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David C Stuckey - One of the best experts on this subject based on the ideXlab platform.

  • iron deficiency and bioavailability in anaerobic batch and submerged membrane bioreactors sambr during organic Shock Loads
    Bioresource Technology, 2016
    Co-Authors: Balachandran Ketheesan, David C Stuckey, Pham Minh Thanh
    Abstract:

    This study examined the effects of Fe(2+) and its bioavailability for controlling VFAs during organic Shock Loads in batch reactors and a submerged anaerobic membrane bioreactor (SAMBR). When seed grown under Fe-sufficient conditions (7.95±0.05mgFe/g-TSS), an organic Shock resulted in leaching of Fe from the residual to organically bound and soluble forms. Under Fe-deficient seed conditions (0.1±0.002mgFe/gTSS), Fe(2+) supplementation (3.34mgFe(2+)/g-TSS) with acetate resulted in a 2.1-3.9 fold increase in the rate of methane production, while with propionate it increased by 1.2-1.5 fold compared to non-Fe(2+) supplemented reactors. Precipitation of Fe(2+) as sulphides and organically bound Fe were bioavailable to methanogens for acetate assimilation. The results confirmed that the transitory/long term limitations of Fe play a significant role in controlling the degradation of VFAs during organic Shock Loads due to their varying physical/chemical states, and bioavailability.

  • effect of perchloroethylene pce and hydraulic Shock Loads on a membrane aerated biofilm reactor mabr biodegrading pce
    Journal of Chemical Technology & Biotechnology, 2009
    Co-Authors: Dieudonna Guy Ohandja, David C Stuckey
    Abstract:

    BACKGROUND: A membrane-aerated biofilm reactor (MABR) has previously been used to provide both anaerobic and aerobic conditions for mineralisation of perchloroethylene (PCE). However, very little is known about the stability of this reactor under hydraulic and PCE Shock Loads. An MABR was therefore subjected to sudden hydraulic and PCE Shock Loads in order to investigate its stability under such conditions. RESULTS: After each Shock, the reactor responded with an increase of chemical oxygen demand (COD) and volatile fatty acids (VFA)s, a breakthrough of PCE and its biodegradation intermediates in the effluent, and a decrease in methane production. Although some PCE biodegradation intermediates were found in the effluent during each Shock loading, the MABR performance recovered without the accumulation of any particular PCE biodegradation intermediates during PCE Shock Loads. During the hydraulic Shock Loads, the MABR was unstable at hydraulic retention times (HRTs) of 6 h with PCE and its biodegradation intermediates detected in the effluent. However, these intermediates were degraded when the HRT was reset to 48 h. CONCLUSIONS: This study suggests that MABRs can withstand fluctuations in influent strength and flows which occur in wastewater treatment works. Copyright © 2009 Society of Chemical Industry

  • the effect of organic and hydraulic Shock Loads on the production of soluble microbial products in anaerobic digesters
    Water Environment Research, 2004
    Co-Authors: Sergio Francisco De Aquino, David C Stuckey
    Abstract:

    Anaerobic chemostats were used to investigate the effects of organic and hydraulic Shock Loads on the production of soluble microbial products (SMP). Production of SMP was found to increase during glucose spikes, reaching up 15% of the influent chemical oxygen demand. These SMP appear to be utilization-associated products produced as a result of the temporarily high organic load, and chemical analysis and ultrafiltration experiments revealed that most of these compounds are difficult to identify and that the majority of them are present in the low molecular weight (MW) range. Production of SMP also increased when the hydraulic retention time was reduced from 15 to 3 days, and an increase in DNA concentration in the bulk solution suggested enhanced cell lysis. Although the cause of lysis was not clear, it is believed that most of the SMP produced under such conditions were biomass-associated products following cell death. While the majority of these compounds lay in the low MW range, as much as 35% were found to have MWs greater than 1 kDa. During the period when the anaerobic chemostat was fed no alkalinity and the pH remained lower than 6.5 for more than a week, a slightly higher production of SMP and a shift in the MW distribution towards the production of higher MW SMP was observed.

