Broken into pieces: The challenges of determining sulfonated azo dyes in biological reactor effluents using LC-ESI-MS/MS analysis.

Most studies on the biodegradation of textile azo dyes use color as parameter for measuring the efficiency of degradation. Although widely employed, spectrophotometric methods are susceptible to the interference of metabolites or degradation products from the biological treatment. We propose a method for determination of a model sulfonated azo dye (Direct Black 22, DB22) in wastewater using solid-phase extraction (SPE) and liquid chromatography - electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). MS analysis in negative electrospray ionization mode showed DB22 as the most abundant precursor ion, corresponding to [M-3Na + H]2-, which yields two radical anions of m/z 370.1 and m/z 645 after MS/MS fragmentation by collision-induced dissociation (CID). Calibration curve presented adequate linearity and precision in the range of 120-1500 ng mL-1, and recovery and detection limit were appropriate to the typically employed working concentrations. Nevertheless, we observed that standard heating of DB22 under alkaline conditions to simulate the production of wastewater during dye-baths resulted in loss of MS/MS signal, without affecting color. Further analysis showed that DB22 undergoes hydrolysis and does not remain unaltered in solution. Alternative methods of hydrolysis evaluated resulted in no MS/MS signal as well. SPE-LC-ESI-MS/MS analysis evidenced the structural change of DB22 in aqueous solution while the dyeing-capacity was preserved. This technique has also the potential of being tailored to consider the detection of the hydrolyzed fragments of azo dyes in wastewater for appropriate quantification, but it was not the scope of the current step of this research. Color remains as a more reliable parameter for monitoring azo compounds which are unstable in aqueous solution, while a more robust and holistic method needs to be developed for the speciation of the DB22 products of thermal hydrolysis.

Microbial communities and metabolic pathways involved in reductive decolorization of an azo dye in a two-stage AD system.

Multiple stage anaerobic system was found to be an effective strategy for reductive decolorization of azo dyes in the presence of sulfate. Bulk color removal (56-90%) was achieved concomitant with acidogenic activity in the 1st-stage reactor (R1), while organic matter removal (≤100%) and sulfate reduction (≤100%) occurred predominantly in the 2nd-stage reactor (R2). However, azo dye reduction mechanism and metabolic routes involved remain unclear. The involved microbial communities and conditions affecting the azo dye removal in a two-stage anaerobic digestion (AD) system were elucidated using amplicon sequencing (16S rRNA, fhs, dsrB and mcrA) and correlation analysis. Reductive decolorization was found to be co-metabolic and mainly associated with hydrogen-producing pathways. We also found evidence of the involvement of an azoreductase from Lactococcus lactis. Bacterial community in R1 was sensitive and shifted in the presence of the azo dye, while microorganisms in R2 were more protected. Higher diversity of syntrophic-acetate oxidizers, sulfate reducers and methanogens in R2 highlights the role of the 2nd-stage in organic matter and sulfate removals, and these communities might be involved in further transformations of the azo dye reduction products. The results improve our understanding on the role of different microbial communities in anaerobic treatment of azo dyes and can help in the design of better solutions for the treatment of textile effluents.

Methanotrophic denitrification in wastewater treatment: microbial aspects and engineering strategies.

