Chlorination caused a shift in marine biofilm niches on microfiltration/ultrafiltration and reverse osmosis membranes and UV irradiation effectively inactivated a chlorine-resistant bacterium.

The effect of chlorine disinfection on marine biofilm populations and communities formed on membrane surfaces was investigated under two feedwater conditions: raw seawater and deep bed filtration-treated seawater. As a result of chlorination, the structure of the biofilm community on the microfiltration/ultrafiltration and reverse osmosis membrane coupons shifted significantly at the genus level. However, the total bacterial population was not reduced under the two feedwater conditions. This failure to control the biofilm was attributed to the adaptation and survival of selected bacteria under chlorine stress. Phaeobacter caeruleus, isolated from the biofilm, was examined as a representative chlorine-resistant biofilm-forming bacterium. The number of viable P. caeruleus was significantly reduced (as much as 99.8%) after ultraviolet (UV) disinfection. The results indicated that additional disinfection by UV irradiation can inactivate chlorine-resistant bacteria. Therefore, tandem chlorination-UV disinfection may enhance the efficiency of biofouling control in seawater reverse osmosis processes. The synergistic effects of tandem chlorination-UV irradiation on the marine biofilm community should be investigated in future studies.

Effects of the ammonium loading rate on nitrite-oxidizing activity during nitrification at a high dose of inorganic carbon.

In this study, the effects of the ammonium loading rate (ALR) and inorganic carbon loading rate (ILR) on the nitrification performance and composition of a nitrifying bacterial community were investigated in a moving bed biofilm reactor, using poly(vinyl alcohol) (PVA) sponge cubes as a supporting carrier. Between the two ALRs of 0.36 and 2.16 kg-N m-1 d-1, stable partial nitritation was achieved at the higher ALR. Inorganic carbon was dosed at high levels: 33.1, 22.0, 16.4, 11.0, and 5.4 times the theoretical amount. Nonetheless, nitrification efficiency was not affected by the ILR at the two ALRs. Quantitative PCR analysis of ammonia- and nitrite-oxidizing bacteria revealed that ALR is an important determinant of partial nitritation by accumulating ammonia-oxidizing bacteria in the nitrification system. In comparison, two nitrite-oxidizing bacterial genera (Nitrobacter and Nitrospira) showed almost the same relative abundance at various ALRs and ILRs. Terminal restriction fragment length polymorphism targeting the gene of ammonia monooxygenase subunit A revealed that Nitrosomonas europaea dominated under all conditions.

Exploring the Role of Persulfate in the Activation Process: Radical Precursor Versus Electron Acceptor.

This study elucidates the mechanism behind persulfate activation by exploring the role of various oxyanions (e.g., peroxymonosulfate, periodate, and peracetate) in two activation systems utilizing iron nanoparticle (nFe0) as the reducing agent and single-wall carbon nanotubes (CNTs) as electron transfer mediators. Since the tested oxyanions serve as both electron acceptors and radical precursors in most cases, oxidative degradation of organics was achievable through one-electron reduction of oxyanions on nFe0 (leading to radical-induced oxidation) and electron transfer mediation from organics to oxyanions on CNTs (leading to oxidative decomposition involving no radical formation). A distinction between degradative reaction mechanisms of the nFe0/oxyanion and CNT/oxyanion systems was made in terms of the oxyanion consumption efficacy, radical scavenging effect, and EPR spectral analysis. Statistical study of substrate-specificity and product distribution implied that the reaction route induced on nFe0 varies depending on the oxyanion (i.e., oxyanion-derived radical), whereas the similar reaction pathway initiates organic oxidation in the CNT/oxyanion system irrespective of the oxyanion type. Chronoamperometric measurements further confirmed electron transfer from organics to oxyanions in the presence of CNTs, which was not observed when applying nFe0 instead.

The biostimulation of anaerobic digestion with (semi)conductive ferric oxides: their potential for enhanced biomethanation.

