Filterable Fraction Research Articles

Utilization of low-molecular-weight organic compounds by the filterable fraction of a lotic microbiome.

ABSTRACTFilterable microorganisms participate in dissolved organic carbon (DOC) cycling in freshwater systems, however their exact functional role remains unknown. We determined the taxonomic identity and community dynamics of prokaryotic microbiomes in the 0.22 µm-filtered fraction and unfiltered freshwater from the Conwy River (North Wales, UK) in microcosms and, using targeted metabolomics and 14C-labelling, examined their role in the utilization of amino acids, organic acids and sugars spiked at environmentally-relevant (nanomolar) concentrations. To identify changes in community structure, we used 16S rRNA amplicon and shotgun sequencing. Unlike the unfiltered water samples where the consumption of DOC was rapid, the filtered fraction showed a 3-day lag phase before the consumption started. Analysis of functional categories of clusters of orthologous groups of proteins (COGs) showed that COGs associated with energy production increased in number in both fractions with substrate addition. The filtered fraction utilized low-molecular-weight (LMW) DOC at much slower rates than the whole community. Addition of nanomolar concentrations of LMW DOC did not measurably influence the composition of the microbial community nor the rate of consumption across all substrate types in either fraction. We conclude that due to their low activity, filterable microorganisms play a minor role in LMW DOC processing within a short residence time of lotic freshwater systems.

Cell Plasticity and Genomic Structure of a Novel Filterable Rhizobiales Bacterium that Belongs to a Widely Distributed Lineage.

Rhizobiales bacterium strain IZ6 is a novel filterable bacterium that was isolated from a suspension filtrate (<0.22 µm) of soil collected in Shimane Prefecture, western Japan. Additional closely related isolates were recovered from filterable fractions of terrestrial environmental samples collected from other places in Japan; the Gobi Desert, north-central China; and Svalbard, Arctic Norway. These findings indicate a wide distribution of this lineage. This study reports the cell variation and genomic structure of IZ6. When cultured at lower temperatures (4 °C and 15 °C), this strain contained ultra-small cells and cell-like particles in the filtrate. PacBio sequencing revealed that this chromosome (3,114,641 bp) contained 3150 protein-coding, 51 tRNA, and three rRNA genes. IZ6 showed low 16S rRNA gene sequence identity (<97%) and low average nucleotide identity (<76%) with its closest known relative, Flaviflagellibacter deserti. Unlike the methylotrophic bacteria and nitrogen-fixing bacteria in related genera, there were no genes that encoded enzymes for one-carbon-compound utilization and nitrogen fixation in the IZ6 genome; the genes related to nitrate and nitrite reductase are retained and those related to the cell membrane function tend to be slightly enriched in the genome. This genomic information helps elucidate the eco-physiological function of a phenotypically heterogeneous and diverse Rhizobiales group.

Archaea dominate the microbial community in an ecosystem with low-to-moderate temperature and extreme acidity

BackgroundThe current view suggests that in low-temperature acidic environments, archaea are significantly less abundant than bacteria. Thus, this study of the microbiome of Parys Mountain (Anglesey, UK) sheds light on the generality of this current assumption. Parys Mountain is a historically important copper mine and its acid mine drainage (AMD) water streams are characterised by constant moderate temperatures (8–18 °C), extremely low pH (1.7) and high concentrations of soluble iron and other metal cations.ResultsMetagenomic and SSU rRNA amplicon sequencing of DNA from Parys Mountain revealed a significant proportion of archaea affiliated with Euryarchaeota, which accounted for ca. 67% of the community. Within this phylum, potentially new clades of Thermoplasmata were overrepresented (58%), with the most predominant group being “E-plasma”, alongside low-abundant Cuniculiplasmataceae, ‘Ca. Micrarchaeota’ and ‘Terrestrial Miscellaneous Euryarchaeal Group’ (TMEG) archaea, which were phylogenetically close to Methanomassilicoccales and clustered with counterparts from acidic/moderately acidic settings. In the sediment, archaea and Thermoplasmata contributed the highest numbers in V3-V4 amplicon reads, in contrast with the water body community, where Proteobacteria, Nitrospirae, Acidobacteria and Actinobacteria outnumbered archaea. Cultivation efforts revealed the abundance of archaeal sequences closely related to Cuniculiplasma divulgatum in an enrichment culture established from the filterable fraction of the water sample. Enrichment cultures with unfiltered samples showed the presence of Ferrimicrobium acidiphilum, C. divulgatum, ‘Ca. Mancarchaeum acidiphilum Mia14’, ‘Ca. Micrarchaeota’-related and diverse minor (< 2%) bacterial metagenomic reads.ConclusionContrary to expectation, our study showed a high abundance of archaea in this extremely acidic mine-impacted environment. Further, archaeal populations were dominated by one particular group, suggesting that they are functionally important. The prevalence of archaea over bacteria in these microbiomes and their spatial distribution patterns represents a novel and important advance in our understanding of acidophile ecology. We also demonstrated a procedure for the specific enrichment of cell wall-deficient members of the archaeal component of this community, although the large fraction of archaeal taxa remained unculturable. Lastly, we identified a separate clustering of globally occurring acidophilic members of TMEG that collectively belong to a distinct order within Thermoplasmata with yet unclear functional roles in the ecosystem.

