Students' environmental concerns and opinions: a Chinese perspective

This study aims at comparing broadly the environmental concerns and opinions between Hong Kong and Beijing students. This is based on an earlier study in Australia which adopted a qualitative approach, using five open-ended question items. In their written comments the children's environmental opinions and concerns were explored. In general, upper primary students tended to be concerned more about the social environment relating to society, while junior and senior secondary students expressed more concern about the social environment relating to the nation and global issues.     

Analysis and characterization of cultivable heavy metal-resistant bacterial endophytes isolated from Cd-hyperaccumulator Solanum nigrum L. and their potential use for phytoremediation

This study investigates the heavy metal-resistant bacterial endophytes of Cd-hyperaccumulator Solanum nigrum L. grown on a mine tailing by using cultivation-dependent technique. Thirty Cd-tolerant bacterial endophytes were isolated from roots, stems, and leaves of S. nigrum L. and classified by amplified ribosomal DNA-restriction analysis into 18 different types. Phylogenetic analysis based on 16S rDNA sequences showed that these isolates belonged to four groups: Actinobacteria (43%), Proteobacteria (23%), Bacteroidetes (27%) and Firmicutes (7%). All the isolates were then characterized for their plant growth promoting traits as well as their resistances to different heavy metals; and the actual plant growth promotion and colonization ability were also assessed. Four isolates were re-introduced into S. nigrum L. under Cd stress and resulted in Cd phytotoxicity decrease, as dry weights of roots increased from 55% to 143% and dry weights of above-ground from 64% to 100% compared to the uninoculated ones. The total Cd accumulation of inoculated plants increased from 66% to 135% (roots) and from 22% to 64% (above-ground) compared to the uninoculated ones. Our research suggests that bacterial endophytes are a most promising resource and may be the excellent candidates of bio-inoculants for enhancing the phytoremediation efficiency.     

The relationship between mixed-liquor particle size and solids retention time in the activated sludge process

Particle size distribution (PSD) analysis was used to evaluate the quality of mixed liquors collected from different activated sludge process modifications (i.e., conventional activated sludge, modified Ludzack-Ettinger, high-purity oxygen, step-anoxic, and oxidation ditch). An experiment protocol was developed to define the allowable sample holding time and provide representative and repeatable results. Samples of 26 treatment plants, with a total of 37 samples, were tested. A new indicator, called mean particle size (MPS), was introduced to describe the integrated mean particle size. The results of MPSs of three cut-off sizes (0.5 to 50, 100, and 200 microm) showed that the average size of mixed-liquor biosolids increased with increasing solids retention time (SRT), and the number of particles in the sedimentation supernatant decreased with increasing SRT. Particle deflocculation occurred after excessive sample holding time, and analysis within 12 hours generally eliminated sample holding problems. The results provide a methodology using PSD for characterizing mixed-liquor biosolids.     

Inherent risk assessment—A new concept to evaluate risk in preliminary design stage

Quantitative Risk Assessment (QRA) has been a very popular and useful methodology which is widely accepted by the industry over the past few decades. QRA is typically carried out at a stage where complete plant has been designed and sited. At that time, the opportunity to include inherent safety design features is limited and may incur higher cost. This paper proposes a new concept to evaluate risk inherent to a process owing to the chemical it uses and the process conditions. The risk assessment tool is integrated with process design simulator (HYSYS) to provide necessary process data as early as the initial design stages, where modifications based on inherent safety principles can still be incorporated to enhance the process safety of the plant. The risk assessment tool consists of two components which calculate the probability and the consequences relating to possible risk due to major accidents. A case study on the potential explosion due to the release of flammable material demonstrates that the tool is capable to identify potential high risk of process streams. Further improvement of the process design is possible by applying inherent safety principles to make the process under consideration inherently safer. Since this tool is fully integrated with HYSYS, re-evaluation of the inherent risk takes very little time and effort. The new tool addresses the lack of systematic methodology and technology, which is one of the barriers to designing inherently safer plants.     

Carbon content of common airborne fungal species and fungal contribution to aerosol organic carbon in a subtropical city

Interest in the role and contribution of fungi to atmospheric aerosols and processes grows in the past decade. Substantial data or information such as fungal mass or carbon loading to ambient aerosols is however still lacking. This study aimed to quantify the specific organic carbon content (OC per spore) of eleven fungal species commonly found airborne in the subtropics, and estimated their contribution to organic carbon in aerosols. The specific OC contents showed a size-dependent relationship (r = 0.64, p < 0.05) and ranged from 3.6 to 201.0 pg carbon per spore or yeast cell, giving an average of 6.0 pg carbon per spore (RSD 51%) for spore or cell size less than 10 μm. In accounting for natural variations in the composition and abundance of fungal population, weighted-average carbon content for field samples was adopted using the laboratory determined specific OC values. An average of 5.97 pg carbon per spore (RSD 3.8%) was enumerated from 28 field samples collected at the university campus. The mean fungal OC concentration was 3.7, 6.0 and 9.7 ng m^?3 in PM_2.5, PM_2.5–10 and PM₁₀, respectively. These corresponded to 0.1%, 1.2% and 0.2% of the total OC in PM_2.5, PM_2.5–10 and PM₁₀, respectively. In the study period, rain provided periods with low total OC but high fungal prevalence and fungi contributed 7–32% OC in PM_2.5–10 or 2.4–7.1% OC in PM₁₀. More extensive studies are deserved to better understand the spatial-, temporal- and episodic dependency on the fungal OC contribution to the atmospheric aerosols.     

