Structure and Properties of Cocoons and Silk Fibers Produced by Attacus atlas

Silk fibers in the three layers of Attacus atlas (A. atlas) cocoons have morphological structure and tensile properties similar to that of Bombyx mori silk. Attempts are being made to produce silk for commercial applications from cocoons of relatively unknown wild insects due to the unique properties of the fibers and as a source of income and employment. In this research, A. atlas cocoons were used to study the chemical composition, morphology, physical structure and tensile properties of the silk fibers in the cocoons and ability of the fibers to support the attachment and proliferation of mouse fibroblast cells. It was found that A. atlas cocoons consists of outer, intermediate and inner layer with average breaking tenacity of 4.1, 4.3 and 3.6 g/den, respectively similar to that of B. mori silk (4.3–5.2 g/den). The heavier cocoons, less restrictive rearing conditions and good properties of the fibers compared to B. mori silk makes A. atlas a potential alternative to common silks for commercial scale silk production. A. atlas fibers had about 80 % higher optical densities of cells and extensive growth of F-actin compared to B. mori silk fibers.     

Determination of specific gravity of municipal solid waste

This investigation was conducted to evaluate experimental determination of specific gravity (G_s) of municipal solid waste (MSW). Water pycnometry, typically used for testing soils was adapted for testing MSW using a large flask with 2000 mL capacity and specimens with 100–350 g masses. Tests were conducted on manufactured waste samples prepared using US waste constituent components; fresh wastes obtained prior and subsequent to compaction at an MSW landfill; and wastes obtained from various depths at the same landfill. Factors that influence specific gravity were investigated including waste particle size, compaction, and combined decomposition and stress history. The measured average specific gravities were 1.377 and 1.530 for as-prepared/uncompacted and compacted manufactured wastes, respectively; 1.072 and 1.258 for uncompacted and compacted fresh wastes, respectively; and 2.201 for old wastes. The average organic content and degree of decomposition were 77.2% and 0%, respectively for fresh wastes and 22.8% and 88.3%, respectively for old wastes. The G_s increased with decreasing particle size, compaction, and increasing waste age. For fresh wastes, reductions in particle size and compaction caused occluded intraparticle pores to be exposed and waste particles to be deformed resulting in increases in specific gravity. For old wastes, the high G_s resulted from loss of biodegradable components that have low G_s as well as potential access to previously occluded pores and deformation of particles due to both degradation processes and applied mechanical stresses. The G_s was correlated to the degree of decomposition with a linear relationship. Unlike soils, the G_s for MSW was not unique, but varied in a landfill environment due both to physical/mechanical processes and biochemical processes. Specific gravity testing is recommended to be conducted not only using representative waste composition, but also using representative compaction, stress, and degradation states.     

Geographic information systems (GIS) based model of dairy manure transportation and application with environmental quality consideration

Survey information was used to develop a minimum cost spatial dairy manure transportation model where environmental quality and crop nutrient requirements were treated as constraints. The GIS model incorporated land use types, exact locations of dairy farms and farmlands, road networks, and distances from each dairy farm to receiving farmlands to identify dairy manure transportation routes that minimized costs relative to environmental and other constraints. Our analyses indicated that the characteristics of dairy manure, its bulk and relatively low primary N, P₂O₅ and K₂O nutrient levels limit the distribution areas or distances between the farms and the land over which the manure can be economically spread. Physical properties of the land limit the quantities of nutrients that can be applied because of excess nutrient buildup in soil and potential to harm nearby waterbodies and downstream people and places. Longer distances between dairy and farmland favor the use of commercial fertilizers due to the high cost of manure transportation. At $0.08 per ton per km transportation cost, the optimal cut-off distances for dairy manure application is 30 km for N and 15 km each for P₂O₅ and K₂O consistent rules. An analysis of dairy manure application to different crop types suggest that, on average, 1 ha of land requires 61 tons of dairy manure to meet the recommended N, P₂O₅ and K₂O needs.     

