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

A box filled with sandy soil was constructed to investigate the redox zones of landfill leachate pollution plume and the distribution and varying characteristics of contaminants and redox sensitive substrates. Results indicated that the distribution and variation of pollutants and redox sensitive substrates were influenced by redox environment; Eh of water in methanogenic/sulfate reduction zone, iron reduction zone, nitrate reduction zone and oxygen reduction zone is -148.2, -95.4, 30.6 and 223.2 mV; conductivity is 211.4, 55.2, 29.4 and 17.8 mS/m, and pH is 7.13, 6.49, 6.38 and 6.21, respectively. Methanogenic/sulfate reduction zone play significant roles for attenuation of the most organic pollutants such as ethylbenzene, dimethylbenzene, benzene, and TCE etc. Most heavy metals could deposit in methanogenic/sulfate reduction zone sediments, except As and Cd, and the highest content of Cr, Ni, Pb and Zn is 28.21, 11.58, 9.05 and 23.5 mg/kg, respectively. Concentration of CO2, sulfide, HCO3, NH4+, TOC, Fe2, NO2- and SO4(2-) are decrease with the distance away from the pollution source.
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PMID:[Distribution of pollutants and redox sensitive substrates in landfill leachate pollution plume]. 1906 52

A number of methods for denitrification were studied including Electro-Fenton method, hydrogenotrophic as well as innovative Fe(2+) mediated denitrification and their technical feasibility in terms of changes in TOC and nitrate concentrations, effect of different Fenton's reagent dosage, current and the effect of the pH was investigated. This study was carried out using tailor made electrodialytic reactor. It was found that the highest TOC removal was achieved at pH 2.2 and 2.4 (77.1% and 97.8%, respectively) at the anode and the lowest accumulation of 33% at pH of 6.2 at the cathode. The highest TOC removal in terms of using different H(2)O(2) concentrations was achieved at 40 mM reaching as high as 97.3%. Regardless experimental strategy, initially nitrates migrated towards the cathode due to the strong hydraulic gradient under the applied electric current. During the course of experiments, nitrates were transported towards the anode where their concentration decreased. The highest nitrate removal was achieved at 0.12 mA cm(-2) electric current density (94.8%) at the anode and a complete removal at the cathode. Hydrogenotrophic denitrification was the highest reaching 92.5%, however, when Fe(2+) ions as electron donor was used for the destruction of nitrates, only 66.6% removal was achieved. Denitrification using only Fe(2+) ions was a factor 1.4 less than using electrically generated hydrogen or a Fenton's reagent.
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PMID:Electro-Fenton, hydrogenotrophic and Fe2+ ions mediated TOC and nitrate removal from aquaculture system: different experimental strategies. 1907 Apr 82

Phenol was selected as a model pollution substrate. The influences and mechanism of inorganic anions on its oxidation were investigated in neutral solution at low temperature and atmospheric pressure. Results showed that phenol could be removed efficiently by CuO and H2O2 with 94.7% removal rate in 10 min, which followed hydroxyl radical oxidation mechanism. Inorganic anions influenced the oxidation with different mechanisms. Higher concentration would lead to more significant influences. HCO3(-) accelerated the inefficient decomposing of H2O2. The decomposing rate constants increased from 0.3738 min(-1) at concentration of 0 mmol x L(-1) to 0.5347 min(-1) at concentration of 20 mmol x L(-1). The TOC removal rate constants decreased from 0.267 min(-1) to 0.0194 min(-1) correspondingly. HPO4(2-) retarded the H2O2 decomposing and inhibited the phenol oxidation. The decomposing rate constants of H2O2 and the removal rate constants of TOC decreased from 0.3738 min(-1), 0.267 min(-1) to 0.0338 min(-1), 0.0338 min(-1) respectively. Cl(-) was good at H2O2 decomposing and phenol removal with simultaneously increasing the H2O2 decomposing rate constants and the TOC removal rate constants from 0.3738 min(-1), 0.267 min(-1) to 0.6040 min(-1), 0.3879 min(-1) respectively. NO3(-) and SO4(2-) had few influences on H2O2 decomposing and phenol removal.
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PMID:[Influences of inorganic anions on oxidation of phenol by CuO-H2O2]. 1940 97

