Total Organic Carbon Depletion Research Articles

Maturation study of vitrinite in carbonaceous shales and coals: Insights from hydrous pyrolysis

The presence of vitrinite in sedimentary rocks of post-Silurian age allows its reflectance to be used to estimate the thermal maturation of organic matter in petroleum systems. Increasing reflectance of vitrinite, which is primarily driven by aromaticity, depends primarily on the time and temperature attributes of its evolutionary pathway. This study evaluated carbonaceous shales proximal to coal measures and coal samples via isothermal hydrous pyrolysis (HP) to compare differences in the maturation pathways of vitrinite. Sample residues were analysed via vitrinite reflectance (VRo), geochemical screening tests (organic carbon and programmed temperature pyrolysis), and infrared spectroscopy. The study included samples from Indian and North American basins, to observe differences in vitrinite evolution with respect to enclosing mineral matrix, starting degree of aromaticity, organic matter types, stratigraphic age, and depositional environment. The organic content of HP residues shows an intuitive response to the thermal stress of HP, e.g., a general depletion of total organic carbon (TOC) content, pyrolyzate (S2), and hydrogen index with increasing HP temperature. Infrared proxies including C-factor and CH2/CH3 generally decrease with increasing thermal maturity indicating loss of O via CO2 generation and the thermal cracking of aliphatic organic matter. Tmax, production index (PI), and VRo show intuitive increasing values with respect to HP temperature. The least mature sample (0.48 ± 0.05% VRo) generally experienced the maximum change in these parameters during maturation, whereas the most mature sample (0.99 ± 0.06% VRo) generally showed the least change. This observation is consistent with higher kinetic barriers to reaction in more aromatic vitrinite which contains higher bond dissociation energies. Devolatilization of vitrinite during HP causes formation of gas evacuation vacuoles and contraction cracks in the vitrinite grains of both coal and carbonaceous shale. Similarities in vitrinite response to HP between coal and carbonaceous shale suggest that thermal evolution of the vitrinite maceral is principally controlled by inherent rate-limiting kinetic parameters related to its molecular structure. Whereas, the stratigraphic age, sedimentary environment, surrounding organic matter, lithology, and catalysis by mineral composition have less effect. To further improve our understanding of vitrinite aromatization and kinetic parameters, future studies of vitrinite reflectance thermal evolution with temperature should include coal and carbonaceous shale from the same stratigraphic section and extant woody tissue from modern vascular plants.

A generalized kinetic model for electro-assisted catalytic wet air oxidation of triclosan on Ni@NiO/graphite electrode

Electro-assisted catalytic wet air oxidation (ECWAO) is an efficient technique for wastewater treatment under ambient condition. In this work, the mineralization kinetics of triclosan (TCS) in an ECWAO process with Ni@NiO/graphite-felt (GF) electrode is studied. The TCS mineralization follows a pseudo-first order kinetics in the ECWAO process. A general kinetic model, based on the depletion of total organic carbon (TOC) as a lumped parameter, is developed. Such a kinetic model suggests the optimized ECWAO operating conditions of initial concentration of TOC at 40 mg L−1, applied current at 25 mA, and temperature at 308 K. In addition, the ECWAO is also effective for the treatment of biosphenol A (BPA) and sulfamethoxazole (SMX). Under the optimal conditions, TCS, BPA and SMX are mineralized by 92.9 ± 1.5, 90.8 ± 1.7 and 90.6 ± 1.0% within 120 min, with specific energy consumptions (SECs) of 2.2 ± 0.3, 1.4 ± 0.5, and 2.8 ± 0.6 kW h kg-TOC−1, respectively.

Fungal biodegradation and multi-level toxicity assessment of vinasse from distillation of winemaking by-products