Microbial diversity and metabolic networks in acid mine drainage habitats.

Acid mine drainage (AMD) emplacements are low-complexity natural systems. Low-pH conditions appear to be the main factor underlying the limited diversity of the microbial populations thriving in these environments, although temperature, ionic composition, total organic carbon, and dissolved oxygen are also considered to significantly influence their microbial life. This natural reduction in diversity driven by extreme conditions was reflected in several studies on the microbial populations inhabiting the various micro-environments present in such ecosystems. Early studies based on the physiology of the autochthonous microbiota and the growing success of omics-based methodologies have enabled a better understanding of microbial ecology and function in low-pH mine outflows; however, complementary omics-derived data should be included to completely describe their microbial ecology. Furthermore, recent updates on the distribution of eukaryotes and archaea recovered through sterile filtering (herein referred to as filterable fraction) in these environments demand their inclusion in the microbial characterization of AMD systems. In this review, we present a complete overview of the bacterial, archaeal (including filterable fraction), and eukaryotic diversity in these ecosystems, and include a thorough depiction of the metabolism and element cycling in AMD habitats. We also review different metabolic network structures at the organismal level, which is necessary to disentangle the role of each member of the AMD communities described thus far.

Ensiling Characteristics and the In situ Nutrient Degradability of a By-product Feed-based Silage.

This study was conducted to evaluate the ensiling characteristics and the in situ degradability of a by-product feed (BF)-based silage. Before ensilation, the BF-based mixture was composed of 50% spent mushroom substrate, 21% recycled poultry bedding, 15% ryegrass straw, 10.8% rice bran, 2% molasses, 0.6% bentonite, and 0.6% microbial inoculant on a wet basis and ensiled for up to 4 weeks. The BF-based silage contained on average 39.3% moisture, 13.4% crude protein (CP), and 52.2% neutral detergent fiber (NDF), 49% total digestible nutrient, and 37.8% physically effective NDF1.18 on a dry matter (DM) basis. Ensiling the BF-based silage for up to 4 weeks affected (p<0.01) the chemical composition to a small extent, increased (p<0.05) the lactic acid and NH3-N content, and decreased (p<0.05) both the total bacterial and lactic acid bacterial counts from 109 to 108 cfu/g when compared to that before ensiling. These parameters indicated that the silage was fermented and stored well during the 4-week ensiling period. Compared with rice or ryegrass straws, the BF-based silage had a higher (p<0.05) water-soluble and filterable fraction, a lower insoluble degradable DM and CP fraction (p<0.05), a lower digestible NDF (p<0.05) fraction, a higher (p<0.05) DM and CP disappearance and degradability rate, and a lower (p<0.05) NDF disappearance and degradability rate. These results indicated that cheap, good-quality BF-based roughage could be produced by ensiling SMS, RPB, rice bran, and a minimal amount of straw.

