Total Organic Carbon Ratio Research Articles

Quantitative estimation of overpressure caused by oil generation in petroliferous basins

Oil generation can be the dominant overpressure mechanism in low permeability source rocks because of the volume increase upon conversion of organic matter to less dense oil during the petroleum generation process. To quantitatively express the relationship between oil generation and overpressure in source rocks, an equation for the pressure change due to oil generation was derived to quantitatively estimate the overpressure generated in the source rock by considering of the episodic fluid expulsion and parameters, such as the residual oil coefficient, source rock porosity, transformation ratio, TOC (total organic carbon), hydrogen index, the compressibility of Type I kerogen, oil and pore water. The equation was then calibrated with the results from physical simulation experiments in a closed pyrolysis system. Sensitivity analyses on the residual oil coefficient, TOC and hydrogen index were performed to investigate the dominant parameters controlling overpressure due to oil generation. A good correlation was achieved between measured overpressure from the physical simulation experiments and the calculated data using the derived equations for the pressure change due to oil generation, suggesting that the equation can be used to quantitatively estimate overpressure caused by oil generation in source rocks. Many parameters can affect overpressure caused by oil generation, including residual oil coefficient, source rock porosity, TOC, hydrogen index, and transformation ratio. Sensitivity analyses indicate that the most effective parameter on the pressure change due to oil generation in the source rocks is the residual oil coefficient, implying that the internal pressure seal for the source rock is the most important parameter for overpressure development caused by oil generation. Overpressure cannot be generated from oil generation if the residual oil coefficient is less than 0.75. Source rock TOC and hydrogen index have moderate effects on the pressure change caused by oil generation. Overpressure can be generated when the TOC content is as low as 0.5% provided the source rocks have a good internal pressure seal.

Palaeoclimatic changes in the NW Iberian ­Peninsula during the last 3000 years inferred from ­diagenetic ­proxies in the Ría de Muros sedimentary record

The Ria de Muros is the northernmost of the 4 Rias Baixas and, like the others, is subject to seasonal upwelling. The high organic carbon content of its sediments (average 2.4%) is due to the consequent high primary production together with significant continental input from river discharge and runoff. This high organic carbon content not only favours early diagenesis, but does so to an extent that depends on the relative proportions of labile marine organic carbon and refractory terres- trial organic carbon. Thus, changes in early diagenesis reflected in the mineralogy and/or composi- tion of the Ria's sediments can throw light on the degree of oceanic influence in the Ria, and hence on changes in the circulation and ventilation of its water masses and/or the climate on shore. In this study of sediment cores taken in the outer Ria de Muros, the combined use of textural analysis, mag- netic properties (magnetic susceptibility (κ), ratio of anhysteretic to isothermal remanent magnetisa- tion (ARM:IRM), and median destructive field (MDF)) and geochemical parameters (total concentra- tions of diagenetically stable and mobile elements in sediment and pore water) allowed the identification of a current redox front and 2 palaeosedimentary redox fronts in the sediment record. These fronts originated during periods of high marine/terrestrial organic matter ratio (as inferred from the ratio of total organic carbon to total nitrogen (TOC:TN) and δ 13 C). Sedimentation rates calcu- lated from 14 C dating results identify these periods as known periods of increased upwelling and reduced continental input due to colder, drier climate in the NW Iberian Peninsula, namely the Little Ice Age, the Dark Ages, and first cold period of the Upper Holocene.

Importance of organic matter lability for monomethylmercury production in sulfate-rich marine sediments

Sediment cores were collected from two shallow sites in the Venice Lagoon, Italy, in order to study the lability of organic matter and the methylation rate of inorganic Hg(II). Measurements were made of concentrations of total Hg and monomethylmercury (MMHg), Hg(II) methylation rates, concentrations of total organic carbon and total nitrogen in the sediments, and dissolved sulfate, sulfide, and alkalinity in sedimentary pore waters. A positive linear relationship was detected between the specific Hg(II) methylation rate constant and the fraction of total Hg comprised of MMHg (%MMHg/Hg), indicating that short-term Hg(II) methylation rate reflects a long-term accumulation of MMHg in sediment. In addition, the %MMHg/Hg and specific Hg(II) methylation rate constant in sediment increased with decreasing ratios of total organic carbon to total nitrogen (C/N), whereas concentrations of dissolved sulfate, sulfide, and alkalinity in pore water remained constant. This result suggests that the Hg(II) methylation rate was affected by lability of organic matter. In particular, surface sediments, which contained large fractions of fresh algal organic material (C/N = 5.8–7.8), showed higher Hg(II) methylation rates than did deeper sediments (C/N > 10). Our results indicate that the C/N ratio can be used as a proxy for the lability of organic matter that influences Hg(II) methylation rate in sulfate-rich marine sediments.