The wastewaters from distilleries of winemaking by-products, a scarcely studied type of vinasse, were treated by white-rot fungal strains from species Irpex lacteus, Ganoderma resinaceum, Trametes versicolor, Phlebia rufa and Bjerkandera adusta. The main objectives of this study were to evaluate fungal performance during vinasse biodegradation, their enzyme patterns and ecotoxicity evolution throughout treatment. Despite all strains were able to promote strong (>80%) dephenolization and reduction of total organic carbon (TOC), P. rufa was less affected by vinasse toxicity and exhibit better decolorization. In batch cultures at 28 °C and pH 4.0, the first phase of P. rufa biodegradation kinetics was characterized by strong metabolic activity with simultaneous depletion of TOC, phenolics and sugars. The main events of second phase are the increase of peroxidases production after the peak of laccase activity, and strong color removal. At the end of treatment, it was observed highly significant (p < 0.001) abatement of pollution parameters (83–100% removal). Since water reclamation and reuse for e.g. crop irrigation is a priority issue, vinasse ecotoxicity was assessed with bioindicators representing three different phylogenetic and trophic levels: a marine bacterium (Aliivibrio fischeri), a freshwater microcrustacean (Daphnia magna) and a dicotyledonous macrophyte (Lepidium sativum). It was observed significant (p < 0.05) reduction of initial vinasse toxicity, as evaluated by these bioindicators, deserving special mention an almost complete phytotoxicity elimination.

Bioremediation of contaminated urban river sediment with methanol stimulation: Metabolic processes accompanied with microbial community changes

The intense pollution of urban river sediments with rapid urbanization has attracted considerable attention. Complex contaminated sediments urgently need to be remediated to conserve the ecological functions of impacted rivers. This study investigated the effect of using methanol as a co-substrate on the stimulation of the indigenous microbial consortium to enhance the bioremediation of petroleum hydrocarbons (PHs) and polycyclic aromatic hydrocarbons (PAHs) in an urban river sediment. After 65 days of treatment, the PAHs degradation efficiencies in the sediment adding methanol were 4.87%–40.3% higher than the control. The removal rate constant of C31 was 0.0749 d−1 with 100 mM of supplied methanol, while the corresponding rate was 0.0399 d−1 in the control. Four-ring PAHs were effectively removed at a degradation efficiency of 65%–69.8%, increased by 43.3% compared with the control. Sulfate reduction and methanogenesis activity were detected, and methane-producing archaea (such as Methanomethylovorans, with a relative abundance of 25.87%–58.53%) and the sulfate-reducing bacteria (SRB, such as Desulfobulbus and Desulfobacca) were enriched. In addition, the chemolithoautotrophic sulfur-oxidizing bacteria (SOB, such as Sulfuricurvum, with a relative abundance of 34%–39.2%) were predominant after the depletion of total organic carbon (TOC), and markedly positively correlated with the PHs and PAHs degradation efficiencies (P < 0.01). The SRB and SOB populations participated in the sulfur cycle, which was associated with PHs and PAHs degradation. Other potential functional bacteria (such as Dechloromonas) were also obviously enriched and significantly positively correlated with the TOC concentration after methanol injection (P < 0.001). This study provides a new insight into the succession of the indigenous microbial community with methanol as a co-substrate for the enhanced bioremediation of complexly contaminated urban river sediments.

Long-term soil carbon loss and accumulation in a catchment following the conversion of forest to arable land in northern Laos

Quantifying the magnitude of soil organic carbon loss linked to the conversion of forest to arable land in tropical environments requires long-term estimates of soil redistribution trends within the catchment. In order to assess the cumulative soil carbon loss that occurred since deforestation and cropping started in 1967, a multidisciplinary study was carried out in a small catchment (67ha) with a swamp area in its middle part, characterized by steep slopes under shifting cultivation of upland rice, typical for northern Laos's landscapes. Using 137Cs and total organic carbon (TOC) inventories, it was possible to estimate a soil TOC depletion rate of 0.039kgCm−2yr−1 in 42 years (1963–2005), corresponding to ca. 21% of its initial content in the top 10cm. Because farmers preferred clearing more fertile soils located downhill and leave forest on poorer soils on the crests, the redistribution of 137Cs and TOC along slopes of the catchment was mainly controlled by the topographic position of soils and the cultivation frequency. Estimates of soil TOC accumulation in wetlands with δ13C measurements and sediment volumes by electrical resistivity tomography showed that TOC accumulation rates were linked to land use change since the 1960s with three successive periods corresponding to undisturbed forest, deforestation-first rice crop and rice-fallow rotations. Forest clearing triggered a higher soil TOC delivery to the swamp (19.6±5.5kgCha−1yr−1) over 8 years (1967–1975) than the former undisturbed forest (8.5±1.8kgCha−1yr−1) and crop-fallow rotations over 30 years (1975–2005, 6.4±4.8kgCha−1yr−1). Due to the small size of the area covered by the swamp, only a limited fraction of eroded soil organic carbon (ca. 7wt.%) was stored in wetlands of the catchment. Mineralization apparently played a key role for soil TOC depletion since first forest clearing.

