A design chart for estimation of horizontal displacement in municipal landfills

This paper describes the development of a design chart for the estimation of maximum horizontal displacement within a municipal landfill using the height and the side slope of the landfill. The design chart is based on the results of a finite element parametric study in which the behaviour of the municipal solid waste (MSW) was modeled using a non-linear elastic hyperbolic model. The model input parameters, i.e. non-linear stiffness, shear strength and unit weight of MSW, were obtained from laboratory testing data and an extensive stochastic numerical modelling exercise. Non-linear variations of unit weight as well as Young’s modulus of MSW with depth were incorporated in the finite element analyses. The validity of the design chart was assessed using field monitoring results from a large landfill located in Ontario, Canada.     

Biofiltration of airstreams contaminated with MTBE

The treatment of groundwater contaminated with low concentrations of methyl tertiary butyl ether (MTBE) is of nationwide concern. Many treatment techniques include removing MTBE vapors from groundwater, resulting in airstreams that require treatment. One method used for air‐phase MTBE treatment is biofiltration. In a biofilter, the vapors pass through a reactor that contains MTBE‐biodegrading organisms attached to a porous media. This article reports the results of a biofiltration study to treat air contaminated with MTBE at concentrations of 0.2 to 0.33 mg/l, concentrations frequently encountered in the field. The results indicate that MTBE removal at these low concentrations is not as efficient as removals seen at higher concentrations. Activated carbon was shown to be a superior biofiltration medium, compared with media that do not adsorb MTBE vapors. Activated carbon was especially helpful in treatment shock loads of MTBE. © 2002 Wiley Periodicals, Inc.     

Use of adjuvants to minimize leaching of herbicides in soil

Excessive leaching of herbicides affects their efficacy against target weeds and results in contamination of groundwater. Use of adjuvants that can weakly bind herbicides and in turn release them slowly is a valuable technique to prolong the efficacy of herbicides and to minimize their leaching into groundwater. Effects of activated charcoal, three humic substances (Enersol SP 85%, Enersol 12%, and Agroliz), or a synthetic polymer (Hydrosorb) on the leaching of bromacil, dicamba, and simazine were investigated in leaching columns using a Candler fine sand (Typic Quartzipsamment). The addition of adjuvants had no harmful effects on physical properties of the soil as evident from lack of its affects on water percolation. When no adjuvants were used, 69%, 37%, and 4% of applied dicamba, bromacil, and simazine, respectively, were leached in the first pore volume of leachate (⋍3.2 cm rainfall). With five pore volumes of leachate (⋍16 cm rainfall), bromacil and dicamba were leached completely and only 80% of simazine was leached. Using Enersol 12% adjuvant resulted in a 13%–18% reduction in leaching of dicamba and bromacil in five pore volumes of leachate. The leaching of simazine was significantly decreased when any of the five adjuvants mentioned above were used. However, the decrease in leaching was significantly greater when using Enersol SP 85% or Enersol 12% (24%–28%) than when using the other adjuvants (12%–16%).     

The optimal extinction of a renewable natural resource

This paper examines conditions for extinction when the net benefits from a renewable resource are a nonlinear function of the harvest rate. As in the linear case, extinction depends on the size of the interest rate relative to the growth potential of the species. Here, however, the size of the initial resource stock is also crucial. It is shown that extinction is optimal if the interest rate is greater than the growth potential of the species, but only for small initial stocks. Indeed, if the initial stock is sufficiently high, extinction need not be optimal even if the interest rate is infinite.     

