The effect of dissolved oxygen concentration (DO) on oxygen diffusion and bacterial community structure in moving bed sequencing batch reactor (MBSBR)

Characterizing algal-bacterial symbiotic biofilms: Insights into coexistence of algae and anaerobic microorganisms

This study constructed an integrated algae/partial nitrification/anammox biofilm system and operated it for 240 days. The total nitrogen removal efficiency exceeded 90 %. The structure, compositions, and function of this symbiotic biofilm, which played a pivotal role in the system, were analyzed in detail. Microscope photos and fluorescence in situ hybridization both showed that bacteria and algae were well integrated. The dissolved oxygen gradient further confirmed that different functional microorganisms grew at varying depths within biofilm. Algae formed an oxygen-producing zone (0-0.48 mm), followed by ammonia oxidizing bacteria (AOB) consuming oxygen to form an oxygen-consuming zone (0.48-0.86 mm), and anaerobic ammonia oxidizing bacteria (AnAOB) removed nitrogen in anaerobic zone (>0.86 mm). Chlorella, Nitrosomonas and Candidatus_Kuenenia were identified as the dominant algae, AOB and AnAOB, with relative abundances of 11.80 %, 19.77 % and 3.07 %, respectively. This layered biofilm benefitted providing a suitable environment for various microorganisms to survive within a complex biofilm.

Sequential bio-treatment of ammonia-rich wastewater from Chinese medicine residue utilization: Regulation of dissolved oxygen

To effectively treat actual ammonia-rich Chinese medicine residue (CMR) resource utilization wastewater, we optimized an anaerobic-microaerobic two-stage expanded granular sludge bed (EGSB) and moving bed sequencing batch reactor (MBSBR) combined process. By controlling dissolved oxygen (DO) levels, impressive removal efficiencies were achieved. Microaeration, contrasting with anaerobic conditions, bolstered dehydrogenase activity, enhanced electron transfer, and enriched the functional microorganism community. The increased relative abundance of Synergistetes and Proteobacteria facilitated hydrolytic acidification and fostered nitrogen and phosphorus removal. Furthermore, we examined the impact of DO concentration in MBSBR on pollutant removal and microbial metabolic activity, pinpointing 2.5 mg/L as the optimal DO concentration for superior removal performance and energy conservation.

The enrichment characterisation of Nitrospira under high DO conditions

Nitrite-oxidizing bacteria (NOB) are crucial to nitrification and nitrogen elimination in wastewater treatment. Mass reports exist on the links between NOB and other microorganisms, for instance, ammonia-oxidizing bacteria (AOB). However, a few studies exist on the enrichment characterisation of NOB under high dissolved oxygen (DO) conditions. In this study, NOB was designed to be enriched individually under high DO conditions in a continuous aeration sequencing batch reactor (SBR), and the kinetic characterisation of NOB was evaluated. The analysis revealed that the average NO2--N removal rate was steady above 98%, with DO and NO2--N being 3-5 mg L-1 and 50-450 mg L-1, respectively. The NO2--N removal efficiency of the system was significantly enhanced and better than in other studies. The high-throughput sequencing suggested that Parcubacteria_ genera_incertae_sedis was the first dominant genus (21.99%), which often appeared in the NOB biological community with Nitrospira. However, the dominant genus NOB was Nitrospira rather than Nitrobacter (8.49%). This result suggested that Nitrospira was capable of higher NO2--N removal. But lower relative abundance indicated that excessive NO2--N had an adverse effect on the enrichment and activity of Nitrospira. In addition, the nitrite half-saturation constant (KNO2) and the oxygen half-saturation constant (KO) were 1.71 ± 0.19 mg L-1 and 0.95 ± 0.10 mg L-1, respectively. These results showed that the enriched Nitrospira bacteria had different characteristics at the strain level, which can be used as a theoretical basis for wastewater treatment plant design and optimisation.

Comparing biofilm reactors inoculated with Shewanella for decolorization of Reactive Black 5 using different carrier materials

This study assessed the performance of biofilm reactors inoculated with azo dye degrading Shewanella for the decolorization of Reactive Black 5 (RB5), using three different carrier materials, namely almond shell biochar, moving bed biofilm reactor (MBBR), and polypropylene carrier (PPC). The reactors were fed with low-nutrient artificial wastewater containing RB5, and all three carriers showed good RB5 decolorization performance, with varying efficiencies. Liquid Chromatography-Mass Spectrometry analysis revealed distinct RB5 degradation pathways associated with each carrier, influenced by carrier materials and microbial communities. The MBBR carrier exhibited good stability due to its rough surface and microbial aggregates. Sequencing results highlighted differences in the microbial community structures among the carriers. Shewanella predominated the functional bacteria in the MBBR and PPC carriers, while the biochar carrier fostered highly efficient degrading microbial communities. The physicochemical properties of carrier materials significantly influenced the microbial community and RB5 degradation efficiency. These findings provide valuable insights for optimizing biofilm reactors for dye-containing wastewater treatment.

Effect of Operating Parameters on the Performance of Integrated Fixed-Film Activated Sludge for Wastewater Treatment

Integrated fixed-film activated sludge (IFAS) is a hybrid wastewater treatment process that combines suspended and attached growth. The current review provides an overview of the effect of operating parameters on the performance of IFAS and their implications for wastewater treatment. The operating parameters examined include hydraulic retention time (HRT), solids retention time (SRT), dissolved oxygen (DO) levels, temperature, nutrient loading rates, and aeration. Proper control and optimization of these parameters significantly enhance the treatment efficiency and pollutant removal. Longer HRT and appropriate SRT contribute to improved organic matter and nutrient removal. DO levels promote the growth of aerobic microorganisms, leading to enhanced organic matter degradation. Temperature influences microbial activity and enzymatic reactions, impacting treatment efficiency. Nutrient loading rates must be carefully managed to avoid system overload or inhibition. Effective aeration ensures uniform distribution of wastewater and biofilm carriers, optimizing contact between microorganisms and pollutants. IFAS has been used in water reuse applications, providing a sustainable and reliable water source for non-potable uses. Overall, IFAS has proven to be an effective and efficient treatment process that can provide high-quality effluent suitable for discharge or reuse. Understanding the effects of these operating parameters helps to optimize the design and operation for efficient wastewater treatment. Further research is needed to explore the interactions between different parameters, evaluate their impact under varying wastewater characteristics, and develop advanced control strategies for improved performance and sustainability.

Evaluation of nitrogen removal and nitrous oxide turnovers in granule-based simultaneous nitrification and denitrification system

Nitrous oxide (N₂O) is an inevitable intermediate generated during the nitrogen removal process of granule-based simultaneous nitrification and denitrification (SND) system. In order to alleviate N₂O production while maintaining a desired total nitrogen (TN) removal level in this system, a comprehensive evaluation of the contribution pathways and process parameters affecting N₂O turnovers is keenly required. Therefore, mathematical models were applied to evaluate the impact of operating conditions and unravel potential mechanisms on TN removal performance and N₂O production. Simulation results show that higher N₂O production (11.6 %-14.2 %) occurs at higher dissolved oxygen (DO) concentrations, lower chemical oxygen demand (COD) levels, longer hydraulic retention time (HRT) and larger granule size in the granular SND system. The relative conversion rates of nitrogenous components in different regions within the granule influence N₂O turnovers, with the nitrification process occurring only in the region 200 μm inward from the granule surface and denitrification working throughout the entire granule. In the inner region of the granule (0-300 μm), the heterotrophic bacteria (HB) denitrification pathway dominates N₂O production as a source of N₂O. While in the outer region (300-450 μm), HB denitrification acts as a sink for N₂O and regulates N₂O turnovers (i.e. production and reduction of N₂O) together with the hydroxylamine (NH₂OH) pathway that is the main contributor of N₂O production. Moreover, simultaneous adjustment of multiple operating parameters within a certain range can lower the N₂O production factor (<0.5 %) while achieving the desired TN removal efficiency (>80 %), resulting in a feasible N₂O mitigation strategy.