Heterogeneous photocatalysed degradation of two selected pesticide derivatives, triclopyr and daminozid in aqueous suspensions of titanium dioxide

Heterogeneous photocatalysed degradation of two selected pesticide derivatives, triclopyr ( 1) and daminozid ( 2), has been investigated in aqueous suspensions of titanium dioxide by monitoring the change in substrate concentration employing the UV Spectroscopic analysis technique and depletion of Total Organic Carbon (TOC) content as a function of irradiation time. The degradation kinetics were studied under different conditions such as reaction pH, substrate and catalyst concentration, different types of TiO 2 and in the presence of electron acceptors such as hydrogen peroxide (H 2O 2), potassium bromate (KBrO 3) and ammonium persulphate (NH 4) 2S 2O 8 in addition to molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other photocatalysts. The pesticide derivative triclopyr ( 1) was found to degrade faster as compared to daminozid ( 2). An attempt was also made to identify the intermediate products formed during the photooxidation process using GC/MS analysis. Probable pathways for the formation of products have been proposed.

Soil organic matter properties after 40 years of different use of organic and mineral fertilisers

Organic inputs can help maintain soil fertility by improving chemical and biological soil properties. The effects of 40 years of organic, mineral and mixed fertilisations on soil organic properties were evaluated in a continuous maize system. The following properties were analysed: total organic carbon (TOC), humic carbon (HC) and its molecular weight distribution, HC/TOC and the hormone—(auxin and gibberellin-like) activities of the humic substances and their effects on two key enzymes (nitrate reductase (NR) and glutamine synthetase (GS)) involved in nitrate assimilation in maize seedlings. Farmyard manure fertilisation sustained TOC in the top layers while mineral treatments alone or mixed with organic exhibited a minor influence on the organic matter evolution: over 40 years the average TOC depletion was 23% with liquid manure and mixed fertilisations, 43% with mineral fertilisers alone and 51% in the control. The different treatments also influenced the HC molecular complexity. Farmyard fertilisations improved the production of humus with a high degree of policondensation, a fraction usually linked to soil fertility; the absence of organic fertiliser inputs determined the opposite, with a higher percentage of non-complex and light-weight humus. The hormone-like and biochemical activities of humus substances were evident with the organic and mixed fertilisations. The humus extracted by the soil treated with farmyard manure exhibited the best gibberellin-like activity and the highest increases of NR (+42%) and GS (+49%) activities with respect to the control. The other treatments showed intermediate stimulations as in the case of mixed fertilisations (NR + 22% and GS + 24%), or no activities as in the case of mineral inputs.

Titanium dioxide mediated photocatalyzed degradation of a textile dye derivative, acid orange 8, in aqueous suspensions

Titanium dioxide mediated photocatalysed degradation of a textile dye derivative, acid orange 8(1), was investigated in aqueous suspensions of titanium dioxide by monitoring the depletion of total organic carbon (TOC) content as a function of irradiation time under a variety of conditions. The degradation kinetics were studied under different conditions such as pH, catalyst concentration, substrate concentration, different types of TiO 2 and in the presence of electron acceptors such as hydrogen peroxide (H 2O 2) and potassium bromate (KBrO 3) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient compared with other photocatalysts. The dye was found to be adsorbed on the surface of the photocatalyst at acidic pH.

Photocatalytic degradation of dimethyl terephthalate in aqueous suspensions of titanium dioxide

The photocatalytic degradation of dimethyl terephthalate (DMT, 1) has been investigated in aqueous suspensions of titanium dioxide (TiO2) by monitoring the depletion of Total Organic Carbon (TOC) content as a function of irradiation time under a variety of conditions. The degradation kinetics were studied using different parameters such as pH, substrate and photocatalyst concentration, a different kind of titanium dioxide and the presence of electron acceptors such as H2O2, KBrO3 and (NH4)2S2O8 in addition to molecular oxygen. The photocatalytic activity was better for Degussa P25 as compared to the other photocatalysts. From the obtained kinetic data a detailed account of the influence of various parameters on the degradation rate for the mineralization of the compound is given. The degradation products were analyzed using the GC/MS technique and probable pathways for the formation of different products have been proposed.

