Microbial community analysis of an aerobic nitrifying-denitrifying MBR treating ABS resin wastewater

Effect of salinity on biological nitrogen removal from wastewater and its mechanism

The nitrogen discharge from saline wastewater will cause significant pollution to the environment. As a high-efficiency and low-cost treatment method, biological treatment has a promising application prospect in the removal of nitrogen from high-salt wastewater. However, the inhibitory effect of high salt on microorganisms increases the difficulty of its treatment. This review discusses the influence of salinity on the nitrogen removal process, considering both traditional and novel biological techniques. Common methods to enhance the effectiveness of biological nitrogen removal processes and their mechanisms of action in engineering practice and research, including sludge acclimation and inoculation of halophilic bacteria, are also introduced. An outlook on the future development of biological nitrogen removal processes for high-salt wastewater is provided to achieve environmentally friendly discharge of high-salt wastewater.

Thauera sp. for efficient nitrate removal in continuous denitrifying moving bed biofilm reactor

Thauera is the most widely found dominant denitrifying genus in wastewater. In earlier study, MBBR augmented with a specially developed denitrifying five-membered bacterial consortium (DC5) where Thauera was found to be the most abundant and persistent genus. Therefore, to check the functional potential of Thauera in the removal of nitrate-containing wastewater in the present study Thauera sp.V14 one of the member of the consortium DC5 was used as the model organism. Thauera sp.V14 exhibited strong hydrophobicity, auto-aggregation ability, biofilm formation and denitrification ability, which indicated its robust adaptability short colonization and nitrate removal efficiency. Continuous reactor studies with Thauera sp.V14 in 10 L dMBBR showed 91% of denitrification efficiency with an initial nitrate concentration of 620 mg L-1 within 3 h of HRT. Thus, it revealed that Thauera can be employed as an effective microorganism for nitrate removal from wastewater based on its performance in the present studies.

Nitrification performance and bacterial community dynamics in a membrane bioreactor with elevated ammonia concentration: The combined inhibition effect of salinity, free ammonia and free nitrous acid on nitrification at high ammonia loading rates

The responses of the operational performance and bacterial community structure of a nitrification membrane bioreactor (MBR) to elevated ammonia loading rate (ALR) were investigated. Effective nitrification performance was achieved at high ALR up to 3.43 kg NH₄⁺-N/m³·d, corresponding to influent NH₄⁺-N concentration of 2000 mg/L. Further increasing influent NH₄⁺-N concentration to 3000 mg/L, the MBR system finally became completely inefficient due to the combined inhibition effect of salinity, free ammonia and free nitrous acid on nitrification. Ammonia-oxidizing bacteria (AOB) Nitrosomonas were enriched with the increase of ALR. The relative abundance of Nitrosomonas in the sludge with ALR of 2.57 kg NH₄⁺-N/m³·d was up to 14.82%, which were 9-fold and 53-fold higher than that in seed sludge and the sludge with ALR of 0.10 kg NH₄⁺-N/m³·d, respectively. The phylogenetic analysis of AOB amoA genes showed that Nitrosomonas europaea/mobilis lineage are chiefly responsible for catalyzing ammonia oxidation at high ALRs.

Designing Multi-Stage 2 A/O-MBR Processes for a Higher Removal Rate of Pollution in Wastewater

Multi-stage A/O-MBR processes were designed to improve wastewater treatment efficiency; three different designs were carried out and compared in this study. The 2(A/O)-MBR process, i.e., with two sets of anoxic/oxic tanks in series, showed better effluent quality than A/O-MBR and 3(A/O)-MBR processes. The removal rates of COD, NH4+-N, TP and TN were 95.29%, 89.47%, 83.55% and 78.58%, respectively, complying satisfactorily with China’s urban sewage treatment plant pollutant discharge standards. In terms of membrane fouling, the 3(A/O)-MBR process demonstrated the lowest fouling propensity. The microbial community structure in each bioreaction tank was analyzed, the results from which matched with the process efficiency and fouling behavior.

