Bioaugmentation treatment for coking wastewater containing pyridine and quinoline in a sequencing batch reactor

E-peroxone with a novel GDE decorated with hydrophobic membrane for the degradation of pyridine: Stability, byproducts and toxicity

E-peroxone process is an emerging electrochemical oxidation process, based on ozone and the in-situ cathodic generation of H2O2, but the stability of cathode is one of the key restraining factors. In this study, we designed a multilayer gas diffusion electrode (GDE) decorated with a commercial hydrophobic membrane for the degradation of pyridine. It was found that a proper control of membrane pore sizes and hot-pressing temperature can significantly promote the GDE stability. Subsequently, key operational parameters of the constructed E-peroxone system were investigated, including the ozone concentration, current density, pH value, electrolyte type and initial concentration of pyridine. The degradation pathways were proposed according to six identified transformation products. The toxicity variation along the degradation progress was evaluated with microbial respiration tests and Toxicity Estimation Software Tool (T.E.S.T.) calculation and an efficient detoxification capacity of E-peroxone was observed. This research provides a theoretical basis and technical support for the development of highly efficient and stable E-peroxone system for the elimination of toxic organic contaminants.

New insights into the typical nitrogen-containing heterocyclic compound-quinoline degradation and detoxification by microbial consortium: Integrated pathways, meta-transcriptomic analysis and toxicological evaluation

As the primary source of COD in industrial wastewater, quinoline has aroused increasing attention because of its potential teratogenic, carcinogenic, and mutagenic effects in the environment. The activated sludge isolate quinoline-degrading microbial consortium (QDMC) efficiently metabolizes quinoline. However, the molecular underpinnings of the degradation mechanism of quinoline by QDMC have not been elucidated. High-throughput sequencing revealed that the dominant genera included Diaphorobacter, Bacteroidia, Moheibacter and Comamonas. Furthermore, a positive strong correlation was observed between the key bacterial communities (Diaphorobact and Bacteroidia) and quinoline degradation. According to metatranscriptomics, genes associated with quorum sensing, ABC transporters, component systems, carbohydrate, aromatic compound degradation, energy metabolism and amino metabolism showed high expression, thus improving adaptability of microbial community to quinoline stress. In addition, the mechanism of QDMC in adapting and resisting to extreme environmental conditions in line with the corresponding internal functional properties and promoting biogegradation efficiency was illustrated. Based on the identified products, QDMC effectively mineralized quinoline into low-toxicity metabolites through three major metabolic pathways, including hydroxyquinoline, 1,2,3,4-H-quinoline, 5,6,7,8-tetrahydroquinoline and 1-oxoquinoline pathways. Finally, toxicological, genotoxicity and phytotoxicity studies supported the detoxification of quinoline by the QDMC. This study provided a promising approach for the stable, environmental-friendly and efficient bioremediation applications for quinoline-containing wastewater.

Enhanced treatment of synthetic wastewater by bioaugmentation with a constructed consortium

Bioaugmentation by adding well-functioning mixed microorganism consortia represents a potentially useful approach to improve contaminant removal in wastewater treatment plants (WWTPs). However, unfavorable environmental conditions (i.e., low temperatures) can severely inhibit microbial activity, drawing our attention to constructing cold-tolerant microorganism preparations and investigating their availability in practical applications. Here we screened four in situ functional isolates from the activated sludge of secondary sedimentation tanks in WWTPs to construct a psychrophilic microbial consortium, which was used to perform bioaugmentation for enhanced removal of nitrogen and phosphorus under low temperatures. The consortium was established by cocultivation of four isolates, characterized by 16 S rRNA as the COD-degrading bacterium Aeromonas sp. Z3, aerobic denitrifying bacterium Acinetobacter sp. HF9, nitrifying bacterium Klebsiella sp. X8, and polyphosphate-accumulating bacterium Pseudomonas sp. PC5 respectively. The microorganism preparation was composed of Z3, HF9, X8, and PC5 under the ratio of 1: 1: 3: 1, which can exert optimal pollutant removal under the conditions of 12 °C, 6.0-9.0 pH, 120-200 r‧min-1, and a dosage of 5% (V/V). A 30-day continuous operation of the bioaugmented and control sequencing batch reactors (SBRs) was investigated, and the bioaugmented SBR showed a shorter start-up stage and a more stable operating situation. Compared to the control SBR, the COD, NH4+-N, TN, and TP removal efficiency of the bioaugmented SBR increased by an average of 7.95%, 9.05%, 9.54%, and 7.45% respectively. The analysis of the microbial community revealed that the introduced isolates were dominant in the activated sludge and that functional taxa such as Proteobacteria, Bacteroidota, and Actinobacteria were further enriched after a period of bioaugmentation. The study provides some basis and guidance for the practical application of how to strengthen the stable operation of WWTPs under low temperatures.

