In situ methane enrichment in anaerobic digestion

A major cost consideration in the use of anaerobic digestion to convert biomass and waste to utility-grade gas is the expense of separating CO(2) from the product gas. Anaerobic digestion has a number of inherent properties that can be exploited to increase the methane content of the gas directly produced by the digester, the most important of which is the high solubility of CO(2)(40-60 times that of methane) in water under digestion conditions. The methane enrichment concept examined in this study involved the recirculation of a liquid stream from the digester through a CO(2) desorption process and the return of the liquid stream back to the digester for absorption of additional CO(2) produced by the conversion of organic materials. A steady-state equilibrium model predicted that a digester gas methane content exceeding 94% could be achieved with this scheme using modest recirculation rates provided a desorption process could be designed to achieve a 60+% CO(2) removal efficiency in the degassing of the liquid recycle stream. Using fixed-film laboratory digesters operated on synthetic feedstocks, the technique of methane enrichment was tested under pressurized and unpressurized conditions. A 93 + 2% methane gas stream was produced from a volatile-acid-fed bench-scale digester simulating the methanogenic stage of two-phase digestion under conditions of (1) a pH swing achieved without caustic addition that allowed digestion at pH 7. 5 and air stripping at pH 6. 5-7. 0, (2) digester pressurization to 30 psig, and (3) a recycle rate of 0. 33 L/L reactor/day. Significant but lower levels of methane enrichment were achieved with the single-stage digester at the low experimental recycle rate. However, the narrow range among all experiments of CO(2) desorption efficiencies achieved in air stripping the recycle stream (35-60% CO(2) removal) suggests that comparable methane enrichment-may be achieved with unpressurized single-stage digestion using greater recycle rates. A materials balance analysis of data from an unpressurized, single-stage digester employing no chemical addition and using laboratory degassing efficiencies indicated that 94% methane could be produced at recycle rates of less than 1. 4 L/L reactor/day with a methane loss of less than 2%.     

In situ field measurement of leaf water potential using thermocouple psychrometers

Thermocouple psychrometers are the only instruments which can measure the in situ water potential of intact leaves, and which can possibly be used to monitor leaf water potential. Unfortunately, their usefulness is limited by a number of difficulties, among them fluctuating temperatures and temperature gradients within the psychrometer, sealing of the psychrometer chamber to the leaf, shading of the leaf by the psychrometer, and resistance to water vapor diffusion by the cuticle when the stomates are closed. Using Citrus jambhiri, we have tested several psychrometer design and operational modifications and showed that in situ psychrometric measurements compared favorably with simultaneous Scholander pressure chamber measurements on neighboring leaves when the latter were corrected for the osmotic potential.     

Bacteriophage tracer experiments in groundwater

Three tracer experiments employing three different bacteriophage were performed at one groundwater site near Beverley, Humberside. In two of the experiments the bacteriophage were injected into the aquifer by a borehole at a distance of 366 m from the pumping borehole. In the other experiment they were injected at a distance of 122 m. Regular samples were taken of water abstracted at the pumping boreholes as well as from the injection boreholes. The objectives were to: (1) investigate the pattern of bacteriophage recovery from the aquifer; (2) calculate the total number of bacteriophage recovered and the rate of their migration; and (3) detect any differences in bacteriophage behaviour which could be directly related to the morphology of the three bacteriophage. In all experiments the pattern of recovery was similar, exhibiting a peak of high numbers reaching the pumping borehole soon after injection. The highest percentage of original inoculum recovered was 1.9%. In the majority of cases, however, recovery was usually one log₁₀ lower than this. The fastest migration rates were very rapid, reaching 2.8 cm/s in one experiment. No variation in percentage recovery or transit time could be directly attributed to morphology of bacteriophage. The most important factor governing the pattern of migration was undoubtedly the hydrogeological conditions.     

