Horizontal-flow Anaerobic Immobilized Sludge Research Articles

Removing organic matter from sulfate-rich wastewater via sulfidogenic and methanogenic pathways.

The simultaneous organic matter removal and sulfate reduction in synthetic sulfate-rich wastewater was evaluated for various chemical oxygen demand (COD)/sulfate ratios applied in a horizontal-flow anaerobic immobilized sludge (HAIS) reactor. At higher COD/sulfate ratios (12.5 and 7.5), the removal of organic matter was stable, likely due to methanogenesis. A combination of sulfate reduction and methanogenesis was clearly established at COD/sulfate ratios of 3.0 and 1.9. At a COD/sulfate ratio of 1.0, the organic matter removal was likely influenced by methanogenesis inhibition. The quantity of sulfate removed at a COD/sulfate ratio of 1.0 was identical to that obtained at a ratio of 1.9, indicating a lack of available electron donors for sulfidogenesis. The sulfate reduction and organic matter removal were not maximized at the same COD/sulfate ratio; therefore, competitive inhibition must be the predominant mechanism in establishing an electron flow.

Performance of horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating synthetic substrate subjected to decreasing COD to sulfate ratios

The performance of a bench-scale horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating a synthetic substrate under increasing influent sulfate (SO42-) concentrations was investigated. The synthetic substrate was composed of glucose, methanol and ammonium acetate, besides bicarbonate and trace metal nutritional solution. The reactor was filled with polyurethane foam cubic matrices for biomass immobilization. Influent chemical oxygen demand (COD) was kept almost constant along the experiments (2162 ± 250 mg.l−1) while influent sulfate concentration was increased from 9 to 501 mg.l−1, resulting in COD/SO42- ratio of 249, 66, 19.7 and 4.3 in the four experimental phases tested. After a short start-up period, no significant variations in COD removal efficiency were observed for the COD to sulfate ratios evaluated. Although sulfate reduction was expected to interfere with the methanogenic process, detrimental effects on the overall reactor performance were not observed. Moreover, monitoring parameters indicated that the reactor achieved stable operational conditions immediately after short transient periods following the increase of influent sulfate concentrations. Microscopic analysis of the sludge within the reactor permitted to observe the presence of both methanogenic and sulfate reducing bacteria, indicating that syntrophism and not competition seemed to be the predominant relationship between these two groups under the COD to sulfate ratios assayed.

Influence of the tracer characteristics on hydrodynamic models of packed-bed bioreactors

A bench-scale horizontal-flow anaerobic immobilized sludge (HAIS) reactor filled with porous ceramic spheres (5 mm diameter) was used for evaluating the effects of the tracer characteristics on the residence time distribution (RTD) curves and on the parameters of the hydrodynamic mathematical models. Stimulus-response assays were carried out with bromophenol blue, dextran blue, eosin Y, mordant violet, rhodamine WT and bromocresol green as tracers. The reactor was operated at the hydraulic residence time (HRT) of approximately 2 hours and the flow characteristics were evaluated by fitting the single-parameter models of dispersion and N-continuous stirred tank reactors (CSTR) in series to the experimental data. Tracer characteristics were found to affect deeply the form of RTD curves and the apparent degree of mixing observed in the responses were attributed to the tracer diffusion into the porous media, except for dextran blue. The best adjustment was obtained for the N-CSTR in series model. Thereafter, dextran blue and rhodamine WT were used in hydrodynamic experiments in the HAIS reactor operating with additional residence times. Values of N ranging from 34 to 62 were obtained from the dextran blue experiments for HRT ranging from 2 to 7 hours. The application of the statistical analysis ANOVA one-way method indicated that there was no significant statistical difference in the flow-pattern within the range of hydraulic residence times applied. The mean N value of 9 was obtained from the experiments with rhodamine WT. Such disagreement in the responses was attributed to the diffusion of rhodamine WT into the porous media, interfering in the shape of the experimental curves.

Performance of horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating synthetic substrate subjected to decreasing COD to sulfate ratios

2−) concentrations was investigated. The synthetic substrate was composed of glucose, methanol and ammonium acetate, besides bicarbonate and trace metal nutritional solution. The reactor was filled with polyurethane foam cubic matrices for biomass immobilization. Influent chemical oxygen demand (COD) was kept almost constant along the experiments (2162 ± 250 mg.l−1) while influent sulfate concentration was increased from 9 to 501 mg.l−1 resulting in COD/SO42− ratio of 249, 66, 19.7 and 4.3 in the four experimental phases tested. After a short start-up period, no significant variations in COD removal efficiency were observed for the COD to sulfate ratios evaluated. Although sulfate reduction was expected to interfere with the methanogenic process, detrimental effects on the overall reactor performance were not observed. Moreover, monitoring parameters indicated that the reactor achieved stable operational conditions immediately after short transient periods following the increase of influent sulfate concentrations. Microscopic analysis of the sludge within the reactor permitted to observe the presence of both methanogenic and sulfate reducing bacteria, indicating that syntrophism and not competition seemed to be the predominant relationship between these two groups under the COD to sulfate ratios assayed.

