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The seismic fragility analysis involves employing an ensemble of ground motion records to establish the seismic performance. This paper investigates the effect of number of ground motion records in the considered ensemble on the calculated post-earthquake failure probability of subway structure. A two-dimensional (2D) finite element model was established considering the soil-subway station underground structure interaction. The cloud and incremental dynamical analysis (IDA) methods are employed to compute the seismic demand of the structure and the seismic fragility curves considering different ensembles of ground motion records. The results revealed that the number of records have a significant influence on the structure seismic fragility analysis in both cloud and IDA methods. It is suggested that the optimal ensemble size should comprise 300 ground motion records in the cloud-based seismic fragility analysis, and 24 ground motion records in the IDA method. The results also showed that the failure probability of structure predicted by the cloud method is greater than that predicted by the IDA method. These findings provide practical guidance for the performance-based seismic design of underground structures. • The optimal ensemble size of earthquake records for cloud method was studied. • The optimal ensemble size of earthquake records for IDA method was studied. • The seismic fragility curves computed by the cloud and IDA methods have been compared. [ABSTRACT FROM AUTHOR]

The seismic response of soils consisting of uniform sandy soils with two different relative densities Dr (50% and 90%) was investigated using the RPI geotechnical centrifuge facility, with a one-dimensional earthquake simulator at 60 g. The seismic soil structure interaction between the sand, buried box culvert, and surface foundations was also studied. The models were subjected to three earthquakes with different amplitudes and frequencies. Model settlements were recorded from 1 g to 60 g and during the seismic shakings; the ground response parameters were assessed. Rocking of structures was observed to be small for the box culverts compared to the surface foundation due to the soil confinement. The effect of kinematic soil structure interaction between the dry sand, box culverts and foundations was also explored. Kinematic soil culvert interaction was found to lead to a large reduction in the peak ground acceleration at the soil surface, which can reach up to 50%. Further numerical modeling was performed to investigate the effect of soil cover height on the kinematic soil culvert interaction and these results are also discussed in the paper. [ABSTRACT FROM AUTHOR]

The response of box culverts to static loads is controlled by soil arching. Soil arching is a result of a complex soil culvert interaction (SCI) due to the relative stiffness between the culvert and the surrounding soil, and is a critical consideration in culvert design. The factors that affect soil arching on box culverts include the soil height above the culvert, the geometrical configuration of the box culvert and the properties of the soil around it. Box culverts are typically designed using formulae that assume simplified behaviors and in some cases rely on considerable empiricism. In the present study, small scale centrifuge physical model tests were conducted to investigate SCI considering the height and density of soil above the culvert and the geometry of the culvert. The results of these centrifuge tests were used to calibrate and verify a numerical model that was used to further investigate the response of box culverts to static loads. The results have been evaluated for bending moment and soil culvert interaction factors. The results demonstrated that the soil culvert interaction factors are not only a function of the height of soil column above the culvert, but also a function of the culvert thickness, soil elastic modulus and Poisson’s ratio. Therefore, the results were used to establish charts and equations that can be employed to assess the design values of the static soil pressure and static bending moment for box culverts. [ABSTRACT FROM AUTHOR]

Abstract: Owing to their simplicity and reasonable accuracy, Beam on Nonlinear Winkler Foundation (BNWF) models are widely used for the analysis of laterally loaded piles. Their main drawback is idealizing the soil continuum with discrete uncoupled springs representing the soil reactions to pile movement. Static p–y curves, obtained from limited full-scaled field tests, are generally used as a backbone curve of the model. However, these empirically derived p–y curves could not incorporate the effects of various pile properties and soil continuity. The strain wedge method (SWM) has been improved to assess the nonlinear p–y curve response of laterally loaded piles based on a three-dimensional soil–pile interaction through a passive wedge developed in front of the pile. In this paper, the SWM based p–y curve is implemented as the backbone curves of developed BNWF model to study the nonlinear response of single pile under cyclic lateral loading. The developed nonlinear model is capable of accounting for various important soil–pile interaction response features such as soil and pile yielding, cyclic degradation of soil stiffness and strength under generalized loading, soil–pile gap formation with soil cave-in and recompression, and energy dissipation. Some experimental tests are studied to verify the BNWF model and examine the effect of each factor on the response of laterally loaded pile embedded in sand and clay. The experimental data and computed results agree well, confirming the model ability to predict the response of piles under one-way and two-way cyclic loading. The results show that the developed model can satisfactorily simulate the pile stiffness hardening due to soil cave in and sand densification as observed in the experiment. It is also concluded from the results that the gap formation and soil degradation have significant effects on the increase of lateral pile-head deflection and maximum bending moment of the pile in cohesive soils. [Copyright &y& Elsevier]