Low-temperature synthesis of functionalized activated carbon from blackboard (Alstonia scholaris) with improved selectivity for 2-methylpyridine removal: batch and column analyses

Coal tar industry has been reported to discharge 2-methylpyridine (2Mp) in concentrations up to 150 mg L^-1. For removal of 2Mp, activated carbon was synthesized from blackboard tree ground bark (BA) by the novel technique of prior cooling (which helped decrease heat generation and volatile gas emission). The material was successfully functionalized with carboxylic group which enhanced 2Mp uptake. Batch sorption of 2Mp was carried out on both BA and carboxyl functionalized BA (CFA). Acetonitrile-water (55:45) was used as eluent in uHPLC quantification of 2Mp. Interaction mechanism of 2Mp with both sorbents was studied by using characterization techniques (SEM, FTIR and EDS). Carboxyl groups present on CFA were found to interact with 2Mp molecules, leading to their removal from synthetic solution. Carboxylation helped in lowering the intrinsic moisture content of the sorbent. Proton leaching from carboxyl groups of CFA was found to be negligible. Specific surface areas for CFA and BA were found as 211.15 m² g^-1 and 156.32 m² g^-1, respectively. Batch experimentation showed that CFA had twice the adsorption capacity compared to BA (27.0 and 15.5 mg g^-1, respectively). Pseudo-second-order kinetics and Langmuir isotherm-based equilibria were observed. Intraparticle diffusion was the rate-limiting step. Top-down fixed bed studies were performed using a 2-cm-diameter column by varying flow rate, bed depth and 2Mp concentration, respectively. The Thomas model could successfully emulate the steep slopes of the breakthrough curves, implying good sorbent saturation.

Advances in treatment of coking wastewater - a state of art review

Coking wastewater poses a serious threat to the environment due to the presence of a wide spectrum of refractory substances such as phenolic compounds, polycyclic aromatic hydrocarbons and heterocyclic nitrogenous compounds. These toxic substances are difficult to treat using conventional treatment methods alone. In recent years much attention has been given to the effective treatment of coking wastewater. Thus, this review seeks to provide a brief overview of recent developments that have taken place in the treatment of coking wastewater. In addition, this article addresses the complexity and the problems associated with treatment followed by a discussion on biological methods with special focus on bioaugmentation. As coking wastewater is refractory in nature, some of the studies have been related to improving the biodegradability of wastewater. The final section focuses on the integrated treatment methods that have emerged as the best solution for tackling the highly unmanageable coking wastewater. Attention has also been given to emerging microwave technology which has tremendous potential for treatment of coking wastewater.

Biological detoxification and decolorization enhancement of azo dye by introducing natural electron mediators in MFCs

Reactive red 2 (RR2) is a highly recalcitrant and toxic azo dye that can cause the collapse of biological treatment system. Although MFC can decolorize RR2 effectively, its performance is still inevitably affected by toxicity. Anthraquinone can enhance MFCs' performance through mediating electron transfer. In this study, an anthraquinone-rich natural plants (B.rheum (Rheum offcinale Baill)) was extracted and then added to MFCs. The optimal dosage was selected and the enhanced effects were investigated. The results showed that adding 5%(V/V) extract resulted in the optimal performance elevation of MFC. When 5% extract was added together with RR2, 15.63% and 1.33-fold improvement in RR2 decolorization efficiency and rate were achieved compared with the control group. Meanwhile, higher power density (2.75 W/m³), coulombic efficiency (6.45%), and lower internal resistance (233.69 Ω) were also observed when 5% B.rheum extract and RR2 were added. B.rheum extract in MFCs enhanced microbial activity and enriched the dye-degrading microorganisms, such as Enterobacter, Raoultella, Comamonas and Shinella. B.rheum extract acts as "antidote" in alleviating the biotoxicity of RR2 was firstly illustrated in this study. The results provided a new strategy for using plant-source electron mediators to simultaneously improve biological detoxification, bioelectricity generation and dye decolorization in bioelectrochemical system.