Prokaryotic ultramicroforms in a Sphagnum peat bog of upper Volga catchment

The waters of small lakes located in swampy catchment areas of upper Volga contain considerable amounts of ultrasmall microbial cells that pass through 0.22-μm-pore-size filters. As shown in our previous study [1], most of these cells represent the bacterial genera Herbaspirillum, Herminiimonas, Curvibacter, and Burkholderia of the class Betaproteobacteria, as well as euryarchaea of the uncharacterized clade LDS. The aim of the present study was to investigate the possible effect of the waters draining swampy areas on the composition of the filterable microbial fraction in lakes fed by swampy catchments. To address this question molecular identification was performed of prokaryotic ultramicroforms in the peat of the ombrotrophic Sphagnum bog Obukhovskoe, located, like the lakes studied previously [1], in the Mologa-Sheksna catchment area. The number of filterable microorganisms in 1 g wet peat was 3.8 × 106 cells, or 0.5% of total microbial cell number in the peat. From the DNA of the filterable cell fraction, 100 clones of bacterial and 77 clones of archaeal 16S rRNA genes were obtained. The bacterial clone library contained 16S rRNA gene sequences representing the classes Beta- and Gammaproteobacteria (the genera Janthinobacterium and Pseudomonas, respectively) and the phylum Bacteroidetes (the genera Chryseobacterium and Epilithonimonas) and differed significantly from the clone library of bacterial ultramicroforms of lake water. By contrast, the pools of filterable archaea in bogs and lakes were essentially similar. They were represented by the euryarchaeal clade LDS and methanogens of the orders Methanobacteriales and Methanosarcinales. Additionally, the pool of filterable archaea of the bog included methanogens of the order Methanomicrobiales and representatives of the uncharacterized euryarchaeal clade RC-V (Rice Cluster V) and of the phylum Thaumarchaeota.

A comparative molecular analysis of water‐filled limestone sinkholes in north‐eastern Mexico

Sistema Zacatón in north-eastern Mexico is host to several deep, water-filled, anoxic, karstic sinkholes (cenotes). These cenotes were explored, mapped, and geochemically and microbiologically sampled by the autonomous underwater vehicle deep phreatic thermal explorer (DEPTHX). The community structure of the filterable fraction of the water column and extensive microbial mats that coat the cenote walls was investigated by comparative analysis of small-subunit (SSU) 16S rRNA gene sequences. Full-length Sanger gene sequence analysis revealed novel microbial diversity that included three putative bacterial candidate phyla and three additional groups that showed high intra-clade distance with poorly characterized bacterial candidate phyla. Limited functional gene sequence analysis in these anoxic environments identified genes associated with methanogenesis, sulfate reduction and anaerobic ammonium oxidation. A directed, barcoded amplicon, multiplex pyrosequencing approach was employed to compare ∼100,000 bacterial SSU gene sequences from water column and wall microbial mat samples from five cenotes in Sistema Zacatón. A new, high-resolution sequence distribution profile (SDP) method identified changes in specific phylogenetic types (phylotypes) in microbial mats at varied depths; Mantel tests showed a correlation of the genetic distances between mat communities in two cenotes and the geographic location of each cenote. Community structure profiles from the water column of three neighbouring cenotes showed distinct variation; statistically significant differences in the concentration of geochemical constituents suggest that the variation observed in microbial communities between neighbouring cenotes are due to geochemical variation.

Effect of biopolymer clusters on the fouling property of sludge from a membrane bioreactor (MBR) and its control by ozonation

Organic substances in the liquid phase of the sludge in a membrane bioreactor (MBR) have a profound impact on membrane fouling. In this study, a single-fibre microfiltration apparatus was developed to investigate the fouling propensity of MBR sludge and the effectiveness of ozonation in membrane fouling mitigation. The results show that biopolymer clusters (BPC) in the MBR suspension had a significant influence on the fouling potential of the sludge. An increase in BPC concentration by 20% and 60% from around 3.5 mg/l in the mixed sludge liquor drastically increased the fouling rate by 120% and 300%, respectively. Ozonation of the BPC solution greatly reduced the detrimental role of BPC in membrane fouling. An ozone dose of 0.03 mg/mg TOC of BPC could reduce the mean BPC size from 38 to 27 μm, which was further reduced to 12 μm at 0.3 mg O 3/mg TOC of BPC. In addition to BPC destruction, ozonation apparently also modified the surface properties of BPC, resulting in an increase in the filterable fraction and a decrease in the liquid viscosity. Based on the experimental findings, an approach for MBR membrane fouling control is proposed that applies ozonation to the supernatant containing BPC in a side-stream application.

