Predicting anaerobic biogasification potential of ingestates and digestates of a full-scale biogas plant using chemical and biological parameters

The aim of this work was to develop simple and fast tests to predict anaerobic biogasification potential (ABP) of ingestates and digestates from a biogas plant. Forty-six samples of both ingestates and digestates were collected within an eight-month observation period and were analyzed in terms of biological and chemical parameters, namely, ABP test, oxygen demand in a 20-h respirometric test (OD20), total solids (TS), volatile solids (VS), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), ammonia, cell solubles (CS), acid detergent fibers (ADF), lignin (ADL), cellulose, and hemicellulose. Considering both quantitative (VS and TOC) and qualitative aspects (OD20 and CS) of organic matter (OM), four models (linear regressions; 0.80相似文献   

Does Auxin Binding Protein 1 Control Both Cell Division and Cell Expansion?

The Auxin-Binding Protein 1 (ABP1) was identified over 30 years ago thanks to it''s high affinity for active auxins. ABP1 plays an essential role in plant life yet to this day, its function remains ‘enigmatic.’ A recent study by our laboratory shows that ABP1 is critical for regulation of the cell cycle, acting both in G₁ and at the G₂/M transition. We showed that ABP1 is likely to mediate the permissive auxin signal for entry into the cell cycle. These data were obtained by studying a conditional functional knock-out of ABP1 generated by cellular immunization in the model tobacco cell line, Bright Yellow 2.Key Words: auxin responses, auxin-binding protein 1, immunomodulation, cellular immunisation     

Biotransformations of Chloroguaiacols, Chlorocatechols, and Chloroveratroles in Sediments

The occurrence of trichloro- and tetrachloroguaiacols, -catechols, and -veratroles and their transformation was studied in freshwater and brackish water sediments putatively exposed to bleachery discharge. The samples contained both chloroguaiacols and chlorocatechols, of which >90% could not be removed by simple extraction. The bound concentrations varied and ranged from 550 μg kg of organic C⁻¹ for 3,4,5-trichloroguaiacol to 8,250 μg kg of organic C⁻¹ for tetrachlorocatechol. Chlorinated substrates added to the aqueous phase were rapidly bound to the sediment with K_p values between 1.3 and 2.8 ml kg of organic C⁻¹ for the chloroguaiacols and chloroveratroles and 22 to 36 ml kg of organic C⁻¹ for the chlorocatechols. Sediment samples incubated aerobically brought about O-methylation of 4,5,6-trichloroguaiacol to 3,4,5-trichloroveratrole in a yield of ca. 25%. Under anaerobic conditions, however, de-O-methylation of both the chloroguaiacols and chloroveratroles took place with synthesis of the corresponding chlorocatechols. In separate experiments, the chlorocatechols were not completely stable under anaerobic conditions, but their ultimate fate has not yet been resolved. Sediment which had been autoclaved twice at 121°C for 20 min was unable to bring about any of these transformations; we therefore conclude that they were mediated by biological processes. These results emphasize that, in determining the fate of chloroguaiacols and related compounds discharged into the aquatic environment, the cardinal roles of sorption to the sediment phase and of the oxygen tension must be taken into account. We propose a hypothetical guaiacol cycle to accommodate our observations.     

Two-stage biological treatment of olive mill wastewater with whey as co-substrate

Olive mill wastewater (OMW) is a highly polluting wastewater, caused by a high organic load and phenol content. These characteristics suggest that it may be suitable for aerobic treatment and anaerobic bacterial digestion. Aerobic treatment coupled with anaerobic bacterial digestion may be economically feasible as the methane produced is a valuable energy source while simultaneously purifying the OMW. In an attempt to improve the overall performance of the process, the addition of a co-substrate such as whey to the aerobic treatment pre-treatment of OMW by the yeast Candida tropicalis was studied.The two-stage system operated satisfactorily up to an organic loading rate (OLR) of 3.0 kg COD L⁻¹ day⁻¹ with a biogas production rate of 1.25 L_biogas L_reactor⁻¹ day⁻¹ and a total COD reduction in excess of 93% (62% COD reduction in aerobic pretreatment and 83% COD reduction in anaerobic digestion). Fifty-four percent of the phenol was biodegraded during the aerobic treatment stage, and biogas with between 68% and 75% methane was produced during anaerobic digestion.     

