Arsenic contaminated site at an abandoned copper smelter plant: waste characterization and solidification/stabilization treatment

A preliminary survey of an arsenic contaminated site from an abandoned copper smelting facility and feasibility study of using solidification/stabilization (S/S) process to treat the contaminant waste were undertaken. It was found that the waste, located in the three-flue gas discharge tunnels, contained 2-40% arsenic. The pH of the contaminated waste is extremely low (ranging from 1.8 to 3.6). The X-ray diffraction evidence indicates that the arsenic particles present in the flue gas mainly exist as As(III), or As(2)O(3). The total amount of arsenic contaminated waste is estimated to be 700 ton in the studied area. About 50% of the particle sizes are less than 2 mm. Arsenic is easily extracted from wastes with a variety of leaching solutions. In order to meet the arsenic leaching standard of the toxicity characteristic leaching procedure (TCLP), an extremely high cement dosage is required in the S/S process (cement/waste weight ratio>6). The waste with lower particle size having higher specific surface area exhibits somewhat positive effect on the S/S performance. The use of fly ash from municipal waste incinerators, in conjunction with the reduced amount of cement, is able to meet the TCLP arsenic and lead standards. The use of lime alone could meet the TCLP arsenic standard, but lead leaching concentrations exceeded leaching Pb standard. The results of semi-dynamic leaching tests of some solidified samples indicate higher accumulated arsenic leaching concentrations after only a few leachant renewals.     

Effects of experimental parameters on NF(3) decomposition fraction in an oxygen-based RF plasma environment

Clean procedure is one of the major emitters of perfluorinated compounds (PFCs) in semiconductor manufacturing. Nitrogen trifluoride (NF(3)) is increasingly the process gas of choice for eliminating PFC emissions. However, its toxic to human and similar global warming potential compared to most other PFCs made NF(3) warranted much more investigation. This study demonstrated a radio-frequency plasma system for decomposing NF(3). The effects of experimental parameters: input power, O(2)/NF(3) ratio, operational pressure and NF(3) feeding concentration on NF(3) decomposition fraction (eta(NF3)) and energy efficiency E(NF3) were examined in detail. The analytical results demonstrated that the NF(3) was almost completely decomposed (>99%) at input power=30W, [NF(3)](in)=1.0% and eta(NF3) increased with input power. However, adding O(2) to the system inhibited NF(3) decomposition and decreased E(NF3). Moreover, eta(NF3) and E(NF3), decreased with gradually increasing operational pressure. Notably, increasing the NF(3) feeding concentration increased molecule density, reducing eta(NF3), but increasing E(NF3). Furthermore, the products detected in the NF(3)/O(2)/Ar plasma system were NO(2), NO, N(2)O, SiF(4), N(2) and F(2). Potential reaction pathways in the oxygen-based NF(3) plasma environment were built-up and elucidated.     

Performance of a constructed wetland treating intensive shrimp aquaculture wastewater under high hydraulic loading rate

A water treatment unit, mainly consisting of free water surface (FWS) and subsurface flow (SF) constructed wetland cells, was integrated into a commercial-scale recirculating aquaculture system for intensive shrimp culture. This study investigated performance of the treatment wetlands for controlling water quality. The results showed that the FWS-SF cells effectively removed total suspended solids (55-66%), 5-day biochemical oxygen demand (37-54%), total ammonia (64-66%) and nitrite (83-94%) from the recirculating water under high hydraulic loading rates (1.57-1.95 m/day). This led to a water quality that was suitable for shrimp culture and effluent that always satisfied the discharge standards. The area ratios of wetlands to culture tank being demonstrated (0.43) and calculated (0.096) in this study were both significantly lower than the reported values. Accordingly, a constructed wetland was technically and economically feasible for managing water quality of an intensive aquaculture system.     

A Routing and Scheduling System for Infectious Waste Collection

Most hospitals and clinics in Taiwan do not have on-site treatment facilities for their infectious waste and must rely on outside agencies for their collection and treatment. The problem of optimally routing and scheduling the collection of medical waste from a disperse group of facilities is recognized as a periodic vehicle routing problem. This study develops a computer system to solve the resulting optimization problem based on a two-phased approach proposed earlier. The first phase solves a standard vehicle routing problem to determine a set of individual routes for the collection vehicles. The second phase uses a mixed integer programming method to assign routes to particular days of the week. The computer system is user-friendly and consists of several Visual Basic programs while the geographical information system is incorporated to facilitate input and output interface and database management. An illustrative example for the infectious waste of 348 hospitals in the Tainan City area demonstrates the effectiveness of the system.     