Effect of fresh green waste and green waste compost on mineral nitrogen, nitrous oxide and carbon dioxide from a Vertisol

Incorporation of organic waste amendments to a horticultural soil, prior to expected risk periods, could immobilise mineral N, ultimately reducing nitrogen (N) losses as nitrous oxide (N₂O) and leaching. Two organic waste amendments were selected, a fresh green waste (FGW) and green waste compost (GWC) as they had suitable biochemical attributes to initiate N immobilisation into the microbial biomass and organic N forms. These characteristics include a high C:N ratio (FGW 44:1, GWC 35:1), low total N (<1%), and high lignin content (>14%). Both products were applied at 3 t C/ha to a high N (plus N fertiliser) or low N (no fertiliser addition) Vertisol soil in PVC columns. Cumulative N₂O production over the 28 day incubation from the control soil was 1.5 mg/N₂O/m², and 11 mg/N₂O/m² from the control + N. The N₂O emission decreased with GWC addition (P < 0.05) for the high N soil, reducing cumulative N₂O emissions by 38% by the conclusion of the incubation. Analysis of mineral N concentrations at 7, 14 and 28 days identified that both FGW and GWC induced microbial immobilisation of N in the first 7 days of incubation regardless of whether the soil environment was initially high or low in N; with the FGW immobilising up to 30% of available N. It is likely that the reduced mineral N due to N immobilisation led to a reduced substrate for N₂O production during the first week of the trial, when soil N₂O emissions peaked. An additional finding was that FGW + N did not decrease cumulative N₂O emissions compared to the control + N, potentially due to the fact that it stimulated microbial respiration resulting in anaerobic micro sites in the soil and ultimately N₂O production via denitrification. Therefore, both materials could be used as post harvest amendments in horticulture to minimise N loss through nitrate-N leaching in the risk periods between crop rotations. The mature GWC has potential to reduce N₂O, an important greenhouse gas.     

A methodology to determine gaseous emissions in a composting plant

Environmental impacts associated to different waste treatments are of interest in the decision-making process at local, regional and international level. However, all the environmental burdens of an organic waste biological treatment are not always considered. Real data on gaseous emissions released from full-scale composting plants are difficult to obtain. These emissions are related to the composting technology and waste characteristics and therefore, an exhaustive sampling campaign is necessary to obtain representative and reliable data of a single plant. This work proposes a methodology to systematically determine gaseous emissions of a composting plant and presents the results obtained in the application of this methodology to a plant treating source-separated organic fraction of municipal solid waste (OFMSW) for the determination of ammonia and total volatile organic compounds (VOC). Emission factors from the biological treatment process obtained for ammonia and VOC were 3.9 kg Mg OFMSW⁻¹ and 0.206 kg Mg OFMSW⁻¹ respectively. Emissions associated to energy use and production were also quantified (60.5 kg CO₂ Mg OFMSW⁻¹ and 0.66 kg VOC Mg OFMSW⁻¹). Other relevant parameters such as energy and water consumption and amount of rejected waste were also determined. A new functional unit is presented to relate emission factors to the biodegradation efficiency of the composting process and consists in the reduction of the Respiration Index of the treated material. Using this new functional unit, the atmospheric emissions released from a composting plant are directly related to the plant specific efficiency.     

Spatial variability of soil gas concentration and methane oxidation capacity in landfill covers

In order to devise design criteria for biocovers intended to enhance the microbial oxidation of landfill methane it is critical to understand the factors influencing gas migration and methane oxidation in landfill cover soils. On an old municipal solid waste landfill in north-western Germany soil gas concentrations (10, 40, 90 cm depth), topsoil methane oxidation capacity and soil properties were surveyed at 40 locations along a 16 m grid. As soil properties determine gas flow patterns it was hypothesized that the variability in soil gas composition and the subsequent methanotrophic activity would correspond to the variability of soil properties. Methanotrophic activity was found to be subject to high spatial variability, with values ranging between 0.17 and 9.80 g CH₄ m⁻² h⁻¹_. Considering the current gas production rate of 0.03 g CH₄ m⁻² h⁻¹, the oxidation capacity at all sampled locations clearly exceeded the flux to the cover, and can be regarded as an effective instrument for mitigating methane fluxes. The methane concentration in the cover showed a high spatial heterogeneity with values between 0.01 and 0.32 vol.% (10 cm depth), 22.52 vol.% (40 cm), and 36.85 vol.% (90 cm). The exposure to methane raised the oxidation capacity, suggested by a statistical correlation to an increase in methane concentration at 90 cm depth. Methane oxidation capacity was further affected by the methanotroph bacteria pH optimum and nutrient availability, and increased with decreasing pH towards neutrality, and increased with soluble ion concentration). Soil methane and carbon dioxide concentration increased with lower flow resistance of the cover, as represented by the soil properties of a reduced bulk density, increase in air capacity and in relative ground level.     

