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PubMed1995

Technologies for in situ cleanup of contaminated sites.

Groundwater contamination by non-aqueous phase liquids (NAPLs) and denser than water non-aqueous phase liquids (DNAPLs) poses one of the greatest remedial challenges in the field of environmental engineering. Due to low water solubilities and aqueous diffusivities, conventional pump-and-treat technologies have a poor record of success in remediation of DNAPL contaminated aquifers. Better success has been found with the removal of volatile LNAPLs due to higher gaseous diffusivities, propensity for aerobic biodegradation, and ease of pumping and handling large quantities of gas. An evaluation of in situ cleanup technologies on the basis of their applicability to in situ treatment of NAPL contaminated aquifers is presented. Emphasis is placed on treatment of the separate phase occurring in the saturated zone. Soil washing, air sparging, biodegradation, electro-osmosis, enhanced steam extraction, stabilization/solidification, treatment walls, radio frequency heating, and containment systems and barriers are among the in situ technologies reviewed. In the context of the governing contaminant fate and transport processes, the relative merits of each technology are assessed on the basis of its theoretical background, field implementability, level of demonstration and performance, waste, technical and site applicability/limitations, commercial availability, and cost and residuals management.

Decontamination↗
PubMed1982

Training of trainers in the Caribbean Basin Water Management Project.

This article discusses the Caribbean Basin Water Management Project, a joint venture of 10 Caribbean countries, the Canadian International Development Agency (CIDA), the Government of the Netherlands, and PAHO. In 1977 an assessment of the project revealed that though training activities were carried out, most of them were designed for engineers and technicians-a small percentage of all employees-who did not pass on their knowledge to their coworkers. The training of trainers program was initiated to encourage improved communication among staff members. The fundamental precept of this program is that training should be a basic component of management activities. The article outlines the criteria for selecting participants for the training workshops, stressing that the prospective candidates should be in supervisory positions where training is part of their job. Instructors should also be carefully selected, and, as in the case of the participants, should have a long-term commitment to the water utility. At the end of the workshop series, the trainees should be able to make a task analysis, write and evaluate performance objectives, demonstrate communication techniques, use training aids, develop and implement an instructional sequence, and apply evaluation mechanisms. The article summarizes the benefits of the program, such as increased productivity of the supervisors, better communication between supervisors and the staff, and improved attitudes on the part of the staff toward their work.

International Cooperation↗
PubMed2006

Assessment of uncertainties in the modelling of CSOs.

Engineers generally use simulation tools such as SWMM, MOUSE, HYDROWORKS, etc. to simulate the operation of sewer systems. Equations used by these models to represent the hydraulics of sewer systems are well known as well as their performance. Thus assessment of the performance needs to suppose that the user is an expert who is able to describe each facility in the most accurate way according to the model. In Western Europe, important parts of sewer systems are old and combined structures. Such structures very often include very complicated special structures, especially within CSO facilities. Experience shows that the performance limits of the models do not rely on the accuracy of the equations, but on the ability of the modeller to describe these special structures properly. The objective of this research is to assess the part of errors and uncertainties which originate from modellers' inconsistencies in the description of special structures. Even if the results are obtained with specific software (CANOE), results can easily be generalised to other models, since the equations used (Barré de Saint Venant, etc.) are almost the same.

Computer Simulation↗
PubMed2006

Redesign of portable suction equipment cases: an engineering approach to a disinfection problem.

BACKGROUND: Patients with tracheostomies carry a case for suctioning supplies. A returned case cultured positive for Staphylococcus aureus even after it had been cleaned with a disinfectant. The purposes of this study were to determine (1) the source of the S aureus and (2) how to provide a microbiologically safe case for the next patient. METHODS: Reviews of patient and environmental cultures plus pulsed-field gel electrophoresis (PFGE) were used to determine the source of the S aureus. Repeated wiping with various detergents/disinfectants did not remove the S aureus from the case, which could not be immersed for cleaning because of a chipboard component. We designed a case made of denim with a washable synthetic fiber to provide shape. The new cases were purposefully contaminated and laundered and then cultured. RESULTS: PFGE indicated that the S aureus was from the patient who had most recently used the case. Contamination of the denim case with the original S aureus, followed by laundering, resulted in a case that was free of the S aureus. These results were repeated for other pathogens. CONCLUSION: Commercially available cases for suction equipment can become contaminated with pathogens from the user and may be difficult to disinfect. By making the case out of washable materials, less expensive cases, which could be readily disinfected, resulted.

Disinfection↗
PubMed2001

Numerical and experimental hydrodynamic studies of a lagoon pilot.

