stirred tank reactors inoculated with C. tropicalis, activated sludge, and their co-existing system in aerobic condition were operated for 150 days. Results demonstrated that the inoculation of C. tropicalis in the co-existing system remarkably improved the carbon, nitrogen, and phosphorus removal efficiencies. The co-existing system had increased carbon, nitrogen, and phosphorus removal efficiencies (92%, 73%, and 63%, respectively); decreased biomass (reduced from 1200 mg/L to 500 mg/L); and C. tropicalis as the dominant strain. The relative abundance of traditional nitrogen- and phosphorus-removing microorganisms, such as Mycobacterium, Flavonifactor, and Devsia, increased in the co-existing system. Metagenomic analysis showed that the presence of the PCYT2, EPT1, and phnPP genes and more complexed metabolism pathways in the co-existing system might be responsible for the more activated metabolism process.

Hydroxylamine and nitrite are removed effectively by Streptomyces mediolani strain EM-B2

Biological nitrogen removal is primarily conducted by bacteria and fungi rather than actinomycetes. However, accumulations of nitrite and hydroxylamine could significantly impair the biological nitrogen removal process. A strain of Streptomyces mediolani, termed EM-B2, was isolated from a cow dung fermentation biogas digester. The strain removed more than 99% of ammonium and 78% of total nitrogen in the presence of glucose and under environmental conditions of 30 °C, a carbon/nitrogen ratio of 15, 7.4 mg/L dissolved oxygen and a pH range of 7.5-9.0. Maximal removal rates were 2.29 mg/L/h for ammonium, 1.90 mg/L/h for nitrate and 2.01 mg/L/h for nitrite. The removal efficiencies of hydroxylamine and total nitrogen peaked at 81.48% and 60.38%, respectively. Notably, hydroxylamine and nitrite were never detected during the heterotrophic nitrification and aerobic denitrification. Nitrate rather than nitrite was accumulated from the process of hydroxylamine oxidation. These findings indicate that S. mediolani strain EM-B2 performs heterotrophic nitrification and aerobic denitrification, and can be used to remove hydroxylamine and nitrite from wastewater.

Water flow and temperature drove epiphytic microbial community shift: Insight into nutrient removal in constructed wetlands from microbial assemblage and co-occurrence patterns

The impacts of water flow and low temperature on nutrient removal and underlying ecological mechanism of epiphytic microbial community in constructed wetlands remain to be fully illustrated. In this study, low temperature inhibited the decrease of TN, NH₄⁺-N, TP, and COD concentrations in water, but water flow decreased NH₄⁺-N and COD concentrations strikingly. The relative conductivity, soluble sugar, and protein of M. spicatum increased, while the total chlorophyll contents decreased significantly under the stress of water flow and low temperature. Temperature affected the alpha-diversity and composition of the microbial community, while water flow caused differences in community distribution. Deterministic processes dominated in microbial community assembly with increasing environmental stress. Co-occurrence network analysis demonstrated that Chlorophyta, Verrucomicrobia, Proteobacteria, Bacteroidetes, and Firmicutes phyla were the dominant hubs in September, however, low temperatures caused a shift to Metazoan dominated network, demonstrating diminished nutrient removal capacity.

Enhanced removal of antibiotic resistance genes by nanoscale iron-cobalt particles modified with Ginkgo biloba L. leaf: Combining Illumina MiSeq sequencing and oligotyping analysis

The addition of second metal (Co) to nanoscale iron particles (NIPs) is an attractive strategy to improve catalytic capacity. However, the nanoparticles tend to form chain-like aggregates. In this study, bacterial 16S rRNA gene, antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) from secondary effluent were significantly removed by Ginkgo biloba L. modified nanoscale iron-cobalt particles (GNICPs). When the Co loading, initial pH value, DO and dosage were 10%, 7.33, 8.94 mg/L and 1.12 g/L, some ARGs and MGEs could be reduced below the detection limit at the 2nd or 3rd cycle. Illumina MiSeq sequencing demonstrated that negative correlations were found between ARGs and reaction time/cycles. The predicted microbial functions by FAPROTAX database indicated GNICPs were effective in eliminating human_pathogens_all. Furthermore, oligotyping revealed all ARGs and MGEs were positively correlated with oligotype 10, which indicated GNICPs removed oligotype 10 easily.