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We present a reliable and robust open dynamic chamber for measuring greenhouse gas exchange in peatlands with minimal disturbance of the ground. This chamber, called "skirt-chamber", is based on a transparent plastic film, placed above an open frame made of sparse interwoven wires, and expanded around the base of the chamber below a steel chain that ensures contact to the ground, avoiding damage, trenching or cutting vegetation. Gas exchange is determined using a portable gas analyzer from a mass balance in which the imperfect sealing of the chamber to the ground is quantified through the injection a methane pulse. The method was tested on a pristine peatland dominated by Sphagnum magellanicum located on Navarino Island at the subantarctic Magellanic ecoregion in Chile. Our results indicate that, the skirt-chamber allowed determining methane fluxes and ecosystem respiration, in about 20 minutes, with a limit of detection of 0.185 mg CH4 m-2 h-1, and 173 mg CO2 m-2 h-1, respectively. We conclude that the skirt-chamber is a minimally-intrusive, fast, portable, and inexpensive method that allows the quantification of greenhouse gas emissions with high spatial resolution in remote locations and without delay.

A previously developed surface probe method, which allows for instantaneous methane (CH4) flux measurement, was used to establish CH4 emission maps of a municipal landfill with a final clay cover and equipped with a gas recollection system. In addition to spatial variations, the method was applied at 7 different times over a total timeframe of 65 h and under similar weather conditions to determine the intrinsic temporal variations of CH4 emissions; i.e., the temporal variation related to the dynamic of the landfill rather than the one driven by external factors. Furthermore, continuous CH4 fluxes, with a data acquisition frequency of 1 Hz, were measured during 12 h at a single position, and for one hour at 22 locations of the landfill, spanning a large range of CH4 emission magnitudes. A simple model for the numerical characterization of spatiotemporal variability of the landfill emission was used and allowed us to separately quantify the temporal and spatial variability. This model showed that, in the landfill tested, the temporal distribution of CH4 emissions resulted more homogeneous than the spatial distribution. Other attributes of the temporal and spatial distributions of CH4 emissions were also established including the anisotropic nature of the spatial distribution and, contrastingly, the stochastic temporal variability of such emissions.

Three solid polymers; Kraton, Elvax, and Desmopan, previously suggested to be used in three-phase reactors, were evaluated for their ability to enhance oxygen transfer in a bubble column. These vectors were first characterized through determination of particle size distribution, surface roughness, specific surface area, density, void fraction and thermal stability. Oxygen transfer was then determined with a non-coalescing medium using polymer volume fractions from 0 to 75% in a 4 L bubble column operated at air flow rates ranging from 1 to 6 L/min. The results showed that the oxygen transfer was significantly improved in presence of 10 and 25% of Kraton and Elvax, compared with control experiment with no polymer. A maximum oxygen transfer improvement of 90%, compared with control, was observed with 10% Kraton. With Desmopan, no positive effect on oxygen transfer was observed regardless of the vector percentage used. Phase’s dispersion and oxygen transfer was further explored in presence of 10% Kraton. Gas holdup, Sauter mean bubble diameter and vector dispersion were characterized by means of high speed digital image analysis. The results showed that the enhancement of oxygen transfer mediated by Kraton was mainly caused by an increase of gas holdup and consequently of the gas/liquid surface area.

Metal–organic frameworks (MOFs) are a new class of hybrid porous materials built from organic linkers and inorganic metals, and have been used as adsorbent materials for the removal of heavy metals present in wastewater. While MOFs reduce the toxicity of wastewater by removing heavy metals, it has been reported that they can present some inhibitory effects, intrinsically or through the release of their metal cluster, although these aspects have only rarely been reported. In this work, the toxicity of [Co2(btec)(bipy)(DMF)2]n (MOF-Co), as well as its impact on the toxicity exerted by As(III), was examined using activated sludge in the treatment of synthetic wastewater as an experimental model. Toxicity was assessed through microrespirometry using a wide range of MOF-Co and As(III) concentrations in different configurations. In each case, inhibition was quantified, and the main kinetic parameters were determined. The obtained results confirmed the noncompetitive inhibitory effect of As(III), as well as a significant reduction (by up to 98%) in this inhibitory effect in the presence of MOF-Co. It is concluded that MOF-Co has no effect on activated sludge and might be an efficient material for the removal of heavy metals in wastewater, although further studies are required to establish efficient application and recovery methods.

An airlift reactor filled with Raschig rings in the downcomer section only was designed to allow for the characterization of biofilm biomass at several superficial liquid velocities. The reactor was inoculated with activated sludge and operated with synthetic wastewater containing acetate. After steady state was reached, the kinetic parameters of the process were determined at each superficial liquid velocity by an in-situ pulse respirometry method. Subsequently, the biofilm contained in the reactor was disaggregated, resuspended in a mineral medium, and reintroduced in the reactor, without Raschig rings, i.e., a standard airlift reactor. The kinetic parameters of the bioprocess were determined again, by the same respirometry method. That strategy allowed for the estimation of apparent and intrinsic kinetic parameters; i.e., with and without mass transfer limitation, respectively. Moreover, the method also allowed for the determination of the internal and external effectiveness factors and mass transfer resistances. The results shown that the hydrodynamic conditions had a strong effect on the kinetic parameters but none on the stoichiometric parameters. The external mass transfer accounted for up to 70% of the total mass transfer resistance. It is concluded that respirometry is a useful tool for the characterization of biofilms, in actual random packing reactors.

The Cuatro Cienegas Basin (CCB) in the Chihuahuan desert is characterized by the presence of over 500 ponds located in an endorheic basin. These ponds are subsaline ecosystems characterized by a low productivity and a particularly high sulfate concentration, comparable to marine environments. This study focused on assessing the main physicochemical parameters in these ponds along with the characterization of the CH4 dynamics through the determination of fluxes, dissolved CH4 concentrations, and net methanotrophic and methanogenic activity. Despite a sulfate concentration ranging from 1.06 to 4.73 g L−1, the studied ponds showed moderate but clear CH4 production and emission, which suggests that methanogenesis is not completely outcompeted by sulfate reduction. CH4 fluxes ranged from 0.12 to 0.98 mg m−2 d−1, which falls within the higher range of marine emissions and within the lower range reported for coastal saline lagoons and saline ponds. During summer, significant CH4 production in the oxic water column was observed. In addition to CH4, CO2 fluxes were determined at levels from 0.2 to 53 g m−2 d−1, which is within the range recorded for saline lakes in other parts of the world. Our results provide additional evidence that subsaline/saline aquatic ecosystems play an important role in the emission of greenhouse gases to the atmosphere.