Functional gene expression of oil-degrading bacteria resistant to hexadecane toxicity

Contamination with oil poses a threat to the environment and to human health worldwide. Biological methodologies have proved to be economical, versatile and efficient for the remediation of pollutants. In this paper, a highly efficient oil-degrading bacterial strain USTB-2 was isolated from an oil production well of Dagang oil field in Tianjin, China. The 16S rRNA sequence of USTB-2 showed 100% similarity with that of Bacillus subtilis BSn5. Hexadecane is one of the most important components in petroleum. The half inhibitory ratio (IC₅₀) of hexadecane inhibited organisms, determined by microcalorimetry, was lower in USTB-2 than in B. BSn5. The results indicate that the strain USTB-2 degrades hexadecane to make it less toxic compared with the normal strain. RT-PCR was used to evaluate the expression of oil-degrading enzymes, specifically 4-hydroxyphenylacetate 3-monooxygenase genes (HPMO). A sharp increase in the expression of HPMO genes was observed for USTB-2, while the expression of HPMO genes in reference strain B. BSn5 remained relatively stable. These methods can be used to study the metabolic potential of microorganisms for in situ oil decontamination.     

Gasification characteristics of sewage sludge combined with wood biomass

The gas products from gasification processes have been considered to have some limitations in gas composition and heating value from the previous studies. Gasification characteristics of sewage sludge and wood mixture were investigated using different mixing ratios with the purpose of better quality of gas product suitable for energy/power generation. The gasification experiment was performed by an indirectly heated fluidized bed reactor. As reaction temperature increased from 600 to 900 °C, the yield of gas product increased with higher generation of CO, H₂ and CH₄ by more activated gas conversion reactions. As the equivalence ratio increased from 0.2 to 0.4, composition ratio of CO₂ increased while CO, CH₄, H₂ decreased as expected. Several operating variables including mixing ratio of wood with dried sludge were also tested. From this initial stage of experiment, optimal operating conditions for the bubbling fluidized bed gasifier, could be considered 900 °C in temperature; 0.2 in equivalence ratio and 40 % in wood mixing ratio within test variables range. These results will be more thoroughly investigated for the application to the larger scale pilot system.     

Recycling of iron and silicon from drinking water treatment sludge for synthesis of magnetic iron oxide@SiO<Subscript>2</Subscript> composites

More attention has been paid to the deterioration of water bodies polluted by drinking water treatment sludge (DWTS) in recent years. It is important to develop methods to effectively treat DWTS by avoiding secondary pollution. We report herein a novel investigation for recovery of Si and Fe from DWTS, which are used for the synthesis of two iron oxide@SiO₂ composites for adsorption of reactive red X-3B (RRX-3B) and NaNO₂. The results show that Fe³⁺ (acid-leaching) and Si⁴⁺ (basic-leaching) can be successfully recovered from roasted DWTS. Whether to dissolve Fe(OH)₃ precipitation is the key point for obtaining Fe₃O₄ or γ-Fe₂O₃ particles using the solvothermal method. The magnetic characteristics of Fe₃O₄@SiO₂ (390.0 m² g^?1) or Fe₂O₃@SiO₂ (220.9 m² g^?1) are slightly influenced by the coated porous SiO₂ layer. Peaks of Fe–O stretching vibration (580 cm^?1) and asymmetric Si–O–Si stretching vibrations (1080 cm^?1) of Fe₃O₄@SiO₂ indicate the successful coating of a thin silica layer (20–150 nm). The adsorption capacity of RRX-3B and NaNO₂ by Fe₃O₄@SiO₂ is better than that of Fe₂O₃@SiO₂, and both composites can be recycled through an external magnetic field. This method is an efficient and environmentally friendly method for recycling DWTS.     

A High-Volume Sampler for the Determination of Particle Size Distributions in Ambient Air

A size selective particle sampler has been developed for continuous sampling of the urban aerosol over periods ranging from hours to weeks, providing relatively large sample weights. The system, which is now operating in New York City, uses a parallel array of two-stage samplers. The cyclones used as the first stage collectors have 50% particle retention at 3.5,2.5,1.5 and 0.5 µm aerodynamic diameter, respectively. Undersize particles which pass through the cyclones are captured on glass fiber filters. Equal intake velocities are assured by using flow equalizers on the inlets to the cyclones. Accurate control of the flow through the cyclones is obtained by the use of an integrated circuit pressure transducer in conjunction with a specially designed feedback control circuit. The collection efficiencies of the cyclone were calibrated using monodisperse ferric oxide test aerosols tagged with Tc-99m. Mass balances of the par-ticulates collected on the cyclones and filters are obtained for the five sampling stages. Preliminary results show the distributions of the total suspended particulates in New York City to be bimodal. The distributions of lead, copper, and manganese with particle size are also discussed.