The definition of contaminant source release is a necessary element of contaminant mass transport simulation in the saturated zone. At many sites the release history is unknown, and there has been a significant body of research to develop inverse models to define finite release histories. Instead of rigorously defining the source history, a mass balance-based approach is tested to explicitly account for uncertainty in rectangular pulse release variables. The approach has been incorporated into a spreadsheet model which uses a one-dimensional solution to the advection dispersion equation, which readily lends itself to Monte Carlo applications. After the model was tested with synthetic data sets, the model was calibrated and verified using a concentration data set collected at a Superfund site. Model calibration with synthetic and actual data resulted in a reasonable domain of source history parameters and the model provided reasonable results when the mass of contaminant in the aquifer was assumed to be random.
In this paper some of the practical issues involved in the development and application of an extraction-photodegradation remediation technology for polychlorinated biphenyl (PCB) impacted weathered soils are addressed. The extraction of PCBs from weathered soils was investigated using the conventional Soxhlet extraction and by shake extraction using different solvents. The shake extraction has the potential for up-scaling to a field technology. The photodegradation of the extracted PCBs was investigated under direct ultraviolet light at 254 nm wavelength as well as under photosensitized light at 350 nm. The production of biphenyl, a by-product of the dechlorination of PCBs was investigated and it was found to degrade in the same ultraviolet system.
Groundwater contaminated with the high explosive Demolition eXplosive, or hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) may also contain the nitroso-RDX metabolites hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX). Although adsorption to activated carbon effectively removes RDX from contaminated water, the treatability of the nitroso-RDX compounds by adsorption has not been previously reported. Single-component isotherms were completed and the Freundlich parameters (K and 1/n) were calculated for adsorption of these compounds to Calgon F400 from unbuffered high purity water under aerobic and anoxic (<1 mg/L dissolved oxygen) conditions. Under both conditions, MNX was the most adsorbable, followed by RDX, DNX, and TNX. The presence of dissolved oxygen slightly increased the Freundlich parameters for all compounds except TNX. Under aerobic conditions, Freundlich capacity parameters (K) ranged from 46.4 (mg/g)(L/mg)1/n for TNX to 164.2 (mg/g)(L/mg)1/n for MNX, while under anoxic conditions, K ranged from 47.1 (mg/g)(L/mg)1/n for TNX to 133.6 (mg/g)(L/mg)1/n for MNX. Additional testing showed that 7 days were sufficient for adsorption equilibration in most cases. Simplified granular activated carbon (GAC) column modeling demonstrated that the presence of these compounds in groundwater can reduce GAC service life.
Models describing adsorption equilibrium have not been derived for the sorption onto the biosorbents including both virgin and immobilized biomasses. Biosorption involves interaction of biopolymer-based surfaces with different types of pollutants which may be different for virgin and immobilized biosorbents. In the present study, 16 different isotherm models have been studied using equilibrium data obtained from biosorbents. Biosorbents, both virgin (prepared from two types of macrofungus biomass) and immobilized forms have been used. Results show that in general the accuracy of models to fit experimental data improves with the degree of freedom. Most widely used isotherm models, i.e., Langmuir and Freundlich, could be used to describe the sorption equilibrium of biosorptive processes for both virgin and immobilized biomasses. Comprehensive equilibrium analysis has assisted in understanding the mechanistic aspects associated with different types of sorbate-sorbent interactions.
Wind tunnel experiments were conducted to evaluate the effectiveness of two commercially available fixatives in controlling the mobility of soil particles on soil mounds when exposed to wind forces. The fixatives tested included two commercially available materials: (1) RoadMaster which consists of 38% calcium chloride solution and (2) DuraSoil which consists of a solution of alkanes and alkylated saturated compounds. Soil samples were placed in an open-loop low-speed wind tunnel and exposed to wind forces ranging from 10 to 30 mi per hour (mi/h). The amount of soil loss/displaced and particulate matter (PM10) generated were monitored in relation to soil moisture content and application rate of selected fixatives. The results showed that increase in soil moisture and amount of fixative used had a significant effect in controlling the particulate matter (PM10) concentrations and the amount of soil displaced by the wind forces. The calcium chloride solution was applied by spraying onto the soil samples. However, DuraSoil mixture was applied by pouring the fixative using pipettes due to its high viscosity.