The determination of residence time is of major interest in terms of the characterisation, design and modelling of most environmental engineering processes, where a proper and homogeneous fluid distribution is often essential, and especially in the domain of wastewater or waste material treatment. In this paper, two different numerical methods for obtaining theoretical predictions of residence time distributions using the finite volume method are used. The first one consists of solving a transport equation of the local mean age of the fluid, which is the average time that a fluid particle takes to reach any point of the domain from a supply inlet. The result obtained is a spatial distribution of the local mean age of the fluid, which may be displayed as isocontours in the space domain considered. The second one consists of injecting a virtual particle stream (i.e. a fluid particle having the same density as the surrounding fluid, and treated numerically as a tracer) and measuring the time elapsed between the injection and the termination of the trajectory using a Lagrangian reference frame. The result obtained is expressed as an exit time distribution and may be displayed as a histogram. Finally, a comparison with measurements of mean residence times of tracers in a lagoon is made in order to establish the relevance of this method in concrete form. The prediction enables the instantaneous determination of the geometrical characteristics of the flow that contribute actually to the residence time dispersion. Its appropriate use prior to the design of water treatment and waste material treatment installations should contribute to prevent undesirable flow patterns such as short-circuiting and dead spaces.

Models, Theoretical↗
PubMed1996

Managing electromagnetic fields from residential electrode grounding systems: a predecision analysis.

Several epidemiological studies have linked exposure to electromagnetic fields (EMFs) with health effects, including leukemia and brain cancer, but the research is still inconclusive. In particular, no clear causal mechanism has been identified by which EMFs may promote cancers. Nevertheless, the concerns raised by the positive epidemiological studies have led to increasing efforts to reduce EMFs from a number of sources. One source of EMFs are home grounding systems that are connected through water pipes in homes to water mains. This paper analyzes whether home owners who are concerned about electromagnetic fields exposure from home grounding systems should take any action to reduce fields. Assuming that the grounding system produces elevated magnetic fields (e.g., 2-3 mG or higher), this study investigates several readily available alternatives and evaluates them with respect to five criteria: risk reduction, cost, fire risk increase, worker risk, and electrical shock risk. Because of the lack of conclusive evidence about an EMF-cancer relationship, this study uses a parameterized approach that makes conditional estimates of health risk depending on future research outcomes and on the nature of the EMF/health effects relationship. This type of analysis, which is called predecision analysis because of its preliminary nature, is therefore highly dependent on a set of assumptions. Nevertheless, this predecision analysis had some fairly clear results. First, waiting for more research or taking a fairly inexpensive corrective action (insulating the water pipe to reduce ground current flow) seem to be the main contenders for the best decision for many different assumptions and parameters. Second, the choice between these two actions is very sensitive to variations in assumptions and parameters. Homeowners who accept the base-case assumptions and parameters of this study should prefer to wait. If any of the base-case parameters are changed to more pessimistic estimates or if psychological concerns (like worry and regret) are considered, then the best action is to insulate the pipe to reduce the current flow through the water pipes.

Construction Materials↗
PubMed1986

Patterns of mortality among plumbers and pipefitters.

A proportionate mortality ratio (PMR) study was undertaken of 7,121 members and retirees of the United Association of Plumbers and Pipefitters in California who died in 1960-79. The PMR for all malignant neoplasms was 1.24, with a major contribution from lung cancers (PMR = 1.41). Lung cancer PMRs were consistently elevated, through the 20-year study period, across the pipe trades and within different birth cohorts. Sixteen mesothelioma deaths occurred, suggesting asbestos as a risk factor. PMRs for malignancies of the stomach, kidney, brain, and lymphopoietic system were also elevated, especially among plumbers. Chronic rheumatic heart disease, emphysema, liver cirrhosis, and all external causes of death were the major non-cancer causes with significantly elevated PMRs. There were significant deficits in diabetes mellitus, all pneumonia, chronic nephritis, and vascular lesions of the central nervous system (CNS). PMRs for successive birth cohorts among all study subjects revealed decreasing emphysema risk, suggesting previous reduction of a risk factor for this disease. Among plumbers, PMRs for death due to several non-respiratory malignancies showed an increasing trend with recency of birth cohort.

Adult↗
PubMed1988

Screening for occupational disease among workers in a high-risk trade: examination of cost, yield, and potential for increased efficiency.

We evaluated the cost and yield of a general health surveillance program emphasizing the identification of occupationally related diseases among workers in a high-risk trade. Of approximately 4,000 eligible members of two local plumbers and pipefitters unions, 639 were screened in this program. Screening tests indicated either by specific occupational exposures (eg, chest X-ray, spirometry, and audiometry) or general clinical risk factors (urine analysis for those with a positive urine dipstick, and stool heme occult testing for those over 45 years of age) proved to be far less costly for each positive finding than those procedures (physical examination, complete blood count, and blood chemistry panel) that were not specifically indicated. A discriminant analysis revealed predictor variables (age, years in the trade, and presence of respiratory symptoms) that, in subsequent screening efforts, could be used in the unscreened population either to identify individuals who are more likely to have any positive test result or to "tailor" the content of the initial screening program for a single individual. Increasing the yield and decreasing the direct costs of screening activities may make programs like these more affordable. In addition, this program assisted workers in filing for compensation and thus served to promote the appropriate transfer of cost for the identification and management of occupational diseases from traditional forms of payment to workers' compensation insurance programs.