The effect of biostimulation with ferric oxides, semiconductive ferric oxyhydroxide, and conductive magnetite on the anaerobic digestion of dairy wastewater was examined in a batch mode. The reactors supplemented with ferric oxyhydroxide (R2) and magnetite (R3) showed significantly enhanced biomethanation performance compared with the control (R1). The removal of chemical oxygen demand (COD) after 30 days was 31.9, 59.3, and 82.5% in R1, R2, and R3, respectively. The consumed COD was almost fully recovered as biogas in R2 and R3, while only 79% was recovered in R1. The total energy production as biogas was accordingly 32.2, 71.0, and 97.7 kJ in R1, R2, and R3, respectively. The reactors also differed in the acid formation profile with more propionate and butyrate found in R1 and more acetate found in R3. The enhanced biomethanation seems to be associated with variations in the bacterial community structure supposedly induced by the ferric oxides added. In contrast, no evident variation was observed in the archaeal community structure among the reactors. The potential electric syntrophy formed between Methanosaeta concilii-like methanogens and electroactive iron-reducing bacteria, particularly Trichococcus, was likely responsible for the enhanced performance. The stimulated growth of fermentative iron reducers may also have contributed by altering the metabolic characteristics of the bacterial communities to produce more favorable acidogenic products for methanogenesis. The overall results suggest the potential of biostimulation with (semi)conductive ferric oxides to enhance the rate and efficiency of the biomethanation of organic wastes. This seems to be potentially attractive, as increasing attention is being paid to the energy self-sufficiency of waste/wastewater treatment processes today.

Resource recovery using whey permeate to cultivate Phellinus linteus mycelium: Solid-state and submerged liquid fermentation.

The growth characteristics of Phellinus linteus mycelium were assessed and compared under solid-state fermentation (SSF) and submerged liquid fermentation (SLF) systems on whey permeate medium. Response surface methodology was used to investigate the growth rates of mycelia under various conditions of operating temperature (TO), initial pH, and substrate concentration ([S]). The optimal growth conditions of P. linteus mycelium were determined to be 26.1°C, pH 4.6, and 60.3g of lactose/L in the SSF system, and 29.0°C, pH 5.0, and 65.3g of lactose/L in the SLF system. The maximum growth rates were predicted to be 1.92 ± 0.01 mm/d in SSF and 192.1 ± 0.0mg/L per day in SLF. Random trials were conducted to experimentally validate the evaluated optimal conditions. The differences between the modeled and observed values were only 5.3% in the SSF system and 6.1% in the SLF system. Significant engineering factors differed between the fermentation techniques; TO was significant in both cultivation systems, whereas initial pH was significant in SSF but [S] was significant in SLF. Our findings can be used to guide the operation of the bioconversion process for cultivating P. linteus mycelium using whey permeate wastewater.

Assessment of bacterial community structure in nitrifying biofilm under inorganic carbon-sufficient and -limited conditions.

In this work, nitrification and changes in the composition of the total bacterial community under inorganic carbon (IC)-limited conditions, in a nitrifying moving bed biofilm reactor, was investigated. A culture-independent analysis of cloning and sequencing based on the 16S rRNA gene was applied to quantify the bacterial diversity and to determine bacterial taxonomic assignment. IC concentrations had significant effects on the stability of ammonia-oxidation as indicated by the reduction of the nitrogen conversion rate with high NH4(+)-N loadings. The predominance of Nitrosomonas europaea was maintained in spite of changes in the IC concentration. In contrast, heterotrophic bacterial species contributed to a high bacterial diversity, and to a dynamic shift in the bacterial community structure, under IC-limited conditions. In this study, individual functions of heterotrophic bacteria were estimated based on taxonomic information. Possible key roles of coexisting heterotrophic bacteria are the assimilation of organic compounds of extracellular polymeric substances produced by nitrifiers, and biofilm formation by providing a filamentous structure and aggregation properties.

