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.     

Phenotypic Properties and Microbial Diversity of Methanogenic Granules from a Full-Scale Upflow Anaerobic Sludge Bed Reactor Treating Brewery Wastewater

Methanogenic granules from an anaerobic bioreactor that treated wastewater of a beer brewery consisted of different morphological types of granules. In this study, the microbial compositions of the different granules were analyzed by molecular microbiological techniques: cloning, denaturing gradient gel electrophoresis and fluorescent in situ hybridization (FISH), and scanning and transmission electron microscopy. We propose here that the different types of granules reflect the different stages in the life cycle of granules. Young granules were small, black, and compact and harbored active cells. Gray granules were the most abundant granules. These granules have a multilayer structure with channels and void areas. The core was composed of dead or starving cells with low activity. The brown granules, which were the largest granules, showed a loose and amorphous structure with big channels that resulted in fractured zones and corresponded to the older granules. Firmicutes (as determined by FISH) and Nitrospira and Deferribacteres (as determined by cloning and sequencing) were the predominant Bacteria. Remarkably, Firmicutes could not be detected in the brown granules. The methanogenic Archaea identified were Methanosaeta concilii (70 to 90% by FISH and cloning), Methanosarcina mazei, and Methanospirillum spp. The phenotypic appearance of the granules reflected the physiological condition of the granules. This may be valuable to easily select appropriate seed sludges to start up other reactors.     

Analysis of Microbial Community during Biofilm Development in an Anaerobic Wastewater Treatment Reactor

The formation, structure, and biodiversity of a multispecies anaerobic biofilm inside an Upflow Anaerobic Sludge Bed (UASB) reactor fed with brewery wastewater was examined using complementary microbial ecology methods such us fluorescence in situ hybridization (FISH), denaturing gradient gel electrophoresis (DGGE), and cloning. The biofilm development can be roughly divided into three stages: an initial attachment phase (0-36 h) characterized by random adhesion of the cells to the surface; a consolidation phase (from 36 h to 2 weeks) defined by the appearance of microcolonies; and maturation phase (from 2 weeks to 2 months). During the consolidation period, proteobacteria with broad metabolic capabilities, mainly represented by members of alpha-Proteobacteria class (Oleomonas, Azospirillum), predominated. Beta-, gamma-, delta- (both syntrophobacteria and sulfate-reducing bacteria) and epsilon- (Arcobacter sp.) Proteobacteria were also noticeable. Archaea first appeared during the consolidation period. A Methanospirillum-like methanogen was detected after 36 h, and this was followed by the detection of Methanosarcina, after 4 days of biofilm development. The mature biofilm displayed a hill and valley topography with cells embedded in a matrix of exopolymers where the spatial distribution of the microorganisms became well-established. Compared to the earlier phases, the biodiversity had greatly increased. Although alpha-Proteobacteria remained as predominant, members of the phyla Firmicutes, Bacteroidete, and Thermotogae were also detected. Within the domain Archaea, the acetoclastic methanogen Methanosaeta concilii become dominant. This study provides insights on the trophic web and the shifts in population during biofilm development in an UASB reactor.     

Molecular Characterization of Microbial Population Dynamics during Sildenafil Citrate Degradation