Predicting microbial community compositions in wastewater treatment plants using artificial neural networks

BACKGROUND

Activated sludge (AS) of wastewater treatment plants (WWTPs) is one of the world's largest artificial microbial ecosystems and the microbial community of the AS system is closely related to WWTPs' performance. However, how to predict its community structure is still unclear.

RESULTS

Here, we used artificial neural networks (ANN) to predict the microbial compositions of AS systems collected from WWTPs located worldwide. The predictive accuracy R²_1:1 of the Shannon-Wiener index reached 60.42%, and the average R²_1:1 of amplicon sequence variants (ASVs) appearing in at least 10% of samples and core taxa were 35.09% and 42.99%, respectively. We also found that the predictability of ASVs was significantly positively correlated with their relative abundance and occurrence frequency, but significantly negatively correlated with potential migration rate. The typical functional groups such as nitrifiers, denitrifiers, polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), and filamentous organisms in AS systems could also be well recovered using ANN models, with R²_1:1 ranging from 32.62% to 56.81%. Furthermore, we found that whether industry wastewater source contained in inflow (IndConInf) had good predictive abilities, although its correlation with ASVs in the Mantel test analysis was weak, which suggested important factors that cannot be identified using traditional methods may be highlighted by the ANN model.

CONCLUSIONS

We demonstrated that the microbial compositions and major functional groups of AS systems are predictable using our approach, and IndConInf has a significant impact on the prediction. Our results provide a better understanding of the factors affecting AS communities through the prediction of the microbial community of AS systems, which could lead to insights for improved operating parameters and control of community structure. Video Abstract.

Achieving nitrogen removal with low material and energy consumption through partial nitrification coupled with short-cut sulfur autotrophic denitrification in a single-stage SBR

An innovative partial nitrification and short-cut sulfur autotrophic denitrification (PN-SSAD, NH₄⁺-N → NO₂^--N → N₂) coupled system in a single-stage SBR was proposed to treat low C/N wastewater with low material and energy consumption. Nearly 50 % alkalinity consumption and 40 % sulfate production were reduced in S⁰-SSAD compared with S⁰-SAD, whereas the autotrophic denitrification rate was increased by 65 %. In S⁰-PN-SSAD, the TN removal efficiency reached almost 99 % without additional organic carbon. Furthermore, pyrite (FeS₂) rather than S⁰ served as the electron donor to optimize the PN-SSAD process. The practical sulfate production in S⁰-PN-SSAD and FeS₂-PN-SSAD were about 38 % and 52 % lower than complete nitrification and sulfur autotrophic denitrification (CN-SAD), respectively. Thiobacillus was the major autotrophic denitrification bacteria in S⁰-PN-SSAD (34.47 %) and FeS₂-PN-SSAD (14.88 %). Nitrosomonas and Thiobacillus played a synergistic effect in the coupled system. FeS₂-PN-SSAD is expected as an alternative technology for nitrification and heterotrophic denitrification (HD) in treating low C/N wastewater.

Start-up phase optimization of pyrite-intensified hybrid sequencing batch biofilm reactor (PIHSBBR): Mixotrophic denitrification performance and mechanism

Pyrite-based autotrophic denitrification (PAD) is an emerging biological process to diminish nitrate pollution, but the relatively low NO₃^--N removal rate limits its practical application. In this research, a pyrite-intensified hybrid sequencing batch biofilm reactor (PIHSBBR) was designed to treat low C/N ratio domestic wastewater. The results showed that PIHSBBR could achieve optimal removal of COD, NH₄⁺-N, and TN under the aeration rate of 1.0 L/L∙min and the hydraulic retention time (HRT) of 8 h, with removal rates of 69.67 ± 4.37%, 77.04 ± 4.84%, and 63.92 ± 6.66%, respectively. The PAD efficiency in PIHSBBR during the stable operation was not high (13.05-31.01%), and the main nitrogen removal pathway in PIHSBBR, especially in the aerobic zone, was simultaneous nitrification and denitrification (SND). High-throughput sequencing analysis unraveled that Planctomycetota (3.65%) had a high abundance in the anoxic zone of PIHSBBR, implying that anaerobic ammonium oxidation (anammox) might have occurred in the anoxic zone. In addition, the nitrogen cycle function gene with the highest abundance was nirBD, indicating the possible presence of dissimilatory nitrate reduction to ammonium (DNRA) within the system (aerobic and anoxic zones). Our research can provide useful information for the improvement and future application of PIHSBBR.

Impact of aerobic/anoxic alternation number on performance, microbial community and functional genes of sequencing batch biofilm reactor treating mariculture wastewater

The performance, microbial community and functional genes of a sequencing batch biofilm reactor (SBBR) were investigated in treating mariculture wastewater under different aerobic/anoxic alternation number. The removal efficiency of chemical oxygen demand (COD) and NH₄⁺-N kept at 95.66 ± 1.83 % and 90.28 ± 2.42 % under aerobic/anoxic alternation number between 1 and 4. The total nitrogen (TN) removal efficiency gradually decreased from 94.45 ± 1.12 % to 83.06 ± 1.25 % with the increase of aerobic/anoxic alternative number from 1 to 4. The nitrification rates and their corresponding enzymatic activities increased slightly with the increase of aerobic/anoxic alternation number, whereas the denitrifying process had the contrary results. The variation of aerobic/anoxic alternation number obviously affected the microbial diversity and abundance. The microbial network structure and keystone taxa were different under different aerobic/anoxic alternation number. The functional genes abundance for the denitrification pathway decreased with the increase of aerobic/anoxic alternation number.

A study on the efficiency of the sequential batch reactor on the reduction of wastewater pollution from oil washing

Industrial pollution discharges from washing fuel oils pose severe problems for the environment, particularly for the marine environment receiving these discharges. This work evaluates the biological treatment performance of wastewater (90 m³/h) rich in organic matter with low biodegradability using a sequential batch reactor (SBR) on a laboratory scale. The test using SBR was carried out for 25 days on a continuous cycle of 24 h (30 min of filling, 17 h of aeration, 4 h of anoxia, 2 h of settling, and 30 min of emptying). The feasibility of alternative sources of microorganisms from urban wastewater. The performance of the batch sequencing reactor was evaluated using turbidity, total suspended solids, chemical oxygen demand (COD), biological oxygen demand (BOD), ammonium, nitrate, and phenol as indicators. The results obtained showed that the COD/BOD ratio and the pollutant load vary from one campaign to another. The removal efficiency of COD, BOD, TSS (Total suspended solids), ammonium, nitrate, and phenol varies from 81%, 91%, 72%, 100%, 52%, and 63%. Thus, SBR-type treatment could be an interesting way to reduce pollution due to its simplicity, less space occupation, low energy consumption, and not requiring highly qualified personnel.

Effect of hydrodynamics on the transformation of nitrogen in river water by regulating the mass transfer performance of dissolved oxygen in biofilm

Biofilms drive crucial ecosystem processes in rivers. This study provided the basis for overall quantitative calculations about the contribution of biofilms to the nitrogen cycle. At the early stage of biofilm formation, dissolved oxygen (DO) could penetrate the biofilms. As the biofilm grew and the thickness increased, then the mass transfer of DO was restricted. The microaerobic layer firstly appeared in biofilm under the turbulent flow conditions, with the appearance of the microaerobic and anaerobic layer, the nitrification and denitrification reaction could proceed smoothly in biofilm. And the removal efficiency of total nitrogen (TN) increased as the biofilm matured. Under the turbulent flow conditions, mature biofilms had the smallest thickness, but the highest proportion the anaerobic layer to the biofilm thickness, the highest density, and the highest nitrogen removal efficiency. However, the nitrogen removal efficiency of biofilm was the lowest under laminar flow conditions. The difference of layered structure of biofilm and the DO flux in biofilm explained the difference of nitrogen migration and transformation in river water under different hydrodynamic conditions. This study would help control the growth of biofilm and improve the nitrogen removal capacity of biofilm by regulating hydrodynamic conditions.

