Decrease In Total Organic Carbon Research Articles

Degradation and toxicity depletion of RB19 anthraquinone dye in water by ozone-based technologies.

This research investigated the discoloration and mineralization of Reactive Blue 19 (RB19) anthraquinone dye by single ozonation, single UV radiation and ozonation jointed with UV radiation (O3/UV). The problem was approached from two points of view: with the objective of color removal or the mineralization of solution. In each case, the optimum operating conditions were different. Ozonation was the most effective treatment for color removal, while the combined O3/UV treatment was for mineralization. Major intermediates of the dye degradation were identified by gas chromatography/mass spectrometry and a degradation pathway was proposed. In addition, a clear decrease of the toxicity of the dye was achieved at the end of the experiments. The effect of initial dye concentration, pH, ozone dose, and UV radiation on the degradation of the dye and decrease of total organic carbon was investigated, in order to establish the optimal operating conditions to achieve discoloration, mineralization or a combination of both.

Degradation of sewage sludge compost disposed on the soil

This study aimed to monitor degradation of compost from undigested sewage sludge disposed on soil surface or incorporated it. The sewage sludge was blended with wood sawdust during a 90-day composting to achieve a C/N ratio of 9. Each waste was dosed based on its total content of nitrogen and on an annual dose of 500 kg ha-1, which is broadly recommended for forage fertilization. After incorporation and surface applied (five replicates each), waste mineralization was monitored for 131 days by samplings taken from both conditions for further analyses. The samples were measured for total organic carbon (TOC); easily oxidizable carbon (OOC); total nitrogen (TN); ammonia and nitric nitrogen, and from them the total organic nitrogen (ON); volatile solids; and water content. The findings pointed to a decrease in TOC, OOC and ON contents throughout monitoring, regardless of disposal method, however, most remarkable whether incorporated to the soil, computing mineralization rates above 87%.

Vermicomposting of cow dung, kitchen waste and sewage sludge with bagasse using Eisenia fetida

The sugar cane industry produces significant amounts of cane trash and bagasse. Inappropriate disposal of agro-wastes can lead to environmental problems. Converting wastes such as cane trash and bagasse (Bg) to a fertilizer and conditioner is the aim of sustainable waste management in sugar cane industry. Cow dung (CD), kitchen waste (KW), and sewage sludge (SS) were mixed with bagasse as amendment in different proportions: Bg:CD (1:1), Bg:CD (1:2), Bg:SS (1:1), Bg:SS (1:2), Bg:KW (1:1) and Bg:KW (1:2) in triplicate treatment with Eisenia fetida . Chemical analysis of the samples showed a significant decrease in total organic carbon (TOC) (20%-54%), total Kjeldahl nitrogen (TKN) (9.5%-39.7%) and C:N ratio (12%-31.2%), while total potassium (31.4%-54%) and available phosphorus (32%-55%) contents increased during vermicomposting. A significant difference was observed among weight and number of worms in control with other treatments at the end of vermicomposting. According to obtained results vermicomposting is an efficient method for sustainable recycling different classes of waste produced in sugar cane agro-industry.

Peatland development and climate changes in the Dajiuhu basin, central China, over the last 14,100 years

Abstract Peatlands are one of the optimal archives for paleoclimate research and their records contain a detailed history of climatic and environmental variations during their formation. Here we collected a peat profile from the Dajiuhu basin in central China and analyzed several geochemical proxies, such as Total Organic Carbon (TOC), Total Nitrogen (TN), Titanium (Ti) and Aluminum (Al), to investigate the history of peat development. The results show that the peat growth was initiated after around 12.8 cal ka BP at the sampling site and the TOC and TN contents kept stable during the Holocene except during the periods of 10.5–9.0 cal ka BP and recent 1.5 cal ka BP. However, compared with other TOC records in the Dajiuhu basin, the history of peat development varied greatly in different sampling sites, indicating that the peat development in the Dajiuhu basin probably responds to both climate changes and local geological and hydrological conditions. Investigations of the interactions between climate change and peat development record in this study suggest that peat development presented significant responses to the large and rapid decreases in East Asian Summer Monsoon intensity, such as the 9.2 ka monsoon weakening event. However, the obvious long-term decreasing trend of monsoon precipitation during the mid-late Holocene did not lead to the degradation of the Dajiuhu peat, probably resulting from relatively stable temperature. In addition, the sharp decrease of TOC and TN values in the surface 15 cm of Dajiuhu peat was probably attributed to increased human activity.

