80 research outputs found
Manganese removal from groundwater: Role of biological and physico-chemical autocatalytic processes
No full textIn The Netherlands, Belgium and other European countries, manganese is removed from groundwater by aeration followed by rapid (sand) filtration. Although manganese removal from groundwater has been studied extensively, the mechanisms that control the ripening of filter media are not yet fully understood. This thesis highlights the role of the formation of a manganese oxide coating on virgin filter media. Characterization and identification of the media revealed that Birnessite was the manganese oxide responsible for effective manganese removal. This study confirmed that Birnessite formed at the beginning of the ripening process was of biological origin. As filter ripening progressed, the origin of the Birnessite became predominantly physico-chemical, although biological manganese oxidation still contributed to the overall removal of manganese. The formation of Birnessite at the start of filter media ripening was negatively influenced by a high filter back wash frequency. Molecular DNA analyses showed that Pseudomonas species are most likely involved at the start of the manganese oxide formation process.Based on the knowledge that manganese removal in conventional groundwater treatment is initiated biologically, long ripening times may be reduced by creating conditions favouring the growth of manganese oxidizing bacteria, e.g., by limiting the back wash frequency and/or intensity. Finally it was shown that the use of freshly prepared manganese oxide, containing Birnessite, can completely eliminate the need for filter media ripening. The results of this research enable the development of an innovative manganese removal process to shorten or completely eliminate long periods of ripening of virgin filter media, as well as significantly prolonging the lifetime of the filter media.<br/
Managing project complexity: A study into adapting early project phases to improve project performance in large engineering projects
No full textEngineering projects become increasingly more complex and project complexity is assumed to be one of the causes for projects being delivered late and over budget. However, what this project complexity actually comprised of was unclear. To improve the overall project performance, this study focuses on identifying the potential causes of complexity in projects. Moreover, it is investigated how the early project phase could be adapted to the complexity of the project. The research is performed with companies of the NAP network, which brings together companies from the entire value chain in the Dutch process industry. The study is structured in four phases and included exploratory case studies, a quantitative survey, explanatory case studies and an evaluative survey. By combining qualitative and quantitative work, this study is an example of successfully applying a mixed methods approach in project management research. The main results of this study are the TOE (Technical, Organizational, External) framework to grasp project complexity and recommendations on managing project complexity in the early project phase. To improve project performance the role of integrated teams (joint owner / contractor teams) as well as thorough application of risk management is shown to be crucial.TSETechnology, Policy and Managemen
Pure methane from CO<sub>2</sub> hydrogenation using a sorption enhanced process with catalyst/zeolite bifunctional materials
No full textMethanation is a potential large-scale option for CO2 utilization, and it is one of the solutions for decreasing carbon emission and production of synthetic green fuels. However, the CO2 conversion is limited by thermodynamics in conventional reaction conditions. However, around 100 % conversion can be obtained using sorption enhanced CO2 methanation according to Le Chatelier's principle, where water is removed during the reaction using zeolite as a sorbent. In this work 5%Ni5A, 5%Ni13X, 5%NiL and 5%Ni2.5%Ce13X bifunctional materials with both catalytic and water adsorption properties were tested in a fixed bed reactor. The overall performance of the bifunctional materials decreased on going from 5%Ni2.5%Ce13X, 5%Ni13X, 5%Ni5A, to 5%NiL. The CO2 conversion and CH4 selectivity were approaching 100 % during prolonged stability testing in a 100 reactive adsorption – desorption cycles test for 5%Ni2.5%Ce13X, and only a slight decrease of the water uptake capacity was observed.</p
Pneumatically actuated hand tool
No full textAbstract of NL 9401195 (A) Pneumatically actuated hand tool for carrying out a mechanical operation, provided with an exchangeable gas cartridge in which the gas which is required for pneumatic actuation is stored. More particularly, the hand tool is provided with at least one pneumatic motor, at least one transmission mechanism, with means which execute the mechanical operation, and with a control circuit for controlling the supply of gas from the gas cartridge to the pneumatic motor, the transmission mechanism being connected on one side to the pneumatic motor and on the other side to the means which carry out the mechanical operation.; In a further refinement of the invention, the transmission mechanism is designed in such a manner that it is a constant force supplied by the pneumatic motor, converted into a force which, during the entire mechanical operation, virtually corresponds to the force required to carry out the mechanical operation
Learning to understand: disentangling the outcomes of stakeholder participation in climate change governance
