Biomedical subjects

P N Lens

Publications and source records attributed to P N Lens.

9 recordsLinked to original sources

PubMed2001

Effect of the liquid upflow velocity on thermophilic sulphate reduction in acidifying granular sludge reactors.

The effect of the superficial liquid upflow velocity on the acidifying and sulfate reducing capacity of thermophilic (55 degrees C; pH 6.0) granular sludge bed reactors treating partly acidified wastewater was investigated. A comparison was made between a UASB and an EGSB reactor, operated at an upflow velocity of 1 m.h-1 and 6.8 m.h-1, respectively. Both reactors were inoculated with a mixture of mesophilic sulphidogenic, thermophilic sulphidogenic and thermophilic methanogenic sludge (ratio 2:1:1). They were fed a synthetic wastewater containing starch, sucrose, lactate, propionate and acetate and a low sulphate concentration (COD/SO4(2-) ratio of 10). At the end of the experiment, the sulphate level of the influent was slightly increased to a COD/SO4(2-) ratio of 8. The reactors were operated at a hydraulic retention time of about 5 h and the imposed volumetric organic loading rates (OLR) ranged from 4.9 to 40.0 g COD l-1d-1. When imposing an OLR of 40.0 g COD l-1d-1, the acidification efficiency dropped to 80% and the sulphate reduction efficiency decreased to 50% in the UASB reactor. In the EGSB reactor, the sulphate reduction efficiency dropped to 30% directly following the OLR increase to 40 g COD l-1d-1, but recovered rapidly to 100% (at an OLR of 35 g COD l-1d-1) until the end of the experiment. In the UASB reactor, there was a net acetate and propionate production. At the higher organic loading rates, propionate was converted to n-butyrate and n-valerate. These back reactions did not occur in the EGSB reactor, in which an active methanogenic population developed, leading to a net acetate removal (up to 50%) and a high gas loading rate (up to 8.5 l l-1d-1). In both reactors, the effluent sulphide concentration was always below 200 mg l-1, of which about 90% was present as undissociated H2S (under the given conditions--pH 5.8-6.1 and 55 degrees C). The biogas (including CH4 and CO2) production rates in the UASB were very low, i.e. < 31 biogas l-1 reactor d-1, resulting in negligible amounts (< 20%) of H2S stripped from the reactor liquid. In the EGSB reactor, the biogas production rates reached up to 8.5 l l-1d-1, resulting in H2S stripping efficiencies up to 75%.

Anaerobiosis↗

PubMed2001

Cluster structure of anaerobic aggregates of an expanded granular sludge bed reactor.

The metabolic properties and ultrastructure of mesophilic aggregates from a full-scale expanded granular sludge bed reactor treating brewery wastewater are described. The aggregates had a very high methanogenic activity on acetate (17.19 mmol of CH(4)/g of volatile suspended solids [VSS].day or 1.1 g of CH(4) chemical oxygen demand/g of VSS.day). Fluorescent in situ hybridization using 16S rRNA probes of crushed granules showed that 70 and 30% of the cells belonged to the archaebacterial and eubacterial domains, respectively. The spherical aggregates were black but contained numerous whitish spots on their surfaces. Cross-sectioning these aggregates revealed that the white spots appeared to be white clusters embedded in a black matrix. The white clusters were found to develop simultaneously with the increase in diameter. Energy-dispersed X-ray analysis and back-scattered electron microscopy showed that the whitish clusters contained mainly organic matter and no inorganic calcium precipitates. The white clusters had a higher density than the black matrix, as evidenced by the denser cell arrangement observed by high-magnification electron microscopy and the significantly higher effective diffusion coefficient determined by nuclear magnetic resonance imaging. High-magnification electron microscopy indicated a segregation of acetate-utilizing methanogens (Methanosaeta spp.) in the white clusters from syntrophic species and hydrogenotrophic methanogens (Methanobacterium-like and Methanospirillum-like organisms) in the black matrix. A number of physical and microbial ecology reasons for the observed structure are proposed, including the advantage of segregation for high-rate degradation of syntrophic substrates.

Acetates↗

PubMed2001

Anaerobic treatment for C and S removal in "zero-discharge" paper mills: effects of process design on S removal efficiencies.

