Impact of Operational Factors, Inoculum Origin, and Feedstock Preservation on the Biochemical Methane Potential.

Anaerobic digestion for the valorization of organic wastes into biogas is gaining worldwide interest. Nonetheless, the sizing of the biogas plant units require knowledge of the quantity of feedstock, and their associated methane potentials, estimated widely by Biochemical Methane Potential (BMP) tests. Discrepancies exist among laboratories due to variability of protocols adopted and operational factors used. The aim of this study is to verify the influence of some operational factors (e.g., analysis frequency, trace elements and vitamins solution addition and flushing gas), feedstock conservation and the source of inoculum on BMP. Among the operational parameters tested on cellulose degradation, only the type of gas used for flushing headspace of BMP assays had shown a significant influence on methane yields from cellulose. Methane yields of 344 ± 6 NL CH4 kg-1 VS and 321 ± 10 NL CH4 kg-1 VS obtained from assays flushed with pure N2 and N2/CO2 (60/40 v/v). The origin of inoculum (fed in co-digestion) only significantly affected the methane yields for straw, 253 ± 3 and 333 ± 3 NL CH4 kg-1 VS. Finally, freezing/thawing cycle effect depended of the substrate (tested on biowaste, manure, straw and WWTP sludge) with a possible effect of water content substrate.

Fast prediction of organic wastes methane potential by near infrared reflectance spectroscopy: A successful tool for farm-scale biogas plant monitoring.

Currently, there is a growing worldwide interest for the treatment of wastes, and especially farm wastes, by anaerobic digestion. Biochemical methane potential is a key parameter for the design, optimisation and monitoring of the anaerobic digestion process, but it is also time consuming (4-7 weeks). Near infrared reflectance spectroscopy seems a promising method to predict the biochemical methane potential of a wide range of organic substrates. This study compares a 'global' predictive model mainly built with biogas plant feedstocks, and a more 'agricultural' specific one built with farm wastes only (e.g. manures and crop residues). The global model was calibrated with 245 samples and the specific one with 171 samples. In parallel, validation sets composed of 36 farm wastes and eight other wastes (sludge, fruit residues and vegetables) were used to evaluate and compare both models. Satisfying results were obtained on the validation sets considering, respectively for the global and the specific models, a root mean square error of prediction of 44 and 34 NL CH4 kg-1 volatile solid, a coefficient of determination of 0.76 and 0.83, and a ratio of performance to deviation of 2.0 and 2.4. In general rules, the specific model was better than the global one in the prediction of farm wastes methane potential. However, thanks to its larger sample variability, the global one was more robust, especially towards the 'other' wastes, which can be introduced punctually in agricultural biogas plant.

New Bio-Indicators for Long Term Natural Attenuation of Monoaromatic Compounds in Deep Terrestrial Aquifers.

Deep subsurface aquifers despite difficult access, represent important water resources and, at the same time, are key locations for subsurface engineering activities for the oil and gas industries, geothermal energy, and CO2 or energy storage. Formation water originating from a 760 m-deep geological gas storage aquifer was sampled and microcosms were set up to test the biodegradation potential of BTEX by indigenous microorganisms. The microbial community diversity was studied using molecular approaches based on 16S rRNA genes. After a long incubation period, with several subcultures, a sulfate-reducing consortium composed of only two Desulfotomaculum populations was observed able to degrade benzene, toluene, and ethylbenzene, extending the number of hydrocarbonoclastic-related species among the Desulfotomaculum genus. Furthermore, we were able to couple specific carbon and hydrogen isotopic fractionation during benzene removal and the results obtained by dual compound specific isotope analysis (𝜀C = -2.4‰ ± 0.3‰; 𝜀H = -57‰ ± 0.98‰; AKIEC: 1.0146 ± 0.0009, and AKIEH: 1.5184 ± 0.0283) were close to those obtained previously in sulfate-reducing conditions: this finding could confirm the existence of a common enzymatic reaction involving sulfate-reducers to activate benzene anaerobically. Although we cannot assign the role of each population of Desulfotomaculum in the mono-aromatic hydrocarbon degradation, this study suggests an important role of the genus Desulfotomaculum as potential biodegrader among indigenous populations in subsurface habitats. This community represents the simplest model of benzene-degrading anaerobes originating from the deepest subterranean settings ever described. As Desulfotomaculum species are often encountered in subsurface environments, this study provides some interesting results for assessing the natural response of these specific hydrologic systems in response to BTEX contamination during remediation projects.

Anaerobic biodegradation of BTEX by original bacterial communities from an underground gas storage aquifer.

BTEX biodegradation by an indigenous deep subsurface microbial community was evaluated in a water sample collected in the area of an underground gas storage. Five different sulfate-reducing microbial communities able to use at least either benzene, toluene, ethylbenzene, or xylene (BTEX) compounds were studied. A total of 21 different bacterial phylotypes were identified, each community containing three to nine bacterial phylotypes. Archaeal phylotypes were retrieved from only three communities. The analysis of 16S rRNA gene sequences showed that i) these consortia were mainly composed of novel species, some of which belonging to bacterial groups not previously suspected to be involved in BTEX anaerobic degradation, ii) three consortia were dominated by an uncultured Pelobacter sp. previously detected in biodegraded oil reservoirs, iii) a deeply branching species distantly affiliated to Thermotogales was abundant in two consortia, and that iv) Firmicutes related to the Desulfotomaculum and Carboxydocella genera represented the only three detectable phylotypes in a toluene-degrading consortium. This work shows that subdominant microbial populations present in a deep subsurface aquifer used for seasonal underground gas storage could be involved in the natural attenuation of the traces of BTEX coinjected with methane in the deep subsurface.

Development of a biomarker for metal bioavailability: the lettuce fatty acid composition.

Because Lactuca sativa L. is a plant widely used in ecotoxicological analyses, a study was developed to determine whether the fatty acid composition of lettuce leaves could be used as an additional biomarker of soil contamination by metals such as Pb, Cu, Zn, and Cd. Unlike seed germination or seedling growth, the fatty acid composition of lettuce leaves differed significantly between uncontaminated and field metal-contaminated soils. Hence, this lipid biomarker might provide an early indication of a plant's exposure to metals and the potential bioavailability of metals, and could facilitate or strengthen the diagnosis of soil contamination. Not only is the experimental protocol cheap, rapid, and easy, but the values of the lipid biomarker are highly reproducible when seedlings are grown at the same light intensity. In addition, the values of the biomarker did not vary greatly when 14- to 18-day-old plants were analyzed and when slight differences were introduced in the experimental conditions used to determine the leaf fatty acid composition.