Influence of transitional states on the microbial ecology of anaerobic digesters treating solid wastes

A better understanding of the microbial ecology of anaerobic processes during transitional states is important to achieve a long-term efficient reactor operation. Five wastes (pig manure, biodiesel residues, ethanol stillage, molasses residues, and fish canning waste) were treated in five anaerobic reactors under the same operational conditions. The influence of the type of substrate and the effect of modifying feeding composition on the microbial community structure was evaluated. The highest biomethanation efficiency was observed in reactors fed with fish canning waste, which also presented the highest active archaeal population and the most diverse microbial communities. Only two Bacteria populations could be directly related to a particular substrate: Ilyobacter with biodiesel residues and Trichococcus with molasses residues. Results showed that the time to achieve steady-state performance after these transitional states was not dependent on the substrate treated. But reactors needed more time to handle the stress conditions derived from the start-up compared to the adaptation to a new feeding. Cluster analyses showed that the type of substrate had a clear influence on the microbiology of the reactors, and that segregation was related to the reactors performance. Finally, we conclude that the previous inoculum history treating solid waste and higher values of active Archaea population are important factors to face a successful change in substrate not entailing stability failure.     

Influence of diligent disintegration on anaerobic biomass and performance of microbial fuel cell

Objectives

To enhance the performance of microbial fuel cells (MFC) by increasing the surface area of cathode and diligent mechanical disintegration of anaerobic biomass.

Results

Tannery effluent and anaerobic biomass were used. The increase in surface area of the cathode resulted in 78% COD removal, with the potential, current density, power density and coulombic efficiency of 675 mV, 147 mA m^?2, 33 mW m^?2 and 3.5%, respectively. The work coupled with increased surface area of the cathode with diligent mechanical disintegration of the biomass, led to a further increase in COD removal of 82% with the potential, current density, power density and coulombic efficiency of 748 mV, 229 mA m^?2, 78 mW m^?2 and 6% respectively.

Conclusions

Mechanical disintegration of the biomass along with increased surface area of cathode enhances power generation in vertical MFC reactors using tannery effluent as fuel.

     

Influence of sulfate reduction on the microbial dechlorination of pentachloroaniline in a mixed anaerobic culture

The reductive dechlorination of pentachloroaniline (PCA) was investigated in the absence and presence of sulfate in batch assays using a PCA-dechlorinating mixed anaerobic culture with methanol as the external electron donor at neutral pH and 22°C. PCA at an initial concentration of 7.8 μM was sequentially dechlorinated to dichlorinated anilines in the sulfate-free culture and the culture amended with 300 mg sulfate-S/L. At an initial concentration of 890 mg sulfate-S/L, a higher sulfate reduction rate was achieved, but PCA dechlorination was not observed until the sulfate concentration dropped to about 100 mg S/L. The transient inhibition of PCA is attributed to competition between sulfate reducing and dechlorinating species for electron donor, more likely for H₂ resulting from methanol fermentation. A long-term (118 days) PCA dechlorination assay with the sulfate-amended culture, which included five feeding cycles, resulted in accumulation of both sulfide (886 mg S/L) and acetate (1,900 mg COD/L). Under these conditions, the sulfate reducers were inhibited, while the rate and pathway of PCA dechlorination were not affected. The results of this study show that the rate of sulfate reduction rather than the sulfate concentration alone dictates the outcome of the competition between sulfate reducers and either dechlorinators or methanogens. The findings of the present study have significant implications relative to the fate and transport of PCA and its dechlorination products in sulfate-laden subsurface systems.     

Influence of co-substrates on structure of microbial aggregates in long-chain fatty acid-fed anaerobic digesters

