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Query: UMLS:C1835664 (TOC)
 2,763 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A greenhouse experiment was performed to investigate the influence of pH TOC, and fractionation of Pb on phytoavailability of Pb in the rhizosphere of lettuce. And the Low molecular-weight organic acids (LMWOAs) were used to evaluate the phytoavailability of soil Pb to lettuce. The results show that the pH is lower in the rhizosphere compared to the bulk soil, and the rhizosphere becomes more acidic with increasing Pb (NO3)2 applied. In contrast, the TOC content is higher in the rhizospherer compared to the bulk soil, and more TOC accumulates in the rhizosphere with increasing Pb (NO3)2 applied. The concentrations of different fractions in rhizosphere soils follow the order of exchangeable > carbonate bound > Fe-Mn oxide bound > organic bound > residual, and for bulk soil the order is carbonate bound > Fe-Mn oxide bound > exchangeable > organic bound > residual. Compared with bulk soils, exchangeable Pb increases significantly in rhizosphere. With increasing Pb (NO3)2 applied, the transformation of residual Pb to carbonate bound and exchangeable Pb may have happened and results in the accumulation of carbonate bound and exchangeable Pb. The air-drying increases the concentration of exchangeable, carbonate bound and Fe-Mn oxide bound Pb and decreases organic bound and residual Pb. Rhizosphere and bulk soils were extracted by low molecular-weight organic acids(LMWOAs) to fractionate Pb fraction of soil pools, which is considered as the phytoavailable Pb. The results show that phytoavailable Pb in rhizosphere is much higher compared to bulk soil, and phytoavailable Pb increases with increasing Pb (NO3)2 applied due to acidification processes and accumulated TOC in the rhizosphere. Air-drying process also increases the phytoavailable Pb. The root-induced changes of Pb availability in the rhizosphere might also be related to the Pb species, especially carbonate bound and exchangeable Pb. Correlation analysis indicates that application of wet fresh rhizosphere soils and LMWOAs should be recommended in the future study on the phytoavailability of soil Pb to lettuce.
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PMID:[Phytoavailable lead in rhizosphere of lettuce]. 1711 30

Nitrobenzene (NB) was selected as the model pollutant in water and the efficiency and mechanism of degradation of NB in aqueous solution by O3/H2O2 were investigated. The effects of pH, H2O2 dose and the inhibitor or accelerant of .OH on the removal rate of NB were studied. H2O2 could obviously improve the ozonation decay rate of NB when the pH value of the solution was below 7. The removal rate of NB was enhanced remarkably while H2O2 dose was increased from 1.0 m g/L. to 4.0 mg/L. However, as H2O2 dose increased from 4.0 mg/L to 20 mg/L, the removal efficiency of NB decreased. Different quantities of H2O2 were yielded in different reaction phases of single ozonation system. Both systems of single ozonation and H2O2-catalysed ozonation could not reduce TOC observably. During the NB degradation process, organonitrogen was almost completely converted to nitrate and the pH value of the solution reduced significantly. Results of LC-MS and GC-MS analysis showed that the main intermediate products were phenolic compounds and carbonyl compounds. A possible reaction pathway of the catalytic ozonation of NB was also proposed. It was found that the catalytic ozonation of NB could be divided into two steps. First, hydroxyl radical attacked phenyl ring to form phenolic compounds, then the ring was opened, forming into various aliphatic compounds or being mineralized to inorganic compounds.
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PMID:[Effect and mechanism of degradation of nitrobenzene in aqueous solution by O3/H2O2]. 1711 34

River and sediment have unique carbon dynamics and are important sources of the dominant greenhouse gases (GHG), carbon dioxide (CO2) and methane (CH4). To understand the relationship between CO2/CH4 emissions and water quality/sediment characteristics, we have investigated critical parameters in the river water. Eight parameters of water quality (dissolved oxygen, oxidation-reduction potential [ORP], chemical oxygen demand, biochemical oxygen demand [BOD5], suspended solid, nitrate [NO3-], NH4+, and bacteria) and four sediment characteristics (total organic carbon [TOC], total nitrogen [T-N], NO3-, and ammonium [NH4+]) were measured in two of the larger rivers in Taiwan, and relevant environmental conditions were recorded. The experimental results indicated that CO2 emissions from the river were mainly affected by BOD5 concentrations and the levels of bacteria. CH4 emissions, on the other hand, were greatly affected by the ORP in the river. The correlation between CO2 emissions and sediment characteristics was insignificant (R2 < 0.3). However, TOC and T-N in the sediment may lead to increases in CH4 emissions into the atmosphere. A deeper analysis of the relationship between the different parameters and GHG emissions by ANOVA and the multiple regression method revealed that CO2 emission (y) was significantly related to bacteria number (x1) and BOD concentration (X2). The regression equation takes the form y = 0.00032x1 + 3.18089x2 + 25.37304. Also, the regression relationship between CH4 emission (y) and ORP (x) in the river can be described as y = -0.825216x + 169.02257. The relationship between CH4 emission and sediment characteristics may be described as y = 5.073962x1(TOC) + 2.871245x2(T-N) - 12.3262. Extra sampling data were collected to examine the feasibility of the developed multiple regression equations. The experimental results suggest that the emissions of such GHGs as CO2 and CH4 from rivers can be predicted using the regression equations developed here. Moreover, the emissions may be reduced by manipulating the proper factors.
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PMID:Relationship between carbon dioxide/methane emissions and the water quality/sediment characteristics of Taiwan's main rivers. 1738 98