Little is known about pharmaceutical and personal care products pollutants (PPCPs), but there is a growing interest in how they might impact the environment and microbial communities. The widespread use of Viagra (sildenafil citrate) has attracted great attention because of the high usage rate, the unpredictable disposal and the unknown potential effects on wildlife and the environment. Until now information regarding the impact of Viagra on microbial community in water environment has not been reported. In this research, for the first time, the genetic profile of the microbial community, developing in a Viagra polluted water environment, was evaluated by means of the 16S and 18S rRNA genes, for bacteria and fungi, respectively, amplified by polymerase chain reaction (PCR) and separated using the denaturing gradient gel electrophoresis (DGGE) technique. The DGGE results revealed a complex microbial community structure with most of the population persisting throughout the experimental period. DNA sequences from bands observed in the different denaturing gradient gel electrophoresis profiles exhibited the highest degree of identity to uncultured bacteria and fungi found previously mainly in polluted environmental and treating bioreactors. Biotransformation ability of sildenafil citrate by the microbial pool was studied and the capability of these microorganisms to detoxify a polluted water ecosystem was assessed. The bacterial and fungal population was able to degrade sildenafil citrate entirely. Additionally, assays conducted on Daphnia magna, algal growth inhibition assay and cell viability determination on HepG2 human cells showed that biotransformation products obtained from the bacterial growth was not toxic. The higher removal efficiency for sildenafil citrate and the lack of toxicity by the biotransformation products obtained showed that the microbial community identified here represented a composite population that might have biotechnological relevance to retrieve sildenafil citrate contaminated sites.     

Determination of the Microbial Population in Thermophilic Anaerobic Reactor: Comparative Analysis by Different Counting Methods

This paper describes the determination of the microbial population, in terms of the number, biomass and composition, of single and two-phase, laboratory-scale thermophilic (55°C) anaerobic reactors, under steady-state conditions. Epifluorescence microscopy with DAPI (4′,6-diamidine-2-phenylindole) as fluorochrome was used to determine the total number of micro-organisms in the reactors, and autofluorescence microscopy for the number of the autofluroescent methanogenic populations. The results obtained by the direct count methods were compared to the quantity of biomass contained in the system, determined by volatile suspended solids. The viable bacterial population was determined by plating techniques using an anaerobic chamber. The total bacterial and F420 autofluorescent populations of single-stage digesters increase when the hydraulic retention time decreases; nevertheless, the percentages of the autofluorescent methanogens remain constant at 13%. In the two-stage reactors, the percentages of this group are 99% and 26% of the total population in the acidogenic and methanogenic factors, respectively. In the single-stage reactors, biomass determinations can be used to estimate microbial concentrations, and vice versa, as there is a high positive correlation between microorganism concentration and biomass. It was obtained a high correlation between direct counts by epifluorescence microscopy and viable plate counts for the combined system studied.     

Anaerobic Reactor Design Concepts for the Treatment of Domestic Wastewater

Since the earlier anaerobic treatment systems, the design concepts were improved from classic reactors like septic tanks and anaerobic ponds, to modern high rate reactor configurations like anaerobic filters, UASB, EGSB, fixed film fluidized bed and expanded bed reactors, and others. In this paper, anaerobic reactors are evaluated considering the historical evolution and types of wastewaters. The emphasis is on the potential for application in domestic sewage treatment, particularly in regions with a hot climate. Proper design and operation can result in a high capacity and efficiency of organic matter removal using single anaerobic reactors. Performance comparison of anaerobic treatment systems is presented based mostly on a single but practical parameter, the hydraulic retention time. Combined anaerobic reactor systems as well as combined anaerobic and non-anaerobic systems are also presented.     

Microbial and Physicochemical Characteristics of Compact Anaerobic Ammonium-Oxidizing Granules in an Upflow Anaerobic Sludge Blanket Reactor