Microbial colonization of polyurethane foam matrices in horizontal-flow anaerobic immobilized-sludge reactor

This paper presents the anaerobic biomass characterization and the bacterial framework inside polyurethane foam matrices taken from a horizontal-flow anaerobic immobilized-sludge (HAIS) reactor treating a glucose-based substrate. Ultrastructure polyurethane foam analyses carried out using scanning electron microscopy (SEM) in samples treated with hexamethyldisylazane showed three different patterns of biomass retention inside the polyurethane foam matrices: micro-granules ranging from 270 μm to 470 μm were entrapped in the porous medium thin multi-cellular films were attached to the inner surface, and individual cells adhered to the support. The use of SEM and epifluorescence microscopy permitted inferences to be made on the bacteriological composition of the immobilized sludge formed by different morphotypes (rods, cocci and filaments) and on the ecological significance of their framework inside the matrices. Polyurethane matrices were found to offer excellent conditions for anaerobic growth and retention, favoring the flux of substrate and products. Such outstanding characteristics were confirmed by the short start-up period observed during the operation of the HAIS reactor.

Intrinsic Kinetic Parameters of Substrate Utilization by Anaerobic Sludge Along the Horizontal-Flow Anaerobic Immobilized Sludge (HAIS) Reactor

This paper reports on experiments aiming at the estimation of kinetic parameters of substrate utilization by anaerobic sludge immobilized in polyurethane foam matrices at different positions along the horizontal-flow anaerobic immobilized sludge (HAIS) reactor length. The methodology used is based on the minimization of mass transfer resistances by the establishment of adequate environmental and operational conditions. The experiments were carried out in an incubator shaker at 250 rpm. Each assay was performed utilizing substrate and bioparticles taken from five sampling ports along the HAIS reactor treating a glucose-based synthetic substrate. Each assay lasted 12 hours and two flasks were taken every 3 hour for chemical oxygen demand (COD) analyses. The specific substrate utilization rates were obtained from the COD profiles of substrate concentration in the bulk liquid along the experimental time and the intrinsic kinetic parameters were estimated considering Monod type (rmax and Ks) and first order (K1) models. The intrinsic kinetic parameters estimated for each HAIS reactor segment ranged from 0.201 to 0.002 mg COD.mg−1.VSS.h−1 for rmax, from 1221 to 49mg COD.l−1 for Ks and from 8.94 × 10−5 to 1.51 × 10−5 l.mg−1 VSS.h−1 for K1. Such a variation in intrinsic kinetic parameters was attributed to changes in substrate and sludge composition along the reactor length.

Spatial and temporal variations of monitoring performance parameters in horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating synthetic substrate

This paper reports on experiments with a lab-scale horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating synthetic substrate aiming to observe temporal and spatial variations of its monitoring performance parameters. The bench-scale HAIS reactor was filled with polyurethane foam matrices containing immobilized anaerobic sludge taken from an upflow anaerobic sludge blanket (UASB) reactor treating diluted piggery wastewater. A synthetic substrate composed of glucose as the main carbon source (chemical oxygen demand — COD of 2090 mg 1 −1) was used for feeding the HAIS reactor in two experiments with bed porosities (ε) of 0.4 and 0.24 and at hydraulic detention times (HDT) of 8.0 and 4.8 h, respectively. The temperature was maintained at 30°C, and COD, volatile fatty acids (VFA), total alkalinity (TA) and pH were monitored in the effluent stream (length to diameter ratio — L/D of 20) and intermediate ports along the reactor's length (L/D of 4, 8, 12 and 16). CH 4 concentration in the gas was determined daily for evaluating the start-up period duration. The short start-up period duration (6 days) in both the experiments confirmed that a HAIS reactor can provide favorable environmental conditions for rapid biomass acclimatization, growth and retention. COD removal efficiencies of 98% were attained in the first experiment (ε of 0.4) and the effluent VFA concentration was lowered to 15 mg 1 −1. At the L/D ratio of 4 in the first sampling port, corresponding to a HDT of 1.6 h, the COD removal efficiency achieved 72%. In the second experiment (ε of 0.24), the maximum COD removal efficiency was 80% and the effluent VFA leveled 350 mg 1 −1. Channeling due to the low bed porosity was found to be the main factor responsible for the poor performance of the reactor operating at ε of 0.24.

