好氧-厌氧混合污泥启动微生物燃料电池产电性能及微生物群落动态特征

【目的】为探讨好氧-厌氧混合污泥启动微生物燃料电池(Microbial fuel cell,MFC)产电性能以及MFC对微生物群落的选择作用,【方法】以乳酸为底物,应用不依赖于培养的微生物分子生物学技术解析单室MFC启动过程中微生物群落的组成和结构动态学特征。【结果】结果表明,MFC经过3个周期启动成功,最高输出电压230 m V。当MFC外电阻为1656Ω时,最大功率密度11.15 W/m3,电池运行稳定。混合污泥启动MFC以后,阳极生物膜微生物群落结构同种泥差异较大,且多样性降低。生物膜中微生物类群按丰度依次为β-变形菌纲(Betaproteobacteria)24.90%、拟杆菌门(Bacteroidetes)21.30%、厚壁菌门(Firmicutes)9.70%、γ-变形菌纲(Gammaproteobacteria)8.50%、δ-变形菌纲(Deltaproteobacteria)7.90%、绿弯菌门(Chloroflexi)4.20%以及α-变形菌纲(Alphaproteobacteria)3.60%。有利于生物膜形成与稳定的动胶菌属(Zoogloea)和不动杆菌属(Acinetobacter)序列丰度分别占生物膜群落的5.00%和3.90%,与MFC产电能力直接相关的地杆菌属(Geobacter)序列由混合污泥中的0.60%上升至阳极生物膜中的2.60%。【结论】本研究表明,MFC阳极生物膜在驯化过程中对污泥中的微生物进行淘汰和选择,最终驯化形成了有利于生物膜形成与稳定、有机物厌氧发酵与产电的微生物菌群。     

自然微生物挂膜处理水产养殖废水的效果及微生物群落分析

以弹性填料和流化床填料为硝化反应的生物挂膜材料, 聚羟基丁酸/戊酸共聚酯(PHBV)为反硝化反应的碳源和生物膜载体, 通过微生物自然挂膜处理低C/N比水产养殖废水, 去除水体中的氨氮、亚硝酸盐氮及总氮。应用Miseq高通量测序技术对生物膜的微生物群落组成和结构进行分析。结果表明: 温度25—30℃, 该处理系统首次挂膜成功需要4周, 启动后运行稳定, 对2种不同来源和氮污染程度的养殖废水均有较好的脱氮效果, 氨氮、亚硝酸盐氮及总氮的去除率均在90%以上。硝化生物膜(a)的优势菌分别归属变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)和厚壁菌门(Firmicutes)。反硝化生物膜(b)微生物群落的多样性指数和丰度指数均远大于前者, 主要为变形菌门、厚壁菌门、拟杆菌门、螺旋体门(Spirochaetae)及绿菌门(Chlorobi)。其中, 归属于变形菌门β-变形菌纲(Betaproteobacteria)的丛毛单胞菌科(Comamonadaceae)和红环菌科(Rhodocyclaceae)在2种生物膜中占比均较高。由于所处环境(载体, 碳源、溶氧等)不同, 在属分类水平上, 2种生物膜的细菌群落结构表现出明显差异。生物膜a中属的种类仅为b的三分之二, 相对丰度>0.5%的优势菌属, a为8个, b为18个。其中, 隶属丛毛单胞菌科和红环菌科未知属的优势种群分别占到a、b总序列数的56.67%和45.51%。磁螺菌属(Magnetospirillum)和硝化螺菌属(Nitrospira)是a中特有的优势功能菌群, 梭菌属(Clostridium)、动胶菌属(Zoogloea)、管道杆菌属(Cloacibacterium)、脱硫弧菌属(Desulfovibrio)等具有反硝化功能的菌群为b的优势菌属。     