The Effect of Organism Density on Bioaccumulation of Contaminants from Sediment in Three Aquatic Test Species: A Case for Standardizing to Sediment Organic Carbon

Laboratory methods for measuring bioaccumulation of organic contaminants from sediment into aquatic organisms continue to improve, but some aspects are still in need of standardization. From a review of published methods, we noted that the loading density of organisms was determined inconsistently and was primarily based on either sediment volume or total organic carbon (TOC). The rationale mainly expressed for standardizing to TOC was to minimize the depletion of sediment contaminants. However, even when density was standardized to TOC, the relative amount of TOC provided (i.e., ratio of TOC to organism dry weight [dw]) was highly variable. In this study, we examined the effect of organism density (standardized to sediment TOC or volume) on bioaccumulation in three freshwater organisms. The oligochaete Lumbriculus variegatus, mayfly nymph Hexagenia spp., and fathead minnow Pimephales promelas were exposed for 28days to two field-contaminated sediments that varied in concentration of PCBs and TOC. Densities tested were 50:1 and 27:1 ratios of TOC to organism dw and 140ml sediment/g wet weight (ww) biomass, yielding low to high organism densities. Bioaccumulation in Hexagenia spp. was significantly higher at the lowest organism density compared with the highest organism density when exposed to site 2 sediment (1.1% TOC) but only with tissue concentrations expressed on a ww basis. Otherwise, there was no significant effect of density on bioaccumulation in organisms exposed to sediments from site 1 (12% TOC) or site 2. Survival of Hexagenia spp. was adversely affected at the highest organism density when the relative amount of TOC was low. The results of this study support the recommendation of standardizing organism density relative to a particular amount of TOC for invertebrate species. A 27:1 ratio of TOC:organism dw was selected as a standard organism density for a new bioaccumulation method because survival, growth, and bioaccumulation were not impacted relative to a 50:1 ratio, and less sediment was required. This density is recommended as an appropriate ratio for sediment bioaccumulation assessments in general.

Soil Organic Carbon, Carbon Fractions and Nutrients as Affected by Land Use in Semi-Arid Region of Loess Plateau of China

Cropland (CP), native grassland (NG) and two shrub land treatments which were converted from cropland in 1985: seabuckthorn ( Hippophae rhamnoides L.) (ST), and branchytamarisk ( Tamarix ramosissima) (BT) were investigated to evaluate effects of land use conversion on soil organic carbon (SOC) and soil nutrients in the semi-arid region of the Loess Plateau of China. Total organic carbon (TOC), light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), total N (TN), nitrate nitrogen (NO − 3-N) and nitrite nitrogen (NO − 2-N), ammonium nitrogen (NH +4-N), total P, and available P (AP) were measured. The results showed that SOC in NG, ST and BT were 12.7%, 27.7% and 34.8% higher than that of the cropland, respectively. LFOC, light fraction (LF) dry matter, ratio of TOC to TN (C/N) and the ratio of TOC to AP (C/P) were higher in the shrub land or native grassland than in the cropland. Cropland had the highest TN, the sum of NO − 3-N and NO − 2-N, TP and AP due to the use of chemical fertilizers. TOC significantly correlated with LFOC, HFOC and C/N. LFOC significantly correlated with dry matter of the LF and C/N. TN, the sum of NO − 3-N and NO − 2-N and AP were significantly negatively correlated with TOC and LFOC. Therefore, land use conversion from cropland to shrub land, or maybe grassland, contributed to SOC sequestration and improved soil nutrients stabilization.