To improve denitrification performance and effective degradation of organic pollutants from micro-polluted groundwater simultaneously, a novel three-dimensional (3D) bio-electrochemical reactor was developed, which introduced activated carbon into a traditional two-dimensional (2D) reactor as the third electrode. The static and dynamic characteristics of the reactor were investigated with special attentions paid to the performance comparison of these two reactors. In the 3D reactor both TOC and nitrate removal efficiency were greatly improved, and the formation of nitrite byproduct is considerably reduced, comparing with that of the 2D reactor. The role of activated carbon biofilm was explored and possible remediation mechanisms for the 2D and 3D reactors were suggested. In such a 3D reactor, the denitrification rate improved greatly to 0.288 mg NO(3)-N/cm(2)/d and the current efficiency could reach as high as 285%. Further, it demonstrated good performance stably against variable conditions, indicating very promising in application for groundwater remediation.
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PMID:Enhancement on the simultaneous removal of nitrate and organic pollutants from groundwater by a three-dimensional bio-electrochemical reactor. 1946 95

The photocatalytic degradation of diuron, which is one of phenylurea herbicides, was carried out in the presence of platinized TiO(2) photocatalyst. Platinization was found to increase the rate of diuron degradation. When 0.2wt.% of platinum was deposited onto the surface of TiO(2), an initial diuron concentration of 10 mg L(-1) was completely degraded after 20 min. Furthermore, the first-order rate constant for diuron degradation by Pt-TiO(2) was ca. 4 times higher than P-25 TiO(2). In addition, the photocatalytic activity of Pt-TiO(2) was appeared under visible light. The decrease of TOC as a result of mineralization of diuron was observed during the photocatalytic process. The degree of diuron mineralization was about 97% under UV irradiation after 8h. The formations of chloride, nitrate and ammonium ions as end-products were observed during the photocatalytic system. The decomposition of diuron gave four kinds of intermediate products. The degradation mechanism of diuron was proposed on the base of the evidence of the identified intermediates. Based on these results, the photocatalytic reaction by Pt-TiO(2) could be useful technology for the treatment of wastewater containing diuron.
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PMID:Photocatalytic degradation of diuron in aqueous solution by platinized TiO2. 1960 34

Batch ultrasonic treatments (sonication) were performed on two waste activated sludge (WAS) samples, BNR-WAS from the biological nitrogen removal unit and BNPR-WAS from the biological nitrogen and phosphorus removal unit of two Shanghai municipal WWTPs, to determine the effects of sonication time and intensity on the amount and distribution of the organic, N and P species released from the samples. The concentration profiles of COD, TOC fractions in different molecular weight (MW) ranges (<2 kDa, 2-100 kDa, and >100 kDa), TN, organic-N, NH(3)-N, TP and PO(4)-P were monitored during the treatment at three sonication intensity levels (0.167, 0.330 and 0.500 W/mL). Species releases increased with sonication time and/or intensity; the release rates were accelerated when the sonication intensity was above a critical level between 0.330 and 0.500 W/mL. After 1 h of treatment, 37.9%, 37.5% and 50.8% of the organic content (measured as COD) of BNR-WAS were released, while the same for BNPR-WAS were 40.9%, 55.3% and 56.9%. It also resulted in the release of 40.9%, 38.7%, and 52.1% of total nitrogen from BNR-WAS, relative to 46.2%, 61.6%, and 70.4% of the same from BNPR-WAS; most released nitrogen were organic-N (65.0% and 84.9%), followed by NH(3)-N (34.7% and 14.9%) and trace amounts of nitrate and nitrite. More total phosphorus of a higher orthophosphate content was released from BNRP-WAS (>60% release after 1 h of sonication, 80% was PO(4)-P) than from BNR-WAS (<50% release, 40% was PO(4)-P). The differences in the releases as well as the molecular weight distribution pattern of the soluble TOC species were due to the different structure and composition of the sludge samples. Sonication is a viable sludge treatment process when it is combined with a phosphorus recovery process to remove most of the released PO(4)-P so that the supernatant may be returned for further biological treatment.
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PMID:Characteristics of organic, nitrogen and phosphorus species released from ultrasonic treatment of waste activated sludge. 2002 95

Concentrations of inorganic, mercuric mercury (Hg(II)), methyl mercury (MeHg) and ancillary chemistry measured in first-order streams draining 0-4 (N = 20) and 4-10 (N = 27) year-old clear-cuts of former Norway Spruce Picea abies (Karst.) forest stands were compared with concentrations in streams draining >70 year-old Norway Spruce reference stands (N = 10). Concentrations of MeHg, and ratios of MeHg TOC(-1) and Hg(II) TOC(-1), were significantly (p < 0.01) elevated in 0-4 year-old clear-cuts, as compared to references. The only ancillary variable showing a significant elevation for 0-4 year-old clear-cuts was Mn (p < 0.02). The 4-10 year-old clear-cuts showed intermediate concentrations with nonsignificant differences as compared to references. pH, nitrate, sulfate, Ca, Fe, TOC, TON, and the aromaticity of TOC (SUVA(254 nm)) showed nonsignificant differences between clear-cut age classes and references. Assuming that MeHg and Hg(II) are mobilized from soil to stream to a similar relative extent as a consequence of clear-cutting, a calculation showed that (1)/(6) of the elevated MeHg concentration was due to enhanced mobilization from soil and (5)/(6) was due to new methylation of Hg(II) 0-4 years after clear-cut. New methylation after clear-cut is suggested to be stimulated by an increased availability of electron donors for methylating bacteria, as a consequence of degradation of logging residue ("slash") and soil organic matter. A subdivision of sites situated above and below the highest postglacial coastline (HC) revealed a significant elevation of MeHg, MeHg TOC(-1) and Hg(II) TOC(-1) (p < 0.05) beyond their references in 0-4 year-old clear-cuts above (but not below) the HC. This suggests that postglacial deposits of FeS(s) and FeS(2)(s) were not an important factor for elevation of MeHg after clear-cut.
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PMID:Elevated concentrations of methyl mercury in streams after forest clear-cut: a consequence of mobilization from soil or new methylation? 2002 48