驯化对生物阴极微生物燃料电池中阴极微生物群落多样性的影响

【背景】生物阴极微生物燃料电池因其构造成本低和阴极可持续性发展的优点而成为一种很有前途的废水处理系统,但阴极微生物的氧化还原性能限制了其在实际应用中的推广。【目的】为了提高生物阴极的性能,需要深入了解影响阴极氧化还原性能的微生物群落。【方法】利用16S rRNA基因高通量测序技术分析对比原始接种污泥样品和驯化后阴极电极上生物膜样品多样性及结构变化。【结果】测序结果表明,原始接种污泥样品与驯化后阴极电极生物膜样品中微生物群落种类和结构存在显著差异,驯化后阴极电极生物膜样品中变形菌门(Proteobacteria)、γ-变形菌纲(Gammaproteobacteria)和特吕珀菌属(Trueperaceae)相对丰度比例高于原始污泥样品,成为优势菌群。【结论】驯化对系统阴极电极生物膜群落影响显著,随着产电量的输出,优势菌群不断富集,最终形成一个适应该实验环境下的新的微生物群落。对优势菌群结构和变化进行探讨,为生物阴极的研究补充更多生物学方面的理论基础。     

以聚羟基丁酸戊酸共聚酯为碳源去除循环水养殖系统的硝酸盐及生物膜中微生物群落动态

【目的】利用聚羟基丁酸戊酸共聚酯(PHBV)作为固体碳源和生物膜载体,去除循环水养殖系统的硝酸盐,并研究固体碳源反硝化反应器不同运行阶段生物膜中微生物群落结构的动态变化。【方法】采用PCR-DGGE技术对反硝化反应器中微生物群落结构的动态变化进行了分析,采用传统纯培养方法分离反应器中降解PHBV的细菌。【结果】连接固相反硝化反应器能使循环水养殖系统中积累的硝酸盐显著降低,并维持在较低水平(小于10 mg/L),而常规循环水养殖系统中硝酸盐浓度持续增加。系统发育树聚类分析结果表明,反硝化反应器生物膜细菌归属于变形菌门(β-proteobacteria、γ-proteobacteria和δ-proteobacteria)、厚壁菌门(Firmicutes)和拟杆菌门(Bacteroidetes)。反应器运行初期(40 d)的优势种群主要为Acidovorax和Bacillus;运行后期(150 d)的优势种群依次为Clostridium、Desulfitobacterium、Dechloromonas、Pseudoxanthomonas和Flavobacterium。从反应器中分离到的PHBV降解菌株分别归属于Acidovorax、Methylibium、Pseudoxanthomonas和Dechloromonas。【结论】利用PHBV为碳源能有效去除循环水养殖系统的硝酸盐。明确了反硝化反应器在运行过程中,碳源表面生物膜的优势菌群及其动态变化。     

模拟增温对青海湖鸟岛土壤微生物的影响

【背景】土壤微生物对其生存的微环境变化极为敏感,鸟岛作为湖滨湿地,对气候变化具有敏感性,但目前关于青海湖鸟岛的土壤微生物鲜有研究。【目的】探究气候变暖后青海湖鸟岛土壤微生物群落特征的变化。【方法】利用开顶箱模拟增温,通过高通量测序方法了解温度升高后土壤细菌及真菌的群落结构以及多样性的变化情况。【结果】温度的升高并未改变青海湖鸟岛土壤微生物的优势菌群,细菌优势菌群为变形菌门和酸杆菌门;真菌优势菌门为子囊菌门,优势菌纲为座囊菌纲。但增温改变了土壤微生物的群落结构,显著升高了拟杆菌门、蓝细菌门、Patescibacteria及球囊菌纲的相对丰度,显著降低了锤舌菌纲的相对丰度。土壤微生物群落的多样性指数也发生了变化,温度上升后微生物的ACE指数及Chao1指数均降低,细菌的Simpson指数及真菌的Shannon指数降低。【结论】青海湖鸟岛土壤微生物对温度升高的响应明显,增温改变了土壤细菌拟杆菌门、蓝细菌门、Patescibacteria的相对丰度及真菌的球囊菌纲、锤舌菌纲的相对丰度,降低了土壤微生物的多样性。     