Simultaneous nitrification-denitrification in biofilm systems for wastewater treatment: Key factors, potential routes, and engineered applications

Simultaneous nitrification-denitrification (SND) is an advantageous bioprocess that allows the complete removal of ammonia nitrogen through sequential redox reactions leading to nitrogen gas production. SND can govern nitrogen removal in single-stage biofilm systems, such as the moving bed biofilm reactor and aerobic granular sludge system, as oxygen gradients allow the development of multilayered biofilms including nitrifying and denitrifying bacteria. Environmental and operational conditions can strongly influence SND performance, biofilm development and biochemical pathways. Recent advances have outlined the possibility to reduce the carbon and energy consumption of the process via the "shortcut pathway", and simultaneously remove both N and phosphorus under specific operational conditions, opening new possibilities for wastewater treatment. This work critically reviews the factors influencing SND and its application in biofilm systems from laboratory to full scale. Operational strategies to enhance SND efficiency and hints to reduce nitrous oxide emission and operational costs are provided.

Isolation and Nitrogen Removal Efficiency of the Heterotrophic Nitrifying-Aerobic Denitrifying Strain K17 From a Rare Earth Element Leaching Site

K17, an indigenous and heterotrophic nitrifying-aerobic denitrifying bacterium, was isolated from the soil of a weathered crust elution-deposited rare earth ore leaching site in Longnan County, China. Strain K17 was identified as Pseudomonas mosselii. In this study, the morphological characteristics of strain K17 were observed and the optimal ammonia nitrogen removal conditions for the strain were studied using a single-factor experiment. Key enzyme activities were determined, and we also explored the ammonia nitrogen removal process of strain K17 on simulated leaching liquor of the rare earth element leaching site. Based on the determination of ammonia nitrogen removal and enzyme activity, it was found that strain K17 has both heterotrophic nitrifying and aerobic denitrifying activities. In addition, single-factor experiments revealed that the most appropriate carbon source for strain K17 was sodium citrate with a C/N ratio of 10 and an initial NH₄⁺-N concentration of 100 mg/l. Furthermore, the optimal initial pH and rotation speed were 7 and 165 r/min, respectively. Under optimal conditions, the ammonia nitrogen removal efficiency of strain K17 was greater than 95%. As an indigenous bacterium, strain K17 has great potential for treating residual ammonium leaching solutions from rare earth element leaching sites.

Optimization of airflow and aeration cycles in a new structured bed reactor configuration for carbon and nitrogen removal

The Structured Bed Reactor with Recirculation and Intermittent Aeration (SBRRIA) is a reactor configuration that presents high efficiency of organic matter and nitrogen removal, besides low sludge production. However, operational parameters, as the recirculation rate, aeration time, and airflow, are not fully established. A bench-scale structured bed reactor with intermittent aeration was fed with synthetic effluent simulating the characteristics of sanitary sewage. The reactor was operated for 280 days with an operational hydraulic retention time (HRT) of 10 h. The reactor was operated without effluent recirculation for the first time since this approach was not yet reported, and was named Structured Bed Reactor with Intermittent Aeration (SBRIA). The COD removal was higher than 81% for all operational conditions, and the total nitrogen removal ranged from 10 to 80%. The highest efficiencies were obtained with an aeration time of 1 h 45 min (total cycle of 3 h) and an airflow rate of 4.5 L.min^-1. Different nitrification and denitrification behaviours were observed, resulting in nitrification efficiencies over 90% when the reactor was submitted to higher aeration times and denitrification efficiencies above 90% when the reactor was submitted to low aeration times. The airflow ranges tested in this study affected the nitrification and the total nitrogen efficiencies. Even without effluent recirculation, the temporal profile showed that there were no peaks in the concentration of the nitrogen forms in the reactor effluent, saving electrical energy up to 75% due to pumping.

Removal of Escherichia coli from domestic sewage using biological sand filters: Reduction effect and microbial community analysis

The recycling of sewage is an economical option to solve the water resource pressure. However, to avoid health risks to humans, pathogens in sewage must be removed before reuse. In this study, a biological sand filter (BSF) was used to remove pathogen indicator Escherichia coli (E. coli) from sewage. The biolayer (schmutzdecke layer) formation process of BSFs, operation performance, factors affecting E. coli removal and microbial community structure were evaluated. The results of schmutzdecke layer culture showed that a large number of microorganisms were attached to the upper medium of BSFs. At the same time, the BSFs could reduce both conventional contaminants and E. coli. The E. coli removal experiments revealed that the removal rate of E. coli was about 96.1% at higher effective medium depth (50 cm), the removal rate was about 95% when set hydraulic loading rate (HLR) to 0.16 m³/m²/h and the removal efficiency reached 93.6% at lower influent bacteria concentration. Finally, the microbial community analysis indicated that different BSFs had similar microbial structure, and the microbial abundance in the schmutzdecke layer was higher than that in the bottom layer in the same BSFs. Besides, Biological action played a significant role in the removal of E. coli, including the bacteriolysis of Bdellovibrio and the competition between other bacteria and E. coli. In summary, BSF was a promising technology for removing E. coli from sewage.

Modification of expanded clay carrier for enhancing the immobilization and nitrogen removal capacity of nitrifying and denitrifying bacteria in the aquaculture system

In aquaculture systems, the treatment of nitrogen pollution has always been a center of attention due to its impact on productiveness. The bioremediation method based on simultaneous nitrification and denitrification was often used to effectively remove ammonium, nitrite, and nitrate compounds. In addition, the attachment and biofilm formation of the nitrogen-converting bacteria on carriers had superior removal efficiency over the suspended bacteria. Thus, this study focused on the fabrication of a porosity floatable expanded clay (EC) carrier that provided the basic structure for the immobilization of the nitrifiers Nitrosomonas sp., Nitrobacter sp., and the denitrifier Bacillus sp. The EC was also coated with alginate and essential nutrient to support the cohesion and growth of bacteria. Especially, the selected Bacillus sp. previously proved was able to reduce nitrite/nitrate in aerobic conditions. The co-immobilization of these three aerobic bacteria on the prepared carrier would simply the treatment process in practical use. Initial results showed that the integration of essential nutrients (N, P, K) on alginate coated EC (EC_Alg_N) increased bacterial density to (57 ± 3) × 10⁷ - (430 ± 30) × 10⁸ CFU/g, which then led to the enhancement of removal efficiency up to 91.62 ± 0.67% in the medium containing initial nitrogen content of 60 mg-N/L. The nitrogen removal efficacy of bacterial immobilized EC_Alg_N remained at 83.95 ± 0.15% after being reused for 6 cycles. In conclusion, the bacterial immobilized EC_Alg_N could be a potential material for nitrogen polluted wastewater treatment in aquaculture systems.

Nutrient removal effect and characteristics of integrated floating beds at low temperature

To investigate the effect of combined floating beds on nutrient removal under low temperature, an integrated floating bed with corn flakes (IFB-CF) and an integrated floating bed with light ceramsite (IFB-LC) were constructed in parallel. IFB-LC was used as control group under water temperatures of 9.3-14 °C and a water exchange time of 168 h. Nitrogen and phosphorus removal efficiency, the nutrient level of a hydrophyte (Oenanthe javanica), and the microbial population characteristics of the combined floating bed were investigated. For IFB-CF removal efficiencies, the degradation quantities of total nitrogen (TN), NO₃^--N, and NH₄⁺-N for IFB-CF were 13.58 ± 0.67 mg/L, 4.40 ± 0.61 mg/L, and 9.21 ± 0.38 mg/L, respectively; in contrast, degradation quantities for IFB-LC were lower (6.41 ± 1.47 mg/L, 2.15 ± 0.40 mg/L, and 5.95 ± 0.46 mg/L, respectively). The reductions in COD (Chemical Oxygen Demand, using K₂Cr₂O₇ as oxidizer) for IFB-LC and IFB-CF were 86.89% and 66.06%, respectively. Using the MiSeq high throughput sequencing method, we analysed microbial community structure and diversity on the base material surface of the IFB-CF and IFB-LC. The results showed 15 phyla, 165 genera, and 78 families on the surface of the IFB-CF. The phylum, genus, and family with the highest abundances were Proteobacteria (48.29%), Trichococcus (10.39%), and Comamonadaceae (12.45%), respectively. We identified 15 phyla, 144 genera, and 93 families on the surface of the IFB-LC. The phylum, genus, and family with the highest abundances were Proteobacteria (46.10%), Dyadobacter (22.67%), and Cytophagaceae (28.75%), respectively. The Chao, ACE, and Shannon & Simpson indices for the IFB-LC were 4081, 6295, and 5.10, and 0.05, respectively; for the IFB-CF they were 4938, 7461, 5.77, and 0.02, respectively. Catalase (CAT) and Peroxidase (POD) concentrations in Oenanthe javanica for IFB-LC were 35.48 u/gFW/min and 1.03 u/gFW/min, respectively; for IFB-CF they were 32.33 u/gFW/min and 1.25 u/gFW/min, respectively. The nutritional energies of IFB-CF and IFB-LC were 107 kJ/100g and 84 kJ/100g. Using the Mondal model of TN removal, k (half-saturation constant) values for IFB-LC and IFB-CF were 35.67 mg/L and 39.23 mg/L, respectively, with a correlation coefficient (R²) of 0.97.

