Performance and mechanism of urea hydrolysis in partial nitritation system based on SBR

Insight into simultaneous urea hydrolysis and total nitrogen removal in textile printing wastewater: Focus on the impact of sodium sulfate salinity

The textile printing industry discharges large volumes of effluent containing high concentrations of urea and nitrogenous compounds. Anoxic-oxic (AO) treatment is a promising method for treating printing wastewater. However, the effect of sodium sulfate (Na2SO4) salinity on the urea hydrolysis and nitrogen removal simultaneously in the AO process has received little attention. In this study, five batch reactors were used to treat synthetic printing wastewater with high urea and nitrogen concentrations. A strategy was applied to increase the Na2SO4 concentration from 0 to 19 g/L in the anoxic stage of each reactor. The effect of Na2SO4 on urea hydrolysis, total nitrogen removal and COD removal, sludge characteristics, and bacterial community structure were investigated. The findings showed that urea hydrolysis increased with increasing Na2SO4 concentration. The main mechanism of urea removal was intracellular hydrolysis, with a urea removal efficiency (URE%) of approximately 98% in all batch reactors. In addition, under the stress of Na2SO4, the total nitrogen and COD removal performances were partially inhibited. The most significant removal performances after AO treatment were observed at 0 g/L Na2SO4, with nitrogen and COD removal efficiencies of 88% and 95%, respectively. When Na2SO4 concentration reached 19 g/L, the sludge settling performance and compactness were enhanced. The extracellular polymeric substance (EPS) components in the sludge were dependent on their ability of removing organics. Bacterial community diversity analysis revealed that the enrichment of the Proteobacteria, Firmicutes, and Gemmatimonadota phyla in the anoxic stages of batch reactors was related to intracellular urea hydrolysis. Bacteriodota and Chloroflexi were responsible for total nitrogen removal in all anoxic and oxic stages. This research will develop the understanding of Na2SO4 salinity impact on simultaneous urea hydrolysis and nitrogen removal during AO treatment process.

Globally distributed marine Gemmatimonadota have unique genomic potentials

BACKGROUND

Gemmatimonadota bacteria are widely distributed in nature, but their metabolic potential and ecological roles in marine environments are poorly understood.

RESULTS

Here, we obtained 495 metagenome-assembled genomes (MAGs), and associated viruses, from coastal to deep-sea sediments around the world. We used this expanded genomic catalog to compare the protein composition and update the phylogeny of these bacteria. The marine Gemmatimonadota are phylogenetically different from those previously reported from terrestrial environments. Functional analyses of these genomes revealed these marine genotypes are capable of degradation of complex organic carbon, denitrification, sulfate reduction, and oxidizing sulfide and sulfite. Interestingly, there is widespread genetic potential for secondary metabolite biosynthesis across Gemmatimonadota, which may represent an unexplored source of novel natural products. Furthermore, viruses associated with Gemmatimonadota have the potential to "hijack" and manipulate host metabolism, including the assembly of the lipopolysaccharide in their hosts.

CONCLUSIONS

This expanded genomic diversity advances our understanding of these globally distributed bacteria across a variety of ecosystems and reveals genetic distinctions between those in terrestrial and marine communities. Video Abstract.

Enrichment of biofertilizer-type hydrogen-oxidizing bacteria on urea containing Cu(II)