Abstract: The paper shows implementation of in-plant control measures in two pasta plants and conducts economic analysis for revenues from these modifications. In order to reuse wastewater, 12 end-of-pipe samples for each plant were tested for physico-chemical characteristics using standard methods. The results showed that the adopted in-plant modifications such as installation of water flow meters, spring valves on water hoses, and design of a steam condensate recovery system contributed efficiently in saving water and energy consumption throughout the pasta plants. An estimated annual benefit of $228,245 can be achieved. Cost benefit analysis for the implemented environmental improvements proved to be very economic with a short payback period and resulted in great savings. [ABSTRACT FROM AUTHOR]

The Nakamura method, which utilizes the Horizontal to Vertical Spectral Ratio (HVSR) analysis, is widely used for seismic microzonation studies. The HVSR is an easy tool for estimation of site response resonances based on recorded ambient noise; however, it gives amplifications at resonant frequencies that are poorly correlated to the actual amplifications during strong ground motion. Generally, the site response, including any resonant effects, depends on the amplitude, frequency and duration of ground motion. An approach was proposed previously by McGuire [1], in which the transfer function of the soil response was approximated as a Single Degree of Freedom (SDOF) oscillator with one resonant frequency, obtained from the maximum in HVSR. A new approach is developed here, in which the entire HVSR curve is approximated by a manageable set of parallel band-pass resonators. Each individual oscillator is defined by three parameters: center frequency, gain, and steepness (Q factor). This approximation allows for the development and use of an analytical model of the HVSR curve. The application of the new approach is demonstrated on data recorded by the stations of the Southern Ontario Seismic Network (SOSN/Polaris), which have well studied characteristics and site response [2,3]. Data collected at each site consists of noise recordings to obtain the HVSR, as well as earthquake records. The analytical HVSR curves for each station are used to remove the site effect component from the recorded seismograms. • Development of modified bandpass filter for spectral smoothing of microtremor and earthquake data. • Procedure for automatic HVSR approximation using modified band-pass filters. • Estimation of earthquake spectra using site-specific response approximation. [ABSTRACT FROM AUTHOR]

Abstract The environmental and ecological impacts associated with concrete industry represent a major sustainability challenge. However, employing materials that would otherwise be considered waste in designing concrete mixtures can increase its sustainability along with reducing harmful impact of waste disposal. Therefore, this study attempts to increase concrete sustainable benefits through reusing treated oil sand waste (TOSW) as a replacement for natural sand. Concrete mixture for continuous flight auger (CFA) piles was selected in order to examine the practicality of the proposed technique. Fresh and hardened properties along with durability performance of CFA concrete mixtures incorporating 10%, 20%, 30% and 40% TOSW as partial replacement of sand were investigated. Results show that the incorporation of TOSW, up to 30%, did not adversely affect the performance of CFA concrete mixtures. Moreover, the leaching of heavy metals from tested concrete was very low leading to a less harmful environment impact. Reusing of TOSW as partial replacement for sand in concrete mixtures for CFA piles is potentially feasible with environmental ecological and economic benefits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Quantify the seismic performance index limit values of prefabricated subway station. • Select the optimal ground motion intensity measure of prefabricated structure. • Give the seismic fragility curves of the prefabricated subway station structure. • Compare the seismic fragility of prefabricated structure and CIP structure. To promote the acceptance of prefabricated technology in underground engineering, the numerical seismic fragility analysis of a prefabricated underground structures was scrutinized. A method to quantify the limit values of the seismic performance index of rectangular prefabricated subway station structure was proposed. In addition, seismic fragility curves of the two-story three-span prefabricated subway station structure were constructed based on peak ground velocity (PGV) and peak ground acceleration (PGA), which can be used as an effective tool to quickly evaluate the seismic performance of this type of prefabricated underground structure, and compared with the cast-in-place subway station structure. The results demonstrate that the ground motion and site class have an intertwined influence on the dynamic response of the underground structures. That is, as the site equivalent shear wave velocity decreases, the ground motion characteristics have a greater influence on the underground structure dynamic response and its susceptibility to damage. For shallow buried multi-layer underground prefabricated structures, the PGV is the best seismic intensity measure (IM) for all site classes. The prefabricated subway station structure is found to be less vulnerable to damage than the cast-in-place subway station structure. [ABSTRACT FROM AUTHOR]