Nature of non-transferrin-bound iron: studies on iron citrate complexes and thalassemic sera

Despite its importance in iron-overload diseases, little is known about the composition of plasma non-transferrin-bound iron (NTBI). Using 30-kDa ultrafiltration, plasma from thalassemic patients consisted of both filterable and non-filterable NTBI, the filterable fraction representing less than 10% NTBI. Low filterability could result from protein binding or NTBI species exceeding 30 kDa. The properties of iron citrate and its interaction with albumin were therefore investigated, as these represent likely NTBI species. Iron permeated 5- or 12-kDa ultrafiltration units completely when complexes were freshly prepared and citrate exceeded iron by tenfold, whereas with 30-kDa ultrafiltration units, permeation approached 100% at all molar ratios. A g = 4.3 electron paramagnetic resonance signal, characteristic of mononuclear iron, was detectable only with iron-to-citrate ratios above 1:100. The ability of both desferrioxamine and 1,2-dimethyl-3-hydroxypyridin-4-one to chelate iron in iron citrate complexes also increased with increasing ratios of citrate to iron. Incremental molar excesses of citrate thus favour the progressive appearance of chelatable lower molecular weight iron oligomers, dimers and ultimately monomers. Filtration of iron citrate in the presence of albumin showed substantial binding to albumin across a wide range of iron-to-citrate ratios and also increased accessibility of iron to chelators, reflecting a shift towards smaller oligomeric species. However, in vitro experiments using immunodepletion or absorption of albumin to Cibacron blue-Sepharose indicate that iron is only loosely bound in iron citrate-albumin complexes and that NTBI is unlikely to be albumin-bound to any significant extent in thalassemic sera.

Speciation and Environmental Fate of Chromium in Rivers Contaminated with Tannery Effluents

AbstractRedox and size speciation of chromium in rivers contaminated with tannery wastewater was carried out to provide insight into its transport and removal mechanisms. Total chromium was determined with Inductively Coupled Plasma‐Mass Spectrometry and Cr (VI) with Catalytic Adsorption Stripping Voltammetry. For the size speciation, particles were retained with a cartridge filter (cut‐off 1.2 μm) and the total filterable fraction was further fractionated with Tangential Flow Filtration to determine the concentrations of chromium associated with the High Molecular Weight Colloidal (HMWC), Low Molecular Weight Colloidal (LMWC) and Truly Dissolved (TD) fractions. Two fluvial systems of similar sizes, but located in contrasting climatic zones, were selected for comparison: the Sebou‐Fez system in Morocco and Dunajec River‐Czorsztyn Reservoir system in Poland. Particulate Cr dominated in the Sebou‐Fez system (about 90 %); while in the Dunajec‐Czorsztyn system, it represented only 17–53 % of the total chromium in raw water. Still, the partition coefficients [Kd] were of the same magnitude. Chromium (III) was the only form detected in Sebou‐Fez, whereas in Dunajec‐Czorsztyn Cr (VI) was also present with its proportion increasing downstream from the input of tannery wastewater due to the preferential removal of Cr (III). In the filtered water in Morocco a large fraction of Cr occurred in the HMWC fraction (50–70 %) at the two most contaminated sites, while the LMWC and TD forms prevailed at the non‐contaminated sites in the Sebou River. At a very high concentration, in the water in the proximity of tanneries (well above the theoretical saturation level) Cr precipitated as polynuclear Cr‐hydroxide. In Dunajec‐Czorsztyn, the partition of Cr (III) was approximately equal between the HMWC, LMWC and TD fractions, in contrast to Cr (VI) which occurred almost exclusively in the TD fraction. In both systems, Cr (III) was rapidly removed from the water to the sediments. The confluence of the Sebou with the Fez and the Czorsztyn reservoir trapped efficiently Cr (III) preventing its spreading over long distances. Cr (VI) showed conservative behavior and bypassed the Czorsztyn Reservoir. This study provides a first set of data on the partitioning of Cr (III) and Cr (VI) between the particulate, the colloidal and truly dissolved fractions in fluvial systems contaminated with tannery effluents. It also suggests that, in these systems, truly dissolved Cr (III) can be adequately modeled from the total filterable concentrations.

Growth of Vibrio cholerae O1 in red tide waters off California.