A COMPUTERIZED DATA BASE FOR FLOOD PREDICTION MODELING1

ABSTRACT: A computerized geographic information system (GIS) was created in support of data requirements by a hydrologic model designed to predict the runoff hydrograph from ungaged basins. Some geomorphologic characteristics (i.e., channel lengths) were manually measured from topographic maps, while other parameters such as drainage area and number of channels of a specified order, land use, and soil type were digitized and manipulated through use of the GIS. The model required the generation of an integrated Soil Conservation Service (SCS) curve number for the entire basin. To this end, soil associations and land use (generated from analysis of Landsat satellite data) were merged in the GIS to acquire a map representing SCS runoff curve numbers. The volume of runoff obtained from the Watershed Hydrology Simulation (WAHS) Model using this map was compared to the volume computed by hydrograph separation and found to be accurate within 19 percent error. To quantify the effect of changing land use on basin hydrology, the GIS was used to vary percentages from the drainage area from forest to bare soil. By changing the basin runoff curve numbers, significant changes in peak discharge were noted; however, the time to peak discharge remained essentially independent of change in area of land use. The GIS capability eliminated many of the more traditional manual phases of data input arid manipulation, thereby allowing researchers to concentrate on the development and calibration of the model and the interpretation of presumably more accurate results.     

Genotoxic fungicide methyl thiophanate as an oxidative stressor inducing 8-oxo-7,8-dihydro-2′ -deoxyguanosine adducts in DNA and mutagenesis

Dimethyl 4,4′ -(O-phenylene)bis(3-thioallophanate), commonly known as methyl thiophanate (MT), is a systemic fungicide and suspected carcinogen to humans. In this study, the oxidative potential of this category-III acute toxicant has been ascertained based on its capacity of inducing reactive oxygen species (ROS) and promutagenic 8-oxo-7,8-dihydro-2′ -deoxyguanosine (8-oxodG) adducts in DNA. The discernible MT dose-dependent reduction in fluorescence intensity of a cationic dye rhodamine (Rh-123) in human lymphocytes and increased fluorescence intensity of 2′,7′-Dichlorodihydro fluorescein diacetate (DCFH-DA) treated cells signifies decreased mitochondrial membrane potential (Δ Ψ m) due to intracellular ROS generation. The ³²P-post-labeling assay demonstrated the MT-induced 8-oxodG adduct formation in calf thymus DNA. Thus, it is concluded that MT, as a potent oxidative stressor, produces ROS leading to mitochondrial dysfunction, oxidative DNA damage and mutagenesis.     

Effect of addition of pond ash and fly ash on properties of ash-clay burnt bricks.

Two industrial solid waste products generated by Indian coal-fired power plants, namely pond ash and fly ash, were used in combination with local clay to develop building bricks. The clay were mixed with the two different ashes in the range 10 to 90 wt.%, hydraulically pressed and fired at 1000 degrees C. The fired products were characterized for various quality properties required for building bricks. The properties of the optimal compositions were compared with conventional red clay bricks including the developed microstructures and the comparative study generally showed that te ash-clay bricks were of superior quality to the conventional products.     

Tree seedling establishment in dry tropics: an urgent need of interaction studies

The current anthropogenic activities and climate change are increasingly becoming a growing global concern for dry tropical forests. Worldwide, these ecologically important forests have degraded considerably since the past few decades due to such factors. These factors have harmful consequences on the vegetation structure and diversity especially tree seedlings, which may further aggravate climate change. Generally, the vegetation recovery is very slow and unpredictable in the dry tropics due to complex interaction among tree seedling, site (particularly, soil) and climatic conditions. We inculcated that a better understanding of the behavior of individuals of different tree species at seedling stage in dry forests is of immense importance. It is increasingly being recognized for explaining and managing the future composition of plant communities under changing environmental conditions. In this regard, the multi-factorial interaction studies under various resource–disturbance combinations are needed in dry tropical ecosystems to understand the: (1) impact of relative variability in resources and disturbances on the responses of tree seedlings of native species and (2) how the later relates to distinct functional and life history traits of the individual tree species. Most importantly, such studies would improve our limited understanding of how variation (natural and man-made) in nutrient availability, under the influence of other local environmental factors (such as water, light, grass competition, herbivory, fire, allelopathy and enhanced CO₂ conditions), would affect the dynamics of dry tropical forest community. It may help in the proper management of these forests. Moreover, it may prove helpful in the current climate change scenario, as change in forest community dynamics may have consequences on soil C sequestration and CO₂ efflux at global scale.