Rapid-extraction oxidation process to recover and reuse copper chromium and arsenic from industrial wood preservative sludge

Chromated copper arsenate (CCA) wood preservative can form insoluble sludges when the hexavalent chromium component is reduced by wood extractives, wood particles and preservative additives in the solution. This sludge accumulates in treating solution work tanks, sumps and in-line filters and must be disposed of as hazardous wastes by waste disposal companies at high costs. A number of commercial sludges were investigated and found to contain 18-94% copper, chromium and arsenic as oxides combined with sand, oil, wood particles, additives and wood extractives. We have developed a multi-stage recycling process whereby approximately 97% of the CCA components are recovered from the sludge. It involves extraction with sodium hypochlorite to remove and oxidize chromium (more than 90%) and extract most of the arsenic (approx. 80%) followed by extraction of the copper and remaining arsenic and chromium with phosphoric acid. The phosphoric acid extract contains some trivalent chromium, which is subsequently oxidized by sodium hypochlorite. The combined oxidized extract containing CrVI, CuII and AsV was compatible with CCA treating solutions and could be re-used commercially for treating wood without having a significant effect on the preservative fixation rate or the leach resistance of the treated wood. A cost analysis showed that the economic savings from recovery of CCA chemicals and reduced landfill costs exceeded the variable costs for materials and energy for the process by as much as Can $966 per tonne of sludge if sodium sulfite can be acquired in bulk quantities for the process.     

Fatal accidents in nighttime vs. daytime highway construction work zones

INTRODUCTION: Awareness about worker safety in nighttime construction has been a major concern because it is believed that nighttime construction creates hazardous work conditions. However, only a few studies provide valuable comparative information about accident characteristics of nighttime and daytime highway construction activities. METHOD: This study investigates fatal accidents that occurred in Illinois highway work zones in the period 1996-2001 in order to determine the safety differences between nighttime and daytime highway construction. The lighting and weather conditions were included into the study as control parameters to see their effects on the frequency of fatal accidents occurring in work zones. RESULTS: According to this study, there is evidence that nighttime construction is more hazardous than daytime construction. The inclusion of a weather parameter into the analysis has limited effect on this finding. IMPACT ON INDUSTRY: The study justifies establishing an efficient work zone accident reporting system and taking all necessary measures to enhance safety in nighttime work zones.     

Optimization of carbon dioxide absorption in a continuous bubble column reactor using response surface methodology

Carbon dioxide absorption using amine based solvents is a well-known approach for carbon dioxide removal. Especially with the increasing concerns about greenhouse gas emissions, there is a need for an optimization approach capable of multifactor calibration and prediction of interactions. Since conventional methods based on empirical relations are not efficiently applicable, this study investigates use of Response Surface Methodology as a strong optimization tool. A bubble column reactor was used and the effect of solvent concentration (10.0, 20.0 and 30.0 vol%), flow rate (4.0, 5.0 and 6.0 L min⁻¹), diffuser pore size (0.5, 1.0 and 1.5 mm) and temperature (20.0, 25.0 and 30.0°C) on the absorption capacity and also overall mass transfer coefficient was evaluated. The optimization results for maintaining maximum capacity and overall mass transfer coefficient revealed that different optimization targets led to different tuned operational factors. Overall mass transfer coefficient decreased to 34.7 min⁻¹ when the maximum capacity was the desired target. High reaction rate along with the highest absorption capacity was set as desirable two factor target in this application. As a result, a third scenario was designed to maximize both mass transfer coefficient and absorption capacity simultaneously. The optimized condition was achieved when a gas flow rate of 5.9 L min⁻¹, MEA solution of 29.6 vol%, diffuser pore size of 0.5 mm and temperature of 20.6°C was adjusted. At this condition, mass transfer coefficient reached a maximum of 38.4 min⁻¹, with a forecasted achievable absorption capacity of 120.5 g CO₂ per kg MEA.     