Estimation of Potentially Toxic Elements Contamination in Anthropogenic Soils on a Brown Coal Mining Dumpsite by Reflectance Spectroscopy: A Case Study

In order to monitor Potentially Toxic Elements (PTEs) in anthropogenic soils on brown coal mining dumpsites, a large number of samples and cumbersome, time-consuming laboratory measurements are required. Due to its rapidity, convenience and accuracy, reflectance spectroscopy within the Visible-Near Infrared (Vis-NIR) region has been used to predict soil constituents. This study evaluated the suitability of Vis-NIR (350–2500 nm) reflectance spectroscopy for predicting PTEs concentration, using samples collected on large brown coal mining dumpsites in the Czech Republic. Partial Least Square Regression (PLSR) and Support Vector Machine Regression (SVMR) with cross-validation were used to relate PTEs data to the reflectance spectral data by applying different preprocessing strategies. According to the criteria of minimal Root Mean Square Error of Prediction of Cross Validation (RMSEP_cv) and maximal coefficient of determination (R²_cv) and Residual Prediction Deviation (RPD), the SVMR models with the first derivative pretreatment provided the most accurate prediction for As (R²_cv) = 0.89, RMSEP_cv = 1.89, RPD = 2.63). Less accurate, but acceptable prediction for screening purposes for Cd and Cu (0.66 ˂ R²_cv) ˂ 0.81, RMSEP_cv = 0.0.8 and 4.08 respectively, 2.0 ˂ RPD ˂ 2.5) were obtained. The PLSR model for predicting Mn (R²_cv) = 0.44, RMSEP_cv = 116.43, RPD = 1.45) presented an inadequate model. Overall, SVMR models for the Vis-NIR spectra could be used indirectly for an accurate assessment of PTEs’ concentrations.     

Isotope Labeling and Microautoradiography of Active Heterotrophic Bacteria on the Basis of Assimilation of 14CO2

Most heterotrophic bacteria assimilate CO₂ in various carboxylation reactions during biosynthesis. In this study, assimilation of ¹⁴CO₂ by heterotrophic bacteria was used for isotope labeling of active microorganisms in pure cultures and environmental samples. Labeled cells were visualized by microautoradiography (MAR) combined with fluorescence in situ hybridization (FISH) to obtain simultaneous information about activity and identity. Cultures of Escherichia coli and Pseudomonas putida assimilated sufficient ¹⁴CO₂ during growth on various organic substrates to obtain positive MAR signals. The MAR signals were comparable with the traditional MAR approach based on uptake of ¹⁴C-labeled organic substrates. Experiments with E. coli showed that ¹⁴CO₂ was assimilated during both fermentation and aerobic and anaerobic respiration. The new MAR approach, HetCO₂-MAR, was evaluated by targeting metabolic active filamentous bacteria, including “Candidatus Microthrix parvicella” in activated sludge. “Ca. Microthrix parvicella” was able to take up oleic acid under anaerobic conditions, as shown by the traditional MAR approach with [¹⁴C]oleic acid. However, the new HetCO₂-MAR approach indicated that “Ca. Microthrix parvicella,” did not significantly grow on oleic acid under anaerobic conditions with or without addition of NO₂⁻, whereas the addition of O₂ or NO₃⁻ initiated growth, as indicated by detectable ¹⁴CO₂ assimilation. This is a metabolic feature that has not been described previously for filamentous bacteria. Such information could not have been derived by using the traditional MAR procedure, whereas the new HetCO₂-MAR approach differentiates better between substrate uptake and substrate metabolism that result in growth. The HetCO₂-MAR results were supported by stable isotope analysis of ¹³C-labeled phospholipid fatty acids from activated sludge incubated under aerobic and anaerobic conditions in the presence of ¹³CO₂. In conclusion, the novel HetCO₂-MAR approach expands the possibility for studies of the ecophysiology of uncultivated microorganisms.     