FISH法对垃圾渗滤液硝化生物膜发育的观察与分析

氨氧化细菌的培养和快速检测一直是高浓度氨氮废水处理工程的调试和运行监测中的难点问题。利用荧光原位杂交(FISH)方法,对广州大田山垃圾填埋场渗滤液好氧处理过程中复合生物膜反应器不同挂膜时间的填料和相应时期的悬浮污泥中氨氧化菌的群落结构和动态变化进行了监测,并且用扫描电子显微镜(SEM)观察了相应时间段的生物膜的表面情况。结果表明,在挂膜初期,细菌首先在填料表面的凹陷处定居,随着挂膜时间的延长,填料上的细菌总数在增加。挂膜7d的填料上,氨氧化菌占全菌的比例为60%左右,挂膜20d的填料上,氨氧化菌占全菌的比例为40%左右;挂膜50d的填料上,已经形成了完整的生物膜菌群结构,其中氨氧化菌是最主要的优势菌群,它占全菌的比例保持在35%左右,这个比例在106d和155d的生物膜上仍然保持稳定。与填料同时取样的悬浮污泥,其氨氧化菌占全菌的比例远远低于同时期的填料上的比例,并且较不稳定。当出水氨氮浓度由30mg/L升高到70mg/L左右时,悬浮污泥中氨氧化菌的比例有所降低,而完整生物膜上氨氧化菌的比例仍然保持在30%左右并且对氨氮的去除起了主要的作用。     

山东地区盐碱土花生种子际土壤微生物群落结构的研究

【目的】以不同含盐量的滨海盐土、内陆盐碱土和中等肥力非盐碱土壤为实验对象,探讨花生种子在吸水膨胀与萌发过程中,不同类型盐碱土对种子际土壤微生物多样性变化的影响。【方法】采集不同含盐量的滨海盐土、内陆盐碱土和中等肥力非盐碱土壤,通过对各样品中细菌的16S r RNA基因的V3-V4区进行PCR扩增,利用Illumina Hiseq高通量测序技术对12份V3-V4高变区PCR产物进行测序,并对测序数据进行生物信息学分析。【结果】(1)盐碱土壤的种子际细菌群落多样性高于非盐碱土壤,且以东营青坨滨海盐土种子际土壤细菌群落多样性较高。(2)不同类型土壤样本微生物群落结构在纲水平存在明显差异。4种土壤类型种子际土壤细菌共分属于6个菌纲,分别为Proteobacteria、Actinobacteria、Actinobacteria、Bacteroidetes、Acidobacteria和Firmicutes菌纲,并均以Proteobacteria和Actinobacteria菌纲为主要菌纲。全样本菌落结构分析结果表明,4种类型土壤中不同吸胀时间内种子际微生物菌落在门、属水平上的类型和丰度差异最为显著(P0.05)。(3)beta多样性分析和各样本遗传距离(phylogenetic distances)聚类树图分析表明,4个土壤类型的12个土壤样本种子际土壤中微生物群落均可聚为2大类。【结论】土壤含盐量越高其种子际土壤细菌群落多样性较高。不同类型土壤样本微生物群落结构在纲水平存在明显差异,以Proteobacteria和Actinobacteria菌纲为主要菌纲。种子吸胀萌发时间影响种子际微生物菌落在门、属水平上的类型和丰度,但对相同土壤类型样本间遗传距离无影响。     