A pilot-scale subsurface constructed wetland wastewater treatment system was sampled for one year to study the effects of bed aspect ratio, substrate medium size, water depth, HLR (hydraulic loading rate) and temperature (season) on removal of volatile alkylsulfides such as DMS (dimethylsulfide) and DMDS (dimethyldisulfide). The yearly experimental results demonstrated that the system showed good performance for DMS and DMDS removal in wastewater under different HLR ranging from 12 cm x d(-1) to 86 cm x d(-1). The system could remove 86% of DMS, and 95% of DMDS, respectively. ANOVA statistical analysis shows that HLR and temperature (season) are major factors controlling the system performance for the target analytes. According to ANOVA test, the HLR caused significant differences (p < 0.01) on the average DMS effluent concentrations, and temperature (season) caused significant differences (p < 0.01) on the average DMS and DMDS effluent concentrations. However, bed aspect ratio, substrate medium size and water depth did not cause significant differences (p > 0.05) on the average DMS and DMDS effluent concentrations. A survey of dissolved oxygen and ORP indicates that the constructed wetlands system showed strong reduced condition. On the basis of investigations of electron acceptors (such as SO4(2-), NO3- and NO2-) and dissolved organic pollutants (such as TOC and acetic acid) concentrations along with the length of constructed wetlands, it can be concluded that sulfate reduction and methanogenisis were estimated to be significant for DMS and DMDS removal in constructed wetland beds.
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PMID:[Effect of design and operation parameters on volatile alkylsulfides removal in subsurface constructed wetlands]. 2039

Two Fe/AC catalysts prepared with different iron precursors (iron nitrate and iron pentacarbonyl) and the same AC support have been tested in H(2)O(2) decomposition in presence and absence of methanol, a known strong scavenger of hydroxyl radicals, to investigate the selectivity towards .OH formation in this reaction and their behavior in the CWPO of phenol. The catalyst prepared with iron nitrate, with the most oxidized surface and the highest Fe surface content, seems to favor a higher selectivity towards .OH formation in CWPO allowing for complete phenol conversion and a significant TOC removal, with the highest mineralization degree at 50 degrees C and atmospheric pressure. Fe/AC catalysts were more efficient in the CWPO of phenol than in methanol presence due to a better use of the oxidant since adsorbed phenol on catalyst surface minimizes inefficient H(2)O(2) decomposition to H(2)O and O(2)(g). The influence of the initial H(2)O(2) concentration on phenol oxidation with this catalyst was also studied. A theoretical stoichiometric amount of H(2)O(2) for complete oxidation of phenol was chosen as the best starting concentration since auto-scavenging reactions can be minimized and it is sufficient for oxidizing phenol and the aromatic intermediates.
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PMID:Selectivity of hydrogen peroxide decomposition towards hydroxyl radicals in catalytic wet peroxide oxidation (CWPO) over Fe/AC catalysts. 2048 49

Irrigation of willow and poplar short-rotation coppice with landfill leachate is an increasingly interesting treatment option. Minimal leaching to groundwater and disturbance to plant growth must be ensured, but in such systems, where various site-specific factors interact, a case-specific approach is needed to determine potential hazards. This paper compares the effect of leachate irrigation on willow grown in clay lysimeters and poplar grown in sand lysimeters. Leachate irrigation increased willow biomass production, but not that of poplar. Near-zero nitrate-N concentrations were found in drainage water for both species after 2 years of irrigation. Ability to retain total N and P, and TOC was relatively high for willow, taking into account the large amounts supplied, and better than for poplar. To reduce environmental risks the irrigation load should be reduced, but if leachate concentrations are reduced, the irrigation load can be as high as 6mm/day.
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PMID:Landfill leachate treatment with willows and poplars--efficiency and plant response. 2065 Jun 25


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