Bayesian Statistical Modeling of Disinfection Byproduct (DBP) Bromine Incorporation in the ICR Database

Statistical models are developed for bromine incorporation in the trihalomethane (THM), trihaloacetic acids (THAA), dihaloacetic acid (DHAA), and dihaloacetonitrile (DHAN) subclasses of disinfection byproducts (DBPs) using distribution system samples from plants applying only free chlorine as a primary or residual disinfectant in the Information Collection Rule (ICR) database. The objective of this study is to characterize the effect of water quality conditions before, during, and post-treatment on distribution system bromine incorporation into DBP mixtures. Bayesian Markov Chain Monte Carlo (MCMC) methods are used to model individual DBP concentrations and estimate the coefficients of the linear models used to predict the bromine incorporation fraction for distribution system DBP mixtures in each of the four priority DBP classes. The bromine incorporation models achieve good agreement with the data. The most important predictors of bromine incorporation fraction across DBP classes are alkalinity, specific UV absorption (SUVA), and the bromide to total organic carbon ratio (Br:TOC) at the first point of chlorine addition. Free chlorine residual in the distribution system, distribution system residence time, distribution system pH, turbidity, and temperature only slightly influence bromine incorporation. The bromide to applied chlorine (Br:Cl) ratio is not a significant predictor of the bromine incorporation fraction (BIF) in any of the four classes studied. These results indicate that removal of natural organic matter and the location of chlorine addition are important treatment decisions that have substantial implications for bromine incorporation into disinfection byproduct in drinking waters.

Radiocarbon and Stable Carbon Isotope Ratio Data from a 4.7-Mlong Sediment Core of Lake Baikal (Southern Siberia, Russia)

A sediment core (VER99G12; core length, 4.66 m) was taken from the Buguldeika Saddle of Lake Baikal in 1999. Radiocarbon measurements of total organic carbon (TOC) and pollen concentrate fractions from the VER99G12 core were performed by a Tandetron accelerator mass spectrometry (AMS) system (Model-4130, HVEE) at Nagoya University. The AMS 14C ages showed that the VER99G12 core spans the past ∼30 cal ka BP (from the MIS 3 to present), and the average sedimentation rate of this core was calculated to be 13.6 cm/kyr based on the calibrated ages. This means that the time resolution of VER99G12 sediment samples in this study is better than ∼70–80 yr/cm. Stable carbon isotope ratios of TOC (δ13CTOC) in the VER99G12 core varied widely from about 26.6‰ to 31.3‰ during the last glacial/post-glacial transition period (about 17–12 cal ka BP). Therefore, a rapid change in the carbon sources in Lake Baikal occurred in the last glacial/post-glacial transition period is concluded.

A novel reforming method for hydrogen production from biomass steam gasification

In this work, an experimental study of biomass gasification in different operation conditions has been carried out in an updraft gasifier combined with a porous ceramic reformer. The effects of gasifier temperature, steam to biomass ratio (S/B), and reforming temperature on the gas characteristic parameters were investigated with and without porous ceramic filled in reformer. The results indicated that considerable synergistics effects were observed as the porous ceramic was filled in reformer leading to an increase in the hydrogen production. With the increasing gasifier temperature varying from 800 to 950 °C, hydrogen yield increased from 49.97 to 79.91 g H 2/kg biomass. Steam/biomass ratio of 2.05 seemed to be optimal in all steam-gasification runs. The effect of reforming temperature for water-soluble tar produced in porous ceramic reforming was also investigated, and it was found that the conversion ratio of total organic carbon (TOC) contents is between 71.08% and 75.74%.

Spatial and temporal variation of organic carbon in the northern South China Sea revealed by sedimentary records

Three sediment cores were taken from the Pearl River estuary and adjacent northern South China Sea (SCS). These sediment cores span the time interval 1900–2000 AD. The stratigraphy of the concentration, the ratio of total organic carbon (TOC) to total nitrogen (TN) and stable isotope ( δ 13C org) of organic carbon (OC) from three high-resolution sediment cores were analyzed. The stratigraphic profiles of OC concentration, TOC/TN ratios and δ 13C org for the near past 100 yrs indicate that terrestrial organic matter decreases from 68.3% to 27.4% of the TOC in the Pearl River estuary, while Dapeng Bay (offshore east of Hong Kong) apparently had throughout little terrestrial organic matter input. The highest deposited OC occurs at the Humen River mouth and the OC concentrations are higher in the outer estuary than in the inner shelf of the northern SCS. The deposited OC at the River mouth increased with time, which could be caused by the high precipitation of land-derived organic matter and the high input of terrestrial organic matter, which is likely related to the rapid urbanization and industrial development in the Pearl River Delta since the 1970s. The OC concentrations did not exhibit an obvious increase with time in most areas of the Pear River estuary and adjacent inner shelf of the SCS, but the algal-derived OC concentration inferred from the δ 13C org values increased with time especially from 1980 to 2000 in the outer Pearl River estuary and Dapeng Bay. This increase is presumably caused by enhanced primary marine productivity supported by higher anthropogenic nutrient inputs.