新疆低阶煤本源生物甲烷转化中微生物群落组成及变化

【目的】探究新疆低阶煤生物甲烷转化过程微生物群落组成及多样性。【方法】采用厌氧培养方法和末端限制性片段长度多态性技术(Terminal restriction fragment length polymorphism,T-RFLP)分析新疆低阶煤本源微生物对甲烷转化及有机酸含量的影响,分析新疆哈密大南湖长焰煤生物甲烷转化过程中微生物群落动态变化。【结果】研究表明长焰煤和褐煤对本源微生物产甲烷影响较小,随着低阶煤生物甲烷转化时间的延长,甲烷产量呈上升趋势,转化60 d后长焰煤甲烷产量高达10.28 m L/g,挥发性有机酸(VFA)浓度则最低;微生物多样性指数变化不明显,不同转化时间微生物主要类群为放线菌门(Actinobacteria),拟杆菌门(Bacteroidetes),厚壁菌门(Firmicutes),变形菌门(Proteobacteria);甲烷菌的群落结构相对于细菌较简单,在整个低阶煤生物转化产甲烷过程中共有古菌类群为甲烷八叠球菌属(Methanosarcina)、甲烷盐菌属(Methanohalobium)、甲烷叶菌属(Methanolobus)、甲烷食甲基菌属(Methanomethylovorans),它们是构成群落结构的基本菌群。【结论】低阶煤生物甲烷转化过程微生物群落具有丰富的多样性,且不同时期多样性有较大差异。甲烷菌群落结构相对于细菌较简单,共有类群明显。     

454高通量焦磷酸测序法鉴定膜生物反应器膜污染优势菌种

【目的】对诱发膜-生物反应器(Membrane bioreactors,MBR)膜污染的优势菌种进行研究。【方法】利用454高通量焦磷酸测序法对MBR污泥混合液样品与膜污染物样品中微生物信息进行统计,并对两组样品的Chao丰度指数与Shannon生物多样性指数计算,对测序结果进行系统发育学分析。【结果】从污泥混合液样品与膜污染物样品中获得9 353与7 504条优化序列,发现膜污染物中微生物丰度与多样性均高于污泥混合样品。借助基因频谱对OTU分布特点进行统计,表明源于污泥混合液中的微生物在膜表面定殖生长过程中发生了种群变化,在膜面污染物样品中,β-变形菌纲丰度显著降低,α-变形菌纲、γ-变形菌纲与Phycisphaerae在微生物种群结构中比重增加。【结论】454焦磷酸测序分析表明,黄色单胞菌(Xanthomonadaceae),嗜热厌氧杆菌(Thermoanaerobacter),Phycisphaera以及2株尚未培养出的细菌(Candidate_division_TM7及Candidate_division_OD1)是诱发MBR膜污染的优势菌种(微生物丰度1%)。诱发膜污染的细菌既包括了黏性高、表面疏水的种类(如γ-变形菌),从而引发细菌在膜表面的定殖,也包括了代谢能力强的物种(如Candidate_division_OD1)可以确保种间递氢顺畅。     

基于高通量测序的4种硝化细菌富集培养物微生物群落结构分析

【目的】比较分析4种硝化细菌富集培养物(以铵盐为氮源的淡水富集物A、以亚硝酸盐为氮源的淡水富集物B、以铵盐为氮源的低温淡水富集物C和以亚硝酸盐为氮源的海水富集物D)的微生物群落结构与组成。【方法】分别提取样品的总DNA,采用高通量测序技术,分析微生物群落的组成、丰度和多样性。【结果】在不同微生物的分类水平,4个样品共检测到24门47纲129属。4个样品的优势菌门均为变形菌门;样品A、B、C的优势菌纲为β-变形菌纲和γ-变形菌纲,样品D的优势菌纲为γ-变形菌纲、δ-变形菌纲和芽孢杆菌纲;而优势菌属各不相同,其中样品A为亚硝化单胞菌属(24.56%),样品B为链霉菌属(7.15%),样品C为噬菌弧菌属(19.36%)和类诺卡氏菌属(19.35%),样品D为嗜酸菌属(13.6%)和柄杆菌属(11.5%)。共检测出7种具有硝化功能的细菌,其中样品A、B和D中主要是亚硝化单胞菌属,占比分别为24.56%、4.94%和0.63%,样品C主要为Nitrospirillum(0.69%)和硝化螺旋菌属(0.69%)。此外在样品中还检测到红灯食烷菌、羽扇豆根瘤菌等有益菌,以及弧菌属、伯克霍尔德菌等致病菌。【结论】阐述了4个样品微生物群落结构的多样性,确定了不同培养物中起主要作用的硝化细菌类群以及其它与环境物质循环相关或具有特殊生理特性的菌群,研究结果为硝化细菌富集培养物的实际应用奠定了基础。     

