Characterization of microbial community in an aerobic moving bed biofilm reactor applied for simultaneous nitrification and denitrification

A continuous-flow moving bed biofilm reactor (MBBR) under aerobic conditions was established for simultaneous nitrification and denitrification (SND), and microbial communities were investigated by a combination of denaturing gel gradient electrophoresis (DGGE) and fluorescence in situ hybridization (FISH). DGGE analysis has revealed more similar microbial community structures formed in the biofilms with more similar carbon nitrogen (C/N) ratios. FISH analysis shows that the dominance of both Betaproteobacteria ammonia-oxidizing bacteria and Nitrospira-like nitrite-oxidizing bacteria were negatively correlated to C/N ratios. Sequence analysis of DGGE bands has indicated the presence of anoxic denitrifying bacteria Agrobacterium tumefaciens and Rhizobium sp., suggesting that the oxygen gradient inside the biofilm may be responsible for the mechanism of SND in aerobic MBBRs. The study confirms that appropriate control of microbial community structure resulting from optimal C/N ratio is beneficial in improving SND, thus optimizing nitrogen removal in aerobic MBBR. The established SND-based MBBR can save operation space and time in comparison to the traditional nitrogen removal process, and might be very attractive for future practical applications.     

Start-up and bacterial community compositions of partial nitrification in moving bed biofilm reactor

Partial nitrification (PN) has been considered as one of the promising processes for pretreatment of ammonium-rich wastewater. In this study, a kind of novel carriers with enhanced hydrophilicity and electrophilicity was implemented in a moving bed biofilm reactor (MBBR) to start up PN process. Results indicated that biofilm formation rate was higher on modified carriers. In comparison with the reactor filled with traditional carriers (start-up period of 21 days), it took only 14 days to start up PN successfully with ammonia removal efficiency and nitrite accumulation rate of 90 and 91%, respectively, in the reactor filled with modified carriers. Evident changes of spatial distributions and community structures had been detected during the start-up. Free-floating cells existed in planktonic sludge, while these microorganisms trended to form flocs in the biofilm. High-throughput pyrosequencing results indicated that Nitrosomonas was the predominant ammonia-oxidizing bacterium (AOB) in the PN system, while Comamonas might also play a vital role for nitrogen oxidation. Additionally, some other bacteria such as Ferruginibacter, Ottowia, Saprospiraceae, and Rhizobacter were selected to establish stable footholds. This study would be potentially significant for better understanding the microbial features and developing efficient strategies accordingly for MBBR-based PN operation.

     

Effective anaerobic treatment of fresh leachate from MSW incineration plant and dynamic characteristics of microbial community in granular sludge

We investigated the treatment of fresh leachate from municipal solid waste incineration plants with high-strength organics using a lab-scale expanded granular sludge bed (EGSB) reactor. The reactor was operated at a mesophilic temperature (33 °C) for 118 days. The influent chemical oxygen demand (COD) of the leachate gradually increased to over 70,000 mg/L, and the organic loading rate increased to 18 kg COD/(m³?day). An average COD removal efficiency of 86.7 % was achieved when the reactor was fed with raw leachate, which suggests the feasibility of the EGSB process for leachate treatment. The microbial communities in the sludge from the reactor during the trial operation were constructed by denaturing gradient gel electrophoresis, clone libraries, and real-time quantitative polymerase chain reaction. The dominant group for archaea was Methanosaeta, with 68.4 % proportion at the start of the operation, and then changed to Methanosarcina, with a proportion of 62.3 %, after 118 days of operation. The dominant group of eubacteria was confirmed to be Firmicutes throughout the operation process, with the proportion increasing from >50 to 81.2 %. Almost all the operational taxonomic units of Firmicutes belonged to the order Clostridiales, with characteristic spore formation. The microbial diversity of the population was low under raw leachate as feed in the reactor. The dynamics of the microbial community in the anaerobic granular sludge was discussed relating with the operating status of the EGSB reactor.     