Glaciomarine sedimentation and its paleoceanographic implications along the fjord margins in the South Shetland Islands, Antarctica during the last 6000 years

Two 3 m long cores were collected from Maxwell and Admiralty Bays on King George Island, one of the South Shetland Islands, West Antarctica. These cores were examined for their benthic foraminifer ( Globocassidulina biora), δ 18O and δ 13C records, diatom abundance counts and biogenic constituents (carbon and silica). These high-resolution data were used to reconstruct the paleoceanography of the bays and to link the marine record with deglaciation of the South Shetland Islands Ice Cap. In Maxwell Bay, extremely low diatom abundance, the depletion of total organic carbon (TOC) and biogenic silica (bioSi), and enriched δ 18O between 6200 and 4000 BP indicate that this period was characterized by cold conditions with deposition of waterlain till (unit 1) just seaward of the grounding line, low sedimentation, limitation of primary production on surface water, and lack of meltwater supply. Deglaciation along the Maxwell Bay margin was dated from about 4000 BP until at least 2700 BP, with increasing TOC, bioSi and diatom abundance, and decreasing the C/N ratio up core. At this time, subglacial meltwater streams began to emanate from the glacier front. Sediment-laden meltwater plumes from these streams deposited interlaminated sand and mud (unit 2) in the ice-proximal zone. Deglaciation was followed by marked climatic warming at around 2700 BP, with evidence of TOC and bioSi maxima, depleted-δ 18O, and markedly increased diatom valves. With further glacier recession, diatomaceous pebbly mud (unit 3) was deposited in open marine conditions. A large influx of organic materials by enhanced production during this period caused both rapid depletion of CaCO 3 in sediment and resulted in marked increase in sedimentation since 2700 BP at 200 m water depth along the Maxwell Bay margin (Core S-19). In contrast, the shallower platform along the Admiralty Bay margin (Core S-2) was deglaciated later about 1900 BP, that is, 2000 years after the Maxwell Bay margin. This is possible, as Core S-19 is situated (>200 m water depth) more distal to the fjord head glacier, while Core S-2 in Admiralty Bay lies on a shallower platform (<45 m water depth). In spite of certain correlation problems, we tentatively correlate our results to other studies of Holocene environments in Antarctica, and from that it can be suggested that the climatic optimum at 4000 to 2700 BP and preceding cold event at 6200 to 4000 BP were of circumpolar significance. Since 2700 BP, the contrast between the maritime position of the South Shetland Islands and the continental climate of Antarctic Peninsula, where the Neoglacial appears to have begun ca. 2700 BP, however, implies that the westerly stormtracks transporting humid, warm air from northwest would not be weakened and displaced northwards from the South Shetland Islands.

The Sonochemical Degradation of Azobenzene and Related Azo Dyes: Rate Enhancements via Fenton's Reactions

The sonochemical degradation of aqueous solutions of azobenzene and related azo dyes (methyl orange, o-methyl red, and p-methyl red) was performed at 500 kHz and 50 W, under air, O2, or Ar saturation at 288 K. Reaction products and intermediates were identified by HPLC-ES-MS. Total organic carbon (TOC) was also determined as a function of reaction time. We propose a reaction mechanism based on the observed species and the extent and rate of TOC depletion. The addition of OH radicals to the azo double bond is considered to be the first step of the sequence of oxidative bond cleavages leading to the production of carboxylic acids, quinones, carbon dioxide, and nitrate ions as the main degradation products. The effects of the dye structures and of the background gas on the sonochemical bleaching rates were also investigated. The reaction rates for o-methyl red were approximately 30−40% faster than those for the other compounds. This appears to be a strong influence by a carboxylic group ortho to the azo grou...

Phenoxyalkanoic acid herbicides in municipal landfill leachates

Analysis of leachates from six U.S. municipal landfills revealed the presence of chlorinated 2-phenoxypropionic acid herbicides; however, none of the more widely used acetic acid analogues was present at quantifiable levels. All the leachates contained MCPP. 2,4-DP and silvex were detected in four of the six. The herbicide 2,4-DB was also found in four of the leachates. These compounds persisted in the leachates during 2-3 years of storage while significant depletion of total organic carbon (TOC) in general and of low molecular weight carboxylic acids in particular was observed