Since the seismic performance of prefabricated underground structures is not yet clear, they not have been constructed in high seismic intensity areas or poor sites. This paper aims to study the applicability of rectangular prefabricated (semi-rigid prefabricated, ASF, and rigid prefabricated, AMT) underground structures in soft soil sites located in high seismic intensity areas. The structures were compared with cast-in-place (CIP) underground structures. Three-dimensional soil-structure interaction advanced finite element models were established to simulate the seismic behavior of the three types of underground structures (ASF, AMT and CIP) constructed in two different sites (soft rock site and soft soil site). The pre-earthquake stress states, dynamic responses, and post-earthquake performance states of the three underground structures were systematically analyzed, considering various static and dynamic conditions. Additionally, the results of dynamic time history were compared with those of the standard procedures available in the literature. The results demonstrated that: i) site conditions have a significant effect on the structures' static and dynamic responses, ii) the seismic response in soft soil site is much larger than that in soft rock site, but the ratio of response of prefabricated underground structures to that of CIP is almost the same for both soft soil and soft rock sites. Furthermore, as the peak ground acceleration increases, the percentage difference of inter-story displacement ratio (IDR) between ASF, AMT and CIP underground structures in soft soil site decreases, and iii) prefabricated underground structures can be used in both soft rock and soft soil sites. In addition, the seismic performance of ASF is better than that of the AMT structure, which is better than that of the CIP structure. However, when the ASF structure is built in a site with high seismic intensity and poor soil conditions, special consideration must be given to waterproofing measures for wall-slab joints or setting up tongue and groove to improve the connection stiffness and reduce the deformation. • The applicability of CIP structure specifications to prefabricated structures. • Research the applicability of prefabricated structures in different sites. • Provide recommendation for the design and construction of splicing joint. • The results of dynamic time history were compared with those of the R–F procedures. [ABSTRACT FROM AUTHOR]

[Display omitted] • A prefabricated underground structure is introduced, and a FEM is established. • The seismic responses of prefabricated and cast-in-place structure are compared. • The influence of the splicing properties of the structure are investigated. The development and application of prefabricated assembly technology has become an important measure to achieve industrial optimization and upgrading and sustainable development of construction engineering. The application of prefabricated assembly technology in underground engineering is in its infancy, and the seismic research on prefabricated underground structures is scarce. Therefore, this paper establishes refined finite element models (FEMs) of prefabricated and cast-in-place underground structures based on an actual project of a subway station. The developed FEMs are used to conduct a series of seismic time-history analyses considering soil-structure interaction to compare the responses of a prefabricated underground structure with rigid splicing joints or non-rigid splicing joints with that of a cast-in-place underground structure of the same structural form. In addition, the influence of the splicing properties of different parts on the inter-story displacement and internal forces of the prefabricated underground structure are systematically investigated. Tt was found that the inter-story displacement and component deformation for prefabricated underground structures with rigid joints are basically the same as those of the cast-in-place underground structure; however, both the internal force and damage at the bottom of center column decrease slightly. On the other hand, prefabricated underground structures with non-rigid splicing joints experience a slight increase (less than5%) in inter-story displacement, but more obvious mid-span deflection of the laminated slab. However, the internal force response and damage degree of their center column are significantly reduced compared to cast-in-place structures. It was also revealed that the bonding strength of new-old concrete interface of the horizontal laminated components is the main factor that reduces the lateral stiffness and causes redistribution of the prefabricated underground structures' internal forces. [ABSTRACT FROM AUTHOR]

The liquefaction behavior and cyclic resistance ratio (CRR) of reconstituted samples of non-plastic silt and sandy silts with 50% and 75% silt content are examined using constant-volume cyclic and monotonic ring shear tests along with bender element shear wave velocity ( V s ) measurements. Liquefaction occurred at excess pore water pressure ratios ( r u ) between 0.6 and 0.7 associated with cumulative cyclic shear strains ( γ ) of 4% to 7%, after which cyclic liquefaction ensued with very large shear strains and excess pore water pressure ratio ( r u >0.8). The cyclic ring shear tests demonstrate that cyclic resistance ratio of silt and sandy silts decreases with increasing void ratio, or with decreasing silt content at a certain void ratio. The results also show good agreement with those from cyclic direct simple shear tests on silts and sandy silts. A unique correlation is developed for estimating CRR of silts and sandy silts (with more than 50% silt content) from stress-normalized shear wave velocity measurements ( V s1 ) with negligible effect of silt content. The results indicate that the existing CRR– V s1 correlations would underestimate the liquefaction resistance of silts and sandy silt soils. [ABSTRACT FROM AUTHOR]