Simultaneous removal of phosphorous and nitrogen by ammonium assimilation and aerobic denitrification of novel phosphate-accumulating organism Pseudomonas chloritidismutans K14

Pseudomonas chloritidismutans K14, a novel phosphate-accumulating organism with the capacity to perform ammonium assimilation, aerobic denitrification, and phosphorus removal, was isolated from aquaculture sediments. It produced no hemolysin, and showed susceptibility to most antibiotics. Optimum conditions were achieved with sodium pyruvate as a carbon source, a C/N ratio of 10, pH of 7.5, temperature of 27 °C, P/N ratio of 0.26, and shaking at 140 rpm. Under optimum conditions, the highest removal efficiencies of ammonium, nitrite, and nitrate were 99.82%, 99.11%, and 99.78%, respectively; the corresponding removal rates were 6.27, 4.51, and 4.99 mg/L/h. The strain removed over 98% of phosphorus, and over 87% of chemical oxygen demand. The highest biomass nitrogen during ammonium assimilation was 99.18 mg/L; no gaseous nitrogen was produced. The genes involved in nitrogen and phosphorus removal were amplified by PCR. This study demonstrated the potential application prospects of strain K14 for nitrogen and phosphorus removal.

Treatment of wastewater with high carbon-to-nitrogen ratio using a waterfall aeration biofilm reactor combined with sequencing batch reactor: Microbial community structure and metabolism analysis

A low-cost and high-efficiency waterfall aeration biofilm reactor (WABR) combined with a sequencing batch reactor (SBR) was established to treat wastewater with a C/N ratio of 50. Three WABR-SBR systems with different fillers were used. In the stable operation phase, the removal efficiency of chemical oxygen demand was R1 (approximately 99%), R2 (97-99%), and R3 (96-99%); the effluent concentration of NH₄⁺-N was 0.5 mg/L without nitrite or nitrate accumulation. High-throughput 16S rRNA sequencing revealed that the dominant phyla in the microbial community structure were Proteobacteria, Bacteroidetes, and Planctomycetes. Quantitative PCR was used to quantify the nitrification and denitrification gene expressions (Nitrobacter, nirS, and nirK) to evaluate the simultaneous nitrification and denitrification processes. Both anammox and denitrifying bacteria were abundant. Metagenomic annotation of genes that revealed the metabolic pathways of carbohydrates, amino acids, and the two dominant enzymes (GH and GT) provide valuable information for microbial ecology analysis.

Preparation and performance evaluation of novel magnetic porous carriers in fluidized bed bioreactor for wastewater treatment

Biofilm process is a promising wastewater treatment technology and biofilm carrier (biocarrier) is regarded as the core of this process. However, the traditional commercial biocarriers have their inherent drawbacks, therefore, the development of new-type biocarrier to enhance wastewater treatment efficiency is significantly important to biofilm-based reactors. In this study, based on radical suspension polymerization, a novel kind of magnetic porous carriers (PMCs) was prepared by modifying the porous polymer carriers (PPCs) with inorganic particles, and then applied in a fluidized bed bioreactor (FBBR) with a low packing ratio of 10 % (v/v) to synthetic wastewater treatment. The results showed that this novel biocarrier possesses paramagnetism with saturation magnetization of 1.01emu/g, low density (1.26 g/cm³), excellent hydrophilicity (surface water contact angle approaching zero) and rough surface. Besides, compared with the PPCs, the developed PMCs have larger pores (up to 50 μm or more), in which the larger-sized microbes are able to colonize. Moreover, as compared to the PPCs-based FBBR, the PMCs-based reactor achieved shorter time (7 days) for biofilm formaiton and significantly enhanced NH₃-N removal efficiency ( nearly 20 % increase at the level of influent NH₃-N concentration about 100 mg/L). High-throughput sequencing (HTS) results indicated that this new biocarrier could promote biodiversity and improve the abundance of Nitrosomonadales (the functional bacteria for ammonia removal in the bio-system), thus enhancing the ammonification process. Therefore, the developed PMCs could be preferable biocarriers for biofilm formation and provide an alternative to the traditional suspended biocarrier, demonstrating a promising potential, even at a lower filling ratio, to enhance the pollutants removal performance.

Simultaneous nitrification and denitrification in continuous flow MBBR with novel surface-modified carriers

ABSTRACTMoving-Bed Biofilm Reactor (MBBR) process is an ideal preference for simultaneous nitrification and denitrification (SND) attributing to the longer sludge age and aerobic/anoxic microenvironment along biofilm. However, conventional carriers generally exhibit negative charge and surface hydrophobicity, which are unbeneficial for biofilm formation. In this study, novel surface-modified carriers with favourable hydrophilicity (surface contact angle dropped to 60.2 ± 2.3°) and positive surface charge (+11.7 ± 1.1 mV, pH 7.0) were prepared via polymer blending and implemented for SND in continuous flow MBBR system. Results indicated SND started up quickly with more biomass in MBBR filled with surface-modified carriers. At the operation condition of low dissolved oxygen level (0.75 ± 0.25 mg/L), pH of 7.5 ± 0.5, 23 ± 2°C and C/N ratio of 7, COD, NH₄⁺-N and TN removal efficiencies were 90.5%, 88.6% and 76.6% respectively in MBBR filled with surface-modified carriers, which ensured the effluent met the first grade A of the Discharge Standard of China. On the contrary, COD, NH₄⁺-N and TN removal efficiencies were 89.7%, 82.3% and 60.4% respectively in the control reactors filled with conventional polyethylene carriers. The worse performance of the control reactor was mainly attributed to the less biomass and lower functional bacteria abundance developed on conventional carriers. Moreover, novel carriers provided a favourable niche for more types of functional bacteria, of which autotrophic nitrification, anoxic denitrification, heterotrophic nitrification and aerobic denitrification co-existed and participated in nitrogen removal.

Toxic Effect of Ammonium Nitrogen on the Nitrification Process and Acclimatisation of Nitrifying Bacteria to High Concentrations of NH4-N in Wastewater

The aim of the conducted research was to assess the effectiveness of the nitrification process, at different concentrations of ammonium nitrogen, in biologically treated wastewater in one of the largest municipal and industrial wastewater treatment plants in Poland. The studies also attempted to acclimate nitrifying bacteria to the limited concentration of ammonium nitrogen and determined the efficiency of nitrification under the influence of acclimated activated sludge in the biological wastewater treatment system. The obtained results indicate that the concentration of ammonium nitrogen above 60.00 mg·dm−3 inhibits nitrification, even after increasing the biomass of nitrifiers. The increase in the efficiency of the nitrification process in the tested system can be obtained by using the activated sludge inoculated with nitrifiers. For this purpose, nitrifiers should be preacclimated, at least for a period of time, allowing them to colonize the activated sludge. The acclimated activated sludge allows reducing the amount of ammonium nitrogen in treated sewage by approx. 35.0%. The process of stable nitrification in the biological treatment system was observed nine days after introducing the acclimated activated sludge into the aeration chamber.