With the utilization of pesticides and fertilizers (e.g. urea), the presence of nitrogen and heavy metals (e.g. copper) can enter and pollute the environment. Biofertilizers can be used to replace chemical fertilizers to increase crop yields and reduce environmental stress. The utilization of hydrogen-oxidizing bacteria (HOB) to be biofertilizers has recently attracted more attention. However, the enrichment of HOB on urea and the effect of copper are undetermined. HOB were successfully enriched using urea in this investigation. The average urea conversion rate (AUCR) was 180.08 mgN/L/d with a hydraulic retention time of 10 h. Microbial community (R1) was dominated by Hydrogenophaga (83.92%), a biofertilizer-type HOB. After addition of 5.47 mg/L Cu2+, the AUCR was decreased by 16%-151.18 mgN/L/d, and the growth of HOB was inhibited by 48%. Meanwhile, inhibition was also reflected by the increase of polysaccharide content (20.27 ± 0.57 to 33.45 ± 2.53 mg/gVSS) and protein content (106.19 ± 19.39 to 125.14 ± 24.73 mg/gVSS) of extracellular polymeric substances in the HOB. The resulting microbial community (R2) was changed to Azospiralium-dominated flora (91.33%). Both enriched microbial communities (R1 and R2) exhibited the abilities of ACC degradation and phosphate solubilization. This study demonstrates that employing urea can directly enrich biofertilizer-type HOB and copper-tolerant HOB can be obtained in a 5.47 mg/L Cu2+ environment. The results provide potential methods to obtain biofertilizer from copper-containing urea wastewater via HOB.

Nitrogen source affects non-aeration microalgal-bacterial biofilm growth progression and metabolic function during greywater treatment

The non-aeration microalgal-bacteria symbiotic system has attracted great attention due to excellent pollutants removal performance and low greenhouse gas emission. This study investigated how nitrogen (N) sources (ammonia, nitrate and urea) impact biofilm formation, pollutants removal and microbial niches in a microalgal-bacterial biofilm. Results showed that functional genus and enzymes contributed to organics biodegradation and carbon fixation, N transformation and assimilation enabled efficient pollutants removal without CO2 emission. Urea achieved the maximum chemical oxygen demand (89.2%) and linear alkylbenzene sulfonates (95.3%) removal. However, Nitrate significantly influenced microbial community structure and enabled the highest removal of total N (89.7%). Multifarious functional groups enabled the fast adsorption of pollutants, which favored the continuous transformation and fixing of carbon and N. But N source significantly affects the carbon and N dissimilation and fixing pathways. This study offers a promising alternative method that achieving low-carbon-footprint and cost-saving greywater treatment.

Sand consolidation using enzyme-induced carbonate precipitation: new insights on temperature and particle size effects

Sand production is a major issue in the oil and gas industry. Unconsolidated sand can be produced with the oil or gas a cause many issues to the production facilities. Enzyme-induced carbonate precipitation (EICP) is a promising method for sand consolidation and is characterized by its environment friendliness. Numerous studies have shown its effectiveness in ambient conditions. However, oil and gas downhole well operations are high pressure and high-temperature conditions. The objective of this study is to investigate effect of high temperature on EICP reaction and its efficiency in terms of uniformity to consolidate different types of sand samples. In this paper, the behavior of EICP solutions is examined in high temperatures from 25 to 90 °C. The study shows that high temperature environment doesn't handicap efficiency but in contrast it can favor the reaction if optimum concentration of reactants has been selected. The temperature effect is also discussed in terms of controllability of reaction which can favor application of reaction. Qualitive analysis shows when EICP solutions containing more than 50,000 ppm of metal ions and stoichiometrically surplus urea requires exposure to heat for reaction progress. The effect of sand particle size and its implication on the consolidation process was examined. Particle size of fine and medium sand ranged from 125 to 250 µm and 250 to 425 µm respectively while for coarse sand 70% sand particle size was between 425 and 700 µm. Designed EICP solutions achieve 9,000 psi for medium and almost 5,000 psi intrinsic specific energy for coarse sand samples. However, treated samples were subject to non-uniform distribution of strength of which can be up to 8,000 psi difference between top and bottom half of the samples.