No full textStakeholder participation is increasingly seen as beneficial for short and long term responses to climate change risks. Past research highlights the role social networks play as both a key outcome of participation, as well as an important step towards other environmental governance goals. This paper focuses on the social relation of mutual understanding, which is often discussed in the environmental governance literature, but has yet to be studied as an empirical social network in its own right. Our paper builds and tests a conceptual framework linking participation to mutual understanding and social learning. We analyze three waves of network and perceptions data gathered on stakeholders participating in the Integrated Coastal Resiliency Assessment (ICRA) project, a 2.5 year-long project aimed at developing a collaborative research assessment on the vulnerabilities to climate change experienced by an island community located in the Chesapeake Bay, USA. Our findings suggest that participation (measured as co-attendance in project events) leads to the formation of mutual understanding ties among stakeholders, but these ties do not necessarily lead to more similarity in stakeholders’ perceptions on climate change. We reflect on these findings, and the project more broadly, noting that our study lends support to scholars arguing that feelings of mutual understanding are potentially more important for certain forms of collective action, as opposed to whether or not stakeholders increase their shared beliefs or perceptions about the environmental problem in question.Transport and Logistic
Tropospheric composition and circulation of Uranus with ALMA and the VLA
No full textWe present Atacama Large Millimeter/submillimeter Array (ALMA) and Very Large Array (VLA) spatial maps of the Uranian atmosphere taken between 2015 and 2018 at wavelengths from 1.3 mm to 10 cm, probing pressures from ~1 to ~50 bar at spatial resolutions from 0 1 to 0 8. Radiative transfer modeling was performed to determine the physical origin of the brightness variations across Uranus's disk. The radio-dark equator and midlatitudes of the planet (south of ~50°N) are well fit by a deep H2S mixing ratio of 8.7+3.1- 1.5 ×10- 4 ( 37+13-6 × solar) and a deep NH3 mixing ratio of 1.7+0.7-0.4 ×10-4 ( 1.4+0.50.3× solar), in good agreement with models of Uranus's disk-averaged spectrum from the literature. The north polar region is very bright at all frequencies northward of ~50°N, which we attribute to strong depletions extending down to the NH4SH layer in both NH3 and H2S relative to the equatorial region; the model is consistent with an NH3 abundance of 4.7+2.1- 1.8 ×10-7 and an H2S abundance of <1.9×10-7 between ~20 and ~50 bar. Combining this observed depletion in condensible molecules with methane-sensitive near-infrared observations from the literature suggests large-scale downwelling in the north polar vortex region from ~0.1 to ~50 bar. The highest-resolution maps reveal zonal radio-dark and radio-bright bands at 20°S, 0°, and 20°N, as well as zonal banding within the north polar region. The difference in brightness is a factor of ~10 less pronounced in these bands than the difference between the north pole and equator, and additional observations are required to determine the temperature, composition, and vertical extent of these features.Astrodynamics & Space Mission
The application of automated feedback and feedforward control to a LED-based photocatalytic reactor
No full textAn optimal photon utilization is important for the economic performance of a photocatalytic reactor. However, for the desired reactor performance, it is often difficult to predict the required photon utilization. In this work, automated feedback and feedforward controllers are investigated to maintain the reactor conversion close to a desired value by adjusting the photon irradiance within a LED-based photocatalytic reactor for toluene degradation. The feedback controller was able to control the conversion during a set-point tracking experiment and was able to mitigate the effects of catalyst deactivation in an automated fashion. The feedforward controller was designed based on an empirical steady-state model to mitigate the effect of changing toluene inlet concentration and relative humidity, which were measured input disturbances. The results demonstrated that feedback and feedforward control were complementary and could mitigate the effects of disturbances effectively such that the photocatalytic reactor operated close to desired conditions at all times. The presented work is the first example of how online analytical technologies can be combined with “smart” light sources such as LEDs to implement automated process control loops that optimize photon utilization. Future work may expand on this concept by developing more advanced control strategies and exploring applications in different areas.Intensified Reaction and Separation SystemsChemE/Product and Process Engineerin
Room-temperature stability of Pt nanogaps formed by self-breaking
No full textWe present a method to make Pt nanometer-spaced electrodes that are free of metallic particles and stable at ambient conditions. The nanogaps are fabricated using feedback-controlled electromigration to form few-atom contacts. When performing this procedure at elevated temperatures (>420?K), the Pt contacts undergo self-breaking so that nanometer separated electrode pairs are formed. Once cooled down to lower temperatures, the nanogaps stabilize and can be characterized in detail. We find that current-voltage characteristics can be well fitted to a Simmons model for tunneling and gap-size fluctuations at room temperature determined from these fits stay within 0.6 Å for at least 50 h.Kavli Institute of NanoscienceApplied Science
A compressive strength model for recycled aggregate systems
No full textStructural EngineeringCivil Engineering and Geoscience
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