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

Simultaneous Cr(VI) reduction and phenol degradation was observed in a fixed-film bioreactor consisting of a coculture of phenol-degrading bacteria, Pseudomonas putida DMP-1, and Cr(VI)-reducing bacteria, Escherichia coli ATCC 33456. Near complete Cr(VI) reduction and phenol degradation was observed during steady-state operation of the reactor under loadings of 5-21 mg Cr(VI) l-1 d-1 and 840-3350 mg phenol l-1 d-1. 2-hydroxymuconic semialdehyde (2HMSA), succinate, and acetate were the detected steady-state organic acid metabolites which accounted for 13-23% of TOC in the effluent. Optimum Cr(VI) reduction rate was observed under a Cr(VI) loading of approximately 26.5 mg Cr(VI) l-1 d-1 just before system overload. System overload was characterized by the increase in effluent Cr(VI) and phenol concentrations. System resilience to Cr(VI) toxicity was demonstrated by rapid recovery of biological activity and reduced effluent Cr(VI) and phenol concentrations after off-loading the system from overloaded conditions.
Water Res 2001 Jun
PMID:Simultaneous chromium(VI) reduction and phenol degradation in a fixed-film coculture bioreactor: reactor performance. 1133 38

The degradation of 2,4-Dichlorophenol (from now on 2,4-DCP) has been carried out on Nafion-Fe (1.78%) in the presence of H2O2 under visible light irradiation. A solution containing 2,4-DCP (TOC 72 mg C/L)) is seen to be mineralized in approximately 1 h in the presence of H2O2 (10 mM) under solar simulated visible light (80 mW cm-2) at pH values between 2.8 and 11. Homogeneous photo-assisted Fenton reactions were capable of mediating 2,4-DCP degradation only up to pH 5.4. The degradation kinetics of 2,4-DCP on Nafion-Fe membranes was more favorable than the one observed during Fenton photo-assisted processes at pH 2.8. The degradation of 2,4-DCP was investigated as a function of the substrate, oxidant concentration and applied light intensity. The Nafion-Fe was seen to be effective over many cycles during the photo-catalytic degradation of 2,4-DCP showing an efficient and stable performance during 2,4-DCP degradation without leaching out Fe(3+)-ions into the solution. Evidence is presented that the degradation at the surface of the Nafion-Fe membrane seems to be controlled by mass transfer and not by chemical reaction of the species in solution. The approach used to degrade 2,4-DCP is shown to be valid for other chloro-carbons like 4-chlorophenol, 2,3-chlorophenol and 2,4,5-trichlorophenol.
Water Res 2001 Jun
PMID:Degradation of 2,4-dichlorophenol by immobilized iron catalysts. 1133 46

It was verified by laboratory-scale experiments that the two-port ozone injection method was more advantageous for reaction efficiency in the ozone-hydrogen peroxide treatment than the conventional one-port ozone injection method under the condition of same ozone dose. The reason for this effectiveness was also investigated in detail by computer simulations in the wide range of the rate constant of OH radical reacting with TOC (kTOC). The laboratory-scale experiments revealed that the amount of TOC decomposed (delta TOC) increased by up to 41% by the two-port injection method, indicating a 27% improvement in delta O3/delta TOC. A detailed investigation of these experimental results by computer simulations showed that by injecting ozone in two ports the amount of ozone consumed for the OH radical formation was increased more remarkably than that of ozone consumed for the radical chain reactions, and that the amount of OH radical reacting with TOC was increased more strikingly than that with ozone. Furthermore, it was found that the smaller the kTOC value with 10(5)-10(9) M-1s-1 was, the more advantageous for the reaction efficiency the two-port injection method was.
Water Sci Technol 2001
PMID:Investigation of radical reactions for efficiency improvement in ozone-hydrogen peroxide treatment. 1138 Jan 81

Heterogenous catalytic ozonation of 2-chlorophenol (2-CP) in the presence of gamma-alumina as a solid catalyst has been investigated in this research. It showed that the rate for degradation of TOC could increase from 21% to 43%. The pseudo-first reaction constants of 2-CP could increase from 0.8688 min-1 to 0.1270, increasing by approximately 40%. At the same time, the consumption of ozone was only half that of ozone alone. This research also explored the effects of the catalyst dosage, pH values and removal kinetics of 2-CP. In addition, three consecutive running with the same catalyst revealed insignificant reduction of the activity. Furthermore, the elimination of toxicity was evaluated by Microtox analysis. The detoxification was more stable and with good results.
Water Sci Technol 2001
PMID:Heterogeneous catalytic ozonation of 2-chlorophenol aqueous solution with alumina as a catalyst. 1138 Jan 82