Combined partial denitrification-anammox with urea hydrolysis (U-PD-Anammox) process: A novel economical low-carbon method for nitrate-containing wastewater treatment

For the sake of exploring a new economical and low-carbon alternative for real nitrate-containing wastewater treatment, a new combined partial denitrification-anammox with urea hydrolysis (U-PD-Anammox) process was developed. The nitrogen removal performance of this process was investigated through long-term operation in a sequencing batch reactor (SBR) and two submerged anaerobic biological filters (SABF). Results showed that the average NO₃^--N to NO₂^-N transformation ratio improved to 82.6% with organic carbon source to NO₃^-N ratio of 1.8, and urea hydrolysis provided sufficient NH₄⁺-N and inorganic carbon to anammox process for nitrogen removal. The influent NH₄⁺-N/NO₂^--N ratio for subsequent anammox reactor could be adjacent to the optimal ratio of 1.32 during the whole operation. The combined process showed efficient nitrogen removal performance with 85% NO₃^--N removal, 93.8% total nitrogen removal and total nitrogen loading rate as 1.1 ± 0.5 kg N/(m³·d). High-throughput sequencing analysis results revealed that Genera Thauera, Hyphomicrobium and Candidatus Brocadia were the dominant species responsible for partial denitrification, urea hydrolysis and anammox, respectively. The proposed process was more economically and environmental-friendly than the traditional denitrification process with 51.7% operational cost reduction, 99.7% N₂O and 60% CO₂ emission decrement, facilitating the sustainable development of the nitrate-containing wastewater treatment industry in the future.

Simultaneous removal of urea nitrogen and inorganic nitrogen from high-salinity wastewater by Halomonas sp. H36

To treat high-salt urea wastewater by microbial hydrolysis, it is necessary to overcome the dual problems of incomplete removal of nitrogen (N) from mixed strains and inhibition of microbial activity by high salt (NaCl) concentrations. In this paper, the mechanism of NaCl tolerance of Halomonas sp. H36 was investigated. Using molecular biology and enzymatic methods, it was proven that the strain's N-removal enzymes (urease; ammonia monooxygenase, AMO; nitrite reductase, NIR; nitrate reductase, NAR) played a key role in the removal of N, and the N-removal pathway was clarified. For the strain used to treat simulated ship domestic sewage, the urea nitrogen (CO(NH₂)₂-N)-removal rate was 88.52%, the ammonia nitrogen (NH₄⁺-N)-removal rate was 91.16%, the total nitrogen (TN)-removal rate was 90.25%, and nitrite nitrogen (NO₂^--N) and nitrate nitrogen (NO₃^--N) did not accumulate. It was proven for the first time that Halomonas sp. H36 has the function of simultaneous urea hydrolysis-nitrification-denitrification with urea as the initial substrate and can simultaneously remove urea nitrogen and inorganic nitrogen from high-salt urea wastewater.

Dynamic calibration of process-wide partial-nitritation modeling with airlift granular for nitrogen removal in a full-scale wastewater treatment plant

A main challenge in rapid nitrogen removal from rejected water in wastewater treatment plants (WWTPs) is growth of biomass by nitrite-oxidizing bacteria (NOB) and ammonia-oxidizing bacteria (AOB). In this study, partial nitritation (PN) coupled with air-lift granular unit (AGU) technology was applied to enhance nitrogen-removal efficiency in WWTPs. For successful PN process at high-nitrogen-influent conditions, a pH of 7.5-8 for high free-ammonia concentrations and AOB for growth of total bacterial populations are required. The PN process in a sequential batch reactor (SBR) with AGU was modeled as an activated sludge model (ASM), and dynamic calibration using full-scale plant data was performed to enhance aeration in the reactor and improve the nitrite-to-ammonia ratio in the PN effluent. In steady-state and dynamic calibrations, the measured and modeled values of the output were in close agreement. Sensitivity analysis revealed that the kinetic and stoichiometric parameters are associated with growth and decay of heterotrophs, AOB, and NOB microorganisms. Overall, 80% of the calibrated data fit the measured data. Stage 1 of the dynamic calibration showed NO₂ and NO₃ values close to 240 mg/L and 100 mg/L, respectively. Stage 2 showed NH₄ values of 200 mg/L at day 30 with the calibrated effluent NO₂ and NO₃ value of 250 mg/L. In stage 3, effluent NH₄ concentration was 200 mg/L at day 60.