Biotreatment of petroleum refinery wastewater in vertical surface-flow constructed wetland vegetated with Eichhornia crassipes: lab-scale experimental and kinetic modelling

The objectives of this study were to evaluate the potential of vertical surface flow constructed wetland (VSF-CW) vegetated with Eichhornia crassipes to treat petroleum refinery secondary wastewater under tropical conditions. Also, to provide a comparative evaluation of biotreatment kinetic models (traditional first order and other alternative kinetic models) proposed to describe the removal kinetics of organics (biochemical oxygen demand (BOD) and chemical oxygen demand (COD)), nitrate-nitrogen and total petroleum hydrocarbons (TPH) in wetland systems. The refinery secondary wastewater was characterized and treated in five VSF-CWs. Eichhornia crassipes were planted in three VSF-CWs and the remaining two VSF-CWs served as the unvegetated control. The wastewater relatively had high levels of turbidity (18.30 ± 3.88 NTU), BOD (20.40 ± 2.20 mg/L), COD (86 ± 6.0 mg/L), TPH (16.6 ± 1.76 mg/L), oil and grease (18.4 ± 2.00 mg/L), heavy metals (Cadmium (0.034 ± 0.01 mg/L), Lead (0.12 ± 0.05 mg/L), Chromium (0.47 ± 0.01 mg/L), Iron (1.54 ± 0.25 mg/L) and Nickel (0.09 ± 0.01 mg/L)) and Chloride (1412 ± 9.6 mg/L). The vegetated VSF-CWs significantly performed better than the unvegetated control and resulted in the removal efficiencies of 91.5% turbidity, 94.6% BOD₅, 80.2% COD, 92.6% TPH, 90.4% oil and grease, 94% cadmium, 92.5% lead, 93% chromium, 94.8% iron, 92.2% nickel, and 57.7% chloride. The results suggested that the proposed kinetic models were applicable for understanding the removal mechanisms of organics, nitrate-nitrogen and hydrocarbons in VSF-CW systems. Thus, Eichhornia crassipes planted VSF-CW has the potential of treating refinery secondary wastewater to discharge permissible limits.

Exploring the linkage between bacterial community composition and nitrous oxide emission under varied DO levels through the alternation of aeration rates in a lab-scale anoxic-oxic reactor

Dissolved oxygen (DO) level is crucial in shaping bacterial community and impacts biological nitrogen removal and nitrous oxide (N₂O) emission. Online gaseous and off-line dissolved N₂O under varying DO levels through aeration rate alternations were measured in lab-scale anoxic-oxic reactors. It showed that sharp changes in DO levels caused immediate N₂O emission increase, while the total average gaseous N₂O emission stabilized at 0.011%, 0.046%, 0.308% and 0.229% of influent nitrogen as DO in oxic tanks averaged at 0.58, 1.67, 3.2 and 6.12 mg/L, respectively. Process with an average DO concentration of 1.67 mg/L had the highest microbial diversity and relative abundances of potential denitrifers and ammonia-oxidizing bacteria (NOB), while the least ammonia-oxidizing bacteria (AOB) were detected, which contributed to efficient nitrogen removal and minor N₂O emission. In conclusion, regulation and control of denitrifiers, AOB and NOB with the determination of a proper DO set point is feasible for N₂O mitigation.

