Stephan Fuchs

The oxidation of carbon monoxide by oxygen over platinum, palladium and rhodium catalysts from 10−10 to 1 bar

Abstract The noble metal catalysed oxidation of CO by O2 has been studied on polycrystalline foils, ribbons and wires of Pt, Pd and Rh as well as on a variety of supported Pt catalysts. At temperatures from 180 to 600 °C, the partial pressure ratio was changed over the range 0.01 ⩽ pCO/pO2 ⩽ 50 at partial pressures varying over the range 10−6 ⩽ pi (mbar) ⩽ 40. In the total pressure region below 1 mbar, the results agree very well with model experiments conducted under ultra-high vacuum. The rate values measured at total pressures exceeding 1 mbar correspond to the highest activities ever observed on noble metal catalysts. Even at low temperatures and high gas velocities up to 14 m s−1, such values were mass transfer limited since the reaction was not inhibited by CO. Neither the structure nor the support influence the reaction in the case of supported Pt catalysts. The well-defined geometry of the experimental set up allowed an estimation of the appropriate mass-transfer coefficients and the calculation of the intrinsic reaction rate. The results clearly indicate that in the region where the reaction is first order with respect to the limiting component the intrinsic first-order rate constant has the same value as under high vacuum conditions within the precision of the approach. Thus the apparent gap between the rates of CO oxidation observed in model experiments and under ambient pressure must be attributed to the influence of mass-transfer limitations.

Two-phase anaerobic digestion of partially acidified sewage sludge: a pilot plant study for safe sludge disposal in developing countries

The unsafe disposal of wastewater and sludge in different areas of developing countries results in significant environmental pollution, particularly for groundwater, thus increasing the risk of waterborne diseases spreading. In this work, a two-phase anaerobic digestion process for post-treatment of partially acidified sewage sludge was investigated to evaluate its feasibility as a safe sludge disposal system. Pilot tests showed that an effective sludge stabilization can be achieved (total volatile solids content<65%, organic acid concentration<200 mg/L at flow rate=50 L/d and hydraulic residence time=18 d) as well as a relative low faecal coliform density (<1000 most probable number per g total solids), showing that land application of the sludge without restrictions is possible according to US Environmental Protection Agency criteria for safe sludge disposal. A biogas production as high as 390 L/d with a 60% methane content by volume was achieved, showing that energy production from biogas may be achieved as well.

Design and development of decentralized water and wastewater technologies: a combination of safe wastewater disposal and fertilizer production

Modern wastewater treatment plants are often inappropriate for communities in developing countries. Such communities lack the funding, resources and skilled labour required to implement, operate, and maintain these plants. This research was conducted to investigate and establish an appropriate wastewater treatment system for the district of Gunung Kidul, Indonesia. Due to its lack of water during the dry season, this district is considered one of the poorest areas in the nation. First, wastewater was stored in septic tank units for a retention time of 26 days. Anaerobic conditions occurred, resulting in an 80% reduction of initial COD. The retained sludge was well stabilized with great potential, if dewatered, for reuse as fertilizer. Consequently, supernatant was separated for experiments consisting of lab scale aerobic sand filtering unit. Through filtration, further removals of COD (about 30%) and pathogens were achieved. Rich in nitrogen, the resulting effluent could be used for irrigation and soil conditioning. With faecal sludge and also a mixture of septic sludge and food waste, the hydrolysis stage of anaerobic digestion was examined. This paper discusses the laboratory findings in Karlsruhe and the design and implementation of a treatment system in Glompong, Indonesia.

The oxidation of carbon monoxide by oxygen over polycrystalline platinum, palladium and rodium from UHV to normal pressure

The oxidation of CO by O2 was studied over polycrystalline foils, stripes and wires of Pt, Pd and Rh as well as over Pt on different supports. The partial pressures were in the range 10−6≤pi/mbar≤40, the partil pressure ratio was varied in the range 0.01≤pCO/pO2≤50 and the temperature was varied between 180° and 600°C. For total pressure lower than 1 mbar the results agree perfectly with observatios of White et al [1]–[3] in the UHV range. For total pressure higher than 1 mbar the highest activities report so far could be observed using foils and supported catalysts. The measured reaction rates were controlled by mass transport with the exception of the CO-inhibition region even at low temperatures and high gas velocities of 10 m/s. No influence of Pt-catalyst structure or support could be observed. In the region, where the reaction is first order with respect to CO and zeroth order with respect to O2 one can approximately calculate the intrinsic reaction rates. They are a linear extrapolation from the UHV-results: impingement rates and sticking coefficients of the reactants are rate determining even at normal pressure.