Vibrio cholerae serotype O1 is autochthonous to estuarine and coastal waters. However, its population dynamics in such environments are not well understood. We tested the proliferation of V. cholerae N16961 during a Lingulodinium polyedrum bloom, as well as other seawater conditions. Microcosms containing 100-kDa-filtered seawater were inoculated with V. cholerae or the 0.6- micro m-pore-size filterable fraction of seawater assemblages. These cultures were diluted 10-fold with fresh 100-kDa-filtered seawater every 48 h for four cycles. Growth rates ranged from 0.3 to 14.3 day(-1) (4.2 day(-1) +/- 3.9) for V. cholerae and 0.1 to 9.7 day(-1) (2.2 +/- 2.8 day(-1)) for bacterial assemblage. Our results suggest that dissolved organic matter during intense phytoplankton blooms has the potential to support explosive growth of V. cholerae in seawater. Under the conditions tested, free-living V. cholerae was able to reach concentrations per milliliter that were up to 3 orders of magnitude higher than the known minimum infectious dose (10(4) cell ml(-1)) and remained viable under many conditions. If applicable to the complex conditions in marine ecosystems, our results suggest an important role of the growth of free-living V. cholerae in disease propagation and prevention during phytoplankton blooms.

Application of ultrafiltration and stable isotopic amendments to field studies of mercury partitioning to filterable carbon in lake water and overland runoff

Results from pilot studies on colloidal phase transport of newly deposited mercury in lake water and overland runoff demonstrate that the combination of ultrafiltration, and stable isotope amendment techniques is a viable tool for the study of mercury partitioning to filterable carbon. Ultrafiltration mass balance calculations were generally excellent, averaging 97.3, 96.1 and 99.8% for dissolved organic carbon (DOC), total mercury (Hg T), and methylmercury (MeHg), respectively. Sub nanogram per liter quantities of isotope were measurable, and the observed phase distribution from replicate ultrafiltration separations on lake water agreed within 20%. We believe the data presented here are the first published colloidal phase mercury data on lake water and overland runoff from uncontaminated sites. Initial results from pilot-scale lake amendment experiments indicate that the choice of matrix used to dissolve the isotope did not affect the initial phase distribution of the added mercury in the lake. In addition there was anecdotal evidence that native MeHg was either recently produced in the system, or at a minimum, that this ‘old’ MeHg partitions to the same subset of DOC that binds the amended mercury. Initial results from pilot-scale overland runoff experiments indicate that less than 20% of newly deposited mercury was transported in the filterable fraction (<0.7 μm). There is some indication of colloidal phase enrichment of mercury in runoff compared to the phase distribution of organic carbon, but the mechanism of this enrichment is unclear. The phase distribution of newly deposited mercury can differ from that of organic carbon and native mercury, suggesting that the quality of the carbon (available ligands), not the quantity of carbon, regulates partitioning. Further characterization of DOC is needed to clarify the underlying mechanisms.

234Th/238U disequilibrium as an indicator of the seasonal export flux of particulate organic carbon in the North Water

Abstract Water-column deficits of 234Th (half-life=24.1 d) relative to its parent 238U were used to estimate fluxes of 234Th and particulate organic carbon (POC) through the euphotic zone of the North Water, a polynya in northern Baffin Bay. Samples collected in May 1998, early in the seasonal development of the polynya, showed small deficits of 234Th in the upper 100 m. Deficits were greater in July 1998 and August–September 1999. Sinking fluxes of POC were calculated from the water-column 234Th deficits by multiplying the latter by the POC/234Th ratio on sinking particles (assumed to be the >70-μm filterable fraction). POC fluxes were greatest in July 1998 (mean 27.4±13.4 mmol C m−2 d−1) and declined in August 1999 (mean 8.7±1.7 mmol C m−2 d−1), largely due to a decrease in the POC/Th ratio in the 1999 samples. Regionally, POC fluxes were greatest in the western and northern portions of the North Water in July 1998 and markedly lower in the west in August 1999. This pattern resembles spatial and temporal changes in primary production in the polynya determined independently. POC fluxes determined from water-column 234Th profiles agreed within factors of 2–5 with values determined from floating sediment traps deployed in the upper 100 m. Thorium-based indices of new production (ThE ratios) obtained within the polynya encompassed a wide range (0.1–0.9), with western areas showing substantially higher transfer efficiency of carbon fixed by phytoplankton at the surface. Thorium-derived POC fluxes at 100 m for both July 1998 and August 1999 correlated positively with biomass of the dominant diatom in the North Water, Chaetoceros socialis, suggesting that regional variations in carbon export can be further understood by factors controlling the distribution of this species.