A review on the applications of ultrasonic technology in membrane bioreactors

Membrane bioreactors (MBRs) have received increasing attention in the field of wastewater treatment in recent years. However, membrane fouling is the main problem of MBRs, limiting their widespread and large applications. Membrane cleaning methods can be mainly classified into four types including chemical, physical, physico-chemical and biological clean the fouled membrane. In recent years, ultrasonication has been reported as a promising cleaning technique for the membranes fouled in MBRs. Ultrasonic irradiation can clean the fouled membrane by creating important physical phenomena including microjets, microstreams and shock waves. Moreover, the ultrasonic method can be combined with other cleaning methods e.g. chemical cleaning and backwashing in order to improve the cleaning efficiency. It should be noted that the application of ultrasonic in the MBR system is not limited to the cleaning of membrane. The pretreatment of the wastewater by ultrasonic irradiation or ultrasound coupled with other methods, e.g. ozonation, prior to MBR system, can decrease the organic loading of the wastewater and subsequently postpone the fouling of the membrane. This paper critically reviews the recent advances in the applications of ultrasound in MBR systems. Emerging issues associated with application of on-line ultrasound and also hybrid on-line ultrasound for controlling the membrane fouling in MBR systems are critically reviewed. Moreover, application of the ultrasound in ex-situ form for cleaning the fouled membranes and pretreatment of wastewater prior to the MBR system is discussed.

Temporal variation of bacterial population and response to physical and chemical parameters along a petrochemical industry wastewater treatment plant

The petrochemical industry has played a considerable role in generation and release of waste in the environment. Activated sludge and facultative lagoons are commonly used for domestic and industrial wastewater treatment due to their low-cost and minimal need for operational requirements. Microorganisms present in wastewater treatment plant (WWTP) are responsible for most nutrient removal. In this study, microbiological and physicochemical parameters were used to estimate changes in bacterial community in a petrochemical industrial WWTP. The activated sludge was the place with higher heterotrophic bacterial quantification. Denitrifying bacteria was reduced at least 5.3 times throughout all collections samples. We observe a decrease in the total Kjeldahl nitrogen, oxygen demand and phosphate throughout the WWTP. In this work, we also use Matrix-Assisted Laser Desorption Ionisation-Time-of-Flight Mass Spectrometry (MALDI-TOF MS) for bacteria isolates identification comparing with 16S rDNA sequencing. The MALDI-TOF MS allowed the identification of 93% of the isolates and only 5% show different results from 16S rDNA sequencing showing that the MALDI-TOF MS can be a tool for identifying environmental bacteria. The observation of microbial community dynamics in the WWTP is important in order to understand the functioning of the ecological structure formed in a specific environment.

Coupled anaerobic ammonium oxidation and hydrogenotrophic denitrification for simultaneous NH4-N and NO3-N removal

Nitrate removal during anaerobic ammonium oxidation (anammox) treatment is a concern for optimization of the anammox process. This study demonstrated the applicability and long-term stability of the coupled anammox and hydrogenotrophic denitrification (CAHD) process as an alternative method for nitrate removal. Laboratory-scale fixed bed anammox reactors (FBR) supplied with H₂ to support denitrification were operated under two types of synthetic water. The FBRs showed simultaneous NH₄-N and NO₃-N removal, indicating that the CAHD process can support NO₃-N removal during the anammox process. Intermittent H₂ supply (e.g. 5 mL/min for a 1-L reactor, 14/6-min on/off cycle) helped maintain the CAHD process without deteriorating its performance under long-term operation and resulted in a nitrogen removal rate of 0.21 kg-N/m³/d and ammonium, nitrate, and dissolved inorganic nitrogen removal efficiencies of 73.4%, 80.4%, and 77%, respectively. The microbial community structure related to the CAHD process was not influenced by changes in influent water quality, and included the anammox bacteria 'Candidatus Jettenia' and a Sulfuritalea hydrogenivorans-like species as the dominant bacteria even after long-term reactor operation, suggesting that these bacteria are key to the CAHD process. These results indicate that the CAHD process is a promising method for enhancing the efficiency of anammox process.

Counter-diffusion biofilms have lower N2O emissions than co-diffusion biofilms during simultaneous nitrification and denitrification: Insights from depth-profile analysis