Extension of EU Emissions Trading Scheme to Other Sectors and Gases: Consequences for Uncertainty of Total Tradable Amount

Emissions trading in the European Union (EU), covering the least uncertain emission sources of greenhouse gas emission inventories (CO₂ from combustion and selected industrial processes in large installations), began in 2005. During the first commitment period of the Kyoto Protocol (2008–2012), the emissions trading between Parties to the Protocol will cover all greenhouse gases (CO₂, CH₄, N₂O, HFCs, PFCs, and SF₆) and sectors (energy, industry, agriculture, waste, and selected land-use activities) included in the Protocol. In this paper, we estimate the uncertainties in different emissions trading schemes based on uncertainties in corresponding inventories. According to the results, uncertainty in emissions from the EU15 and the EU25 included in the first phase of the EU emissions trading scheme (2005–2007) is ±3% (at 95% confidence interval relative to the mean value). If the trading were extended to CH₄ and N₂O, in addition to CO₂, but no new emissions sectors were included, the tradable amount of emissions would increase by only 2% and the uncertainty in the emissions would range from −4 to +8%. Finally, uncertainty in emissions included in emissions trading under the Kyoto Protocol was estimated to vary from −6 to +21%. Inclusion of removals from forest-related activities under the Kyoto Protocol did not notably affect uncertainty, as the volume of these removals is estimated to be small.     

Photo-Stabilisation and UV Blocking Efficacy of Coated Macro and Nano-Rutile Titanium Dioxide Particles in Paints and Coatings

Surface treated macro and nanoparticle TiO₂ samples have been prepared, characterised and their efficiency as UV blockers evaluated in clear coatings and paints. The particle size of the ‘base’ TiO₂ has been optimised to block UV radiation and the surface treatment developed to deactivate the photocatalytic activity of the surface of the TiO₂ particles. The resultant UV blockers have been evaluated in both solvent and water-based clear coatings. Nanoparticle TiO₂ has been prepared from ‘seed’ and the particle size was controlled by calcination. It was found that the choice of particle size is a compromise between UVA absorption, UVB absorption, visible transmission and photoactivity. It has been demonstrated that TiO₂ with a crystallite size of 25 nm yields a product with the optimum properties. A range of dispersants was successfully used to disperse and mill the TiO₂. Both organic and inorganic dispersants were used; 2-amino-2-methyl-1-propanol and 1-amino-2-propanol (MIPA) and P₂O₅ and Na₂SiO₃ respectively. The surface of the nano-TiO₂ was coated with mixed oxides of silicon, aluminium, zirconium and phosphorous. Addition of the resultant coated nano-rutiles to an Isocyanate Acrylic clear coating prolonged the lifetime of that coating compared to the blank. Generally, a surface treatment based on SiO₂, Al₂O₃ and P₂O₅ was more successful than one based on ZrO₂, Al₂O₃ and P₂O₅. Higher addition levels of the surface treatment were beneficial for protecting the polymeric coating. The UV blocker products were also evaluated in a water-based acrylic, first a water-based dispersion of the UV blocker was prepared before addition to the acrylic. The dispersions and resultant acrylic thin films were evaluated using UV/Vis spectroscopy and durability assessed. The ratio of absorbance at 300:500 nm for the water-based dispersion was shown to be a good predictor of both the transparency of the resultant acrylic thin film and the durability of that film, in terms of weight loss. Macro grade titanium dioxide pigments were also prepared and coated with treatments of silica, alumina and siloxane and their photo-stabilising activity in alkyd paint film assessed and found to be directly related to the electron–hole pair mobility and trapping as determined by micro-wave spectroscopy.     