The Vaca Muerta–Quintuco system (Tithonian–Valanginian) in the Neuquén Basin, Argentina: A view from the outcrops in the Chos Malal fold and thrust belt

The Vaca Muerta–Quintuco system (uppermost lower Tithonian–lower Valanginian) is a thick shallowing-upward sedimentary cycle consisting of dark bituminous shales, marlstones, limestones, and sandstones, cropping out in the Neuquen Basin, west–central Argentina. This paper analyzes three outcrop sections in Chos Malal area, northem Neuquen province. Detailed facies analysis allows us to differentiate six facies associations, representing basinal to proximal outer ramp facies of a homoclinal carbonate ramp system (Vaca Muerta Formation) and basinal to shoreface facies of a mixed carbonate–siliciclastic shelf system (Quintuco Formation), prograding westward from the eastern margin of the basin. Two sequence hierarchies were recognized: 5 composite depositional sequences (third order) and 15 high-frequency sequences (fourth order). Fluctuations in organic matter content within the Vaca Muerta Formation suggest a relationship with depositional sequences, finding the highest values associated with transgressive systems tract, whereas the transition to the Quintuco Formation shows a strong decrease in total organic carbon. The x-ray diffraction studies show an increase of clay minerals and quartz in the transgressive systems tract of the Vaca Muerta Formation and an increase in the content of calcite in highstand systems tracts. This pattern is reversed in the Quintuco Formation. Our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter, clay minerals, facies, stacking pattern, and relative sea level changes in this exceptional shale oil and shale gas unconventional reservoir. This study may be helpful for a better postulate of petrophysical and geomechanical models for unconventional exploration.

Evolution and recovery of original total organic carbon for carbonate source rocks with different total organic carbon in the Tazhong area, Tarim Basin, China

ABSTRACTSource rocks generate and expel hydrocarbon with thermal evolution, which lead to a decrease of total organic carbon (TOC) content. A new quantitative model for original total organic carbon (TOCo) content evolution and recovery was proposed, and then was used to the carbonate source rocks with different TOCs (CSRDTOC) in the Tazhong area, Tarim Basin, China. Studies showed that the higher the TOC of source rocks, the bigger the range of TOC reduction and recovery coefficient. When vitrinite reflectance (VR) is equal to 2.5%, recovery coefficients of TOCo = 0.2%, 0.4%, and 1.0% are 1.43, 1.66, and 2.01, respectively. It must restore TOCo when we evaluate source rocks at the stage of high overmaturity and predict oil and gas resources.

Biomarkers and inorganic proxies in the paleoenvironmental reconstruction of mires: The importance of landscape in Las Conchas (Asturias, Northern Spain)

We determined the lipid distributions (n-alkanes, n-alkan-2-ones, n-alkanoic acids), total organic carbon (TOC), total nitrogen (TN), Ca/Mg and ash content in Las Conchas mire, a 3.2m deep bryophyte-dominated mire in Northern Spain covering 8000calyr BP. Bog conditions developed in the bottom 20cm of the profile, and good preservation of organic matter (OM) was inferred from n-alkanoic acid distribution, with the exception of the uppermost 20cm (last ca. 200yr). Microbial synthesis of long chain saturated fatty acids from primary OM likely produced a dominance of short chain n-alkanoic acids with a bimodal distribution, as well as the lack of correspondence between the n-alkane and n-alkanoic acid profiles in the upper 20cm. This was accompanied by an increase in ash content, a decrease in TOC and variation in n-alkane ratios, thereby suggesting significant changes in the mire, namely drainage and transformation to a meadow, in the last ca. 200yr. The distribution of n-alkan-2-ones indicated an increase in bacterial source from the bottom of the record to 94cm, whereas their distribution in the upper part could be attributed mainly to plant input and/or the microbial oxidation of n-alkanes. The different n-alkane proxies showed variations, which we interpreted in terms of changes in vegetation (Sphagnum vs. non-Sphagnum dominated phases) during the last 8000calyr BP. C23 was the most abundant homolog throughout most of the record, thereby suggesting dominant humid conditions alternating with short drier phases. However, such humid conditions were not linked to paleoclimatic variation but rather to geomorphological characteristics: Las Conchas mire, at the base of the Cuera Range, receives continuous runoff—even during drier periods—which is not necessarily accompanied by additional mineral input to peat, producing the development of Sphagnum moss typical of waterlogged ecotopes and damp habitats. Thus, although geochemical proxies indicated an ombrotrophic regime in the mire, geomorphological characteristics may make a considerable contribution to environmental conditions.