A modified method was used to increase the adsorption of heavy metals from aqueous solutions by using sawdust. Sawdust was collected from waste timber industry and modified with different tartaric acid concentrations (0.1 to 1.5 M) at 90°C for 90 min. The performance of the modified sawdust and unmodified sawdust have also been studied. The batch removal of the selected heavy metals, Cu(II), Zn(II), and Cd(II), from aqueous solutions under different experimental conditions was carried out in this study. The adsorption capacities of tartaric acid modified sawdust (TMSD) and nonmodified sawdust (NESD) were compared. The effect of initial metal concentration, temperature, pH, time, and adsorbent dosage on the removal of the metallic species have been reported. Two different of kinetic models viz. Lagergren-first-order and pseudosecond-order equations, were used to investigate the adsorption mechanism. The batch sorption kinetics and the applicability of the Langmuir, Freundlich, and Dubinin-Radushkevich adsorption isotherms for the present system have been tested at 25±2°C. NESD and TMSD were found to remove heavy metals from aqueous solutions efficiently.
The Kaoping River Basin, located in southern Taiwan, flows through approximately 171 km and drains toward the South Taiwan Strait. It is the largest and the most intensively used river basin in Taiwan. However, due to the concentrated rainfall in the wet season, short rivers and rapid flows, poor flow conditions, uneven time distribution of flows, and rapid rise of flow peak cause the unevenly distributed water resource in this region. Based on the results from the water resource analysis and water demand evaluation, a shortage of water supply in the basin would occur in 5 years. Sustainable water resource management strategies have been proposed to effectively utilize the limited water resource in the basin. The proposed strategies include construction of water collection gallery system, installation of riverbank infiltration system, installation of groundwater recharge and extraction systems, recycling the effluent from the secondary wastewater-treatment plant, and replacement of old water supply pipes. These measures are more sustainable and more environmentally acceptable compared with other traditional construction measures (e.g., reservoir and long-distance water transportation conduit). Results and experience obtained from this study will be helpful in developing water resource management strategies for other similar river basins.
This study is performed to develop a comprehensive software package entitled “simulation of chemical industrial accident (SCIA).” The SCIA can be integrated with geographical information system (GIS) to predict and display the risk and consequence of chemical hazards from two categories of hazardous materials, namely toxic and flammable materials. This paper describes how the existing models are used for predicting accident scenarios and their impact to humans and the environment. The technique for assessing the consequences from chemical accidents is developed by integrating the models in the system with the help of the GIS tools. The software is coded in Visual Basic, and is compatible with Windows working environments. The validity of the software has been confirmed by comparing the results of several applications with other commercial software. The software is a user-friendly and effective tool for evaluating the consequences of major chemical accidents, process decision making for land-use planning namely locating suitable hazardous installations, hazardous waste disposal areas and emergency response plan.
Aluminum enters municipal solid waste (MSW) landfills from untreated raw curbside trash (MSW), industrial waste, and aluminum production wastes variously called dross, baghouse fines, salt cake, and other designations. Aluminum related reactions can arise and become problematic for landfill operations by generating undesirable heat, liquid leachate, and gases, such as hydrogen, hydrogen sulfide, carbon monoxide, and ammonia. Temperature excursions up to ∼150°C(300°F) and landfill gas pressures exceeding 210 kPa have been observed. Water from the MSW, precipitation, injection, and/or surface water management can result in sufficient water to trigger problematic aluminum related reactions. Another source of water in a MSW landfill is leachate recirculation, which is not recommended if substantial aluminum is present in the landfill mass because it can lead to a problematic aluminum related reaction. This paper examines the chemical reactions involving aluminum in landfills and the negative consequences of introducing aluminum into MSW landfills regardless of its origin. Proposals for mitigating aluminum reactions are also presented.
The hydration characteristics of C3 S were studied in the presence of chromium (III) for up to 7 days. Chromium was introduced by either direct incorporation (as Cr2 O3 ) during C3 S preparation or during the subsequent hydration with a chromium ( CrCl3 ) solution. Levels of Cr(III) used were 1 and 3% by wt. of C3 S . The chemically combined water content and free lime content were determined after 3 and 6 h and 1, 3, and 7 days of hydration. The results showed a retardation effect for the hydration of C3 S in the presence of Cr, especially during the first hours of hydration. This retardation effect was more evident in C3 S–Cr incorporated mixes than in C3 S mixes hydrated in Cr-containing solutions. X-ray diffraction examination was performed on selected samples. The immobilization percentage of Cr(III) by C3 S during hydration was determination by atomic absorption spectroscopy. A high degree of Cr immobilization (93.27–99.39%) was found after 7 days of hydration.