AIMS: The purpose of this study was to investigate the influence of co-substrates, such as glucose and cysteine, on the structure of microbial aggregates in anaerobic digesters treating oleate, a long-chain fatty acid (LCFA). METHODS AND RESULTS: Transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) were used to examine the structure of microbial aggregates. Fluorescence in situ hybridization (FISH) techniques were also used to characterize and localize the different trophic groups present in the aggregates. Oleate was found to inhibit the methanogenic activity and formation of granular biomass in digesters. The addition of co-substrates, such as glucose and cysteine either singly or in combination, increased the methanogenic activity and formation of granular biomass. Glucose was more effective than cysteine in reducing the inhibition by oleate on the methanogenic bacteria and in enhancing the formation of granules. CONCLUSIONS: The addition of nutrient substrate, such as glucose and cysteine could decrease the toxicity of LCFA on anaerobic granulation. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggest that the addition of other substrates might decrease the toxicity of LCFA on the granulation of biomass in anaerobic digesters and enhance methanogenic activity. A combination of TEM, CLSM and FISH techniques provides a better tool for visualizing microbial aggregates and for differentiating and localizing different microbial groups within these aggregates.     

Influence of polyaluminum chloride on microbial characteristics in anaerobic membrane bioreactors for sludge digestion

In this study, two parallel lab-scale anaerobic membrane bioreactors (AnMBRs), one of which was dosed with polyaluminum chloride (PAC) for membrane fouling control, were operated for treating excess activated sludge collected from a wastewater treatment plant (WWTP). The AnMBRs were inoculated with anaerobic digested sludge collected from an anaerobic digester of another WWTP. The microbial community of digested sludge and cake layer in AnMBRs, as well as that of excess sludge, was analyzed through polymerase chain reaction coupled with denaturing gradient gel electrophoresis (PCR-DGGE) and Illumina MiSeq. The dynamic variation of archaeal community in AnMBRs was not as obvious as that of bacterial community based on the PCR-DGGE results. Under the circumstance of stable operation, Cloacimonetes, Chloroflexi, Bacteroidetes, Proteobacteria, Firmicutes, and Ignavibacteriae were observed as the predominant phyla in digested sludge based on the Illumina results. In addition to that, the cake layer possessed similar predominant phyla with the digested sludge but owned a higher diversity. Furthermore, overlapping bacterial communities were discovered between the excess sludge and digested sludge. However, the abundance of aerobic bacteria was substantially reduced, while the abundance of anaerobic microorganisms like phylum Cloacimonetes and Smithella was enriched in digested sludge over time. Additional PAC dosing, on the one hand, affected the bioavailable substrate, thus further changing the microbial community structure; on the other hand, aluminum itself also affected specific microbial communities. Besides, PAC dosing indirectly influenced the bacterial diversity in AnMBR as well.

     

High resolution single cell analytics to follow microbial community dynamics in anaerobic ecosystems

Analyzing natural anaerobic microbial communities is a challenge and interpretation of the respective members' performances arduous. Strict anaerobes are often slow-growing and difficult to cultivate due to their unknown physiological capacities. Additionally, abiotic micro-environmental data are difficult to assess, limiting the information on the eco-chemical background in natural environments. This review describes how qualitative and quantitative data can be obtained on anaerobic microbial communities isolated from anoxic environments and treated under laboratory conditions. It gives information on how community composition ('phylogenetic fingerprint') and community structure ('cytometric fingerprint') can be described by PCR-based and single cell-based techniques, respectively. A cell sorting step combined both approaches and enabled quantitative and more precise community resolution. The community dynamics found were swift and strong, despite low and slow changes in measured abiotic parameters. Therefore, the community structure itself mirrored variation in the constructed long term (6years) ecosystem in a most sensitive way and can be used as sensor for the ecosystems situation. New statistical tools are presented allowing suddenly changing performances of complex communities to be detected and community (in) stabilities to be monitored and/or predicted.     

Carbon balance of anaerobic granulation process: carbon credit

The concept of carbon credit arose out of increasing awareness of the need to reduce emissions of greenhouse gases to combat global warming which was formalized in the Kyoto protocol. In addition to contribution to sustainable development with energy recovery in the form of methane, carbon credits can be claimed by application of advanced anaerobic processes in wastewater treatment for reducing emissions of greenhouse gases. As anaerobic granular systems are capable of handling high organic loadings concomitant with high strength wastewater and short hydraulic retention time, they could render much more carbon credits than other conventional anaerobic systems. This study investigated the potential carbon credit derived from laboratory-scale upflow anaerobic sludge blanket (UASB) reactors based on a carbon balance analysis. Methane emission reduction could be calculated by calculating the difference of UASB reactors and open lagoon treatment systems. Based on the 2.5l bench-scale reactor, the total CH(4) emissions reduction was calculated as 29 kg CO(2)/year. On scaling up to a typical full-scale anaerobic digester, the total CH(4) emissions reduction could achieve 46,420 tons CO(2) reduction/year. The estimated carbon credits would amount to 278,500 US$ per year by assuming a carbon price of 6 US$ per metric ton CO(2) reduction. The analysis postulated that it is financially viable to invest in advanced anaerobic granular treatment system from the revenue generated from carbon credits.     