Effect of ozone exposure on the oxidation of trace organic contaminants in wastewater

Three tertiary-treated wastewater effluents were evaluated to determine the impact of wastewater quality (i.e. effluent organic matter (EfOM), nitrite, and alkalinity) on ozone (O 3) decomposition and subsequent removal of 31 organic contaminants including endocrine disrupting compounds, pharmaceuticals, and personal care products. The O 3 dose was normalized based upon total organic carbon (TOC) and nitrite to allow comparison between the different wastewaters with respect to O 3 decomposition. EfOM with higher molecular weight components underwent greater transformation, which corresponded to increased O 3 decomposition when compared on a TOC basis. Hydroxyl radical ( OH) exposure, measured by parachlorobenzoic acid ( pCBA), showed that limited OH was available for contaminant destruction during the initial stage of O 3 decomposition ( t < 30 s) due to the effect of the scavenging by the water quality. Advanced oxidation using O 3 and hydrogen peroxide did not increase the net production of OH compared to O 3 under the conditions studied. EfOM reactivity impacted the removal of trace contaminants when evaluated based on the O 3:TOC ratio. Trace contaminants with second order reaction rate constants with O 3 ( k O 3 ) > 10 5 M −1 s −1 and OH ( k OH) > 10 9 M −1 s −1, including carbamazepine, diclofenac, naproxen, sulfamethoxazole, and triclosan, were >95% removed independent of water quality when the O 3 exposure ( ∫ O 3 ⅆ t ) was measurable (0–0.8 mg min/L). O 3 exposure would be a conservative surrogate to assess the removal of trace contaminants that are fast-reacting with O 3. Removal of contaminants with k O 3 < 10 M − 1 s − 1 and k OH > 10 9 M −1 s −1, including atrazine, iopromide, diazepam, and ibuprofen, varied when O 3 exposure could not be measured, and appeared to be dependent upon the compound specific k OH. Atrazine, diazepam, ibuprofen and iopromide provided excellent linear correlation with pCBA ( R 2 > 0.86) making them good indicators of OH availability.

Hydrogen-rich gas production from biomass steam gasification in an updraft fixed-bed gasifier combined with a porous ceramic reformer

This paper investigates the hydrogen-rich gas produced from biomass employing an updraft gasifier with a continuous biomass feeder. A porous ceramic reformer was combined with the gasifier for producer gas reforming. The effects of gasifier temperature, equivalence ratio (ER), steam to biomass ratio ( S/ B), and porous ceramic reforming on the gas characteristic parameters (composition, density, yield, low heating value, and residence time, etc.) were investigated. The results show that hydrogen-rich syngas with a high calorific value was produced, in the range of 8.10–13.40 MJ/Nm 3, and the hydrogen yield was in the range of 45.05–135.40 g H 2/kg biomass. A higher temperature favors the hydrogen production. With the increasing gasifier temperature varying from 800 to 950 °C, the hydrogen yield increased from 74.84 to 135.4 g H 2/kg biomass. The low heating values first increased and then decreased with the increased ER from 0 to 0.3. A steam/biomass ratio of 2.05 was found as the optimum in the all steam gasification runs. The effect of porous ceramic reforming showed the water-soluble tar produced in the porous ceramic reforming, the conversion ratio of total organic carbon (TOC) contents is between 22.61% and 50.23%, and the hydrogen concentration obviously higher than that without porous ceramic reforming.