Stringent environmental laws in Europe and Northern America lead to the development towards closure of the process water streams in pulp and paper mills. Application of a "zero-discharge" process is already a feasible option for the board and packaging paper industry, provided in-line treatment is applied. Concomitant energy conservation inside the mill results in process water temperatures of 50-60 degrees C. Thermophilic anaerobic treatment complemented with appropriate post-treatment is considered as the most cost-effective solution to meet re-use criteria of the process water and to keep its temperature. In the proposed closed-cycle, the anaerobic treatment step removes the largest fraction of the biodegradable COD and eliminates "S" as H2S from the process stream, without the use of additional chemicals. The anaerobic step is regarded as the only possible location to bleed "S" from the process water cycle. In laboratory experiments, the effect of upward liquid velocity (Vupw) and the specific gas loading rate (Vgas) on the S removal capacity of thermophilic anaerobic bio-reactors was investigated. Acidifying, sulphate reducing sludge bed reactors were fed with partly acidified synthetic paper mill wastewater and were operated at 55 degrees C and pH 6. The reactors were operated at organic loading rates up to 50 g COD.l-1.day-1 at COD/SO4(2-) ratios of 10. The effect of Vupw was researched by comparing the performance of a UASB reactor operated at 1.0 m.h-1 and an EGSB reactor, operated at 6.8 m.h-1. The Vupw had a strong effect on the fermentation patterns. In the UASB reactor, acidification yielded H2, acetate and propionate, leading to an accumulation of reducing equivalents. These were partly disposed of by the production of n-butyrate and n-valerate from propionate. In the EGSB reactor net acetate consumption was observed as well as high volumetric gas (CO2 and CH4) production rates. The higher gas production rates in the EGSB reactor resulted in higher S-stripping efficiencies. The effect of Vgas was further researched by comparing 2 UASB reactors which were sparged with N2 gas at a specific gas loading rate of 30 m3.m-2.day-1. In contrast to the regular UASB reactors, the gas-supplied UASB showed a more stable performance when the organic loading rates were increased. Also, the H2S stripping efficiency was 3-4 times higher in the gas-supplied UASB, reaching values of 67%. Higher values were not obtained owing to the relatively poor sulphate reduction efficiencies.

Bacteria, Anaerobic↗

PubMed2001

The biological sulfur cycle: novel opportunities for environmental biotechnology.

Although the study of sulfur cycle bacteria was already started around the 1890s by the famous microbiologists Winogradsky and Beijerinck, there are nowadays still many new discoveries to be made about the metabolic properties, phylogenetic position and ecological behaviour of bacteria that play a role in the biological sulfur cycle. The current interest of the scientific community in the biological sulfur cycle is very high, especially because of the many special organisms that have recently been discovered in the deep sea and other environments characterised by extreme conditions (such as high salt, low/high pH or temperature) and also in bioreactor environments. This paper highlights some of these new discoveries and relates them to environmental biotechnology. It is concluded that the micro-organisms from the sulfur cycle offer unique opportunities for sulfur pollution abatement and sulfur recovery.

Bacteria↗

PubMed2001

New developments in reactor and process technology for sulfate reduction.

Sulfate reduction has been regarded in the past as an unwanted process in anaerobic treatment of sulfate-rich wastewaters. Research efforts were primarily focused on H2S toxicity, competition between sulfidogenic and methanogenic microorganisms and suppression of sulfidogenesis. More recently, the potential sulfidogenesis for treating a wide range of wastestreams contaminated with oxidized sulfurous compounds and/or heavy metals was also appreciated. Heavy metals can be removed by the formation and subsequent precipitation of poorly soluble metal sulfides. Basically two approaches can be distinguished in wastewater treatment: passive treatment using low-cost technologies and active treatment in newly developed bioreactors. Both strategies are discussed.

Bioreactors↗

PubMed1998

Anaerobic treatment of sulphate-rich wastewaters.