Freshwater ecosystems are important contributors to the global greenhouse gas budget and a comprehensive assessment of their role in the context of global warming is essential. Despite many reports on freshwater ecosystems, relatively little attention has been given so far to those located in the southern hemisphere and our current knowledge is particularly poor regarding the methane cycle in non-perennially glaciated lakes of the maritime Antarctica. We conducted a high-resolution study of the methane and carbon dioxide cycle in a lake of the Fildes Peninsula, King George Island (Lat. 62°S), and a succinct characterization of 10 additional lakes and ponds of the region. The study, done during the ice-free and the ice-seasons, included methane and carbon dioxide exchanges with the atmosphere (both from water and surrounding soils) and the dissolved concentration of these two gases throughout the water column. This characterization was complemented with an ex-situ analysis of the microbial activities involved in the methane cycle, including methanotrophic and methanogenic activities as well as the methane-related marker gene abundance, in water, sediments and surrounding soils. The results showed that, over an annual cycle, the freshwater ecosystems of the region are dominantly autotrophic and that, despite low but omnipresent atmospheric methane emissions, they act as greenhouse gas sinks.

Considerable variability in methane production and emissions has been reported in mangroves, explained by methane inhibition and oxidation. In this study, soil pore waters were collected from mangrove forests located in the Gulf of California (Mexico) exposed to shrimp farm disturbance. The δ13C of dissolved inorganic carbon (DIC) and CH4 were analyzed along with the δ13C of the soil organic matter to assess the proportion of CO2 derived from methanogenesis, its main pathway, and the fraction of methane oxidized. We performed slurry incubation experiments to fit the isotope–mass balance approach. Very low stoichiometric ratios of CH4/CO2 were measured in pore waters, but isotope mass balances revealed that 30–70% of the total CO2 measured was produced by methanogenesis. Mangrove soils receiving effluent discharges shifted the main methanogenesis pathway to CO2 reduction because of an increase in refractory organic matter. Isotope–mass balances of incubations indicated that methane was mainly oxidized by anaerobic oxidation of methane (AOM) coupled to sulfate reduction, and the increase in recalcitrant organic matter should fuel AOM as humus serves as a terminal electron acceptor. Since methanogenesis in mangrove soils is strongly controlled by the oxygen supply provided by mangrove roots, conservation of the forest plays a crucial role in mitigating greenhouse gas emissions., CONACyT: PROFAPI, Spanish Ministry of Science and Innovation (Grant: CGL2014-54502) and CSIC (Grant: I-COOP+2020–COOPA20433) funded this research.

The impact of cultural eutrophication on carbon cycling in subtropical reservoirs was assessed using high-resolution measurements of dissolved gas concentration, atmospheric exchange, and uptake/production rates of methane, carbon dioxide, and oxygen. Seasonal measurements were performed in two reservoirs that pertain to the same hydrological basin but are drastically different in terms of allochthonous carbon input. These results were used to feed a mass balance model, from which a large number of overall parameters were determined to explicitly describe the dynamics and spatial attributes of the carbon cycle in the reservoirs. A single graphical representation of each reservoir was created to facilitate an overall appraisal of the carbon cycle. The impact of cultural eutrophication was profound and resulted in a complete redistribution of how the various bioprocesses participated in the methane, carbon dioxide, and oxygen cycles. Among several identified impacts of eutrophication, it was observed that while eutrophication triggered increased methane production, this effect was followed by a similar increase in methane emissions and methanotrophic rates, while gross primary production was depleted.

Methane (CH4) seepage; i.e., steady or episodic flow of gaseous hydrocarbons from subsurface reservoirs, has been identified as a significant source of atmospheric CH4. However, radiocarbon data from polar ice cores recently brought into question the magnitude of fossil CH4 seepage naturally occurring. In northern high latitudes, seepage of subsurface CH4 is impeded by permafrost and glaciers, which are under an increasing risk of thawing and melting in a globally warming world, implying the potential release of large stores of CH4 in the future. Resolution of these important questions requires a better constraint and monitoring of actual emissions from seepage areas. The measurement of these seeps is challenging, particularly in aquatic environments, because they involve large and irregular gas flowrates, unevenly distributed both spatially and temporally. Large macroseeps are particularly difficult to measure due to a lack of lightweight, inexpensive methods that can deployed in remote Arctic environments. Here, we report the use of a mobile chamber for measuring emissions at the surface of ice-free lakes subject to intense CH4 macroseepage. Tested in a remote Alaskan lake, the method was validated for the measurement of fossil CH4 emissions of up to 1.08 × 104 g CH4 m-2 d-1 (13.0 L m-2 min-1 of 83.4 % CH4 bubbles), which is within the range of global fossil methane seepage and several orders of magnitude above standard ecological emissions from lakes. In addition, this method allows for low diffusive flux measurements. Thus, the mobile chamber approach presented here covers the entire magnitude range of CH4 emissions currently identified, from those standardly observed in lakes to intense macroseeps, with a single apparatus of moderate cost.