The goal of this study was to investigate the effectiveness of a membrane-aerated biofilm reactor (MABR), a representative of counter-current substrate diffusion geometry, in mitigating nitrous oxide (N₂O) emission. Two laboratory-scale reactors with the same dimensions but distinct biofilm geometries, i.e., a MABR and a conventional biofilm reactor (CBR) employing co-current substrate diffusion geometry, were operated to determine depth profiles of dissolved oxygen (DO), nitrous oxide (N₂O), functional gene abundance and microbial community structure. Surficial nitrogen removal rate was slightly higher in the MABR (11.0 ± 0.80 g-N/(m² day) than in the CBR (9.71 ± 0.94 g-N/(m² day), while total organic carbon removal efficiencies were comparable (96.9 ± 1.0% for MABR and 98.0 ± 0.8% for CBR). In stark contrast, the dissolved N₂O concentration in the MABR was two orders of magnitude lower (0.011 ± 0.001 mg N₂O-N/L) than that in the CBR (1.38 ± 0.25 mg N₂O-N/L), resulting in distinct N₂O emission factors (0.0058 ± 0.0005% in the MABR vs. 0.72 ± 0.13% in the CBR). Analysis on local net N₂O production and consumption rates unveiled that zones for N₂O production and consumption were adjacent in the MABR biofilm. Real-time quantitative PCR indicated higher abundance of denitrifying genes, especially nitrous oxide reductase (nosZ) genes, in the MABR versus the CBR. Analyses of the microbial community composition via 16S rRNA gene amplicon sequencing revealed the abundant presence of the genera Thauera (31.2 ± 11%), Rhizobium (10.9 ± 6.6%), Stenotrophomonas (6.8 ± 2.7%), Sphingobacteria (3.2 ± 1.1%) and Brevundimonas (2.5 ± 1.0%) as potential N₂O-reducing bacteria in the MABR.

Performance evaluation of semi continuous vertical flow constructed wetlands (SC-VF-CWs) for municipal wastewater treatment

The present study demonstrated the understating of municipal wastewater treatment in five types of CWs operated under semi continuous vertical flow mode. All CWs treatment conditions show the significantly lower pollutants concentrations. The average NH₄⁺-N, TN, NO₂^--N, NO₃^--N, SO₄^2-, and PO₄^3- removal efficiency in the ISs-CWs were 83.60%, 82.43%, 15.61%, 48.93%, 80.45%, and 78.94% respectively. The average NO₂^--N removal efficiency shows that highest nitrite accumulation occurred in the Cont-CWs followed by C-CWs. The lowest increase in the biomass (127.5%) was observed in the Eichhornia crassipes planted in the ISs-CWs. The ISs filtration barrier created in the constructed wetlands was sufficient enough to remove all the pollutants. Principal components EFA 2D deformation plots show the distribution of the various nitrogenous species in the constructed wetlands along different components.

Oxygen transfer dynamics and activated sludge floc structure under different sludge retention times at low dissolved oxygen concentrations

In activated sludge systems, the aeration process consumes the most energy. The energy cost can be dramatically reduced by decreasing the operating dissolved oxygen (DO) concentration. However, low DO may lead to incomplete nitrification and poor settling performance of activated sludge flocs (ASFs). This study investigates oxygen transfer dynamics and settling performances of activated sludge under different sludge retention times (SRTs) and DO conditions using microelectrodes and microscopic techniques. Our experimental results showed that with longer SRTs, treatment capacity and settling performances of activated sludge improved due to smaller floc size and less extracellular polymeric substances (EPS). Long-term low DO conditions produced larger flocs and more EPS per unit sludge, which produced a more extensive anoxic area and led to low oxygen diffusion performance in flocs. Long SRTs mitigated the adverse effects of low DO. According to the microelectrode analysis and fractal dimension determination, smaller floc size and less EPS in the long SRT system led to high oxygen diffusion property and more compact floc structure that caused a drop in the sludge volume index (SVI). In summary, our results suggested that long SRTs of activated sludge can improve the operating performance under low DO conditions.

