Search PubMed⌕ Search

Biomedical subjects

T A Larsen

Publications and source records attributed to T A Larsen.

At least 19 recordsLinked to original sources
PubMed2006

Treatment processes for source-separated urine.

The separate collection and treatment of urine has attracted considerable attention in the engineering community in the last few years and is seen as a viable option for enhancing the flexibility of wastewater treatment systems. This comprehensive review focuses on the status of current urine treatment processes and summarises the properties of collected urine. We distinguish between seven main purposes of urine-treatment processes: hygienisation (storage), volume reduction (evaporation, freeze-thaw, reverse osmosis), stabilisation (acidification, nitrification), P-recovery (struvite formation), N-recovery (ion-exchange, ammonia stripping, isobutylaldehyde-diurea (IBDU) precipitation), nutrient removal (anammox) and handling of micropollutants (electrodialysis, nanofiltration, ozonation). The review shows clearly that a wide range of technical options is available to treat collected urine effectively, but that none of these single options can accomplish all seven purposes. Depending on the overall goal of the treatment process, a specific technical solution or a combination of solutions can be found to meet the requirements. Such combinations are not discussed in this paper unless they are explicitly presented in the literature. Except for 'evaporation' and 'storage', none of the processes described have so far advanced beyond the laboratory stage. Considerable development work remains to be done to optimise urine-processing techniques in order to create marketable products.

Environmental Restoration and Remediation↗
PubMed2003

From waste treatment to integrated resource management.

Wastewater treatment was primarily implemented to enhance urban hygiene. Treatment methods were improved to ensure environmental protection by nutrient removal processes. In this way, energy is consumed and resources like potentially useful minerals and drinking water are disposed of. An integrated management of assets, including drinking water, surface water, energy and nutrients would be required to make wastewater management more sustainable. Exergy analysis provides a good method to quantify different resources, e.g. utilisable energy and nutrients. Dilution is never a solution for pollution. Waste streams should best be managed to prevent dilution of resources. Wastewater and sanitation are not intrinsically linked. Source separation technology seems to be the most promising concept to realise a major breakthrough in wastewater treatment. Research on unit processes, such as struvite recovery and treatment of ammonium rich streams, also shows promising results. In many cases, nutrient removal and recovery can be combined, with possibilities for a gradual change from one system to another.

Conservation of Energy Resources↗
PubMed2003

Nutrients in urine: energetic aspects of removal and recovery.

The analysis of different removal and recovery techniques for nutrients in urine shows that in many cases recovery is energetically more efficient than removal and new-production from natural resources. Considering only the running electricity and fossil energy requirements for the traditional way of wastewater treatment and fertiliser production, the following specific energy requirements can be calculated: 45 MJ kg(-1)N for denitrification in a WWTP, 49 MJ kg(-1)p for P-precipitation in a WWTP, 45 MJ kg(-1)N for N-fertiliser and 29 MJ kg(-1)p for P-fertiliser production. These numbers are higher than the values derived for thermal volume reduction of urine (35 MJ kg(-1)N for eliminating 90% water) or production of struvite (102 MJ kg(-1)N, including 2.2 kg P). Considering only the electricity and fossil energy for the traditional way of wastewater treatment and fertiliser production, the energy value of 1 PE urine is 0.87 MJ PE(-1) d(-1) (fertiliser value: 0.44, wastewater treatment: 0.43 MJ PE(-1) d(-1)). A more detailed life cycle assessment (LCA) of the entire urine collection system, including the required materials and the environmental burden, support the energy analysis. The LCA compares conventional denitrification in a wastewater treatment plant with collecting urine in households, reducing the volume by evaporation and using it as a multi-nutrient fertiliser. The primary energy consumption for recovery and reuse of urine, including the nutrients N, P and K, is calculated with 65 MJ kg(-1)N, compared with 153 MJ kg(-1)N derived for the conventional 'recycling over the atmosphere'.

Chemical Precipitation↗
PubMed2003

How farmers in Switzerland perceive fertilizers from recycled anthropogenic nutrients (urine).