Long‐Term Study of Properties of a Xerofluvent of the Guadalquivir River Valley under Organic Fertilization

The long‐term effect of inorganic and organic fertilization in a vegetable crop rotation on soil chemical and biochemical properties was investigated in a trial in southern Spain. Two crops were grown in succession, potato (Solanum tuberosum L.) and a mixed‐cropped strawberry–onion (Fragaria vesca L.–Allium cepa L.). Total organic carbon (TOC), Kjeldahl‐N, bicarbonate‐extractable P (Olsen‐P), ammonium acetate extractable‐potassium (AAE‐K), microbial biomass carbon (Cmic), and enzyme activity (dehydrogenase, β‐glucosidase, protease, and alkaline phosphatase) were determined in soils in the seventh and eighth year of management comparison. The metabolic quotient (qCO2) and the Cmic to TOC ratio were also calculated. Organically fertilized soils showed significant increases in TOC and Kjeldahl‐N, available‐P, AAE‐K, microbial biomass C, and enzymatic activities compared with those found under inorganically fertilized soils. The qCO2 values were greater in inorganic than in organic fertilized plots indicating a lower microbial community respired at a greater rate in inorganic fertilized soils. The Cmic to TOC ratio in organic plots was lower than in inorganic plots indicating that microorganism in inorganically fertilized soils could have a better efficiency in the conversion of C sources to microbial biomass. Long‐term organic fertilization positively affected soil organic matter content, thus improving soil chemical and biological fertility under arid environmental conditions in southwest Spain. However precautions must be taken as excessive accumulation of some nutrients, particularly N and P, can arise from the long‐term use of compost.

Atributos microbianos e químicos do solo em sistemas de produção convencional e orgânico de maçãs no estado de Santa Catarina

O estudo foi realizado no município de Urupema-SC, com o objetivo de avaliar os efeitos dos sistemas de produção convencional e orgânico de maçãs sobre a biomassa microbiana do solo, sua atividade e as relações com o C e o N do solo. Foram feitas amostragens de solo junto à copa de 24 plantas distribuídas em uma grade de 45 x 54 m em pomares submetidos aos dois sistemas de produção, na profundidade de 0-10 cm, nos períodos de dezembro/2002 e junho/2003, para quantificação de teores de C da biomassa microbiana (CBM), C orgânico total do solo (COT), N da biomassa microbiana (NBM), N total do solo (NT), respiração basal (C-CO2) e obtenção das relações CBM:COT, NBM:NT e quociente metabólico (qCO2). O pomar orgânico (PO) apresentou, nas duas épocas de amostragem, os maiores teores de CBM, COT e a maior relação CBM:COT, comparado ao pomar convencional (PC). Os atributos NBM e NT e a relação NBM:NT mostraram-se menos sensíveis às mudanças ocasionadas pelos sistemas de manejo dos pomares e épocas de amostragem. O C-CO2 não apresentou diferença entre tratamentos, sendo apenas significativo quanto à época de amostragem, enquanto para o qCO2 os maiores valores encontrados foram no PC.

Potential of Carbon Accumulation in No‐Till Soils with Intensive Use and Cover Crops in Southern Brazil

The area under no-till (NT) in Brazil reached 22 million ha in 2004-2005, of which approximately 45% was located in the southern states. From the 1970s to the mid-1980s, this region was a source of carbon dioxide to the atmosphere due to decrease of soil carbon (C) stocks and high consumption of fuel by intensive tillage. Since then, NT has partially restored the soil C lost and reduced the consumption of fossil fuels. To assess the potential of C accumulation in NT soils, four long-term experiments (7-19 yr) in subtropical soils (Paleudult, Paleudalf, and Hapludox) varying in soil texture (87-760 g kg(-1) of clay) in agroecologic southern Brazil zones (central region, northwest basaltic plateau in Rio Grande Sul, and west basaltic plateau in Santa Catarina) and with different cropping systems (soybean and maize) were investigated. The lability of soil organic matter (SOM) was calculated as the ratio of total organic carbon (TOC) to particulate organic carbon (POC), and the role of physical protection on stability of SOM was evaluated. In general, TOC and POC stocks in native grass correlated closely with clay content. Conversely, there was no clear effect of soil texture on C accumulation rates in NT soils, which ranged from 0.12 to 0.59 Mg ha(-1) yr(-1). The C accumulation was higher in NT than in conventional-till (CT) soils. The legume cover crops pigeon pea [Cajanus cajan (L.) Millsp] and velvet beans (Stizolobium cinereum Piper & Tracy) in NT maize cropping systems had the highest C accumulation rates (0.38-0.59 Mg ha(-1) yr(-1)). The intensive cropping systems also were effective in increasing the C accumulation rates in NT soils (0.25-0.34 Mg ha(-1) yr(-1)) when compared to the double-crop system used by farmers. These results stress the role of N fixation in improving the tropical and subtropical cropping systems. The physical protection of SOM within soil aggregates was an important mechanism of C accumulation in the sandy clay loam Paleudult under NT. The cropping system and NT effects on C stocks were attributed to an increase in the lability of SOM, as evidenced by the higher POC to TOC ratio, which is very important to C and energy flux through the soil.