基于好氧反硝化及反硝化聚磷菌强化的低温低碳氮比生活污水生物处理中试研究

【背景】低碳氮比生活污水很难达标处理,多级A/O工艺、生物强化技术及生物膜技术的有机结合可有效解决这一问题。【目的】开发出一种泥膜共生多级A/O工艺并进行中试研究,驯化出高效脱氮除磷菌剂并对系统进行生物强化。【方法】通过测定中试设备出水及污水处理厂出水化学需氧量(Chemical oxygen demand,COD)、氨氮(NH_4~+-N)、硝氮(NO_3~--N)、总氮(Total nitrogen,TN)、总磷(Total phosphorus,TP)对比分析两种工艺的污染物去除效能,利用高通量测序技术对比生物强化技术对系统微生物群落结构的影响。【结果】中试设备对COD、NH_4~+-N、NO_3~--N、TN、TP的去除效果均优于污水处理厂的处理工艺;驯化的低温好氧反硝化菌TN去除率最大值可达84.21%,驯化的低温反硝化聚磷菌群对磷的去除率最高可达85.75%;利用驯化菌群对中试设备进行生物强化后较好地改善了系统NH_4~+-N、NO_3~--N、TN、TP的去除效果;经生物强化后,具有好氧反硝化和反硝化聚磷功能的Pseudomonas菌群明显增多。【结论】泥膜共生多级A/O工艺对于低碳氮比生活污水的处理具有很好的效果,利用生物强化技术可有效提高低温条件下系统污染物去除效能。     

Nitrogen removal performance and microbial community structure dynamics response to carbon nitrogen ratio in a compact suspended carrier biofilm reactor

A compact suspended carrier biofilm reactor (SCBR) was developed for simultaneous nitrification and denitrification (SND) in a single reactor and the performance of nutrient removal was investigated. Microbial community structure response to different ratio of carbon to nitrogen (C/N) was determined by denaturing gel gradient electrophoresis (DGGE) profiles of 16S rDNA V3 region and amoA gene amplifications. In addition, the population dynamics of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were estimated by fluorescence in situ hybridization (FISH) with 16S rDNA-targeted oligonucleotide probes. Results showed that the compact SCBR was efficient in nutrient removal with COD_Cr removal efficiency over 90% and SND efficiency (E_SND) about 83.3%. The diversity of microbial community structure was positively correlated with C/N ratio, while the three communities of amoA gene were relativity homogenous. The population of nitrifiers was in inverse proportions to C/N ratio with the average fraction of AOB and NOB to all bacteria 5.4, 4.8, 3.1% and 4.6, 3.5, 2.7% respectively as C/N ratio changing from 3:1, 5:1 to 10:1. Therefore we could reach a conclusion that the compact SCBR was practical to treat municipal wastewater and the shift of microbial community monitored by molecular technologies could offer guidance to the process optimization in engineering.     