Quantification of Hg excretion and distribution in biological samples of mercury-dental-amalgam users and its correlation with biological variables

This is the first study conducted to quantify the excretion and distribution of mercury (Hg) with time (days) in the biological samples collected from Hg dental amalgam users (MDA). The individuals, with Hg-based dental filling were selected, and their biological samples (red blood cells (RBCs), plasma, urine, hair, and nails) were collected on first, third, and 12th day of fillings. The concentrations of Hg observed in the biological samples of MDA were also correlated with the biological variables such as age, weight, restoration, fish consumption, number, and surface area of fillings. The concentrations of Hg in the biological samples of MDA were found 6–8 times higher than the non-amalgam users (control). The concentrations of Hg in the RBCs (4.39 μg/L), plasma (3.02 μg/L), and urine (22.5 μg/L) on first day of filling were found comparatively higher than the concentrations observed on third day (2.15, 1.46, and 12.3 μg/L for RBCs, plasma, urine, respectively) and 12th day (3.05, 2.5, 9.12 μg/L for RBCs, plasma, urine, respectively), while Hg concentrations were found lower in the hair and nails on third day of fillings (1.53 μg/g for hair and 2.35 μg/g for nails) as compared to the 12th day (2.95 μg/g for hair and 3.5 μg/g for nails). The correlations were found significant (p ˂ 0.05) between Hg concentrations in the biological samples of MDA and biological variables (the number of restoration, fish consumption, number, and surface area of fillings), while no significant (p ˃ 0.05) correlations were observed for Hg concentrations in the biological samples with age and weight of MDA. These observations unveil the fact that the use of Hg-based dental filling is the undesirable exposure to Hg which should be replaced by composite (a safer filling material).

     

Hydrogeochemical comparison and effects of overlapping redox zones on groundwater arsenic near the Western (Bhagirathi sub-basin, India) and Eastern (Meghna sub-basin, Bangladesh) margins of the Bengal Basin

Although arsenic (As) contamination of groundwater in the Bengal Basin has received wide attention over the past decade, comparative studies of hydrogeochemistry in geologically different sub-basins within the basin have been lacking. Groundwater samples were collected from sub-basins in the western margin (River Bhagirathi sub-basin, Nadia, India; 90 samples) and eastern margin (River Meghna sub-basin; Brahmanbaria, Bangladesh; 35 samples) of the Bengal Basin. Groundwater in the western site (Nadia) has mostly Ca-HCO(3) water while that in the eastern site (Brahmanbaria) is much more variable consisting of at least six different facies. The two sites show differences in major and minor solute trends indicating varying pathways of hydrogeochemical evolution However, both sites have similar reducing, postoxic environments (p(e): +5 to -2) with high concentrations of dissolved organic carbon, indicating dominantly metal-reducing processes and similarity in As mobilization mechanism. The trends of various redox-sensitive solutes (e.g. As, CH(4), Fe, Mn, NO(3)(-), NH(4)(+), SO(4)(2-)) indicate overlapping redox zones, leading to partial redox equilibrium conditions where As, once liberated from source minerals, would tend to remain in solution because of the complex interplay among the electron acceptors.     

DDT residue in soil and water in and around abandoned DDT manufacturing factory

Dichlorodiphenyltrichloroethane (DDT) belongs to one of the most hazardous groups of chemicals called persistent organic pollutants. Many organochlorine pesticides including p,p(')-DDT are long lasting due to their non-degradability can travel to distant places and being fat soluble can accumulate in animals and human bodies. Due to the persistent nature of p,p(')-DDT, its adverse environmental and health impacts, the present study was undertaken to examine the residual p,p(')-DDT in and around abandoned p,p(')-DDT manufacturing factory in Amman Gharh, Nowshera, NWFP. Samples of soil, sediments and water were collected in and around the factory area, nearby p,p(')-DDT stores, main factory drain leading to river Kabul and nearby villages. Standard procedures were used for the collection, transportation and storage of samples for analyses. Extraction of each sample for p,p(')-DDT analyses was carried out in triplicates using Soxhelt extraction. p,p(')-DDT contents in the samples were analyzed by capillary GC with electron capture detector. Most of the samples collected up to half kilometer distance from the site of the DDT factory were found contaminated. Further the level of p,p(')-DDT decreased with increasing depth from top to bottom and with distance from the site. The results indicate that there is no immediate threat to underground water reservoirs.     