Adolescent↗
PubMed2002

Study of high- and low-current-configuration homes from the 1988 Denver Childhood Cancer Study.

An epidemiological study conducted by Savitz et al. reported that residential wire codes were more strongly associated with childhood cancer than were measured magnetic fields, a peculiar result because wire codes were originally developed to be a surrogate for residential magnetic fields. The primary purpose of the study reported here, known as the Back to Denver (BTD) study, was to obtain data to help in the interpretation of the original results of Savitz et al. The BTD study included 81 homes that had been occupied by case and control subjects of Savitz et al., stratified by wire code as follows: 18 high current configuration (HCC) case homes; 20 HCC control homes; 20 low current configuration (LCC) case homes; and 23 LCC control homes. Analysis of new data acquired in these homes led to the following previously unpublished conclusions. The home-averaged (i.e., mean of fields measured in subjects' bedrooms, family/living rooms, and rooms where meals normally eaten) spot 60 Hz, 180 Hz, and harmonic (i.e., 60-420 Hz) magnetic fields were associated with wire codes. The 180 Hz and harmonic components, but not the 60 Hz component, were associated with case/control status. Measured static magnetic fields were only weakly correlated (rapproximately 0.2) between rooms in homes. The BTD data provide little support for, but are too sparse to definitively test, the 1995 resonance hypothesis proposed by Bowman et al. Case and control homes had similar concentrations of copper in their tap water. Copper concentration was not associated with wire codes nor with the level of electric current carried by a home's water pipe. These results of the BTD study suggest that future case/control studies investigating power frequency magnetic fields might wish to include measurements of 180 Hz or harmonic magnetic fields in order to examine their associations (if any) with disease status.

Case-Control Studies↗
PubMed2002

Contact voltage measured in residences: implications to the association between magnetic fields and childhood leukemia.

We measured magnetic fields and two sources of contact current in 36 homes in Pittsfield, MA. The first source, V(P-W), is the voltage due to current in the grounding wire, which extends from the service panel neutral to the water service line. This voltage can cause contact current to flow upon simultaneous contact with a metallic part of the water system, such as the faucet, and the frame of an appliance, which is connected to the panel neutral through the equipment-grounding conductor. The second is V(W-E), the voltage between the water pipe and earth, attributable to ground currents in the water system and magnetic induction from nearby power lines. In homes with conductive water systems and drains, V(W-E) can produce a voltage between the faucet and drain, which may produce contact current into an individual contacting the faucet while immersed in a bathtub. V(P-W) was not strongly correlated to the magnetic field (both log transformed) (r = 0.28; P < 0.1). On the other hand, V(W-E) was correlated to the residential magnetic field (both log transformed) (r = 0.54; P < 0.001), with the highest voltages occurring in homes near high voltage transmission lines, most likely due to magnetic induction on the grounding system. This correlation, combined with both frequent exposure opportunity for bathing children and substantial dose to bone marrow resulting from contact, lead us to suggest that contact current due to V(W-E) could explain the association between high residential magnetic fields and childhood leukemia.

Child↗
PubMed1995

Childhood cancer in relation to indicators of magnetic fields from ground current sources.

This study examines childhood cancer risk in relation to certain factors likely to indicate magnetic field exposure from ground currents in the home. Substantial ground currents are most often found in homes having conductive plumbing, in which an uninterrupted metallic path in the water pipes and water main connects the grounding systems of neighboring houses. Information on plumbing conductivity was obtained from water suppliers for the homes of 347 cases and 277 controls identified in an earlier study of magnetic field exposure and childhood cancer in the Denver area. An increased cancer risk was observed for children in homes with conductive plumbing: The matched odds ratio was 1.72 (1.03-2.88) and increased to 3.00 (1.33-6.76) when analysis was limited to cases and controls who were residentially stable from the reference date to the study date. A measurement metric likely to indicate active ground currents (measurements having above-median intensity and a nonvertical orientation of < 55 degrees from the horizontal) was identified. In contrast to measured field intensity alone, for which only modest associations with cancer have been reported, this metric shows a high and significant cancer risk [matched O.R. = 4.0 (1.6-10.0)] consistent over a range of intensity and angle cutpoints. Such elevated nonvertical fields were also associated with cancer in an independent data set, which was gathered to study adult nonlymphocytic leukemia in the Seattle area. The associations of cancer with conductive plumbing and with this exposure metric both suggest that cancer risk is increased among persons with elevated magnetic field exposure from residential ground currents.