  • hydrogen production in anaerobic reactors during Shock Loads influence of formate production and h2 kinetics
    Water Research, 2001
    Co-Authors: Ravi K Voolapalli, David C Stuckey
    Abstract:

    In this article the role of hydrogen as a process monitoring tool in methanogenic systems was studied by considering the influence of several key system parameters. Hydrogen production was found to be influenced mainly by the inocula's source pH, and varied only slightly with external pH and HCO3− levels. When an inoculum adapted to above neutral conditions (pH>7) was Shocked, reducing equivalents were selectively channelled through formate, while high hydrogen production was noticed with acidically (pH<6.5) adapted inocula. The results also revealed that the production of hydrogen or formate during Shock Loads was not strongly associated with microbial morphology (granules or flocs) as high electron fluxes were possible through either during acidogenesis. Shock load experiments in continuous reactors revealed that neither hydrogen nor formate accumulated to any significant degree, nevertheless digester recovery took a long time due to the slow kinetics of volatile fatty acid degradation. Selective formate production under neutral pH environments, coupled with high hydrogenotrophic activity, was found to be responsible for the dampened hydrogen response during the early phases of gradually Shocked systems (step change). Based on these results it appears that the role of hydrogen as a process monitoring tool has been overemphasised in the literature.

  • stability enhancement of anaerobic digestion through membrane gas extraction under organic Shock Loads
    Journal of Chemical Technology & Biotechnology, 1998
    Co-Authors: Ravi K Voolapalli, David C Stuckey
    Abstract:

    A novel submerged silicone membrane extraction technique for removing the dissolved gases, CO2 and H2, was explored as a method for enhancing the stability of anaerobic digesters under Shock Loads. The effectiveness of this strategy was demonstrated during a five-fold step increase in the feed concentration from 4 kg m−3 to 20 kg m−3 Chemical Oxygen Demand (COD) to two anaerobic chemostats, a control and a membrane reactor, operating under steady state. Data revealed that membrane extraction of CO2 enabled neutral pH values to be maintained during the Shock, in contrast to the control; and this appeared to enhance acetate degradation. In addition, while liquid phase hydrogen removal was only partially successful due to a biofilm building up on the membrane, it also appeared to enhance the rate of volatile fatty acid degradation, and hence improved reactor stability. Floc sizes were monitored during the course of the Shock load experiment and found to decrease from 46 μm to 30 μm over 35 days in the control, but from 37 μm to <5 μm in the membrane reactor. This decrease in floc size was postulated to be due to the growth of a relatively pure methanogenic biofilm on the membrane. © 1998 Society of Chemical Industry

Eugenio Foresti - One of the best experts on this subject based on the ideXlab platform.

  • Effects of Feed Time, Organic Loading and Shock Loads in Anaerobic Whey Treatment by an AnSBBR with Circulation
    Applied Biochemistry and Biotechnology, 2008
    Co-Authors: Roberto A. Bezerra Jr., Marcelo Zaiat, José A. D. Rodrigues, Suzana M. Ratusznei, Eugenio Foresti
    Abstract:

    The aim of this work was to investigate the effect of different feeding times (2, 4, and 6 h) and organic loading rates (3, 6 and 12 gCOD l^−1 day^−1) on the performance of an anaerobic sequencing batch reactor containing immobilized biomass, as well as to verify the minimum amount of alkalinity that can be added to the influent. The reactor, in which mixing was achieved by recirculation of the liquid phase, was maintained at 30 ± 1°C, possessed 2.5 l reactional volume and treated 1.5 l cheese whey in 8-h cycles. Results showed that the effect of feeding time on reactor performance was more pronounced at higher values of organic loading rates (OLR). During operation at an OLR of 3 gCOD l^−1 day^−1, change in feeding time did not affect efficiency of organic matter removal from the reactor. At an OLR of 6 gCOD l^−1 day^−1, reactor efficiency improved in relation to the lower loading rate and tended to drop at longer feeding times. At an OLR of 12 gCOD l^−1 day^−1 the reactor showed to depend more on feeding time; higher feeding times resulted in a decrease in reactor efficiency. Under all conditions Shock Loads of 24 gCOD l^−1 day^−1 caused an increase in acids concentration in the effluent. However, despite this increase, the reactor regained stability readily and alkalinity supplied to the influent showed to be sufficient to maintain pH close to neutral during operation. Regardless of applied OLR, operation with feeding time of 2 h was which provided improved stability and rendered the process less susceptible to Shock Loads.