Anaerobic technologies are consolidated for sewage treatment and are the core processes for mining marketable products from waste streams. However, anaerobic effluents are supersaturated with methane, which represents a liability regarding greenhouse gas emissions. Meanwhile, anaerobic technologies are not capable of nitrogen removal, which is required to ensure environmental protection. Methane oxidation and denitrification processes can be combined to address both issues concurrently. Aerobic methane oxidizers can release intermediate organic compounds that can be used by conventional denitrifiers as electron donors. Alternatively, anoxic methanotrophic species combine methane oxidation with either nitrate or nitrite reduction in the same metabolism. Engineered systems need to overcome the long doubling times and low NOx consumption rates of anoxic methanotrophic microorganisms. Another commonly reported bottleneck of methanotrophic denitrification relates to gas-liquid mass transfer limitations. Although anaerobic effluents are supersaturated with methane, experimental setups usually rely on methane supply in a gaseous mode. Hence, possibilities for the application of methane-oxidation coupled to denitrification in full scale might be overlooked. Moreover, syntrophic relationships among methane oxidizers, denitrifiers, nitrifiers, and other microorganisms (such as anammox) are not well understood. Integrating mixed populations with various metabolic abilities could allow for more robust methane-driven wastewater denitrification systems. This review presents an overview of the metabolic capabilities of methane oxidation and denitrification and discusses technological aspects that allow for the application of methanotrophic denitrification at larger scales.

A new device to select carriers for biomass immobilization and application in an aerobic/anaerobic fixed-bed sequencing batch biofilm reactor for nitrogen removal.

This study proposes a new approach to selecting a biofilm carrier for immobilization using dissolved oxygen (DO) microsensors to measure the thickness of aerobic and anaerobic layers in biofilm. The biofilm carriers tested were polyurethane foam, mineral coal (MC), basaltic gravel, and low-density polyethylene. Development of layers in the biofilm carrier surface was evaluated using a flow cell device, and DO profiles were conducted to determine the size of the layers (aerobic and anaerobic). MC was the biofilm carrier selected due to allowing the development of larger aerobic and anaerobic layers in the biofilm (896 and 1,058 µm, respectively). This ability is supposed to improve simultaneous nitrogen removal by nitrification and denitrification biological processes. Thus, as a biofilm carrier, MC was used in a fixed-bed sequencing batch biofilm reactor (FB-SBBR) for treatment of wastewater with a high ammonia concentration (100-400 mgNH4+-N L-1). The FB-SBBR (15.0 L) was filled with matrices of the carrier and operated under alternating aeration and non-aeration periods of 6 h each. At a mean nitrogen loading rate of 0.55 ± 0.10 kgNH4+-N m-3 d-1, the reactor attained a mean nitrification efficiency of 95 ± 9% with nitrite as the main product (aerobic period). Mean denitrification efficiency during the anoxic period was 72 ± 13%.

Poultry slaughterhouse wastewater treatment plant for high quality effluent.

This paper assesses a wastewater treatment plant (WWTP) regarding the technology used, as well as organic matter and nutrient removal efficiencies aiming to optimize the treatment processes involved and wastewater reclamation. The WWTP consists of a dissolved air flotation (DAF) system, an upflow anaerobic sludge blanket (UASB) reactor, an aerated-facultative pond (AFP) and a chemical-DAF system. The removal efficiencies of chemical oxygen demand (COD) (97.9 ± 1.0%), biochemical oxygen demand (BOD) (98.6 ± 1.0%) and oil and grease (O&G) (91.1 ± 5.2%) at the WWTP, the nitrogen concentration of 17 ± 11 mg N-NH3 and phosphorus concentration of 1.34 ± 0.93 mg PO4(-3)/L in the final effluent indicate that the processes used are suitable to comply with discharge standards in water bodies. Nitrification and denitrification tests conducted using biomass collected at three AFP points indicated that nitrification and denitrification could take place in the pond.

Sulfidogenesis interference on methane production from carbohydrate-rich wastewater.