Bacteriophage tracer experiments in groundwater

Three tracer experiments employing three different bacteriophage were performed at one groundwater site near Beverley, Humberside. In two of the experiments the bacteriophage were injected into the aquifer by a borehole at a distance of 366 m from the pumping borehole. In the other experiment they were injected at a distance of 122 m. Regular samples were taken of water abstracted at the pumping boreholes as well as from the injection boreholes. The objectives were to: (1) investigate the pattern of bacteriophage recovery from the aquifer; (2) calculate the total number of bacteriophage recovered and the rate of their migration; and (3) detect any differences in bacteriophage behaviour which could be directly related to the morphology of the three bacteriophage. In all experiments the pattern of recovery was similar, exhibiting a peak of high numbers reaching the pumping borehole soon after injection. The highest percentage of original inoculum recovered was 1.9%. In the majority of cases, however, recovery was usually one log10 lower than this. The fastest migration rates were very rapid, reaching 2.8 cm/s in one experiment. No variation in percentage recovery or transit time could be directly attributed to morphology of bacteriophage. The most important factor governing the pattern of migration was undoubtedly the hydrogeological conditions.     

Quantification of methane oxidation in the rice rhizosphere using 13C-labelled methane

In this paper isotope ratio mass spectrometry is used to determine the methane (CH₄) oxidation fraction in the rhizosphere of intact rice plant-soil systems. Earlier studies on quantification of the methane oxidation were based on inhibition or incubation procedures which strongly interfered with the plant-soil system and resulted in a large variability of the reported fractions, while other studies considered stable isotopes at natural abundance levels to investigate methanotrophy in the rhizosphere of rice. The current work is the first that used ¹³C-labelled CH₄ as additive and calculated the oxidation fraction from the ratio between the added ¹³C-labelled CH₄ and its oxidation product ¹³CO₂. Both labelled gases could be distinguished from the natural abundance percentages. The oxidation fraction for methane was found to be smaller than 7%, suggesting that former approaches overestimate the methane oxidation fraction.     

In situ toxicity tests of fishes in acid waters

Toxicity of waters within the North Branch of the Moose River to various life stages of lake trout (Salvelinus namaycush), brook trout (Salvelinus fontinalis), creek chub (Semotilus atromaculatus), and blacknose dace (Rhinichthys atratulus) were examined in situ. Study sites were selected that were expected to range from toxic to favourable water quality. For example, pH varied from 4.25 to 7.17, inorganic monomeric Al ranged from ND (< 0.01 mg/l) to 0.40 mg/l, and Ca, from 0.41 to 4.27 mg/l.Toxicity tests were conducted at times when the life stages would naturally occur in these waters and were continued until a range of mortality was observed at the various sites. These experiments suggested that the extent of the drainage system that is toxic to fish increases during snowmelt and major runoff events. Summer base flow water quality was generally the least toxic.Critical life stages were upon hatching and as early feeding fry. In general, young of the year fish were the most tolerant life stage tested. Yearling and adult fish, however, were very sensitive. Blacknose dace were the most sensitive fish of the four species tested, and brook trout were the most tolerant.Hydrogen ion (H⁺) concentration was the most toxic variable in the majority of tests. Inorganic monomeric Al was the most toxic in several, and the combination of H⁺ and Al seemed to cause increased toxicity in many instances. A three-variable model employing hours of exposure, H⁺ concentration, and inorganic monomeric Al predicted mortality quite well. A simple two-variable model using H⁺ and color was nearly as good (R² from 0.49 to 0.94).Documented differences in toxicity among sites and species agreed with observed patterns of fish distribution. These in situ results indicated that laboratory estimates of safe levels of pH and concentrations of Al can result in mortality of fishes in surface waters subject to acidification.     

In situ bioremediation of monoaromatic pollutants in groundwater: a review

Monoaromatic pollutants such as benzene, toluene, ethylbenzene and mixture of xylenes are now considered as widespread contaminants of groundwater. In situ bioremediation under natural attenuation or enhanced remediation has been successfully used for removal of organic pollutants, including monoaromatic compounds, from groundwater. Results published indicate that in some sites, intrinsic bioremediation can reduce the monoaromatic compounds content of contaminated water to reach standard levels of potable water. However, engineering bioremediation is faster and more efficient. Also, studies have shown that enhanced anaerobic bioremediation can be applied for many BTEX contaminated groundwaters, as it is simple, applicable and economical.

