Artificial aggregate made from waste stone sludge and waste silt

In this research, waste stone sludge obtained from slab stone processing and waste silt from aggregate washing plants were recycled to manufacture artificial aggregate. Fine-powdered stone sludge was mixed with waste silt of larger particle size; vibratory compaction was applied for good water permeability, resulting in a smaller amount of solidifying agent being used. For the densified packing used in this study, the mix proportion of waste stone sludge to waste silt was 35:50, which produced artificial aggregate of more compact structure with water absorption rate below 0.1%. In addition, applying vibratory compaction of 33.3 Hz to the artificial aggregate and curing for 28 days doubled the compressive strength to above 29.4 MPa. Hence, recycling of waste stone sludge and waste silt for the production of artificial aggregate not only offers a feasible substitute for sand and stone, but also an ecological alternative to waste management of sludge and silt.     

Fines migration from soil daily covers in Hong Kong landfills

Laboratory tests using 240 mm diameter columns were conducted to study fines migration in conditions that simulate daily soil covers in Hong Kong municipal solid waste landfills. Five factors suspected to affect fines migration were examined: moisture content at soil compaction, overburden pressure, pumping rate, cover thickness, and soil-waste interface condition. The results show that moisture content at compaction, cover thickness, and soil-waste interface are the most influential parameters on fines migration in completely decomposed granite daily covers. The measured equivalent sizes of migratory fines from the soil covers were in the range of 4–140 μm. The majority of migratory fines migrated during first permeations, representing 64–86% of the total by mass. Larger particles tended to migrate from the soil mass during the saturation process. In a typical run, about 0.0018% of the total cover soil (by dry weight) was washed out during a typical 1 h rainfall event. The results of the laboratory studies point to important engineering implications on the operation of local MSW landfills regarding the use of sandy daily covers.     

Comparison of ozone uptake and sensitivity between a phytotron study with young beech and a field experiment with adult beech (Fagus sylvatica)

Chamber experiments on juvenile trees have resulted in severe injury and accelerated loss of leaves along with reduced biomass production under chronically enhanced O3 levels. In contrast, the few studies conducted on adult forest trees in the field have reported low O3 sensitivity. In the present study, young beech in phytotrons was more sensitive to O3 than adult beech in the field, although employed O3 regimes were similar. The hypotheses tested were that: (1) differences in O3 uptake were caused by the ontogenetically higher stomatal conductance of young compared to adult trees, (2) the experimental settings in the phytotrons enhanced O3 uptake compared to field conditions, and (3) a low detoxification capacity contributes to the higher O3 sensitivity of the young trees. The higher O3 sensitivity of juvenile beech in the phytotrons is demonstrated to relate to both the experimental conditions and the physiological responsiveness inherent to tree age.     

Modeling competitive adsorption of molybdate, sulfate, selenate, and selenite using a Freundlich-type multi-component isotherm

This study examined the interactions of MoO4(2-) + SO4(2-), MoO4(2-) + SeO4(2-), and MoO4(2-) + SeO3(2-) systems on gamma-Al2O3 to better understand the competitive adsorption of these anions in the natural environment. The Freundlich isotherms of anionic adsorption onto gamma-Al2O3 in single and binary solutes were also investigated to estimate the competition between these anions. Experimental results indicate that a higher concentration of competitive solute yields a higher efficiency of the competitive solute's prevention of MoO4(2-) adsorption. The most significant result was found in the MoO4(2-) + SeO3(2-) system. The Freundlich isotherm constant (n) increases with the competitive solute concentration. The suitability of a Freundlich-type isotherm, the Sheindorf-Rebuhn-Sheintuch (SRS) equation, and the modified SRS equation in representing the competitive adsorption of MoO4(2-), SO4(2-), SeO4(2-), and SeO3(2-) on gamma-Al2O3 surface, was also examined. Each set of isotherm data was found to conform to linear SRS expressions, allowing competition coefficients to be derived on a concentration basis for each binary-solute system. The competition coefficient aij and relative affinity coefficients alphaij can be seen as a way to quantify competitive interactions. The proposed SRS and modified SRS equations are simple mathematical expressions accounting for competitive interactions of anions present in a mixture for the range of concentrations over which each individual component exhibits Freundlich behavior.     

As(V) adsorption on amorphous iron oxide: Triple layer modelling

The adsorption of As(V) by amorphous iron oxide was investigated at 25°C, 0.01 M NaNO₃ background electrolyte as a function of solution pH(4–10) at three initial As(V) concentrations and two Fe(III) concentrations. As(V) adsorption increased with decreasing pH. A modified Langmuir isotherm has been used for describing an equilibrium partition existing between solid and liquid phases. The triple-layer model was used for simulating As(V) adsorption on iron oxide surface. This model was able to describe As(V) adsorption over the pH range 4–10, all at the concentrations of As(V) and Fe(III) studied. =Fe(H₂AsO₄)⁰, = Fe(HAsO₄)⁻ and = Fe(AsO₄)²⁻ have been shown through simulation with inner-sphere complexation products to be more consistent with experimental adsorption observations than complexation with other surface species.     

