Biomedical subjects

R Stegmann

Publications and source records attributed to R Stegmann.

At least 19 recordsLinked to original sources

PubMed2006

Fundamental processes and implications during in situ aeration of old landfills.

Results of investigations from many old landfills in Germany and Europe indicate that significant emissions occur under conventional landfill operating conditions (i.e., anaerobic conditions). Significant emissions via the gas phase are predicted to last at least three decades after landfill closure, while leachate emissions are predicted to continue for many decades, potentially even lasting for centuries. When considering the specific type and quality, and quite often lack of, protection barriers associated with old landfills, these leachate and gas emissions may result in a significant negative impact on the environment. However, complete sealing of the landfill only temporarily reduces emissions because dry-conservation of the biodegradable waste fraction results, thus not allowing any severe reduction in the emission and hazardous potential of the landfill to occur. If noticeable damage of the surface capping system occurred in these landfills, infiltrating water would restart the interrupted emission formation. In contrast, aerobic in situ stabilization by means of low pressure aeration attempts to stabilize and modify the inventory of organic matter inside the landfill, acting to reduce the emission potential in a more sustainable manner. By enabling faster and more extensive aerobic degradation processes in the landfill (compared with anaerobic processes), the organics (e.g., hydrocarbons) are degraded significantly faster, resulting in an increased carbon discharge via the gas phase, as well as reduced leachate concentrations. Because carbon dioxide (CO(2)) is the main compound in the extracted off-gas (instead of methane (CH(4)), which dominated under anaerobic landfill conditions), the negative impact of diffuse LFG emissions towards an increased global warming effect may be significantly lowered. With respect to leachate quality, a reduction of organic compounds as well as ammonia-nitrogen can be expected. In addition to these positive ecological effects, aerobic in situ stabilization is associated with significant cost savings potential due to both quantitative and qualitative reductions in the aftercare period. This paper describes the fundamental processes and implications of in situ landfill aeration. Additionally, possible criteria for defining an endpoint of the active aeration process are presented and discussed.

Air Pollutants↗

PubMed2005

Penetrating eye injuries in South African children: aetiology and visual outcome.

PURPOSE: To assess the aetiology, prognosis, and visual outcome of penetrating eye injuries in South African children. METHODS: In all, 100 consecutive patients, aged 16 years and under, with penetrating ocular injuries undergoing surgery between January 2001 and November 2002 were prospectively evaluated. RESULTS: Most children (66%) were injured during play. In all, 55% of penetrating eye injuries occurred at home, and all injuries to children under the age of 6 years occurred there. Most injuries occurred in the absence of a caregiver (85%). Sticks, wire, and glass caused half of all injuries (48%). The most common mechanism of injury was impact with a sharp object (46%). Only 25% of injured presented to the hospital within 24 h of injury; the more severe the sustained injury and the younger the patient, the earlier was attendance at the clinic. Most patients (71%) regained best-corrected visual acuity (Snellen equivalent) of 20/200 or better, and 51% regained 20/40 or better. Patient age and delay of presentation were not of prognostic value. Indicators of poor visual outcome were identified as wound size greater than 11 mm in length, mixed corneoscleral type wounding, and involvement of the lens and posterior segment in the injury. CONCLUSIONS: Penetrating eye injuries in African children, reviewed here, generally occur when children are at play in a domestic setting. Effective prevention should stress parental awareness, careful supervision, greater home safety, safe toys, and avoidance of hazardous games.

Adolescent↗

PubMed2005

Pollutant release and pollutant reduction--impact of the aeration of landfills.

The in situ stabilization of old deposits aims for a lasting and controlled reduction of pollutant emissions from the deposited waste in order to diminish expenditure and the duration of landfill aftercare measures. The stabilization operation so far, observed over a period of 1-2 years at three landfills in Germany, shows that leachate contamination is permanently reduced, biodegradation processes are significantly accelerated and main settlements take place within a short period of time.

Air↗

PubMed2005

Behaviour of biodegradable plastics in composting facilities.