Characterization of Polish Sewage Sludges with Respect to Fertility and Suitability for Land Application

Twenty-one varieties of sewage sludge from municipal, municipal-industrial and industrial areas were analysed for their suitability for agricultural purposes. The samples were taken from an agricultural area of Poland characterised by a low level of industrialisation. The sewage sludges were characterised for total organic carbon and nitrogen, pH, available phosphorous and potassium, cation exchange capacity, total exchangeable bases, the degree of base saturation, the total trace metals (such as Cd, Co, Ni, Pb, Cu, Mn, Zn, Sr, V, Cr) and the content of polycyclic aromatic hydrocarbons (16 PAHs from EPA list). The results showed that the studied sludges can potentially enhance soil's agronomic properties. However in a few cases, the pH, ratio of total organic carbon to total nitrogen (TOC/Nt) and electrical conductivity were the exceptions. Trace metal contents in the sewage sludge studied varied widely (statistical significant) as a result of the size of the sewage producing unit, and especially, the content of industrial sludge. The results obtained for PAHs in sewage sludge showed a clear differentiation in the content of PAHs, which ranged from 2039 to 36439 μg/kg. The predominant contribution of 3- and 4-ring PAHs was observed. In the case of 6 sewage sludges the PAH content twice exceeded the allowable value.

Transformation of organic matter during co-composting of pig manure with sawdust

Co-composting of pig manure with sawdust was studied in order to characterize the organic transformation during the process, using both chemical and spectroscopic methods. Humic acids (HA) and fulvic acids (FA) were fractionated from immature and mature pig manure compost, and characterized. After 63 days of composting, the ratio of total organic carbon and soluble organic carbon decreased to a satisfactory low level and the solid and soluble C/N ratios decreased rapidly for the first 35 days before attaining a constant value, indicating compost maturity. Humification could be responsible for the increase in humic acid proportion during composting. The increase in the aromatic bonds after composting, as indicated by the reduction of C/H and C/O ratios of HA and FA, resulted in a more stabilized product. A substantial increase in high molecular weight compounds along with a small increase in low molecular weight compounds was found in mature compost. Moreover the HA also had more complex organic compounds at this stage. Fluorescence spectral analysis showed an increase in the maximum wavelength of HA associated with the contents of aromatic structures in solution. A decrease in relative absorbance of HA at 1160 cm −1, 2950 cm −1 and 2850 cm −1 was seen in the FTIR spectra indicating the decomposition of complex organic constituents, into simpler ones. Increase in the aromatic compounds with higher stability could account for the relative increase in the absorbance of HA at 1650 cm −1 and 1250 cm −1 of the mature compost. The composition of FA was not much altered, indicating most of the degradation of organic matter occurred in HA. Data from organic carbon, C/N ratio, elemental analysis, E 4/ E 6 ratio, gel chromatography, fluorescence and FTIR spectra indicated an increase in polycondensed structures and the presence of more stable organic matter in the mature compost.

Relation between PAH and black carbon contents in size fractions of Norwegian harbor sediments

Distributions of total organic carbon (TOC), black carbon (BC), and polycyclic aromatic hydrocarbons (PAH) were investigated in different particle size fractions for four Norwegian harbor sediments. The total PAH (16-EPA) concentrations ranged from 2 to 113 mg/kg dry weight with the greatest fraction of PAH mass in the sand fraction for three of the four sediments. TOC contents ranged from 0.84% to 14.2% and BC contents from 0.085% to 1.7%. This corresponds to organic carbon (OC = TOC − BC) contents in the range of 0.81–14% and BC:TOC ratios of 1.3–18.1%. PAH isomer ratios suggested that the PAH in all four sediments were of pyrogenic origin. Furthermore, stronger correlations between PAH versus BC ( r 2 = 0.85) than versus OC ( r 2 = 0.15) were found. For all size fractions and bulk sediments, the PAH-to-BC ratios for the total PAHs were on average 6 ± 3 mg PAH/g BC. These results suggest that PAH distributions were dominated by the presence of BC, rather than OC. As sorption to BC is much stronger than sorption to OC, this may result in significantly lower dissolved concentrations of PAH than expected on the basis of organic carbon partitioning alone.