Two anaerobic fixed-structured bed reactors were fed with synthetic wastewater simulating the soluble fraction of sugarcane vinasse to evaluate the interference of sulfidogenesis on methanogenesis. The reactors running in parallel were subjected to the same operating conditions. The influent organic matter concentration (in term of chemical oxygen demand (COD)) remained close to 4,000 mgCOD L(-1) and the hydraulic retention time was 24 hours. One reactor, the methanogenic (control reactor), received sulfate only to provide the sulfur required as a nutrient to the methanogenic biomass. The other one, the sulfidogenic/methanogenic reactor (SMR), received sulfate concentration corresponding to COD/sulfate ratios of 4, 5 and 3. In the last phase, the COD removal efficiencies were higher than 96% in both reactors and the SMR achieved 97% of sulfate removal efficiency (COD/sulfate ratio of 3 and influent sulfate concentration close to 1,300 mgSO4(2-) L(-1)). Both reactors also had similar methane yields in this phase, close to 350 mLCH4 gCODremoved(-1) at standard temperature and pressure. These results indicated no significant inhibition of methanogenic activity under the sulfidogenic conditions assessed.

The influence of the buffering capacity on the production of organic acids and alcohols from wastewater in anaerobic reactor.

Some bacteria common in anaerobic digestion process can ferment a broad variety of organic compounds to organic acids, alcohols, and hydrogen, which can be used as biofuels. Researches are necessary to control the microbial interactions in favor of the alcohol production, as intermediary products of the anaerobic digestion of organic compounds. This paper reports on the effect of buffering capacity on the production of organic acids and alcohols from wastewater by a natural mixed bacterial culture. The hypothesis tested was that the increase of the buffering capacity by supplementation of sodium bicarbonate in the influent results in benefits for alcohol production by anaerobic fermentation of wastewater. When the influent was not supplemented with sodium bicarbonate, the chemical oxygen demand (COD)-ethanol and COD-methanol detected in the effluent corresponded to 22.5 and 12.7 % of the COD-sucrose consumed. Otherwise, when the reactor was fed with influent containing 0.5 g/L of sodium bicarbonate, the COD-ethanol and COD-methanol were effluents that corresponded to 39.2 and 29.6 % of the COD-sucrose consumed. Therefore, the alcohol production by supplementation of the influent with sodium bicarbonate was 33.6 % higher than the fermentation of the influent without sodium bicarbonate.

Continuous anaerobic bioreactor with a fixed-structure bed (ABFSB) for wastewater treatment with low solids and low applied organic loading content.

This paper describes a new type of anaerobic bioreactor with a fixed-structure bed (ABFSB) in which the support for the biomass consists of polyurethane foam strips placed along the length of the bioreactor. This configuration prevents the accumulation of biomass or solids in the bed as well as clogging and channeling effects. In this study, complex synthetic wastewater with a chemical oxygen demand of 404.4 mg O(2) L(-1) is treated by the reactor. The ABFSB, which has a working volume of 4.77 L, was inoculated with anaerobic sludge obtained from an upflow anaerobic sludge blanket bioreactor. A removal efficiency of 78 % for organic matter and an effluent pH of 6.97 were achieved. An analysis of the organic volatile acids produced by the ABFSB indicated that it operated under stable conditions during an experimental run of 36 days. The stable and efficient operation of the bioreactor was compared with the configurations of other anaerobic bioreactors used for complex wastewater treatment. The results of the study indicate that the ABFSB is a technological alternative to packed-bed bioreactors.

Nitrogen and sulfide removal from effluent of UASB reactor in a sequencing fed-batch biofilm reactor under intermittent aeration.

Simultaneous nitrification/denitrification (SND) coupled with sulfide oxidation may be suitable for the post treatment of effluents from anaerobic reactors. These effluents contain ammonium, which must be nitrified, and sulfide, which could be used as an endogenous electron donor for autotrophic denitrification. The SND process occurred in a sequencing fed-batch biofilm reactor of 8h cycles, operated under intermittent aeration. The effect of the start-up period and the feeding strategy were evaluated. The previous establishment of nitrification process with subsequent application of sulfide in low concentrations was the best start-up strategy to enable the occurrence of SDN. The fed-batch mode with sulfide application in excess only in the anoxic periods was the best feeding strategy, providing average efficiencies of 85.7% and 53.0% for nitrification and denitrification, respectively. However, the low overall nitrogen removal efficiency and some operational constraints indicated that autotrophic denitrification using sulfide in a single SBR was not suitable for SND under the assayed conditions.