An extensive database of mechanical properties of municipal solid waste (MSW) is available as a result of significant advances made in the past few years in terms of understanding its mechanical behavior. It is, however, difficult to interpret and use this database in practice because of inherent heterogeneity of MSW and the variations in the sampling and testing procedures. The database also appears to be dominated by shear strength properties and contains limited information on elastic properties. As such, it is rather difficult to estimate the deformation within landfills and to quantify its effect on the performance and the integrity of leachate and gas collection systems installed within landfills. This paper presents results from an extensive on-going research program at the University of Saskatchewan to study the mechanical behavior of MSW. This research program includes laboratory and field testing of intact and recompacted MSW samples and numerical simulations incorporating stochastic modeling. A...
The effects of cocontaminants, such as extractable organics and transformer oil (TO) on the remediation of polychlorinated biphenyl (PCB) impacted soils by hydrogen peroxide (H2O2), have been investigated. Presence of transformer oil is found to adversely affect the PCB degradation. About 20 and 60% of Aroclor 1254 were remediated by 15 and 30% H2O2, respectively, in soils which did not contain TO. When TO was introduced, no Aroclor 1254 degradation was observed with 15% H2O2 and a limited amount of about 20% of Aroclor 1254 degraded with 30% H2O2 treatment. The impact of cocontaminants on major Aroclor 1254 congeners 101, 87, 110, 118, 105, and 138 were also found to be limited in the presence of TO.
The transition from an agricultural based society to an industrial and commercial based society resulted in urbanization in the case of Kaohsiung City. However, in accordance with development, the parks, the green spaces, the rivers, and other natural resources of urban areas should support the concept of biodiversity and promote the ideals of sustainable development, creating rich and exciting views within the city. The ecological corridors of urban areas should not only provide for the propagation of wild animals and organisms, it should also strike a balance in the ecosystem, improve the quality of life for the residents, and strive for the ideals of sustainable development. The study found that Kaohsiung City has its excellent conditions due to the fact that the opening of the harbor and the ecological corridor can be used to direct the wind and through natural convection, lower the city's temperature. Consequently, it will lower the usage of air condition and energy consumption, creating a green urban environment and building a sustainable city.
Computer waste has considerable reverse flow in terms of reuse and recycles. The reuse component is particularly significant for developing nations like India. The hierarchy of prevention, reuse, recycle/treatment, and disposal in a landfill is a universally accepted approach to waste management. This approach becomes complex to practice if due considerations are given to cost, health, environment issues, and socially perceived risk in decision making. Shifting from one stage of hierarchy to another becomes an involved decision requiring an integrated approach to visualize the tradeoffs between these factors. Also, to be able to reach the best possible configuration of such waste management systems, it is necessary to consider its reappearance in future years. The present study proposes a methodology for estimating the optimum reuse span for a waste and demonstrates the same by applying the same to a personal computer. The results of the example problem clearly demonstrate the variation in optimum reuse span for different objectives/priorities. The results can help the decision makers limit the reuse of waste categories beyond a certain age.
A system with a combination of upflow anaerobic sludge blanket (UASB) reactor and constructed wetlands (CWs) has not yet been applied to river water polluted by both sewage and swine wastewater. In this study, a pilot system with a UASB reactor combined with two CW reactors was used to evaluate the feasibility of treating wastewater samples (mixture of sewage and partially treated swine wastewater). To observe the influence of hydraulic retention time (HRT) on the removal efficiency of various pollutants in the wastewater in the UASB reactor, two phases of experiments with HRTs of 6 and 2 h were conducted. The overall system performances between the two phases of experiments did not show obvious differences. The UASB reactor responded well in removing most of the pollutants observed except for ammonia nitrogen (AN) and total phosphorus (TP). The average removal efficiency could reach the levels of 93, 91, 86, 89, and 78% for suspended solids, CODS, BODs, AN, and TP, respectively, with the UASB-CWs systems, which have potentials to be used to improve the water quality in river in practice.