Comparison of microbial communities of activated sludge and membrane biofilm in 10 full-scale membrane bioreactors

Operation of membrane bioreactors (MBRs) for wastewater treatment is hampered by the membrane biofouling resulting from microbial activities. However, the knowledge of the microbial ecology of both biofilm and activated sludge in MBRs has not been sufficient. In this study, we scrutinized microbial communities of biofilm and activated sludge from 10 full-scale MBR plants. Overall, Flavobacterium, Dechloromonas and Nitrospira were abundant in order of abundance in biofilm, whereas Dechloromonas, Flavobacterium and Haliscomenobacter in activated sludge. Community structure was analyzed in either biofilm or activated sludge. Among MBRs, as expected, not only diversity of microbial community but also its composition was different from one another (p < 0.05). Between the biofilm and activated sludge, community composition made significant difference, but its diversity measures (i.e., alpha diversity, e.g., richness, diversity and evenness) did not (p > 0.05). Effects of ten environmental factors on community change were investigated using Spearman correlation. MLSS, HRT, F/M ratio and SADm explained the variation of microbial composition in the biofilm, whereas only MLSS did in the activated sludge. Microbial networks were constructed with the 10 environmental factors. The network results revealed that there were different topological characteristics between the biofilm and activated sludge networks, in which each of the 4 factors had different associations with microbial nodes. These results indicated that the different microbial associations were responsible for the variation of community composition between the biofilm and activated sludge.

Bioaugmentation in a pilot-scale constructed wetland to treat domestic wastewater in summer and autumn

In order to determine whether bioaugmentation is an effective technique in wetlands before the plants were harvested, the nitrogen (N) removal from a constructed wetland (CW) planted with Phragmites was evaluated after inoculating with Paenibacillus sp. XP1 in Northern China. The experiment was loaded with secondary effluent of rural domestic wastewater (RDW) using the batch-loaded method for over a 17-day period in summer and autumn. Chemical oxygen demand (CODcr), ammonia nitrogen (NH3-N), and total nitrogen (TN) decreased significantly in the CW with Phragmites inoculated with Paenibacillus sp. XP1. Four days after treatments were set up, the removal efficiencies were found to be 76.2 % for CODcr, 83 % for NH3-N, and 63.8 % for TN in summer and 69.5 % for CODcr, 76.9 % for NH3-N, and 55.6 % for TN in autumn, which were higher than the control group without inoculation during the entire 17-day experiment. The inoculated bacteria did not have a noticeable effect on total phosphorus (TP) removal in autumn. However, bioaugmentation still keep a low P concentration in the whole CW. First-order kinetic model represented well the CODcr, TN, and TP decay in CWs with bioaugmentation, resulting in very good coefficients of determination, which ranged from 0.97 to 0.99. It indicated that bioaugmentation would be an effective treatment for pollutant removal from RDW in the CWs.

Functional diversity and dynamics of bacterial communities in a membrane bioreactor for the treatment of metal-working fluid wastewater

An extensive microbiological study has been carried out in a membrane bioreactor fed with activated sludge and metal-working fluids. Functional diversity and dynamics of bacterial communities were studied with different approaches. Functional diversity of culturable bacterial communities was studied with different Biolog™ plates. Structure and dynamics of bacterial communities were studied in culturable and in non-culturable fractions using a 16S rRNA analysis. Among the culturable bacteria, Alphaproteobacteria and Gammaproteobacteria were the predominant classes. However, changes in microbial community structure were detected over time. Culture-independent analysis showed that Betaproteobacteria was the most frequently detected class in the membrane bioreactor (MBR) community with Zoogloea and Acidovorax as dominant genera. Also, among non-culturable bacteria, a process of succession was observed. Longitudinal structural shifts observed were more marked for non-culturable than for culturable bacteria, pointing towards an important role in the MBR performance. Microbial community metabolic abilities assessed with Biolog™ Gram negative, Gram positive and anaerobic plates also showed differences over time for Shannon's diversity index, kinetics of average well colour development, and the intensely used substrates by bacterial community in each plate.