  • Whey Treatment by AnSBBR with Circulation: Effects of Organic Loading, Shock Loads, and Alkalinity Supplementation
    Applied Biochemistry and Biotechnology, 2007
    Co-Authors: Roberto A. Bezerra, Marcelo Zaiat, José A. D. Rodrigues, Suzana M. Ratusznei, Eugenio Foresti
    Abstract:

    The main objective of this work was to investigate the effect of volumetric loading rate (VLR), Shock load, and alkalinity supplementation on the efficiency and stability of an Anaerobic Sequencing Batch Biofilm Reactor (AnSBBR) containing polyurethane foam cubes. Mixing in the reactor, which was kept at 30 ± 1°C, occurred by recirculating the liquid phase. The reactor treated 2.5 l cheese whey in 8-h cycles, at concentrations of 1, 2, and 4 g COD l^−1, which corresponded to VLRs of 3, 6, and 12 g COD l^−1 day^−1, respectively. Application of single-cycle Shock Loads of 6, 12, and 24 g COD l^−1 day^−1 did not impair reactor performance. In addition, for VLRs of 3, 6, and 12 g COD l^−1 day^−1, alkalinity supplementation to the influent, at the end of each assay, could be reduced to 75, 50, and 50%, respectively, in relation to supplementation at the beginning of the assay. During reactor operation a viscous polymer-like material was formed between the polyurethane foam cubes, which increased at higher VLR. Finally, addition of salts to the influent improved reactor efficiency.

  • Influence of organic Shock Loads in an ASBBR treating synthetic wastewater with different concentration levels.
    Bioresource Technology, 2007
    Co-Authors: Mariana Bueno Moreira, Suzana Maria Ratusznei, José Alberto Domingues Rodrigues, Marcelo Zaiat, Eugenio Foresti
    Abstract:

    Abstract Safe application of the anaerobic sequencing biofilm batch reactor (ASBBR) still depends on deeper insight into its behavior when faced with common operational problems in wastewater treatments such as tolerance to abrupt variations in influent concentration, so called Shock Loads. To this end the current work shows the effect of organic Shock Loads on the performance of an ASBBR, with a useful volume of 5 L, containing 0.5-cm polyurethane cubes and operating at 30 °C with mechanical stirring of 500 rpm. In the assays 2 L of two types of synthetic wastewater were treated in 8-h cycles. Synthetic wastewater I was based on sucrose–amide–cellulose with concentration of 500 mg COD/L and synthetic wastewater II was based on volatile acids with concentration ranging from 500 to 2000 mg COD/L. Organic Shock Loads of 2–4 times the operation concentration were applied during one and two cycles. System efficiency was monitored before and after application of the perturbation. When operating with concentrations from 500 to 1000 mg COD/L and Shock Loads of 2–4 times the influent concentration during one or two cycles the system was able to regain stability after one cycle and the values of organic matter, total and intermediate volatile acids, bicarbonate alkalinity and pH were similar to those prior to the perturbations. At a concentration of 2000 mg COD/L the reactor appeared to be robust, regaining removal efficiencies similar to those prior to perturbation at Shock Loads twice the operation concentration lasting one cycle and stability was recovered after two cycles. However, for Shock Loads twice the operation concentration during two cycles and Shock Loads four times the operation concentration during one or two cycles filtered sample removal efficiency decreased to levels different from those prior to perturbation, on an average of 90–80%, approximately, yet the system managed to attain stability within two cycles after Shock application. Therefore, this investigation envisions the potential of full scale application of this type of bioreactor which showed robustness to organic Shock Loads, despite discontinuous operation and the short times available for treating total wastewater volume.

  • performance and stability of an anaerobic fixed bed reactor subjected to progressive increasing concentrations of influent organic matter and organic Shock Loads
    Journal of Environmental Management, 2005
    Co-Authors: Ariuska Karla Barbosa Amorim, Marcelo Zaiat, Eugenio Foresti
    Abstract:

    Abstract Data on the performance of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor subjected to step increases of organic loading rates (OLR) and to organic Shock Loads (OSL) are presented and discussed. The tubular reactor (100 cm long and 5 cm diameter) with a useful volume of 1995 mL was filled with polyurethane foam cubic matrices holding immobilized biomass and fed with synthetic wastewater. The reactor was operated at the controlled temperature of 30±1 °C and hydraulic retention time of 7 h. After about 15 days, the HAIB reactor attained operating stability. Thereafter, it was subjected to step increases of the applied OLR that ranged from 6.8 to 18.8 kg COD/m 3  d. After steady state had been achieved at each step, OSL corresponding to approximately three times the operating OLR were applied for 7 h. No disturbance was observed due to the step increase in OLR. An increase in effluent chemical oxygen demand (COD) and volatile fatty acids (VFA) concentrations and a decrease in the percentage of methane in the biogas were observed due to OSL applications. However, stability of the monitoring parameters was always restored approximately 17 h after the application of OSL for all conditions tested.