A two-stage aerobic/anaerobic denitrifying horizontal bioreactor designed for treating ammonium and H(2)S simultaneously.

A two-stage bioreactor was operated for a period of 140 days in order to develop a post-treatment process based on anaerobic bioxidation of sulfite. This process was designed for simultaneously treating the effluent and biogas of a full-scale UASB reactor, containing significant concentrations of NH(4) and H(2)S, respectively. The system comprised of two horizontal-flow bed-packed reactors operated with different oxygen concentrations. Ammonium present in the effluent was transformed into nitrates in the first aerobic stage. The second anaerobic stage combined the treatment of nitrates in the liquor with the hydrogen sulfide present in the UASB-reactor biogas. Nitrates were consumed with a significant production of sulfate, resulting in a nitrate removal rate of 0.43 kgNm(3)day(-1) and ≥92 % efficiency. Such a removal rate is comparable to those achieved by heterotrophic denitrifying systems. Polymeric forms of sulfur were not detected (elementary sulfur); sulfate was the main product of the sulfide-based denitrifying process. S-sulfate was produced at a rate of about 0.35 kgm(3)day(-1). Sulfur inputs as S-H(2)S were estimated at about 0.75 kgm(3)day(-1) and Chemical Oxygen Demand (COD) removal rates did not vary significantly during the process. DGGE profiling and 16S rRNA identified Halothiobacillus-like species as the key microorganism supporting this process; such a strain has not yet been previously associated with such bioengineered systems.

Toxic effects of cadmium (Cd²âº) on anaerobic biomass: kinetic and metabolic implications.

Cadmium ion (Cd(2+)) toxicity on anaerobic systems, used for organic matter removal, was assessed by studying its effect on kinetic parameters and metabolic changes. This fundamental study was performed in a continuous fixed bed anaerobic bioreactor that treated synthetic wastewater simulating domestic sewage. The biomass was immobilized on a fixed bed made of polyurethane foam. Under influent cadmium concentrations of 0.0, 0.4, 4.4 and 6.2 mg Cd(2+) L(-1) the organic matter removal efficiencies were 84%, 82%, 72% and 52%, respectively. At influent concentration of 6.2 mg Cd(2+) L(-1) the reactor had reached its limit for cadmium toxicity. In the removal of dissolved organic matter, the first-order apparent kinetic coefficients (k(1)(app)) were 0.84, 0.67 and 0.10 h(-1) for the operations with 0.0, 0.4 and 4.4 mg Cd(2+) L(-1), respectively. The apparent inhibition coefficient for cadmium (k(i)(app)) was 1.69 mg L(-1). Despite the toxic effects of cadmium on anaerobic organic matter removal at large Cd(2+) concentrations, the results demonstrated that the anaerobic process was suitable for cadmium concentrations below 29.8 mg Cd(2+) L(-1), considering the bioavailable fraction of adsorbed cadmium in the support when the cadmium influent concentration was 6.2 mg Cd(2+) L(-1).

Determination of the intrinsic kinetic parameters of sulfide-oxidizing autotrophic denitrification in differential reactors containing immobilized biomass.

Nitrogen removal coupled with sulfide oxidation has potential for the treatment of effluents from anaerobic reactors because they contain sulfide, which can be used as an endogenous electron donor for denitrification. This work evaluated the intrinsic kinetics of sulfide-oxidizing autotrophic denitrification via nitrate and nitrite in systems containing attached cells. Differential reactors were fed with nitrified synthetic domestic sewage and different sulfide concentrations. The intrinsic kinetic parameters of nitrogen removal were determined when the mass transfer resistance was negligible. This bioprocess could be described by a half-order kinetic model for biofilms. The half-order kinetic coefficients ranged from 0.425 to 0.658 mg N(1/2) L(-1/2) h(-1) for denitrification via nitrite and from 0.190 to 0.609 mg N(1/2) L(-1/2) h(-1) for denitrification via nitrate. In this latter, the lower value was due to the use of electrons donated from intermediary sulfur compounds whose formation and subsequent consumption were detected.