High-rate partial nitritation using porous poly(vinyl alcohol) sponge.

Poly(vinyl alcohol) (PVA) has been utilized as a support material for the immobilization of nitrifying bacteria without the comprehensive survey of partial nitritation. In the present study, the activities of nitrifiers and the maximum nitrogen conversion rate of partial nitritation with PVA sponge-cubes were specified according to different conditions. The selective enrichment of ammonia-oxidizing bacteria (AOB) on PVA sponge-cubes was achieved by the competition between AOB and nitrite-oxidizing bacteria for dissolved oxygen. The efficiency of ammonia oxidation was proportional to the concentration of HCO3 (-) with the molar ratio of HCO3 (-)-C/NH4 (+)-N = 1.91 and a half of the ratio was applied to the further experiments to ensure stable partial nitritation. The maximum nitrogen conversion rate of partial nitritation was dependent on the volume, not the size of sponge-cubes. The partial nitritation showed the superior rate performance of 3.09 kg N/m(3) day with the packing ratio of 32 % of 5 × 5 × 5 mm(3) PVA sponge-cubes.

Start-up strategy of single-stage partial nitrification-anammox process for anaerobic digestion effluent.

The objective of this study was to improve the nitrogen removal efficiency and reduce the start-up period of a single-stage partial nitritation-anammox (SPNA) system using iron particle-integrated anammox granules (IP-IAGs). Anammox granules were enriched in sequencing batch and expanded granular sludge bed (EGSB) reactors. The EGSB reactor produced larger and more uniform granules with higher specific anammox activity. IP-IAGs were then inoculated into a two-stage partial nitritation-anammox reactor treating anaerobic digestion (AD) effluent, followed by an internal recirculation strategy to acclimate the granules to oxygen exposure for SPNA. Finally, the SPNA process operated to treat real AD effluent under optimal conditions of 0.05 L/min aeration intensity (0.01 vvm) and 24 h of hydraulic retention time, achieving TNRE of 86.01 ± 2.64 % and nitrogen removal rate of 0.74 ± 0.04 kg-N/m3·d for 101 d.

Comprehensive assessment of chlorination disinfection on microplastic-associated biofilms.

Chlorination on microplastic (MP) biofilms was comprehensively investigated with respect to disinfection efficiency, morphology, and core microbiome. The experiments were performed under various conditions: i) MP particles; polypropylene (PP) and polystyrene (PS), ii) MP biofilms; Escherichia coli for single-species and river water microorganisms for multiple-species, iii) different chlorine concentrations, and iv) different chlorine exposure periods. As a result, chlorination effectively inactivated the MP biofilm microorganisms. The disinfection efficiency increased with increasing the free chlorination concentration and exposure periods for both single- and multiple-species MP biofilms. The multiple-species MP biofilms were inactivated 1.3-6.0 times less than single-species MP biofilms. In addition, the PP-MP biofilms were more vulnerable to chlorination than the PS-MP biofilms. Morphology analysis verified that chlorination detached most MP biofilms, while a small part still remained. Interestingly, chlorination strongly changed the biofilm microbiome on MPs; the relative abundance of some microbes increased after the chlorination, suggesting they could be regarded as chlorine-resistant bacteria. Some potential pathogens were also remained on the MP particles after the chlorination. Notably, chlorination was effective in inactivating the MP biofilms. Further research should be performed to evaluate the impacts of residual MP biofilms on the environment.

Iron particle-integrated anammox granules in baffled reactor: Enhanced settling property and nitrogen removal performance.