Effects of Acid Rain on Competitive Releases of Cd, Cu, and Zn from Two Natural Soils and Two Contaminated Soils in Hunan, China

Leaching experiments of rebuilt soil columns with two simulated acid rain solutions (pH 4.6–3.8) were conducted for two natural soils and two artificial contaminated soils from Hunan, south-central China, to study effects of acid rain on competitive releases of soil Cd, Cu, and Zn. Distilled water was used in comparison. The results showed that the total releases were Zn>Cu>Cd for the natural soils and Cd>Zn≫Cu for the contaminated soils, which reflected sensitivity of these metals to acid rain. Leached with different acid rain, about 26–76% of external Cd and 11–68% external Zn were released, but more than 99% of external Cu was adsorbed by the soils, and therefore Cu had a different sorption and desorption pattern from Cd and Zn. Metal releases were obviously correlated with releases of TOC in the leachates, which could be described as an exponential equation. Compared with the natural soils, acid rain not only led to changes in total metal contents, but also in metal fraction distributions in the contaminated soils. More acidified soils had a lower sorption capacity to metals, mostly related to soil properties such as pH, organic matter, soil particles, adsorbed SO₄ ²⁻, exchangeable Al³⁺ and H⁺, and contents of Fe₂O₃ and Al₂O₃.     

Quantifying dry NH3 deposition to an ombrotrophic bog from an automated NH3 field release system

Providing an accurate estimate of the dry component of N deposition to low N background, semi-natural habitats, such as bogs and upland moors dominated by Calluna vulgaris is difficult, but essential to relate nitrogen deposition to effects in these communities. To quantify the effects of NH₃ inputs to moorland vegetation growing on a bog at a field scale, a field release NH₃ fumigation system was established at Whim Moss (Scottish Borders) in 2002. Gaseous NH₃ from a line source was released along of a 60 m transect, when meteorological conditions (wind speed >2.5 m s^?1 and wind direction in the sector 180–215°) were met, thereby providing a profile of decreasing NH₃ concentration with distance from the source. In a complementary study, using a NH₃ flux chamber system, the relationships between NH₃ concentrations and cuticular resistances were quantified for a range of NH₃ concentrations and micrometeorological conditions for moorland vegetation. Cuticular resistances increased with NH₃ concentration from 11 s m^?1 at 3.0 μg m^?3 to 30 s m^?1 at 30 μg m^?3. The NH₃ concentration data and the concentration-dependent canopy resistance are used to calculate NH₃ deposition taking into account leaf surface wetness. The implications of using an NH₃ concentration-dependent cuticular resistance and the importance for refining critical loads are discussed.     

Water transport in polylactic acid (PLA), PLA/ polycaprolactone copolymers, and PLA/polyethylene glycol blends

Polylactic acid (PLA) is a hydrolytically degradable aliphatic polyester, and water vapor permeability may have a significant influence on the rate of degradation. A method is devised to use bags prepared from PLA films and filled with molecular sieves to determine the water vapor permeability in the polymer, its copolymers with caprolactone, and blends with polyethylene glycol. The “solution-diffusion” model is used to determine the permeability parameters. These include the solubility coefficient,S, a measure of the equilibrium water concentration available for hydrolysis and the diffusion coefficient,D, which characterizes the rate of water vapor diffusion into the film under specific conditions. Values ofS andD at 50‡C and 90% relative humidity ranged from 400 × 10^-6 to 1000 × 10^-6 cm³ (STP)/(cm³ Pa) and 0.20 × 10^-6 to 1.0 × 10^-6 cm²/s, respectively. TheS andD coefficients were also measured at 20 and 40‡C and compared to those of other polymers. The degree of crystallinity was found to have little influence on the measured permeability parameters. The heat of sorption, δH_S, and the activation energy of diffusion, E_D, were used to show that the permeability process is best described by the “water cluster” model for hydrophobic polymers. Finally, the diffusion coefficient is used to compare the rate of water diffusion to the rate of water consumption by ester hydrolysis. Results indicate that hydrolytic degradation of PLA is reaction-controlled.     