Anaerobic ammonium oxidation (anammox) is a promising new process to treat high-strength nitrogenous wastewater. Due to the low growth rate of anaerobic ammonium-oxidizing bacteria, efficient biomass retention is essential for reactor operation. Therefore, we studied the settling ability and community composition of the anaerobic ammonium-oxidizing granules, which were cultivated in an upflow anaerobic sludge blanket (UASB) reactor seeded with aerobic granules. With this seed, the start-up period was less than 160 days at a NH₄⁺-N removal efficiency of 94% and a loading rate of 0.064 kg N per kg volatile suspended solids per day. The formed granules were bright red and had a high settling velocity (41 to 79 m h⁻¹). Cells and extracellular polymeric substances were evenly distributed over the anaerobic ammonium-oxidizing granules. The high percentage of anaerobic ammonium-oxidizing bacteria in the granules could be visualized by fluorescent in situ hybridization and electron microscopy. The copy numbers of 16S rRNA genes of anaerobic ammonium-oxidizing bacteria in the granules were determined to be 4.6 × 10⁸ copies ml⁻¹. The results of this study could be used for a better design, shorter start-up time, and more stable operation of anammox systems for the treatment of nitrogen-rich wastewaters.The anaerobic ammonia oxidation (anammox) process is a recently discovered biological nitrogen removal technology in which ammonia is oxidized to nitrogen gas with nitrite as the electron acceptor (5, 29, 32). In contrast to heterotrophic denitrification (6, 26), the anammox process does not require external electron donors (e.g., methanol) due to their chemolithoautotrophic lifestyle. Furthermore, if this process is combined with a partial nitrification step, only half of the ammonium needs to be nitrified to nitrite, which together with the remaining ammonium can subsequently be converted into nitrogen through the anammox process. This reduces the oxygen demand of the system and leads to further reduction in operational costs (27).The anaerobic ammonium-oxidizing bacteria (anammox bacteria) have a low growth rate (18), with a doubling time at best estimated as 7 to 11 days (18, 28). The yield of the anammox bacteria has been determined to be 0.066 mol C biomass mol⁻¹ ammonium consumed, and the maximum ammonium consumption rate is ∼45 nmol mg⁻¹ protein min⁻¹ (18). Given the low growth rate and low yield, very efficient biomass retention is essential to retain the anammox bacteria within the reactor systems during cultivation (19). The enrichment of anammox bacteria from a mixed inoculum requires the optimization of conditions favorable for the anammox bacteria and generally takes 200 to 300 days (5, 6, 27). Thus, conditions that would reduce the start-up time of anammox reactors would positively effect the implementation of the process. Several sources of inocula, such as activated sludge (4), nitrifying activated sludge (27), and anaerobic sludge (6), have been used for the start-up of anammox reactors with start-up times of as long as 1,000 days (27).Aerobic granules have been reported to have high microbial diversity (31) and compact structure with very good settling properties resulting in an efficient means of biomass retention. These properties, including interspecies competition and mass transfer, result in the stratification of microbial species with anoxic pockets in the interior of the granules that may be suitable to harbor anammox bacteria. Therefore, the main objective of this study was to investigate the feasibility of start-up of the anammox process by seeding the reactor with aerobic granular sludge by using an upflow anaerobic sludge blanket (UASB) reactor. After the successful start-up and the formation of anammox granules, the structure and physicochemical properties of the anammox granules and the reactor performance were characterized. Microbial community analysis revealed that the dominant anammox species was related to a species of anammox bacteria present in anammox biofilms.     

Structure and Dynamics of Anaerobic Bacterial Aggregates in a Gas-Lift Reactor

Anaerobic mixed-culture aggregates, which converted glucose to acetic, propionic, butyric, and valeric acids, were formed under controlled conditions of substrate feed (carbon limitation) and hydraulic regimen. The continuous-flow system used (anaerobic gas-lift reactor) was designed to retain bacterial aggregates in a well-mixed reactor. Carrier availability (i.e., liquid-suspended sand grains) proved necessary for bacterial aggregate formation from individual cells during reactor start-up. Electron microscopic examination revealed that incipient colonization of sand grains by bacteria from the bulk liquid occurred in surface irregularities, conceivably reflecting local quiescence. Subsequent confluent biofilm formation on sand grains proved to be unstable, however. Substrate depletion in the bulk liquid is assumed to weaken deeper parts of the biofilm due to cellular lysis, after which production of gas bubbles and liquid shearing forces cause sloughing. The resulting fragments, although sand free, were nevertheless large enough to be retained in the reactor and gradually grew larger through bacterial growth and by clumping together with other fragments. In the final steady state, high cell densities were maintained in the form of aggregates, while sand had virtually disappeared due to sampling losses and wash-out. Numerical cell densities within aggregates ranged from 10¹²/ml at the periphery to very low values in the center. The cells were enmeshed in a polymer matrix containing polysaccharides; nevertheless, carbon sufficiency was not a prerequisite to sustain high hold-up ratios.     