Interactive oxidation of photoelectrocatalysis and electro-Fenton for azo dye degradation using TiO 2–Ti mesh and reticulated vitreous carbon electrodes

A crystallized TiO 2 thin film was prepared by electrolytic anodization of a pure Ti mesh in sulfuric acid–phosphoric acid–hydrogen peroxide and hydrofluoric acid–sodium fluorid–hydrogen peroxide electrolyte solutions. The TiO 2 particles directly grown on the Ti mesh surface had the regular anatase crystal structure. The TiO 2 thin film showed a multiporous structure and the mean micropore size was about 260 nm. The azo dye orange-G degradation reaction was studied in an undivided cell by using the air-diffusion reticulated vitreous carbon as the cathode for the H 2O 2 electrogeneration and TiO 2–Ti mesh as the photoanode for the photoelectrocatalysis under ultraviolet light irradiation. The heterogeneous photoelectrocatalysis and the homogeneous electro-Fenton reaction simultaneously occurred in one reaction system, while H 2O 2 was produced by a two-electron reduction of oxygen and the ferrous ion was supplied by the dosing or electrogeneration method. In the photo-electro-integrated oxidation reaction system, both the degradation rate and the removal ratio of total organic carbon were enhanced for orange-G dye which was ascribed to interactive oxidation processes of photoelectrocatalysis, electro-Fenton and electrooxidation reaction. Ion chromatogram results indicate that the total mineralization reaction was much delayed to produce inorganic ions and groups although the complete decolorizing degradation could be achieved for orange-G dye.

Organic Matter Fractions Involved in Degradation and Humification Processes During Composting

The changes in the different organic matter (OM) fractions of lignocellulosic wastes during composting were studied and related to OM humification parameters and compost maturation degree. For this purpose, four mixtures of lignocellulosic materials (lemon tree prunings, cotton waste, brewery waste, olive husk, olive leaves and the solid fraction of olive mill wastewater) were composted in a static pile system with forced ventilation. The evolution of the parameters humic acid to NaOH-extractable organic carbon proportion or PAH (HAC/EXC × 100), humic to fulvic acid ratio (HAC/FAC), cation exchange capacity to total organic carbon ratio (CEC/TOC), and water-soluble organic carbon to organic nitrogen ratio (HOC/Organic-N), clearly reflected the increase in the degree of humification and stability of the OM during the composting process in all four mixtures. The concentration of water-soluble carbohydrates was significantly correlated with PAH, HAC/FAC and the HOC/Organic-N ratio in only two mixtures along the composting processes. In general, there were statistically significant correlations between the polyphenol concentration in different fractions (water soluble, NaOH extractable, and fulvic and humic acids) and the humification parameters and maturity indices, especially with PAH, HAC/FAC and HOC/Organic-N, which shows the participation of these compounds in the synthesis of humic substances. On the other hand, the lignocellulosic compounds, lignin, cellulose and hemicellulose, seem to play an important role in the increase of cationic exchange sites in the OM, as can be seen from their correlation with CEC/TOC ratio.

Stable carbon isotope ratios in lake and swamp sediments as a proxy for prehistoric forest clearance and crop cultivation in the Neotropics

Close correspondence between stable carbon isotope ratios (δ 13 C), pollen, and charcoal profiles in sediment cores from Laguna Zoncho and Machita swamp, Costa Rica, shows that prehistoric forest clearance and crop cultivation can be detected in the stable carbon isotope ratios of total organic carbon (δ 13C TOC ). Analyses of I´ 13C TOC complement evidence from pollen, charcoal, and phytoliths and provide a proxy that is sensitive to the intensity and/or proximity to core sites of prehistoric forest clearance and agriculture in watersheds. Stable carbon isotope analyses are particularly useful in situations in which other evidence of forest clearance and agriculture is limited.