Under strong earthquakes, subway station structures situated in potentially liquefiable soils may experience complex seismic response scheme when the structure base slab is embedded in non-liquefiable soils while the sidewalls and top slab are buried in liquefiable soils (hereinafter referred to as a "liquefiable sites"). This paper investigates the dynamic seismic responses of multi-story underground structures in liquefiable sites employing an advanced three-dimensional nonlinear finite element model. The results indicate that the seismic response of underground structures is primarily determined by the soil displacement and the soil-structure stiffness ratio. In addition, the seismic response of the soil-underground structure system is strongly influenced by the distinct characteristics of the input ground motion. Seismic input motions rich in low-frequency components are more likely to cause saturated sand layers to liquefy and are likely to trigger more pronounced flow deformations, leading to severe damage to underground structures. Generally, liquefied soils are prone to significant horizontal displacements (i.e., lateral spreading); however, due to the reduced soil-structure stiffness ratio, the soil ability to induce shear deformation in the structure is diminished, and hence the structure does not undergo large horizontal deformations same as that of the soil. Additionally, structures may exhibit a slight tendency to uplift after the earthquake. These observations can inform the seismic design of underground structures in liquefiable sites. • Visualization of post-earthquake damage to underground structures in liquefiable site. • Adverse effects of low-frequency seismic motion on liquefied soil. • Monitoring the slip characteristics of liquefiable soil and structures. • Capturing the special state of liquefiable soil and structure after earthquake. [ABSTRACT FROM AUTHOR]

Three-dimensional nonlinear finite element analyses are conducted to evaluate the seismic performance of rectangular prefabricated and cast-in-place underground structures considering soil-structure interaction. The finite element models are developed based on a prefabricated subway station project in Beijing. The seismic loading conditions, damage evolution, structure deformation, internal forces and the performance index limits values are compared for prefabricated (assembly monolithic (AMT) and assembly spliced (ASF)) and cast-in-place (CIP) underground structures. Numerical results indicated that the degree of plastic damage at center column of prefabricated underground structure was less than that for CIP underground structure. The failure mechanism of both types of underground structures was the same, the central column first lost its bearing capacity then the side wall failed. The column's internal force of ASF structure was significantly reduced compared with that of CIP structure, and the most unfavorable seismic position of the three structures is the bottom of the lower column. It was also found that vertical ground motion can significantly accelerate prefabricated underground structural destroy, but it has little effect on the horizontal displacement. Finally, index limits are quantified for four seismic performance levels of prefabricated underground structures, which can be considered in performance-based design of prefabricated underground structures. • The differences between the prefabricated underground structure and the cast-in-place underground structure are compared. • The effect of vertical ground motion on seismic performance of underground structure is analyzed. • Index limits are proposed for four seismic performance levels of prefabricated underground structures. [ABSTRACT FROM AUTHOR]

Abstract: The patent-pending integrated waste-to-energy system comprises both a novel biohydrogen reactor with a gravity settler (Biohydrogenator), followed by a second stage conventional anaerobic digester for the production of methane gas. This chemical-free process has been tested with a synthetic wastewater/leachate solution, and was operated at 37°C for 45d. The biohydrogenator (system (A), stage 1) steadily produced hydrogen with no methane during the experimental period. The maximum hydrogen yield was 400mL H2/g glucose with an average of 345mL H2/g glucose, as compared to 141 and 118mL H2/g glucose for two consecutive runs done in parallel using a conventional continuously stirred tank reactor (CSTR, System (B)). Decoupling of the solids retention time (SRT) from the hydraulic retention time (HRT) using the gravity settler showed a marked improvement in performance, with the maximum and average hydrogen production rates in system (A) of 22 and 19L H2/d, as compared with 2–7L H2/d in the CSTR resulting in a maximum yield of 2.8mol H2/mol glucose much higher than the 1.1–1.3mol H2/mol glucose observed in the CSTR. Furthermore, while the CSTR collapsed in 10–15d due to biomass washout, the biohydrogenator continued stable operation for the 45d reported here and beyond. The methane yield for the second stage in system (A) approached a maximum value of 426mL CH4/gCOD removed, while an overall chemical oxygen demand (COD) removal efficiency of 94% was achieved in system (A). [Copyright &y& Elsevier]