Anaerobic biotransformation and potential impact of quinoline in an anaerobic methanogenic reactor treating synthetic coal gasification wastewater and response of microbial community

Phenolic and quinoline compounds are the most primary organic pollutants in coal gasification wastewater (CGW), but the biotransformation of quinoline compounds under methanogenic condition and their potential impacts on treatment performance of CGW are still unclear. Anaerobic biotransformation pathways of quinoline in an upflow anaerobic sludge blanket reactor treating synthetic CGW and response of microbial community were firstly investigated. The result indicated that the degradation of 2(1 H)-quinolinone was the rate-limiting step for the complete conversion of quinoline under methanogenic condition. The reactor performed stably at total phenols concentration of 1000 mg L^-1 with a gradual increase of quinoline concentration from 100 to 600 mg L^-1. However, the reactor performance was rapidly deteriorated from 98% of COD removal to about 80% at quinoline concentration of 1200 mg L^-1 resulting from the accumulation of 2(1 H)-quinolinone. Correspondingly, phenol utilization rate of sludge was significantly reduced by 61% while quinoline utilization rate of sludge was increased by 132%. As phenol degraders, Syntrophorhabdus gradually predominated along with the increase of quinoline concentration, but Syntrophus declined inversely. Compared with syntrophs, acetotrophic methanogens could quickly adapt to quinoline toxicity and tolerate higher quinoline stress. Therefore, anaerobic digestion is an effective method for eliminating quinoline and phenol in CGW.

Characterisation of thiocyanate degradation in a mixed culture activated sludge process treating coke wastewater

Microbial degradation of thiocyanate (SCN^-) has been reported to suffer from instability highlighting the need for improved understanding of underlying mechanisms and boundaries. Respirometry, batch tests and DNA sequencing analysis were used to improve understanding of a mixed culture treating coke wastewater rich in SCN^-. An uncultured species of Thiobacillus was the most abundant species (26%) and displayed similar metabolic capabilities to Thiobacillus denitrificans and Thiobacillus thioparus. Thiocyanate was hydrolysed/oxidised to NH₄⁺-N, HCO₃^- and SO₄^2-. Nevertheless, at 360-2100 mg SCN^-/L a breakdown in the degradation pathway was observed. Respirometry tests demonstrated that NH₄⁺-N was inhibitory to SCN^- degradation (IC₅₀: 316 mg/L). Likewise, phenol (180 mg/L) and hydroxylamine (0.25-16 mg/L) reduced SCN^- degradation by 41% and ca. 7%, respectively. The understanding of the SCN^- degradation pathways can enable stable treatment efficiencies and compliance with effluent of <4 mg SCN/L, required by the Industrial Emissions Directive.

Nitrogen removal from coke making wastewater through a pre-denitrification activated sludge process

Under the Industrial Emissions Directive (IED), coke production wastewater must be treated to produce an effluent characterised by a total nitrogen (TN) <50 mg/L. An anoxic-aerobic activated sludge pilot-plant (1 m³) fed with coke production wastewater was used to investigate the optimal operational requirements to achieve such an effluent. The loading rates applied to the pilot-plant varied between 0.198-0.418 kg COD/m³.day and 0.029-0.081 kg TN/m³.day, respectively. The ammonia (NH₄⁺-N) removals were maintained at 96%, after alkalinity addition. Under all conditions, phenol and SCN^- remained stable at 96% and 100%, respectively with both being utilised as carbon sources during denitrification. The obtained results showed that influent soluble chemical oxygen demand (sCOD) to TN ratio of should be maintained at >5.7 to produce an effluent TN <50 mg/L. Furthermore, nitrite accumulation was observed under all conditions indicating a disturbance to the denitrification pathway. Overall, the anoxic-aerobic activated sludge process was shown to be a robust and reliable technology to treat coke making wastewater and achieve the IED requirements. Nevertheless, the influent to the anoxic tank should be monitored to ensure a sCOD:TN ratio >5.7 or, alternately, the addition of an external carbon source should be considered.