Silver nanoparticles (AgNPs) are widely used in a high number of industrial applications and are becoming prevalent in wastewater effluents. It is known that AgNPs exert a toxic effect on activated sludge processes, but to what extent and under which conditions are still largely unknown. The inhibitory effect of AgNPs on a synthetic wastewater treatment process was tested using pulse microrespirometry (i.e., a pulse of substrate is injected into a microreactor system). Several conditions were tested, including AgNP concentration, substrate to biomass ratio (S0/X0) and exposure time. The inhibitory effects were quantified through the percentage of inhibition of the exogenous and endogenous respiration rates as well as through determination of the half saturation constant (KS), inhibition constant (KI) and maximum oxygen uptake rate (OURmax). The results indicated that AgNPs exert uncompetitive inhibition and the concentration that caused a 50% of inhibition (IC50) of the exogenous respiration rate was 3.32 ± 0.16 mg L−1. The inhibitory effect of AgNPs on the endogenous respiration was relatively lower, with an IC50 of 7.12 ± 0.11 mg L−1. Overall, it was observed that an increase in the S0/X0 ratio resulted in higher inhibition and that the inhibitory effects of AgNPs decreased with exposure time.

Photoreactors are now largely used in a span of applications but are complex systems that would still benefit from a better constraint of their kinetic behaviour. Among others, the determination of the Photosynthetic-Irradiance (PI) curve in photoreactors, which describes the correlation between light irradiance and activity of the algal or algal-bacterial culture, is of utmost importance for modelling, optimization, and control purposes. Habitually, PI curves in photoreactors are determined through incubation done under a range of irradiance, and even if many remarkable advances have been achieved in the methods applied, there is still a need for a simple, robust, polyvalent and fast method. We present here a method based on a modified respirometer, commercially available, that allows to measure the dissolved oxygen production/uptake, simultaneously in 24 replicates under a controlled irradiance. This so-called photo-microrespirometric method, was applied successfully to the determination of PI curves of a microalgal-bacterial culture obtained from a pilot-scale pond treating the liquid fraction of an anaerobic digestate. The PI curves obtained, in a few hours of experimental work, were well fitted by the Bernard-Remond's kinetic model. In addition to PI curves, the method allowed for the quantification of the inhibitory effect of dissolved oxygen as well as the response time of the photoactivation and photoinhibition.

Microrespirometry is a recently developed method that combines classical respirometry and microreactor systems, for the characterization of microbial cultures. This method, which allows multiple simultaneous replicates from a single low-volume biomass sample, can improve and simplify the model calibration exercise by providing more and better experimental data. To follow up on the interest in microrespirometry, two model wastewater treatment processes were set up and used for model calibration: an aerobic degradation of 4-chlorophenol by acclimated sludge, and a synthetic wastewater treatment by activated sludge, which were well described by a Haldane model and a modified ASM3 model, respectively. For each process, the model parameters were estimated by model fitting, minimizing the objective function for each replicate independently, and minimizing the objective function for all replicates simultaneously (multiresponse approach). Parameter confidence intervals were determined for all parameter estimates, and the impacts of measurement errors, number of replicates, and parameter correlation were assessed. It was observed that the multiresponse approach presents several advantages, including single-step parameter estimation, independent of the number of replicates, and determination of confidence intervals that include the main sources of uncertainty. It was concluded that microrespirometry is a high-throughput and convenient method for model calibration.

Anaerobic oxidation of methane (AOM) is a biological process that plays an important role in reducing the CH4 emissions from a wide range of ecosystems. Arctic and sub-Arctic lakes are recognized as significant contributors to global methane (CH4) emission, since CH4 production is increasing as permafrost thaws and provides fuels for methanogenesis. Methanotrophy, including AOM, is critical to reducing CH4 emissions. The identity, activity, and metabolic processes of anaerobic methane oxidizers are poorly understood, yet this information is critical to understanding CH4 cycling and ultimately to predicting future CH4 emissions. This study sought to identify the microorganisms involved in AOM in sub-Arctic lake sediments using DNA- and phospholipid-fatty acid (PLFA)- based stable isotope probing. Results indicated that aerobic methanotrophs belonging to the genus Methylobacter assimilate carbon from CH4, either directly or indirectly. Other organisms that were found, in minor proportions, to assimilate CH4-derived carbon were methylotrophs and iron reducers, which might indicate the flow of CH4-derived carbon from anaerobic methanotrophs into the broader microbial community. While various other taxa have been reported in the literature to anaerobically oxidize methane in various environments (e.g. ANME-type archaea and Methylomirabilis Oxyfera), this report directly suggest that Methylobacter can perform this function, expanding our understanding of CH4 oxidation in anaerobic lake sediments.

It is commonly assumed that methane (CH4) released by lakes into the atmosphere is mainly produced in anoxic sediment and transported by diffusion or ebullition through the water column to the surface of the lake. In contrast to that prevailing idea, it has been gradually established that the epilimnetic CH4 does not originate exclusively from sediments but is also locally produced or laterally transported from the littoral zone. Therefore, CH4 cycling in the epilimnion and the hypolimnion might not be as closely linked as previously thought. We utilized a high-resolution method used to determine dissolved CH4 concentration to analyze a Siberian lake in which epilimnetic and hypolimnetic CH4 cycles were fully segregated by a section of the water column where CH4 was not detected. This layer, with no detected CH4, was well below the oxycline and the photic zone and thus assumed to be anaerobic. However, on the basis of a diffusion-reaction model, molecular biology, and stable isotope analyses, we determined that this layer takes up all the CH4 produced in the sediments and the deepest section of the hypolimnion. We concluded that there was no CH4 exchange between the hypolimnion (dominated by methanotrophy and methanogenesis) and the epilimnion (dominated by methane lateral transport and/or oxic production), resulting in a vertically segregated lake internal CH4 cycle.

Microorganisms in aerobic granules formed in sequencing batch reactors (SBR) remove contaminants, such as xenobiotics or dyes, from wastewater. The granules, however, are not stable over time, decreasing the removal of the pollutant. A better understanding of the granule formation and the dynamics of the microorganisms involved will help to optimize the removal of contaminants from wastewater in a SBR. Sequencing the 16S rRNA gene and internal transcribed spacer PCR amplicons revealed that during the acclimation phase the relative abundance ofAcinetobacterreached 70.8%. At the start of the granulation phase the relative abundance ofAgrobacteriumreached 35.9% and that ofDipodascus89.7% during the mature granule phase. Fluffy granules were detected on day 43. The granules with filamentous overgrowth were not stable and they lysed on day 46 resulting in biomass wash-out. It was found that the reactor operation strategy resulted in stable aerobic granules for 46 days. As the reactor operations remained the same from the mature granule phase to the end of the experiment, the disintegration of the granules after day 46 was due to changes in the microbial community structure and not by the reactor operation.