Cultivation-independent analysis of archaeal and bacterial communities of the formation water in an Indian coal bed to enhance biotransformation of coal into methane

Biogenic origin of the significant proportion of coal bed methane has indicated the role of microbial communities in methanogenesis. By using cultivation-independent approach, we have analysed the archaeal and bacterial community present in the formation water of an Indian coal bed at 600–700 m depth to understand their role in methanogenesis. Presence of methanogens in the formation water was inferred by epifluorescence microscopy and PCR amplification of mcrA gene. Archaeal 16S rRNA gene clone library from the formation water metagenome was dominated by methanogens showing similarity to Methanobacterium, Methanothermobacter and Methanolinea whereas the clones of bacterial 16S rRNA gene library were closely related to Azonexus, Azospira, Dechloromonas and Thauera. Thus, microbial community of the formation water consisted of predominantly hydrogenotrophic methanogens and the proteobacteria capable of nitrogen fixation, nitrate reduction and polyaromatic compound degradation. Methanogenic potential of the microbial community present in the formation water was elucidated by the production of methane in the enrichment culture, which contained 16S rRNA gene sequences showing close relatedness to the genus Methanobacterium. Microcosm using formation water as medium as well as a source of inoculum and coal as carbon source produced significant amount of methane which increased considerably by the addition of nitrite. The dominance of Diaphorobacter sp. in nitrite amended microcosm indicated their important role in supporting methanogenesis in the coal bed. This is the first study indicating existence of methanogenic and bacterial community in an Indian coal bed that is capable of in situ biotransformation of coal into methane.     

Treatment of domestic wastewater in an up-flow anaerobic sludge blanket reactor followed by moving bed biofilm reactor

The performance of a laboratory-scale sewage treatment system composed of an up-flow anaerobic sludge blanket (UASB) reactor and a moving bed biofilm reactor (MBBR) at a temperature of (22–35 °C) was evaluated. The entire treatment system was operated at different hydraulic retention times (HRT’s) of 13.3, 10 and 5.0 h. An overall reduction of 80–86% for COD_total; 51–73% for COD_colloidal and 20–55% for COD_soluble was found at a total HRT of 5–10 h, respectively. By prolonging the HRT to 13.3 h, the removal efficiencies of COD_total, COD_colloidal and COD_soluble increased up to 92, 89 and 80%, respectively. However, the removal efficiency of COD_suspended in the combined system remained unaffected when increasing the total HRT from 5 to 10 h and from 10 to 13.3 h. This indicates that, the removal of COD_suspended was independent on the imposed HRT. Ammonia-nitrogen removal in MBBR treating UASB reactor effluent was significantly influenced by organic loading rate (OLR). 62% of ammonia was eliminated at OLR of 4.6 g COD m⁻² day⁻¹. The removal efficiency was decreased by a value of 34 and 43% at a higher OLR’s of 7.4 and 17.8 g COD m⁻² day⁻¹, respectively. The mean overall residual counts of faecal coliform in the final effluent were 8.9 × 10⁴ MPN per 100 ml at a HRT of 13.3 h, 4.9 × 10⁵ MPN per 100 ml at a HRT of 10 h and 9.4 × 10⁵ MPN per 100 ml at a HRT of 5.0 h, corresponding to overall log₁₀ reduction of 2.3, 1.4 and 0.7, respectively. The discharged sludge from UASB–MBBR exerts an excellent settling property. Moreover, the mean value of the net sludge yield was only 6% in UASB reactor and 7% in the MBBR of the total influent COD at a total HRT of 13.3 h. Accordingly, the use of the combined UASB–MBBR system for sewage treatment is recommended at a total HRT of 13.3 h.     

To study the performance of biocarriers in moving bed biofilm reactor (MBBR) technology and kinetics of biofilm for retrofitting the existing aerobic treatment systems: a review

Moving bed biofilm reactor (MBBR) incorporates benefits provided by both attached and suspended growth systems. It is an advanced high rate wastewater treatment technology with high treatment efficiency; low capital, operational, maintenance and replacement cost; single reliable and robust operation procedure. Moreover, this technology is applicable to wide range of wastewater flows ranging from 10,000 to 150,000 m³ day^?1. The MBBR has proved to be effective in removing up to 90 % chemical oxygen demand and 95 % biochemical oxygen demand with nutrients from the effluent stream at optimum condition, provided there is sufficient retention time. It is a cost-effective way of upgrading existing wastewater treatment system as it is efficient, compact and easy to operate. This process can be provided for new sewage treatment works or for retrofitting existing wastewater treatment plants where a higher treated effluent standard is required without any running and capital cost. The performance of MBBR depends on the percent of media provided in the reactor, surface area of the biocarrier, dissolved oxygen and the organic loading. Various mathematical models are also described in this review paper which is generally used to calculate the reactor volume, effluent organic concentration and substrate removal rate.     