Impact of Substratum Surface on Microbial Community Structure and Treatment Performance in Biological Aerated Filters

The impact of substratum surface property change on biofilm community structure was investigated using laboratory biological aerated filter (BAF) reactors and molecular microbial community analysis. Two substratum surfaces that differed in surface properties were created via surface coating and used to develop biofilms in test (modified surface) and control (original surface) BAF reactors. Microbial community analysis by 16S rRNA gene-based PCR-denaturing gradient gel electrophoresis (DGGE) showed that the surface property change consistently resulted in distinct profiles of microbial populations during replicate reactor start-ups. Pyrosequencing of the bar-coded 16S rRNA gene amplicons surveyed more than 90% of the microbial diversity in the microbial communities and identified 72 unique bacterial species within 19 bacterial orders. Among the 19 orders of bacteria detected, Burkholderiales and Rhodocyclales of the Betaproteobacteria class were numerically dominant and accounted for 90.5 to 97.4% of the sequence reads, and their relative abundances in the test and control BAF reactors were different in consistent patterns during the two reactor start-ups. Three of the five dominant bacterial species also showed consistent relative abundance changes between the test and control BAF reactors. The different biofilm microbial communities led to different treatment efficiencies, with consistently higher total organic carbon (TOC) removal in the test reactor than in the control reactor. Further understanding of how surface properties affect biofilm microbial communities and functional performance would enable the rational design of new generations of substrata for the improvement of biofilm-based biological treatment processes.     

Coexistence of nitrifiers, denitrifiers and Anammox bacteria in a sequencing batch biofilm reactor as revealed by PCR-DGGE

Aims:  The bacterial diversity in a sequencing batch biofilm reactor (SBBR) treating landfill leachate was studied to explain the mechanism of nitrogen removal.
Methods and Results:  The total microbial DNA was extracted from samples collected from landfill leachate and biofilm of the reactor with the removal efficiencies of NH₄⁺-N higher than 97% and that of chemical oxygen demand (determined by K₂Cr₂O₇, COD_Cr) higher than 86%. Denaturing gradient gel electrophoresis (DGGE) fingerprints based on total community 16S rRNA genes were analyzed with statistical methods, and excised DNA bands were sequenced. The results of phylogenetic analyses revealed high diversity within the SBBR biofilm community, and DGGE banding patterns showed that the community structure in the biofilm remained stable during the running period.
Conclusions:  A coexistence of nitrifiers, including ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, denitrifiers, including aerobic or anaerobic denitrifying bacteria and Anammox bacteria were detected, which might be the real matter of high removal efficiencies of NH₄⁺-N and COD_Cr in the reactor.
Significance and Impact of the Study:  The findings in this study indicated that PCR-DGGE analysis could be used for microbial community detection as prior method, and the SBBR technique could provide preferable growing environment for bacteria with N removal function.     

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.     

微生物电解池阳极生物膜功能菌群构建及群落特征分析

【目的】微生物电解电池(MEC)是近几年快速发展的利用电极呼吸微生物快速降解有机质,通过较小的辅助外加电压直接生成氢气的新工艺。MEC能够有效地富集高效率电子传递功能菌群,是未来工艺放大和快速启动的关键。【方法】采用不同驯化方法构建MEC电极微生物菌群,通过单链构象多肽性技术(Single-strand conformation poly-morphism,SSCP)快速检测分析启动后电子传递功能菌群特征。【结果】阳极生物膜接种MEC可以实现2 d的快速启动,库仑效率达到20%以上,7 d获得稳定产氢,氢气转化率达到30%,能量回收效率达到90%以上。通过SSCP群落分析发现,采用微生物燃料电池阳极生物膜构建的MEC主要电子传递功能相关的菌群包括Pseudomonas sp.、Flavobacterium sp.、Ochrobactrum sp.,而直接由产氢MEC阳极生物膜新启动的MEC功能菌群组成丰度更大,包括电子传递效能更高的Desulfovibrio、Pseudomonas和Shewanella成为主要优势电子传递菌群。通过稳定产氢运行,MEC阳极生物膜优势菌群中存在的较大比例的厌氧菌与电子传递辅助菌对体系的快速稳定运行十分重要。【结论】与MFC阳极生物膜相比,MEC生物膜作为启动菌源能够获得多样性更丰富的电极功能菌群,其库仑效率和产氢效率更具优势。     