Aquatic ecosystems are subject to spatiotemporal variations that are important to quantify and understand for a proper assessment of their diversity and complexity. The objective of the present study was to develop a simple model that gives a numerical value to homogeneity and other spatiotemporal attributes for an easier analysis of aquatic ecosystem structure. The model allows for the comparison among different ecosystems, or different periods of time or zones of a given aquatic ecosystem. The model developed sets a numerical value to homogeneity, establishes the fraction of the ecosystem that contains a given percentage of the total amount of a compound, quantifies the fraction of the aquatic ecosystem in which no detectable levels of the measured compound are found, identifies the fraction of the ecosystem that represents an adequate habitat for a given process, and defines a simplified bidimensional vector of heterogeneity. This model is applicable to the two main maps used in the field of limnology: maps showing a particular parameter over two spatial dimensions, and maps showing a particular parameter over one spatial and one temporal dimension. The model was tested with different parameters obtained from three contrasting aquatic ecosystems, a highly polluted Mexican highland reservoir, a naturally acidic German bog lake, and a mesotrophic Patagonian lake.

An open dynamic chamber for the continuous monitoring of diffusive and ebullitive fluxes of methane (CH4) in aquatic ecosystems was designed and developed. This method is based on a standard floating chamber in which a well-defined carrier gas flows. The concentration of CH4 is measured continuously at the outlet of the chamber, and the flux is determined from a mass balance equation. The method was carefully tested in a laboratory and was subsequently applied to two lakes, in Mexico, with contrasting trophic states. We show here that the method allows for the continuous quantification of CH4 diffusive flux higher than 25 × 10-6 g m-2 h-1, the determination of ebullitive flux, and the individual characterization of bubbles larger than 1.50-1.72 mm in diameter. The method was also applied to determine carbon dioxide emissions (CO2). In that case, the method was less sensitive but allowed for the characterization of diffusive fluxes higher than 10 mg CO2 m-2 h-1 and of bubbles larger than 5.3-8.4 mm in diameter. This high-throughput method can be adapted to any gas detector at low cost, making it a convenient tool to better constrain greenhouse gas emission from freshwater ecosystems.

Mexico City is a large city, populated by 8.8 million inhabitants. This population density, combined with poor wastewater management, results in aquatic ecosystems receiving a large volume of wastewater which may promote methane (CH4) emission. We measured water quality and CH4 emission from 11 aquatic ecosystems in Mexico City during 1 year, including reservoirs, rivers, lakes, canals and chinampas (system of floating garden on shallow lakes). The total CH4 emission from aquatic ecosystems was estimated as 3679 Mg CH4 year−1, which represents 3.5 % of the annual CH4 emission of Mexico City. The main contributors are chinampas (33 %), followed by lakes (27 %), reservoirs (19 %), rivers (12 %) and canals (9 %). Water quality indicators were positively correlated with CH4 emission, therefore a decrease in untreated wastewater discharge may result in a significant reduction of the greenhouse gas footprint of Mexico City, after a transitional period during which the organic content of the sediment would be degraded.

Metabolic activities of microalgae and heterotrophic bacteria were characterized in terms of dissolved O2 uptake and production rates under dark and light conditions, assessing the contribution of both microbial groups to the O2 balance during wastewater treatment. Up to 13 kinetic and stoichiometric parameters were determined, allowing a quantitative description of the O2 production and uptake dynamics. Under dark conditions, the maximum specific O2 uptake rates for microalgae and bacteria were 14.73 ± 2.02 mgO2 gVSS−1 h−1 and 2.37 ± 1.52 mgO2 gVSS−1 h−1, respectively. Microalgae were therefore the largest O2 consumers under dark conditions, being responsible for up to 86 % of the total heterotrophic respiration. Under light conditions (photosynthetic metabolism for microalgae and heterotrophic metabolism for bacteria), microalgae supported a maximum specific O2 production rate of 13.76 ± 1.48 mgO2 gVSS-1 h-1, while bacteria supported a maximum specific O2 uptake of 2.37 ± 1.52 mgO2 gVSS-1 h-1. The oxygenation performance of the microalgal community was therefore superior to the O2 respiration of heterotrophic bacteria under light conditions. The kinetic characterization performed provides critical information about the photosynthetic oxygenation potential, microbial growth and heterotrophic O2 uptake, which is essential for design, optimization, and modeling of wastewater treatment processes.

Key pathways for the anaerobic oxidation of methane (AOM) have remained elusive, particularly in organic rich ecosystems. In this work, the occurrence of AOM driven by humus-catalyzed dissimilatory iron reduction was investigated in sediments from a coastal mangrove swamp. Anoxic sediment incubations supplied with both goethite (α-FeOOH) and leonardite (humic substances (HS)) displayed an average AOM rate of 10.7 ± 0.8 μmol CH4 cm−3 day−1, which was 7 and 3 times faster than that measured in incubations containing only goethite or HS, respectively. Additional incubations performed with 13C-methane displayed Pahokee Peat HS-mediated carbonate precipitation linked to 13CH4 oxidation and ferrihydrite reduction (~1.3 μmol carbonate cm−3 day−1). These results highlight the role of HS on mitigating greenhouse gases released from wetlands, not only by mediating the AOM process, but also by enhancing carbon sequestration as inert minerals (calcite, aragonite and siderite).