Azo dye as part of co-substrate in a biofilm electrode reactor-microbial fuel cell coupled system and an analysis of the relevant microorganisms

In general, refractory organics were hardly used as co-substrate in bioelectrochemical system. This study established a coupled bioelectrochemical system composed of a biofilm electrode reactor and a microbial fuel cell for using the azo dye X-3B as part of co-substrate. The two units degraded the azo dye X-3B stepwise while using it as part of co-substrate. Our results indicated that the removal efficiency of X-3B increased 28.5% using the coupled system compared with a control system. Moreover, the addition of the co-substrate glucose, which was necessary for MFC electricity generation, was reduced on the premise of stable removal efficiency in the coupled system to prevent resource waste due to using X-3B as part of co-substrate. The intermediate products of X-3B degradation were further explored using gas chromatography-mass spectrometry and a X-3B degradation pathway was proposed at the same time. Microbial communities were analyzed, illustrating that the mechanism of X-3B degradation was dependent on bioelectrochemistry rather than on microbial degradation.

Isolation and characterization of organic matter-degrading bacteria from coking wastewater treatment plant

As a step toward bioaugmentation of coking wastewater treatment 45 bacteria strains were isolated from the activated sludge of a coking wastewater treatment plant (WWTP). Three strains identified as Bacillus cereus, Pseudomonas synxantha, and Pseudomonas pseudoaligenes exhibited high dehydrogenase activity which indicates a strong ability to degrade organic matter. Subsequently all three strains showed high naphthalene degradation abilities. Naphthalene is a refractory compound often found in coking wastewater. For B. cereus and P. synxantha the maximum naphthalene removal rates were 60.4% and 79.8%, respectively, at an initial naphthalene concentration of 80 mg/L, temperature of 30 °C, pH of 7, a bacteria concentration of 15% (V/V), and shaking speed of 160 r/min. For P. pseudoaligenes, the maximum naphthalene removal rate was 77.4% under similar conditions but at 35 °C.

Bioaugmentation of a continuous-flow self-forming dynamic membrane bioreactor for the treatment of wastewater containing high-strength pyridine

For the treatment of high-strength pyridine containing wastewater, a bioaugmented continuous-flow self-forming dynamic membrane bioreactor (CSFDMBR), which was consisted of a continuous flow airlift reactor (CFAR) and a dynamic membrane bioreactor (DMBR), was developed in this study. The results indicated that through the bioaugmentation by Rhizobium sp. NJUST18, CSFDMBR could be successfully started, which was confirmed by complete removal of pyridine, efficient nitrification, and significant increase of biomass. Pyridine could be effectively degraded in the CSFDMBR even at influent pyridine loading rate as high as 9.0 kg m^-3 day^-1, probably due to the efficient biomass retention in the CSFDMBR, which could be attributed to the formation of aerobic granules and the key role of dynamic membrane. CSFDMBR presented good polishing performance in treating pyridine wastewater, with effluent total organic carbon (TOC) and turbidity as low as 22.5 ± 6.8 mg L^-1 and 3.8 ± 0.5 NTU, respectively. Membrane fouling could be effectively controlled, as indicated by backwash period as long as 60 days. The observed efficient performance highlights the potential for the full-scale application of the bioaugmented CSFDMBR, particularly for highly recalcitrant pollutant removal.

Quinoline-degrading strain Pseudomonas aeruginosa KDQ4 isolated from coking activated sludge is capable of the simultaneous removal of phenol in a dual substrate system

Quinoline is a refractory organic compound in the treatment of coking wastewater. The isolation of high efficiency quinoline-degrading bacteria from activated sludge and the evaluation of their degradation characteristics in the presence of phenol or in the actual coking wastewater are important for the improvement of effluent quality. The novel bacterial strain Pseudomonas aeruginosa KDQ4 was isolated from a quinoline enrichment culture obtained from the activated sludge of a coking wastewater treatment plant. The optimum temperature and initial pH for quinoline degradation were 33-38°C and 8-9, respectively. KDQ4 completely degraded 400 mg/L of quinoline within 24 h and 800 mg/L of phenol within 30 h. In the dual-substrate system, the removal efficiencies of quinoline and phenol at the same initial concentration (200 mg/L) by KDQ4 were 89% and 100% within 24 h, respectively, indicating that KDQ4 could simultaneously and quickly degrade quinoline and phenol in a coexistence system. Moreover, KDQ4 was able to adapt to actual coking wastewater containing high quinoline and phenol concentrations and rapidly remove them. KDQ4 also exhibited heterotrophic nitrification and aerobic denitrification potential under aerobic conditions. These results suggested a potential bioaugmentation role for KDQ4 in the removal of nitrogen-heterocyclic compounds and phenolics from coking wastewater.