Full-scale bioreactor pretreatment of highly toxic wastewater from styrene and propylene oxide production

The wastewater originating from simultaneous production of styrene and propylene oxide (SPO) is classified as highly polluted with chemical oxygen demand level in the range 5965 to 9137mgL(-1)-as well as highly toxic. The dilution factor providing for a 10 percent toxic effect of wastewater samples in a test with Paramecium caudatum was 8.0-9.5. Biological approach for pretreatment and detoxification of the wastewater under full-scale bioreactor conditions was investigated. The number of suspended microorganisms and the clean up efficiency were increased up to 5.5-6.58×10(8)CFUmL(-1) and 88 percent, respectively during the bioreactor's operation. Isolates in the Citrobacter, Burkholderia, Pseudomonas, and Paracoccus genera were dominant in the mature suspended, as well as the immobilized microbial community of the bioreactor. The most dominant representatives were tested for their ability to biodegrade the major components of the SPO wastewater and evidence of their role in the treatment process was demonstrated. The investigated pretreatment process allowed the wastewater to be detoxified for conventional treatment with activated sludge and was closely related to the maturation of the bioreactor's microbial community.

Characterization of nitrifying microbial community in a submerged membrane bioreactor at short solids retention times

This study investigated the nitrifying bacterial community in membrane bioreactor (MBR) at short solids retention times (SRTs) of 3, 5 and 10 days. The denaturing gradient gel electrophoresis results showed that different types of ammonia-oxidizing bacteria (AOB) can survive at different operating conditions. The diversity of AOB increased as the SRT increased. The real-time PCR results showed that the amoA gene concentrations were similar when MBRs were stabilized, and it can be a good indicator of stabilized nitrification. The results of clone library indicated that Nitrosomonas was the dominant group of AOB in three reactors. The microarray results showed that Nitrospira was the dominant group of nitrite-oxidizing bacteria (NOB) in the system. All groups of AOB and NOB except Nitrosolobus and Nitrococcus were found in MBR, indicated that the nitrifying bacterial community structure was more complicated. The combination of some molecular tools can provide more information of microbial communities.

Comparative analysis of the enzyme activities and the bacterial community structure based on the aeration source supplied to an MBR to treat urban wastewater

A comparative analysis was performed in a pilot-scale membrane bioreactor (MBR) treating urban wastewater supplied with either pure oxygen (O2) or air, to assess the influence of each aeration source on the diversity and activity of the bacterial communities in the sludge. The MBR was operated in three experimental stages with different concentrations of volatile suspended solids (VSS) and temperature, and under both aeration conditions. α-Glucosidases, proteases, esterases and phosphatases were tested as markers of organic matter removal in the sludge, and the diversity of the bacterial community was analysed by fingerprinting (temperature-gradient gel electrophoresis of partially-amplified 16S-rRNA genes). Redundancy analysis (RDA) revealed that temperature and VSS concentration were the only factors that significantly influenced the levels of enzyme activities and the values of both the Shannon-Wiener diversity index (H') and the functional organisation index (Fo), while the bacterial community structure experienced significant changes depending on the aeration source supplied in each experimental stage.

Simultaneous removal of organic matter and nitrogen by a heterotrophic nitrifying-aerobic denitrifying bacterial strain in a membrane bioreactor

A heterotrophic nitrifying-aerobic denitrifying bacterial strain, Bacillus methylotrophicus L7, was inoculated solely into a submerged membrane bioreactor (MBR) for continuous treatment of artificial sewage. The running conditions were also optimized for improvement of the treatment efficiency. The results indicated that inoculation of this single strain in a single reactor under constant aerobic conditions resulted in simultaneous removal of organic matter and nitrogen, in striking contrast to traditional aerobic nitrification-anaerobic denitrification treatment system and the sequencing batch reactor (SBR) systems. The optimal running conditions for the MBR were dissolved oxygen (DO) 4.5 mg/L, pH 7.5, loading ammonia <100 mg/L, and C/N ratio 3.5. Under these conditions, the removal percentages of chemical oxygen demand (COD), NH4(+)-N, and TN as high as 96%, 77.5% and 53%, respectively, were achieved without nitrite accumulation.