Composting is a preferred treatment strategy for biodegradable plastics (BDPs). In this sense, the collection of BDPs together with organic household wastes is a highly discussed possibility. Under the aspect of the behaviour of BDPs in composting facilities, a telephone survey was carried out with selected composting facility operators. They were interviewed with respect to treated wastes, content of impurities, processes for impurity separation, experiences with biodegradable plastics and assumptions to the behaviour of biodegradable plastics in their facility. Forty percent of the facilities had some experiences with BDPs due to test runs, and also since the occurrence of BDPs in their waste was known. The majority of the operators expressed apprehension regarding an increase of impurities resulting from a combined collection of biowaste and BDPs. In the facilities, measures for the impurity separation from the biowaste were used in common practice - in 33% of the cases, separation of disturbing plastics was done before composting, in 33% after composting, and in 13% before and after composting. The most important separation processes for conventional plastics were sieving and manual sorting. In two cases air classification was also used. When asked about the separation possibility of the conventional but not of the biodegradable plastics in their facilities, the majority of operators were not in a position to comment or they replied that it was not an option. No problems were seen in most cases if the impurity separation follows composting. If impurity separation takes place before composting it was often assumed that the BDPs are mainly separated by sieving. In conclusion, in more than half of the cases, BDPs would not be composted if delivered to a composting facility. Under the actual conditions regarding the collection and the treatment/disposal possibilities, an application of BDPs seems to only be reasonable for clean (i.e., source separated on their own) fractions of BDPs.

Biodegradation, Environmental↗

PubMed2005

Development of a simple and sensitive method for the characterization of odorous waste gas emissions by means of solid-phase microextraction (SPME) and GC-MS/olfactometry.

A solid-phase microextraction (SPME) method has been developed for the extraction of odorous compounds from waste gas. The enriched compounds were characterized by gas chromatography-mass spectrometry (GC-MS) and gas chromatography followed by simultaneous flame ionization detection and olfactometry (GC-FID/O). Five different SPME fiber coatings were tested, and the carboxen/polydimethylsiloxane (CAR/PDMS) fiber showed the highest ability to extract odorous compounds from the waste gas. Furthermore, parameters such as exposure time, desorption temperature, and desorption time have been optimized. The SPME method was successfully used to characterize an odorous waste gas from a fat refinery prior to and after waste gas treatment in order to describe the treatment efficiency of the used laboratory scale plant which consisted of a bioscrubber/biofilter combination and an activated carbon adsorber. The developed method is a valuable approach to provide detailed information of waste gas composition and complements existing methods for the determination of odors. However, caution should be exercised if CAR/PDMS fibers are used for the quantification of odorous compounds in multi-component matrices like waste gas emissions since the relative affinity of each analyte was shown to differ according to the total amount of analytes present in the sample.

Chemistry Techniques, Analytical↗

PubMed2005

Analytical determination of the suitability of different processes for the treatment of odorous waste gas.

In order to determine the efficiency of different treatment systems for the reduction of odorous emissions, a gas chromatographic method followed by simultaneous mass spectrometry and olfactometry (GC-MS/O) was developed. Samples from a coffee bean roasting and a fat and oil processing plant were analyzed, respectively. The results were compared with the data obtained by olfactometric measurements. At a coffee bean roasting plant, cooling gases were analyzed prior to and after treatment in a full scale bioscrubber. The GC-MS/O analysis showed that the amounts of aldehydes and ketones decreased after treatment of cooling gases of coffee bean roasting in the bioscrubber, whereas the contents of the heterocyclic compounds, like pyridine and the pyrazines, and acetophenone and guaiacol remained almost unchanged. The amounts of dimethyl disulfide, 3-hydroxy-2-butanone, and the carboxylic acids increased after bioscrubber treatment. Furthermore, the performance of each stage of a combined experimental plant for the treatment of exhaust air of fat and oil processing was investigated. This treatment plant consisted of a bioscrubber, a biofilter, and an activated carbon adsorber. The important odor-active compounds of the exhaust air of fat and oil processing were the typical fat oxidation products (aldehydes, ketones) and with lower importance 2-pentylfuran, a few terpenes and aromates. Again, the key odor-active compounds, aldehydes and ketones, were degraded in the bioscrubber. Further degradation of aliphatic, unsaturated, methylated, and cyclic alkanes, as well as aromates, terpenes, and furans by the biofilter was observed. After the last treatment stage, the activated carbon filter, only small amounts of aliphatic, unsaturated, methylated, and cyclic alkanes and aromates remained in the waste gas. For both applications, the results of the developed GC-MS/O method correlated very well with olfactometric measurements.