Bioaugmentation: An Emerging Strategy of Industrial Wastewater Treatment for Reuse and Discharge

A promising long-term and sustainable solution to the growing scarcity of water worldwide is to recycle and reuse wastewater. In wastewater treatment plants, the biodegradation of contaminants or pollutants by harnessing microorganisms present in activated sludge is one of the most important strategies to remove organic contaminants from wastewater. However, this approach has limitations because many pollutants are not efficiently eliminated. To counterbalance the limitations, bioaugmentation has been developed and consists of adding specific and efficient pollutant-biodegrading microorganisms into a microbial community in an effort to enhance the ability of this microbial community to biodegrade contaminants. This approach has been tested for wastewater cleaning with encouraging results, but failure has also been reported, especially during scale-up. In this review, work on the bioaugmentation in the context of removal of important pollutants from industrial wastewater is summarized, with an emphasis on recalcitrant compounds, and strategies that can be used to improve the efficiency of bioaugmentation are also discussed. This review also initiates a discussion regarding new research areas, such as nanotechnology and quorum sensing, that should be investigated to improve the efficiency of wastewater bioaugmentation.

Electrochemical degradation of pyridine by Ti/SnO2-Sb tubular porous electrode

Diffusion in electrochemistry is a critical issue for water purification. Electrocatalytic reactor system in improving water quality is a useful way to induce convection to enhance diffusion. This study focuses on the preparation and the characterization of Ti/SnO2-Sb tubular porous electrode for degrading pyridine wastewater. The electrode as an anode in reactor system is prepared by coating SnO2-Sb as an electro-catalyst via Pechini method on the tubular porous Ti. Scanning Electron Microscopy, Energy Dispersive Spectrum, X-ray Diffraction and Pore Distribution are employed to evaluate the structure and morphology of the electrodes coatings, and Linear Sweep Voltammetry and Cyclic Voltammetry are used to illustrate the electrochemical properties of the electrodes coatings. Furthermore, the electrochemical oxidation performance of Ti/SnO2-Sb tubular porous electrode is characterized by degrading pyridine wastewater. The effects of flow and static pattern, initial pyridine concentration, supporting electrolyte concentration, current density and pH on the performance of the reactor were investigated in the electrocatalytic reactor system. The results indicated that the removal ratio of pyridine reaches maximum which is 98% under the optimal operation conditions, that are 100 mg L(-1) initial pyridine concentration, 10 g L(-1) supporting electrolyte concentration, 30 mA cm(-2) current density and pH 3. Transition state calculation based on the density function theory was combined with High Performance Liquid Chromatography, Gas Chromatography and Ionic Chromatography results to describe the pathway of pyridine degradation.

Cooperative Mn(II) oxidation between two bacterial strains in an aquatic environment

In natural or engineered environments, diverse interspecific interactions among two or more microbial taxa may profoundly affect the transformation of organic compounds in the media. Little is known, however, about how these organisms and interactions affect the transformation of heavy metals. Recently, we found an interaction between two non-Mn(II)-oxidizing (when in monoculture) strains, Arthrobacter sp. QXT-31 and Sphingopyxis sp. QXT-31, which, when cultured in combination, resulted in Mn(II)-oxidizing activity in synthetic media. In order to study the occurrence likelihood of cooperative Mn(II) oxidation in natural water and discharged effluent, we initially identified an optimal ratio of the two strains in a combined culture, as well as the impacts of external factors on the cooperative oxidation. Once preferred initial conditions were established, we assessed the degree and rate of Mn(II) oxidation mediated by the combined QXT-31 strains (henceforth referred to as simply 'QXT-31') in three different water types: groundwater, domestic sewage and coking wastewater. Results showed that Mn(II) oxidation only occurred when the two strains were within a specific ratios range. When introduced to the test waters at the preferred ratio, QXT-31 demonstrated high Mn(II)-oxidizing activities, even when relative abundance of QXT-31 was very low (roughly 1.6%, calculated by 454 pyrosequencing events on 16S rcDNA). Interestingly, even under low relative abundance of QXT-31, removal of total organic carbon and total nitrogen in the test waters was significantly higher than the control treatments that were not inoculated with QXT-31. Data from our study indicate that cooperative Mn(II) oxidation is most likely to occur in natural aquatic ecosystems, and also suggests an alternative method to treat wastewater containing high concentrations of Mn(II).