We studied acceptance of a urine-based fertilizer product using a mail survey of 467 Swiss farmers. We distinguished among four production types: organic or IP farming, and with or without vegetable production. Considering that the idea of urine-based fertilizers is new, acceptance among the answering farmers was surprisingly high, with 57% explicitly stating that they thought it was a good or very good idea, and 42% willing to purchase such a product. The farmers of different production types did not differ strongly in their attitude towards urine-based fertilizers. Especially IP and vegetable farmers, who purchased additional fertilizers anyway, seem willing to accept urine-based fertilizers, hereby preferring a grainy, odorless ammonium nitrate fertilizer. Absolutely essential is a hazard-free product: 30% of all farmers had concerns regarding micropollutants. Based on fertilizer data, we demonstrate an existing demand for the nutrients N, P, and K in Switzerland, which could be partially substituted by a recycled urine product. Finally, we discuss methodological requirements of social science surveys. To obtain representative data on an entire population in a mail survey, multiple contacts with respondents are necessary. We argue that information and participation of stakeholders at an early stage is essential for successful technology transfer.

Adult↗
PubMed2003

Investigating consumer attitudes towards the new technology of urine separation.

The technology of urine separation and the recycling of anthropogenic nutrients as fertilizer in agriculture are considered as major innovations to improve the sustainability of today's urban wastewater management. The acceptance of consumers will be key for the introduction of the new technology. Citizens will have to make important decisions in their role as tenants and owners of houses and as consumers buying products fertilized with urine. Consumer attitudes towards the new technology were explored in a number of citizen focus groups in Switzerland. Focus groups are deliberate, moderated group discussions with informed citizens on a certain topic. The information was provided by a computer based information system specifically designed for this purpose. The acceptance of individual citizens for the new technology proved to be quite high. The majority of the citizens expressed their willingness to move into an apartment with NoMix toilets and to buy food fertilized with urine. However, they were not willing to accept additional financial costs or efforts. Arguments related to long-term sustainability (closing nutrient cycles) were of less importance than arguments that relate directly to the effects of micropollutants on human and ecosystem health. For the introduction of the new technology on a wide scale it will thus be crucial to explore the fate and effects of micropollutants.

Agriculture↗
PubMed2003

Nitrification and autotrophic denitrification of source-separated urine.

In laboratory experiments, source-separated urine was stabilised with nitrification and denitrified via nitritation and anaerobic ammonium oxidation. The highest total ammonia concentration in the influent was 7,300 gN/m3, the maximum pH 9.2. In a moving bed biofilm reactor (MBBR) with Kaldnes biofilm carriers, we stabilised urine as a 1:1 ammonium nitrate solution. The maximum nitrification rate was 380 gN/m3/d corresponding to 1.7 gN/m2(biofilm)/d. Nitrite ammonium solutions were produced in a continuous flow stirred tank reactor (CSTR) with 4.8 days sludge retention time (SRT) at 30 degrees C and in a sequencing batch reactor (SBR) with more than 30 days SRT. Nitrate build-up was negligible in both reactors. Nitritation rates were 780 gN/m3/d in the CSTR and 280 gN/m3/d in the SBR, respectively. However, shortening the cycles would increase nitritation in the SBR. High concentrations of nitrous acid, salts, and presumably hydroxylamine suppressed nitrite oxidation in the nitritation reactors. In all three nitrification reactors, maximally 50% of the influent total ammonia was oxidised without pH control. None of the common inhibition or limitation approaches could explain why ammonia oxidation always stopped at pH values around 6. In a batch experiment, we showed that source-separated urine can be denitrified autotrophically by anammox bacteria.

Ammonia↗
PubMed2001

Waste design and source control lead to flexibility in wastewater management.

The concepts of waste design and source control are introduced as contracts between wastewater handling agencies and consumers and consumers and industry respectively. Waste design serves to produce waste streams that are optimized in composition and time sequence for easy transport and treatment. Source control makes services and installations available, which allow the consumer to adhere to the specification of waste design. Increased delegation of responsibility to the consumer is expected to result in more flexible wastewater handling systems.

Community Participation↗
PubMed2001

Interaction analysis of stakeholders in water supply systems.

An analysis of the characteristic goals, strategies and rules of behavior of relevant stakeholders allows the efficacy and potential risks of past and current engineering and management concepts to be estimated. The study is driven by the observable shift from security to cost-centered strategies by water utilities and the difficulties of balancing technical and financial needs in an uncertain future. Its benefits include a methodology with a twofold result. With the aid of domain knowledge from experts involved in a participatory process, the interactions of a subset of stakeholders are quantified and documented in a rule catalog. This leads to an improved understanding of their decision-making rules. An agent-based model comprising these stakeholders' rules of behavior in subsequently development. Once the model is validated with data sets from a real utility, multiple-scenario testing helps to explore different strategies and can be used to generate ideas for developing flexible management and design schemes. Despite the complexity of the system described, simple model rules which are repeated annually can replicate the general development of both capacity and cost-related parameters. Scenario simulations show the effects of different management strategies on key parameters such as capacity, water price and financial debt.