This paper reviews microbiology and metabolism of monoaromatic biodegradation and in situ bioremediation for BTEX removal from groundwater under aerobic and anaerobic conditions. It also discusses the factors affecting and limiting bioremediation processes and interactions between monoaromatic pollutants and other compounds during the remediation processes.     

In situ measurement of algal growth potential in aquatic ecosystems by immobilized algae

Cells of the green algaSelenastrum capricornutum were immobilized in alginate beads. The alga was able to grow inside these beads without being grazed by zooplankton. For P-limited immobilized cells, however, a lower µ _m and initial slope of the Monod growth curve µ _m /K _s were found than for free cells.To study the feasibility of immobilized algae to estimate algal growth potentialin situ in aquatic ecosystems, a series of experiments were conducted in indoor model ecosystems (microcosms) and in a small stream. The use of immobilized algae allowed a continuous registration of algal growth potential integrated over periods with natural fluctuations in the environment. The method of encapsulation of the algae can, however, still be improved. The alginate matrix is exposed to marked degradation by microorganisms when incubated in polluted streams for a period longer than two weeks. The applicability of other types of matrices should be tested.Author for correspondence     

In situ measurement of HMG-CoA reductase activity in digitonin-permeabilized hepatocytes

An assay procedure for HMG-CoA reductase is described which allows rapid measurement of the activity of this enzyme in isolated rat hepatocytes. In a one step procedure digitonin permeabilizes the plasma membrane and at the same time HMG-CoA reductase activity is measured. Digitonin at a concentration of 64 micrograms per mg of cell protein was found to be optimal for exposing microsomal HMG-CoA reductase to the assay components. The enzyme assay is linear with time up til 5 min and with protein concentrations in the range of 0.06-0.6 mg of cell protein per assay. It is shown that cellular enzyme activity is affected by preincubation of intact hepatocytes with a variety of short-term modulators of hepatic cholesterogenesis.     

In situ measurement of superoxide and hydroxyl radicals by frequency mixing detection technique

Frequency mixing magnetic detection (FMMD) was used to detect superoxide from hypoxanthine and xanthine reaction and to detect hydroxyl radical from the Fenton reaction. FMMD was also applied to measure the reactive oxygen species (ROS) level released from microglial cells. We could assess the formation and extinction of the free radicals without a spin trap reagent. The FMMD signal amplitude scaled with the concentration of the radicals. It was verified that no signals are obtained from the substrates and reagents. Based on the observations and on previous research, we suggest that the FMMD signals originate from superoxide and hydroxyl radicals, indicating that FMMD can be used to detect O-centered radicals. Subsequent analysis of free radicals generated from living microglial cells showed that there were significant differences between the activated microglial cells and resting ones. The results of this research are promising regarding the applications of FMMD for in situ measurement of free radicals from various sources, including the cell.     

In situ localization of small RNAs in plants by using LNA probes

Small RNAs have crucial roles in numerous aspects of plant biology. Despite our current understanding of their biogenesis and mechanisms of action, the biological function of small RNAs, particularly miRNAs, remains largely unknown. To decipher small RNA function, knowledge about their spatiotemporal patterns of expression is essential. Here we report an in situ hybridization method for the precise localization of small RNAs in plants by using locked nucleic acid (LNA) oligonucleotide probes. This method has been adapted from protocols used to detect messenger RNAs in formaldehyde-fixed and paraffin-embedded tissue sections, but it includes essential optimizations in key prehybridization, hybridization and posthybridization steps. Most importantly, optimization of probe concentration and hybridization temperature is required for each unique LNA probe. We present the detailed protocol starting from sectioned tissues, and we include troubleshooting tips and recommended controls. This method has been used successfully in several plant species and can be completed within 2-6 d.     