Nitrifying Bacteria in Wastewater Reservoirs

Deep wastewater reservoirs are used throughout Israel to store domestic wastewater effluents for summer irrigation. These effluents contain high concentrations of ammonia (≤5 mM) that are frequently toxic to photosynthetic microorganisms and that lead to development of anoxic conditions. Population dynamics of nitrifying bacteria and rates of nitrification were studied in two wastewater reservoirs that differed in organic load and degree of oxygenation and in the laboratory under controlled conditions, both by serial dilutions in mineral medium and microscopically with fluorescein isothiocyanate-conjugated antibodies prepared against local isolates. The difference in counts by the two methods was within 1 order of magnitude. In the laboratory, an O₂ concentration of 0.2 mg liter⁻¹ was close to optimal with respect to growth of NH₃ oxidizers on domestic wastewater, while O₂ concentrations of 0.05 mg liter⁻¹ supported significant rates of nitrification. It was found that even hypertrophic anaerobic environments such as the anaerobic hypolimnion of the wastewater reservoir or the anaerobic settling ponds are capable of sustaining a viable, although not actively nitrifying, population of Nitrosomonas spp. and Nitrobacter spp., in contrast to their rapid decline when maintained anaerobically in mineral medium in the laboratory. Nitrification rates of NH₃ in effluents during storage in the reservoirs were slower by 1 to 2 orders of magnitude compared with corresponding rates in water samples brought to the laboratory. The factors causing this inhibition were not identified.     

Modeling Soil Organic Carbon at Regional Scale by Combining Multi-Spectral Images with Laboratory Spectra

There is a great challenge in combining soil proximal spectra and remote sensing spectra to improve the accuracy of soil organic carbon (SOC) models. This is primarily because mixing of spectral data from different sources and technologies to improve soil models is still in its infancy. The first objective of this study was to integrate information of SOC derived from visible near-infrared reflectance (Vis-NIR) spectra in the laboratory with remote sensing (RS) images to improve predictions of topsoil SOC in the Skjern river catchment, Denmark. The second objective was to improve SOC prediction results by separately modeling uplands and wetlands. A total of 328 topsoil samples were collected and analyzed for SOC. Satellite Pour l’Observation de la Terre (SPOT5), Landsat Data Continuity Mission (Landsat 8) images, laboratory Vis-NIR and other ancillary environmental data including terrain parameters and soil maps were compiled to predict topsoil SOC using Cubist regression and Bayesian kriging. The results showed that the model developed from RS data, ancillary environmental data and laboratory spectral data yielded a lower root mean square error (RMSE) (2.8%) and higher R² (0.59) than the model developed from only RS data and ancillary environmental data (RMSE: 3.6%, R²: 0.46). Plant-available water (PAW) was the most important predictor for all the models because of its close relationship with soil organic matter content. Moreover, vegetation indices, such as the Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI), were very important predictors in SOC spatial models. Furthermore, the ‘upland model’ was able to more accurately predict SOC compared with the ‘upland & wetland model’. However, the separately calibrated ‘upland and wetland model’ did not improve the prediction accuracy for wetland sites, since it was not possible to adequately discriminate the vegetation in the RS summer images. We conclude that laboratory Vis-NIR spectroscopy adds critical information that significantly improves the prediction accuracy of SOC compared to using RS data alone. We recommend the incorporation of laboratory spectra with RS data and other environmental data to improve soil spatial modeling and digital soil mapping (DSM).     