This study evaluates iron particle-integrated anammox granules (IP-IAGs) to enhance wastewater treatment efficiency. The IP-IAGs resulted in notable improvements in settleability and nitrogen removal. The settling velocity of IP-IAGs increased by 17.91 % to 2.92 ± 0.20 cm/s, and the total nitrogen removal efficiency in batch mode improved by 6.82 %. These changes indicate enhanced biological activity for effective treatment. In continuous operation, the IP-IAGs reactor showed no accumulation of nitrite until 40 d, reaching a peak nitrogen removal rate (NRR) of 1.54 kg-N/m3·d and a nitrogen removal efficiency of 82.61 %. Furthermore, a partial nitritation-anammox reactor that treated anaerobic digestion effluent achieved a NRR of 1.41 ± 0.09 kg-N/m3·d, proving the applicability of IP-IAGs in real wastewater conditions. These results underscore the potential of IP-IAGs to enhance the efficiency and stability of anammox-based processes, marking a significant advancement in environmental engineering for wastewater treatment.

Thickness of hydrogel for nitrifying biomass entrapment determines the free ammonia susceptibility differently in batch and continuous modes.

Hydrogels immobilizing nitrifying bacteria with different thicknesses of 0.55 and 1.13 cm (HG-0.55 and HG-1.13, respectively) were produced. It was recognized that the thickness of media is a crucial parameter that affects both the stability and efficiency of wastewater treatment. Batch mode experiments were conducted to quantify specific oxygen uptake rate (SOUR) values at various total ammonium nitrogen (TAN) concentrations and pH levels. In the batch test, HG-0.55 exhibited 2.4 times higher nitrifying activity than HG-1.13, with corresponding SOUR values of 0.00768 and 0.00317 mg-O2/L mL-PVA min, respectively. However, HG-0.55 was more susceptible to free ammonia (FA) toxicity than HG-1.13, resulting in a reduction of 80% and 50% in SOUR values for HG-0.55 and -1.13, respectively, upon increasing the FA concentration from 15.73 to 118.12 mg-FA/L. Continuous mode experiments were conducted to assess the partial nitritation (PN) efficiency in practical applications, where continuous wastewater inflow maintains low FA toxicity through high ammonia-oxidizing rates. With step-wise TAN concentration increases, HG-0.55 experienced a gentler increase in FA concentration compared to HG-1.13. At a nitrogen loading rate of 0.78-0.95 kg-N/m3 day, the FA increase rate for HG-0.55 was 0.0179 kg-FA/m3 day, while that of HG-1.13 was 0.0516 kg-FA/m3 day. In the batch mode, where wastewater is introduced all at once, the high accumulation of FA posed a disadvantage for the FA-susceptible HG-0.55, which made it unsuitable for application. However, in the continuous mode, the thinner HG-0.55, with its larger surface area and high ammonia oxidation activity, proved to be suitable and demonstrated its effectiveness. This study provides valuable insights and a framework for the utilization strategy of immobilized gels in addressing the toxic effects of FA in practical processes.

Comparative insight of pesticide transformations between river and wetland systems.

The widespread use of pesticides threatens the environment and ecosystems. Despite the positive effects of plant protection products, pesticides also have unexpected negative effects on nontarget organisms. The microbial biodegradation of pesticides is one of the major pathways for reducing their risks at aquatic ecosystems. The objective of this study was to compare the biodegradability of pesticides in simulated wetland and river systems. Parallel experiments were conducted with 17 pesticides based on the OECD 309 guidelines. A comprehensive analytical method, such as target screening combined with suspect and non-target screening, was performed to evaluate the biodegradation via identification of transformation products (TPs) using LC-HRMS. As evidence of biodegradation, we identified 97 TPs for 15 pesticides. Metolachlor and dimethenamid had 23 and 16 TPs, respectively, including Phase II glutathione conjugates. The analysis of 16S rRNA sequences for microbials characterized operational taxonomic units. Rheinheimera and Flavobacterium, which have the potential for glutathione S-transferase, were dominant in wetland systems. Estimation of toxicity, biodegradability, and hydrophobicity using QSAR prediction indicated lower environmental risks of detected TPs. We conclude that the wetland system is more favorable for pesticide degradation and risk mitigation mainly attributed to the abundance and variety of the microbial communities.