Air Pollution↗

PubMed2005

Odour management and treatment technologies: an overview.

There is a large variety of options available for the effective treatment of odorous emissions. The most important physical, chemical and biological treatment processes are shortly described and their favourable applications, as well as their limits, are highlighted. But for a sustainable solution of an industrial odour problem, there is more involved than just the installation of a waste gas treatment system. This article focuses on a general and systematic approach towards extensive odour management. First of all, an odour assessment should be worked out where all actual and potential odour emission sources are recorded and characterised. A special focus should be set on fugitive emissions, which may have an enormous impact on the overall odour problem. They need to be captured before they can be supplied to a treatment system. According to the composition and condition of the waste gases, an appropriate treatment system must be selected. For this purpose, test systems have been developed and are presented in this article.

Absorption↗

PubMed2005

A macrokinetic model for dimensioning of biofilters for VOC and odour treatment.

Biofiltration is a cost-effective and environmentally sustainable technology for the treatment of exhaust gases from a variety of sources. Although the process setup is relative simple, many physical, chemical, and microbiological processes are involved. Microkinetic models attempting to cover all of these processes are often more complex than reliable; on the other hand, many macrokinetic approaches have a tendency to oversimplification. In order to develop a simple and accurate protocol to derive biofilter design criteria from experimental trials, a macrokinetic model based on chemical engineering fundamentals was developed. The model covers first-order kinetics as well as kinetics shifting from first-order at low substrate concentrations to zero-order at elevated concentrations and can be applied to single VOCs and odours as measured by olfactometry.

Bioreactors↗

PubMed2005

Odour control at biowaste composting facilities.

There are several options to effectively reduce odorous emissions at composting facilities depending on the type of composting system used. Some of the more relevant measures for open and enclosed composting facilities are presented in this article. Results from different investigations on odour reduction efficiencies of biological waste gas treatment systems at various scales are presented. Biofilter/bioscrubber combinations were used and different biofilter materials were tested. The more relevant odorous substances in the waste gas were identified, and their reduction in the different systems was measured. The biofilter proved to be mainly responsible for efficient odour degradation. The investigations presented in this article revealed that screened compost was very effective, and proved to be a low cost biofilter material for odour degradation purposes. Screened compost showed higher degradation rates than a coke-compost mixture newly developed by the University of Leipzig. Furthermore, it seems that enclosed systems have advantages when compared to conventional open single bed biofilters.

Air Pollution↗

PubMed2005

The potential to reduce emissions of airborne microorganisms by means of biological waste gas treatment systems.

Investigations regarding the reduction of airborne germs in the waste gas of biowaste composting processes have been carried out at the Hamburg University of Science and Technology and the University of Leipzig. Numerous waste gas treatment plants, ranging from laboratory-scale to technical-scale, have been available at the institutes of these two project partners. All plants consisted of bioscrubber/biofilter combinations. The results showed that these biological systems designed for odour control are able to successfully reduce bioaerosol emissions, even though a reduction to background levels could not be achieved. The bioscrubber, if equipped with a droplet separator, proved to be mainly responsible for the reduction, whereas the biofilter acted as a source for microbial emissions originating from the filter material. It could be observed that the microbial population changed while passing the treatment system, indicating the ability of biological waste gas treatment systems to retain potentially pathogenic microorganisms from waste gases.

Air Microbiology↗

PubMed2003

Investigation and optimization of composting processes-test systems and practical examples.

To determine the optimal course of composting it is useful to carry out experiments. The selection of the right experimental set-up depends on the question of concern. Each set-up is useful for a particular application and has its limits. Two test systems of different scales (up to 1500 ml; up to 100 l) are introduced. The purpose and importance of each system design shall be highlighted by application examples: (1). Suitability of a liquid industrial residue as composting accelerator; (2). Determination of the compost maturity; (3). Behaviour of odor-reducing additives during waste collection and composting; (4). Production of tailor-made compost with respect to Nitrogen (5). Suitability of O(2)-enriched air for acceleration of composting. Small-scale respiration experiments are useful to optimize parameters which have to be adjusted during substrate pre-treatment and composting, with the exception of particle size and temperature, and to reduce the number of variants which have to be investigated in greater detail in larger scale experiments. As all regulation possibilities such as aeration, moistening, turning can be simulated with the technical scale set-up, their complex cooperation can be taken into consideration. Encouraging composting variants can be tested, compared and optimized.

