Specific methanogenic activity in an anaerobic-aerobic reactor applied to the treatment of domestic residual water

The specific methanogenic activity (SMA) test is an important tool for the monitoring of anaerobic digestion. This paper presents the behavior of the methanogenic archaea of an anaerobic sludge under different conditions of oxygenation in a fixed-bed anaerobic-aerobic reactor treating domestic sewage. The reactor was operated in a continuous manner under different liquid recycle ratios from aerobic to anaerobic zones in order to remove carbon and nitrogen. The application of the SMA test was adapted from several authors and the measurement of the accumulated methane in the reactor was carried out by means of gas chromatography. Methanogenic organisms were not inhibited by the presence of oxygen. In contrast, the values of CH, production rate by sludge exposed to oxygen were greater than those obtained for strictly anaerobic sludge.

Solution of a heterogeneous modeling of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor by the sequencing method

A modeling study was completed to develop a methodology that combines the sequencing and finite difference methods for the simulation of a heterogeneous model of a tubular reactor applied in the treatment of wastewater. The system included a liquid phase (convection diffusion transport) and a solid phase (diffusion reaction) that was obtained by completing a mass balance in the reactor and in the particle, respectively. The model was solved using a pilot-scale horizontal-flow anaerobic immobilized biomass (HAIB) reactor to treat domestic sewage, with the concentration results compared with the experimental data. A comparison of the behavior of the liquid phase concentration profile and the experimental results indicated that both the numerical methods offer a good description of the behavior of the concentration along the reactor. The advantage of the sequencing method over the finite difference method is that it is easier to apply and requires less computational time to model the dynamic simulation of outlet response of HAIB.

Application of an anaerobic packed-bed bioreactor for the production of hydrogen and organic acids

This study investigates the feasibility of an anaerobic bioreactor for treating low contents of organic matter to generate organic acids and hydrogen. The device employed for this purpose was a horizontal packed-bed bioreactor fed with glucose-based synthetic wastewater and operated with hydraulic retention times from 0.5 to 2 h. A microbial biofilm was developed without previous inoculation, using expanded clay beads (4.8-6.3 mm) as support material. Alkalinity was found to be the main parameter affecting the production of hydrogen and organic acids, and the system produced optimal output when operating without a buffer agent. The average hydrogen production was 2.48, 2.15 and 1.81 molH(2) mol(-1) of glucose for NaHCO3 influent concentrations of 0, 1000 and 2000 mg L-1, respectively. The operational regime of the bioreactor, the support material and the controlled alkalinity were effective in selecting and immobilizing microbial fermenting biofilms, which successfully produced hydrogen and organic acids throughout the operating period. Exploratory assays indicated the feasibility of organic acid extraction using an anionic polymeric resin. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Influence of carbon source and inoculum type on anaerobic biomass adhesion on polyurethane foam in reactors fed with acid mine drainage

This paper analyzes the influence of carbon source and inoculum origin on the dynamics of biomass adhesion to an inert support in anaerobic reactors fed with acid mine drainage. Formic acid, lactic acid and ethanol were used as carbon sources. Two different inocula were evaluated: one taken from an UASB reactor and other from the sediment of a uranium mine. The values of average colonization rates and the maximum biomass concentration (C(max)) were inversely proportional to the number of carbon atoms in each substrate. The highest C(max) value (0.35 g TVS g(-1) foam) was observed with formic acid and anaerobic sludge as inoculum. Maximum colonization rates (v(max)) were strongly influenced by the type of inoculum when ethanol and lactic acid were used. For both carbon sources, the use of mine sediment as inoculum resulted in a v(max) of 0.013 g TVS g(-1) foam day(-1), whereas 0.024 g TVS g(-1) foam day(-1) was achieved with anaerobic sludge. (C) 2011 Elsevier Ltd. All rights reserved.