Influence of methane enrichment by aeration of recirculated supernatant on microbial activities during anaerobic digestion

A methane enrichment process (MEP) was evaluated that involved air purging of recycled digester contents to strip CO₂ and increase biogas methane content. The objective of this work was to determine if the aeration resulted in oxygen inhibition of microbial activities involved in anaerobic digestion of municipal solid waste. To assess the degree of biological perturbation associated with the MEP, the reactor effluent was sampled twice while the MEP was operating and twice while it was not operating. Analyses were run on composite samples (representing several different sample ports of the non-mixed reactor) and samples of digester effluent entering and leaving the MEP process. The analyses included volatile organic acids (VOA), effluent solids content, dehydrogenase activity, specific methanogenic activities (SMA), and enzyme-linked immunosorbent assay (ELISA) for methanogenic, sulfate-reducing, and cellulolytic bacterial species. Methane enrichment in these experiments occurred with the methane content of the biogas exceeding 90%. There were no effects of the MEP on effluent VOA concentration. The MEP had no effect on volatile solids (VS) levels of composite samples representing the non-mixed digester contents, however, VS was reduced in effluent passing through the MEP. Although MEP had an inhibitory effect on anaerobic populations leaving the MEP process, no inhibitory effects were observed in measurements of microbial activities in digester samples, including specific methane production rate, dehydrogenase, and numbers of specific organisms estimated using ELISA techniques.     

Characterization of microbial community dynamics during the anaerobic co-digestion of thermally pre-treated slaughterhouse wastes with glycerin addition

Bioprocess and Biosystems Engineering - Microbial community dynamics during the anaerobic co-digestion of pig manure, pasteurized slaughterhouse waste and glycerin were studied in a lab-scale CSTR....     

Changes in the microbial community during repeated anaerobic microbial dechlorination of pentachlorophenol

Pentachlorophenol (PCP) has been widely used as a pesticide in paddy fields and has imposed negative ecological effect on agricultural soil systems, which are in typically anaerobic conditions. In this study, we investigated the effect of repeated additions of PCP to paddy soil on the microbial communities under anoxic conditions. Acetate was added as the carbon source to induce and accelerate cycles of the PCP degradation. A maximum degradation rate occurred at the 11th cycle, which completely transformed 32.3 μM (8.6 mg L^?1) PCP in 5 days. Illumina high throughput sequencing of 16S rRNA gene was used to profile the diversity and abundance of microbial communities at each interval and the results showed that the phyla of Bacteroidates, Firmicutes, Proteobacteria, and Euryarchaeota had a dominant presence in the PCP-dechlorinating cultures. Methanosarcina, Syntrophobotulus, Anaeromusa, Zoogloea, Treponema, W22 (family of Cloacamonaceae), and unclassified Cloacamonales were found to be the dominant genera during PCP dechlorination with acetate. The microbial community structure became relatively stable as cycles increased. Treponema, W22, and unclassified Cloacamonales were firstly observed to be associated with PCP dechlorination in the present study. Methanosarcina that have been isolated or identified in PCP dechlorination cultures previously was apparently enriched in the PCP dechlorination cultures. Additionally, the iron-cycling bacteria Syntrophobotulus, Anaeromusa, and Zoogloea were enriched in the PCP dechlorination cultures indicated they were likely to play an important role in PCP dechlorination. These findings increase our understanding for the microbial and geochemical interactions inherent in the transformation of organic contaminants from iron rich soil, and further extend our knowledge of the PCP-transforming microbial communities in anaerobic soil conditions.     