Characteristics of pipe corrosion scales in untreated water distribution system and effect on water quality in Peshawar,Pakistan

This study investigated the characteristics of iron corrosion scales in pipes at tube well, overhead tank, and consumers’ end in older untreated water distribution system in Peshawar city, Pakistan. Effect of water quality conditions on corrosion scales and that of scales on drinking water quality in such systems was also assessed by undertaking a comparison with new piped distribution systems. The scales were analyzed for chemical composition and morphology using X-ray diffraction (XRD), inductively coupled plasma (ICP), and a scanning electron microscope (SEM), while water quality was examined for physicochemical and biological characteristics. The main crystalline phases of corrosion scales were goethite, magnetite, siderite, and quartz. From tube well to consumers’ end, goethite increased from 36 up to 48%, quartz declined from 22 to 15%, while magnetite fluctuated and siderite disappeared. Elemental composition of scales showed the deposition of Zn, Al, Mn, Cr, Pb, Cu, As, and Cd with Zn (13.9 g/kg) and Al (3.6 g/kg) in highest proportion. The SEM analysis illustrated the presence of microbial communities indicating the formation of biofilms in the corrosion scales. The significant difference (P <?0.05) in levels of dissolved oxygen (DO), Cl^?, SiO₄^4?, electrical conductivity (EC), SO₄^2?, NO₃^?, alkalinity, hardness, and trace metals between old (DS-O) and new piped systems indicated their role in corrosion scale formation/destabilization and the effect of scale dissolution on water quality. In DS-O, EC, Cu, and Mn were significantly higher (P?<?0.05), whereas turbidity, EC, DO, and SiO₄^4? significantly increased from source to consumers’ end implying a higher dissolution of scales and lowered corrosion rates in DS-O to utilize SiO₄^4? and DO for iron oxidation.

     

The financial development-environmental degradation nexus in the United Arab Emirates: the importance of growth,globalization and structural breaks

Environmental Science and Pollution Research - This article revisits the nexus between financial development and environmental degradation by incorporating economic growth, electricity consumption...     

Towards sustainable environment: why green energy technology diffusion is sluggish in South Africa?

Environmental Science and Pollution Research - Energy security, job development, and minimal environmental damage are just a few of the reasons why green energy technologies have gained popularity....     

Effects of using arsenic–iron sludge wastes in brick making

The arsenic–iron sludge generated in most of the treatment systems around the world is discharged into the nearest watercourse, which leads to accumulative rise of arsenic and iron concentrations in water. In this study, attempts were made to use the arsenic–iron sludge in making bricks and to analyze the corresponding effects on brick properties. The water treatment plant sludge is extremely close to brick clay in chemical composition. So, the sludge could be a potential substitute for brick clay. This study involved the addition of sludge with ratios 3%, 6%, 9% and 12% of the total weight of sludge–clay mixture. The physical and chemical properties of the produced bricks were then determined and evaluated and compared to control brick made entirely from clay. Results of different tests indicated that the sludge proportion and firing temperature were the two key factors in determining the quality of bricks. The compressive strength of 3%, 6%, 9% and 12% sludge containing brick samples were found to be 14.1 MPa, 15.1 MPa, 9.4 MPa and 7.1 MPa, respectively. These results indicate that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion. Leaching characteristics of burnt bricks were determined with the variation of pH at a constant temperature. The optimum amount of sludge that could be mixed with clay to produce good bonding of clay–sludge bricks was found to be 6% (safely maximum) by weight.