Performance and kinetic evaluation of anaerobic moving bed biofilm reactor for treating milk permeate from dairy industry

High strength milk permeate derived from ultra-filtration based cheese making process was treated in an anaerobic moving bed biofilm reactor (AMBBR) under mesophilic (35 °C) condition. Total chemical oxygen demand (TCOD) removal efficiencies of 86.3–73.2% were achieved at organic loading rates (OLR) of 2.0–20.0 g TCOD L⁻¹ d⁻¹. A mass balance model gave values of methane yield coefficient (Y_G/S) and cell maintenance coefficient (k_m) of 0.341 L CH₄ g⁻¹ TCOD_removed and 0.1808 g TCOD_removed g⁻¹ VSS d⁻¹, respectively. The maximum substrate utilization rate U_max was determined as 89.3 g TCOD L⁻¹ d⁻¹ by a modified Stover–Kincannon model. Volumetric methane production rates (VMPR) were shown to correlate with the biodegradable TCOD concentration through a Michaelis–Menten type equation. Moreover, based on VMPR and OLR removed from the reactor, the sludge production yield was determined as 0.0794 g VSS g⁻¹ TCOD_removed.     

Performance evaluation and kinetic modeling of the start-up of a UASB reactor treating municipal wastewater at low temperature

A kinetic modeling-based study was carried out to evaluate the start-up performance of a 10-L up-flow anaerobic sludge blanket (UASB) reactor treating municipal wastewater under different organic and hydraulic loading conditions. The reactor was operated for 105 days (around 4 months) below 20 °C and with three different hydraulic retention times of 24, 12 and 5 h. Imposed volumetric organic loading rates (OLR) ranged from 0.57 (±0.05) to 11.78 (±0.85) kg TCOD/m³-day. Although relatively high incoming volumetric OLR values were employed to the system, the UASB reactor demonstrated a favorable performance on the anaerobic treatability of municipal wastewater, and no process failure was recorded in the start-up stage. On the basis of experimental results, the modified Stover–Kincannon model was successfully applied to define the start-up kinetics with a very high value of the correlation coefficient (R = 0.9729). Maximum substrate utilization rate constant and saturation constant of the modified Stover–Kincannon model were determined as U _max = 1.996 g/L-day and K _B = 1.536 g/L-day, respectively.     

Effect of pre-aeration and inoculum on the start-up of batch thermophilic anaerobic digestion of municipal solid waste

In this study, a short pre-aeration step was investigated as pre-treatment for thermophilic anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). It was found that pre-aeration of 48 h generated enough biological heat to increase the temperature of bulk OFMSW to 60 °C. This was sufficient self-heating of the bulk OFMSW for the start-up of thermophilic anaerobic digestion without the need for an external heat source. Pre-aeration also reduced excess easily degradable organic compounds in OFMSW, which were the common cause of acidification during the start-up of the batch system. Careful consideration however must be taken to avoid over aeration as this consumes substrate, which would otherwise be available to methanogens to produce biogas. To accelerate methane production and volatile solids destruction, the anaerobic digestion in this study was operated as a wet process with the anaerobic liquid recycled through the OFMSW. Appropriate anaerobic liquid inoculum was found to be particularly beneficial. It provided high buffer capacity as well as suitable microbial inoculum. As a result, acidification during start-up was kept to a minimum. With volatile fatty acids (VFAs-acetate in particular) and H₂ accumulation typical of hydrolysis and fermentation of the easily degradable substrates during start-up, inoculum with high numbers of hydrogenotrophic methanogens was critical to not only maximise CH₄ production but also reduce H₂ partial pressure in the system to allow VFAs degradation. In a lab-scale bioreactor, the combined pre-aeration and wet thermophilic anaerobic digestion was able to stabilise the OFMSW within a period of only 12 days. The stabilised inert residual material can be used as a soil amendment product.     

Anaerobic co-digestion of organic wastes

Over the last years anaerobic digestion has been successfully established as technology to treat organic wastes. The perspective of turning, through a low-cost process, organic wastes into biogas, a source of renewable energy and profit, has certainly increased the interest around this technology and has required several studies aimed to develop methods that could improve the performance as well as the efficiency of this process. The present work reviews the most interesting results achieved through such studies, mainly focusing on the following three aspects: (1) the analysis of the organic substrates typically co-digested to exploit their complementary characteristics; (2) the need of pre-treating the substrates before their digestion in order to change their physical and/or chemical characteristics; (3) the usefulness of mathematical models simulating the anaerobic co-digestion process. In particular these studies have demonstrated that combining different organic wastes results in a substrate better balanced and assorted in terms of nutrients, pre-treatments make organic solids more accessible and degradable to microorganisms, whereas mathematical models are extremely useful to predict the co-digestion process performance and therefore can be successfully used to choose the best substrates to mix as well as the most suitable pre-treatments to be applied.     