Determination of first-order landfill gas modeling parameters and uncertainties

Using first-order kinetic empirical models to estimate landfill gas (LFG) generation and collection rates is well recognized in the literature. The uncertainty in the estimated LFG generation rates is a major challenge in evaluating performance of LFG collection and LFG to energy facilities. In this investigation, four methods for quantifying first-order LFG generation model parameters, methane generation potential, L₀, and methane generation rate constant, k, were evaluated. It was found that the model is insensitive to the approach taken in quantifying the parameters. However, considering the recognition of using the model in the literature, the optimum method to estimate L₀ and k is to determine L₀ using disposed municipal solid waste composition and laboratory component specific methane potential values. The k value can be selected by model fitting and regression using the first-order model if LFG collection data are available. When such data are not available, k can be selected from technical literature, based on site conditions. For five Florida case-study landfills L₀ varied from 56 to 77 m³ Mg⁻¹, and k varied from 0.04 to 0.13 yr⁻¹ for the traditional landfills and was 0.10 yr⁻¹ for the wet cell. Model predictions of LFG collection rates were on average lower than actual collection. The uncertainty (coefficient of variation) in modeled LFG generation rates varied from ±11% to ±17% while landfills were open, ±9% to ±18% at the end of waste placement, and ±16% to ±203% 50 years after waste placement ended.     

Investigation of the application of an enzyme-based biodegradability test method to a municipal solid waste biodrying process

This paper presents a study to evaluate the recently developed enzymatic hydrolysis test (EHT) through its repeated application to a waste treatment process. A single waste treatment facility, involving a biodrying process, has been monitored using three different methods to assess the biodegradable content of the organic waste fractions. These test methods were the anaerobic BMc, aerobic DR4 and the EHT, which is a method based on the enzymatic hydrolysis of the cellulosic content of waste materials. The input municipal solid waste (MSW) and the output solid recovered fuel (SRF) and organic fines streams were sampled over a period of nine months from a single mechanical biological treatment (MBT) facility. The EHT was applied to each stream following grinding to <10 mm and <2 mm, in order to investigate the effect of particle size on the release of dissolved organic carbon (DOC) from enzyme hydrolysis. The output organic fines were found to more biodegradable than the MSW input and SRF output samples in each of the test methods, significantly (p < 0.05) for the EHT and DR4 methods, on the basis of DOC released and oxygen consumed, respectively. The variation between sample replicates for the EHT was higher where sample sizes of <2 mm were analysed compared to sizes of <10 mm, and the DOC release at each phase of the EHT was observed to be higher when using particle sizes of <2 mm. Despite this, additional sample grinding from the <10 mm to a smaller particle size of <2 mm is not sufficiently beneficial to the analysis of organic waste fractions in the EHT method. Finally, it was concluded that as similar trends were observed for each test method, this trial confirms that EHT has the potential to be deployed as a practical operational biodegradability monitoring tool.     

An innovative example of herb residues recycling by gasification in a fluidized bed

A utilization way of herb residues is designed to convert herb residues to gas fuel in industrial-scale by a circulating fluidized bed gasifier in this paper. The product gas is used in the production of Chinese medicine, and the heat of the flue gas from the boiler can be used in herb residues drying to realize the energy recycling and no herb residues discharge. The gasification characteristics of herb residues in the circulating fluidized bed of 300 kg/h were investigated for about 200 h. The results indicated that the gas composition and tar yield were affected by biomass flow rate, equivalence ratio (ER), moisture content and char circulating. The lower heating value of product gas was 4–5 MJ/m³ using herb residues as feedstock. When mean biomass flow rate was at 5.5 kg m^?2 s^?1 and ER at 0.35, the product gas reached a good condition with lower heating value of 4.89 MJ/m³ and cold gas efficiency of 62.36%. When the moisture content changed from 12.5% to 18.7%, the concentrations of H₂, CO and CO₂ changed from 4.66% to 6.92%, 11.23% to 10.15%, and 16.55% to 17.82% respectively, and the tar content in gas decreased from 15.1 g/m³ to 14.4 g/m³ when the moisture content increased from 12.5% to 15.4%. There are metal oxides in the ash of herb residues, especially CaO, MgO, K₂O, Al₂O₃, and Fe₂O₃ which have obvious function on tar catalytic decomposition. The ash that attaches to the char particles can decrease the tar yield and improve the quality of gas after returning to the gasifier.     