Laboratory-scale evaluation of fluidized bed reactor technology for biotreatment of maleic anhydride process wastewater

Fluidized bed reactor (FBR) technology has emerged in recent years as an attractive approach for the biotreatment of chemical industry wastestreams. A laboratory-scale FBR study was conducted to investigate the feasibility of utilizing FBR technology for the biotreatment of maleic anhydride wastewater generated during manufacturing operations. The maleic anhydride wastestream contains a mixture of maleic acid, fumaric acid, phthalic acid and di-n-butylphthalate (DBP). The FBR removed >98% of chemical oxygen demand (COD) and total organic carbon (TOC) from the wastewater at a chemical loading rate of 4.86 kg of COD m^–3 bed day^–1. Maleic acid, fumaric acid or phthalic acid were not detected in the FBR effluent indicating removal of these diacids. Residues of DBP adsorbed to granular activated carbon (GAC) stabilized at low levels indicating that the >99% removal efficiency for DBP in the FBR resulted from microbial degradation. Solids measurements showed microbial biomass levels on the GAC ranging from 10500 to 32400 mg L^–1 and effluent solids production ranged from 0.027 to 0.041 kg solids kg^–1 COD treated. This laboratory-scale study demonstrated that FBR technology was highly effective for the biotreatment of the maleic anhydride wastestream and may offer several advantages over traditional activated sludge systems.     

Microbial community structure and dynamics in anaerobic fluidized‐bed and granular sludge‐bed reactors: influence of operational temperature and reactor configuration

Methanogenic community structure and dynamics were investigated in two different, replicated anaerobic wastewater treatment reactor configurations [inverted fluidized bed (IFB) and expanded granular sludge bed (EGSB)] treating synthetic dairy wastewater, during operating temperature transitions from 37°C to 25°C, and from 25°C to 15°C, over a 430‐day trial. Non‐metric multidimensional scaling (NMS) and moving‐window analyses, based on quantitative real‐time PCR data, along with denaturing gradient gel electrophoresis (DGGE) profiling, demonstrated that the methanogenic communities developed in a different manner in these reactor configurations. A comparable level of performance was recorded for both systems at 37°C and 25°C, but a more dynamic and diverse microbial community in the IFB reactors supported better stability and adaptative capacity towards low temperature operation. The emergence and maintenance of particular bacterial genotypes (phylum Firmicutes and Bacteroidetes) was associated with efficient protein hydrolysis in the IFB, while protein hydrolysis was inefficient in the EGSB. A significant community shift from a Methanobacteriales and Methanosaetaceae towards a Methanomicrobiales‐predominated community was demonstrated during operation at 15°C in both reactor configurations.     

A one dimensional moving bed biofilm reactor model for nitrification of municipal wastewaters

This work presents a one-dimensional model of a moving bed bioreactor (MBBR) process designed for the removal of nitrogen from raw wastewaters. A comprehensive experimental strategy was deployed at a semi-industrial pilot-scale plant fed with a municipal wastewater operated at 10–12 °C, and surface loading rates of 1–2 g filtered COD/m² d and 0.4–0.55 g NH₄-N/m² d. Data were collected on influent/effluent composition, and on measurement of key variables or parameters (biofilm mass and maximal thickness, thickness of the limit liquid layer, maximal nitrification rate, oxygen mass transfer coefficient). Based on time-course variations in these variables, the MBBR model was calibrated at two time-scales and magnitudes of dynamic conditions, i.e., short-term (4 days) calibration under dynamic conditions and long-term (33 days) calibration, and for three types of carriers. A set of parameters suitable for the conditions was proposed, and the calibrated parameter set is able to simulate the time-course change of nitrogen forms in the effluent of the MBBR tanks, under the tested operated conditions. Parameters linked to diffusion had a strong influence on how robustly the model is able to accurately reproduce time-course changes in effluent quality. Then the model was used to optimize the operations of MBBR layout. It was shown that the main optimization track consists of the limitation of the aeration supply without changing the overall performance of the process. Further work would investigate the influence of the hydrodynamic conditions onto the thickness of the limit liquid layer and the “apparent” diffusion coefficient in the biofilm parameters.