Jeongha You - One of the best experts on this subject based on the ideXlab platform.

  • cracking behavior of tungsten armor under elm like thermal Shock Loads a computational study
    Nuclear materials and energy, 2015
    Co-Authors: Ewald Werne, Jeongha You
    Abstract:

    Abstract In this work, the cracking behavior of tungsten under edge-localized mode (ELM)-like thermal Shock Loads was investigated on the basis of a rigorous computational fracture mechanical analysis combined with the finite element method. Typical transient thermal Shock Loads of ELM conditions were considered with a relevant range of power density and base temperature for a loading duration of 1 ms. Crack initiation and progressive growth were predicted using the extended finite element method and the J -integral was calculated for the assumed precrack by means of the virtual crack extension method. For a power density of 1 GW/m 2 and higher, a crack is preferably initiated near the edge of the loading area and is then followed by a gradual horizontal kinking, parallel to the loading surface. The crack formation is predicted for the power density of 0.6 GW/m 2 and above, and when the base temperature is higher than 600 °C, almost no cracks is predicted. The numerically predicted cracking behavior agrees in general with the experimental observations.

G Lettinga - One of the best experts on this subject based on the ideXlab platform.

  • the effect of lauric acid Shock Loads on the biological and physical performance of granular sludge in uasb reactors digesting acetate
    Journal of Chemical Technology & Biotechnology, 2007
    Co-Authors: Arjen Rinzema, Arne Alphenaar, G Lettinga
    Abstract:

    The specific activity of acetotrophic methanogens and the physical behaviour of granular sludge in laboratory-scale upflow anaerobic sludge bed (UASB) reactors subjected to Shock Loads of lauric acid in the absence and presence of calcium were studied. In the absence of calcium, lauric acid completely inhibited acetotrophic methanogens above a threshold level of 100 mg C12:0dm−3, whereas no inhibition occurred below this threshold concentration. Addition of an equivalent amount of calcium to wastewater containing lauric acid prevented inhibition of acetotrophic methanogens at least up to 1500 mg C12:0dm−3. Addition of less than an equivalent amount of calcium apparently removed more than a stoichiometric amount of lauric acid: 50 % inhibition occurred at approximately 700 mg ‘free’ or excess C12:0dm−3. The results indicate that complete sludge wash-out from conventional UASB reactors is likely to occur within 2-8 h if the system is overloaded with an influent containing more than 100 mg C12:0dm−3. Calcium did not prevent wash-out.

  • the effects of hydraulic and organic Shock Loads on the robustness of upflow anaerobic sludge blanket reactors treating sewage
    Water Science and Technology, 2006
    Co-Authors: R C Leitao, S T Santaellla, A C Van Haandel, G Zeeman, G Lettinga
    Abstract:

    In this investigation, the robustness and stability of UASB reactors was evaluated on the basis of four indicators: (i) COD removal efficiency; (ii) effluent variability; (iii) pH stability; and (iv) recovery time. The experiments were carried out using six pilot-scale UASB reactors fed with domestic sewage and operated under different operational conditions. After establishment of a "steady-state", organic and hydraulic Shock Loads (six times the loading rate during six hours) were imposed. The results show that the UASB reactors are robust systems with regards to COD removal efficiency and pH stability when exposed to Shock Loads. However, this reactor cannot attenuate the imposed fluctuation in the influent COD. A secondary treatment unit is needed to retain the expelled sludge occurring as a result of a hydraulic Shock load, or prior to the Shock, a sufficient amount of sludge needs to be discharged from the reactor.

Nilanjan Mitra - One of the best experts on this subject based on the ideXlab platform.

  • On core compressibility of sandwich composite panels subjected to intense underwater Shock Loads
    Journal of Applied Physics, 2014
    Co-Authors: Ritwik Ghoshal, Nilanjan Mitra
    Abstract:

    Novel analytical models have been proposed in this study which extends current available fluid-structure interaction (FSI) theories for explosion induced Shock loading on monolithic and laminated composite plates to sandwich composite panels, featuring core compression. The proposed models have been asymptotically validated against other FSI existing theories in low pressure range. A qualitative comparative analysis of the proposed models has been made with other existing FSI theories from the viewpoint of energy conservation. Core compression as predicted by the proposed models can be utilized for more economical, robust design of blast resistant sandwich composite structures. © 2014 AIP Publishing LLC.