Ozonation and O3/H2O2 oxidation of reactive dyestuffs and simulated textile dye-bath were investigated. Effects of reaction pH, initial dye concentration, H2O2 concentration and assisting chemicals on treatment efficiency were examined. We found considerable improvement in COD and colour removal rates at pH = 11, that was almost the actual pH of the prepared textile wastewater, whereas in particular increasing the initial dyestuff concentration had an adverse effect upon oxidation rates. Removal of colour, COD and TOC were found to be fairly sensitive to the introduction of soda that is frequently applied as an auxiliary chemical during the reactive dyeing process. The addition of H2O2 had negligible effect on COD removal efficiency and decolorization rate compared to ozonation alone at different pH values. Accordingly it can be inferred that the theoretically expected effect of OH radical scavengers (e.g. carbonate, chloride) present in the synthetic dye-bath as well as introduced radical formation promoters (e.g. H2O2, OH-) were probably hidden due to the complexity of the synthetic wastewater matrix. Biodegradability of the ozonated dye-bath was accelerated by a factor of three corresponding to a 233% relative enhancement. The inhibition of the oxygen uptake rate decreased from 91% to 75% within only 5 min treatment time.
Water Sci Technol 2001
PMID:Partial oxidation of reactive dyestuffs and synthetic textile dye-bath by the O3 and O3/H2O2 processes. 1138 Jan 83

This study investigated the decomposition of high strength p-nitrophenol (PNP) of 2,000 mg/l (3,400 mg of COD/1,250 mg of TOC) by catalytic wet air oxidation. Multi-component heterogeneous catalysts were used as catalysts for this purpose. The study results using a batch reactor showed that catalyst "D" (Mn-Ce-Zr 22.4 g plus CuSO4 1.0 g; Mn-Ce-Zr-Cu [CuSO4]) was more effective (56-74%) than catalyst "A" (Mn-Ce-Zr 22.4 g) under the given conditions (O2 partial pressure of 1.0 MPa; temperature of 170-190 degrees C; 30 min of reaction time). The best result was obtained when 2 g of Mn-Ce-Zr-Cu [CuSO4] was used per 1L of PNP aqueous solution. COD and TOC removal efficiencies were 18% and 23% without catalysts during 20 min of reaction at 190 degrees C. They were improved to 79% and 71% with 2 g/L of Mn-Ce-Zr-Cu [CuSO4] under the same conditions. The ratio of BOD5/COD was measured to evaluate biodegradability. It was 0.05 without catalyst and increased to 0.33 with 2 g/L of Mn-Ce-Zr-Cu [CuSO4] for 20 min of reaction.
Water Sci Technol 2001
PMID:Catalytic wet air oxidation of p-nitrophenol (PNP) aqueous solution using multi-component heterogeneous catalysts. 1138 Jan 84

This study has determined the purification performance and the basic principles for the design of an anaerobic SBR (ASBR) to be used to treat wastewater generated in the food industries. Two ASBR's were set up and one fed with a slaughterhouse effluent at low concentration, the other with concentrated dairy wastewater. The maximum loading rate applied should not exceed 4.5 g of COD/L/day for the dilute effluent and 6 g of COD/L/day for the concentrated effluent. At higher loading rates, the reactors become difficult to operate, mainly because of sludge removal problems, and purification efficiency declines. A detailed study of the kinetics (TOC, VFA, rate of biogas production) throughout one treatment cycle led to the development of a simple control strategy based on the monitoring of the biogas production rate which was then applied to the reactor treating the dairy wastewater. After automation, the reactor worked free of problems at an average pollution load of 5.4 g of COD/L/day.
Water Sci Technol 2001
PMID:The anaerobic SBR process: basic principles for design and automation. 1138 7