Effects of various ions on the dechlorination kinetics of hexachlorobenzene by nanoscale zero-valent iron

The effect of several anions and cations normally co-present in soil and groundwater contamination sites on the degradation kinetics and removal efficiency of hexachlorobenzene (HCB) by nanoscale zero-valent iron (NZVI) particles was examined. The degradation kinetics was not influenced by the HCO(3)(-), Mg(2+), and Na(+) ions. It was enhanced in the presence of the Cl(-) and SO(4)(2-) ions due to their corrosion promotion. The NO(3)(-) competes with HCB so it inhibits the degradation reaction. The Fe(2+) ions would inhibit the degradation reaction due to passivation layer formed, while it was enhanced in the presence of Cu(2+) ions resulted from the reduced form of copper on NZVI surfaces. These observations lead to a better understanding of HCB dechlorination with NZVI particles and can facilitate the remediation design and prediction of treatment efficiency of HCB at remediation sites.     

Adsorption behavior of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) on boehmite

Understanding the interaction of perfluorochemicals, persistent pollutants with known human health effects, with mineral compounds in surface water and groundwater environments is essential to determining their fate and transport. Kinetic experiments showed that adsorption equilibrium can be achieved within 48 h and the boehmite (AlOOH) surface is receptive to perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) adsorption. The adsorption isotherms estimated the maximum adsorption capacities of PFOS and PFOA on boehmite as 0.877 μg m⁻² and 0.633 μg m⁻², respectively. Compared to the adsorption capacity on γ-alumina, the abundant hydroxyl groups on boehmite surfaces resulted in the 2-3 times higher adsorption of PFOS and PFOA. Increasing solution pH led to a moderate decrease in PFOS and PFOA adsorption, owing to an increase in ligand exchange reactions and the decrease of electrostatic interactions. The presence of NaCl and CaCl₂ in solution demonstrated negative effects for PFOS and PFOA adsorption on boehmite surfaces, with potential mechanisms being electrical double layer compression, competitive adsorption of chloride, and the Ca²⁺ bridging effect between perfluorochemicals.     

MODIFIED WATER QUANTITY RECEIVING MODEL FOR FLORIDA CONSERVATION AREAS1

ABSTRACT: The Conservation Areas in South Florida have been considered as one of the major water storage areas to provide a water supply for the Everglades National Park and Lower East Coast (LEC). Due to the increasing water demands of the area, additional backpumping of the surplus runoff from the LEC area into the Conservation Areas has been considered as one of several alternative plans. The Receiving Water Quantity (EPA, 1971) model has been adapted and modified to be applicable in the Conservation Areas to investigate the possible impact of additional inflow under various backpumping cases. The modification of the model included Manning's roughness coefficient, depth of flow, width of hypothetical channels through marsh areas, rainfall input, seepage rate, etc. The use of the Monte Carlo technique for area computations was found to be easy and time saving both in area and weighting rainfall input to each node. Comparison of results generated by this modified model with the recorded values in Conservation Areas 1 and 2A indicated that the model not only can be a very good evaluation tool to simulate the hydraulic regime of the Conservation Areas system but also a proper tool for investigating the impact of additional inflow resulting from the backpumping related to the water use planning and management.     

A TECHNIQUE USED TO DETERMINE RANDOM POINT POSITION1

ABSTRACT: The Monte Carlo method is a procedure which takes advantage of the high speed of electronic computer in solving complex problems in physical and mathematical fields. A rigid technique to determine whether a random point falls within an arbitrary-shaped boundary is not available. This study is to present a new technique which can be used to determine whether a random point falls within any shape of boundary, together with its range of application. A modified fixed random walk procedure is also developed to solve the problems of groundwater movement. A flowchart and computer program are also demonstrated. Comparisons of this newly developed method are made with other approximate solutions. The results indicates that the new technique is more applicable and powerful than other methods.