Inhibition of nitrification by sulfide was assessed using sludge obtained from a steady-state nitrifying reactor. Independent batch activity assays were performed with ammonium and nitrite as substrate, in order to discriminate the effect of sulfide on ammonium and nitrite oxidation. In the absence of sulfide, substrate affinity constants (K S,NH4 = 2.41 ± 0.11 mg N/L; K s, NO2 = 0.74 ± 0.03 mg N/L) and maximum specific rates (q max,NH4 = 0.086 ± 0.008 mg N/mg microbial protein h; q max,NO2 = 0.124 ± 0.001 mg N/mg microbial protein h) were determined. Inhibition of ammonium oxidation was no-competitive (inhibition constant (K i , NH4 ) of 2.54 ± 0.12 mg HS(-)-S/L) while inhibition of nitrite oxidation was mixed (competitive inhibition constant (K' i , NO2 ) of 0.22 ± 0.03 mg HS(-)-S/L and no-competitive inhibition constant (K i , NO2 ) of 1.03 ± 0.06 mg HS(-)-S/L). Sulfide has greater inhibitory effect on nitrite oxidation than ammonium oxidation, and its presence in nitrification systems should be avoided to prevent accumulation of nitrite. By simulating the effect of sulfide addition in a continuous nitrifying reactor under steady-state operation, it was shown that the maximum sulfide concentration that the sludge can tolerate without affecting the ammonium consumption efficiency and nitrate yield is 1 mg HS(-)-S/L.

Methanotrophic bacteria play an important role oxidizing a significant fraction of methane (CH4) produced in lakes. Aerobic CH4 oxidation depends mainly on lake CH4 and oxygen (O2) concentrations, in such a manner that higher MO rates are usually found at the oxic/anoxic interface, where both molecules are present. MO also depends on temperature, and via methanogenesis, on organic carbon input to lakes, including from thawing permafrost in thermokarst (thaw)-affected lakes. Given the large variability in these environmental factors, CH4 oxidation is expected to be subject to large seasonal and geographic variations, which have been scarcely reported in the literature. In the present study, we measured CH4 oxidation rates in 30 Alaskan lakes along a north-south latitudinal transect during winter and summer with a new field laser spectroscopy method. Additionally, we measured dissolved CH4 and O2 concentrations. We found that in the winter, aerobic CH4 oxidation was mainly controlled by the dissolved O2 concentration, while in the summer it was controlled primarily by the CH4 concentration, which was scarce compared to dissolved O2. The permafrost environment of the lakes was identified as another key factor. Thermokarst (thaw) lakes formed in yedoma-type permafrost had significantly higher CH4 oxidation rates compared to other thermokarst and non-thermokarst lakes formed in non-yedoma permafrost environments. As thermokarst lakes formed in yedoma-type permafrost have been identified to receive large quantities of terrestrial organic carbon from thaw and subsidence of the surrounding landscape into the lake, confirming the strong coupling between terrestrial and aquatic habitats and its influence on CH4 cycling.

Uncertainties in the magnitude and seasonality of various gas emission modes, particularly among different lake types, limit our ability to estimate methane (CH4) and carbon dioxide (CO2) emissions from northern lakes. Here we assessed the relationship between CH4 and CO2 emission modes in 40 lakes along a latitudinal transect in Alaska to lakes' physicochemical properties and geographic characteristics, including permafrost soil type surrounding lakes. Emission modes included direct ebullition, diffusion, storage flux, and a newly identified ice-bubble storage (IBS) flux. We found that all lakes were net sources of atmospheric CH4 and CO2, but the climate warming impact of lake CH4 emissions was 2 times higher than that of CO2. Ebullition and diffusion were the dominant modes of CH4 and CO2 emissions, respectively. IBS, ~10% of total annual CH4 emissions, is the release to the atmosphere of seasonally ice-trapped bubbles when lake ice confining bubbles begins to melt in spring. IBS, which has not been explicitly accounted for in regional studies, increased the estimate of springtime emissions from our study lakes by 320%. Geographically, CH4 emissions from stratified, mixotrophic interior Alaska thermokarst (thaw) lakes formed in icy, organic-rich yedoma permafrost soils were 6-fold higher than from non-yedoma lakes throughout the rest of Alaska. The relationship between CO2 emissions and geographic parameters was weak, suggesting high variability among sources and sinks that regulate CO2 emissions (e.g., catchment waters, pH equilibrium). Total CH4 emission was correlated with concentrations of soluble reactive phosphorus and total nitrogen in lake water, Secchi depth, and lake area, with yedoma lakes having higher nutrient concentrations, shallower Secchi depth, and smaller lake areas. Our findings suggest that permafrost type plays important roles in determining CH4 emissions from lakes by both supplying organic matter to methanogenesis directly from thawing permafrost and by enhancing nutrient availability to primary production, which can also fuel decomposition and methanogenesis.

Anaerobic oxidation of methane (AOM) is a microbial process that consumes dissolved methane (CH4) in anoxic sediments and soils and mitigates CH4 release to the atmosphere. The degree to which AOM limits global biospheric CH4 emissions is not fully understood. In marine sediments, where the process was first described, AOM is responsible for oxidizing >90% of the CH4 produced. More recently, AOM has been observed in soils, peatlands, and freshwater ecosystems. In lakes, where sediment anoxia, organic carbon turnover, and CH4 production are common, AOM is not well studied but could represent a significant CH4 sink and constraint on emissions. Here, we present evidence for the occurrence of AOM in the sediment of thirteen lakes that span a global climatic and trophic gradient. We further quantified and modeled AOM patterns and studied potential microbial controls of AOM using laboratory incubations of sediment and stable isotope measurements in three of the thirteen lakes. We demonstrate that AOM is widespread in freshwater lake sediments and accounts for 29%–34% (95% confidence interval) of the mean total CH4 produced in surface and near-surface lake sediments.

Net methane (CH4) emission from lakes depends on two antagonistic processes: CH4 production (methanogenesis) and CH4 oxidation (methanotrophy). It is unclear how climate warming will affect the balance between these processes, particularly among lakes of different trophic status. Here we show that methanogenesis is more sensitive to temperature than methanotrophy, and that eutrophication magnifies this temperature sensitivity. Using laboratory incubations of water and sediment from ten tropical, temperate and subarctic lakes with contrasting trophic states, ranging from oligotrophic to hypereutrophic, we explored the temperature sensitivity of methanogenesis and methanotrophy. We found that both processes presented a higher temperature sensitivity in tropical lakes, followed by temperate, and subarctic lakes; but more importantly, we found that eutrophication triggered a higher temperature sensitivity. A model fed by our empirical data revealed that increasing lake water temperature by 2 °C leads to a net increase in CH4 emissions by 101–183% in hypereutrophic lakes and 47–56% in oligotrophic lakes. We conclude that climate warming will tilt the CH4 balance towards higher lake emission and that this impact will be exacerbated by the eutrophication of the lakes.