Distribution of active organic matter in the soil profiles of natural and agricultural ecosystems

The amount of active (potentially mineralizable) organic carbon (C0) in the 1-m-deep layer of typical chernozem, dark-gray forest soil, and gray forest soil was estimated for virgin plots and arable land. It was shown that C0 is mainly found in the topsoil (0–20 cm), where its pool reaches 32–60% of the total amount of C0 in the layer of 0–100 cm. The C0 content and its portion in the total organic carbon decrease down the soil profiles. The disturbance of the structure of the pool of active organic carbon—the loss of the moderately mineralizable (0.1 > k2 > 0.1 day–1) fraction—takes place in the upper horizon of plowed soils. The total pool of C0 in the upper meter of typical chernozem under cropland and under meadow-steppe cenosis comprises 2.8 and 5.2 t/ha, respectively; for the dark gray forest soil under cropland and forest, it reaches 5.5 and 9.8 t/ha, respectively; and for the gray forest soil under cropland and forest, 2.4 and 3.4 t/ha, respectively. The pools of C0 in the typical chernozem. dark gray forest, and gray forest soils are comparable with the values of the annual C–CO2 emission from the soils of these zones.

Assessment of toxicity and biodegradability on activated sludge of priority and emerging pollutants

ABSTRACTSeveral methods for evaluating the toxicity and biodegradability of hazardous pollutants (chlorinated compounds, chemical additives and pharmaceuticals) have been studied in this work. Different bioassays using representative bacteria of marine and terrestrial ecosystems such as Vibrio fischeri and Pseudomonas putida have been used to assess the ecotoxicity. Activated sludge was used to analyse the effect of those pollutants in a biological reactor of a sewage treatment plant (STP). The results demonstrate that none of the compounds is toxic to activated sludge, except ofloxacin to P. putida. The additives tested can be considered moderately toxic according to the more sensitive V. fischeri assays, whereas the EC50 values of the pharmaceuticals depend on the specific microorganism used in each test. Regarding the biodegradability, respirometric measurements were carried out for fast biodegradability assessment and the Zahn–Wellens test for inherent biodegradability. The evolution of the specific oxygen uptake rate (SOUR) showed that only diethyl phthalate was easily biodegradable and acetylsalicylic acid was partially biodegradable (98% and 65% degradation, respectively). The persistence of dichloromethane, ofloxacin and hidrochlorothiazide was confirmed along the 28 days of the Zahn-Wellens test whereas 1,1,1-trichloroethane showed inherent biodegradability (74% removal). Most of the chlorinated compounds, pharmaceuticals, bisphenol A and ethylenediaminetetraacetic acid were partially degraded in 28 d with total organic carbon (TOC) reduction ranging from 21% to 51%. Sulphamethoxazole showed certain biodegradation (50% removal) with TOC decrease around 31%, which indicates the formation of non-biodegradable by-products.