Role of heterotrophic nitrifiers and aerobic denitrifiers in simultaneous nitrification and denitrification process: A non-conventional nitrogen removal pathway in wastewater treatment

Bacterial species capable of performing both nitrification and denitrification in a single vessel under similar conditions have gained significance in the wastewater treatment scenario considering their unique character of performing the above reactions under heterotrophic and aerobic conditions respectively. Such a novel strategy often referred to as simultaneous nitrification and denitrification (SND) has a tremendous potential in dealing with various wastewaters having low C:N content, considering that the process needs very little or no external carbon source and oxygen supply thus adding to its cost-effective and environmentally friendly nature. Though like other microorganisms, heterotrophic nitrifiers and aerobic denitrifiers convert inorganic or organic nitrogen-containing substances into harmless dinitrogen gas in the wastewater, their ecophysiological role in the global nitrogen cycle is still not yet fully understood. Attempts to highlight the role played by the heterotrophic nitrifiers and aerobic denitrifiers in dealing with nitrogen pollution under various environmental operating conditions will help in developing a mechanistic understanding of the SND process to address the issues faced by the traditional methods of aerobic autotrophic nitrification-anaerobic heterotrophic denitrification.

Enhancing stability of aerobic granules by microbial selection pressure using height-adjustable influent strategy

Optimizing granules size distribution is critical for both reactor performance and stability. In this research, an optimal size range of 1800 to 3000 μm was proposed regarding mass transfer and granules stability based on granules developed at DO around 8.0 mg L^-1 with the feed COD:N:P at 100:5:1. A height-adjustable influent strategy was applied to facilitate the nutrient storage of granules at optimum size range via microbial selective pressure. Results suggested insufficient hydraulic shear stress led to overgrowth of granules size. High abundance of filamentous bacteria (Thiothrix sp.) was observed in oversized granules, which detached and affected the remaining granules, resulting in severe sludge bulking. Strong hydraulic shear stress suppressed uncontrolled growth of granules. However, fewer abundance of simultaneous nitrification and denitrification (SND) bacterium was acquired, which led to unfavored SND effect and total nitrogen (TN) removal efficiency. The height-adjustable influent strategy facilitated the poly-β-hydroxybutyrate (PHB) storage of granules at optimum size range, while limiting the overgrowth of granules size. Additionally, more than 87.51% of total granules situated in optimal sizes range, which led to higher abundance of SND bacterium and higher TN removal efficiency.

Temperature-induced difference in microbial characterizations accounts for the fluctuation of sequencing batch biofilm reactor performance

Generally, the purification performance of bioreactors could be influenced by temperature variation via shaping different microbial communities. However, the underlying mechanisms remain largely unknown. Here, the variation trends of microbial communities in three sequencing batch biofilm reactors (SBBRs) under four different temperatures (15, 20, 25, 30 °C) were compared. It was found that temperature increment led to an obvious enhancement in nutrient removal which was mainly occurred in the aerobic section. Meanwhile, distinct differences in dominant microbial communities or autotrophic nitrifiers were also observed. The performance of the SBBR reactors was closely associated with nitrifier communities since the treated wastewater was characterized by a severe lack of carbon sources (mean effluent COD ≤ 14.4 mg/L). Spearman correlation unraveled that: most of the differentiated microbes as well as the dominant potential functions were strongly associated with nutrient removal, indicating the temperature-induced difference in microbial community well explained the distinction in purification performance.

Comparison of an integrated short-cut biological nitrogen removal process with magnetic coagulation treating swine wastewater and food waste digestate

An integration of two processes, magnetic coagulation (MC) and short-cut biological nitrogen removal (SBNR), coupled with a sequencing batch membrane bioreactor (SMBR) controlled by an automatic real-time control strategy (RTC), was developed to treat different characteristics of high strength wastewater. The treatment efficiency and microbial community-diversity of the proposed method was evaluated and investigated using swine wastewater and food waste (FW) digestate. The MC showed high removal of TSS (89.1 ± 1.5%, 92.21 ± 1.8%), turbidity (90.58 ± 2.1%, 95.1 ± 2.1%), TP (88.5 ± 1.9%, 92.1 ± 1.5%), phosphate (87.76 ± 1.6%, 91.22 ± 1.5%), and SMBR achieved stable and excellent removal of COD (96.05 ± 0.2%, 97.39 ± 0.2%), TN (97.30 ± 0.3%, 97.44 ± 0.3%) andNH₄⁺-N (99.07 ± 0.2%, 98.54 ± 0.2%) for swine wastewater and FW digestate, respectively. The effluent COD andNH₄⁺-N concentrations were found to meet their discharge standards. The microbial community comparison showed similar diversity and richness, and genus Diaphorobacter and Thaurea were dominant in denitritation, and Nitrosomonas was dominant in nitritation treating both swine wastewater and FW digestate.

Biodegradation of organophosphorus pesticides in moving bed biofilm reactors: Analysis of microbial community and biodegradation pathways

We investigated the performance of a lab-scale moving bed biofilm reactor (MBBR) with respect to general bioconversion processes and biotransformation of two commonly used organophosphorus pesticides, Chlorpyrifos (CHL) and Malathion (MAL). The reactor was operated for 300 days under different organic loads by changing hydraulic retention time (HRT). The decrease in organic load resulted in the formation of a thinner biofilm and the growth of more biomass in the bulk, which greatly shifted bioconversion processes. The low organic loading supported more nitrification in the reactor, but an opposite trend was observed for denitrification, which was enhanced at higher organic loading where the formation of anoxic zones in the thick biofilm was favored. 70% and 55% removal corresponding to 210 and 165 µg/m²/d occurred for MAL and CHL, respectively, at an HRT of 3 h and progressively increased with higher HRTs. Phylogenetic analysis revealed a shift in composition and abundance of taxa throughout the reactor operation where lower loading rate supported the growth of a more diverse and evenly distributed community. The analysis also highlighted the dominance of heterotrophic communities such as Flavobacterium and Acinetobacter johnsonii, which could be involved in the biotransformation of CHL and MAL through co-metabolism.

Development of Strategies for AOB and NOB Competition Supported by Mathematical Modeling in Terms of Successful Deammonification Implementation for Energy-Efficient WWTPs

Novel technologies such as partial nitritation (PN) and partial denitritation (PDN) could be combined with the anammox-based process in order to alleviate energy input. The former combination, also noted as deammonification, has been intensively studied in a frame of lab and full-scale wastewater treatment in order to optimize operational costs and process efficiency. For the deammonification process, key functional microbes include ammonia-oxidizing bacteria (AOB) and anaerobic ammonia oxidation bacteria (AnAOB), which coexisting and interact with heterotrophs and nitrite oxidizing bacteria (NOB). The aim of the presented review was to summarize current knowledge about deammonification process principles, related to microbial interactions responsible for the process maintenance under varying operational conditions. Particular attention was paid to the factors influencing the targeted selection of AOB/AnAOB over the NOB and application of the mathematical modeling as a powerful tool enabling accelerated process optimization and characterization. Another reviewed aspect was the potential energetic and resources savings connected with deammonification application in relation to the technologies based on the conventional nitrification/denitrification processes.

Nitrogen removal and microbial community diversity in single-chamber electroactive biofilm reactors with different ratios of the cathode surface area to reactor volume

Removal of nitrogen compounds is particularly important domestic wastewater treatment. Our recent study reported the successful removal of nitrogen in single-chamber electroactive biofilm reactors (EBRs) under aeration-free conditions. We hypothesized that the oxygen diffused from the air-cathode is a key factor in the removal of nitrogen in the EBR. If so, the effect of the penetrated oxygen would vary according to the ratio of the air-cathode surface area to the reactor volume (AV ratio) and the hydraulic retention time (HRT). In this study, single-chamber EBRs with three different AV ratios: 125 m²/m³ (EBR-125), 250 m²/m³ (EBR-250), and 500 m²/m³ (EBR-500) were evaluated for the removal of nitrogen under different HRTs of 0.5-6 h. The higher the AV ratio, the greater the increase in nitrification. The total nitrogen (TN) removal efficiency of EBR-125 and EBR-250 decreased as the HRT decreased, while that of EBR-500 increased. EBR-250 showed the highest TN removal (62.0%) with well-balanced nitrification (83.9%) and denitrification (75.1%) at an HRT of 6 h. However, EBR-500 appeared to be superior for practical application because it showed a comparable TN removal (59%) at a substantially short HRT of 1 h. The microbial communities that were involved in the nitrogen cycle varied according to whether the biofilms were located on the anodes, separators, and cathodes but were similar among EBRs with different AV ratios. Nitrifying bacteria were detected in the biofilms that were presented on the cathodes (approximately 7.8% of the total phylotypes), while denitrifying bacteria were mainly found in biofilm that were located on the anodes (approximately 23.3%). Anammox bacteria were also detected on the anode (approximately 3.7%) and in the separator biofilms (approximately 1.9%) of all the EBRs. These results suggest that both the A/V ratio and the HRT could affect the counter diffusion of substrates (NH₄⁺ and organic compounds) and oxygen in the biofilms and allow interactions between a diversity of microorganisms for the successful removal of nitrogen in EBRs. These findings are expected to aid in the development of new applications using EBR for energy-saving wastewater treatment.