Activated sludge processes are often inhibited by nickel, cadmium, and cobalt. The inhibitory effect of these heavy metals on a synthetic wastewater treatment process was tested through pulse microrespirometry; i.e., pulse of substrate injected in a microreactor system. The inhibitory effect was tested under different conditions including the heavy metals, substrate and biomass concentrations, and exposure time. The inhibitory effect was quantified by the percentage of inhibition, half saturation constant (KS), inhibition constant (KI), and maximum oxygen uptake rate (OURmax). The results indicated that, in a range of concentration from 0 to 40 mg L−1, the three heavy metals exerted an uncompetitive and incomplete inhibitory effect, with a maximum inhibition of 67, 57, and 53% for Ni, Co, and Cd, respectively. An increase of the biomass concentration by 620% resulted in a decrease of the inhibition by 47 and 69% for Co and Cd, respectively, while no effect was observed on Ni inhibition. An increase of the substrate concentration by 87% resulted in an increase of the inhibition by 24, 70, and 47% for Ni, Co and Cd, respectively. In the case of nickel and cadmium, an increase in the exposure time to the heavy metals also increased the inhibition.

Toxic compounds, such as 4-chlorophenol (4-CP), which is a common pollutant in wastewater, are removed efficiently from sequencing batch reactors (SBRs) by microorganisms. The bacterial community in aerobic granules formed during the removal of 4-CP in a SBR was monitored for 63days. The SBR reactor was operated with a constant filling and withdrawal time of 7 and 8min and decreasing settling time (30, 5, 3 and 2min) to induce the formation of aerobic granules. During the acclimation period lasting 15days (30min settling time) had a strong effect on the bacterial community. From day 18 onwards, Sphingobium and Comamonadaceae were detected. Rhizobiaceae were dominant from day 24 to day 28 when stable aerobic granules were formed. At day 35, fluffy granules were formed, but the bacterial community structure did not change, despite the changes in the reactor operation to inhibit filamentous bacteria growth. This is the first report on changes in the bacterial community structure of aerobic and fluffy granules during granulation process in a reactor fed with 4-CP and the prediction of its metabolic pathways.

The assessment of microbial processes is often done in Microbioreactor systems (MBRs), which allow for parallel cultivation in multiple independent wells. MBRs often include dissolved oxygen sensors, which are convenient for process characterization through oxygen uptake rate and other respirometric determinations. In order to assess respirometric potential of MBRs, a complete assessment of the DO fluorescent quenching sensors was done, showing that they presented a typical error of 0.56%, a signal to noise ratio of 189, a response time from 5.7 to 7.2 s and no drift over a period of 24 h. Then, K L a in the MBR was measured with different cassette and cap designs, liquid volumes, agitation rates, gas flow rates, temperatures and ionic strengths. K L a ranged from 8 to 90 h −1 , with a standard deviation between replicates from 2.8 to 17.5%. From these results and a numerical simulation, it was shown that the MBR tested allow the determination of oxygen uptake rates in a range from 0.038 to 3390 mg L −1 h −1 , with a determination error less than 15%. Besides OUR determination, it was concluded that the MBR tested is also a convenient tool for dynamic pulse respirometry methods, based on experimental confirmation with four different cultures.

We have developed a novel microrespirometric method to characterize the inhibitory effects due to heavy metals on activated sludge treatment. This method was based on pulse dynamic respirometry and involved the injection of several pulses of substrate and inhibitors, of increasing concentration. Furthermore, we evaluated the inhibitory effects of heavy metals (copper and zinc), substrate and biomass concentrations, and pH on activated sludge activity. While higher biomass concentrations counteracted the inhibitory effects of both copper and zinc, higher substrate concentrations predominantly augmented the inhibitory effect of copper but no significant change in inhibition by zinc was observed. pH had a clear but relatively small effect on inhibition, partially explained by thermodynamic speciation. We determined the key kinetic parameters; namely, the half saturation constant (K S ) and the maximum oxygen uptake rate (OUR max ). The results showed that higher heavy metal concentrations substantially decreased K S and OUR max suggesting that the inhibition was uncompetitive.

Respirometry, which consists in the measurement of the oxygen uptake rate, is a method commonly used to determine kinetic and stoichiometric parameters of biological processes. In the present work, a novel microrespironetry method, which involves standard respirometry procedures but in a microreactor array, was developed and assessed, based on a standard commercial apparatus. First, the volumetric oxygen transfer coefficient ( K L a ), which is important for the interpretation of respirometric data, was determined under an exhaustive set of experimental conditions. K L a ranged from 2.2 to 48.0 h −1 , which is similar to K L a typically found in standard respirometers. Then, the method was assessed through the determination of the maximum specific growth rate, the half-saturation constant and the growth yield of axenic and mixed cultures of autotrophic and heterotrophic bacteria. The selected cultures were Pseudomonas putida F1, Nitrobacter winogradskyi , an activated sludge and a nitrifying consortium. Additionally to reporting parameters for these cultures, this report shows that the microrespirometry method allowed for the determination of stoichiometric and kinetic parameters. Simultaneous tests done with a single culture sample, made possible by the microreactor array, allowed parameters determination with a lower standard error than observed with traditional respirometry and with much less experimental effort.

The literature concerning methane (CH4) emissions from temperate and boreal lakes is extensive, but emissions from tropical and subtropical lakes have been less documented. In particular, methane emissions from Mexican lakes, which are often polluted by anthropogenic carbon and nutrient inputs, have not been reported previously. In this work, methane emissions from six Mexican lakes were measured, covering a broad range of organic inputs, trophic states, and climatic conditions. Methane emissions ranged from 5 to 5,000 mg CH4 m−2 day−1. Water samples from several depths in each lake were analyzed for correlation between water quality indicators and methane emissions. Trophic state and water quality indexes were most strongly correlated with methane fluxes. The global methane flux from Mexican freshwater lakes was estimated to be approximately 1.3 Tg CH4 year−1, which is about 20% of methane and 4.4% of total national greenhouse gas emissions. Data for untreated wastewater releases to the environment gave an emission factor of 0.19 kg CH4 kg−1 of Biochemical Oxygen Demand, which is superior to that previously estimated by the IPCC for lake discharges. Thus, the large volume of untreated wastewater in Mexico implies higher methane emission than previously estimated.