Application of plasma-sprayed TiO2 coatings for industrial (tannery) wastewater treatment

Fine-structured photocatalytic TiO2 coatings were deposited by atmospheric plasma spraying (APS) on austenitic stainless steel coupons. One commercial spray-dried nanostructured TiO2 powder and five spray-dried powders obtained from suspensions containing mixtures of submicrometric and nanometric TiO2 particles were used as feedstock materials. Coating microstructure and phase composition were characterised using FEG-SEM and XRD techniques. The photocatalytic activity of the coatings was determined by measuring the degradation of methylene blue dye in aqueous solution. The experimental data were observed to follow a pseudo-first-order kinetic. The kinetic constants displayed a clear relationship with coating anatase content.The photocatalytic decontamination capability of one of these APS coatings was subsequently investigated by treating an industrial tannery wastewater. The photocatalytic experiments with these TiO2 coated coupons were carried out in a self-designed reactor. Partial degradation of the pollutants was observed, owing to a decrease in Total Organic Carbon (TOC), in addition to a significant decolouration effect, mainly relating to the removal of aromatic organic compounds typically present in tannery wastewater. The results demonstrate the potential use of plasma-sprayed photocatalytic TiO2 coatings in tannery wastewater treatment.

Phosphatase activity and its relationship with physical and chemical parameters during vermicomposting of filter cake and cattle manure.

Recycling of phosphorus (P) from organic residues (ORs) is important to develop environmentally friendly agriculture. The use of this P source depends on phosphatase enzymes, which can be affected by a chain of parameters during maturation of ORs. In this study the phosphatase activity levels throughout vermicomposting of filter cake (FC) and cattle manure (CM) were correlated with different physical and chemical parameters in an effort to increase the knowledge about recycling of P from ORs. FC presented higher total nitrogen content (TNC), total organic carbon (TOC), humic acid (HA) content, water-soluble P (WSP), phosphatase activities and nanopore volume than CM during vermicomposting. Decreases in TOC of CM resulted from carbohydrate mineralization, which was not observed for FC. CM showed increased hydrophobic index during vermicomposting while FC showed a slight decrease. Phosphatase activities correlated positively with TOC, pH and WSP and negatively with HA content for both vermicomposts. Nanopore volume was negatively correlated with phosphatase activities for FC but not for CM. No correlations between hydrophobicity and phosphatase activities were found for FC. Increased hydrophobicity throughout vermicomposting of CM could be partially associated with decreases in phosphatase levels.

Combined process for removal of tetracycline antibiotic – Coupling pre-treatment with a nickel-modified graphite felt electrode and a biological treatment

Biodegradability improvement of tetracycline-containing solutions after an electrochemical pre-treatment was examined. Cyclic voltammetry with a nickel electrode revealed a significant electrochemical activity of tetracycline, in both oxidation and reduction. Electrochemical treatment was therefore performed in a home-made flow cell using a nickel-modified graphite felt electrode as the working electrode. Optimal conditions, namely 100 mg l−1 initial tetracycline, above 0.45 V potential, and between 1 and 6 ml min−1 flow rate, led to a more than 99% conversion yield of tetracycline in oxidation in alkaline conditions, after only a single pass through the percolation cell. However, total organic carbon (TOC) analyses revealed a low mineralization level, i.e., always below 31%, underscoring the importance of a combined electrochemical and biological treatment. This was confirmed by the favorable trends of the COD/TOC ratio, decreasing from 2.7 to 1.9, and the average oxidation state, increasing from 0.044 to 1.15, before and after oxidation pretreatment at 0.7 V and 3 ml min−1 flow rate. Electrolyzed solutions appeared biodegradable, since BOD5/COD increased from 0 to 0.46 for untreated and pretreated TC at 0.7 V/SCE. Biological treatment showed only biosorption for non-pretreated tetracycline, while after 11.5 days of culture, the mineralization of solutions electrolyzed in oxidation was 54%, leading to a 69% overall TOC decrease during the combined process.

