Partitioning gas tracer tests for measurement of water in municipal solid waste

A key component in the operation of almost all bioreactor landfills is the addition of water to maintain optimal moisture conditions. To determine how much water is needed and where to add it, in situ methods are required to measure water within solid waste. Existing technologies often result in measurements of unknown accuracy, because of the variability of solid waste materials and time-dependent changes in packing density, both of which influence most measurement methods. To overcome these problems, a new technology recently developed by hydrologists for measuring water in the vadose zone--the partitioning gas tracer test--was tested. In this technology, the transport behavior of two gas tracers within solid waste is used to measure the fraction of the void space filled with water. One tracer is conservative and does not react with solids or liquids, while a second tracer partitions into the water and is separated from the conservative tracer during transport. This technology was tested in four different solid waste packings and was capable of determining the volumetric water content to within 48% of actual values, with most measurement errors less than 15%. This technology and the factors that affect its applicability to landfills are discussed in this paper.     

Assessment of contaminant lability during phytoremediation of polycyclic aromatic hydrocarbon impacted soil

Polycyclic aromatic hydrocarbons (PAHs) are recalcitrant compounds, some of which are known carcinogens, often found in high residual soil concentrations at industrial sites. Recent research has confirmed that phytoremediation holds promise as a low-cost treatment method for PAH contaminated soil. In this study, the lability of soil bound PAHs in the rhizosphere was estimated using solid phase extraction resin. An extraction time of 14 days was determined to be appropriate for this study. Resin-extractable PAHs, which are assumed to be more bioavailable, decreased during plant treatments. Significant reductions in the labile concentrations of several PAH compounds occurred over 12 months of plant growth. The differences in concentration between the unplanted and the planted soil indicate that the presence of plant roots, in addition to the passage of time, contributes to reduction in the bioavailability of target PAHs.     

Characterization of metal adsorption kinetic properties in batch and fixed-bed reactors

Copper adsorption kinetic properties in batch and fixed-bed reactors were studied in this paper. The isothermal adsorption experiments showed that the copper adsorption capacity of a granular activated carbon (Filtrasorb 200) increased when ionic strength was higher. The presence of EDTA diminished the adsorption. An intraparticle diffusion model and a fixed-bed model were successfully used to describe the batch kinetic and fixed-bed operation behaviors. The kinetics became faster when the solution pH was not controlled, implying that the surface precipitation caused some metal uptake. The external mass transfer coefficient, the diffusivity and the dispersion coefficient were obtained from the modeling. It was found that both external mass transfer and dispersion coefficients increased when the flow rate was higher. Finally effects of kinetic parameters on simulation of fixed-bed operation were conducted.     

Mechanism of effective nocardioform foam control measures for non-selector activated sludge systems.

Solids retention time (SRT), biological scum trapping and recycle, and the dynamic equilibrium between Nocardioform populations in the foam and the mixed liquor are the controlling factors in activated sludge foaming events caused by Nocardioform bacteria. For the operating modes described in this paper, a cured mixed liquor foaming condition (filament counts of approximately 10(5) intersections/g volatile suspended solids) was only achieved when SRT control, selective wasting, and polymer addition were in effect. Solids retention time control, with the SRT remaining below 1.5 days, and selective wasting will cure a severely foaming mixed liquor, but effects will only be observed after 3 or 4 months after implementation. The combined wastage of Nocardioform bacteria from selective wasting and SRT control can ensure long-term foam control to the operation of a pure-oxygen activated sludge system with foam-trapping features. An SRT of 0.3 days will result in the complete washout of Nocardioform bacteria from the activated sludge system, which can then operate at an SRT of 3 days free of Nocardioform. Polymer addition to mixed liquor is only effective for foam control when a large portion of the system biomass exists as a heavy layer of foam above the mixed liquor.     

Geoengineering and sustainability

ABSTRACT

Geoengineering is regarded by advocates as a creative and responsible technological option in the face of a climate emergency. Critics often see it as a hubristic attempt to play God, with disastrous consequences for the planet and humanity. These antipodal perspectives are represented by the ideal types of Prometheans and Gaians. Prometheans and Gaians typically talk past each other. The geoengineering debate can be made more fruitful by well articulating their respective positions and subsequently situating them in the discourse of sustainability. A sustainability orientation does not answer the troubling question whether geoengineering should be developed and deployed. But it can foster a ‘fusion of horizons’ between Prometheans and Gaians, providing common ground in an otherwise polarized debate and making a more productive dialogue possible.     