Cities↗
PubMed1998

Morphology of protein-protein interfaces.

BACKGROUND: Most soluble proteins are active as low-number oligomers. Statistical surveys of oligomeric proteins have defined the roles of hydrophobicity and complementarity in the stability of protein interfaces, but tend to average structural features over a diverse set of protein-protein interfaces, blurring information on how individual interfaces are stabilized. RESULTS: We report a visual survey of 136 homodimeric proteins from the Brookhaven Protein Data Bank, with images that highlight the major structural features of each protein-protein interaction surface. Nearly all of these proteins have interfaces formed between two globular subunits. Surprisingly, the pattern of hydrophilicity over the surface of these interfaces is quite variable. Approximately one-third of the interfaces show a recognizable hydrophobic core, with a single large, contiguous, hydrophobic patch surrounded by a ring of intersubunit polar interactions. The remaining two-thirds of the proteins show a varied mixture of small hydrophobic patches, polar interactions and water molecules scattered over the entire interfacial area. Ten proteins in the survey have intertwined interfaces formed by extensive interdigitation of the two subunit chains. These interfaces are very hydrophobic and are associated with proteins that require both stability and internal symmetry. CONCLUSIONS: The archetypal protein interface, with a defined hydrophobic core, is present in only a minority of the surveyed homodimeric proteins. Most homodimeric proteins are stabilized by a combination of small hydrophobic patches, polar interactions and a considerable number of bridging water molecules. The presence or absence of a hydrophobic core within these interfaces does not correlate with specific protein functions.

Adenylosuccinate Synthase↗
PubMed1996

Overexpression of Bacillus subtilis phosphoribosylpyrophosphate synthetase and crystallization and preliminary X-ray characterization of the free enzyme and its substrate-effector complexes.

Bacillus subtilis phosphoribosylpyrophosphate (PRPP) synthetase has been expressed to high levels in an Escherichia coli host strain devoid of endogenous PRPP synthetase. A rapid and efficient purification protocol has been developed allowing production of enzyme preparations with purity conforming to the stringent criteria required for crystallization. Crystallization experiments, in combination with dynamic light scattering studies, have led to the production of three crystal forms of the enzyme. These forms include the free enzyme, the enzyme in a binary complex with the substrate adenosine triphosphate (ATP), and the enzyme in a quaternary complex with the substrate analog alpha, beta-methylene adenosine triphosphate (mATP), the substrate ribose-5-phosphate (Rib-5-P), and the allosteric inhibitor adenosine diphosphate (ADP). Diffraction data showed that all three crystal forms are suitable for structure determination. They crystallize in the same hexagonal space group, P6(3), with virtually identical unit cell dimensions of a = b = 115.6 angstroms, c = 107.8 angstrom, and with two molecules in the asymmetric unit. The self-rotation function showed the existence of a non-crystallographic twofold axis perpendicular to the c axis. The availability of the different complexes should allow questions regarding the molecular mechanisms of catalysis and allostery in PRPP synthetase to be addressed.

Adenosine Triphosphate↗
PubMed1995

1994 Molecular Graphics Art Show and Video Show.

The 1994 Molecular Graphics Art Show and Video Show were presented at the 13th annual international meeting of the Molecular Graphics and Modelling Society. The art show--shown in the Mary & Leigh Block Gallery on the campus of Northwestern University, Evanston, Illinois--included original artworks by eighteen artists and the video show included nine original animated works. All were chosen for their ability to present the complexity, diversity, and beauty of the molecular world in visual form. Works from a wide range of disciplines were represented, including work by scientists actively involved in structural research, by commercial illustrators presenting these results to students and physicians, and by fine artists exploring the meanings and implications of these molecules in our lives. Included in this issue of the Journal of Molecular Graphics are comments by the juror of the show, T.J. O'Donnell, a catalogue of the art show, and a catalogue of the video show.

Art↗
PubMed1995

Limited toxicity of prolonged therapy with high doses of amphotericin B lipid complex.

We describe six patients with invasive fungal infections who received large cumulative doses (22.3-73.6 g) of amphotericin B lipid complex (ABLC) over 21-121 weeks. The drug was well tolerated at these very large doses, and there was limited toxicity. Collectively, these patients received ABLC therapy for a mean of 53.8 weeks (range, 21-121 weeks). The mean serum creatinine level at the start of ABLC therapy was 1 mg/dL (range, 0.4-1.9 mg/dL), and at the end of therapy this level was 1.5 mg/dL (range, 1.0-2.0 mg/dL). Over the course of therapy, only two patients had serum creatinine levels of > or = 2 mg/dL, with transient peak serum creatinine levels of 3.5 and 2.8 mg/dL, respectively. Several patients required replacement therapy with oral or intravenous potassium. None of the patients had ABLC-associated toxic effects necessitating discontinuation of the treatment. ABLC may be given in substantially larger doses than conventional amphotericin B, and very high doses of ABLC that are administered over several months appear to be relatively less toxic than those of conventional amphotericin B.