污水处理活性污泥微生物群落多样性研究

为研究污水处理活性污泥微生物多样性,提取了活性污泥宏基因组DNA,并采用细菌通用引物27F和1492R扩增了上海污泥厂活性污泥细菌16S rDNA片段,构建了细菌16S rDNA克隆文库,并对该文库中的微生物群落进行了分析。共获得200条高质量序列并建立系统发育树,结果显示活性污泥主要的细菌类群为变形菌门(Proteobacteria)(91.9%)、厚壁菌门(Firmicures)(4.6%)、拟杆菌门(Bacteroidetes)(2%)、绿弯菌门(Chloroflexi)(0.5%)、硝化螺菌门(Nitrospirae)(1%)。其中,明显的优势菌群为Alcaligenes feacalis(55%)、Pseudomonas aeruginosa(12.8%)和Stenotrophomonas(12.8%),优势菌的产酶能力在活性污泥中显示生态修复功能菌的作用。     

柠檬酸废水IC反应器厌氧颗粒污泥真细菌结构分析

目的:分析柠檬酸工业废水IC厌氧反应器处理时产生的厌氧颗粒污泥中真细菌的菌群结构.方法:构建细菌的16S rDNA克隆文库,对文库中的16S rDNA基因序列进行测序,然后Blast比对,并进行分类、建系统发育树.结果:对获得的77个16S rDNA序列进行测序,按序列相似性≥97％的分类标准,这些序列可分为22个OTU,其中4个优势OTU分别与棒杆菌属(Corynebacterium)、梭菌属(Clostridium)、消化球菌属(Peptococcus)、疣微菌属(Verrucomicrobia)最为相近,其余OTU的克隆数较少.颗粒污泥中的真细菌主要为放线菌纲(Actinobacteria)、梭菌纲(Clostridia)、拟杆菌纲(Bacteroidetes)以及δ-变形菌纲(Deltaproteobacteria)的细菌,分别占克隆总数的34/77、31/77、6/77、6/77.结论:该文研究了柠檬酸废水处理过程中产生的厌氧颗粒污泥中细菌的菌群组成和结构,为深入了解柠檬酸废水的厌氧处理过程提供了一定的理论借鉴作用.     

Anaerobic Digestion of Dairy Manure in a Hybrid Reactor with Biogas Recirculation

Summary A novel anaerobic hybrid reactor (AHR) configuration incorporating floating support media for biomass immobilization and biogas recirculation for enhanced mixing was used for anaerobic digestion of dairy manure. No pretreatment or solid liquid separation was applied. The reactor was operated at high influent volatile solids (VS) and organic loading rates (OLR) of up to 9.87% and 7.30 g VS/l day, respectively. After 149 days of continuous operation the results revealed that a high amount (38.1 g VSS) of biomass was able to attach itself to the support medium being used. The investigated AHR configuration achieved COD, BOD, TS, and VS removal efficiencies of 48–63, 64–78, 55–65, and 59–68%, respectively, at a hydraulic retention time (HRT) of 15 days. The corresponding average methane production value obtained in this study was 0.191 l/g VS added.     