Physical-chemical and operational performance of an anaerobic baffled reactor (ABR) treating swine wastewater

Since hog raising concentrates a huge amount of swine manure in small areas, it is considered by the environmental government organizations to be one of the most potentially pollutant activities. Therefore the main objective of this research was to evaluate by operational criteria and removal efficiency, the performance of a Anaerobic Baffled Reactor (ABR), working as a biological pre-treatment of swine culture effluents. The physical-chemical analyses carried out were: total COD, BOD(5), total solids (TS), fix (TFS) and volatiles (TVS), temperature, pH, total Kjeldahl nitrogen, phosphorus, total acidity and alkalinity. The ABR unit worked with an average efficiency of 65.2 and 76.2%, respectively, concerning total COD and BOD(5), with a hydraulic retention time (HRT) about 15 hours. The results for volumetric organic loading rate (VOLR), organic loading rate (OLR) and hydraulic loading rate (HLR) were: 4.46 kg BOD m(-3) day(-1); 1.81 kg BOD(5) kg TVS(-1) day(-1) and 1.57 m(3) m(-3) day(-1), respectively. The average efficiency of the whole treatment system for total COD and BOD(5) removal were 66.5 and 77.8%, showing an adequate performance in removing die organic matter from swine wastewater.

Biohydrogen production in anaerobic fluidized bed reactors: Effect of support material and hydraulic retention time

This study evaluated two different support materials (polystyrene and expanded clay) for biohydrogen production in an anaerobic fluidized bed reactor (AFBR) treating synthetic wastewater containing glucose (4000 mg L(-1)). The AFBRs contained either polystyrene (R1) or expanded clay (R2) as support materials were inoculated with thermally pre-treated anaerobic sludge and operated at a temperature of 30 degrees C and a pH of approximately 5.5. The AFBRs were operated with a range of hydraulic retention times (HRTs) between 1 and 8 h. For R1 with an HRT of 2 h, the maximum hydrogen yield (HY) was 1.90 mol H(2) mol(-1) glucose, with 0.805 mg of biomass (as total volatile solids, or TVS) attached to each g of polystyrene. For R2 operated at an HRT of 2 h, the maximum HY was 2.59 mol H(2) moll glucose, with 1.100 mg of attached biomass (as TVS) g(-1) expanded clay. The highest hydrogen production rates (HPR) were 0.95 and 1.21 L h(-1) L(-1) for R1 and R2, respectively, using an HRT of 1 h. The H(2) content increased from 16-47% for R1 and from 22-51% for R2. No methane was detected in the biogas produced throughout the period of AFBR operation. These results show that the values of HY, HPR, H(2) content, and g of attached biomass g(-1) support material were all higher for AFBRs containing expanded clay than for reactors containing polystyrene. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Degradation of detergent (linear alkylbenzene sulfonate) in an anaerobic stirred sequencing-batch reactor containing granular biomass

This study aimed to determine the efficiency of an anaerobic stirred sequencing-batch reactor containing granular biomass for the degradation of linear alkylbenzene sulfonate (LAS), a surfactant present in household detergent. The bioreactor was monitored for LAS concentrations in the influent, effluent and sludge, pH, chemical oxygen demand, bicarbonate alkalinity, total solids, and volatile solids. The degradation of LAS was found to be higher in the absence of co-substrates (53%) than in their presence (24-37%). Using the polymerase chain reaction and denaturing gradient gel electrophoresis (PCR/DGGE), we identified populations of microorganisms from the Bacteria and Archaea domains. Among the bacteria, we identified uncultivated populations of Arcanobacterium spp. (94%) and Opitutus spp. (96%). Among the Archaea, we identified Methanospirillum spp. (90%), Methanosaeta spp. (98%), and Methanobacterium spp. (96%). The presence of methanogenic microorganisms shows that LAS did not inhibit anaerobic digestion. Sampling at the last stage of reactor operation recovered 61 clones belonging to the domain bacteria. These represented a variety of phyla: 34% shared significant homology with Bacteroidetes, 18% with Proteobacteria, 11% with Verrucomicrobia, 8% with Fibrobacteres, 2% with Acidobacteria, 3% with Chlorobi and Firmicutes, and 1% with Acidobacteres and Chloroflexi. A small fraction of the clones (13%) were not related to any phylum. Published by Elsevier Ltd.