Stratospheric ozone depletion, UV-B radiation and crop disease

Ultraviolet-B radiation (UV-B: 290-315 nm) is expected to increase as the result of stratospheric ozone depletion. Within the environmental range, UV-B effects on host plants appear to be largely a function of photomorphogenic responses, while effects on fungal pathogens may include both photomorphogenesis and damage. The effects of increased UV-B on plant-pathogen interactions has been studied in only a few pathosystems, and have used a wide range of techniques, making generalisations difficult. Increased UV-B after inoculation tends to reduce disease, perhaps due to direct damage to the pathogen, although responses vary markedly between and within pathogen species. Using Septoria tritici infection of wheat as a model system, it is suggested that even in a species that is inherently sensitive to UV-B, the effects of ozone depletion in the field are likely to be small compared with the effects of variation in UV-B due to season and varying cloud. Increased UV-B before inoculation causes a range of effects in different systems, but an increase in subsequent disease is a common response, perhaps due to changes in host surface properties or chemical composition. Although it seems unlikely that most crop diseases will be greatly affected by stratospheric ozone depletion within the limits currently expected, the lack of a detailed understanding of the mechanisms by which UV-B influences plant-pathogen interactions in most pathosystems is a significant limit to such predictions.     

Influence of pre-treatment step on PAHs analyses in contaminated soils

There is no specific standardization for the pre-treatment of a soil sample for PAHs analyses. The ISO/FDIS 14507 method for soil quality gives a guidance for sample pre-treatment before measurement of organic contaminants in soil. It refers to cryogenic crushing which is not so easy to carry out. So, analysts lead to develop in house methods which can be very different from a laboratory to another and can involve deviations in the pollution quantification. This study has explored different ways of drying, grinding and sieving in order to determine the influence of the soil sample handling on the measured pollutant concentration. It appears that the influence of pre-treatment depends on the soil nature and on the PAHs distribution. As a conclusion, it is advised "light" drying ways like air drying or drying at 40 degrees C in a drying oven instead of more "drastic" ways (freeze-drying, cryogenic crushing) which can induce some losses. Crushing and sieving are also recommended for more reproducible measures.     

Methylmercury, fish consumption, and the precautionary principle

This paper considers several broad issues in the context of probabilistic assessment of the benefits of curtailing mercury (Hg) emissions from U.S. coal-fired power plants, based on information developed from recent literature and epidemiology studies of health effects of methylmercury. Exposure of the U.S. population is considered on the national scale, in large part because of recent questions arising from survey and experimental data about the relative importance of local deposition of airborne Hg. Although epidemiological studies have provided useful information, safe levels of Hg exposure remain uncertain, in part because of other dietary considerations in the populations that were studied. For example, much of the seafood consumed in one of the major studies was also contaminated with polychlorinated biphenyls, as are fish taken from some U.S. fresh waters. The primary epidemiological approach involves cross-study comparisons in relation to mean exposures, rather than detailed critiques of individual effects reported in each study. U.S. exposures are seen to be well below the levels at which adverse health effects are reported. This analysis supports the conclusion that unilateral reduction of Hg emissions from U.S. coal-fired power plants alone is unlikely to realize significant public health benefits.     

Reducing bioassay variability by identifying sources of variation and controlling key parameters in assay protocol

Reducing bioassay variability by identifying sources of variation and controlling important parameters in assay protocol was demonstrated in this study. The variability of a bioassay based on a luminescent bacterium was examined as an example. This assay involved the growth of cells, storage at a low temperature, activation, and exposure to a test sample, and the assay response was bioluminescence inhibition. After determining that measurement error was small and negligible, the total assay variability was decomposed in an initial variance components study into between-batch, between-vial, and between-tube variations. Results indicated that between-vial variations accounted for the majority of the total observed variability and that reducing this type of variation would be beneficial. Five parameters in the assay protocol were determined as factors that potentially affected assay variability significantly. A split-plot design was employed to investigate the effects of these factors and some of their interactions on the assay response. One of the five factors, i.e., activation temperature, turned out to have a significant effect. The variance components study was repeated with better control of activation temperature as well as other parameters. Results indicated that the total variability of the bioassay was reduced by approximately 85%.