Efficient use of Fe metal as an electron transfer agent in a heterogeneous Fenton system based on Fe0/Fe3O4 composites

In this work a novel heterogeneous Fenton system based on Fe(0)/Fe3O4 composites is described. The composites with several Fe(0)/Fe3O4 ratios were prepared by two different methods, i.e. mechanical alloying of Fe(0) and Fe3O4 powders and controlled reduction of Fe3O4 with H2. Reaction studies and detailed Conversion Electron M?ssbauer surface characterization of the composites Fe(0)/Fe3O4, Fe(0), Fe3O4, alpha-Fe2O3 and gamma-Fe2O3 suggested that Fe2+surf species are essential to produce an active Fenton system. Kinetic studies for the oxidation of the dye methylene blue, used as an organic model molecule, and for the peroxide decomposition suggest that the reactions proceed via HO* radicals generated from Fe2+surf species and H2O2 in a Fenton like mechanism. The increase in activity caused by the addition of Fe(0) is discussed in terms of a creation of Fe2+surf species during the preparation of the composite and by an electron transfer mechanism from Fe(0) to Fe3+surf during the Fenton reaction to regenerate the Fe2+surf active species.     

The effect of cyclic aerobic-anoxic conditions on biodegradation of benzoate.

The response of a mixed microbial culture to cyclic aerobic and anoxic (denitrifying) conditions was studied in a chemostat with a 48-hour hydraulic residence time receiving a feed containing benzoate and pyruvate. When the cyclic conditions were 3-hour aerobic and 9-hour anoxic, the bacteria-degraded benzoate aerobically via the catechol 2,3-dioxygenase (C23DO) pathway. The quantity of C23DO remained constant throughout the anoxic period but decreased during the initial portion of the aerobic period before returning to the level present in the anoxic period. Anoxic biodegradation of benzoate was via benzoyl-CoA reductase, which remained constant regardless of the redox condition. The aerobic benzoate uptake capability (AeBUC) of the culture increased during the aerobic period but decreased during the anoxic period. The anoxic benzoate uptake capability (AnBUC) exhibited the opposite response. When the cycle was 6-hour aerobic and 6-hour anoxic, aerobic biodegradation of benzoate proceeded via the protocatechuate 4,5-dioxygenase (P45DO) pathway. The P45DO activity decreased early in the aerobic period, but then increased to the level present during the anoxic period. The level of benzoyl-CoA reductase was constant throughout the cycle. Furthermore, AeBUC and AnBUC responded in much the same way as in the 3/9-hour chemostat. During a 9-hour aerobic and 3-hour anoxic cycle, the culture synthesized both P45DO and C23DO, with the former having significantly higher activity. Unlike the other two cycles, AeBUC changed little during the aerobic period, although AnBUC decreased. The culture was well-adapted to the cyclic conditions as evidenced by the lack of accumulation of either substrate during any cycle tested. This suggests that cyclic aerobic-anoxic processes can be used in industrial wastewater-treatment facilities receiving significant quantities of simple aromatic compounds like benzoate. However, the results showed that the kinetics of benzoate degradation were different under aerobic and anoxic conditions, a situation that must be considered when modeling cyclic bioreactors receiving aromatic compounds.     

Cytoprotective and anti-apoptotic action of HSP70 stress protein in Oreochromis niloticus exposed to residual dilutions of insecticides with fipronil and ethiprole

Abstract

The objective of this research was to investigate the potential damage caused by the residual concentrations of the insecticides Regent^® WS 800 and Curbix^® SC 200, containing fipronil and ethiprole, respectively as active ingredients, on the liver of Oreochromis niloticus. The analyses of HSP70 shock protein labelling and cell death process by TUNEL method were performed in order to measure the effects of the exposure of cell repair system of fish to both insecticides. Statistical analyses showed no significant molecular damage to the hepatic tissue of animals. Nevertheless, variations in HSP70 and DNA fragmentation levels, endpoint of cell repair system response and cellular death, respectively, were observed in several groups. These results indicate that the cell repair machinery was efficient when in contact with residual concentrations of insecticides. However, the DNA fragmentation detected by the TUNEL method suggests that even in face of the cytoprotective action of the HSP70 protein, there are damages that become irreparable. To finish, it is worth mentioning that given the results obtained from residual concentrations, use in the field should be with caution.     