Long-term impact of salinity on the performance and microbial population of an aerobic granular reactor treating a high-strength aromatic wastewater

The effect of salinity over granular biomass treating a mixture of aromatic compounds (phenol, o-cresol and p-nitrophenol) was evaluated in a continuous airlift reactor. To mimic an industrial wastewater, increasing concentrations (from 2.0 to 29.0 g salts L(-1)) of a mixture of salts (MgSO4, NaCl, KCl, CaCl2 and NaHCO3) were introduced in the influent. The gradual salinity increase led to a good acclimation of the biomass obtaining complete biodegradation of the aromatic compounds and no accumulation of metabolic intermediates. However, a deterioration of the morphology of aerobic granules with a complete loss of granulation after 125 days was produced at 29.0 g salts L(-1). At that moment, anaerobic granules were added to promote granulation and after 50 days new aerobic granules were formed. These new aerobic granules remained stable for more than 100 days at the highest salinity condition with 100% removal of the mixture of aromatic compounds.

Bioaugmentation with isolated strains for the removal of toxic and refractory organics from coking wastewater in a membrane bioreactor

The bioaugmentation strains for phenol, pyridine, quinoline, carbazole, and naphthalene degradation were employed to treat coking wastewater in a membrane bioreactor (MBR). The results showed that the bioaugmented MBR was much better in pollutant removal than that of the control MBR with conventional activated sludge. Compared to the control MBR, the bioaugmented MBR displayed an additional 3.2 mg/L of phenol, pyridine, quinoline, naphthalene and carbazole in total by the addition of the degrading strains. Also, about 10 % of the chemical oxygen demand in the effluent was further removed by the bioaugmentation. The pyrosequencing analysis of the sludge in the MBRs revealed that the microbial community shifted in response to the addition of the degrading strains. The diversity of the microbial community increased during the bioaugmentation, and some bacterial taxa favorable to the removal of toxic and refractory pollutants appeared in the bioaugmented MBR. The results indicated that the use of high-efficiency bacteria was a feasible method for industrial coking wastewater treatment.

Biodegradation characterization and immobilized strains' potential for quinoline degradation by Brevundimonas sp. K4 isolated from activated sludge of coking wastewater

A novel quinoline-degrading strain, named K4, was isolated from activated sludge of a coking wastewater treatment plant and identified as Brevundimonas sp. on the basis of its 16s rDNA gene sequence analysis. Its optimum temperature and pH for quinoline degradation were 30 °C and pH 9.0, respectively, and during the biodegradation process, at 100 mg/L initial quinoline concentration, an inoculation amount of 8% (OD600 of 0.23) was the optimal strain concentration. In addition, the kinetics of free K4 strains for quinoline degradation showed that it followed a zero-order equation. Furthermore, compared with free K4 strains, immobilized K4 strains' potential for quinoline degradation was investigated by adding both of them into SBR reactors for actual coking wastewater treatment on operation over 15 days. The results showed that bioaugmentation by both free and immobilized K4 strains enhanced quinoline removal efficiency, and especially, the latter could reach its stable removal after a shorter accommodation period, with 94.8% of mean quinoline removal efficiency.

Bioaugmentation with a pyridine-degrading bacterium in a membrane bioreactor treating pharmaceutical wastewater

The bacterial strain Paracoccus denitrificans W12, which could utilize pyridine as its sole source of carbon and nitrogen, was added into a membrane bioreactor (MBR) to enhance the treatment of a pharmaceutical wastewater. The treatment efficiencies investigated showed that the removal of chemical oxygen demand, total nitrogen, and total phosphorus were similar between bioaugmented and non-bioaugmented MBRs, however, significant removal of pyridine was obtained in the bioaugmented reactor. When the hydraulic retention time was 60 hr and the influent concentration of pyridine was 250-500 mg/L, the mean effluent concentration of pyridine without adding W12 was 57.2 mg/L, while the pyridine was degraded to an average of 10.2 mg/L with addition of W12. The bacterial community structure of activated sludge during the bioaugmented treatment was analyzed using polymerase chain reaction -denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that the W12 inoculum reversed the decline of microbial community diversity, however, the similarity between bacterial community structure of the original sludge and that of the sludge after bioaugmentation decreased steadily during the wastewater treatment. Sequencing of the DNA recovered from DGGE gel indicated that Flavobacteriaceae sp., Sphingobium sp., Comamonas sp., and Hyphomicrobium sp. were the dominant organisms in time sequence in the bacterial community in the bioaugmented MBR. This implied that the bioaugmentation was affected by the adjustment of whole bacterial community structure in the inhospitable environment, rather than being due solely to the degradation performance of the bacterium added.