Dynamics of a Pig Slurry Microbial Community during Anaerobic Storage and Management

The microbial community of a pig slurry on a farm was monitored for 6 months using both molecular and cultural approaches. Sampling was carried out at all the different stages of effluent handling, from the rearing build-up to slurry spreading. Total DNA of each sample was extracted and analyzed by PCR-single-strand conformation polymorphism (SSCP) analysis using primers targeting the 16S rRNA genes from the archaeal and bacterial domains and also the Eubacterium-Clostridium, Bacillus-Streptococcus-Lactobacillus, and Bacteroides-Prevotella groups. A comparison of the SSCP profiles showed that there were rapid changes in the dominant bacterial community during the first 2 weeks of anaerobic storage and that the community was relatively stable thereafter. Several bacterial populations, identified as populations closely related to uncultured Clostridium and Porphyromonas and to Lactobacillus and Streptococcus cultured species commonly isolated from pig feces, remained present and dominant from the rearing build-up to the time of spreading. Enumeration of fecal indicators (enterococci and Escherichia coli) performed in parallel using cultural methods revealed the same trends. On the other hand, the archaeal community adapted slowly during pig slurry storage, and its diversity increased. A shift between two hydrogenotrophic methanogenic Methanobrevibacter populations from the storage pit to the pond was observed. Microorganisms present in pig slurry at the time of spreading could not be detected in soil after spreading by either molecular or cultural techniques, probably because of the detection limit inherent in the two techniques.     

Anaerobic Immobilized Yeast Cell Fermentation and Anaerobic Remediation in Hybrid Reactor for Mineralization of Dicarboxylic Acid Solid Waste

Summary The solid resinous product (SRP) containing unsaturated/saturated dicarboxylic acid residues, phthalic acid and maleic acid is discharged as a solid waste during cracking of benzene over vanadium at temperatures above 500°C in the dicarboxylic acid manufacturing industry. In the present study the solid waste was diluted with water to a concentration of 0.5% w/v for microbial degradation. The waste was fermented in a reactor containing mesoporous activated carbon on which was immobilized Saccharomyces cerevisiae at an optimum residence time of 24 h at pH 6.5. The immobilized-yeast-treated samples were further treated in an upflow anaerobic reactor at an hydraulic retention time (HRT) of 0.1038 days at a hydraulic flow rate of 7.34 × 10⁻³ m³/day and chemical oxygen demand (COD) loading rate of 2.19 kg/m³/day. The pathway followed in the degradation of dicarboxylic acid into end products by anaerobic metabolism in the yeast cell fermentor and in the upflow anaerobic reactor was confirmed through HPLC, Fourier transform infra red spectroscopy and proton and ¹³C NMR spectroscopy.     

Anaerobic Digestion of Renewable Biomass: Thermophilic Temperature Governs Methanogen Population Dynamics