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。     

Effect of starting material particle size on its agglomeration behavior in high shear wet granulation

The effect of anhydrous lactose particle size distribution on its performance in the wet granulation process was evaluated. Three grades of anhydrous lactose were used in the study: “as is” manufacturer grade and 2 particle size fractions obtained by screening of the 60M lactose. Particle growth behavior of the 3 lactose grades was evaluated in a high shear mixer. Compactibility and porosity of the resulting granules were also evaluated. A uniaxial compression test on moist agglomerates of the 3 lactose grades was performed in an attempt to explain the mechanism of particle size effect observed in the high shear mixer. Particle growth of anhydrous lactose in the high shear mixer was inversely related to the particle size of the starting material. In addition, granulation manufactured using the grade with the smallest particle size was more porous and demonstrated enhanced compactibility compared with the other grades. Compacts with similar porosity and low liquid saturation demonstrated brittle behavior and their breakage strength was inversely related to lactose particle size in the uniaxial compression test, suggesting that material with smaller particle size may exhibit more pronounced nucleation behavior during wet granulation. On the other hand, compacts prepared at higher liquid saturation and similar compression force exhibited more plastic behavior and showed lower yield stress for the grade with smallest particle size. The lower yield stress of compacts prepared with this grade may indicate a higher coalescence tendency for its granules during wet granulation.     

Acidification of methanol-fed anaerobic granular sludge bioreactors by cobalt deprivation: Induction and microbial community dynamics

The acidification of mesophilic (30 degrees C) methanol-fed upflow anaerobic sludge bed (UASB) reactors induced by cobalt deprivation from the influent was investigated by coupling the reactor performance (pH 7.0; organic loading rate 4.5 g COD . L(-1) . d(-1)) to the microbial ecology of the bioreactor sludge. The latter was investigated by specific methanogenic activity (SMA) measurements and fluorescence in situ hybridization (FISH) to quantify the abundance of key organisms over time. This study hypothesized that under cobalt limiting conditions, the SMA on methanol of the sludge gradually decreases, which ultimately results in methanol accumulation in the reactor effluent. Once the methanol accumulation surpasses a threshold value (about 8.5 mM for the sludge investigated), reactor acidification occurs because acetogens outcompete methylothrophic methanogens at these elevated methanol concentrations. Methanogens present in granular sludge at the time of the acidification do not use methanol as the direct substrate and are unable to degrade acetate. Methylotrophic/acetoclastic methanogenic activity was found to be lost within 10 days of reactor operation, coinciding with the disappearance of the Methanosarcina population. The loss of SMA on methanol can thus be used as an accurate parameter to predict reactor acidification of methanol-fed UASB reactors operating under cobalt limiting conditions.     

干法造粒工艺在微生态活菌片剂生产中的应用研究

目的为降低生产成本,保证产品质量,研究干法造粒工艺在微生态活菌片剂生产中的应用。方法测定三批干法造粒和粉末直接压片技术获得的片剂的理化指标和贮藏期间活菌数。结果干法造粒工艺生产的片剂其片重、硬度、崩解时限和干燥失重均符合生产质量要求,且提高了产品的贮藏稳定性。结论干法造粒工艺更适用于微生态活菌片剂生产。     

Fluid dynamics of anaerobic fermentation

In beer fermentation, yeast cells are kept in suspension, despite their higher density, by natural agitation created by ascending CO₂ bubbles. Yeast cells are unable to nucleate bubbles but instead release CO₂ in a soluble form in such a way that the medium tends to become supersaturated. A higher concentration of yeast cells and the presence of solid particles cause the formation of bubbles at the bottom of the fermenter and practically only there. The rising bubbles grow and accelerate by sweeping the CO₂ formed throughout the fermenter by the suspended yeast cells, thereby creating a fluid regime. A mathematical expression relating the bubble agitation power to the fermentation parameters was obtained and used to design more efficient fermenter shapes.     