Characteristics of oxygen mass transfer and its impact on pollutant removal performance and microbial community structure in an aerobic fluidized bed biofilm reactor for treatment of municipal wastewater

A laboratory-scale aerobic fluidized bed biofilm reactor (AFBBR) was established to evaluate the oxygen mass transfer (OMT) process and its impact on municipal wastewater treatment performance. Aeration rates had different effects on the OMT of the wastewater and biofilm. In the wastewater, oxygenation performance, oxygen uptake rate (OUR), and volumetric OMT coefficient (k_La) improved under high aeration rates. However, within the biofilm, the OMT process under the aeration rate of 0.096 L/(min·L) were higher than under other conditions [0.064 L/(min·L) and 0.128 L/(min·L)]. The denitrifying bacteria (DNB) abundance under the aeration rate of 0.096 L/(min·L) were improved so that total nitrogen (TN, 66.98 ± 4.23%) and ammonia nitrogen (NH₄⁺-N, 74.70 ± 2.30%) removal were higher than those under other aeration conditions. These results showed that suitable aeration could improve wastewater treatment efficiency through changing the OMT process and microbial community structure.

The Kinetics of Pollutant Removal through Biofiltration from Stormwater Containing Airport De-Icing Agents

The present study aimed to determine the kinetics of pollutant removal in biofilters with LECA filling (used as a buffer to prevent de-icing agents from being released into the environment with stormwater runoff). It demonstrated a significant effect of temperature and a C/N ratio on the rate of nitrification, denitrification, and organic compound removal. The nitrification rate was the highest (0.32 mg N/L·h) at 25 °C and C/N = 0.5, whereas the lowest (0.18 mg N/L·h) at 0 °C and C/N = 2.5 and 5.0. Though denitrification rate is mainly affected by the available quantity of organic substrate, it actually decreased as the C/N increased and was positively correlated with the temperature levels. Its value was found to be the highest (0.31 mg N/L·h) at 25 °C and C/N = 0.5, and the lowest (0.18 mg N/L·h) at 0 °C and C/N = 5.0. As the C/N increased, so did the content of organic compounds in the treated effluent. The lowest organic removal rates were noted for C/N = 0.5, ranging between 11.20 and 18.42 mg COD/L·h at 0 and 25 °C, respectively. The highest rates, ranging between 27.83 and 59.43 mg COD/L·h, were recorded for C/N = 0.5 at 0 and 25 °C, respectively.

Stronger environmental adaptation of rare rather than abundant bacterioplankton in response to dredging in eutrophic Lake Nanhu (Wuhan, China)

Deciphering responses of rare versus abundant bacterioplankton to environmental change, crucial for understanding and mitigating of cyanobacterial blooms, is an important but poorly investigated subject. Using MiSeq sequencing, we investigated the taxonomic and phylogenetic diversity of rare and abundant bacterioplankton in eutrophic Lake Nanhu before and after dredging. We estimated environmental breadths and phylogenetic signals of ecological preferences of rare and abundant bacterioplankton, and investigated community function and bacterioplankton assembly processes. Both taxonomic and phylogenic distances of rare and abundant bacterioplankton communities were significantly positively correlated with the dissimilarity of environmental factors. Threshold indicator taxa analysis and Blomberg's K statistic indicated that rare taxa held broader environmental thresholds and stronger phylogenetic signals for ecological traits than abundant taxa. Environmental adaptations of both rare and abundant taxa exhibited distinct changes after dredging. Higher functional redundancy occurred in the abundant compared to the rare bacterioplankton, with functions of rare bacterioplankton decreasing and for the abundant ones increasing after dredging. The null model revealed that dispersal limitation belonging to stochastic processes determined the abundant bacterioplankton community assembly, whereas variable selection belonging to deterministic processes drove the rare one. Rare bacterioplankton was more environmentally constrained than the abundant one. Dissolved oxygen was the decisive factor in determining the balance between stochasticity and determinism in both rare and abundant bacterioplankton. Our study extends our knowledge of environmental adaptation of rare versus abundant bacterioplankton to massive disturbing measures, i.e. dredging, and allows to estimate dredging performance for mitigating cyanobacterial blooms from a molecular ecology viewpoint.

Evaluating the effect of air flow rate on hybrid and conventional membrane bioreactors: Implications on performance, microbial activity and membrane fouling

This study addressed the impact of air flow rate on the performance, membrane fouling behaviour and microbial community of a sequencing batch conventional membrane bioreactor (SB-MBR) and a sequencing batch hybrid membrane bioreactor (SB-HMBR) with carrier media for biofilm growth. Two different scenarios were evaluated: high (6.4 L min^-1) and low (1.6 L min^-1) air flow rates, associated with high (4.5 mg L^-1) and low (1.5 mg L^-1) dissolved oxygen (DO) concentrations and specific aeration demand per membrane area (SAD_m) of 0.426 and 0.106 m³ m^-2 h^-1, respectively. Both reactors were subjected to alternating non-aerated and aerated conditions for organic matter (as chemical oxygen demand - COD), nitrogen and phosphate removal from a municipal wastewater. From the bacterial community analysis, the key players in nutrient removal processes were assessed. The results showed that COD removal efficiencies were above 95% in both MBRs, regardless of the aeration intensity, while complete ammonium removal was observed at the higher DO. However, nitrifying activity was adversely affected under low DO levels. High nitrification levels were re-established faster in the hybrid MBR, thanks to the presence of biofilm, where nitrifying activity was favoured and the bacterial community profile did not exhibit substantial changes upon DO reduction. A higher denitrification potential was found for the carrier-based MBR, resulting in lower effluent nitrate concentrations. Regarding phosphorus removal, a slight improvement was observed in the SB-HMBR at reduced DO, while in the SB-MBR it remained practically constant. Moreover, the specific phosphate uptake rate exhibited a significant increase, especially in the hybrid MBR, reaching 44.6 mgP gVSS^-1 h^-1. At lower aeration rate, however, worse filterability and higher membrane fouling rates were observed, especially in the conventional MBR. Overall, the results demonstrated that the hybrid MBR better withstood the reduced air flow rate and DO as compared to the conventional counterpart.

Optimization of the pollutant removal in partially unsaturated constructed wetland by adding microfiber and solid carbon source based on oxygen and carbon regulation

The partially unsaturated constructed wetland was demonstrated to be able to enhance the oxygen supplement for the microbial nitrification. However, the fast gravity flow of wastewater on the smooth surface of substrate in unsaturated zone led to a short contact time between wastewater and biofilm on the surface of substrate for the microbial pollutant oxidation process. While, the strengthened oxygen supplement also consumed organic carbon, intensifying the shortage of electron donator for the denitrification process. To further enhance the efficiency of both nitrification and denitrification processes, two strategies were conducted as follows: (1) adding microfiber in unsaturated zone to extend the hydraulic retention time (HRT) and improve the oxygenating efficiency; (2) adding slow-release carbon source (Poly butylenes succinate, PBS) as electron donor in saturated zone for denitrification. Results showed that the ammonia oxidation efficiency reached up to 97.0% in the microfiber-enhanced constructed wetland. Additionally, adding microfiber provided more sites for microbes and increased the total number of microbes in unsaturated zone. The addition of PBS in the saturated zone obviously improved the denitrification efficiency with the total nitrogen (TN) removal rate raising from 20.6 ± 4.0% to 90.4 ± 2.7%, which excellently solved the problem of poor denitrification efficiency caused by low ratio of carbon to nitrogen (C/N). In conclusion, the association of microfiber and PBS in partially unsaturated constructed wetland finally accomplished the thorough nitrogen removal.