Characterisation of road sediments near Bordeaux with emphasis on phosphorus

Road sediments from the region of Bordeaux (France) were analysed for trace metals, hydrocarbons (including Polycyclic Aromatic Hydrocarbons, PAHs) and phosphorus. The aim of the study was to assess their potential risk for the environment. The sediments were collected by means of a sweeper. The particles are mostly sandy clay loam and silty clay loam with 5.6-8.3% CaO. Heavy metal concentrations are generally below the French and Dutch standards for polluted soils, but a few samples have higher concentrations, e.g., 547 mg kg(-1) for Zn, and 222 mg kg(-1) for Pb. PAH concentrations are above the Dutch target value for polluted soils, and could be a threat to the environment: pyrene (2600 microg kg(-1)) and fluoranthene (1400 microg kg(-1)) have the highest concentrations, whereas chrysene (340 microg kg(-1)) has the lowest. Consequently, these sediments must be considered as waste according to the French circular no 2001-39 from 18 June 2001 and cannot be disposed of anywhere. The Standards Measurements and Testing (SMT) protocol for sequential extraction of phosphorus in sediments was used to determine the forms of phosphorus in the samples. Total phosphorus concentration is 620 mg kg(-1) on average, with a maximum of 933 mg kg(-1); organic phosphorus content is low (36 mg kg(-1) on average). The protocol could be slightly amended, especially with regards to organic phosphorus at low concentrations and could then be used for the determination of phosphorus in other materials such as sludge from detention ponds.     

Application of fluidized bed combustion to industrial waste treatment

Landfill and sea-dumping appear to be on their way out as acceptable methods for the disposal of untreated industrial wastes in Taiwan. Recently, there has been interest in the application of fluidized bed technology to waste incineration for efficient energy utilization and environmental protection. A pilot fluidized bed combustion system was used to investigate the incineration performance and parametric test for the waste from an industrial park. According to the experimental results, the appropriate operating conditions, including temperatures of 800-840 degrees C, aeration rates of U(0)/Um(f)-2.0 or so, and on-bed feeding, were recommended to treat such waste. The emissions of SO(x), NO(x) and CO in flue gas meet the ROC-EPA regulation.     

Phosphate recovery from greenhouse wastewater

A study was conducted to investigate the suitability of phosphate recovery from greenhouse wastewaters by using precipitation/crystallization process. More than 90% of the phosphate could be removed from the greenhouse wastewater. Various calcium phosphate salts were obtained in the process; hydroxyapatite [Ca5(PO4)3OH] could be the main product from the precipitates. Phosphate removal was affected by the presence of magnesium ion in wastewaters. An increase of magnesium concentrations in wastewaters decreased phosphate removal rates. The chemical contents of precipitates in terms of calcium, magnesium and phosphate were affected by calcium to magnesium molar ratio. Higher calcium contents were obtained at wastewaters with high calcium to magnesium molar ratio. An addition of magnesium did not affect the potassium contents in the precipitates. K-struvite, MgKPO4 x 6H2O, was not the major product in the precipitate, even with addition of a large quantity of magnesium.     

Responses of Metaphycussp. nr. flavus to semiochemicals released from a scale host, Coccus hesperidum

Summary. Metaphycus sp. nr. flavus (Encyrtidae: Hymenoptera) is a parasitoid species collected from the Mediterranean region which lays its eggs in the immature stages of several economically important soft scale insects (Hemiptera: Coccidae), including brown soft scale, Coccus hesperidum L. (= host insect). Preliminary tests suggested that the parasitoid is most successful in producing offspring when it oviposits in the younger stages of brown soft scale. In Y-olfactometer bioassays measuring wasp choices and residence times, naïve parasitoids were significantly more attracted to yucca leaves infested with 26, 27, or 28 d-old scale than to uninfested leaves, whereas leaves with older (29-30 d-old) scale were no more attractive than uninfested leaves. Parasitoids also spent significantly more time in the arm with yucca leaves infested with 26 d-old scale than in the arm with uninfested leaves. These results are consistent with observations of the parasitoids reproductive success on scale of different ages, whereby older scale are more likely to encapsulate the developing eggs of M. sp. nr. flavusfemales than are younger scale. Further bioassays determined that yucca leaves that had been infested with 26 d-old scale but from which the scale had been removed were as attractive as infested leaves. In contrast, infested yucca leaves from which scale had been removed and the leaves subsequently washed with distilled water were less attractive than infested leaves. Furthermore, the wash water containing scale residues was attractive to female wasps. In total, these results suggest that Metaphycussp. nr. flavus females utilize volatile, water soluble compounds produced by brown soft scale as cues to locate suitable hosts.