Phenotypical variation in a toxic strain of the phytoplankter, Cylindrospermopsis raciborskii (nostocales, cyanophyceae) during batch culture

A nonaxenic strain of Cylindrospermopsis raciborskii Woloszynska (AWT 205) was grown in batch culture, with and without nitrate as the primary N source. Rapid log-phase growth with nitrate was 1.0 doubling/day versus 0.3 doubling/day without nitrate. Cylindrospermopsin (CYN) production was measured by HPLC. The rate of intracellular CYN production matched cell division rate for both the diazotrophies at cell densities less than 10(7) cell/ml. At cell density > 10(7) cell/ml, additional resource limitation in batch culture slowed log-phase growth to 0.04 division/day and cell division and CYN production decoupled. Intracellular CYN concentration increased at a rate of 0.08 doubling/day, twice the cell division rate. Extracellular CYN as a proportion of the total CYN increased from 20% during the rapid growth phase, to 50% during the slow growth phase. The total CYN yield from cultures grown out to stationary phase (55 days) exceeded 2 mg CYN/I. C. raciborskii cells in log-phase growth, exposed to 1 ppm copper (as copper sulphate), lysed within 24 hours. After copper treatment, all CYN was in the filterable fraction. These findings imply that in naturally occurring blooms of C. raciborskii, the movement of intracellular CYN into solution will be the greatest during stationary phase, when intracellular concentrations are highest and cell lysis is more frequent. The application of algicides that promote cell lysis will exacerbate this effect.

Removal, partitioning, and fate of silver and other metals in wastewater treatment plants and effluent‐receiving streams

AbstractWe investigated the removal of silver in five publicly owned treatment works (POTWs) and the fate of Ag in effluent receiving streams. Comparisons were made to several other metals. Silver was removed efficiently (&gt;94%) in all POTWs. The percentage of total Ag removed was independent of the influent Ag concentration, while the concentration of Ag in effluents was directly related to influent concentration. A good correlation (r2 = 0.77) between metal removal (%) and partition coefficient (Kd) indicated that differences among metals in removal efficiency were controlled mainly by metal partitioning (sorption) to particles removed by settling and/or filtration. A large fraction (19–53%) of Ag in the filterable (&lt; 1.0‐μm) fraction of POTW effluents was associated with submicron particles or colloids (&gt;0.05 μm), and the percentage filterable Ag was directly related to DOC concentration (r2 = 0.96). Effluent Ag concentrations (0.06–2.6 μg/L) were several orders of magnitude higher that typical “background” stream levels (1–2 ng/L), but Ag discharged to streams was rapidly dissipated by dilution and incorporation into stream sediments.

Characterization of suspended solids in/out airlift biofilm-reactors

In airlift reactors the biomass is immobilized on small (200-300 μm) carrier particles, suspended in the water phase. If domestic wastewater is treated in these systems, the soluble and colloidal compounds are generally removed with an efficiency of 75±5%. However, the overall treatment results are negatively affected by the high amount of suspended material in the effluent. Different fractions in influent and effluent were analyzed using microscopic techniques and chemical analyses to collect more information about the behavior of suspended solids. Settlable (Se), centrifugable (C), filterable (F) and soluble (So) fractions were obtained by sequential settling, centrifugation and filtration. After correction for sorbed soluble compounds the fractions C, F, and So contributed 30%, 20% and 50% respectively to the COD of presettled wastewater. During periods when biofilms were compact/smooth and the population of protozoa in the reactor was small, size and composition of the C-fraction only slightly changed when passing the reactor. The removal efficiency of this fraction increased from less than 10% to 15-25% if large populations of protozoa were present, which were able to consume more than 99% of the free cells. Additionally, a small amount of settlable compounds (&amp;lt; 20 mg COD/l) was formed in the reactor. This amount increased to 40-60 mg COD/l as soon as the surface of the films changed from smooth to very irregular due to growth of “streamers” and/or filamentous bacteria. Retention of this suspended biomass under these circumstances resulted in the development of an activated sludge process under these circumstances. The advantages of the biofilm process were thus partly lost.

