Modelling the biochemical degradation of solid waste in landfills

This paper describes the concept of a generic spatially distributed numerical model that has been developed to contain and link sub-models of landfill processes in order to simulate solid waste degradation and gas generation in landfills. The model includes the simulation of the transport of leachate and gases, and the consolidation of the solid waste. The structure of the model consists of linked discrete constant volume elements. The paper outlines the theoretical background that provides the framework to contain the numerical procedures that make up the model. Details are also given of the approach to the modelling of the chemistry and microbiology of solid waste degradation.     

Landscape Character and Fish Assemblage Structure and Function in Western Lake Superior Streams: General Relationships and Identification of Thresholds

As part of a comparative watershed project investigating land-cover/land-use disturbance gradients for streams in the western Lake Superior Basin, we examined general relationships between landscape character and fish assemblage structure and function. We also examined the shape of those relationships to identify discontinuity thresholds where small changes in landscape character were associated with marked shifts in the fish assemblages. After completing a geographic analysis of second- and third-order watersheds in the western Lake Superior drainage, we randomly selected 48 streams along mature forest and watershed storage gradients in 2 hydrogeomorphic regions as our study sites. During the summers of 1997 and 1998, we used electrofishing to sample fish assemblages from each stream. Each of the landscape factors was significantly associated with fish assemblage structure and function based on analysis of covariance. Watershed storage was related to the greatest number of fish assemblage characteristics, but hydrogeopmorphic region and mature forest cover were strongly associated as well. The hydrogeomorphic region also mediated relationships between watershed character and fish assemblages. Discontinuity thresholds for our fish assemblages averaged 11% for watershed storage and 50% for watershed mature forest cover based on piecewise regression analysis. Although many of the landscape–fish relationships might have been manifest through effects on in-stream habitat, our results highlight the importance of management and land-use planning decisions at the watershed and landscape scales.Published online     

Nitrogen and phosphorus flux rates from sediment in the lower St. Johns River estuary

Internal cycling of nutrients from the sediment and water column can be an important contribution to the total nutrient load of an aquatic ecosystem. Our objective was to estimate the internal nutrient loading of the Lower St. Johns River (LSJR). Dissolved reactive phosphorus (DRP) and ammonium (NH(4)-N) flux from sediments were measured under aerobic and anaerobic water column conditions using intact cores, to estimate the overall contribution of the sediments to P and N loading to the LSJR. The DRP flux under aerobic water column conditions averaged 0.13 mg m(-2) d(-1), approximately 37 times lower than that under anaerobic conditions (4.77 mg m(-2) d(-1)). The average NH(4)-N released from the anaerobic cores (18.03 mg m(-2) d(-1)) was also significantly greater than in the aerobic cores for all sites and seasons, indicating the strong relationship between nutrient fluxes and oxygen availability in the water column. The mean annual internal DRP load was estimated to be 330 metric tons (Mg) yr(-1), 21% of the total P load to the river, while the mean annual internal load of NH(4)-N was determined to be 2066 Mg yr(-1), 28% of the total N load to the LSJR estuary. As water resource managers reduce external loading to the LSJR the frequency of anaerobic events should decline, thereby reducing nutrient fluxes from the sediment to the water column, reducing the internal loading of DRP and NH(4)-N. Results from this study demonstrate that the internal flux of nutrients from sediments may be a significant portion of the total load and should be accounted for in the total nutrient budget of the river for successful restoration.     

The regional nature of PM2.5 episodes in the upper Ohio River Valley

From October 1999 through September 2000, particulate matter (PM) with aerodynamic diameter > or =2.5 microm (PM2.5) mass and composition were measured at the National Energy Technology Laboratory Pittsburgh site, with a particle concentrator Brigham Young University-organic sampling system and a tapered element oscillating microbalance (TEOM) monitor. PM2.5 measurements had also been obtained with TEOM monitors located in the Pittsburgh, PA, area, and at sites in Ohio, including Steubenville, Columbus, and Athens. The PM data from all these sites were analyzed on high PM days; PM2.5 TEOM particulate mass at all sites was generally associated with transitions from locally high barometric pressure to lower pressure. Elevated concentrations occurred with transport of PM from outside the local region in advance of frontal passages as the local pressure decreased. During high-pressure periods, concentrations at the study sites were generally low throughout the study region. Further details related to this transport were obtained from surface weather maps and estimated back-trajectories using the hybrid single-particle Lagrangian integrated trajectory model associated with these time periods. These analyses indicated that transport of pollutants to the Pittsburgh site was generally from the west to the southwest. These results suggest that the Ohio River Valley and possible regions beyond act as a significant source of PM and its precursors in the Pittsburgh area and at the other regional sites included in this study.     