FISH荧光原位杂交技术在污水生物脱氮研究中的应用

简要介绍了荧光原位杂交（FISH）的基本原理,着重讨论近年来该技术在污水生物脱氮研究中的应用现状和特点。研究表明：FISH技术能够准确地表现污水处理反应器中脱氮菌群落的类型和结构形态。但在关于SRT、DO、C／N比等工艺参数的变化对脱氮反应器中微生物类型、数量和结构的影响等方面的研究还有待深入。FISH技术与PCR—DGGE和16SrRNA／rDNA序列分析等技术相结合是对污水处理构筑物中生物脱氮群落深入研究的发展方向。     

Comparison of long-term performances and final microbial compositions of anaerobic reactors treating landfill leachate

Laboratory scale anaerobic upflow filter, sludge blanket and hybrid bed reactors were operated for 860 days in the treatment of high ammonia landfill leachate. Organic loading was gradually increased from 1.3 to 23.5 kg COD/m3 day in the start-up period and then fluctuated according to the COD concentration of raw leachate. To prevent free ammonia inhibition, influent pH was reduced to 4.5 after Day 181 and consequently COD removal efficiencies above 80% were achieved in all reactors. However, the anaerobic filter and hybrid bed reactor were generally found slightly more efficient and stable than the UASB reactor. In addition to conventional anaerobic reactor control parameters, the complementary techniques of denaturing gradient gel electrophoresis (DGGE), cloning and fluorescent in situ hybridization (FISH) were used to identify and compare the microbial profiles in the reactors at Day 830. Molecular analyses revealed that acetoclastic Methanosaeta species were prevalent in all reactors and configuration did not have an impact on microbial diversity in the long-term.     

Backwash intensity and frequency impact the microbial community structure and function in a fixed-bed biofilm reactor

Linkages among bioreactor operation and performance and microbial community structure were investigated for a fixed-bed biofilm system designed to remove perchlorate from drinking water. Perchlorate removal was monitored to evaluate reactor performance during and after the frequency and intensity of the backwash procedure were changed, while the microbial community structure was studied using clone libraries and quantitative PCR targeting the 16S rRNA gene. When backwash frequency was increased from once per month to once per day, perchlorate removal initially deteriorated and then recovered, and the relative abundance of perchlorate-reducing bacteria (PRB) initially increased and then decreased. This apparent discrepancy suggested that bacterial populations other than PRB played an indirect role in perchlorate removal, likely by consuming dissolved oxygen, a competing electron acceptor. When backwash intensity was increased, the reactor gradually lost its ability to remove perchlorate, and concurrently the relative abundance of PRB decreased. The results indicated that changes in reactor operation had a profound impact on reactor performance through altering the microbial community structure. Backwashing is an important yet poorly characterized procedure when operating fixed-bed biofilm reactors. Compared to backwash intensity, changes in backwash frequency exerted less disturbance on the microbial community in the current study. If this finding can be confirmed in future work, backwash frequency may serve as the primary parameter when optimizing backwash procedures.     

Modeling of an anoxic/methanogenic biofilm: effect of pH calculation within the biofilm

The models of anoxic/methanogenic processes in biofilm reactors published until now have supposed that pH does not change between the bulk liquid and biofilm. These assumptions are not necessarily valid for processes in reactors with biofilms. The present work studied an anoxic/methanogenic biofilm reactor incorporating the pH variation in both bulk and biofilm. Two dynamic models, one including the calculation of pH throughout the biofilm, were solved numerically and compared with each other. The results showed that the inclusion of a pH algorithm calculation produces different profiles and efficiencies on an anoxic/methanogenic biofilm system. Values of C/N ratio higher than 20 mg TOC/mg NO₃–N and values of HRT lower than 4.5 h produce differences of up to 46 % with a traditional model that does not include pH calculation inside the biofilm. Thus, the assumption of a constant pH within the biofilm when using the traditional model does not accurately describe the performance of the system under these conditions, and pH calculation inside the biofilm should be included.