Selection, preparation, and disposal of sodium compounds for dry SOx scrubbers

A program has been initiated to assess an SO₂ removal method wherein dry powdered sodium compounds are injected into the gas stream ahead of the baghouse filter. The compounds are collected on the surface of the filter bags for reaction with the gaseous SO₂. Initial program efforts include a survey of suitable and available sodium compounds, methods of preparing the compounds for injection, and an invistigation of environmentally acceptable methods of disposal.     

National-scale estimation of changes in soil carbon stocks on agricultural lands

Average annual net change in soil carbon stocks under past and current management is needed as part of national reporting of greenhouse gas emissions and to evaluate the potential for soils as sinks to mitigate increasing atmospheric CO2. We estimated net soil C stock changes for US agricultural soils during the period from 1982 to 1997 using the IPCC (Intergovernmental Panel on Climate Change) method for greenhouse gas inventories. Land use data from the NRI (National Resources Inventory; USDA-NRCS) were used as input along with ancillary data sets on climate, soils, and agricultural management. Our results show that, overall, changes in land use and agricultural management have resulted in a net gain of 21.2 MMT C year(-1) in US agricultural soils during this period. Cropped lands account for 15.1 MMT C year(-1), while grazing land soil C increased 6.1 MMT C year(-1). The land use and management changes that have contributed the most to increasing soil C during this period are (1) adoption of conservation tillage practices on cropland, (2) enrollment of cropland in the Conservation Reserve Program, and (3) cropping intensification that has resulted in reduced use of bare fallow.     

Just-noticeable differences in atmospheric haze

This article examines the only available experimental data taken in the natural environment on the ability of an observer to perceive small, incremental changes in the colorfulness of objects seen through atmospheric haze and estimates an appropriate just-noticeable difference (JND) from these data. This experimentally determined threshold of perception is compared to changes in the deciview scale. Based on these experimental results, the deciview scale is found to not be uniform over a wide range of visibility conditions, as has been previously claimed. In addition, a 1-deciview change never produces a perceptible change in haze, as defined by a 95% probability of producing a measurable change in the colorfulness of an object seen through the haze.     

Land treatment and the toxicity response of soil contaminated with wood preserving waste

Soils contaminated with wood preserving wastes, including pentachlo-rophenol (PCP) and creosote, are treated at field-scale in an engineered prepared-bed system consisting of two one-acre land treatment units (LTUs). The concentration of selected indicator compounds of treatment performance included PCP, pyrene, and total carcinogenic polycyclic aromatic hydrocarbons (TCPAHs) was monitored in the soil by taking both composited soil samples at multiple points in time, and discrete soil samples at two points in time. The mean concentration of the indicator compounds and the 95-percent confidence interval (CI) of the composite and discrete samples agreed relatively well, and first-order degradation rate kinetics satisfactorily represented the mean chemical concentration loss of indicator compounds in the LTU. Toxicity of the soil, as measured by Microtox^TM assay of the soil extracts, indicated that toxicity reduction corresponded with indicator compound disappearance. No toxicity effects were observed with time in treated layers of soil (lifts) buried beneath highly contaminated lifts of newly applied soil. This indicated that vertical migration of soluble contaminants from such lifts had little effect on the microbial activity in the underlying treated soil.     

Combined steam distillation and electrochemical peroxidation (ECP) treatment of river sediment contaminated by PCBs

A combined treatment process utilizing steam distillation followed by electrochemical peroxidation (ECP) has been utilized to remove >90% of the polychlorinated biphenyls (PCBs) in St. Lawrence River sediment and destroy 95% of the PCBs recovered in the condensate. 2 l of condensate were collected by boiling 500 grams of sediment containing 4.3 mg PCBs. Most of the PCBs (82.3%) were recovered as a small volume (<1 ml) of yellow oil floating on the condensate and coating glassware surfaces. The aqueous phase PCBs (182 μg/l) were destroyed (95%) by three sequential ECP treatments at 16.8°C and pH 5, utilizing 1 ml of H₂O₂ (3%) and periodically reversed current (0.75–1.0 A @ 10 volts). Oxidation is primarily mediated by hydroxyl radicals produced by the reaction of hydrogen peroxide with electrochemically generated ferrous iron (Fenton's reagent). This work suggests steam extraction, in combination with advanced oxidation technologies, provides an effective treatment strategy for contaminated solids.