Future landfill emissions and the effect of final cover installation--a case study

Municipal solid waste (MSW) landfills are potential long-term sources of emissions. Hence, they need to be managed after closure until they do not pose a threat to humans or the environment. The case study on the Breitenau MSW landfill was performed to evaluate future emission levels for this site and to illustrate the effect of final cover installation with respect to long-term environmental risks. The methodology was based on a comprehensive assessment of the state of the landfill and included analysis of monitoring data, investigations of landfilled waste, and an evaluation of containment systems. A model to estimate future emission levels was established and site-specific predictions of leachate emissions were presented based on scenario analysis. The results are used to evaluate the future pollution potential of the landfill and to compare different aftercare concepts in view of long-term emissions. As some leachable substances became available for water flow during cover construction due to a change in the water flow pattern of the waste, a substantial increase in leachate concentrations could be observed at the site (e.g. concentrations of chloride increased from 200 to 800 mg/l and of ammonia-nitrogen from 140 to about 500 mg/l). A period of intensive flushing before the final cover installation could have reduced the amount of leachable substances within the landfill body and rapidly decreased the leachate concentrations to 11 mg Cl/l and 79 mg NH₄-N/l within 50 years. Contrarily, the minimization of water infiltration is associated with leachate concentrations in a high range for centuries (above 400 mg Cl/l and 200 mg NH₄-N/l) with low concomitant annual emission loads (below 12 kg/year of Cl or 9 kg/year of NH₄-N, respectively). However, an expected gradual decrease of barrier efficiency over time would be associated with higher emission loads of 50 kg of chloride and 30 kg of ammonia-nitrogen at the maximum, but a faster decrease of leachate concentration levels.     

Morphological and Thermal Characterization of Linseed-Oil Based Polymers from Cationic and Thermal Polymerization

Linseed oil-based polymers have been synthesized via cationic and thermal polymerization and characterized through various techniques, such as SEM, DMA, DSC and TGA. The morphology of the polymer samples after extraction reveals the smooth structure of the polymer matrix. With an increase in oil content, the morphology is observed to be more loosely bound. With an increase in linseed oil content in the samples, the room temperature storage modulus (E′) varies from 10.4 × 10⁷ to 1.8 × 10⁷ Pa. The glass transition temperatures measured through DMA of the cationic samples ranges from 70 to −6 °C and the crosslink densities range from 18.4 × 10³ to 3.4 × 10³ mol/m³. The glass transition temperatures of the thermal samples range from 106 to −4 °C and the crosslink densities range from 7.7 × 10³ to 2.4 × 10³ mol/m³. The TGA results show three stages of degradation of the polymer samples and it is also revealed that these polymers are stable up to 200 °C, showing negligible decomposition.     

Acidic bioleaching of heavy metals from sewage sludge

The overall objective of this study was to evaluate the use of controlled bio-acidification prior to land application as a decontamination process to remove heavy metals from sludge. The sulfur-oxidizing bacteria were naturally available in the sludge samples and were activated by providing sulfur and aeration at 28°C–30°C. Activation resulted in bio-acidification to pH 2 within 5–11 days. Successive inoculation of fresh sludges with 5% acidified samples reduced the acidification time to 2–3 days in most samples. Bio-acidification resulted in dissolving significant quantities of heavy metals from all sludge types tested. The maximum solubilization results were: 86%–97% for Ni; 48%–98% for Pb; 26%–71% for Cr; 18%–91% for Zn; 16%–90% for Cu; 7%–60% for Cd. Limited metal solubilization results were observed in the various control samples that accompanied the bio-acidified samples. The leaching results in the control samples were limited to 2%–19% for Ni, 0%–7% for Pb, 0%–5% for Cr, 0.3%–4% for Zn, 0.2%–4% for Cu and 0%–3% for Cd. The results confirmed that Ni and Pb were the easiest metals to dissolve from the various sludge types. On the other hand, the lowest solubilization results were observed for Cu and Cd, and moderate solubilization results were achieved for Cr. The bio-acidification process resulted in moderate gains in terms of improving the suitability of tested sludges for land application. Received: April 19, 1999 / Accepted: November 4, 1999     