Construction and application of a jet-stirred loop reactor

Abstract In this paper, a jet-agitated recycling reactor is presented as a special type of back-mixing system, which enables a reliable investigation of catalytic properties without any contamination of the catalyst. Determination of the operation behaviour indicates the manufactured reactor to be equivalent to a perfectly mixed system with high fluid velocities inside the loop. Investigation of the carbon monoxide oxidation over a platinum foil, as a test reaction, demonstrated the systems excellent suitability for applications in catalytic research. Limitations of transport processes in the kinetics observed could be revealed unambiguously, leading to correct interpretation of the data obtained. On this occasion, the measurement device for the gas velocity over the catalyst proved to be very useful.

Behavior of dissolved trace metals by discharging wastewater effluents into receiving water

Municipal wastewater (WW) discharges induce various environmental impacts on receiving freshwater systems e.g. contribution to metal pollution. Besides the quantity of metal release, metal speciation and possible transformation processes present danger to aquatic biota. In experimental mixtures of WW effluents with receiving waters, discharged dissolved trace metals showed different forms of behavior. Cobalt showed adsorption onto particles, while Cu showed desorption from particulate into dissolved state. In presence of high amounts of river particles, interactions with WW contaminants were elevated.

Development and Evaluation of Appropriate Concepts for Sewage Disposal and Treatment in a Rural Area, Central Java, Indonesia on the Example of the Village Pucanganom

In the province of Yogyakarta in Java, the district of Gunung Kidul is considered to be one of the poorest areas in Indonesia. Here, water shortages greatly affect the population, especially during the dry season, which lasts from April to October. Sanitation Systems in Gunung Kidul consist, either pit latrines or pour flush toilets. Without any treatment the liquid phase infiltrates in to the ground and the septic tanks are hardly ever emptied, thus posing an evident contamination potential to groundwater. So, the current situation about waste water and its treatment is inadequate. Due to this reason within the Integrated Water Resources Management Indonesia Project (IWRM) a so called pilot village Pucanganom was selected to develop an appropriate waste water treatment system considering basis conditions and resultant indicators which were weighted by the Analytical Hierarchy Process Method (AHP). The following paper will describe the application of the method to find an adaptable sanitary system for a village in Gunung Kidul, Indonesia.

Redistribution of methane emission hot spots under drawdown conditions

In the context of reservoirs, sediment trapping, and aquatic greenhouse gas (GHG) production, knowledge about the distribution of hot and low spots is essential for improved measurement strategies. It is also a key to a precise assessment of the GHG emissions of each reservoir. Large numbers of reservoirs are used mainly for hydroelectric power generation and, hence, affected by strong changes in water level. Drawdown events may lead to significant changes in spatial sediment and organic carbon distribution and, consequently, strongly alter the GHG emission patterns of the water body. We combined hydroacoustic sediment classification, sediment magnitude detection, and ebullition flux assessment with in-situ pore water investigations and sediment coring to detect ebullition distribution patterns after strong reservoir drawdown. The research was conducted in the Capivari Reservoir in the southeast of Brazil, which was affected by up to 15 m of drawdown within the last 10 years. Results show severe changes in sediment accumulation and composition. The focusing of sediment divides the reservoir in extreme hot and low spots. Methane pore water concentrations are highly correlated with acoustic backscatter values (r2 = 0.97) as well as with the organic carbon content (r2 = 0.55) and allow for a precise detection of the newly created emission patterns. Highly productive sediment could be acoustically distinguished from non-productive areas. Only 23.6% of the reservoir surface produced 64% of the detected bubbles. An organic carbon content in the sediment of 2.4% was found to be a prerequisite for the formation of GHG emission hot spots. These findings may help to complement the still insufficient knowledge of methane ebullition fluxes from reservoirs with changing water levels.