Influence of biogas-induced mixing on granulation in UASB reactors

Studies have been carried out to correlate biogas-induced mixing and granulation in upflow anaerobic sludge blanket (UASB) reactors, treating low-strength as well as high-strength biodegradable wastewaters. A dimensionless granulation index (GI) has been framed taking into account the mixing in sludge bed due to produced biogas. Analysis of full-scale, pilot-scale and lab-scale UASB reactors treating actual wastewaters reveals the significance of biogas-induced mixing, represented by GI, on granulation of biomass in the reactors. For obtaining proper granulation in UASB reactors (percentage granules greater than 50%, w/w), resulting in higher chemical oxygen demand (COD) removal efficiency, it is recommended to maintain GI values in the range of 15,000–57,000.     

Repeated anaerobic microbial redox cycling of iron

Some nitrate- and Fe(III)-reducing microorganisms are capable of oxidizing Fe(II) with nitrate as the electron acceptor. This enzymatic pathway may facilitate the development of anaerobic microbial communities that take advantage of the energy available during Fe-N redox oscillations. We examined this phenomenon in synthetic Fe(III) oxide (nanocrystalline goethite) suspensions inoculated with microflora from freshwater river floodplain sediments. Nitrate and acetate were added at alternate intervals in order to induce repeated cycles of microbial Fe(III) reduction and nitrate-dependent Fe(II) oxidation. Addition of nitrate to reduced, acetate-depleted suspensions resulted in rapid Fe(II) oxidation and accumulation of ammonium. High-resolution transmission electron microscopic analysis of material from Fe redox cycling reactors showed amorphous coatings on the goethite nanocrystals that were not observed in reactors operated under strictly nitrate- or Fe(III)-reducing conditions. Microbial communities associated with N and Fe redox metabolism were assessed using a combination of most-probable-number enumerations and 16S rRNA gene analysis. The nitrate-reducing and Fe(III)-reducing cultures were dominated by denitrifying Betaproteobacteria (e.g., Dechloromonas) and Fe(III)-reducing Deltaproteobacteria (Geobacter), respectively; these same taxa were dominant in the Fe cycling cultures. The combined chemical and microbiological data suggest that both Geobacter and various Betaproteobacteria participated in nitrate-dependent Fe(II) oxidation in the cycling cultures. Microbially driven Fe-N redox cycling may have important consequences for both the fate of N and the abundance and reactivity of Fe(III) oxides in sediments.     

Influence of extrinsic factors on granulation in UASB reactor

The aim of this mini-review is to synthesize and analyze information on how the process of granulation is affected by environmental and operational conditions in the reactor. The factors reviewed are temperature, pH, alkalinity, organic loading rate, upflow velocity, nature and strength of substrate, nutrients, multivalent cations and heavy metals, microbial ecology of seed sludge, exo-cellular polymer, and addition of natural and synthetic polymers. Careful temperature control and adequate alkalinity is required for generation and maintenance of granules. Nature and strength of substrate in conjunction with intra-granular diffusion to a large extent determines the microstructure of the granules. The divalent cations such as calcium and iron may enhance granulation by ionic bridging and linking exo-cellular polymers. However, their presence in excess may lead to cementation due to precipitation leading to increased ash content and mass transfer limitation. The addition of external additives such as ionic polymers may enhance granulation in the upflow anaerobic sludge blanket reactors.     

A meta-analysis of the microbial diversity observed in anaerobic digesters

In this study, the collective microbial diversity in anaerobic digesters was examined using a meta-analysis approach. All 16S rRNA gene sequences recovered from anaerobic digesters available in public databases were retrieved and subjected to phylogenetic and statistical analyses. As of May 2010, 16,519 bacterial and 2869 archaeal sequences were found in GenBank. The bacterial sequences were assigned to 5926 operational taxonomic units (OTUs, based on ?97% sequence identity) representing 28 known bacterial phyla, with Proteobacteria (1590 OTUs), Firmicutes (1352 OTUs), Bacteroidetes (705 OTUs), and Chloroflexi (693 OTUs) being predominant. Archaeal sequences were assigned to 296 OTUs, primarily Methanosaeta and the uncharacterized WSA2 group. Nearly 60% of all sequences could not be classified to any established genus. Rarefaction analysis indicates that approximately 60% of bacterial and 90% of archaeal diversity in anaerobic digesters has been sampled. This analysis of the global bacterial and archaeal diversity in AD systems can guide future studies to further examine the microbial diversity involved in AD and development of comprehensive analytical tools.