Transgenerational effects of benzotriazole on the gene expression, growth, and reproduction of Daphnia magna.

Due to its widespread and intensive use as a corrosion inhibitor, benzotriazole is ubiquitously detected from a few parts per billion to several hundred parts per million in aquatic environments. The long-term toxicity of benzotriazole is unclear despite its low acute toxicity. Therefore, we investigated the transgenerational effects of benzotriazole at the genomic and individual levels using the freshwater zooplankton Daphnia magna. Maternal exposure to sublethal concentrations (15 and 30 mg/L) of benzotriazole exerted transgenerational effects on D. magna at the genomic and individual levels even in descendants that have never been exposed to benzotriazole. Significant alterations in the expression of Cyp, GST, Vtg1, and Hb and in neonate size were observed in the unexposed F3 generation, confirming the transgenerational effect of benzotriazole. Interestingly, detoxification related genes Cyp and GST were unaffected or downregulated in the exposed generation but upregulated in the following unexposed generations. Furthermore, continuous multigenerational exposure to an environmental concentration (4.3 µg/L) of benzotriazole also upregulated detoxification genes in decent generations but exerted no individual-level effects in subsequent generations.

Alkyl chain length of quaternized SBA-15 and solution conditions determine hydrophobic and electrostatic interactions for carbamazepine adsorption.

Santa Barbara Amorphous-15 (SBA) is a stable and mesoporous silica material. Quaternized SBA-15 with alkyl chains (QSBA) exhibits electrostatic attraction for anionic molecules via the N+ moiety of the ammonium group, whereas its alkyl chain length determines its hydrophobic interactions. In this study, QSBA with different alkyl chain lengths were synthesized using the trimethyl, dimethyloctyl, and dimethyoctadecyl groups (C1QSBA, C8QSBA, and C18QSBA, respectively). Carbamazepine (CBZ) is a widely prescribed pharmaceutical compound, but is difficult to remove using conventional water treatments. The CBZ adsorption characteristics of QSBA were examined to determine its adsorption mechanism by changing the alkyl chain length and solution conditions (pH and ionic strength). A longer alkyl chain resulted in slower adsorption (up to 120 min), while the amount of CBZ adsorbed was higher for longer alkyl chains per unit mass of QSBA at equilibrium. The maximum adsorption capacities of C1QSBA, C8QSBA, and C18QSBA, were 3.14, 6.56, and 24.5 mg/g, respectively, as obtained using the Langmuir model. For the tested initial CBZ concentrations (2-100 mg/L), the adsorption capacity increased with increasing alkyl chain length. Because CBZ does not dissociate readily (pKa = 13.9), stable hydrophobic adsorption was observed despite the changes in pH (0.41-0.92, 1.70-2.24, and 7.56-9.10 mg/g for C1QSBA, C8QSBA, and C18QSBA, respectively); the exception was pH 2. Increasing the ionic strength from 0.1 to 100 mM enhanced the adsorption capacity of C18QSBA from 9.27 ± 0.42 to 14.94 ± 0.17 mg/g because the hydrophobic interactions were increased while the electrostatic attraction of the N+ was reduced. Thus, the ionic strength was a stronger control factor determining hydrophobic adsorption of CBZ than the solution pH. Based on the changes in hydrophobicity, which depends on the alkyl chain length, it was possible to enhance CBZ adsorption and investigate the adsorption mechanism in detail. Thus, this study aids the development of adsorbents suitable for pharmaceuticals with controlling molecular structure of QSBA and solution conditions.

Improved regression model for anaerobic ammonium oxidation by repeated and prolonged batch assay under stressful salinity and pH conditions.