Biogas from dedicated energy crops in Northern Italy: electric energy generation costs

Agricultural anaerobic digestion facilities are increasing in many EU member States and biomass supply is sometimes an issue. Dedicated energy crops (DEC) (mainly Maize, Triticale and Sorghum) are often used to integrate other substrates, such as agricultural residues, manure and organic waste. However, DEC production includes onerous agricultural operations (soil preparation, harvest, transport and storage) and may result in high unit costs (UC) of electric energy (EE, € kWhe⁻¹), compared to other renewable sources. In this work, seven different types of DEC (4 different combinations of crop successions) were cultivated in 30 different parcels, distributed along the Po Valley (northern Italy), using different varieties of seeds for each crop type. All agricultural operations were accounted for their costs (988–3346 € ha⁻¹). Biomass production was measured and reported as average of different parcels for each type of crop (31.2–187 Mg ha⁻¹). Biomass dry matter content and biogas potential were measured on representative samples and the EE obtainable was calculated (7.9–35.3 MWhe ha⁻¹), by assuming conservative factors (CH₄ contents in biogas and electric generation yields). The costs of ensiled biomass sensibly varied (13.8–40 € Mg⁻¹) among crop solutions, as well as the same UC of EE (0.068–0.150 € kWhe⁻¹). These costs were considered together with typical plant management and investment costs (plant size: 0.5–1 MWe): total UC of EE generation through anaerobic digestion (considering 100% DEC) varied in a relatively wide range (0.143–0.279 € kWhe⁻¹). When the biomass mix is ‘blended’ with low-cost residues or organic waste, this range could be lowered to 0.096–187 € kWhe⁻¹. Only this strategy and strong efforts in reducing technological investment/management costs can candidate biogas-based EE as a really competitive renewable alternative to traditional sources, in the next future.     

Noninvasive prediction of vertebral body compressive strength using nonlinear finite element method and an image based technique

Noninvasive prediction of vertebral body strength under compressive loading condition is a valuable tool for the assessment of clinical fractures. This paper presents an effective specimen-specific approach for noninvasive prediction of human vertebral strength using a nonlinear finite element (FE) model and an image based parameter based on the quantitative computed tomography (QCT). Nine thoracolumbar vertebrae excised from three cadavers with an average age of 42 years old were used as the samples. The samples were scanned using the QCT. Then, a segmentation technique was performed on each QCT sectional image. The segmented images were then converted into three-dimensional FE models for linear and nonlinear analyses. A new material model was implemented in our nonlinear model being more compatible with real mechanical behavior of trabecular bone. A new image based MOS (Mechanic of Solids) parameter named minimum sectional strength ((σ_uA)_min) was used for the ultimate compressive strength prediction. Subsequently, the samples were destructively tested under uniaxial compression and their experimental ultimate compressive strengths were obtained. Results indicated that our new implemented FE model can predict ultimate compressive strength of human vertebra with a correlation coefficient (R² = 0.94) better than usual linear and nonlinear FE models (R² = 0.83 and 0.85 respectively). The image based parameter introduced in this study ((σ_uA)_min) was also correlated well with the experimental results (R² = 0.86). Although nonlinear FE method with new implemented material model predicts compressive strength better than the (σ_uA)_min, this parameter is clinically more feasible due to its simplicity and lower computational costs. This can make future applications of the (σ_uA)_min more justified for human vertebral body compressive strength prediction.     

