Frederic Thalasso

Methane emissions from Mexican freshwater bodies: correlations with water pollution

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 5,000xa0mg CH4xa0m−2xa0day−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 CH4xa0year−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 0.19xa0kg CH4xa0kg−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.

Greenhouse gas emissions from stabilization ponds in subtropical climate

Waste stabilization ponds (WSPs) are a cost-efficient method to treat municipal and non-toxic industrial effluents. Numerous studies have shown that WSPs are a source of greenhouse gas (GHG). However, most reports concerned anaerobic ponds (AP) and few have addressed GHG emissions from facultative (FP) and aerobic/maturation ponds (MPs). In this paper, GHG emissions from three WSP in series are presented. These WSPs were designed as anaerobic, facultative and aerobic/maturation and were treating agricultural wastewater. CH4 fluxes from 0.6±0.4 g CH4 m−2 d−1 in the MP, to 7.0±1.0 g CH4 m−2 d−1 in the (AP), were measured. A linear correlation was found between the loading rates of the ponds and CH4 emissions. Relatively low CO2 fluxes (0.2±0.1 to 1.0±0.8 g CO2 m−2 d−1) were found, which suggest that carbonate/bicarbonate formation is caused by alkaline pH. A mass balance performed showed that 30% of the total chemical oxygen demand removed was converted to CH4. It has been concluded that the WSP system studied emits at least three times more GHG than aerobic activated sludge systems and that the surface loading rate is the most important design parameter for CH4 emissions.

Comparison of static and dynamic respirometry for the determination of stoichiometric and kinetic parameters of a nitrifying process.

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 (KS) was better determined by static respirometry with pulses of increasing concentration and the maximum oxygen uptake rate (OURex.max) was better determined by dynamic respirometry coupled to fitting procedure. The best method for combined KS and OURex.max determination was static respirometry with pulses of increasing concentration.

Flocculant in wastewater affects dynamics of inorganic N and accelerates removal of phenanthrene and anthracene in soil

Recycling of municipal wastewater requires treatment with flocculants, such as polyacrylamide. It is unknown how polyacrylamide in sludge affects removal of polycyclic aromatic hydrocarbons (PAH) from soil. An alkaline-saline soil and an agricultural soil were contaminated with phenanthrene and anthracene. Sludge with or without polyacrylamide was added while emission of CO(2) and concentrations of NH(4)(+), NO(3)(-), NO(2)(-), phenanthrene and anthracene were monitored in an aerobic incubation experiment. Polyacrylamide in the sludge had no effect on the production of CO(2), but it reduced the concentration of NH(4)(+), increased the concentration of NO(3)(-) in the Acolman soil and NO(2)(-) in the Texcoco soil, and increased N mineralization compared to the soil amended with sludge without polyacrylamide. After 112d, polyacrylamide accelerated the removal of anthracene from both soils and that of phenanthrene in the Acolman soil. It was found that polyacrylamide accelerated removal of phenanthrene and anthracene from soil.

Characterization of oxygen transfer in a 24-well microbioreactor system and potential respirometric applications

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, KLa in the MBR was measured with different cassette and cap designs, liquid volumes, agitation rates, gas flow rates, temperatures and ionic strengths. KLa 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.

Microrespirometric determination of the effectiveness factor and biodegradation kinetics of aerobic granules degrading 4-chlorophenol as the sole carbon source

In this study, a microrespirometric method was used, i.e., pulse respirometry in microreactors, to characterize mass transfer and biodegradation kinetics in aerobic granules. The experimental model was an aerobic granular sludge in a sequencing batch reactor (SBR) degrading synthetic wastewater containing 4-chlorophenol as the sole carbon source. After 15 days of acclimation, the SBR process degraded 4-chlorophenol at a removal rate of up to 0.9kg CODm(-3)d(-1), and the degradation kinetics were well described by the Haldane model. The microrespirometric method consisted of injecting pulses of 4-chlorophenol into the 24 wells of a microreactor system containing the SBR samples. From the respirograms obtained, the following five kinetic parameters were successfully determined during reactor operation: (i) Maximum specific oxygen uptake rate, (ii) substrate affinity constant, (iii) substrate inhibition constant, (iv) maximum specific growth rate, and (v) cell growth yield. Microrespirometry tests using granules and disaggregated granules allowed for the determination of apparent and intrinsic parameters, which in turn enabled the determination of the effectiveness factor of the granular sludge. It was concluded that this new high-throughput method has the potential to elucidate the complex biological and physicochemical processes of aerobic granular biosystems.

Initial report on methane and carbon dioxide emission dynamics from sub-Antarctic freshwater ecosystems: A seasonal study of a lake and a reservoir

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.

Methane emission from aquatic ecosystems of Mexico City

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 1xa0year, including reservoirs, rivers, lakes, canals and chinampas (system of floating garden on shallow lakes). The total CH4 emission from aquatic ecosystems was estimated as 3679xa0Mg CH4 year−1, which represents 3.5xa0% of the annual CH4 emission of Mexico City. The main contributors are chinampas (33xa0%), followed by lakes (27xa0%), reservoirs (19xa0%), rivers (12xa0%) and canals (9xa0%). 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.

High-throughput microrespirometric characterization of activated sludge inhibition by silver nanoparticles

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.