The aim of this study was to propose repeated and prolonged batch (RPB) assay as a promising specific anammox activity (SAA) methodology assessing the anammox activity under stressed salinity and pH conditions. Response surface analysis (RSA) was used as a regression tool to evaluate statistical significance. The feasibility of RPB was investigated at 0 to 15 g-NaCl/L of salinity and pH 6 to 8 with reflecting the results of preliminary SAA. As a result, conventional SAA was statistically insignificant. In addition, the RSA results obtained from repeated batch did not meet the statistical significance despite ten times iterative reaction. Interestingly, the RPB assay (i.e., applied both repeated and prolonged reaction) was effective to obtain the reliable results. Candidadus Brocadia and Candidadus Jettenia were functional anammox microbiome during RPB. Outcomes of this study suggest that RPB assay can be applied to accurately determine the anammox activity under various stressful conditions.

Application of poly (vinyl alcohol)-cryogels to immobilizing nitrifiers: Enhanced tolerance to shear stress-induced destruction and viability control.

The hardness of poly (vinyl alcohol)-cryogels (PVA-CGs) was improved under three parameter conditions: 7.5 %-12.5 % PVA, 1-5 freezing-thawing cycles (FTCs), and the addition of 0 %-10 % glycerol as a cryoprotectant. This study investigated the effects of shear stress-induced destruction (SSID) on mechanical strength by inducing rapid erosion with a high frictional force. Tolerance to SSID (Tol-SSID) exhibited different sensitivities and trends depending on the above three fabrication parameters. The measured Tol-SSID exhibited consistent and inconsistent trends with tensile strength and swelling, respectively. Tol-SSID evaluation provides new insights into the practically meaningful mechanical strength of PVA-CGs against strong friction, which simulates extreme shear stress in a bioreactor. A PVA-CG with a PVA concentration of 10 % and in two FTCs resulted in Tol-SSID and tensile strength of 88.3 % and 0.59 kPa, respectively. Here, 5 % glycerol was added to maintain the bacterial respiration activity of immobilized nitrifiers of 0.097 mg-O2/g-VSS·min and survival of 88.6 %. The continuous mode of nitrification using the optimized PVA-CG for 10 days resulted in an ammonia removal rate of 0.2173 kg-N/m3·d, which is an improvement over cases without glycerol addition: 0.1426 and 0.1472 kg-N/m3·d for PVA-CGs in two and three FTCs, respectively.

Improved insights into the adaptation and selection of Nitrosomonas spp. for partial nitritation under saline conditions based on specific oxygen uptake rates and next generation sequencing.

Partial nitritation (PN) is a bioprocess that is essential for developing cost-effective biological nitrogen removal processes. Understanding the abundant bacterial communities responsible for nitrification under salt stress conditions is important to achieve a stable PN system for treating saline wastewater. Therefore, in this study, we identified the core nitrifying communities and investigated their correlations with the process parameters in a nitrifying bioreactor that was used for treating saline high-strength ammonia wastewater. A PN system worked efficiently under saline conditions with varying operational factors, such as temperature, dissolved oxygen (DO), and alkalinity. Interestingly, the specific oxygen uptake rate (SOUR) became similar under salt-free and saline media after the salt adaption. Next generation sequencing results suggested that the inactivation of Nitrobacter winogradskyi was a key factor for the PN reaction under salt stress conditions. We also found that Nitrosomonas europaea, a freshwater type ammonia-oxidizing bacteria (AOB), was predominantly found under both salt-free and saline conditions, whereas other halotolerant or halophilic AOB species, including Nitrosomonas nitrosa and Nitrosomonas mobilis, became selectively abundant under saline conditions. This implies that adaptation (training of N. europaea) and selection (presence of N. nitrosa and N. mobilis) were simultaneously attributed to selective ammonia conversion for the PN reaction. The redundancy analysis showed that the salinity and ammonia loading rates were statistically significant process parameters that determined the nitrifying bacterial community, suggesting that these parameters drive the adaptation and selection of the core AOB species during the PN reaction. Furthermore, the correlation analysis revealed that the abundance of N. nitrosa and N. mobilis was critically correlated with the specific oxygen uptake rates in saline media containing ammonia.