Characterization of Microbial Communities in Wastewater Treatment Plants Containing Heavy Metals Located in Chemical Industrial Zones

Water pollution caused by heavy metals (HMs) poses a serious risk to human health and the environment and can increase the risk of diabetes, cancer, and hypertension in particular. In this study, two full-scale wastewater treatment plants (WWTPs) in industrial zones in southern China were selected to analyze the microbial community structure, diversity, similarity, and differentiation in the anoxic/oxic (AO) and anoxic/oxic membrane bioreactor (AO-MBR) units under the stress of HMs. High-throughput sequencing showed that microbial diversity and abundance were higher in the AO process than in the AO-MBR process. In the two WWTPs, the common dominant phyla were Proteobacteria and Bacteroidetes, while the common dominant genera were Gemmatimonadaceae, Anaerolineaceae, Saprospiraceae, and Terrimonas. Manganese (Mn) and zinc (Zn) positively correlated with Saccharimonadales, Nakamurella, Micrococcales, and Microtrichales, whereas copper (Cu) and iron (Fe) positively correlated with Longilinea and Ferruginibacter. Additionally, the relative abundances of Chloroflexi, Patescibacteria, and Firmicutes differed significantly (p < 0.05) between the two processes. These results may provide comprehensive outlooks on the characterization of microbial communities in WWTPs, which could also help to reduce the potential environmental risks of the effluent from WWTPs located in industrial zones.

Phylum Gemmatimonadota and Its Role in the Environment

Bacteria are an important part of every ecosystem that they inhabit on Earth. Environmental microbiologists usually focus on a few dominant bacterial groups, neglecting less abundant ones, which collectively make up most of the microbial diversity. One of such less-studied phyla is Gemmatimonadota. Currently, the phylum contains only six cultured species. However, data from culture-independent studies indicate that members of Gemmatimonadota are common in diverse habitats. They are abundant in soils, where they seem to be frequently associated with plants and the rhizosphere. Moreover, Gemmatimonadota were found in aquatic environments, such as freshwaters, wastewater treatment plants, biofilms, and sediments. An important discovery was the identification of purple bacterial reaction centers and anoxygenic photosynthesis in this phylum, genes for which were likely acquired via horizontal gene transfer. So far, the capacity for anoxygenic photosynthesis has been described for two cultured species: Gemmatimonas phototrophica and Gemmatimonas groenlandica. Moreover, analyses of metagenome-assembled genomes indicate that it is also common in uncultured lineages of Gemmatimonadota. This review summarizes the current knowledge about this understudied bacterial phylum with an emphasis on its environmental distribution.

The benefits of autotrophic nitrogen removal from high concentration of urea wastewater through a process of urea hydrolysis and partial nitritation in sequencing batch reactor

For the sake of high efficiency and saving operational cost for high-concentration urea wastewater treatment, a novel two-stage partial nitritation (PN)-anammox process containing simultaneous urea hydrolysis and PN in sequencing batch reactor (SBR) was investigated. Although the influent urea concentration increased from 500 to 1200 mg/L, the SBR simultaneously achieved urea removal efficiency higher than 98% and stable PN with effluent NO₂^--N/NH₄⁺-N ratio of 1.0-1.3 without any extra alkalinity addition. The intracellular hydrolysis was the dominant mechanism for urea removal and persistent free ammonia inhibition on nitrite-oxidizing bacteria was the main reason for nitrite accumulation of 97.92% in SBR. The subsequent anammox reactor showed efficient nitrogen removal performance with average ammonium removal efficiency, nitrogen removal efficiency and maximum nitrogen removal loading rate of 98.08%, 81.45% and 1.05 kg N·m^-3·d^-1 respectively. High-throughput sequencing results indicated Gemmatimonadetes became the most abundant bacterial phylum related to potential intracellular urea hydrolysis and displayed obvious ammonium-oxidizing bacteria enrichment and nitrite-oxidizing bacteria inhibition in SBR, and the dominant anammox bacteria (Candidatus_Kuenenia) in anammox reactor. The proposed process was proven to be promising for high-concentration urea wastewater treatment, facilitating the sustainable development of the urea industry in the future.