Rational Basis for Designing Horizontal-Flow Anaerobic Immobilized Sludge (HAIS) Reactor for Wastewater Treatment

The conception and development on a rational basis of a new configuration of anaerobic fixed-bed bioreactor for wastewater treatment, the horizontal-flow anaerobic immobilized sludge (HAIS) reactor, is presented. Such a reactor containing immobilized sludge in polyurethane foam matrices was first assayed for treating paper industry wastewater. A very short start-up period was observed and the reactor achieved stable operation by the eighth day. Afterwards, fundamental aspects of the process were investigated in order to obtain a rational basis for HAIS reactor design. A sequence of experiments was carried out for evaluating the cell wash-out from polyurethane foam matrices, the liquid-phase mass transfer coefficient and the intrinsic kinetic parameters, besides the hydrodynamic flow pattern of the reactor. The knowledge of such fundamental phenomena is useful for improving the reactor’s design and operation. Besides, these fundamental studies are essential to provide parameters for simulation and optimization of processes that make use of immobilized biomass

Intrinsic kinetic parameters of substrate utilization by immobilized anaerobic sludge

This article presents a method for evaluating the intrinsic kinetic parameters of the specific substrate utilization rate (r) equation and discusses the results obtained for anaerobic sludge-bed samples taken from a horizontal-flow anaerobic immobilized sludge (HAIS) reactor. This method utilizes a differential reactor filled with polyurethane foam matrices containing immobilized anaerobic sludge which is subjected to a range of feeding substrate flow rates. The range of liquid superficial velocities thus obtained are used for generating data of observed specific substrate utilization rates (r(obs)) under a diversity of external mass transfer resistance conditions. The r(obs) curves are then adjusted to permit their extrapolation for the condition of no external mass transfer resistance, and the values determined are used as a test for the condition of absence of limitation of internal mass transfer. The intrinsic parameters r(max), the maximum specific substrate utilization rate, and K(s), the half-velocity coefficient, are evaluated from the r values under no external mass transfer resistance and no internal mass transfer limitation. The application of such a method for anaerobic sludge immobilized in polyurethane foam particles treating a glucose substrate at 30 degrees C resulted in intrinsic r(max) and K(s), respectively, of 0.330 mg chemical oxygen demand (COD) . mg(-1) volatile suspended solids (VSS) . h(-1) and 72 mg COD . L(-1). In comparison with the values found in the literature, intrinsic r(max) is significantly high and intrinsic K(s) is relatively low. (c) 1997 John Wiley & Sons, Inc.

Method for estimating the kinetics of substrate degradation in horizontal-flow anaerobic immobilized sludge reactors

Apparent and intrinsic kinetic parameters of substrate decomposition were estimated from the profiles of chemical oxygen demand (COD) and volatile fatty acids (VFA) concentrations along the length of the horizontal-flow anaerobic immobilized sludge (HAIS) reactor. The first order substrate utilization kinetic model describes well the experimental data.

Cell wash-out and external mass transfer resistance in horizontal-flow anaerobic immobilized sludge reactor

Polyurethane foam has been studied as a support for anaerobic sludge immobilization in packed-bed bioreactors. Studies about fundamental aspects in reactors containing immobilized sludge in such a type of support must be carried out to permit simulation and optimization of their performance and to provide parameters for safe scale-up. The effect of the liquid superficial velocity on the wash-out of anaerobic biomass and the evaluation of the external mass transfer resistance are presented in this paper. The polyurethane foam cubic matrices were taken from a bench-scale horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating kraft paper industry wastewater submitted to eight different water flow rates in a 10 ml tube segment for cell wash-out evaluation and six different glucose solution flow rates in a 10 ml differential reactor for external mass transfer resistance evaluation. There was a significant wash-out of total suspended solids (23%) but only 9% of volatile suspended solids were washed-out from polyurethane foam matrices when they were subjected to liquid superficial velocities ranging from 0.30 to 2.21 cm.s −1. The external mass transfer resistance decreased with the increase in liquid superficial velocity, but the condition of minimum resistance was not obtained in the applied v s range (0.007–0.075 cm.s −1).

Anaerobic reactors for food processing wastewater treatment: established technology and new developments

This paper presents the features and the most important empirical design parameters of anaerobic filters (AF) and up-flow anaerobic sludge blanket (UASB) reactors which are the main anaerobic process units used for the treatment of low-strength food-processing wastewaters in Brazil. The technology associated with this type of reactors can be considered well established, since they are reliable operating at temperatures ranging from 15 to 30°C and at volumetric organic loading rates (OLR) lower than 5.0 kg COD.m−3.d−1. Recently, a new configuration of anaerobic reactor - the horizontal-flow anaerobic immobilized sludge (HAIS) reactor, has been proposed for the treatment of low-strength wastewaters. The sequence of fundamental and applied researches aiming to establish rational design parameters for the HAIS reactor scale-up is presented here.

Anaerobic reactors for food processing wastewater treatment: Established technology and new developments

This paper presents the features and the most important empirical design parameters of anaerobic filters (AF) and up-flow anaerobic sludge blanket (UASB) reactors which are the main anaerobic process units used for the treatment of low-strength food-processing wastewaters in Brazil. The technology associated with this type of reactors can be considered well established, since they are reliable operating at temperatures ranging from 15 to 30°C and at volumetric organic loading rates (OLR) lower than 5.0 kg COD.m−3.d−1. Recently, a new configuration of anaerobic reactor — the horizontal-flow anaerobic immobilized sludge (HAIS) reactor, has been proposed for the treatment of low-strength wastewaters. The sequence of fundamental and applied researches aiming to establish rational design parameters for the HAIS reactor scale-up is presented here.