Simultaneous removal of NOx,SO2, and Hg from flue gas in FGD absorber with oxidant injection (NaClO2)– full-scale investigation

ABSTRACT

This article presents the results of an industrial-scale study (on 400 MW_e lignite fired unit) of simultaneous NO_x, SO₂, and Hg^T removal in FGD absorber with oxidant injection (NaClO₂) into flue gas. It was confirmed that the injection of sodium chlorite upstream the FGD (Flue Gas Desulfurization) absorber oxidize NO to NO₂, Hg⁰ to Hg²⁺, and enhancing NO_x and Hg^T removal efficiency from exhaust gas in FGD absorber. Mercury removal efficiency grows with the rise of degree of oxidation NO to NO₂ and was limited by the phenomenon of re-emission. For NO_x removal the most critical parameters is slurry pH and temperature. There was no negative effect on sulfur dioxide removal efficiency caused by oxidant injection in tested FGD absorber. Based on the data provided, NO_x and Hg^T emissions can be reduced by adjusting the FGD absorber operating parameters combined with oxidant injection.     

Exchange of sulfur pollution between Bulgaria and Greece

The EMAP model (Eulerian Model for Air Pollution) is applied for calculating the sulfur concentration and deposition fields for 1995 as based upon Bulgarian and Greek sources. The country-to-country budgets show that about 4% of the sulfur oxides emitted by Bulgaria are deposited over Greek territory, estimated at 28 kt S. Only 2% of sulfur compounds emitted by Greece are deposited over Bulgaria, estimated at 6.2 kt S for 1995. This data is in agreement with EMEP/MSC-W estimates and provides more details concerning time and space. The results can be used in decision-making, negotiating and the development of contamination strategies.     

Surfactant solubilization of hydrophobic compounds in soil and water

The soil/water partition coefficient (K_d) of hexachlorobenzene (HCB) ranged from 220 1/kg to 1800 1/kg for eight soils having a wide range of physico-chemical properties. K_d normalised to soil organic carbon (K_oc) was found to be 28000 ± 4800 1/kg. Anionic surfactant dodecylsulphate (DS) present at concentrations above the critical micellar concentration (CMC) caused reductions in the apparent soil/water partition coefficient (K_d ^*) in the range of 3–26 times for most soils and up to 36–91 times for sandy soils. Below CMC, at environmentally relevant surfactant concentrations, K_d ^* was reduced by a factor of 1–13. For clay and calcareous soils significant adsorption/complexation/precipitation of DS occurred. At the lowest DS concentration this produced a two-fold increase in K_d ^*. At increasing DS concentrations this effect was shielded by the solubihzing effect from DS. Monomer (K_mn) and micellar (K_mc) surfactant/water partition coefficients for HCB were determined to be, 980 ± 190 1/kg and 21000 ± 1600 1/kg, respectively.     

Generation and stability of bentonite colloids at the bentonite/granite interface of a deep geological radioactive waste repository

The possible mechanisms of colloid generation at the near field/far field interface of a radioactive repository have been investigated by means of novel column experiments simulating the granite/bentonite boundary, both in dynamic and in quasi-static water flow conditions. It has been shown that solid particles and colloids can be detached from the bulk and mobilised by the water flow. The higher the flow rate, the higher the concentration of particles found in the water, according to an erosion process. However, the gel formation and the intrinsic tactoid structure of the clay play an important role in the submicron particle generation even in the compacted clay and in a confined system. In fact, once a bentonite gel is formed, in the regions where the clay is contacted with water, clay colloids can be formed even in quasi-static flow conditions. The potential relevance of these colloids in radionuclide transport has been studied by evaluating their stability in different chemical environments. The coagulation kinetics of natural bentonite colloids was experimentally studied as a function of the ionic strength and pH, by means of time-resolved light scattering techniques. It has been shown that these colloids are very stable in low saline (approximately 1 x 10(-3) M) and alkaline (pH > or = 8) waters.     

Organochlorine and butyltin residues in walleye pollock (Theragra chalcogramma) from Bering Sea, Gulf of Alaska and Japan Sea