Characterization and kinetics of sulfide-oxidizing autotrophic denitrification in batch reactors containing suspended and immobilized cells.

Sulfide-oxidizing autotrophic denitrification is an advantageous alternative over heterotrophic denitrification, and may have potential for nitrogen removal of low-strength wastewaters, such as anaerobically pre-treated domestic sewage. This study evaluated the fundamentals and kinetics of this process in batch reactors containing suspended and immobilized cells. Batch tests were performed for different NOx-/S2- ratios and using nitrate and nitrite as electron acceptors. Autotrophic denitrification was observed for both electron acceptors, and NOx-/S2- ratios defined whether sulfide oxidation was complete or not. Kinetic parameter values obtained for nitrate were higher than for nitrite as electron acceptor. Zero-order models were better adjusted to profiles obtained for suspended cell reactors, whereas first-order models were more adequate for immobilized cell reactors. However, in the latter, mass transfer physical phenomena had a significant effect on kinetics based on biochemical reactions. Results showed that sulfide-oxidizing autotrophic denitrification can be successfully established for low-strength wastewaters and have potential for nitrogen removal from anaerobically pre-treated domestic sewage.

Influence of carbon sources and C/N ratio on EPS production in anaerobic sequencing batch biofilm reactors for wastewater treatment.

The objective of this work was to evaluate the influence of different carbon sources and the carbon/nitrogen ratio (C/N) on the production and main composition of insoluble extracellular polymers (EPS) produced in an anaerobic sequencing batch biofilm reactor (ASBBR) with immobilized biomass in polyurethane foam. The yield of EPS was 23.6 mg/g carbon, 13.3 mg/g carbon, 9.0 mg/g carbon and 1.4 mg/g carbon when the reactor was fed with glucose, soybean oil, fat acids, and meat extract, respectively. The yield of EPS decreased from 23.6 to 2.6 mg/g carbon as the C/N ratio was decreased from 13.6 to 3.4 gC/gN, using glucose as carbon source. EPS production was not observed under strict anaerobic conditions. The results suggest that the carbon source, microaerophilic conditions and high C/N ratio favor EPS production in the ASBBR used for wastewater treatment. Cellulose was the main exopolysaccharide observed in all experimental conditions.

Pentachlorophenol (PCP) dechlorination in horizontal-flow anaerobic immobilized biomass (HAIB) reactors.

This study verifies the potential applicability of horizontal-flow anaerobic immobilized biomass (HAIB) reactors to pentachlorophenol (PCP) dechlorination. Two bench-scale HAIB reactors (R1 and R2) were filled with cubic polyurethane foam matrices containing immobilized anaerobic sludge. The reactors were then continuously fed with synthetic wastewater consisting of PCP, glucose, acetic acid, and formic acid as co-substrates for PCP anaerobic degradation. Before being immobilized in polyurethane foam matrices, the biomass was exposed to wastewater containing PCP in reactors fed at a semi-continuous rate of 2.0 microg PCP g(-1) VS. The applied PCP loading rate was increased from 0.05 to 2.59 mg PCP l(-1)day(-1) for R1, and from 0.06 to 4.15 mg PCP l(-1)day(-1) for R2. The organic loading rates (OLR) were 1.1 and 1.7 kg COD m(-3)day(-1) at hydraulic retention times (HRT) of 24h for R1 and 18 h for R2. Under such conditions, chemical oxygen demand (COD) removal efficiencies of up to 98% were achieved in the HAIB reactors. Both reactors exhibited the ability to remove 97% of the loaded PCP. Dichlorophenol (DCP) was the primary chlorophenol detected in the effluent. The adsorption of PCP and metabolites formed during PCP degradation in the packed bed was negligible for PCP removal efficiency.