Potential of multisyringe chromatography for the on-line monitoring of the photocatalytic degradation of antituberculosis drugs in aqueous solution

In this study, a multisyringe chromatography system (MSC) using a C18 monolithic column was proposed for the on-line monitoring of the photocatalytic degradation of isoniazid (INH, 10mgL−1) and pyrazinamide (PYRA, 5mgL−1) mixtures in aqueous solution using a small sample volume (200μL) with an on-line filtration device in a fully automated approach. During the photocatalytic oxidation using TiO2 or ZnO semiconductor materials, total organic carbon (TOC) and the formed intermediates were analyzed off-line using ion chromatography, ion exclusion HPLC, and ESI-MS/MS. The results showed that TiO2 exhibits a better photocatalytic activity than ZnO under UV irradiation (365nm) for the degradation of INH and PYRA mixtures, generating 97% and 92% degradation, respectively. The optimal oxidation conditions were identified as pH 7 and 1.0gL−1 of TiO2 as catalyst. The mineralization of the initial organic compounds was confirmed by the regular decrease in TOC, which indicated 63% mineralization, and the quantitative release of nitrate and nitrite ions, which represent 33% of the nitrogen in these compounds. The major intermediates of INH degradation included isonicotinamide, isonicotinic acid, and pyridine, while the ESI-MS/MS analysis of PYRA aqueous solution after photocatalytic treatment showed the formation of pyrazin-2-ylmethanol, pyrazin-2-ol, and pyrazine. Three low-molecular weight compounds, acetamide, acetic acid and formic acid, were detected during INH and PYRA decomposition. PYRA was more resistant to photocatalytic degradation due to the presence of the pyrazine ring, which provides greater stability against OH attack.

Microbial biodegradation of landfill leachates located in São Paulo state, Brazil

Background Leachate is one of the most problems present in landfills, mainly due to large production and the ability to cause serious environmental damages next to these areas. An activated sludge process is commonly used for biodegrading organic contaminants in wastewater using a mixed population of microorganisms. This technology is consolidated for wastewater treatment, and recently has been used as the first step in leachate treatment process. In this work, initially, physical-chemical and biological parameters of the leachate from different landfills (Areais and Bandeirantes, both in SP), were evaluated. Also the microbial consortium present in the sludge from a wastewater plant of the Capuava Petrobras Refinery, (SP) was characterized. Purpose of this work was to study the kinetic properties of the activated sludge process by removal of the pollutant organic matter, represented by the decrease of Total Organic Carbon (TOC). In order to verify the bioremediation efficiency, experiments were developed comparing the leachates before and after biological treatments. Results show that combination of leachate and sludge can decrease the organic load significantly, demonstrating bioremediation efficiency.

Total and labile pools of soil organic carbon in cultivated and undisturbed soils in northern India

Labile fractions of soil organic matter (SOM) have been used as indicators for land use induced changes in soil quality. Differences in soil C pools under row crop production and uncultivated soils may provide information about soil C sequestration. The impact of agroforestry consisting of poplar with wheat, rice–wheat, maize–wheat and sugarcane agro-ecosystems on total organic carbon (TOC) and labile pools, viz. water-extractable (WEOC), hot water-soluble (HWC), KMnO4-oxidizable, microbial biomass and mineralizable C; and organic C fractions of different oxidizability was studied at 22-sites for each land use. Cultivation resulted in decrease in TOC (21–36%) and dehydrogenase activity (by 2.8–3.4mgkg−1soilh−1) compared to uncultivated soils. Labile C pools, except WEOC, were correlated (P<0.05), though the amount extracted by different methods varied considerably suggesting that each method enumerated different fractions of TOC. Agroforestry and sugarcane systems were characterized by very labile C compared with uncultivated soils and the soils under rice–wheat and maize–wheat systems. Conversely, uncultivated soils and the soils under maize–wheat and rice–wheat held greater proportion of organic C in recalcitrant fractions. Results suggest that soil organic C (SOC) pools in agroforestry and sugarcane systems could be decomposed under land use alterations. However, no single soil C pool alone was suitable as a sensitive indicator for land use induced changes in SOM. A composite of soil indicators encompassing labile C, KMnO4-oxidizable C, non-labile and recalcitrant C, mineralizable C, basal soil respiration, and dehydrogenase activity could distinguish different land use systems.