Comparison of denitrifier communities in the biofilms of bioaugmented and non-augmented zeolite-biological aerated filters

The denitrifier communities of a bioaugmented and non-augmented zeolite-biological aerated filter (Z-BAFs) were investigated and compared because the bioaugmented Z-BAF provided better and more stable treatment efficiency for nitrate and nitrite removal. Terminal restriction fragment length polymorphism (T-RFLP) and reverse transcription T-RFLP (RT-T-RFLP) were applied to analyse the denitrifier community diversity in the biofilm collected from each Z-BAF. The results showed that the bioaugmentation technology favourably changed the indigenous denitrifier community and enhanced denitrification under nitrogen loading shocks. The cDNA clone libraries were developed to explore the active denitrifier community structures of both filters. The results showed that the active denitrifiers in both the bioaugmented and non-bioaugmented Z-BAF belonged to alpha-, beta- and gamma-proteobacteria. However, the sequence of the introduced denitrifier (Paracoccus sp. BW001) was not found in the clone library of the bioaugmented filter, which implied that the removal of nitrate and nitrite was attributed mainly to the indigenous denitrifiers in the adjusted bacterial community in the bioaugmented Z-BAF.

Experimental and mathematical methodology on the optimization of bacterial consortium for the simultaneous degradation of three nitrogen heterocyclic compounds

This study aims to establish a systematic method to optimize the bacterial consortium for the simultaneous biodegradation of multixenobiotics in wastewater. Three nitrogen heterocyclic compounds (NHCs), pyridine, quinoline, and carbazole, were chosen as the target compounds with each about 200 mg/L. Different consortia originated from six bacteria for degrading pyridine (Paracoccus sp. BW001 and Shinella zoogloeoides BC026), quinoline (Pseudomonas sp. BW003 and BW004), and carbazole (Pseudomonas sp. BC039 and BC046) were tested for the capacity of NHCs simultaneous degradation. Mathematical methods including dummy-variable-laden kinetic modeling, cubic spline regression and interpolation, and dimensionality reduction were employed to evaluate the complex impacts of cocontaminants and coexisting bacteria on the simultaneous biodegradation, and the most efficient consortium was determined. The influences of cocontaminants on the bacterial degradation activity were far greater than the interactions among the mixed bacteria. Integrating the experimental results and mathematical analysis, consortium M19 (BC026, BW004, BC039, and BC046 with dose rate of 1:1:0.5:0.5) was the best one, which degraded over 95% of pyridine, quinoline, and carbazole simultaneously in 15.4 h. The research methodology in this study could be applied to the optimization of a bacterial consortium which might be used in the bioaugmentation and bioremediation of multixenobiotics removal.

Coverage evaluation of universal bacterial primers using the metagenomic datasets

BACKGROUND

The coverage of universal primers for the bacterial 16S rRNA gene plays a crucial role in the correct understanding of microbial community structure. However, existing studies on primer coverage are limited by the lack of appropriate databases and are restricted to the domain level. Additionally, most studies do not account for the positional effect of single primer-template mismatches. In this study, we used 7 metagenomic datasets as well as the Ribosomal Database Project (RDP) to assess the coverage of 8 widely used bacterial primers.

RESULTS

The coverage rates for bacterial primers were found to be overestimated by previous studies that only investigated the RDP because of PCR amplification bias in the sequence composition of the dataset. In the RDP, the non-coverage rates for all primers except 27F were ≪6%, while in the metagenomic datasets, most were ≫10%. If one considers that a single mismatch near the 3' end of the primer might greatly reduce PCR efficiency, then some phylum non-coverage rates would change by more than 20%. Primer binding-site sequence variants that could not pair with their corresponding primers are discussed.

CONCLUSIONS

Our study revealed the potential bias introduced by the use of universal bacterial primers in the assessment of microbial communities. With the development of high-throughput, next-generation sequencing techniques, it will become feasible to sequence more of the hypervariable regions of the bacterial 16S rRNA gene. This, in turn, will lead to the more frequent use of the primers discussed here.