The operational parameters and mechanism of mineralization of C.I. Reactive Yellow 84 (RY84), one of the azo dyes, in aqueous solution were investigated using sonolytic ozonation (US/O(3) oxidation). Of the pseudo-first-order degradation rate constants of TOC reduction, 9.0 x 10(-4), 7.3 x 10(-3) and 1.8 x 10(-2)min(-1) were observed with US, O3, and a combination of US and O3, respectively. These results illustrate that ozonation combined with sonolysis for removal of TOC is more efficient than ozonation alone or ultrasonic irradiation alone without considering the operating costs. With the initial pH value at 10.0, the ozone dose at 4.5 g h(-1), the energy density of ultrasound at 176 W l(-1), and the initial concentration of RY84 at 100 mg l(-1), the extent of mineralization measured as TOC loss was maximized. The variation of the concentrations of related ions (oxalate, formate, acetate, NO3(-), NO2(-), NH4(+), Cl(-), and SO4(2-)) during the reaction process was monitored. Other organic intermediates detected by GC/MS were N-methyleneaniline, phthalic acid, 4-hydroxyphthalic acid, isocyanatobenzene, aniline, 4-iminocyclohexa-2,5-dien-1-one, butene diacid and urea. Based on these findings, a tentative degradation pathway was proposed.
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PMID:Mineralization of C.I. Reactive Yellow 84 in aqueous solution by sonolytic ozonation. 1754 52

Experimental studies of photocatalytic oxidation (PCO) of VX-gas simulation substance cysteamine-S-phosphate sodium salt (NaHPO3S-CH2-CH2-NH2, CPSS) at various initial concentrations and pH were undertaken. PCO ultimately resulted in complete mineralisation of CPSS. The PCO byproducts of CPSS include acetate, oxalate and trace amounts of formate ions. The formation rates of acetate and phosphate were equal to the rate of degradation of CPSS, which indicates easy breakage of P-S, C-S and C-N bonds. Sulphate was formed more slowly due to stepwise oxidation of reduced sulphur. Amino group, generally transformed to ammonia, was partially oxidised to nitrite and nitrate in alkaline media. The fastest mineralisation in terms of both TOC degradation and phosphate formation was observed in neutral media. Under neutral media conditions, the PCO rate increased linearly with the CPSS concentration increase. The maximum efficiency by TOC degradation was observed as large as 77 mg per Wh of incident UV flux with quantum efficiency 3.8%.
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PMID:Photocatalytic oxidation of VX-simulation substance. 1767 39

A combined system consisting of an up-flow anaerobic sludge blanket (UASB) and an aerobic membrane bioreactor (MBR) was operated at 28-30 degrees C and pH 7.8-8.1 for the treatment of low-strength synthetic wastewater enriched with organic carbon and NH4Cl. The MBR slurry was recirculated into the UASB with a ratio of 50-800%. It was found that nitrite was able to accumulate steadily during the nitrification step in the MBR at a low TOC/NH4+-N ratio. The mixed liquid containing NOX(-)-N in the MBR was recirculated to the UASB, and denitrification rather than methanogenesis became the preferred pathway. Whereas, the less carbon requirement for denitrification via nitrite rather than nitrate allowed methanogenesis to proceed simultaneously in the same reactor. The combination of membrane filtration and partial nitrification in the MBR with simultaneous denitrification and methanogenesis in the UASB could stably reach 98% TOC removal and 48.1-82.8% TN removal with recirculation ratio increasing from 50% to 800%.
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PMID:The integration of methanogenesis with shortcut nitrification and denitrification in a combined UASB with MBR. 1770 46

To evaluate the role of a dam reservoir in the runoff of pollutant loadings from a forested watershed, the input-output budgets in the Ikuno dam reservoir had been investigated for eight years since 1996. The T-N, T-P, TOC and major ionic species in the bulk precipitation, stream water, and outflow were measured. The residence time calculated by using the data of the inflow and outflow was 0.3 year. The average precipitation was 1,772 mm during the investigation period (1996-2004). The direct deposition to water surface was less than one percentage to total loadings of nutrients and major ionic species. The ratios of output to input of TOC, TN, and TP were 1.04 to 1.42, and those of major ionic species were from 0.83 to 0.99 except for NO3(-), which was 1.12. However, the ratios of output to input of major ionic species except for NO3(-) at the Ikuno dam reservoir will be larger, and those of NO3(-), TOC, TN, and TP will be smaller, if we also include rain events. These results suggested that the dam reservoir played a role as a sink for pollutants in forested watershed, and that the pollutant loadings to downstream may decrease.
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PMID:Budgets of major ionic species and nutrients on a dam reservoir in forested watershed. 1771 Oct 26