In situ bioremediation using biosurfactant produced by solid state fermentation

The discovery that certain microorganisms, living within a marine environment, can actually degrade components of oil, has made possible the utilization of biological methods for the treatment of oil spills. A biosurfactant accelerates the process of degradation of pollutant composites. The objective of this work was to study the bioremediation in situ of a diesel oil spill by utilizing a biosurfactant produced through fermentation and then compare it with chemical remediation. The quantification and identification of hydrocarbons were carried out by the process of gas chromatography. The soil indigenous microorganisms were monitored. The experiment with biosurfactant reached reductions of 99% of the aliphatic hydrocarbons, while that of the chemical disperser experiment reached a maximum of 90% reduction in 180 days. In 15 days the biosurfactant removed 77% of the aliphatic hydrocarbons, the diesel oil experiment 8.7% and the chemical disperser only 5%. The biosurfactant was 99% effective for the removal of aromatic polycyclic hydrocarbons, up to 3 rings.     

In situ red bed development by the oxidation of authigenic pyrite in a coastal depositional environment

Exposures of Pleistocene coastal sediments in South Carolina illustrate red bed development in progress. Iron pigmentation in the clays is developed from the oxidation of authigenic pyrite in the drab clays by the action of oxygenated ground waters. Migration of ferrous iron upward, with subsequent oxidation and precipitation higher in the section, gives rise to the red and yellow clays. It is also suggested that this mechanism may be possible in other marine-influenced depositional environments where authigenic sulphides form, such as tidal flat, back barrier, lagoon, etc., or in lithified sediments. Red beds formed in this manner have no paleoclimatic or source are implications.     

Residual radiation effect in the murine spleen. In situ measurement by 125-iodo-deoxyuridine retention

Summary To investigate whether residual radiation damage in hematopoietic tissue is measurable in situ by a change in cell turnover, the retention of the thymidine analogue 5-(125-I)iodo-2-deoxyuridine (125-IUdR) following incorporation into DNA of cells in bone marrow and spleen of mice was measured 35 days after 0–500 rad whole body gamma irradiation.In the bone marrow a rapid and a slow turnover component of 125-IUdR retention were found. Both components were almost identical for unirradiated and irradiated mice. In the spleen the 125-IUdR retention curves exhibited three components with increasingly prolonged half-times. In the second component the half-time was longer in irradiated than in unirradiated mice. This was dose-dependent.The increased half-time of 125-IUdR retention in irradiated spleens may be caused by direct cellular damage of long-lived cells (lymphocytes, early hematopoietic progenitor cells) or/and by diminished stimulation of proliferation by microenvironmental or long-range factors.     

Thermophilic anaerobic oxidation of methane by marine microbial consortia

The anaerobic oxidation of methane (AOM) with sulfate controls the emission of the greenhouse gas methane from the ocean floor. AOM is performed by microbial consortia of archaea (ANME) associated with partners related to sulfate-reducing bacteria. In vitro enrichments of AOM were so far only successful at temperatures ⩽25 °C; however, energy gain for growth by AOM with sulfate is in principle also possible at higher temperatures. Sequences of 16S rRNA genes and core lipids characteristic for ANME as well as hints of in situ AOM activity were indeed reported for geothermally heated marine environments, yet no direct evidence for thermophilic growth of marine ANME consortia was obtained to date. To study possible thermophilic AOM, we investigated hydrothermally influenced sediment from the Guaymas Basin. In vitro incubations showed activity of sulfate-dependent methane oxidation between 5 and 70 °C with an apparent optimum between 45 and 60 °C. AOM was absent at temperatures ⩾75 °C. Long-term enrichment of AOM was fastest at 50 °C, yielding a 13-fold increase of methane-dependent sulfate reduction within 250 days, equivalent to an apparent doubling time of 68 days. The enrichments were dominated by novel ANME-1 consortia, mostly associated with bacterial partners of the deltaproteobacterial HotSeep-1 cluster, a deeply branching phylogenetic group previously found in a butane-amended 60 °C-enrichment culture of Guaymas sediments. The closest relatives (Desulfurella spp.; Hippea maritima) are moderately thermophilic sulfur reducers. Results indicate that AOM and ANME archaea could be of biogeochemical relevance not only in cold to moderate but also in hot marine habitats.