     

Molecular Monitoring of Microbial Population Dynamics During Operational Periods of Anaerobic Hybrid Reactor Treating Cassava Starch Wastewater

This study characterized the microbial community and population dynamics in an anaerobic hybrid reactor (AHR) treating cassava starch wastewater. Methanogens and nonmethanogens were followed during the start-up and operation of the reactor, and linked to operational and performance data. Biomass samples taken from the sludge bed and packed bed zones of the AHR at intervals throughout the operational period were examined by 16S rRNA fluorescence in situ hybridization (FISH). The start-up seed and the reactor biomass were sampled during the feeding of the wastewater with a chemical oxygen demand (COD) value of 8 g L⁻¹ and a hydraulic retention time (HRT) of 8 days. These samples were characterized by the predominance of cells with long-rod morphology similar to Methanosaeta spp. Following a sharp operational change, accomplished by increasing the COD concentration of the organic influent from 8 to 10 g L⁻¹ and reducing the HRT from 8 to 5 days, there was a doubling of the organic loading rate, a reduction of the COD removal efficiency, as well as decreased methane content in the biogas and an accumulation of total volatile acids in the reactor. Moreover, this operational change resulted in a significant population shift from long-rod Methanosaeta-like cells to tetrad-forming Methanosarcina-like cells. The distributions of microbial populations involved in different zones of the AHR were determined. The results showed that nonmethanogens became the predominant population in both sludge and the packed bed zone. However, the percentage of methanogens in the packed bed zone was higher than that in the sludge bed zone. This higher percentage of methanogens was likely caused by the fact that the packed bed zone provided a suitable environmental condition with an appropriate nutrient availability for methanogen growth.     

Rapid start-up of nitrifying MBBRs at low temperatures: nitrification,biofilm response and microbiome analysis

The moving bed biofilm reactor (MBBR), operated as a post carbon removal system, requires long start-up times in comparison to carbon removal systems due to slow growing autotrophic organisms. This study investigates the use of carriers seeded in a carbon rich treatment system prior to inoculation in a nitrifying MBBR system to promote the rapid development of nitrifying biofilm in an MBBR system at temperatures between 6 and 8 °C. Results show that nitrification was initiated by the carbon removal carriers after 22 h of operation. High throughput 16S-rDNA sequencing indicates that the sloughing period was a result of heterotrophic organism detachment and the recovery and stabilization period included a growth of Nitrosomonas and Nitrospira as the dominant ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in the biofilm. Peripheral microorganisms such as Myxococcales, a rapid EPS producer, appear to have contributed to the recovery and stabilization of the biofilm.

     

Characterization of sulfate-reducing bacteria dominated surface communities during start-up of a down-flow fluidized bed reactor

An anaerobic down-flow fluidized bed reactor was inoculated with granular sludge and started-up with sulfate containing synthetic wastewater to promote the formation of a biofilm enriched in sulfate-reducing bacteria (SRB), to produce biogenic sulfide. The start-up was done in two stages operating the reactor in batch for 45 days followed by 85 days of continuous operation. Low-density polyethylene was used as support. The biofilm formation was followed up by biochemical and electron microscopy analyses and the composition of the community was examined by 16S rDNA sequence analysis. Maximum immobilized volatile solids (1.2 g IVS/L_support) were obtained after 14 days in batch regime. During the 85 days of continuous operation, the reactor removed up to 80% of chemical oxygen demand (COD), up to 28% of the supplied sulfate and acetate was present in the effluent. Sulfate-reducing activity determined in the biofilm with ethanol or lactate as substrate was 11.7 and 15.3 g COD/g IVS per day, respectively. These results suggested the immobilization of sulfate reducers that incompletely oxidize the substrate to acetate; the phylogenetic analysis of the cloned 16S rDNA gene sequences showed high identity to the genus Desulfovibrio that oxidizes the substrates incompletely. In contrast, in the granular sludge used as inoculum a considerable number of clones showed homology to Methanobacterium and just few clones were close to SRB. The starting-up approach allowed the enrichment of SRB within the diverse community developed over the polyethylene support.     