Bio-pretreatment of municipal solid waste prior to landfilling and its kinetics

The conventional landfilling does not promote sustainable waste management due to uncontrolled emissions which potentially degrade the environment. Pretreatment of municipal solid waste prior to landfilling significantly enhances waste stabilization, reduces the emissions and provides many advantages. Therefore, pretreatment of municipal solid waste methods were investigated. The major objectives of biological pretreatment are to degrade most easily degradable organic matters of MSW in a short duration under controlled conditions so as to produce desired quality for landfill. To investigate the suitable pretreatment method prior to landfilling for developing countries four pretreatment simulators were developed in the laboratory: (i) anaerobic simulator (R₁), (ii) aerobic pretreatment simulator by natural convection of air (R₂), (iii) aerobic pretreatment simulator by natural convection of air with leachate recirculation (R₃) and (iv) forced aeration and leachate recirculation (R₄). During the pretreatment organic matter, elemental composition, i.e., carbon, hydrogen, nitrogen and settlement were determined for bench scale experiments. A two-component kinetic model is proposed for the biodegradation of organic matter. Biodegradation kinetic constants were determined for readily and slowly degradable organic matter. The biodegradation of organic matter efficiency in terms of kinetic rate constants for the pretreatment simulators was observed as R₄ > R₃ > R₂ > R₁. Biodegradation rate constants for readily degradable matter in simulators R₄ and R₃ were 0.225 and 0.222 per day. R₃ and R₄ simulators were more effective in reducing methane emissions about 45% and 55%, respectively, as compared to anaerobic simulator R₁. Pretreatment of MSW, by natural convection of air with leachate recirculation R₃ is sustainable method to reduce the emissions and to stabilize the waste prior to landfilling.     

Anaerobic treatment of low-strength wastewater with a high fraction of particulate matter in an unconventional two-phase ASBRs system

The results of a two-phase anaerobic system using anaerobic sequencing batch reactors (ASBRs), treating low-strength wastewater (COD ∼ 500 mg/L) with a high fraction of particulate organic matter (70%, COD basis), are presented. Two reactors in series were used; the first one was hydrolytic–acidogenic, while the second one was methanogenic. This configuration was proposed to promote high efficiency solids removal. During the experiment, 69% and 50% efficiencies of total COD removal were obtained for OLRs of 0.63 and 1.22 kgCOD/(m³ d), respectively. Values of the solubilized organic fraction (SOF) achieved in the hydrolytic–acidogenic reactor were within the range of 0.3–0.6 gCOD_solubilized/gpCOD_removed, and the average acidified organic fraction (AOF) was 0.6 gCOD_VFA-produced/gsCOD_fed. The methanogenic reactor had a VFA removal fraction (VFARF) between 0.4 and 0.6 gCOD_VFA-removed/gCOD_VFA-fed for the OLR of 0.63 and 1.22. The two-phase ASBR system is suitable, and can be implemented, for the anaerobic treatment of this kind of wastewater.     

Biotransformation of 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-Hexaazaisowurtzitane (CL-20) by Denitrifying Pseudomonas sp. Strain FA1

The microbial and enzymatic degradation of a new energetic compound, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), is not well understood. Fundamental knowledge about the mechanism of microbial degradation of CL-20 is essential to allow the prediction of its fate in the environment. In the present study, a CL-20-degrading denitrifying strain capable of utilizing CL-20 as the sole nitrogen source, Pseudomonas sp. strain FA1, was isolated from a garden soil. Studies with intact cells showed that aerobic conditions were required for bacterial growth and that anaerobic conditions enhanced CL-20 biotransformation. An enzyme(s) involved in the initial biotransformation of CL-20 was shown to be membrane associated and NADH dependent, and its expression was up-regulated about 2.2-fold in CL-20-induced cells. The rates of CL-20 biotransformation by the resting cells and the membrane-enzyme preparation were 3.2 ± 0.1 nmol h⁻¹ mg of cell biomass⁻¹ and 11.5 ± 0.4 nmol h⁻¹ mg of protein⁻¹, respectively, under anaerobic conditions. In the membrane-enzyme-catalyzed reactions, 2.3 nitrite ions (NO₂⁻), 1.5 molecules of nitrous oxide (N₂O), and 1.7 molecules of formic acid (HCOOH) were produced per reacted CL-20 molecule. The membrane-enzyme preparation reduced nitrite to nitrous oxide under anaerobic conditions. A comparative study of native enzymes, deflavoenzymes, and a reconstituted enzyme(s) and their subsequent inhibition by diphenyliodonium revealed that biotransformation of CL-20 is catalyzed by a membrane-associated flavoenzyme. The latter catalyzed an oxygen-sensitive one-electron transfer reaction that caused initial N denitration of CL-20.     