Long-term stability of hydrogen and organic acids production in an anaerobic fluidized-bed reactor using heat treated anaerobic sludge inoculum

This study evaluates the stability of hydrogen and organic acids production in an anaerobic fluidized-bed reactor (AFBR) that contains expanded clay (2.8-3.35 mm in diameter) as a support medium and is operated on a long-term basis. The reactor was inoculated with thermally pre-treated anaerobic sludge and operated with decreasing hydraulic retention time (HRT), from 8 h to 1 h, at a controlled temperature of 30 degrees C and a pH of about 3.8. Glucose (2000 mg L(-1)) was used as the substrate, generating conversion rates of 92-98%. Decreasing the HRT from 8 h to 1 h led to an increase in average hydrogen-production rates, with a maximum value of 1.28 L h(-1) L(-1) for an HRT of 1 h. In general, hydrogen yield production increased as HRT decreased, reaching 2.29 mol of H(2)/mol glucose at an HRT of 2 h and yielding a maximum hydrogen content of 37% in the biogas. No methane was detected in the biogas throughout the period of operation. The main soluble metabolites (SMP) were acetic acid (46.94-53.84% of SMP) and butyric acid (34.51-42.16% of SMP), with less than 15.49% ethanol. The steady performance of the AFBR may be attributed to adequate thermal treatment of the inoculum, the selection of a suitable support medium for microbial adhesion, and the choice of satisfactory environmental conditions imposed on the system. The results show that stable hydrogen production and organic acids production were maintained in the AFBR over a period of 178 days. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Application of molecular techniques to evaluate the methanogenic archaea and anaerobic bacteria in the presence of oxygen with different COD : sulfate ratios in a UASB reactor

In this paper, the microbial characteristics of the granular sludge in the presence of oxygen (3.0 +/- 0.7 mg O-2 1(-1)) were analyzed using molecular biology techniques. The granules were provided by an upflow anaerobic sludge blanket (UASB) operated over 469 days and fed with synthetic substrate. Ethanol and sulfate were added to obtain different COD/SO42- ratios (3.0, 2.0, and 1.6). The results of fluorescent in situ hybridization (FISH) analyses showed that archaeal cells, detected by the ARC915 probe, accounted for 77%, 84%, and 75% in the COD/SO42- ratios (3.0, 2.0, and 1.6, respectively). Methanosaeta sp. was the predominant acetoclastic archaea observed by optical microscopy and FISH analyses, and confirmed by sequencing of the excised bands of the DGGE gel with a similarity of 96%. The sulfate-reducing bacterium Desulfovibrio vulgaris subsp. vulgaris (similarity of 99%) was verified by sequencing of the DGGE band. Others identified microorganism were similar to Shewanella sp. and Desulfitobacterium hafniense, with similarities of 95% and 99%, respectively. These results confirmed that the presence of oxygen did not severely affect the metabolism of microorganisms that are commonly considered strictly anaerobic. We obtained mean efficiencies of organic matter conversion and sulfate reducing higher than 74%. (C) 2008 Elsevier Ltd. All rights reserved.

Kinetics and Modeling of Fatty Alcohol Ethoxylation in an Industrial Spray Loop Reactor

The kinetics of the ethoxylation of fatty alcohols catalyzed by potassium hydroxide was studied to obtain the rate constants for modeling of the industrial process. Experimental data obtained in a lab-scale semibatch autoclave reactor were used to evaluate kinetic and equilibrium parameters. The kinetic model was employed to model the performance of an industrial-scale spray tower reactor for fatty alcohol ethoxylation. The reactor model considers that mass transfer and reaction occur independently in two distinct zones of the reactor. Good agreement between the model predictions and real data was found. These findings confirm the reliability of the kinetic and reactor model for simulating fatty alcohol ethoxylation processes under industrial conditions.

Development of a Continuous Emulsion Copolymerization Process in a Tubular Reactor

This contribution describes the development of a continuous emulsion copolymerization processs for vinyl acetate and n-butyl acrylate in a tubular reactor. Special features of this reactor include the use of oscillatory (pulsed) flow and internals (sieve plates) to prevent polymer fouling and promote good radial mixing, along with a controlled amount of axial mixing. The copolymer system studied (vinyl acetate and butyl acrylate) is strongly prone to composition drift due to very different reactivity ratios. An axially dispersed plug flow model, based on classical free radical copolymerization kinetics, was developed for this process and used successfully to optimize the lateral feeding profile to reduce compositional drift. An energy balance was included in the model equations to predict the effect of temperature variations on the process. The model predictions were validated with experimental data for monomer conversion, copolymer composition, average particle size, and temperature measured along the reactor length.