Simultaneous nitrification and denitrification in moving bed bioreactor and other biological systems

Moving bed bioreactor (MBBR), used for treatment of municipal and industrial wastewater, is a completely mixed attached growth type system that involves microorganisms which grow as biofilm on the surface of the suspended carriers within the reactor. If the biofilm is thick enough, dissolved oxygen in the reactor would not diffuse into deeper strata and thus anoxic/anaerobic condition develops in those regions facilitating growth of heterotrophic denitrifying bacteria. Autotrophic nitrifiers colonize the outer surface of biofilm in biocarriers as usual. Thus, development of aerobic nitrifying and anoxic denitrifying microorganisms facilitates nitrification and denitrification simultaneously within different zones of the same biofilm. The present paper summarizes the feasibility of nitrogen removal in MBBR systems via autotrophic nitrification followed by heterotrophic denitrification, including various aspects of simultaneous nitrification and denitrification (SND) process in other biofilm units as well. Apart from that, the areas for further investigation are briefly narrated from studies conducted earlier.

Mechanism of nutrient removal enhancement in low carbon/nitrogen wastewater by a novel high-frequency micro-aeration/anoxic (HMOA) mode

In this study, a novel high-frequency micro-aeration/anoxic (HMOA) mode with a high aeration frequency (15 times/h) and short aeration duration (T_aer = 1 h/cycle) was proposed. Compared with continuous aeration modes, the highest nitrogen and phosphorus removal efficiencies were achieved in the sequencing batch reactor (SBR) under HMOA mode when treating wastewater with carbon/nitrogen (C/N) ratios of 4.5 (85% and 97%, respectively) and 3 (77% and 75%, respectively). Metagenomic analysis was utilized to analyse the microbial metabolic mechanism under the HMOA mode. The results showed that under the HMOA mode, the enhanced transduction and metabolism pathways of nitrate, nitrite, oxygen, phosphorus and acetate provided favourable nutritional conditions for the proliferation of denitrifiers and phosphorus accumulating organisms (PAOs), and simultaneously strengthened the survival capacity of nitrifiers under low dissolved oxygen (DO) conditions. In addition, genes involved in carbon metabolism were upregulated by the HMOA mode, which further increased the utility of carbon sources for denitrifier and PAO metabolism. Consequently, the limited carbon source could be fully utilized in nitrogen and phosphorus removal, which improved the efficiency of treating low C/N wastewater. This study proposed a potential aeration mode for microbial metabolism regulation to enhance nutrient removal in biological wastewater treatment processes.

Factors affecting simultaneous nitrification and denitrification (SND) in a moving bed sequencing batch reactor (MBSBR) system as revealed by microbial community structures

The effects of biological factors including dissolved oxygen (DO), pH, carbon/nitrogen (C/N) and hydraulic retention times (HRT) on the performance of simultaneous nitrification and denitrification (SND) in a moving bed sequencing batch reactor (MBSBR) were investigated. A low DO was found to be advantageous to the SND in that nitrification was not inhibited, while pH and C/N ratio were shown to have positive effects on SND, and HRT needed to be controlled in a suitable range. A desirable SND efficiency was obtained at a DO of 2.5 mg L^-1, pH of approximately 8.0, C/N ratio of 10 and HRT of 10 h in the MBSBR. High-throughput sequencing analysis showed that different operating conditions impacted microbial communities, resulting in different nitrogen removal mechanisms. Autotrophic and heterotrophic nitrification together contributed to the good nitrification performance, while denitrification was conducted by combined anoxic and aerobic processes. Furthermore, the results of principal component analyses (PCA) and the abundance of the predominant nitrification and denitrification genera both showed that DO and HRT might be regarded as the dominant variable factors influencing community structure analysis during SND, while the linear discriminant analysis (LDA) effect size (LEfSe) algorithm showed differences in abundance among the biofilm microbial communities with different DO. Overall, the results of this study improve our understanding of the bacterial community structure with different operating conditions in MBSBRs.

Simultaneous nitrification and denitrification process using novel surface-modified suspended carriers for the treatment of real domestic wastewater

Moving-bed biofilm reactor (MBBR) is a well-established technology for simultaneous nitrification and denitrification (SND). In MBBR, biofilm development and pollutant removal performance are strictly governed by the physico-chemical properties of the carriers. In this study, novel surface-modified carriers with enhanced hydrophilicity (surface contact angle of 60.2 ± 2.3°) and positively-charged surfaces (+11.7 ± 1.1 mV, pH 7.0) had been prepared successfully via polymer blending, and they had also been implemented in SND system for the treatment of real domestic wastewater. Results showed that accelerated startup of SND with more biomass on the carriers was observed in MBBR system filled with surface-modified carriers. At low DO level (0.6-0.8 mg L^-1) and low C/N ratio (≤5), highly efficient organics removal and SND performance could be achieved with COD removal, TN removal and SND efficiencies of 79.3-85.7%, 62.0-75.9% and 58.5-71.8%, respectively. The efficient performance of SND in MBBR system filled with surface-modified carriers was mainly attributed to the coexistence of enriched mixtrophic nitrifiers and denitrifiers like autotrophic nitrifers (Nitrosomonas, Nitrospira, Nitrobacter), heterotrophic nitrifers (Rudaea), aerobicdenitrifiers (Dokdonella, Terrimonas), anoxic denitrifiers (Gemmobacter, Ottowia, Methyloversatilis, Thermomonas) and N₂O producer (Mesorhizobium).

Advanced oxygenation efficiency and purification of wastewater using a constant partially unsaturated scheme in column experiments simulating vertical subsurface flow constructed wetlands

The presence of sufficient dissolved oxygen (DO) in a constructed wetland (CW) is vital to the process of removing ammonia nitrogen and organics from wastewater. To achieve total nitrogen removal, which is characterised by enhanced ammonia nitrogen removal, this study offers an efficient strategy to increase the oxygen supply by establishing constant unsaturated zones and baffles in simulating constructed wetlands (SCWs). Henceforth, this strategy is addressed as a partially unsaturated SCW. A centrally located high tube was set up inside the wetland to create an unsaturated zone at a higher level. The effectiveness of the unsaturated zone to supplement the oxygen content was evaluated by comparing with controls (an unaerated SCW and an aerated SCW). The results show the chemical oxygen demand removal rate (85 ± 6%) in the partially unsaturated SCW was equivalent to that in the aerated SCW (83 ± 6%), while the ammonia nitrogen removal rate was 11 times higher compared to that of the unaerated SCW. The removal potential of the partially unsaturated SCW under different HRT (hydraulic retention time)s (12, 24, and 36 h) was examined, and the 36 h-SCW performed the best in the removal of organics and nitrogen. The mechanisms behind the unsaturated zone strategy were studied by analysing water and microbe samples along the pathway. The results from the water quality indicators and the quantitative polymerase chain reactions along the pathway showed the unsaturated zone contributed to the removal of primary organics and ammonia nitrogen. The superior performance of unsaturated zone strategy was discussed further using the enrichment of ammonia-oxidising bacteria, mass of oxygen uptake, and baffle design. The results indicate that the amoA gene/16s rRNA gene abundance ratio and the oxygen uptake (336 ± 44 g m^-3 d^-1) in the partially unsaturated SCW was higher than that observed in the two controls.