Combined machine learning and biomolecular analysis for stability assessment of anaerobic ammonium oxidation under salt stress.

In this study, the stability of the total nitrogen removal efficiency (TNRE) was modeled using an artificial neural network (ANN)-based binary classification model for the anaerobic ammonium oxidation (AMX) process under saline conditions. The TNRE was stabilized to 80.2 ± 11.4% at the final phase under the salinity of 1.0 ± 0.02%. The results of terminal restriction fragment length polymorphism (T-RFLP) analysis showed the predominance of Candidatus Jettenia genus. Real-time quantitative PCR analysis revealed the average abundance of Ca. Jettenia and Kuenenia spp. increased in 3.2 ± 5.4 × 108 and 2.0 ± 2.2 × 105 copies/mL, respectively. The prediction accuracy using operational parameters with data augmentation was 88.2%. However, integration with T-RFLP and real-time qPCR signals improved the prediction accuracy by 97.1%. This study revealed the feasible application of machine learning and biomolecular signals to the stability prediction of the AMX process under increased salinity.

The community analysis of ammonia-oxidizing bacteria in wastewater treatment plants revealed by the combination of double labeled T-RFLP and sequencing.

The functional gene of amoA, which produces the α-subunit of ammonia monooxygenase (AMO), has been analyzed to reveal the microbial community structure of ammonia-oxidizing bacteria (AOB) by culture-independent methods. In this study, the distribution of the amoA gene in 10 wastewater treatment plants (WWTPs) was revealed by the fingerprinting method of terminal restriction fragment length polymorphism (T-RFLP) and comparative sequencing. T-RFLP showed diverse communities of AOB in the modified Ludzack-Ettinger process, in the anaerobic-anoxic-oxic processes, in the hanging biological contactor, and in the sequencing batch reactor. In all of these environments, long solid retention time (SRT) was expected to be the critical factor for maintaining the diverse AOB community structure. Because T-RFLP does not offer sufficient information to confirm the phylogenetic information of AOB, the microbial community structures were analyzed by comparative sequencing for seven samples that were selected by the statistical categorization using principal component analysis (PCA) among 14 samples. The phylogenetic tree of 21 operational taxonomic units (OTUs) among 88 clones obtained in this study revealed that AOB of Nitrosomonas oligotropha and europaea lineages were predominant in WWTPs. Double labeled T-RFLP produced group-specific terminal restriction fragments (T-RFs) representing several groups of AOB and offered advanced resolution comparing with the single labeled T-RFLP.

Insight into functionally active bacteria in nitrification following Na+ and Mg2+ exposure based on 16S rDNA and 16S rRNA sequencing.

Despite increasing interests in osmotic membrane bioreactors, the information regarding the bacterial toxicity effects of reversely transported draw solute (RTDS) is limited. In this study, two representative draw solutes (NaCl and MgCl2) were used at different concentrations (0, 2.5, 5.0, 7.5 and 10.0 g/L) to evaluate their toxicity in a continuous nitrifying bioreactor. Notably, Mg2+ selectively inhibited the activity of ammonia-oxidizing bacteria (AOB), which decreased to 11.3% at 7.5 g-Mg2+/L. The rRNA-based analysis was more effective than the rDNA-based analysis to elucidate the relationship between active communities of nitrifying bacteria and the actual nitrifying performance. Nitrosomonas europaea, a representative AOB, was vulnerable to Mg2+ in comparison to Na+. In contrast, the dominant nitrite-oxidizing bacteria (NOB), Nitrobacter winogradskyi and Nitrolancea hollandica, maintained a relevant level of relative abundance for achieving nitrite oxidation after exposure to 10 g/L Na+ and Mg2+. This fundamental inhibition information of the draw solute can be applied to set the operational regime preventing the critical solute concentration in mixed liquor of nitrifying OMBRs.