The sub-Antarctic Magellanic ecoregion is a part of the world where ecosystems have been understudied and where the CH4 cycling and emissions in lakes has not ever been reported. To fill that knowledge gap, a lake and a reservoir located at 53°S were selected and studied during three campaigns equally distributed over one year. Among the parameters measured were CH4 and CO2 emissions, as well their dissolved concentrations in the water column, which were determined with high spatial resolution. No ebullition was observed and the CH4 flux ranged from 0.0094 to 4.47mmolm-2d-1 while the CO2 flux ranged from -22.95 to 35.68mmolm-2d-1. Dissolved CH4 concentrations varied over more than four orders of magnitude (0.025-128.75μmolL-1), and the dissolved carbon dioxide ranged from below the detection limit of our method (i.e., 0.15μmolL-1) to 379.09μmolL-1. The high spatial resolution of the methods used enabled the construction of bathymetric maps, surface contour maps of CH4 and CO2 fluxes, and transect contour maps of dissolved oxygen, temperature, and dissolved greenhouse gases. Overall, both lakes were net greenhouse gas producers and were not significantly different from temperate lakes located at a similar northern latitudes (53°N), except that ebullition was never observed in the studied sub-Antarctic lakes.

Biodegradation of phenolic compounds in bioreactors is well documented, but the changes in the bacterial populations dynamics during degradation were not that often. A glass bubble column used as reactor was inoculated with activated sludge, spiked with 2-chlorophenol, phenol and m-cresol after 28 days and maintained for an additional 56 days, while the 16S rRNA gene from metagenomic DNA was monitored. Proteobacteria (68.1%) dominated the inoculum, but the bacterial composition changed rapidly. The relative abundance of Bacteroidetes and Firmicutes decreased from 4.8 and 9.4 to

Two-phase partitioning bioreactors (TPPBs) are based on the addition of an organic phase, often called vector, to a bioreactor in order to increase mass transfer of oxygen or gaseous substrates from the gaseous phase to the aqueous phase. In TPPBs, like in any other reactor design, the characterization of the bioprocess is often required for design, control, and operation purposes. Pulse respirometry is a method that allows for microbial processes characterization through the determination of several stoichiometric and kinetic parameters with relatively little experimental effort. Despite its interest and its previous application in countless applications, pulse respirometry has never been applied in TPPBs. In this work, pulse respirometry was assessed in a model TPPB degrading terephthalic acid and using Elvax™ as solid vector to enhance oxygen transfer. The results indicated that the addition of 10 to 20 % Elvax increased oxygen transfer by up to 97 %, compared to control with no vector. Pulse respirometry was successfully applied and allowed for the determination of the growth yield, the substrate affinity constant, and the maximum growth rate, within other. It is concluded that pulse respirometry is a useful method, not only for the characterization of processes in TPPBs but also for the selection of a vector within several brands commercially available.

Respirometry consists in the measurement of the biological oxygen consumption rate under well-defined conditions and has been used for the characterization of countless biological processes. In the field of biotechnology and applied microbiology, several respirometry methods are commonly used for the determination of process parameters. Dynamic and static respirometry, which are based on oxygen measurements with or without continuous aeration, respectively, are the methods most commonly used. Additionally to several respirometry methods, different methods have also been developed to retrieve process parameters from respirometric data. Among them, methods based on model fitting and methods based on the injection of substrate pulse at increasing concentration are commonly used. An important question is then; what respirometry and data interpretation methods should be preferably used? So far, and despite a growing interest for respirometry, relatively little attention has been paid on the comparison between the different methods available. In this work, both static and dynamic respirometry methods and both interpretation methods; model fitting and pulses of increasing concentration, were compared to characterize an autotrophic nitrification process. A total of 60 respirometry experiments were done and exhaustively analysed, including sensitivity and error analyses. According to the results obtained, the substrate affinity constant (K S ) was better determined by static respirometry with pulses of increasing concentration and the maximum oxygen uptake rate (OUR ex.max ) was better determined by dynamic respirometry coupled to fitting procedure. The best method for combined K S and OUR ex.max determination was static respirometry with pulses of increasing concentration.

Background Biological wastewater treatment by nitrification is widely used; however information on inhibition of nitrification by sulfide is still scarce. The aim of this study was to evaluate the inhibitory effect of different initial sulfide concentrations on ammonium and nitrite oxidizing processes. Results In the absence of sulfide, nitrification was completed after 24 h with an ammonium consumption efficiency (ENH4+) of 100.0 ± 2.1% and an ammonium to nitrate conversion yield (YNO3-) of 0.90 ± 0.01 g NO3--N g–1 NH4+-N consumed. At sulfide concentrations lower than 13.5 ± 0.7 mg HS--S L–1, ENH4+ was maintained at 100% after 60 h. At sulfide concentrations ranging from 3.1 to 112.0 mg HS--S L–1, the YNO3- decreased from 0.9 to 0.3 due to an accumulation of nitrite, whereas specific rates decreased by 51 to 92% for NH4+ consumption and by 77 to 97% for NO3- production. The IC50 value (concentration causing 50% inhibition) for ammonium and nitrite oxidation was 2.6 ± 0.3 and 1.2 ± 0.2 mg HS--S L–1, respectively. Conclusion Sulfide provoked an inhibitory effect on both ammonium and nitrite oxidizing processes, nitrite oxidation being the most affected step. This information is relevant for wastewater treatment, indicating that the presence of sulfide in effluents even at low concentration might strongly alter the nitrifying activity of activated sludge and provoke nitrite accumulation.© 2012 Society of Chemical Industry