Removal of carbon and nutrients from low strength domestic wastewater by expanded granular sludge bed-zeolite bed filtration (EGSB-ZBF) integrated treatment concept

The performance of an expanded granular sludge bed (EGSB) reactor coupled with zeolite bed filtration (ZBF) for treating low strength domestic wastewater was monitored at 35 °C for 7 months. The whole operation period of EGSB system was divided into five phases. Each phase ran at up-flow velocity (m/h) of 0.51, 1.02, 3.57, 2.05, 9.69, and hydraulic retention time (HRT) (h) of 6, 3, 0.87, 1.5, 0.32, respectively. The influent chemical oxygen demand (COD) was kept approximate at 150 ± 100 mg/L. Under these conditions, the COD removal efficiency of using EGSB system in five phases reached to 81.08, 57.94, 82.79, 56.58 and 79.52%, respectively. Moreover, since nutrients such as NH₄⁺ and PO₄³⁻ were only removed to a limited extent by EGSB, additional treatment is required. The ZBF was employed in phase 2 as a post-treatment following EGSB. NH₄⁺ and PO₄³⁻ concentrations were decreased by 100%, respectively, in the first 2 or 3 d using fresh zeolite. The simple design and excellent treatment performance indicated that this system could be used as a novel Sewage Integrated Treatment System (SITS) for developing country especially in a tropical area.     

Textiles wastewater treatment using anoxic filter bed and biological wriggle bed-ozone biological aerated filter

In this study, the performance of the anoxic filter bed and biological wriggle bed-ozone biological aerated filter (AFB-BWB-O₃-BAF) process treating real textile dyeing wastewater was investigated. After more than 2 month process operation, the average effluent COD concentration of the AFB, BWB, O₃-BAF were 704.8 mg/L, 294.6 mg/L and 128.8 mg/L, with HRT being 8.1-7.7 h, 9.2 h and 5.45 h, respectively. Results showed that the effluent COD concentration of the AFB decreased with new carriers added and the average removal COD efficiency was 20.2%. During operation conditions, HRT of the BWB and O₃-BAF was increased, resulting in a decrease in the effluent COD concentration. However, on increasing the HRT, the COD reduction capability expressed by the unit carrier COD removal loading of the BWB reactor increased, while that of the O₃-BAF reactor decreased. This study is a beneficial attempt to utilize the AFB-BWB-O₃-BAF combine process for textile wastewater treatment.     

基于16S rRNA和rpoB基因的分子系统发育分析在铜绿假单胞菌鉴定中的应用

为对比16S rRNA和rpo B基因分子系统发育分析与传统表型分类法对铜绿假单胞菌的鉴定,评估16S rRNA和rpo B基因序列分析在铜绿假单胞菌鉴定中的应用,用表型分类方法对临床自动微生物鉴定系统鉴定为铜绿假单胞菌的23株分离株进行再鉴定,PCR扩增23株分离株16S rRNA和rpo B基因片段,并测序进行系统发育分析。结果表明,表型再鉴定结果与自动微生物鉴定系统鉴定结果一致。基于两个基因的系统发育分析均显示分离株p22与不动杆菌属序列聚为一枝,其余22株分离株与铜绿假单胞菌序列聚为一枝。因此p22应鉴定为不动杆菌,16S rRNA和rpo B基因序列分析均能准确鉴定铜绿假单胞菌并能较好建立假单胞菌属内种间关系。     

Anaerobic digestion of long-chain fatty acids in UASB and expanded granular sludge bed reactors