Optimal synthesis of Fenton reactor networks for phenol degradation

There is an increasing need to treat effluents contaminated with phenol with advanced oxidation processes (AOPs) to minimize their impact on the environment as well as on bacteriological populations of other wastewater treatment systems. One of the most promising AOPs is the Fenton process that relies on the Fenton reaction. Nevertheless, there are no systematic studies on Fenton reactor networks. The objective of this paper is to develop a strategy for the optimal synthesis of Fenton reactor networks. The strategy is based on a superstructure optimization approach that is represented as a mixed integer non-linear programming (MINLP) model. Network superstructures with multiple Fenton reactors are optimized with the objective of minimizing the sum of capital, operation and depreciation costs of the effluent treatment system. The optimal solutions obtained provide the reactor volumes and network configuration, as well as the quantities of the reactants used in the Fenton process. Examples based on a case study show that multi-reactor networks yield decrease of up to 45% in overall costs for the treatment plant. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Water Treatment Plant Sludge Discharge to Wastewater Treatment Works: Effects on the Operation of Upflow Anaerobic Sludge Blanket Reactor and Activated Sludge Systems

This experiment examined the effects of the discharge of water treatment plant (WTP) sludge into the following three types of wastewater treatment systems: a pilot-scale upflow anaerobic sludge blanket (UASB) reactor, a pilot-scale activated sludge system, and a full-scale activated sludge sequencing batch reactor (SBR). The UASB reactor received 50 mg of suspended solids ( SS) of WTP sludge per liter of wastewater in the first phase, and, in the second phase, it received 75 mg SS/L. The pilot-scale activated sludge system received 25 and 50 mg SS/L in the first and second phases, respectively. The full-scale WWTP ( SBR) received approximately 74 mg SS/L. The results of the experiments showed that, despite some negative effects on nitrification, there were positive effects on phosphorus removal, and, furthermore, there was the addition of solids in all systems. Water Environ. Res., 82, 392 ( 2010).

Aqueous two-phasemicellar systems in an oscillatory flowmicro-reactor: study of perspectives and experimental performance

BACKGROUND: Aqueous two-phase micellar systems (ATPMS) are micellar surfactant solutions with physical properties that make them very efficient for the extraction/concentration of biological products. In this work the main proposal that has been discussed is the possible applicability and importance of a novel oscillatory flow micro-reactor (micro-OFR) envisaged for parallel screening and/or development of industrial bioprocesses in ATPMS. Based on the technology of oscillatory flow mixing (OFM), this batch or continuous micro-reactor has been presented as a new small-scale alternative for biological or physical-chemical applications. RESULTS: ATPMS experiments were carried out in different OFM conditions (times, temperatures, oscillation frequencies and amplitudes) for the extraction of glucose-6-phosphate dehydrogenase (G6PD) in Triton X-114/buffer with Cibacron Blue as affinity ligand. CONCLUSION: The results suggest the potential use of OFR, considering this process a promising and new alternative for the purification or pre-concentration of bioproducts. Despite the applied homogenization and extraction conditions have presented no improvements in the partitioning selectivity of the target enzyme, when at rest temperature they have influenced the partitioning behavior in Triton X-114 ATPMS. (C) 2011 Society of Chemical Industry

Structural characterization of exopolysaccharides from biofilm of a cariogenic streptococci

Soluble (EPS-SOL), as well as insoluble extracellular polysaccharide (EPS-INSOL), extracted from biofilm of Streptococcus mutans, were analyzed by nuclear magnetic resonance spectroscopy, methylation analysis, and a controlled Smith degradation. EPS-SOL was a branched alpha-glucan containing a (1 -> 6)-and (1 -> 3)-linkages. EPS-INSOL was a branched alpha-glucan with similar linkages, but with a (1 -> 3)-linked main-chain partially substituted at O-6 with Glcp-(1 -> 6)-Glcp-side chains. Biofilm EPS had a distinct chemical structure compared with those synthesized by plankton cells or by purified enzymes from S. mutans, which could indicate different mechanisms for its degradation. (C) 2011 Published by Elsevier Ltd.