A method for extraction of extracellular polymeric substances (EPSs) with a dicyclohexyl-18-crown-6 ether was developed to determine levels of organic and inorganic contaminants sorbed to EPS. The crown ether selectively binds alkaline and alkaline earth metals but not heavy metals. The effectiveness of the extraction procedure was higher than that of 2 other methods tested and comparable with that of a method based on a cation exchange resin. On average it was possible to extract 20% of the TOC, 12% of the total protein content, and 4% of the total carbohydrate content of sludge or biofilm biomass. Metal sorption studies in activated sludge showed no influence of exposure time on the fractionation of metals within the biomass. Metals sorbed mostly to cellular material. In biofilms 12.2% of the cadmium and 9.1% of the zinc added was found in the EPS. In activated sludge EPS contained only 2.9% zinc. The distribution of metals within the biomass was dose dependent. The percentage of metals found in EPS decreased with increasing metal concentration. This indicates a higher affinity of metals for cellular binding sites. Time course experiments in a rotating biofilm annular reactor, which consisted of an external cylinder with removable slides and an internal solid drum, revealed a gradual change in zinc concentration associated with EPS, although the total zinc concentration in the biomass remained constant. Concurrently, the amount of extractable EPS decreased. This was a consequence of a microbial population shift, with bacterial counts decreasing and algal and fungal biomass increasing. Using confocal laser scanning microscopy and the fluorescent metal complexing agent Newport Green for in situ detection of zinc it was shown that metals were bound to algae and fungi in the latter part of the experiment. The biofilm became more and more heterogeneous coinciding with a decrease in EPS. To summarize, the observed sorption behavior of metals cannot be explained with the conventional paradigm of EPS as hydrophilic gel. Obviously, different binding mechanisms must be invoked to explain the role of EPS in the sorption and removal of toxic substances in activated sludge and biofilm systems. It is important to consider the microbial population to understand differences in sorption in different matrices.
Water Sci Technol 2001
PMID:A new method for extraction of extracellular polymeric substances from biofilms and activated sludge suitable for direct quantification of sorbed metals. 1138 69

Expermental results of the effect and mechanism of removing TOC and Ames mutagens from drinking water using AC-NF process showed that the adsorptive ability of AC was limited, depending on the characters of AC and the organic matters in drinking water. But AC can be used as the pretreatment of NF to ensure to meet the requirement of membrane feed. NF can remove the majority of total organic carbon and Ames mutagens effectively to ensure the safety of drinking water. The MR values of TA98 and TA100 of NF permeate were below 2 under the tested doses, and the results of Ames test of NF permeates were completely negative. Therefore, it is feasible to combine AC and NF to obtain the high-grade drinking water.
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PMID:[Removal of TOC and Ames mutagens from drinking water using AC-NF process]. 1138 49

Sediment reference sites were used to establish toxicity standards against which to compare results from sites investigated in San Francisco Bay (California, USA) monitoring programs. The reference sites were selected on the basis of low concentrations of anthropogenic chemicals, distance from active contaminant sources, location in representative hydrographic areas of the Bay, and physical features characteristic of depositional areas (e.g., fine grain size and medium total organic carbon [TOC]). Five field-replicated sites in San Francisco Bay were evaluated over three seasons. Samples from each site were tested with nine toxicity test protocols and were analyzed for sediment grain size and concentrations of trace metals, trace organics, ammonia, hydrogen sulfide, and TOC. The candidate sites were found to have relatively low concentrations of measured chemicals and generally exhibited low toxicity. Toxicity data from the reference sites were then used to calculate numerical tolerance limits to be used as threshold values to determine which test sites had significantly higher toxicity than reference sites. Tolerance limits are presented for four standard test protocols, including solid-phase sediment tests with the amphipods Ampelisca abdita and Eohaustorius estuarius and sea urchin Strongylocentrotus purpuratus embryo/larval development tests in pore water and at the sediment-water interface (SWI). Tolerance limits delineating the lowest 10th percentile (0.10 quantile) of the reference site data distribution were 71% of the control response for Ampelisca, 70% for Eohaustorius, 94% for sea urchin embryos in pore water, and 87% for sea urchins embryos exposed at the SWI. The tolerance limits are discussed in terms of the critical values governing their calculation and the management implications arising from their use in determining elevated toxicity relative to reference conditions.
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PMID:Evaluation and use of sediment toxicity reference sites for statistical comparisons in regional assessments. 1139 36


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