The thermal transformation of Man Made Vitreous Fibers (MMVF) and safe recycling as secondary raw materials (SRM).

This work describes the high temperature reaction sequence of commercial Man Made Vitreous Fibers (MMVF) Cerafiber, Superwool, Rock wool and Glass wool which may be used as substitute for asbestos in some industrial applications. Knowledge of the reaction path and transformation sequence is very important to assess whether carcinogenic crystalline phases are formed during devitrification, which may occur when used as insulators. In addition, knowledge about the nature of the phases formed at high temperature is mandatory to assess if thermally transformed MMVF can be safely recycled as secondary raw material (SRM). In this scenario, this study provides useful information for the optimization of the industrial annealing process aimed to attain a safe, recyclable product. The results of this work show that one of the high-temperature products of Cerafiber and Superwool is cristobalite which is classified as a carcinogenic. It was possible to define the temperature interval at which Cerafiber and Superwool fibers can be safely used as thermal insulators (e.g. insulators in tunnel and/or roller kilns, etc.). As cristobalite is formed in both synthetic fiber products at temperatures higher than 1200 degrees C, their use should be limited to devices operating at lower temperatures. Rock and Glass wool melt upon thermal treatment. As far as the industrial process of inertization is concerned, a maximum firing temperature of 1100 and 600 degrees C is required to melt Rock wool and Glass wool, respectively, with the high-temperature products that can be safely recycled as SRM. Recycling of these products in stoneware tile mixtures were subsequently attempted. The addition of 1-2 wt.% of the melts of Rock and Glass wool gave promising results in terms of viscous sintering reactions and resistance to staining with the only weak characteristic being the color properties of the fired bodies which tend to worsen.

Effects of bed materials on the performance of an anaerobic sequencing batch biofilm reactor treating domestic sewage.

The objective of this study was to determine the best performance of an anaerobic sequencing batch biofilm reactor (AnSBBR) based on the use of four different bed materials as support for biomass immobilization. The bed materials utilized were polyurethane foam (PU), vegetal carbon (VC), synthetic pumice (SP), and recycled low-density polyethylene (PE). The AnSBBR, with a total volume of 7.2L, was operated in 8-h batch cycles over 10 months, and fed with domestic sewage with an average influent chemical oxygen demand (COD) of 358+/-110 mg/L. The average effluent COD values were 121+/-31, 208+/-54, 233+/-52, and 227+/-51 mg/L, for PU, VC, SP, and PE, respectively. A modified first-order kinetic model was adjusted to temporal profiles of COD during a batch cycle, and the apparent kinetic constants were 0.52+/-0.05, 0.37+/-0.05, 0.80+/-0.04, and 0.30+/-0.02 h(-1) for PU, VC, SP, and PE, respectively. Specific substrate utilization rates of 1.08, 0.11, and 0.86 mg COD/mg VS day were obtained for PU, VC, and PE, respectively. Although SP yielded the highest kinetic coefficient, PU was considered the best support, since SP presented loss of chemical constituents during the reactor's operational phase. In addition, findings on the microbial community were associated with the reactor's performance data. Although PE did not show a satisfactory performance, an interesting microbial diversity was found on its surface. Based on the morphology and denaturing gradient gel electrophoresis (DGGE) results, PE showed the best capacity for promoting the attachment of methanogenic organisms, and is therefore a material that merits further analysis. PU was considered the most suitable material showing the best performance in terms of efficiency of solids and COD removal.

Mitochondrial changes induced by natural and synthetic asbestos fibers: studies on isolated mitochondria.