Impact of the acetate/oleic acid ratio on the performance, quorum sensing, and microbial community of sequencing batch reactor system

This study comprehensively investigated the impact of acetate/oleic acid ratios (80%/20%, 60%/40%, 40%/60%, and 20%/80%) on sequencing batch reactor (SBR) with respect to the variations in performance, quorum sensing (QS), and microbial community. Results showed that NH⁺₄-N removal was not affected by the acetate/oleic acid ratios, while the COD, total nitrogen (TN), and PO^3-₄-P removal was considerably affected. The increasing oleic acid ratios led to severe sludge bulking, which was significantly positively correlated with proteins/polysaccharides (p < 0.001). The correlation of QS with the performance and sludge properties was also observed. High-throughput sequencing demonstrated that microbial compositions considerably shifted with varying acetate/oleic acid ratios. Moreover, the potential correlation of bacterial genera with the SBR performance and QS was proposed. This study elucidated the effect of acetate/oleic acid ratios on SBR from microbial viewpoint, which provided insights into fully understanding the essential roles of carbon source on wastewater treatment.

Computational fluid dynamics and factor analysis of a novel swirling demulsified airlift loop reactor for the treatment of refined soybean oil wastewater

A swirling demulsified airlift loop reactor (SD-ALR) was developed for the treatment of oily wastewater with yeasts. Computational fluid dynamics simulations showed that the gas holdup and liquid velocity gradient in the SD-ALR were 2.9% and 0.37 m/s higher than those in the traditional airlift loop reactor. The optimization results of the swirling demulsifier showed that the optimal number and elevation angle of the blades were 8 and 45°, and the optimal installation position was 150 mm from the bottom of the draft tube. The results of treating refined soybean oil wastewater in the SD-ALR showed that the wastewater treatment time was decreased by 8 h, and the removals of chemical oxygen demand and oil content increased by 5.10% ± 0.02% and 9.55% ± 0.40%, respectively, compared with those in the traditional airlift loop reactor. A volumetric mass transfer coefficient model was established for SD-ALR and oily wastewater.

Carbon and nitrogen metabolic pathways and interaction of cold-resistant heterotrophic nitrifying bacteria under aerobic and anaerobic conditions

In this study, both the carbon and nitrogen metabolisms of two heterotrophic nitrification bacteria were investigated under aerobic and anaerobic conditions at 2 °C. Similar catabolism and anabolism trends were observed for the two bacteria in stable experimental systems under aerobic and anaerobic conditions. Based on the nitrogen and carbon balance analysis and adenosine triphosphate (ATP) calculation, we proposed the following metabolic pathways: i) aerobic: except for microbial assimilation, the carbon and nitrogen sources were removed through respiration and nitrification, which provided energy for cell synthesis; and ii) anaerobic: the nitrification process almost stopped and most of the carbon sources decomposed into inorganic carbon, which dissolved in the medium. Based on our proposed metabolic pathways, we speculated that the nitrifying process almost stopped under anaerobic conditions and the nitrification bacteria would degrade more carbon contaminants to produce energy and maintain the cell growth. Furthermore, these bacteria may decompose the non-readily biodegradable carbon through anaerobic degradation. To verify these hypotheses, experiments with two types of synthetic wastewater were conducted: i) synthetic wastewater rich in carbon and poor in nitrogen, and higher carbon removal efficiencies of strain J and strain P (∼25%) were obtained under anaerobic conditions compared with aerobic conditions (∼19%); and ii) synthetic wastewater with recalcitrant carbon sources, and carbon removal efficiencies under anaerobic conditions were higher than those under aerobic conditions. The results of the synthetic wastewater experiments were consistent with the hypotheses and thus validated the metabolic pathways proposed for carbon and nitrogen.

Optimized aeration strategies for nitrogen removal efficiency: application of end gas recirculation aeration in the fixed bed biofilm reactor

Aeration strategy played an important role in reactor performance. In this study, when superficial upflow air velocity (SAV) decreased from 0.16 to 0.08 cm s^-1, low dissolved oxygen concentration (DO) of 2.0 mg L^-1 occurred in reactor. The required depth for anoxic microenvironment in biofilm decreased from 902.3 to 525.9 μm, which enhanced the growth of denitrifying bacteria and total nitrogen (TN) removal efficiency. However, decreasing aeration intensity resulted in insufficient hydraulic shear stress, which led to weak biofilm matrix structure. Mass biofilm detachment and reactor deterioration then occurred after 87 days of operation. An end gas recirculation aeration strategy was proposed to separately manipulate DO and aeration intensity. Low DO and high aeration intensity were simultaneously achieved, which enhanced the metabolism of denitrifying bacteria (such as Flavobacterium sp., Pseudorhodobacter sp., and Dok59 sp.) and EPS-producing bacteria (such as Zoogloea sp. and Rhodobacter sp.). Consequently, high TN removal performance (82.1 ± 2.7%) and stable biofilm structure were achieved.

Zeolite powder based polyurethane sponges as biocarriers in moving bed biofilm reactor for improving nitrogen removal of municipal wastewater

This study aims to enhance nitrogen removal efficiency of a moving bed biofilm reactor (MBBR) by developing a new MBBR with zeolite powder-based polyurethane sponges as biocarriers (Z-MBBR). Results indicated the total nitrogen (TN) removal efficiency and simultaneous nitrification and denitrification (SND) performance in Z-MBBR were nearly 10% higher than those in the conventional MBBR with sponges as biocarriers (S-MBBR). About 84.2 ± 4.8% of TN was removed in Z-MBBR compared to 75.1 ± 6.8% in S-MBBR. Correspondingly, the SND performance in Z-MBBR and S-MBBR was 90.7 ± 4.1% and 81.7 ± 6.5%, respectively. The amount of biofilm attached to new biocarriers (0.470 ± 0.131 g/g carrier) was 1.3 times more than that of sponge carriers (0.355 ± 0.099 g/g carrier). Based on the microelectrode measurements and microbial community analysis, more denitrifying bacteria existed in the Z-MBBR system, and this can improve the SND performance. Consequently, this new Z-MBBR can be a promising option for a hybrid treatment system to better nitrogen removal from wastewater.

Cell membrane characteristics and microbial population distribution of MBBR and IFAS with different dissolved oxygen concentration

This paper investigated the influences of different dissolved oxygen (DO) concentration (0.71-1.32, 2.13-3.02 and 4.31-5.16 mg/L) on cell membrane characteristics and microbial population distribution of moving biofilm reactors. Two representative reactors, i.e., moving bed biofilm reactors and integrated fixed-film activated sludge were operated. Results indicated that both DO concentration of 0.71-1.32 mg/L and 4.31-5.16 mg/L could increase membrane lipid mobile fraction (49.4%-67.4%) of the microbes, however, through prompting the synthesis of branched fatty acids and unsaturated fatty acids, respectively. For the biofilms, the abundance of Bacteroidetes decreased and Actinobacteria increased with the increase of DO levels. The lowest EfOM content and the highest microbial diversities (1.14-1.52) was observed at DO of 2.13-3.02 mg/L. Redundancy analysis showed that changes of DO levels could alter cell membrane properties and bacterial community structures, and subsequently significantly influenced effluent organic matter composition of moving biofilm reactors.

Influence of the Hybrid Sewage Treatment Plant’s Exploitation on Its Operation Effectiveness in Rural Areas

The article evaluates the effectiveness of the removal of organic pollutants—nitrogen and phosphorus—from household sewage in a hybrid bioreactor with a submerged fixed bed. The experiment was carried out in two exploitation variants that were both conducted in a laboratory model of the hybrid bioreactor: (I) cycles of 120 min of aeration and 60 min of no aeration with a constant sewage dosage, and (II) cycles 60 min of aeration and 60 min of no aeration, with a periodic sewage dosage in the no-aeration phase. The experiment was carried out on real sewage primarily treated in a septic tank. The amount of pollution removal was calculated and compared with the mandatory standards according to Polish law. Moreover, the susceptibility of the sewage to the biological treatment, nitrification, and denitrification activity was determined. The research shows a higher effectiveness for the 60/60 model in comparison to the 120/60 model. High operation efficiency was observed regarding the removal of organic pollution and nitrate nitrogen. The tested structure showed very low nitrification activity combined with intense denitrification. These processes were observed in the 60/60 variant. The structure was often overloaded with the nitrate nitrogen, which was considered to be the nitrification process inhibitor. It was suggested that phosphorus was also removed by the denitrifying bacteria.