Characterization of suspended solids in/out airlift biofilm-reactors

In airlift reactors the biomass is immobilized on small (200-300 μm) carrier particles, suspended in the water phase. If domestic wastewater is treated in these systems, the soluble and colloidal compounds are generally removed with an efficiency of 75±5%. However, the overall treatment results are negatively affected by the high amount of suspended material in the effluent. Different fractions in influent and effluent were analyzed using microscopic techniques and chemical analyses to collect more information about the behavior of suspended solids. Settlable (Se), centrifugable (C), filterable (F) and soluble (So) fractions were obtained by sequential settling, centrifugation and filtration. After correction for sorbed soluble compounds the fractions C, F, and So contributed 30%, 20% and 50% respectively to the COD of presettled wastewater. During periods when biofilms were compact/smooth and the population of protozoa in the reactor was small, size and composition of the C-fraction only slightly changed when passing the reactor. The removal efficiency of this fraction increased from less than 10% to 15-25% if large populations of protozoa were present, which were able to consume more than 99% of the free cells. Additionally, a small amount of settlable compounds (< 20 mg COD/l) was formed in the reactor. This amount increased to 40-60 mg COD/l as soon as the surface of the films changed from smooth to very irregular due to growth of “streamers” and/or filamentous bacteria. Retention of this suspended biomass under these circumstances resulted in the development of an activated sludge process under these circumstances. The advantages of the biofilm process were thus partly lost.

Renal excretion of aluminium in the rat: effect of citrate infusion.

When aluminium is administered intravenously to rats, the speciation of the aluminium has a major effect on its renal excretion. Aluminium administered as citrate is much more effectively excreted than that administered as chloride or sulphate. This suggests that citrate could be therapeutically useful in patients who have been exposed to aluminium. Accordingly, we have performed two series of experiments in rats, in which a citrate infusion (intravenous), was begun either immediately after, or one hour after, the administration of an intravenous aluminium sulphate bolus. Both protocols led to markedly enhanced aluminium excretion compared to controls in which only 0.7% NaCl was infused. The enhancement of aluminium excretion was 783% if citrate infusion was begun immediately after aluminium administration, and 335% if the citrate infusion began after an hour delay. The increased excretion was due to an increase in the freely filterable fraction of aluminium. In the control experiments, in which aluminium sulphate administration was followed by 0.7% NaCl infusion, aluminium was found to be deposited in the liver. Administration of citrate one hour after the aluminium bolus did not reduce this liver deposition. The results indicate that a fraction of the plasma aluminium is accessible to the citrate infused and can thereby be converted into a filterable form which can be excreted. It appears that, for maximum therapeutic effect, citrate should be infused as rapidly as possible after an aluminium load, to limit aluminium binding to ligands which allow it to enter cells.

Distribution of Trace Elements in the Filterable and Acid Extractable Fractions of Waters of the Northern Jordan River

Waters of the northern watershed of Lake Kinneret, sampled during the period 1985-1987, were analysed for their acid extractable and filterable major and trace element contents as part of an on-going research project. Water exploitation and reuse, mainly in the Hula Basin, resulted in an increase in concentration of trace elements in the different drainage canals. The distribution of high, exceptional values appears to be random, and cannot be clearly related to time-environmental processes. The highest concentrations of some major and trace elements were consistently recorded in the canal that drains peat soils. Nevertheless, the southern reaches of the Northern Jordan River were only slightly higher in concentration than the pristine sources. This implies that parts of the metal load were eliminated by poorly defined processes. The acid extractable concentrations were usually twice those of the filterable fraction, with the exception of interrelated Fe and AI, which were highly enriched in the suspended phase. The low levels of the element contents in the highly dynamic system prohibited the proposal of a model explaining the observed variations. The trace metal concentrations, generally below the regulation values, were similar to those reported for unpolluted world-wide streams.

Aliphatic and polycyclic aromatic hydrocarbons in urban rain, snow and fog

Rain, snow and fog samples have been collected at an urban site in Switzerland. Concentrations of n-alkanes and polycyclic aromatic hydrocarbons (PAH) were determined in the particulate (⩾ 0.2 μm) and filterable phases. The n-alkanes in the particulate phase were characterized by a carbon preference index (CPI), in the range of C 21–C 33, of 7.1 in summer rain compared to 2.1 in winter rain. n-Alkanes with a CPI of 1.2 occurred in the filtrate of several samples. The presence of these highly water-insoluble n-alkanes in the filterable fraction suggests the formation of intermolecular associations (clusters, aggregates). The PAH patterns in the particulate phases resemble each other in snow, summer and winter rain, indicating similar sources and scavenging mechanisms. Variations in the concentrations of n-alkanes and PAH between seasons and between rain, snow and fog can be explained by the size of the associated particles and hydrometeors (rain droplet, snow flake, fog droplet) and the related scavenging efficiencies. The distribution coefficients obtained by field measurements have been applied to a scavenging model and to an equilibrium model taking hydrophobic partitioning into account.