Persistent organochlorine (OC) and toxic butyltin compounds (BTs) were determined in walleye pollock (Theragra chalcogramma) collected from Gulf of Alaska, Bering Sea and Japan Sea, during 1991 and 1992. Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDTs) and its metabolites were the most abundant compounds ranging up to 3200 and 2500 ng/g on lipid weight, respectively, followed by chlordane compounds (CHLs), hexachlorocyclohexane isomers (HCHs) and hexachlorobenzene (HCB) in the liver of walleye pollock. Concentrations of HCHs and HCB in walleye pollock from these remote areas were higher than those in fishes from the western North Pacific and Japanese coastal waters, indicating atmospheric transport of these compounds to higher latitude regions such as Bering Sea and Gulf of Alaska and/or local input around northern Japan Sea. The concentrations of other OCs were generally comparable to those in fishes from North Pacific Ocean and Japanese waters but significantly lower than in cod-like fishes from North Atlantic and European countries. Among sampling locations, walleye pollock from Japan Sea showed higher concentrations of DDTs and HCHs compared to fishes from Bering Sea and Gulf of Alaska, suggesting greater input of these compounds around Japan Sea. Slower declining trend of DDTs and CHLs and an increasing pattern of PCBs concentrations were found in walleye pollock from Bering Sea during 1982-1992. This may imply a continuous input of these compounds by long-range transport and/or long-term persistency in these cold regions. Compared to the fishes from Japan Sea, walleye pollock from Bering Sea and Gulf of Alaska showed higher proportions of alpha-HCH and p,p'-DDE in the composition of HCH isomers and DDT compounds, respectively. This suggests selective transportability of these compounds during long-range transport to higher latitude remote areas. Concentrations of tributyltin (TBT) in the muscle of walleye pollock ranged from 1.1 to 5.5 ng/g on wet weight. Concentrations of TBT in deep-sea walleye pollock from Gulf of Alaska and Bering Sea were lower than those in Japan Sea.     

Retention of arsenic on hydrous ferric oxides generated by electrochemical peroxidation

Electrochemical peroxidation (ECP), an emerging remediation technology, with direct electric current applied to steel electrode and small addition of H2O2, was used to remove As(III) from contaminated aqueous solutions. Bench scale experiments were conducted to evaluate the sorption and distribution of arsenic between the soluble and solid state hydrous ferric oxides (HFO) formed as part of the ECP process. ECP was effective in removing arsenic from the aqueous solution, with >98% of the applied As(III) adsorbed on HFO. Removal was complete within 3 min of ECP treatment and apparently independent of the initial pH of the water (3.5-9.5). In the absence of H2O2 more As(III) was adsorbed by solid state iron at pH 9.5 than at 3.5 (2600 vs. 1750 microg l(-1)). Thus H2O2 was crucial to oxidize As(III) to As(V) which is more strongly retained by HFO. Removal of As was not significantly affected by the concentration of H2O2 or by current processing time. The optimal operating conditions were pH < 6.5, H2O2 concentration of 10 mg l(-1) and current process time not exceeding 3 min. X-ray diffraction (XRD), diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy and transmission electron microscopy (TEM) were applied to study the HFO deposits. The XRD data indicated the prevalence of poorly ordered Fe minerals in the suspended ECP solids with a dominance of 5 line ferrihydrite in the absence of H2O2. At pH 3.5 and with 100 mg H2O2 l(-1), akaganeite was formed, whereas an incipient hematitic phase, reflection at 0.39 nm, occurred at pH 6.5. DRIFT data indicate that both As(III) and As(V) were specifically adsorbed onto HFO at acid and neutral pH. TEM observations indicated the presence of spherical shape ferrihydrite and provided evidence for possible formation of subrounded hematite and acicular shape goethite.     

Meta-networks for the study of biogeographical traits in ecological networks: the Mexican hummingbird-plant assemblage

Recent studies on ecological networks have quantified the contribution of ecological, historical, and evolutionary factors on the structure of local communities of interacting species. However, the influence of species’ biogeographical traits, such as migratory habits or phylogeographical history, on ecological networks is poorly understood. Meta-networks, i.e., networks that cover large spatial extensions and include species not co-occurring locally, enable us to investigate mechanisms that operate at larger spatial scales such as migratory patterns or phylogeographical distributions, as well as indirect relationships among species through shared partners. Using a meta-network of hummingbird-plant interaction across Mexico, we illustrate the usefulness of this approach by investigating (1) how biogeographical and morphological factors associate with observed interactions and (2) how species-specific biogeographical characteristics associate with species’ network roles. Our results show that all studied hummingbird and plant species in the meta-network were interrelated, either directly or through shared partners. The meta-network was structured into modules, resulting from hummingbirds and plants interacting preferentially with subsets of species, which differed in biogeographical, and, to a lesser extent, morphological traits. Furthermore, migrants and hummingbirds from Nearctic, Transition, and widespread regions had a higher topological importance in the meta-network. Our study illustrates how meta-networks may contribute to our current knowledge on species’ biogeographical traits and biotic interactions, providing a perspective complementary to local-scale networks.