Photocatalytic degradation of 2,4-dinitrophenol (DNP) by multi-walled carbon nanotubes (MWCNTs)/TiO2 composite in aqueous solution under solar irradiation

Nanosized multi-walled carbon nanotubes (MWCNTs)/TiO₂ composite and neat TiO₂ photocatalysts were synthesized by sol-gel technique using tetrabutyl titanate as a precursor. The as prepared photocatalysts were characterized using XRD, SEM, FTIR and UV-vis spectra. The samples were evaluated for their photocatalytic activity towards the degradation of 2,4-dinitrophenol (DNP) under solar irradiation. The results indicated that the addition of an appropriate amount of MWCNTs could remarkably improve the photocatalytic activity of TiO₂. An optimal MWCNTs:TiO₂ ratio of 0.05% (w/w) was found to achieve the maximum rate of DNP degradation. The effects of pH, irradiation time, catalyst concentration, DNP concentration, etc. on the photocatalytic activity were studied and the results obtained were fitted to the Langmuir-Hinshelwood model to study the degradation kinetics. The optimal conditions were an initial DNP concentration of 38.8 mg/L at pH 6.0 with catalyst concentration of 8 g/L under solar irradiation for 150 min with good recyclisation of catalyst. The degree of photocatalytic degradation of DNP increased with an increase in temperature. The MWCNTs/TiO₂ composite was found to be very effective in the decolorization and COD reduction of real wastewater from DNP manufacturing. Thus, this study showed the feasible and potential use of MWCNTs/TiO₂ composite in degradation of various toxic organic contaminants and industrial effluents.     

Bioremediation of Pb-contaminated soil by incubating with Phanerochaete chrysosporium and straw

The bioremediation of the simulated lead (Pb)-contaminated soils by incubating with Phanerochaete chrysosporium and straw was studied at laboratory-scale. The soil pH, Pb concentration, soil microbial biomass, microbial metabolic quotient, microbial quotient and microbial biomass C-to-N ratios were monitored. The above indicators were to study the stress of Pb on soil and the microbial effects during the bioremediation process. It was found that the soils treated with P. chrysosporium and straw showed a much lower concentration of soluble-exchangeable Pb, lower metabolic quotient and biomass C-to-N ratios (0mgkg(-1) dry weight soil, 1.9mg CO(2)-Cmg(-1) biomass carbon and 4.9 on day 60, respectively) and higher microbial biomass and microbial quotient (2258mgkg(-1) dry weight soil and 7.86% on day 60, respectively) compared with the controls. In addition, the kinetic parameters in the model based on logistic equation were calculated by the BIOLOG data. By analyzing those kinetic parameters some information on the metabolic capacity of the microbial community could be obtained. All the results indicated that the bioavailability of Pb in contaminated soil was reduced so that the potential stress of Pb was alleviated, and also showed that the soil microbial effects and the metabolic capacity of microbial community were improved.     

Determination of daily dietary intake of chromium by duplicate diet sampling: in vitro availability study

Intake of chromium was estimated using a duplicate diet sampling method of 108 meals (36 breakfasts, 36 lunches and 36 dinners) from the restaurant of the Hospital of Motril (S.E. Spain), corresponding to 36 consecutive days. Total and dialyzable Cr levels were measured by a validated electro-thermal atomic absorption spectrometry (ETAAS) method. A mean Cr fraction of 26 +/- 12 microg meal (-1) was found. The Cr uptake from meals was directly and significantly (p < 0.001) correlated with their macronutrient (carbohydrates, fibre and protein) content. Cereals and cereal by-products, legumes, dry fruits, meat, potatoes, dairy products and seafood are the primary sources of Cr. The mean Cr fraction dialyzed through dialysis tubing was 1.2 +/- 1.1 microg meal(-1) (4.6 +/- 3.8% as mean Cr dialysability). Cr intake for breakfasts was significantly lower (p < 0.001). A correlation between the logarithmic data of total and dialyzable fraction of Cr in meals (p = 0.020) was found and dialysis ratio enhancement and, therefore, bioavailability increased with total Cr. The dialysed element content present in meals was significantly correlated with fibre, protein, Fe, Na, I, F, sodium, ascorbic acid and vitamin A levels (p < 0.05). At Fe contents in meals higher than congruent with7.5 mg meal(-1) the net absorption of Cr decreased significantly. The mean Cr daily dietary intake (DDI) was 77 +/- 17 microg day (-1) which indicates that no adverse effects in relation to Cr nutrition (deficiency or toxicity) should occur in individuals from the area.     