Particle Surface Hydrophobicity and the Dechlorination of Chloro-Compounds by Iron Sulfides

Halogenated aliphatic compounds (HACs) can be reduced by iron sulfides in aqueous systems. Generally, the thermodynamics and kinetics of dehalogenation reactions are controlled by the mineralogical and particle surface characteristics of the iron sulfide, the composition of the HAC and reaction conditions such as component concentrations, pH and Eh. In this theoretical and experimental investigation of CCl₄ and C₂Cl₆ reduction by FeS and FeS₂, the roles of hydrophobic and hydrophilic sites on the iron sulfides were analyzed. Experimental data obtained through zeta potential measurements, were used along with the Gouy-Chapman model and the simple two-layer surface complexation model to relate iron sulfide surface hydroxyl densities to the degree of HAC dehalogenation. The surface hydroxyl site densities of FeS and FeS₂ were found to be 0.11 sites/nm² and 0.21 sites/nm², respectively. During the dehalogenation reaction process, CCl₄ was found to decrease to its first intermediate product CHCl₃ within the first 20 hours followed by a slower process of conversion to CH₂Cl₂. The results also show that FeS is less hydrated (more hydrophobic) than FeS₂. For CCl₄ and C₂Cl₆, FeS is a better dehalogenator than FeS₂. These results imply that particle surface hydrophobicity is a critical factor in surface-mediated dehalogenation of chlorinated compounds.     

Laboratory studies on the remediation of mercury contaminated soils

Mercury, in contrast to other toxic metals, cycles between the atmosphere, land, and water. During this cycle, it undergoes a series of complex chemical and physical transformations. Because of these transformations, it is found in the environment not only as simple inorganic and organic compounds, but also as complex compounds. As a result, it is difficult to remediate mercury contaminated materials. Laboratory studies were conducted with a mercury contaminated complex waste from an industrial site to evaluate the ability of extractants such as H₂O₂, H₂SO₄ and Na₂S₂O₃ to decontaminate the waste. Up to 87 percent of the total mercury present in the waste was extracted. Mercury was recovered as insoluble mercury sulfide by adding Na₂S solution to the combined filtrates from the H₂O₂ + H₂SO₄ and Na₂S₂O₃ treatment steps. The technique described in this article is capable of recovering mercury in a usable form and can be used as a pretreatment to remediate mercury contaminated waste before laud disposal.     

Multi-response optimization of Fenton process for applicability assessment in landfill leachate treatment

Fenton process, as a pretreatment method, was found to be effective in the primary treatment of mature/medium landfill leachate. However, the main problem of the process is the large amount of produced sludge that requires an accurate feasibility evaluation for operational applications. In this study, the response surface methodology was applied for the modeling and optimization of Fenton process in three target responses, (1) overall COD removal, (2) sludge to iron ratio (SIR) and (3) organics removal to sludge ratio (ORSR), where the latter two were new self-defined responses for prediction of sludge generation and applicability assessment of the process, respectively. The effective variables included the initial pH, [H₂O₂]/[Fe²⁺] ratio and Fe²⁺ dosage. According to the statistical analysis, all the proposed models were adequate (with adjusted R² of 0.9116–0.9512) and had considerable predictive capability (with prediction R² up to 0.9092 and appropriate adequate precision). It was found that all the variables had significant effects on the responses, specifically by their observed role in dominant oxidation mechanism. The optimum operational conditions obtained by overlay plot, were found to be initial pH of 5.7, [H₂O₂]/[Fe²⁺] ratio of 17.72 and [Fe²⁺] of 195 mM, which led to 69% COD removal, 2.4 (l sludge/consumed mole Fe²⁺) of SIR and 16.5 (gCOD removed/l produced sludge) for ORSR in verification test, in accordance with models-predicted values. Finally, it was observed that [H₂O₂]/[Fe²⁺] ratio and Fe²⁺ dosage had significant influence on COD removal, while Fe²⁺ dosage and [H₂O₂]/[Fe²⁺] ratio had remarkable effects on SIR and ORSR responses, respectively.