A seismic mitigation control technology involving arc groove roller bearings (AGRB) for shallow buried underground frame structures is proposed for reducing the horizontal deformation of the central column. Firstly, the working mechanism of AGRB component is described and its mechanical properties are analyzed through pseudo-static analysis. The results show that AGRB offers good vertical bearing capacity and horizontal deformation performance. Secondly, the finite element models of the soil-structure system for subway stations with and without AGRB are established for implementing the nonlinear dynamic time-history analysis. Compared with the observed response of the structures without AGRB, the horizontal deformation, shear force and bending moment of the central column fitted with AGRB are greatly reduced and the maximum seismic mitigation rate is above 80%. In addition, the results demonstrated that utilizing AGRB could greatly reduce the plastic damage area and damage degree of the supporting column, and avoid the occurrence of plastic hinges and shear failure due to insufficient lateral deformation resistance of the central column under high axial compression. Thus the AGRB can be used as an effective design scheme to achieve seismic mitigation control for underground structures. • A mitigation control technology for installing AGRB on the central column of underground subway station is proposed. • The mechanical properties and key influencing parameters of AGRB are investigated. • The validity of AGRB in upgrading the seismic performance of underground structures is verified. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the design, fabrication and commissioning of a single axis laminar shear box for use in seismic soil–structure interaction studies. A laminar shear box is a flexible container that can be placed on a shaking table to simulate vertical shear-wave propagation during earthquakes through a soil layer of finite thickness. The laminar shear box described in this paper was designed to overcome the base shear limitations of a small shaking table at The University of Western Ontario. The design details of the box are provided in addition to results of dynamic tests performed to commission the box. A synthetic clay comprising sodium bentonite mixed with diluted glycerin was used as the model soil and 1-G similitude theory was employed to maintain model to prototype similarity. The model soil was compacted into the container in lifts to achieve soil stiffness that increased with depth. A series of shaking table tests and numerical analyses that were performed to study the performance of the laminar box and non-linear seismic behavior of the model clay are described. The results of this study show that the laminar box does not impose significant boundary effects and is able to maintain 1-D soil column behavior. In addition, the dynamic behavior of the model clay during scaled model tests was found to be consistent with the behavior measured during cyclic laboratory tests. [Copyright &y& Elsevier]

Simplified methods are widely used in the seismic design of underground structures, but they generally ignore the influence of vertical ground motion. This can result in unreliable design because seismic earth pressure induced by vertical ground motion can have a significant adverse effect on their seismic performance. Therefore, this paper proposes an improved pushover analysis method (I-PAM) that applies distributed horizontal and vertical inertial forces to simulate the mechanical behavior of underground structures under both horizontal and vertical ground motions. The profile of load distribution and target displacement is calculated from corresponding site response analysis. A rigorous time-history dynamic analysis method (TDAM) based on the finite element numerical analysis was employed in three case studies to evaluate the performance of the developed I-PAM. The results showed that the I-PAM can accurately predict the structure's peak axial force, bending moment and displacement under the combined action of horizontal and vertical ground motions, especially for lower ground motion intensity. It was also found that the responses of the center column and middle slap were calculated with higher accuracy compared to that of the components in direct contact with soil including sidewalls and top and bottom slabs. The developed I-PAM offers a framework for further development and enhancement of simplified analysis methods for seismic design of underground structures. • The effect of vertical ground motion on daikai subway station is conducted in present study. • The mechanical model of improved pushover analysis method considering vertical ground motion is developed. • The reliability of the improved pushover analysis method is verified by comparison with the dynamic method. [ABSTRACT FROM AUTHOR]