Conservation of Natural Resources↗

PubMed2003

Microbial oxidation of methane from old landfills in biofilters.

Landfill gas emissions are among the largest sources of the greenhouse gas methane. For this reason, the possibilities of microbial methane degradation in biofilters were investigated. Different filter materials were tested in two experimental plants, a bench-scale plant (total filter volume 51 l) and a pilot plant (total filter volume 4 m3). Three months after the beginning of the experiment, very high degradation rates of up to 63 g CH4/(m3h) were observed in the bench-scale plant at mean methane concentrations of 2.5% v/v and with fine-grained compost as biofilter material. However, the degradation rates of the compost biofilter decreased in the fifth month of the experiment, probably due to the accumulation of exopolymeric substances formed by the microorganisms. A mixture of compost, peat, and wood fibers showed stable and satisfactory degradation rates around 20 g/(m3h) at mean concentrations of 3% v/v over a period of one year. In this material, the wood fibers served as a structural material and prevented clogging of the biofilter. Extrapolation of the experimental data indicates that biofilters for methane oxidation have to be at least 100 times the volume of biofilters for odor control to obtain the same cleaning efficiency per unit volume flow of feed gas.

Air Pollution↗

PubMed2000

Tracing the transformation of labelled [1-13C]phenanthrene in a soil bioreactor.

[1-(13)C]-labelled phenanthrene was incubated in a closed bioreactor to study the flux and biotransformation of polycyclic aromatic hydrocarbon (PAH) in contaminated soils on a bulk and molecular level. The degradation of extractable phenanthrene was observed by GC-MS measurements and the mineralisation was monitored by (13)CO(2) production. The transformation of the (13)C-label into non-extractable soil-bound residues was determined by carbon isotopic measurements. With these data we were able to calculate a carbon budget of the (13)C-label. Moreover, the chemical structure of non-extractable bound residues was characterised by applying selective chemical degradation reactions to cleave xenobiotic subunits from the macromolecular organic soil matrix. The obtained low molecular weight products yielded (13)C-labelled compounds which were identified using IRM (isotope ratio monitoring)-GC-MS and structurally characterised with GC-MS. Most of the (13)C-labelled products obtained by chemical degradation of non-extractable bound residues are well-known metabolites of phenanthrene. Thus, metabolites of [1-(13)C]phenanthrene formed during biodegradation appear to be reactive components which are subsequently involved in the bound residue formation. Hydrolysable amino acids of the soil residues were significantly labelled with (13)C as confirmed by IRM-GC-MS measurements. Therefore, phenanthrene-derived carbon was transformed by anabolic microbial processes into typical biologically derived compounds. These substances are likely to be incorporated into humic-like material after cell death.

Journal Article↗

PubMed1999

Viscocanalostomy for open-angle glaucoma in black African patients.

PURPOSE: To study the clinical effectiveness of viscocanalostomy in a population of black African patients with open-angle glaucoma that was uncontrolled on medical treatment. SETTING: Department of Ophthalmology, Medical University of Southern Africa, Medunsa, South Africa. METHODS: In this prospective study viscocanalostomy was performed in 214 eyes of 157 black African patients with open-angle glaucoma that was poorly controlled by medical therapy. The procedure involves the production of superficial and deep scleral flaps. The deep flap is disserted to the plane of Schlemm's canal. From this plane, an intact window in Descemet's membrane is created by gentle pressure at the level of Schwalbe's line using a cellulose sponge. Aqueous humor diffuses through this window into a subscleral space (lake). Reflection of the inner flap unroofs Schlemm's canal, creating a trough leading to 2 entrances into Schlemm's canal (surgical ostia). A delicate cannula is introduced into the entrance of Schlemm's canal left and right and high-viscosity sodium hyaluronate is gently injected into the canal for 4 to 6 mm. The deeper scleral flap is excised (deep sclerectomy) and the superficial flap is sutured securely using 5, 11-0 polyester fiber (Mersilene) sutures. High-viscosity sodium hyaluronate is then injected into the subscleral lake to act as a physical barrier to fibrinogen migration postoperatively. RESULTS: Postoperative intraocular pressure (IOP) of 22 mm Hg or less was achieved without medical therapy in 82.7% of eyes. If a beta blocker was added to the cases not achieving 22 mm Hg or less postoperatively, the success rate increased to 89.0%. The average follow-up was 35 months (range 6 to 64 months). CONCLUSION: Viscocanalostomy produced an encouraging long-term reduction in the IOP of black African patients with glaucoma who would otherwise have had a poor prognosis.