Persistent organic pollutants in the environment: chlordane residues in compost

The half-lives of some persistent organic pollutants (POPs) in environmental compartments such as soil and air can be as long as decades. In spite of the hydrophobicity of many POPs, the literature contains reports of their uptake by, and translocation through, a variety of plants. Both these observations prompt the investigation of whether a vegetation-based environmental compartment such as compost contains significant residues of POPs. Previous reports imply that residues of technical chlordane will be found in compost. Due to its physicochemical properties, technical chlordane provides insights into the fate of POPs in the environment, which are not accessible through determinations of other pollutants in this group. Accordingly, we undertook the first comprehensive examination of technical chlordane residues in a variety of composts, specifically, 13 commercial and 39 municipal compost products, to both characterize and quantify the magnitude of this point source of contamination. Using chiral gas chromatography interfaced to ion trap mass spectrometry, the concentration and the compositional and enantiomeric profiles of chlordane components were determined. Of the 13 commercial products, 9 contained detectable chlordane concentrations, ranging from 4.7 to 292 microg/kg (dry wt.), while all 39 municipal products contained chlordane residues ranging from 13.9 to 415 microg/kg (dry wt.). The residue concentrations and profiles suggest possible feedstock sources for the chlordane in the finished compost product. The data also support the conclusion that some composts contribute to anthropogenic cycling of POPs through the biosphere.     

The fate of hydrogen peroxide as an oxygen source for bioremediation activities within saturated aquifer systems

In situ bioremediation is an innovative technique for the remediation of contaminated aquifers that involves the use of microorganisms to remediate soils and groundwaters polluted by hazardous substances. During its application, this process may require the addition of nutrients and/or electron acceptors to stimulate appropriate biological activity. Hydrogen peroxide has been commonly used as an oxygen source because of the limited concentrations of oxygen that can be transferred into the groundwater using above-ground aeration followed by reinjection of the oxygenated groundwater into the aquifer or subsurface air sparging of the aquifer. Because of several potential interactions of H2O2 with various aquifer material constituents, its decomposition may be too rapid, making effective introduction of the H2O2 into targeted treatment zones extremely difficult and costly. Therefore, a bench-scale study was conducted to determine the fate of H2O2 within subsurface aquifer environments. The purpose of this investigation was to identify those aquifer constituents, both biotic and abiotic, that are most active in controlling the fate of H2O2. The decomposition rates of H2O2 were determined using both equilibrated water samples and soil slurries. Results showed H2O2 decomposition to be effected by several commonly found inorganic soil components; however, biologically mediated catalytic reactions were determined to be the most substantial.     

VARIABILITY IN ADJUSTMENT PREFERENCES TO GROUNDWATER DEPLETION IN THE AMERICAN HIGH PLAINS1

ABSTRACT: This paper explores the adjustments and institutions that residents of the American High Plains prefer in coping with the depletion of the High Plains (Ogallaia) aquifer. The authors identify 48 possible adjustments and report on public preferences for them as determined from a mail survey of 956 respondents in 14 counties. For purposes of analysis, the adjustments are categorized into five groups: user practices, management policies, financial incentives and disincentives, technological fixes, and other. Preferences were also determined among five levels of government to enforce each of the adjustments. Adjustments associated with user conservation practices were generally most preferred while financial incentives and disincentives were least favored. Local groundwater management agencies were the most favored level of institution to administer conservation adjustments followed by the state, county, and federal levels. The most preferred option for 20 adjustments was that no agency should be involved. Respondents in agriculturally related occupations showed less support for water conservation laws and gave greater acceptance to the continuance of existing methods. Irrigators viewed the increasing cost of lifting water as a more serious problem than the depletion of groundwater.     

FINANCING ABATEMENT OF MINE DRAINAGE POLLUTION: CASE STUDY APPALACHIA1

ABSTRACT A financing program for the prevention, control, and abatement of mine drainage pollution was developed using Appalachia as a case example. The financing program was selected by using three performance criteria in a screening process-applicability of financing program to pollution problem, feasibility of program to unit costs and capturing potential benefits, and feasibility of program to economic and legal consideration. Effluent charges with some modifications are suggested as the appropriate financing mechanism.