Influence of total organic carbon deposition on the inventory of gas hydrate in the Indian continental margins

Total organic carbon (TOC) content of marine sediments represents residual carbon, originally derived from terrestrial and marine sources, which has survived seafloor and shallow subseafloor diagenesis. Ultimately, its preservation below the sulfate reduction zone in marine sediments drives methanogenesis. Within the gas hydrate stability zone (GHSZ), methane production along continental margins can supersaturate pore fluids and lead to the formation of gas hydrate. In this paper we examine the inventory and sources of TOC in sediments collected from four regions within the GHSZ along the Indian continental margins. The recovered sediments vary in age from Oligocene to recent. Mean TOC abundance is greatest in the Krishna–Godavari (K–G) Basin and decreases progressively to the Mahanadi basin, Andaman wedge, and Kerala–Konkan (K–K) Basin. This decrease in TOC is matched by a progressive increase in biogenic CaCO3 and increasing distance from terrestrial sources of organic matter and lithogenic materials. Organic carbon sources inferred from C/N and δ13CTOC range from terrestrial (K–G Basin) to mixed marine and terrestrial (Mahanadi Basin), to marine dominant (Andaman wedge and K–K Basin). In the K–G Basin, variation in the bulk δ13CTOC is consistent with changes in C3 and C4 vegetation driven by monsoon variability on glacial-interglacial timescales, whereas in the Mahanadi Basin a shift in the δ13CTOC likely reflects the onset of C4 plant deposition in the Late Miocene. A large shift the δ13CTOC in the K–K basin is consistent with a change from C3 to C4 dominated plants during the middle Miocene. We observe a close relationship between TOC content and gas hydrate saturation, but consider the role of sedimentation rates on the preservation of TOC in the zone of methanogenesis and advective flow of methane from depth. Although TOC contents are sufficient for in situ methanogenesis at all the sites where gas hydrates were observed or inferred from proxy data, seismic, borehole log, pressure core, and gas composition data coupled with relatively high observed gas hydrate saturations suggest that advective gas transport may also play a role in the saturation of methane and the formation of gas hydrates in these regions. Although TOC content may be a first order indicator for gas hydrate potential, the structural and stratigraphic geologic environment along a margin will most likely dictate where the greatest gas hydrate saturations will occur.

A new integrated multi-trophic aquaculture system consisting of Styela clava, microalgae, and Stichopus japonicus

The possibility of the integrated multi-trophic aquaculture (IMTA) model consisting of Styela clava, microalgae, and Stichopus japonicus was examined in this research, in which microalgae could remove dissolvable nutrients produced by S. clava and S. japonicus to maintain the dissolvable nutrients at a lower level, and provide sufficient dissolved oxygen in the water body through photosynthesis at the same time. S. clava helped accumulate organic matter in the sediments, and the content of total organic carbon (TOC) in the sediments was significantly higher in the groups of S. clava than that in the control without ascidian. S. japonicus were able to effectively remove the particulate organic carbon and nitrogen from the sediments, and hence an obvious decrease in TOC and total nitrogen on the surface sediments. It was also found that the reproduction of bacteria on the surface sediments attributed to the biological interference of S. japonicus. It is concluded from our experiments that the IMTA system of microalgae–S. clava–S. japonicus does not have organic matter accumulated in the sediments, or the dissolved organic matter polluted, which indicates that this IMTA model is not only an aquaculture system, but also a system purifying N and P in the water body.

Management of municipal solid wastes and production of liquid biofertilizer through vermic activity of epigeic earthworm Eisenia fetida

BackgroundAnimal and municipal solid wastes (MSW) create environmental pollution. It is one of the most challenging problems which require attention. Efforts were made for the conversion and eco-management of animal and municipal wastes into safe and hygienic products by an epigeic earthworm Eisenia fetida. The excess use of chemical fertilizer and synthetic pesticide has changed the texture of soil and its fertility.ResultThe chemical analysis of different combinations of MSW and animal wastes before and after vermicomposting showed, that there was significant decrease in total organic carbon, C/N ratio and pH in the final vermiwash. The significant increase in the level of total Kjeldahl nitrogen, total potassium, total phosphorus and total calcium was observed after vermicomposting in all the prepared combinations of MSW with different animal dungs.ConclusionIt was recorded that due to the vermic activity, the MSW and animal wastes get changed into nutrient rich, ecofriendly, and biofertilizer. The observations reveal that by vermicomposting not only ecofriendly management of MSW can be achieved but also potent vermiwash can be made which are helpful in increasing the production of crops.