Coprecipitation of arsenic by alum or iron salts produces a large quantity of arsenic-laden sludge (an average of 6.10 g As/dm3 of sludge on dry basis) in conventional arsenic removal plant (ARP). This toxic sludge, along with acclimated composite organic waste slurry containing a mixture of partially digested liquefied market waste, primary sludge of sewage treatment plant, and liquefied water hyacinth at 1–10% by volume of the total, was anaerobically digested for a period of 30–50 days. The maximum removal of arsenic was obtained as 99.69% at a digestion period of 50 days. The minimum biogas generation at 30 days digestion period was found to be 0.560 m3 (at standard temperature and pressure) per cubic meter of composite feed slurry at 10% of ARP sludge. The results show that presence of arsenic in adequately acclimated composite feed sludge does not significantly inhibit the anaerobic digestion process. It may thus be stated that anaerobic digestion of arsenic-laden composite organic waste sludge could be a viable option for the safe and cost-effective disposal of arsenic-laden sludge available from existing arsenic removal water plants in arsenic affected areas.
In the risk-based management approach, the risks associated with human health and the environment in a contaminated site are evaluated and corrective measures are undertaken to reduce the risk level to acceptable limits. In this study, a risk-based management model is developed and applied to a hypothetical aquifer system. The model couples the simulated contaminant transport in the aquifer and the health risk assessment procedure to predict human health risk level and later relate it to the total cost of a proposed groundwater contamination remedial action. Amongst a number of remedial alternatives considered, those consisting of different combinations of pump and treat remediation system are compared with the bioremediation strategy in the study. Later, the computed residual risk and the cost associated with the risk reduction are taken as parameters used for justification of a better remedial alternative. The results highlight the importance of applying an integrated approach for decision making which may include costs, risk levels, and the cost-effectiveness of the various available alternatives. Furthermore, the uncertainty in risk associated with these remedial alternatives for available aquifer parameters due to a given exposure is also studied applying fuzzy set theory. Amongst the various alternatives considered, the bioremediation method is found to be a better alternative even in cases where there is uncertainty in parameter estimation compared to other technologies used for cleanup of hazardous waste.
This research compares performances of an anaerobic two-phase reactor system and a conventional single-phase reactor system in treatment of a synthetic dye wastewater. The two-phase reactor setup used four anaerobic reactors based on upflow anaerobic sludge blanket technology as acid reactors and an expanded granular sludge bed (EGSB) reactor as a methane reactor. An anaerobic reactor based on EGSB technology constituted the single-phase reactor setup. The reactors were operated at different hydraulic retention times (HRTs). The acid reactors removed up to 67% of the influent chemical-oxygen demand (COD) and 77% of the influent dye or color. An average of 10–25% acidification was achieved, and acetic acid, propionic acid, and butyric acid were the major volatile fatty acids produced in the acid reactors. The organic loading or the influent dye concentration did not have any significant effect on acid production or its speciation. The two-phase system could be operated at a HRT as low as 7.5 h with at least 90 and 75% removal of COD and color, respectively. The single-phase system could remove only up to 50% of influent COD and color at a HRT of 9 h. The study, which spanned over a period of 450 days, concludes that a two-phase system produces a better quality of effluent in terms of color and COD than a single-phase anaerobic system when operated under similar conditions. However, the COD mass balance on the two-phase system showed a higher percent of unaccounted COD than the single-phase system.
The use of tire-derived steel, a by-product of tire recycling, for removal of H2S in landfill cover systems was examined through a laboratory study. Experiments under both static and dynamic conditions were conducted. Results demonstrated that tire-derived steel removed H2S to a greater extent relative to a control landfill cover material consisting of sandy soil. In batch experiments, over 98% H2S [550 parts per million (ppm) initial concentration] was removed in 2 min by 20 g of tire-derived steel, compared to only 50% H2S removal in 60 min by the same amount of soil. In column experiments using 100 ppm inlet H2S gas concentrations, after 24-h continuous operation, the outlet H2S concentration increased to over 90 ppm in the sandy soil columns, while it was less than 1 ppm in the tire-derived steel columns. The experimental results showed that the outlet H2S concentrations from the closed columns were higher than that from the open columns, indicating a potential role of oxygen in creating or regenerating reactive surfaces for H2S removal.
The WASP/EUTRO model was used to model a low dissolved oxygen (DO) stream in Taiwan as part of the water quality management effort to restore the stream. The low DO is the result of industrial wastewater discharges causing significant oxygen consumption due to carbonaceous and nitrogenous biochemical oxygen demand in the receiving water. The modeling effort was supported by a field monitoring program including two water quality surveys of the stream. The model calibrated with these two data sets, and also used unit response analysis to calculate the DO deficit contributed by individual loads. The calibrated model was used to evaluate wastewater management alternatives to restore the stream.