Solutions of sodium caprate and sodium laurate were digested in upflow anaerobic sludge bed (UASB) reactors inoculated with granular sludge and in expanded granular sludge bed (EGSB) reactors. UASB reactors are unsuitable if lipids contribute 50% or more to the COD of waste water: the gas production rate required to obtain sufficient mixing and contact cannot be achieved. At lipid loading rates exceeding 2–3 kg COD m⁻³ day⁻¹, total sludge wash-out occurred. At lower loading rates the system was unreliable, due to unpredictable sludge flotation. EGSB reactors do fulfil the requirements of mixing and contact. They accommodate space loading rates up to 30 kg COD m⁻³ day⁻¹ during digestion of caprate or laurate as sole substrate, at COD removal efficiencies of 83–91%, and can be operated at hydraulic residence times of 2 h without any problems. Augmentation of granular sludge in lab-scale EGSB reactors was demonstrated. The new granules had excellent settling properties. Floating layer formation, as well as mixing characteristics in full-scale EGSB reactors require further research.     

养猪微生物发酵床芽胞杆菌空间分布多样性

了解微生物发酵床大栏养猪垫料中的芽胞杆菌多样性和空间分布规律,为微生物发酵床管理、芽胞杆菌新资源挖掘及菌剂开发奠定基础。将发酵床划分为32个方格(4行×8列),采用五点取样法获得每个方格的样品。采用可培养法从32份样品中分离芽胞杆菌菌株,利用16S rRNA基因序列初步鉴定所分离获得的芽胞杆菌种类。利用聚集度指标和回归分析法,分析芽胞杆菌的样方空间分布型。通过Shannon-Wiener多样性指数、Simpson优势度指数、Hill指数及丰富度指数分析,揭示微生物发酵床中芽胞杆菌的空间分布多样性。从32份样品中共获得芽胞杆菌452株,16S rRNA基因鉴定结果表明它们分别隶属于芽胞杆菌纲的2个科、8个属、48个种。其中,种类最多的为芽胞杆菌属(Bacillus),30种;赖氨酸芽胞杆菌属(Lysinibacillus),6种;类芽胞杆菌属(Paenibacillus),5种;短芽胞杆菌属(Brevibacillus),3种;鸟氨酸芽胞杆菌属(Ornithinibacillus)、大洋芽胞杆菌属(Oceanibacillus)、少盐芽胞杆菌属(Paucisalibacillus)和纤细芽胞杆菌属(Gracilibacillus)各1个种。芽胞杆菌种类在发酵床空间分布差异很大,根据其空间出现频次,可分为广分布种类,如地衣芽胞杆菌(Bacillus licheniformis);寡分布种类,如根际芽胞杆菌(B.rhizosphaerae);少分布种类,如弯曲芽胞杆菌(B.flexus)。依据其数量,可分为高含量组优势种群,如地衣芽胞杆菌(B.licheniformis);中含量组常见种群,耐盐赖氨酸芽胞杆菌(Lysinibacillus halotolerans);寡含量组寡见种群,如根际芽胞杆菌(B.rhizosphaerae);低含量组偶见种群,如土地芽胞杆菌(B.humi)。空间分布型聚集度和回归分析测定表明,芽胞杆菌在微生物发酵床的分布类型为聚集分布。微生物发酵床垫料中芽胞杆菌种类总含量高达4.41×108个/g,其种类含量范围为0.01—94.1×106个/g(均值为8.96×106个/g),丰富度指数(D)、优势度指数(λ)、Shannon-Wiener指数(H')和均匀度指数(J')分别为0.4928、0.2634、1.3589和0.9803,其中香农指数最大的单个芽胞杆菌种类为地衣芽胞杆菌(B.licheniformis)。根据芽胞杆菌种类多样性指数聚类分析,当欧式距离λ=17时,可分为高丰富度高含量和低丰富度低含量类型。微生物发酵床的芽胞杆菌种类丰富、数量高,是一个天然的菌剂"发酵罐",有望直接作为微生物菌剂,应用于土壤改良、作物病害防控、污染治理等领域。     

Microbial community composition and dynamics of moving bed biofilm reactor systems treating municipal sewage