Impact of food to microorganism (F/M) ratio and colloidal chemical oxygen demand on nitrification performance of a full-scale membrane bioreactor treating thin film transistor liquid crystal display wastewater

This study investigated impact of food to microorganism (F/M) ratio and colloidal chemical oxygen demand (COD) on nitrification performance in one full-scale membrane bioreactor (MBR) treating monoethanolamine (MEA)/dimethyl sulfoxide (DMSO)-containing thin film transistor liquid crystal display (TFT-LCD) wastewater. Poor nitrification was observed under high organic loading and high colloidal COD conditions, suggesting that high F/M ratio and colloidal COD situations should be avoided to minimize their negative impacts on nitrification. According to the nonmetric multidimensional scaling (NMS) statistical analyses on terminal restriction fragment length polymorphism (T-RFLP) results of ammonia monooxygenase (amoA) gene, the occurrence of Nitrosomonas oligotropha-like ammonia oxidizing bacteria (AOB) was positively related to successful nitrification in the MBR systems, while Nitrosomonas europaea-like AOB was positively linked to nitrification rate, which can be attributed to the high influent total nitrogen condition. Furthermore, Nitrobacter- and Nitrospira-like nitrite oxidizing bacteria (NOB) were both abundant in the MBR systems, but the continuously low nitrite environment is likely to promote the growth of Nitrospira-like NOB.

Micro-environment characteristics and microbial communities in activated sludge flocs of different particle size

Microorganisms in activated sludge flocs (ASF) play important roles in the wastewater treatment process. However, the interplay between micro-environmental variation and microbial responses within ASF is poorly understood. In this study, microelectrodes and molecular culture-independent techniques were applied to detect the internal environment, microbial composition, and distribution in flocs with different particle size. Results showed dissolved oxygen (DO) concentrations within the center of the flocs were less than at the surface, and the DO concentration distributions were distinct in flocs of different particle size. With floc particle size increasing from 100 to 250 μm, the DO concentrations in the floc centers decreased 10-55%, respectively, while no distinct change was observed in flocs of less than 100 μm. Similar phenomenon occurred for the distributions of NH(4)(+) and NO(3)(-) in flocs. Microbial structure indicated bacterial compositions and distributions were heterogeneous and responded to micro-environment variation in flocs of different particle size.

Nitrification performance and microbial ecology of nitrifying bacteria in a full-scale membrane bioreactor treating TFT-LCD wastewater

This study investigated nitrification performance and nitrifying community in one full-scale membrane bioreactor (MBR) treating TFT-LCD wastewater. For the A/O MBR system treating monoethanolamine (MEA) and dimethyl sulfoxide (DMSO), no nitrification was observed, due presumably to high organic loading, high colloidal COD, low DO, and low hydraulic retention time (HRT) conditions. By including additional A/O or O/A tanks, the A/O/A/O MBR and the O/A/O MBR were able to perform successful nitrification. The real-time PCR results for quantification of nitrifying populations showed a high correlation to nitrification performance, and can be a good indicator of stable nitrification. Terminal restriction fragment length polymorphism (T-RFLP) results of functional gene, amoA, suggest that Nitrosomonas oligotropha-like AOB seemed to be important to a good nitrification in the MBR system. In the MBR system, Nitrobacter- and Nitrospira-like NOB were both abundant, but the low nitrite environment is likely to promote the growth of Nitrospira-like NOB.

Impact of herbicide Ametryn on microbial communities in mixed liquor of a membrane bioreactor (MBR)

Ametryn, which is a second generation herbicide, was introduced to a lab-scale MBR at a concentration of 1mg/L and a 20-40% removal was observed at HRT ranging from 7.8 to 15.6h for an average influent Ametryn concentration of 0.8 mg/L. Components of EPS (protein and carbohydrates) increased in the bioreactor and the observed biomass production reduced after the addition of Ametryn. In a batch study, GAC was added to MBR mixed liquor and removal of Ametryn via biodegradation and adsorption were measured. Five common bacterial colony types (Gram negative and positive bacilli and Gram negative cocci) were identified and three of these were resistant to Ametryn up to 5mg/L. GAC was found to be a very effective Ametryn adsorption medium and in some occasions Ametryn may have acted as a nutrient source for bacteria.