Degradation of lead-contaminated lignocellulosic waste by Phanerochaete chrysosporium and the reduction of lead toxicity

Lead, as one of the most hazardous heavy metals to the environment interferes with lignocellulosic biomass bioconversion and carbon cycles in nature. The degradation of lead-polluted lignocellulosic waste and the restrain of lead hazards by solid-state fermentation with Phanerochaete chrysosporium were studied. Phanerochaete chrysosporium effectively degraded lignocellulose, formed humus and reduced active lead ions, even at the concentration of 400 mg/kg dry mass of lead. The highest lignocellulose degradation (56.8%) and organic matter loss (64.0%) were found at the concentration of 30 mg/kg of lead, and at low concentration of lead the capability of selective lignin biodegradation was enhanced. Microbial growth was delayed in polluted substrate at the initial stage of fermentation, and organic matter loss is correlated positively with microbial biomass after 12 day fermentation. It might be because Phanerochaete chrysosporium developed active defense mechanism to alleviate the lead toxicity. Scanning electron micrographs with energy spectra showed that lead was immobilized via two possible routes: adsorption and cation exchange on hypha, and the chelation by fungal metabolite. The present findings will improve the understandings about the degradation process and the lead immobilization pathway, which could be used as references for developing a fungi-based treatment technology for metal-contaminated lignocellulosic waste.     

Fingerprinting metals in urban street dust of Beijing, Shanghai, and Hong Kong

Street dust samples were taken between July and December 2005 at 25 locations in Shanghai, Beijing, and Hong Kong and sieved to 63 microm particle size before elemental analyses by CHN analyzer, XRF and ICP-MS. About 60% of the particles from the Beijing and Shanghai sieved samples were < 10 microm mean diameter, and approximately 20% were < 2 microm mean diameter, so that they are readily resuspendable and respirable with increased risk of adverse health impacts. The optical size distributions determined by electron microscopy were reasonably similar to the mass size distributions of total suspended particulate matter (TSP) at these two megacities. Hong Kong street dust particles were coarser with only about 3% of the sieved samples being < 10 microm. The elemental composition profile of Hong Kong street dust differs considerably from those of Beijing and Shanghai, being more abundant in C, S, Cr, Cu, Ce, and Zn due to higher traffic density. In particular, the vehicle contribution to Hong Kong street dust is shown by order-of-magnitude relative enhancements of Fe and Cr compared with those in TSP sampled nearby, attributed to vehicle iron and stainless-steel wear and tear and rusting contributing to street dust in the street canyons. The concentrations of Cr in Hong Kong street dust, measured from 52Cr and 53Cr by ICP-DRC-MS after a modified three-stage microwave-assisted acid digestion, are higher than those reported elsewhere.     

恩格努依教堂,丹麦

恩格努依教堂，丹麦ＧａｍｍｅｌＨｏｂｒｏｖｅｊＥｎｇｎｊＣｈｕｒｃｈ，Ｄｅｎｍａｒｋ，１９９４设计［丹麦］亨宁·拉申（ＨｅｎｎｉｎｇＬａｒｓｅｎｓＴｅｇｎｅｓｇｕｅＡ／Ｓ）这是一座乡村教堂，占地面积只有９５０ｍ２。它座落在地段的最高处，沿林区边缘的环...     

Profile of PCDD/F levels in serum of general Taiwanese between different gender, age and smoking status

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are persistent organic pollutants that are resistant to environmental and biological degradation and disperse into various environmental compartments throughout the atmosphere, water, soil, sediments, and food. Many factors, such as age, sex, lifestyle, and metabolism, can explain the distribution of serum levels after humans exposed to PCDD/Fs. The aim of our study was therefore to investigate the PCDD/Fs distribution and profile of the general population in northern Taiwan. All selected subjects were between 18 and 65 years old and proportionally chosen from five age groups based on population distribution of each district or county. Higher serum PCDD/F levels were found in the elder than in the young, and in females than in males. In addition, nonsmokers and passive smokers showed higher levels of PCDD/Fs than active smokers. The serum concentrations of 2,3,4,7,8-PeCDF; 1,2,3,7,8-PeCDD; and 1,2,3,6,7,8-HxCDD in some subjects seemed to increase with their age, which might have been caused by the longer half-lives of these substances. In future studies, more information about food consumption, occupational exposure, open-combustion, and other potential factors needs to be collected to clarify the most important factors affecting the distribution of serum PCDD/Fs in the general population in Taiwan.     

Mechanisms and models for anaerobic granulation in upflow anaerobic sludge blanket reactor

Upflow anaerobic sludge blanket (UASB) reactor has been employed in industrial and municipal wastewater treatment for decades. However, the long start-up period required for the development of anaerobic granules seriously limits the application of this technology. In order to develop the strategy for rapid UASB start-up, the mechanisms for anaerobic granulation should be understood. This paper attempts to provide a up-to-date review on the existing mechanisms and models for anaerobic granulation in the UASB reactor, which include inert nuclei model, selection pressure model, multi-valence positive ion-bonding model, synthetic and natural polymer-bonding model, Capetown's model, spaghetti theory, syntrophic microcolony model, multi-layer model, secondary minimum adhesion model, local dehydration and hydrophobic interaction model, surface tension model, proton translocation-dehydration theory, cellular automaton model and cell-to-cell communication model. Based on those previous works, a general model for anaerobic granulation is also proposed. It is expected that this paper would be helpful for researchers to further develop a unified theory for anaerobic granulation and technology for expediting the formation of the UASB granules.