Dissolved gas concentration in environmental water samples is usually determined by headspace equilibration (HE) techniques followed by laboratory analyses. This method generally causes a time delay between field sampling and measurements that (i) impedes feedback of results that would otherwise inform field sampling strategies, (ii) may affect the precision of the results due to biological activity or leakage, and (iii) may require logistically complex procedures for transport and storage of samples. The development of an on-site measurement technique combined with headspace equilibration methods would be beneficial, especially for multiple field measurements in remote areas. In this article, we present a method, based on headspace equilibration but using infrared tunable diode laser absorption spectroscopy (HE-TDLAS) that allows immediate determination of dissolved gas concentrations in environmental water. HE-TDLAS method was first tested in the laboratory and compared with a gas chromatography technique. No significant difference was observed between both methods. HETDLAS method was then used during field experiments for the measurement of dissolved methane concentration in 110 water samples from several Alaskan lakes. Dissolved methane concentrations ranging from 0.014 to 20 mg L−1 were successfully measured with standard errors of 28% to 2%, respectively. A quantification limit of 13.6 mg L−1 and an accuracy of 3.6% were established from the statistical analysis. Results suggest that the HETDLAS method is applicable to many aquatic ecosystems, including wastewater treatment facilities, landfills, rice paddies, and freshwater ecosystems, in which dissolved methane typically occurs in the µg to mg L−1 range.

The hexadecane (HXD) transfer rate (HTR) and the oxygen transfer rate (OTR) were simultaneously evaluated as a single engineering criterion to enhance the production of an oil-degrading bacterial consortium. In order to accomplish the task, a 10-L three-phase airlift bioreactor (ALB) was used. Oxygen transfer volumetric coefficient ( k L a O 2 ) values of 25–49 h−1 were found for several superficial gas velocities (Ug 0.15–2.7 cm s−1). HXD transfer volumetric coefficient (kLaHXD) values of 0.005–0.041 h−1 were obtained for the same range of Ug values. OTR and HTR were calculated as the product of k L a O 2 or kLaHXD and the respective concentration gradient. HXD transfer parameters were evaluated by using an early reported novel technique. During 14 days culture, using constant Ug values, the ratio of HTR to OTR (HTR/OTR) never reached the stoichiometric ratio (0.25 ± 0.05 g HXD (g O2)−1). However, the productivity at the higher assayed constant Ug (2.7 cm s−1) was as good as 1.02 ± 0.03 g SS (L d)−1. We propose a variable Ug strategy that consumes 33% less energy than a higher constant Ug strategy to achieve the same yield and productivity. In this study, the oil-degrading consortium, able to remediate contaminated soils and water, productivity was successfully enhanced with simultaneous HXD and oxygen transfer considerations.

Liming or vermicomposting eliminates pathogens from wastewater sludge, but might affect CO2 and N2O emissions when added to soil. Soil incubated at 40%, 60%, 80% and 100% of its water holding capacity (WHC) was amended with limed or unlimed wastewater sludge, vermicompost or inorganic fertilizer, while emissions of N2O and CO2 and mineral N concentrations were monitored in aerobic incubation experiment for 7 days. Application of unlimed wastewater sludge significantly increased the emission of CO2 compared to the unamended soil, but not the other treatments except when unlimed wastewater sludge was added to soil incubated at 60% WHC. The emission of CO2, was generally largest in soil incubated at 60% WHC and lowest in soil incubated at 100% WHC. The emission of N2O after 1 day was significantly larger in soil amended with unlimed wastewater sludge compared to the other treatments, but not when soil was incubated at 100% WHC. The emission of N2O increased with increased soil water content. The concentration of NH4+ was largest in soil amended with limed or unlimed wastewater sludge and lowest in the unamended soil and soil water content had no clear effect on it. In soil incubated at 40%, 60% and 80% WHC, the largest amount of NO3− was found in soil amended with inorganic fertilizer and vermicompost and the lowest in the soil amended with unlimed wastewater sludge. The concentration of NO3− in soil decreased when the soil water content increased in all treatments, except in the soil amended with unlimed wastewater sludge. It was found that water content affected the emission of CO2 of N2O and the concentration of NO3−, but not the amount of NH4+ and NO2− in soil. Application of unlimed wastewater sludge increased the emissions of CO2 and N2O and the concentrations of NH4+, but decreased the amount of NO3− in soil.

BACKGROUND: The potential of organic liquid solvents and solid polymers to enhance CH4 mass transfer was studied in a twophase partition internal loop airlift reactor operated with gas recirculation under biotic and abiotic conditions. A preliminary screening of the most common liquid solvents (silicone oil 20 cSt, silicone oil 200 cSt and 2,2,4,4,6,8,8-heptametilnonane) and solid polymers (Kraton® G6157, Desmopan® DP9370A and Elvax® 880) resulted in the selection of silicone oil 200 cSt (S200) and Desmopan DP9370A (D9370) for further investigation based on their high affinity for CH4, biocompatibility and nonbiodegradability. RESULTS: Under abiotic conditions, the increase in gas recirculation from 0 to 1 vvm in the absence of a transfer vector increased the overall mass transfer coefficient for oxygen (kLa) by 195%. The presence of S200 and D9370 at 10% (v/v) under operation at 1 vvm of gas recirculation rate mediated an increase in kLa of 100% and 136%, respectively. Likewise, the increase in gas recirculation from 0 to 1 vvm in the absence of a transfer vector and in the presence of S200 during the continuous biodegradation of methane at 3% (v/v) and 7.3 min empty bed residence time resulted in increases in CH4 removal and CO2 production rates of 47% and 36%, respectively. Nevertheless, no significant enhancement in CH4 removal due to the presence of 10% of Desmopan or silicone oil was recorded under operation at 1 vvm. CONCLUSIONS: These results suggest that microbial activity rather than mass transport could be the limiting step in biological CH4 abatement in this system, contrary to that observed in previous studies with stirred tank reactors, where the organic phase addition increased methane biodegradation. c � 2010 Society of Chemical Industry Supporting information may be found in the online version of this article.