Biosolids from the WWTP of Thessaloniki were examined for the leaching of phosphorus (as PO4(3-) -P), nitrogen (as NH4+ (-N) and NO3- (-N)), and organic matter (as TOC and COD), using two tests: (1) a pH static leaching test and (2) a characterization test, relating contaminant release to the liquid to solid (L/S) ratio. Moreover, a Microtox toxicity test was conducted, to examine the pH dependency of the toxicity of the sludge leachate on the Vibrio fischeri bacterium. Maximum phosphorus release was observed at pH < 3 and at pH > 10. Ammonium nitrogen exhibited maximum leachability at near neutral pH conditions, while nitrate nitrogen exhibited a mild increase in the leachate, as the leachant pH increased from 2 to 12. Both TOC and COD exhibited an increase in the leachate concentration, as the leachant pH was increased from 2 to 12. Ecotoxicological analysis showed that maximum toxicity occurred at very low and very high pH-conditions. As liquid-to-solid ratio increased, the leachate concentration (in mg/l) of all parameters studied decreased. The results of the study were used to conduct a release assessment estimate for the case of Thessaloniki.
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PMID:Leaching of nitrogen, phosphorus, TOC and COD from the biosolids of the municipal wastewater treatment plant of Thessaloniki. 1776 30

Vertical and temporal distributions of N and P in soil solution in aquatic-terrestrial ecotone (ATE) of Taihu Lake were investigated, and the relations among N, P, ORP (oxidation reduction potential), TOC, root system biomass and microorganism were studied. As a whole, significant declines in TN, NO3- -N, DON (dissolved organic nitrogen) and TP concentration in soil solution have occurred with increase of the depth, and reached their minima at 60 cm depth, except for NH4+ -N, which increased with depth. The concentration of TP increased gradually from spring to winter in the topsoil, the maximum 0.08 mg/L presented in the winter while the minimum 0.03 mg/L in spring. In the deeper layer, the concentration value of TP fluctuated little. As for the NO3- -N, its seasonal variation was significant at 20 cm depth, its concentration increased gradually from spring to autumn, and decreased markedly in winter. Vertical and temporal distribution of DON is contrary to that of NO3- -N. The results also show that the variation of N and P in the percolate between adjacent layers is obviously different. The vertical variation of TN, TP, NO3- -N, NH4+ -N and DON is significant, of which the variation coefficient of NO3- -N along the depth reaches 100.23%, the highest; while the variation coefficient of DON is 41.14%, the smallest. The results of correlation analysis show that the concentration of nitrogen and phosphorus correlate significantly with TOC, ORP, root biomass and counts of nitrifying bacteria. Most nutrients altered much from 20 to 40 cm along the depth. However, DON changed more between 60 and 80 cm. Results show that soil of 0-60 cm depth is active rhizoplane, with strong capability to remove the nitrogen and phosphorus in ATE. It may suggest that there exists the optimum ecological efficiency in the depth of above 60 cm in reed wetland. This will be very significant for ecological restoration and reestablishment.
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PMID:Vertical and temporal distribution of nitrogen and phosphorus and relationship with their influencing factors in aquatic-terrestrial ecotone: a case study in Taihu Lake, China. 1796 41

Concentrations of dissolved organic carbon (DOC) in freshwaters have increased significantly in Europe and North America, but the driving mechanisms are poorly understood. Here, we test if the significant increase in TOC (total organic carbon, 90-95% DOC) in three acid-sensitive catchments in Norway of 14 to 36% between 1985 and 2003 is related to climate, hydrology, and/or acid deposition. Catchment TOC export increased between 10 and 53%, which was significant at one site only. The seasonal variation in TOC was primarily climatically controlled, while the deposition of SO4 and NO3--negatively related to TOC--explained the long-term increase in TOC. We propose increased humic charge and reduced ionic strength--both of which increase organic matter solubility--as mechanistic explanations for the statistical relation between reduced acid deposition and increased TOC. Between 1985 and 2003, ionic strength decreased significantly at all sites, while the charge density of TOC increased at two of the sites from 1-2 meq g(-1) C to about 5 meq g(-1) C and remained constant at the third site at 5 meq g(-1) C. The solubility of organic matter is discussed in terms of the pH-dependent deprotonation of carboxylic groups and the ionic strength-dependent repulsion of organic molecules.
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PMID:Long-term increase in dissolved organic carbon in streamwaters in Norway is response to reduced acid deposition. 1807 78


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