Nitrogen Fixation Dynamics of Two Diazotrophic Communities in Mono Lake, California

Two types of diazotrophic microbial communities were found in the littoral zone of alkaline hypersaline Mono Lake, California. One consisted of anaerobic bacteria inhabiting the flocculent surface layers of sediments. Nitrogen fixation (acetylene reduction) by flocculent surface layers occurred under anaerobic conditions, was not stimulated by light or by additions of organic substrates, and was inhibited by O₂, nitrate, and ammonia. The second community consisted of a ball-shaped association of a filamentous chlorophyte (Ctenocladus circinnatus) with diazotrophic, nonheterocystous cyanobacteria, as well as anaerobic bacteria (Ctenocladus balls). Nitrogen fixation by Ctenocladus balls was usually, but not always, stimulated by light. Rates of anaerobic dark fixation equaled those in the light under air. Fixation in the light was stimulated by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea and by propanil [N-(3,4-dichlorophenyl)propanamide]. 3-(3,4-Dichlorophenyl)-1,1-dimethyl urea-elicited nitrogenase activity was inhibited by ammonia (96%) and nitrate (65%). Fixation was greatest when Ctenocladus balls were incubated anaerobically in the light with sulfide. Dark anaerobic fixation was not stimulated by organic substrates in short-term (4-h) incubations, but was in long-term (67-h) ones. Areal estimates of benthic N₂ fixation were measured seasonally, using chambers. Highest rates (~29.3 μmol of C₂H₄ m⁻² h⁻¹) occurred under normal diel regimens of light and dark. These estimates indicate that benthic N₂ fixation has the potential to be a significant nitrogen source in Mono Lake.     

Anaerobic degradation of organic compounds at high salt concentrations

A number of obligately anaerobic fermentative bacteria are known to degrade a variety of organic substrates such as sugars, amino acids, and others, in the presence of high salt concentrations (up to 3–4 M) to products such as hydrogen, CO₂, acetate and higher fatty acids, and ethanol. Our understanding of the fate of these products in hypersaline environments is still extremely limited. The occurrence of bacterial sulfate reduction is well established at salt concentrations of up to 24%; however, the bacteria involved have not yet been isolated in pure culture, and the range of electron donors used is unknown. Halophilic or halotolerant methanogenic bacteria using hydrogen/CO₂ or acetate as energy source are notably absent; methanogenesis under hypersaline conditions is probably limited to such substrates as methanol and methylamines, which cannot be expected to be major products of anaerobic degradation of most organic compounds.     

Development of an obligate anaerobe specific biocide

Summary Anaerobic bacteria, such as sulfate-reducing bacteria and clostridia, are capable of generating H₂S and organic acids which corrode metallurgy resulting in millions of dollars of damage to industry annually. The bacteria are obligate anaerobes which grow typically on equipment surfaces under deposits such as biofilms. A successful method of penetrating biofilm and killing the anaerobic bacteria specifically has not been previously presented. We have investigated whether a blend of 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole (metronidazole) and a biodispersant would killDesulfovibrio, Desulfotomaculum, andClostridium species grown in the laboratory and in field applications. We found the blend significantly reduced the anaerobes in laboratory cultures. However, in a bioreactor designed to induced a high level of biofilm production and enhance underdeposit growth of anaerobic bacteria, a 40–58% increase in the antibiotic-biodispersant blend concentration was required. The metronidazole blend killed obligate anaerobic bacteria specifically but was non-toxic to aerobic bacteria and fungi. These results were confirmed in cooling tower field trial studies.