Moving bed biofilm reactor (MBBR) systems are increasingly used for municipal and industrial wastewater treatment, yet in contrast to activated sludge (AS) systems, little is known about their constituent microbial communities. This study investigated the community composition of two municipal MBBR wastewater treatment plants (WWTPs) in Wellington, New Zealand. Monthly samples comprising biofilm and suspended biomass were collected over a 12-month period. Bacterial and archaeal community composition was determined using a full-cycle community approach, including analysis of 16S rRNA gene libraries, fluorescence in situ hybridization (FISH) and automated ribosomal intergenic spacer analysis (ARISA). Differences in microbial community structure and abundance were observed between the two WWTPs and between biofilm and suspended biomass. Biofilms from both plants were dominated by Clostridia and sulfate-reducing members of the Deltaproteobacteria (SRBs). FISH analyses indicated morphological differences in the Deltaproteobacteria detected at the two plants and also revealed distinctive clustering between SRBs and members of the Methanosarcinales, which were the only Archaea detected and were present in low abundance (<5%). Biovolume estimates of the SRBs were higher in biofilm samples from one of the WWTPs which receives both domestic and industrial waste and is influenced by seawater infiltration. The suspended communities from both plants were diverse and dominated by aerobic members of the Gammaproteobacteria and Betaproteobacteria. This study represents the first detailed analysis of microbial communities in full-scale MBBR systems and indicates that this process selects for distinctive biofilm and planktonic communities, both of which differ from those found in conventional AS systems.     

Microbial Community Analysis of Anaerobic Reactors Treating Soft Drink Wastewater

The anaerobic packed-bed (AP) and hybrid packed-bed (HP) reactors containing methanogenic microbial consortia were applied to treat synthetic soft drink wastewater, which contains polyethylene glycol (PEG) and fructose as the primary constituents. The AP and HP reactors achieved high COD removal efficiency (>95%) after 80 and 33 days of the operation, respectively, and operated stably over 2 years. 16S rRNA gene pyrotag analyses on a total of 25 biofilm samples generated 98,057 reads, which were clustered into 2,882 operational taxonomic units (OTUs). Both AP and HP communities were predominated by Bacteroidetes, Chloroflexi, Firmicutes, and candidate phylum KSB3 that may degrade organic compound in wastewater treatment processes. Other OTUs related to uncharacterized Geobacter and Spirochaetes clades and candidate phylum GN04 were also detected at high abundance; however, their relationship to wastewater treatment has remained unclear. In particular, KSB3, GN04, Bacteroidetes, and Chloroflexi are consistently associated with the organic loading rate (OLR) increase to 1.5 g COD/L-d. Interestingly, KSB3 and GN04 dramatically decrease in both reactors after further OLR increase to 2.0 g COD/L-d. These results indicate that OLR strongly influences microbial community composition. This suggests that specific uncultivated taxa may take central roles in COD removal from soft drink wastewater depending on OLR.     

Phylogenetic characterization of bacterial consortia obtained of corroding gas pipelines in Mexico

Characterization of the microbial populations formed in gas pipelines is essential to understand the metallic surface-microbe interaction, their role in metal corrosion, and to implement efficient monitoring and control strategies. Microbial community analysis in a corroded gas pipeline in a petroleum-producing facility in the Southeast region in Mexico was performed by traditional cultivation techniques and identification based on 16S rRNA gene sequence. In all samples, thin bacterial biofilms were observed and pitting corrosion was reveled after removing the biofilms. Six pure or mixed cultures of anaerobic bacteria were obtained and their 16S rRNA libraries were constructed, respectively. At least two members of each RFLP profile were sequenced and the phylogenetic affiliations of cloned bacterial 16S rRNA genes indicated that native biofilms were mainly colonized by Desulfovibrio vulgaris and Desulfovibrio desulfuricans, sulfate-reducing bacteria members; Citrobacter freundii, an Enterobacteriaceae member; Clostridium celerecrescens and Clostridium sporogenes, spore-forming anaerobic species and Cetobacterium somerae, a microaerotolerant, non-spore-forming fusobacteria. Some of these species have been observed consistently in other steel pipelines previously, but Cetobacterium members and C. celerecrescens are described for the fist time in this corroded gas pipeline. The potential role of each species in biofilm formation and steel corrosion is discussed.