Beet silage and beet juice were digested continuously as representative energy crops in a thermophilic biogas fermentor for more than 7 years. Fluorescence microscopy of 15 samples covering a period of 650 days revealed that a decrease in temperature from 60°C to 55°C converted a morphologically uniform archaeal population (rods) into a population of methanogens exhibiting different cellular morphologies (rods and coccoid cells). A subsequent temperature increase back to 60°C reestablished the uniform morphology of methanogens observed in the previous 60°C period. In order to verify these observations, representative samples were investigated by amplified rRNA gene restriction analysis (ARDRA) and fluorescence in situ hybridization (FISH). Both methods confirmed the temperature-dependent population shift observed by fluorescence microscopy. Moreover, all samples investigated demonstrated that hydrogenotrophic Methanobacteriales dominated in the fermentor, as 29 of 34 identified operational taxonomic units (OTUs) were assigned to this order. This apparent discrimination of acetoclastic methanogens contradicts common models for anaerobic digestion processes, such as anaerobic digestion model 1 (ADM1), which describes the acetotrophic Euryarchaeota as predominant organisms.The replacement of fossil fuels by renewable energy sources such as agricultural crops is gaining momentum internationally as a means to decrease emissions from conventional fuel sources impacting global warming (39). Thereby, biogasification using energy crops is the only fuel-producing process with a closed CO₂ and nutrient cycle (8). The production of biogas from plant waste or other organic materials is a feasible strategy in view of both ecology and economy (63). Fodder beet was chosen as the renewable biomass source for a thermophilic biogas fermentor because the European Union decreased the regulatory price for sugar beets in 2006, and therefore many farmers are looking for an alternative use. Furthermore, fodder beet was considered an attractive renewable energy crop due to its high methane yield per hectare (67), as well as the ideal ensiling conditions enabling the storage of beet silage for many years. Furthermore, the sugar beet was only recently identified as one of the most sustainable energy crops with regard to its water footprint when used for biofuel production (22).A long-term experiment was started on 4 July 2001 (see reference 48 for startup details), and the same biogas fermentors are still running stable due to the use of fuzzy logic control (16, 48). During the conversion of biomass to methane, four different microbial processes can be distinguished: hydrolysis, acidogenesis, acetogenesis, and methanogenesis (17, 69). Population changes might therefore impact the entire community by triggering an imbalance that is reflected in the bioreactor performance via accumulation of intermediates such as volatile fatty acids (mainly C₂ and C₃), via pH changes, or via reduced efficiency (52). This work focused on the methanogens which directly reduce CO₂ to CH₄ or use acetate or methylated C₁ compounds as the main substrate to yield methane (35). However, about 65 to 70% of methane produced by methanogens is assumed to originate from acetate (4, 5), and the so-called acetoclastic Euryarchaeota are also dominant in many biogas fermentors used for anaerobic wastewater treatment and sewage sludge digestion (17, 24, 30, 53).Our results seem to contradict these assumptions, as they clearly demonstrate that hydrogenotrophic methanogens can dominate during a thermophilic fermentation process with renewable biomass (16, 49-51). It appears that temperature has a decisive influence on the type of archaeal morphotypes present, as rod-like methanogens dominated at 60°C periods, whereas different morphotypes of methanogens appeared when 55°C conditions were enabled. However, studies elucidating the population dynamics of both acetotrophic and hydrogenotrophic methanogens during the anaerobic digestion of particulate solid biomass for biogas production are rather scarce. These population processes remain somewhat of a “black box” (12) due to the lack of data concerning the microbial consortia involved therein. Molecular biological techniques such as those targeting the 16S rRNA gene represent a valuable addition to culture-based techniques for studying the biodiversity and structure of complex microbial communities. By targeting methanogens, this study aimed to improve our insight into the poorly understood population dynamics of anaerobic digestion processes and how they are linked to operating conditions such as temperature.     

Molecular Analysis of Surfactant-Driven Microbial Population Shifts in Hydrocarbon-Contaminated Soil

We analyzed the impact of surfactant addition on hydrocarbon mineralization kinetics and the associated population shifts of hydrocarbon-degrading microorganisms in soil. A mixture of radiolabeled hexadecane and phenanthrene was added to batch soil vessels. Witconol SN70 (a nonionic, alcohol ethoxylate) was added in concentrations that bracketed the critical micelle concentration (CMC) in soil (CMC′) (determined to be 13 mg g⁻¹). Addition of the surfactant at a concentration below the CMC′ (2 mg g⁻¹) did not affect the mineralization rates of either hydrocarbon. However, when surfactant was added at a concentration approaching the CMC′ (10 mg g⁻¹), hexadecane mineralization was delayed and phenanthrene mineralization was completely inhibited. Addition of surfactant at concentrations above the CMC′ (40 mg g⁻¹) completely inhibited mineralization of both phenanthrene and hexadecane. Denaturing gradient gel electrophoresis of 16S rRNA gene segments showed that hydrocarbon amendment stimulated Rhodococcus and Nocardia populations that were displaced by Pseudomonas and Alcaligenes populations at elevated surfactant levels. Parallel cultivation studies revealed that the Rhodococcus population can utilize hexadecane and that the Pseudomonas and Alcaligenes populations can utilize both Witconol SN70 and hexadecane for growth. The results suggest that surfactant applications necessary to achieve the CMC alter the microbial populations responsible for hydrocarbon mineralization.     