Adolescent↗

PubMed1998

Structural changes of the Escherichia coli GroEL-GroES chaperonins upon complex formation in solution: a neutron small angle scattering study.

We applied neutron scattering in conjunction with deuterium (D-) labeling in order to obtain information about the domain structure of GroEL and GroES isolated and in the complex. Each subunit of the heptameric GroES consists of two domains, a core domain (Met1 to Lys15 and Lys34 to Ala97) and an intervening loop region (Glu16 to Ala33). Neutron scattering shows that both regions change their conformation upon GroEL/GroES complex formation. The interdomain angle between the core regions of the heptameric GroES increases from 120 to 140 degrees, leading to a less dome-like shape of GroES, and the loop regions turn inwards by 75 degrees. The 23 C-terminal amino acids of the 14 GroEL subunits (Lys526 to Met548), which are unresolved in the crystal structure, are located either at the bottom of the cavity formed by the seven-membered GroEL ring or at the inner wall of the cavity. Upon complex formation the apical domains of GroEL move outwards, which facilitates binding of GroES at a Gro-EL-GroES center-to-center distance of (87 +/- 8) A. These structural changes may be important for the dissociation of the unfolded protein bound to the central cavity upon GroES binding. The overall structure determined by neutron scattering in solution tallies with the crystallographic model published after completion of this study. Differences in the conformation of GroES observed in the complex by the two methods support the view that the chaperonin complex is a flexible molecule which might switch in solution between different conformations.

Chaperonin 10↗

PubMed1995

Fate of 14C-labeled anthracene and hexadecane in compost-manured soil.

Experiments were carried out to evaluate the impact of the addition of ripe compost on the degradation of two 14C-labeled hydrocarbon model compounds (anthracene and hexadecane) in soil. The addition of mature compost (20% dry wt./dry wt) stimulated significantly the disappearance of the extractable fraction of both compounds. With compost, 23% of the labeled anthracene was transformed into 14CO2 and 42% was fixed to the soil matrix irreversibly. In the unsupplemented control reactor, more than 88% of the original anthracene could be recovered by either of two organic extraction procedures. THe formation of non-extractable bound residues was significantly less with 14C-hexadecane since only 21% of the labeled carbon had become non-extractable after 103 days. The results presented show that compost could stimulate the depletion of hydrocarbons by either mineralization or the formation of unextractable bound residues (humification). The latter process might be a significant route of depletion in soil especially, for those hydrocarbons that are mineralized only slowly. The meaning of this finding for the assessment of soil bioremediation is discussed.

Alkanes↗

PubMed1989

The role of the limbal cornea in vision.

The eagle retina is bifoveal. The temporal fovea, which can resolve targets subtending half a minute or less must depend upon its peripheral cornea for such sharp resolution. Our studies showed the eagle cornea to be thinner, scatter less light and be more spherical than the human cornea. Further experimental studies determined the resolving power of the human peripheral cornea. Using, normal subjects, pinholes placed at the edge 8 mm dilated pupils yielded 20/30 visual acuity and normal contrast sensitivity measurements. Thus it is recommended that optical iridectomy be considered, in appropriate cases of corneal blindness with patches of clear peripheral cornea when no donor corneal material is available.

Animals↗

PubMed1989

The optical quality of the peripheral cornea.

The cornea can be considered to be an organ divided into a central and peripheral zone. Although the central cornea is responsible for producing a sharp retinal image, our experiments suggest that areas of isolated peripheral cornea can produce retinal images compatible to 20/30 visual acuity.

Contrast Sensitivity↗