This paper investigates the static and cyclic characteristics of a fouled sub-ballast material using static and cyclic triaxial tests. Static triaxial tests were conducted first to determine the peak strength, which was used as the applied stress in the cyclic tests. Moreover, the results of the displacement-controlled static triaxial test were used to assess the shear stiffness and strength during the cyclic stress-controlled loading cycles. Isotropically consolidated drained (CD) compression cyclic triaxial tests were conducted to simulate the long-term response of fouled railway substructure under progressive repetitive loading and unloading cycles. The accumulated plastic strains of the fouled railroad sub-ballast were determined under cyclic loading and unloading conditions. The obtained results indicated that the soil plasticity and effective confining pressure, and relative density are not the only important factors in shaping the damping curves but also the loading rate, and particle size. Both parameters play a major role in determining the behaviour of fine contaminated sub-ballast. The railway operational speed limits were deduced from the stress-strain behaviour of the fouled sub-ballast interlayer zone. It is recommended that the maximum speed of trains in fouled railroad segments be limited to a maximum of 32 km/h. The developed guidelines are aimed to prolong the service lifespan of the fouled track segments, while maintaining safety standards to avoid train derailments, track deterioration, and high maintenance costs. • Soil loading rate and particle size are vital in shaping the damping curves with plasticity, confining pressure, and density. • At fouled railroad segments, operators should restrict train speed to a maximum of 32 km/h, for trains exerting ~300 kPa. • The speed limit of 32 km/h at fouled railroad segments is set to preserve 80% of the shear modulus of the sub-ballast. • The shear modulus of the trackbed of at least 80% of G max minimizes tamping operations and prevent further degradation. • Samples loaded at 5 Hz and 10 Hz, ~train speed 64 km/h and 128 km/hr, were characterized by faster failure response. [ABSTRACT FROM AUTHOR]

• A static pushover test considering soil-structure interaction was designed. • A prefabricated subway station structure was subjected to a static pushover test that simulated the soil-structure interaction. • The FEM was established, and the extended working condition analysis was carried out. Physical and numerical studies were conducted to explore the seismic performance characteristics of multi-story and multi-span prefabricated subway station structures, and to identify its weak parts and damage mode during earthquakes. A two-story three-span prefabricated subway station structure was designed and fabricated with a scale ratio of 1:10 and was subjected to a static pushover test that simulated the soil-structure interaction. The test results were interpreted to determine the horizontal resistance - interstory displacement capacity curve of the station, and the interstory displacement ratio (IDR) limit values under each seismic performance state. The experimental results revealed that the upper layer of the prefabricated subway station structure was more severely damaged than to the lower layer, and that the column ends of the upper layer were the weakest parts of the structure in terms of seismic resistance. The splicing joints were generally reliable, but the side wall-middle span splicing joint showed visible cracks. Furthermore, a finite element model was established based on the physical test configuration and was utilized to analyze the pushover tests. The numerical results indicated that the vertical load significantly accelerates the prefabricated subway station to reach the peak point and limit point of its horizontal bearing capacity. The IDR value of subway station seismic performance level 4 determined by the bearing capacity curve of the column was 30% lower than the IDR value obtained by the structural bearing capacity curve. [ABSTRACT FROM AUTHOR]

Abstract: This study compared biological hydrogen production from glucose in two continuously stirred tank reactors (CSTRs) and two integrated biohydrogen reactor clarifier systems (IBRCSs) comprising CSTRs with gravity settlers to decouple the hydraulic retention time (HRT) from solids retention time (SRT). The four systems were operated at organic loading rates of 6.5–42.8 gCOD/L-d, and HRTs of 8–12 h. The SRT was maintained at 2 days in the two IBRCSs. The decoupling of SRT from HRT not only increased glucose conversion from 29–50% in the CSTR to 99.9% in the IBRCSs, but also the volumetric hydrogen production from 0.55–1.8 in the CSTRs to 2.4–9.6 L/L-d. Biomass yields in the two IBRCSs were 0.09 and 0.13 g VSS/g glucose converted, about 50% lower than the CSTR yields of 0.19 and 0.29 g VSS/g glucose converted. Hydrogen yield increased from 0.5–1.0 mol H2/mol glucose converted in the CSTR to 2.8 mol H2/mol glucose converted in the IBRCSs. The inverse relationship between hydrogen yield and biomass yield observed in this study implies that the hydrogen yield is maximized with the minimization of biomass yield, thus necessitating decoupling of SRT from HRT to ensure sufficient reactor biomass. DGGE analysis confirmed the specificity of the microbial culture in the IBRCSs with the high-hydrogen producing Clostridium species, as compared to the more diverse cultures in the CSTR. [Copyright &y& Elsevier]