Software Sensors to Monitor the Dynamics of Microbial Communities: Application to Anaerobic Digestion

A mass balance based model has been derived to represent the dynamical behavior of the ecosystem contained in an anaerobic digester. The model considers two bacterial populations: acidogenic and methanogenic bacteria. It forms the basis for the design of a software sensor considering both a model of the biological system and on-line gaseous measurements. The software sensor computes the concentration of inorganic carbon and volatile fatty acids (VFA) in the digester. Another software sensor is dedicated to the estimation of the bacterial biomasses. The predictions of the software sensors for a real experiment are very close to the actual off-line measurements. The software sensors monitor the accumulation of VFA and thus very early detect a destabilization of the digester due to overloading. The presented methodology demonstrates the usefulness of advanced monitoring techniques for an improved understanding of the internal working of a biological system.     

Mathematical Modelling of Anaerobic Reactors Treating Domestic Wastewater: Rational Criteria for Model Use

Anaerobic digestion modelling is an established method for assessing anaerobic wastewater treatment for design, systems analysis, operational analysis, and control. Anaerobic treatment of domestic wastewater is a relatively new, but rapidly maturing technology, especially in developing countries, where the combination of low cost, and moderate-good performance are particularly attractive. The key emerging technology is high-rate anaerobic treatment, particularly UASB reactors. Systems modelling can potentially offer a number of advantages to this field, and the key motivations for modelling have been identified as operational analysis, technology development, and model-based design. Design is particularly important, as it determines capital cost, a key motivation for implementers. Published modelling studies for anaerobic domestic sewage treatment are limited in number, but well directed at specific issues. Most have a low structural complexity, with first order kinetics, as compared to the more commonly used Monod kinetics. This review addresses the use of anaerobic models in general, application of models to domestic sewage systems, and evaluates future requirements for models that need to address the key motivations of operational analysis, technology development, and model-based design. For operational analysis and technology development, a complex model such as the ADM1 is recommended, with further extensions as required to address factors such as sulphate reduction. For design, the critical issSues are hydraulics and particles (i.e., biomass and solid substrate) modelling. Therefore, the kinetic structure should be relatively simple (at least two-step), but the hydraulic and particulate model should be relatively complex.     

Microbial Community Dynamics of a Continuous Mesophilic Anaerobic Biogas Digester Fed with Sugar Beet Silage

The aim of the study was to investigate the long‐term fermentation of an extremely sour substrate without any addition of manure. In the future, the limitation of manure and therefore the anaerobic digestion of silage with a very low buffering capacity will be an increasing general bottleneck for energy production from renewable biomass. During the mesophilic anaerobic digestion of sugar beet silage (without top and leaves) as the sole substrate (without any addition of manure), which had an extreme low pH of around 3.3, the highest specific gas production rate (spec. GPR) of 0.72 L/g volatile solids (VS) d was achieved at a hydraulic retention time (HRT) of 25 days compared to an organic loading rate (OLR) of 3.97 g VS/L d at a pH of around 6.80. The methane (CH₄) content of the digester ranged between 58 and 67 %, with an average of 63 %. The use of a new charge of substrate (a new harvest of the same substrate) with higher phosphate content improved the performance of the biogas digester significantly. The change of the substrate charge also seemed to affect the methanogenic population dynamics positively, thus improving the reactor performance. Using a new substrate charge, a further decrease in the HRT from 25 to 15 days did not influence the digester performance and did not seem to affect the structure of the methanogenic population significantly. However, a decrease in the HRT affected the size of the methanogenic population adversely. The lower spec. GPR of 0.54 L/g VS d attained on day 15 of the HRT could be attributed to a lower size of methanogenic population present in the anaerobic digester during this stage of the process. Furthermore, since sugar beet silage is a relatively poor substrate, in terms of the buffering capacity and the availability of nutrients, an external supply of buffering agents and nutrients is a prerequisite for a safe and stable digester operation.