Adolescent↗
PubMed1995

Self-organizing map in recognition of topographic patterns of EEG spectra.

The self-organizing map, a neural network algorithm, was applied to the recognition of topographic patterns in clinical 22-channel EEG. Inputs to the map were extracted from short-time power spectra of all channels. Each location on a self-organized map entails a model for a cluster of similar input patterns; the best-matching model determines the location of a sample on the map. Thus, an instantaneous topographic EEG pattern corresponds to the location of the sample, and changes with time correspond to the trajectories of consecutive samples. EEG segments of "alpha," "alpha attenuation," "theta of drowsiness," "eye movements," "EMG artifact," and "electrode artifacts" were selected and labeled by visual inspection of the original records. The map locations of the labeled segments were different; the map thus distinguished between them. The locations of individual EEG's on the "alpha-area" of the map were also different. The clustering and easily understandable visualization of topographic EEG patterns are obtainable on a self-organized map in real time.

Adolescent↗
PubMed1991

[Prevalence of stroke. A study from 5 municipalities in Troms].

Age-specific prevalence of stroke in a population above 15 years was examined in five municipalities in Northern Norway. The examined population included 16,115 individuals of a total population of 19,850. The WHO-definition of stroke was applied. Average prevalence of stroke in the populations 15 years and over was 18.4 per 1,000. Males debutated five years earlier than females. 79% of stroke patients lived at home and 21% in nursing homes and hospitals.

Adult↗
PubMed1991

Crystal structure analysis of the B-DNA dodecamer CGTGAATTCACG.

The crystal structure of the DNA dodecamer C-G-T-G-A-A-T-T-C-A-C-G has been determined at a resolution of 2.5 A, with a final R factor of 15.8% for 1475 nonzero reflections measured at 0 degrees C. The structure is isomorphous with that of the Drew dodecamer, with the space group P2(1)2(1)2(1) and cell dimensions of a = 24.94 A, b = 40.78 A, and c = 66.13 A. The asymmetric unit contains all 12 base pairs of the B-DNA double helix and 36 water molecules. The structure of C-G-T-G-A-A-T-T-C-A-C-G is very similar to that of C-G-C-G-A-A-T-T-C-G-C-G, with no major alterations in helix parameters. Water peaks in the refined structure appear to represent a selection of peaks that were observed in the Drew dodecamer. The minor-groove spine of hydration at 2.5 A is fragmentary, but as Narendra et al. (1991) [Biochemistry (following paper in this issue)] have observed, lowering the temperature leads to a more complete representation of the spine.

Base Sequence↗
PubMed1989

The structure of DAPI bound to DNA.

The structure of the DNA fluorochrome 4'-6-diamidine-2-phenyl indole (DAPI) bound to the synthetic B-DNA oligonucleotide C-G-C-G-A-A-T-T-C-G-C-G has been solved by single crystal x-ray diffraction methods, at a resolution of 2.4 A. The structure is nearly isomorphous with that of the native DNA molecule alone. With one DAPI and 25 waters per DNA double helix, the residual error is 21.5% for the 2428 reflections above the 2-sigma level. DAPI inserts itself edgewise into the narrow minor groove, displacing the ordered spine of hydration. DAPI and a single water molecule together span the four AT base pairs at the center of the duplex. The indole nitrogen forms a bifurcated hydrogen bond with the thymine O2 atoms of the two central base pairs, as with netropsin and Hoechst 33258. The preference of all three of these drugs for AT regions of B-DNA is a consequence of three factors: (1) The intrinsically narrower minor groove in AT regions than in GC regions of B-DNA, leading to a snug fit of the flat aromatic drug rings between the walls of the groove. (2) The more negative electrostatic potential within the minor groove in AT regions, attributable in part to the absence of electropositive-NH2 groups along the floor of the groove, and (3) The steric advantage of the absence of those same guanine-NH2 groups, thus permitting the drug molecule to sink deeper into the groove. Groove width and electrostatic factors are regional, and define the relative receptiveness of a section of DNA since they operate over several contiguous base pairs. The steric factor is local, varying from one base pair to the next, and hence is the means of fine-tuning sequence specificity.

Base Sequence↗