Asbestos fibers, such as chrysotile and crocidolite, are known to have cytotoxic effects on different cell types. In vivo exposure to asbestos fibers can induce both fibrotic and malignant lung diseases , however, the mechanisms linking exposure to the subsequent development of the diseases are unknown. Numerous investigations suggest the involvement of reactive oxygen species (ROS). ROS are known to damage biological macromolecules including proteins, cell membrane lipids and nucleic acids; alterations of these essential cellular components can alter cell function and can drive the cell to neoplastic transformation or to cell death. Because the mitochondrial respiratory chain is an important source of ROS and RNS (reactive nitogen species) in the cells, we have investigated the effects of aqueous extracts of asbestos (natural and synthetic) fibers on some mitochondrial activities. Our data show that crocidolite fibers release substances in solution that may interfere directly with the mitochondrial cytochrome oxidase complex. Moreover, the calcium ions released from these fibers induce opening of the permeability transition pore of the inner membrane leading to a possible cytotoxic effect due to the release of apoptotic factors normally localized in the mitochondrial intermembrane space. In addition, crocidolite extracts enhance the mitochondrial production of ROS. No significant biochemical effects are exerted by chrysotile, either natural or synthetic, on isolated mitochondria. Nevertheless, all asbestos fibers tested induce morphological alterations visualized by transmission electron microscopy and morphometric analysis.

Anaerobic biodegradation of pentachlorophenol in a fixed-film reactor inoculated with polluted sediment from Santos-São Vicente Estuary, Brazil.

This paper discusses the results of pentachlorophenol (PCP) anaerobic biodegradation in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor operated under methanogenic and halophylic conditions. The system was inoculated with autochthonous microorganisms taken from a site in the Santos-São Vicente Estuary (state of São Paulo, Brazil) severely contaminated with PCP, phenolic compounds, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and heavy metals. The inoculum was previously enriched for methanogenesis activity by changing glucose concentrations and under halophylic condition. PCP was added to the HAIB reactor as sodium salt (NaPCP) at an initial concentration of 5 mg l(-1) and increased to 13, 15, and 21 mg l(-1). Organic matter removal efficiency ranged from 77 to 100%. PCP removal efficiency was 100%. Denaturing gradient gel electrophoresis profile showed changes in the structure of Bacteria domain, which was associated with NaPCP and glucose amendments. The diversity of Archaea remained unaltered during the different phases. Scanning electron microscope examinations showed that cells morphologically resembling Methanosarcina and Methanosaeta predominated in the biofilm. These cells were detected by fluorescence in situ hybridization with the Methanosarcinales (MSMX860) specific probe. The results are of great importance in planning the estuary's restoration by using anaerobic technology and autochthonous microorganisms for bioremediation.

Effects of solid-phase mass transfer on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass.

This work reports on experiments for an anaerobic sequencing batch reactor containing immobilized biomass which aimed at verifying the effects of solid-phase mass transfer on the reactor's overall performance. Four experiments were carried out at 30 degrees C with cubic polyurethane foam particles previously inoculated with anaerobic biomass. Different solid-phase mass transfer conditions were reached in each experiment by varying the size of the bioparticle from 0.5 to 3.0 cm. The reactor was fed with a low-strength synthetic wastewater containing protein, carbohydrates and lipid and the effects of mass transfer were evaluated through dynamic substrate concentration profiles during 8-hour batch cycles. A modified first-order kinetic model provided a good representation of the behavior of the dynamic concentration profiles. The solid-phase mass transfer was found to slightly affect the concentration of effluent organic matter expressed as chemical oxygen demand (COD). The concentration of residual effluent substrate increased as the size of the bioparticle was increased. The cycle time was not affected as the size of the bioparticle was increased from 0.5 to 2.0 cm. However, it was found that the cycle time in a reactor with 3.0-cm cubic particles should be higher than that required in systems with smaller particles. The apparent first-order kinetic parameter was estimated as 0.59+/-0.01 h(-1) for experiments with bioparticle sizes ranging from 0.5 to 2.0 cm, while a value of 0.48 h(-1) was obtained in the experiment with 3.0-cm bioparticles.