Until recently, biological treatment of sulphate-rich wastewater was rather unpopular because of the production of H2S under anaerobic conditions. Gaseous and dissolved sulphides cause physical-chemical (corrosion, odour, increased effluent chemical oxygen demand) or biological (toxicity) constraints, which may lead to process failure. Anaerobic treatment of sulphate-rich wastewater can nevertheless be applied successfully provided a proper treatment strategy is selected. The strategies currently available are discussed in relation to the aim of the treatment: i) removal of organic matter, ii) removal of sulphate or iii) removal of both. Also a whole spectrum of new biotechnological applications (removal of organic chemical oxygen demand, sulphur, nitrogen and heavy metals), recently developed based on a better insight in sulphur transformations, are discussed.

Bacteria, Anaerobic↗

PubMed1998

Nuclear magnetic resonance in environmental engineering: principles and applications.

This paper gives an introduction to nuclear magnetic resonance spectroscopy (NMR) and magnetic resonance imaging (MRI) in relation to applications in the field of environmental science and engineering. The underlying principles of high resolution solution and solid state NMR, relaxation time measurements and imaging are presented. Then, the use of NMR is illustrated and reviewed in studies of biodegradation and biotransformation of soluble and solid organic matter, removal of nutrients and xenobiotics, fate of heavy metal ions, and transport processes in bioreactor systems.

Biodegradation, Environmental↗

PubMed1998

13C-NMR study of propionate metabolism by sludges from bioreactors treating sulfate and sulfide rich wastewater.

Applications of nuclear magnetic resonance (NMR) to study a variety of physiological and biochemical aspects of bacteria with a role in the sulfur cycle are reviewed. Then, a case-study of high resolution 13C-NMR spectroscopy on sludges from bioreactors used for treating sulfate and sulfide rich wastewaters is presented. 13C-NMR was used to study the effect of sulfate and butyrate on propionate conversion by mesophilic anaerobic (methanogenic and sulfate reducing) granular sludge and microaerobic (sulfide oxidizing) flocculant sludge. In the presence of sulfate, propionate was degraded via the randomising pathway in all sludge types investigated. This was evidenced by scrambling of [3-13C]propionate into [2-13C]propionate and the formation of acetate equally labeled in the C1 and C2 position. In the absence of sulfate, [3-13C]propionate scrambled to a lesser extend without being degraded further. Anaerobic sludges converted [2,3-13C]propionate partly into the higher fatty acid 2-methyl[2,3-13C]butyrate during the simultaneous degradation of [2,3-13C]propionate and butyrate. [4,5-13C]valerate was also formed in the methanogenic sludges. Up to 10% of the propionate present was converted via these alternative degradation routes. Labeled butyrate was not detected in the incubations, suggesting that reductive carboxylation of propionate does not occur in the sludges.

Biodegradation, Environmental↗

PubMed1993

Heterogeneous Distribution of Microbial Activity in Methanogenic Aggregates: pH and Glucose Microprofiles.

Methanogenic aggregates, harvested from an upflow anaerobic sludge blanket reactor treating potato starch wastewater, were acclimatized to either glucose or a mixture of sugars and organic nitrogen compounds (i.e., diluted molasses). Both types of granules exhibited internal pH and substrate concentration gradients in mineral medium (pH 7.0, 30 degrees C) as was measured with microelectrodes. Glucose-acclimatized granules suspended in a mineral medium lacking glucose exhibited a distinct internal pH decrease of about 1 U within the granule, suggesting strong metabolism by the acidogenic bacteria. Molasses-acclimatized and aged granules suspended in mineral medium did not exhibit such a pH decrease, suggesting the importance of the metabolic state of these acidogens. The pH gradient did not occur in deactivated granules and was not observable in strongly buffered media (mineral medium containing 33 mM phosphate or reactor liquid). When glucose (0.5 to 5.0 mM) was added to the mineral medium, granules exhibited a convex pH profile. Glucose consumption was located exclusively in the outer 200 to 300 mum of the aggregates (mean diameter = 1.5 mm). The addition of 20 mM 2-bromoethanesulfonic acid to the mineral medium indicated that the higher pH levels in the centre of the granule appeared to be related to the activity of methanogens. It is suggested that acidogenic activity occurs predominantly in the outer 200 to 300 mum of the aggregate and methanogenic activity occurs predominantly in the center of the investigated granules.

Journal Article↗