Adolescent↗
PubMed2002

Hybrid neural network modeling of a full-scale industrial wastewater treatment process.

In recent years, hybrid neural network approaches, which combine mechanistic and neural network models, have received considerable attention. These approaches are potentially very efficient for obtaining more accurate predictions of process dynamics by combining mechanistic and neural network models in such a way that the neural network model properly accounts for unknown and nonlinear parts of the mechanistic model. In this work, a full-scale coke-plant wastewater treatment process was chosen as a model system. Initially, a process data analysis was performed on the actual operational data by using principal component analysis. Next, a simplified mechanistic model and a neural network model were developed based on the specific process knowledge and the operational data of the coke-plant wastewater treatment process, respectively. Finally, the neural network was incorporated into the mechanistic model in both parallel and serial configurations. Simulation results showed that the parallel hybrid modeling approach achieved much more accurate predictions with good extrapolation properties as compared with the other modeling approaches even in the case of process upset caused by, for example, shock loading of toxic compounds. These results indicate that the parallel hybrid neural modeling approach is a useful tool for accurate and cost-effective modeling of biochemical processes, in the absence of other reasonably accurate process models.

Biodegradation, Environmental↗
PubMed2004

Treatment of MEK and toluene mixtures in biofilters: effect of operating strategy an performance during transient loading.

In recent years, biofiltration has been increasingly applied as an air pollution control technology to minimize or eliminate emissions of volatile organic compounds from industrial sources and environmental remediation activities. Although the ability of this technology to maintain high removal efficiency during relatively steady loading conditions has been well established for many waste streams, relatively little research has focused on development of operating strategies that could improve treatment performance during transient loading conditions typical of industrial operations. In the research described herein, two operating strategies were evaluated over a period of 295 days in biofilters treating a model waste gas stream containing a two-component mixture of methyl ethyl ketone (MEK) and toluene. One biofilter was operated as a sequencing batch biofilter (SBB), and the other was operated as a conventional continuous-flow biofilter (CFB). During "normal" steady loading conditions, the model waste stream contained MEK concentrations ranging from 80 to 89 ppmv and toluene concentrations ranging from 28 to 30 ppmv. Both biofilter operating strategies resulted in stable long-term performance with greater than 99% contaminant removal during these normal loading conditions. On a regular basis, the influent MEK and toluene concentrations were temporarily increased to five times the normal influent concentration for the duration of 1 h to test performance during transient "shock loading" conditions. Biofilter performance during the model shock loading conditions demonstrate that SBB operating strategies can result in superior treatment in two important areas: (1) overall mass of contaminants removed and (2) minimum instantaneous removal efficiency.

Air Pollutants↗
PubMed1977

Effects of quantitative shock loadings on the constant recycle sludge concentration activated-sludge process.

The reliability of the process of Ramanathau and Gandy (Biotechnical Bioeng., 13, 125 (1971) for the completely mixed activated-sludge process holding the recycle cell concentration, Xr, as a system constant with respect to step changes in hydraluic retention time was investigated. The experiments were run at initial dilution rates of 1/8, 1/6, 1/4, and 1/2 hr-1 treating a soft drink bottling wastewater. The influent substrate concentration was maintained at 1000 mg/liter chemical oxygen demand and the hydraulic recycle ratio at 0.3. The recycle sludge concentration was maintained at about 7000 mg/liter. It was found that the system could accomodate hydraulic shock loads up to 200% positive changes and down to 50% negative changes without disruption of the effluent quality. Shorter retention time of the range studied, from 2 to 8 hr, has the advantage of shorter response time with respect to the response of the concentration of biological solids in the reactor.

Biodegradation, Environmental↗
PubMed1977

Biodegradability and tissue reaction of random copolymers of L-leucine, L-aspartic acid, and L-aspartic acid esters.

A series of copoly(alpha-amino acids) with varying percentages of hydrophilic (L-aspartic acid) and hydrophobic monomers (L-leucine, beta-methyl-L-aspartate, and beta-benzyl-L-aspartate) were implanted subcutaneously in rats and the macroscopic degradation behavior was studied. Three groups of materials (A,B,C) with different ranges of hydrophilicity were distinguished: A) hydrophobic materials showed no degradation after 12 weeks; B) more hydrophilic materials revealed a gradual reduction in size of the samples, but were still present after 12 weeks; and C) hydrophilic copolymers disappeared within 24 hr. The tissue reactions caused by the materials of group A resembled that of silicone rubber, whereas those of group B showed a more cellular reaction.

Animals↗