Remediation of aquatic environment contaminated with the iminodiacetic acid metal complexes using ferrate(VI)

The aim of this investigation is to assess the applicability of ferrate(VI) in the treatment of M(II)-complexed species viz., Cd(II)-IDA and Ni(II)-IDA from aqueous solutions. The batch reactor operations are performed for various physico-chemical parametric studies. The batch reactor studies indicate that a fast and efficient decomplexation/removal of Cd(II)/Ni(II)-IDA is occurred at varied molar concentrations (0.3–10.0mmol/L) of the complexed species treated with a constant dose of Fe(VI) (i.e., 1.0mmol/L). Moreover, decreasing the pH values from 10.0 to 8.0 is further favored the decomplexation/degradation of these pollutant species. The time dependence data is utilized further in demonstrating the kinetic studies conducted for various molar ratios of M(II)-IDA to Fe(VI) as studied at different pH values (i.e., pH 10.0–8.0). The kinetic results show that the decomplexation/oxidation of complexed species is followed with pseudo-first and pseudo-second order rate kinetics for both the systems studied. Further, these results indicate that the rate of decomposition is followed with first order rate kinetics for both the reactants i.e., Fe(VI) and M(II)-IDA species. This infers that a 1:1 stoichiometry prevails to the decomposition M(II)-IDA species by Fe(VI). The overall rate constant values indicate that decreasing the pH causes to increase the rate of degradation/decomplexation of M(II)-IDA by Fe(VI). Decomplexation/oxidation of the complexes shows that a significant degradation/oxidation of the IDA occurred since a significant decrease in total organic carbon (TOC) is obtained. Again, lower pH values favor the oxidation/mineralization of IDA. Remarkably, a significant removal of free cadmium or nickel is obtained simultaneously. The removal of metal ions is further enhanced raising the pH of the Fe(VI) treated samples to 12.0 and almost 100% of Cd(II) was removed whereas a significant percent of Ni(II) was also removed. These results indicate that the treatment of aqueous wastes contaminated with M(II)-IDA is efficient and effective by Fe(VI).

Archaeal diversity and the extent of iron and manganese pyritization in sediments from a tropical mangrove creek (Cardoso Island, Brazil)

Even though several studies on the geochemical processes occurring in mangrove soils and sediments have been performed, information on the diversity of Archaea and their functional roles in these ecosystems, especially in subsurface environments, is scarce. In this study, we have analyzed the depth distribution of Archaea and their possible relationships with the geochemical transformations of Fe and Mn in a sediment core from a tropical mangrove creek, using 16S rRNA gene profiling and sequential extraction of different forms of Fe and Mn.A significant shift in the archaeal community structure was observed in the lower layers (90–100 cm), coinciding with a clear decrease in total organic carbon (TOC) content and an increase in the percentage of sand. The comparison of the archaeal communities showed a dominance of methanogenic Euryarchaeota in the upper layers (0–20 cm), whereas Crenarchaeota was the most abundant taxon in the lower layers. The dominance of methanogenic Euryarchaeota in the upper layer of the sediment suggests the occurrence of methanogenesis in anoxic microenvironments. The concentrations of Fe-oxyhydroxides in the profile were very low, and showed positive correlation with the concentrations of pyrite and degrees of Fe and Mn pyritization. Additionally, a partial decoupling of pyrite formation from organic matter concentration was observed, suggesting excessive Fe pyritization. This overpyritization of Fe can be explained either by the anoxic oxidation of methane by sulfate and/or by detrital pyrite tidal transportation from the surrounding mangrove soils. The higher pyritization levels observed in deeper layers of the creek sediment were also in agreement with its Pleistocenic origin.