Bacterial community structure and enzyme activities in a membrane bioreactor (MBR) using pure oxygen as an aeration source

A pilot-scale membrane bioreactor was used to treat urban wastewater using pure oxygen instead of air as a source of aeration, to study its influence on bacterial diversity and levels of enzyme activities (acid and alkaline phosphatases, glucosidase, protease, and esterase) in the sludge. The experimental work was developed in two stages influenced by seasonal temperature. Operational parameters (temperature, pH, BOD5, COD, total and volatile suspended solids) were daily monitored, and enzyme activities measured twice a week. Redundancy analysis (RDA) was used to reveal relationships between the level of enzyme activities and the variation of operational parameters, demonstrating a significant effect of temperature and volatile suspended solids. Bacterial diversity was analyzed by temperature-gradient gel electrophoresis of PCR-amplified partial 16S rRNA genes. Significant differences in community structure were observed between both stages. Sequence analysis revealed that the prevalent Bacteria populations were evolutively close to Alphaproteobacteria (44%), Betaproteobacteria (25%) and Firmicutes (17%).

Heterotrophic nitrification and aerobic denitrification by the bacterium Pseudomonas stutzeri YZN-001

A strain YZN-001 was isolated from swine manure effluent and was identified as Pseudomonas stutzeri. It can utilise not only nitrate and nitrite, but also ammonium. The strain had the capability to fully remove as much as 275.08 mg L(-1) NO(3)(-)-N and 171.40 mg L(-1) NO(2)(-)-N under aerobic conditions. Furthermore, At 30°C, the utilization of ammonium is approximately 95% by 18 h with a similar level removed by 72 h and 2 weeks at 10 and 4°C, respectively. Triplicate sets of tightly sealed serum bottles were used to test the heterotrophic nitrifying ability of P. stutzeri YZN-001. The results showing that 39% of removed NH(4)(+)-N was completely oxidised to nitrogen gas by 18 h. Indicating that the strain has heterotrophic nitrification and aerobic denitrification abilities, with the notable ability to remove ammonium at low temperatures, demonstrating a potential using the strain for future application in waste water treatment.

Influence of step increases in hydraulic retention time on (RS)-MCPP degradation using an anaerobic membrane bioreactor

The effects of different hydraulic retention time (HRT) on (RS)-MCPP utilisation was investigated by decreasing the feed flow rate in an anaerobic membrane bioreactor (AnMBR). Results showed an average COD removal efficiency of 91.4%, 96.9% and 94.4% when the reactor was operated at HRT 3, 7 and 17 d, respectively. However, when the HRT was reduced to 1d, the COD removal efficiency declined to just only 60%, confirming the AnMBR is stable to a large transient hydraulic shock loads. The (RS)-MCPP removal efficiency fluctuated from 6% to 39% at HRT 3 d, however when it was increased to 7 and 17 d, the removal efficiency increased to an average of 60% and 74.5%. In addition, (RS)-MCPP specific utilisation rates (SUR) were dependent on the HRT and gradually improved from 18 to 43 μg mg VSS(-1) d(-1) as flow rate increased.

Effects of temperature and temperature shock on the performance and microbial community structure of a submerged anaerobic membrane bioreactor

Effects of temperature and temperature shock on the performance and microbial community structure of a submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping pressate were studied for 416 days. The results showed that the SAnMBR system were highly resilient to temperature variations in terms of chemical oxygen demand (COD) removal. The residual COD in treated effluent was slightly higher at 55 °C than that at 37 and 45 °C. There were no significant changes in biogas production rate and biogas composition. However, temperature shocks resulted in an increase in biogas production temporarily. The SAnMBR could tolerate the 5 and 10 °C temperature shocks at 37 °C and the temperature variations from 37 to 45 °C. The temperature shock of 5 and 10 °C at 45 °C led to slight and significant disturbance of the performance, respectively. Temperature affected the richness and diversity of microbial populations.