The behaviour of ashes and heavy metals during the co-combustion of sewage sludges in a fluidised bed

Co-combustion tests of dry sewage sludges with coal were performed in a pilot bubbling FBC aiming at the characterization of ashes and determining the behaviour of heavy metals in the process. The tests showed compliance with the regulatory levels as far as heavy metal emissions were concerned. The bottom ashes, which accounted for about 70% of the total ash production, were obtained in a granular form, with diameters ranging from 0.5 to 4 mm. The heavy metals were distributed in ashes obtained from different locations of the installation and their concentrations were found to vary depending on the location of capture. The increase in heavy metals content in bottom ashes was not found to lead to higher leachability and ecotoxicity compared to sewage sludges, suggesting that there could be opportunities for their further use. Mercury suffered vaporisation inside the reactor, thus leaving bottom ashes free of contamination by it. However, there was observed a strong retention of mercury in cyclone ashes due to the presence of unburned carbon which probably acted as an adsorbent. The effluent mercury was also found to be mostly associated with the particulate fraction, being less than 20% emitted in gaseous forms. The results suggested that the combustion of the sewage sludge could successfully be carried out and the amount of unburned carbon leaving the combustor but captured in cyclone was large enough to ensure substantial retention of mercury at low temperatures, hence could contribute to an improvement of the mercury release which still remains an issue of great concern to resolve during combustion of waste materials.     

Mobility control: How injected surfactants and biostimulants may be forced into low‐permeability units

Recovering dense nonaqueous‐phase liquid (DNAPL) remains one of the most difficult problems facing the remediation industry. Still, the most common method of recovering DNAPL is to physically remove the contaminants using common technologies such as total fluids recovery pumps, vacuum systems, and “pump‐and‐treat.” Increased DNAPL removal can be attained using surfactants to mobilize and/or solubilize the pollutants. However, very little is understood of the methods developed by petroleum engineers beginning in the 1960s to overcome by‐passed, low‐permeability zones in heterogeneous oil reservoirs. By injecting or causing the formation of viscous fluids in the subsurface, petroleum engineers caused increased in‐situ pressures that forced fluid flow into low permeability units as well as the higher permeability thief zones. Polymer flooding involves injecting a viscous aqueous polymer solution into the contaminated aquifer. Foam flooding involves injecting surfactant to decontaminate the high‐permeability zones and then periodic pulses of air to cause a temporary viscous foam to form in the high‐permeable zones after all DNAPL is removed. Later surfactant pulses are directed by the foam into unswept low‐permeable units. These methods have been applied to DNAPL removal using surfactants but they can also be applied to the injection of bio‐amendments into low‐permeability zones still requiring continued remediation. Here we discuss the principles of mobility control as practiced in an alluvial aquifer contaminated with chlorinated solvent and coal tar DNAPLs as well as some field results. © 2003 Wiley Periodicals, Inc.     

Structure-biodegradation relationships of polymeric materials. 1. Effect of degree of oxidation on biodegradability of carbohydrate polymers

The biodegradability of oxidized starch and inulin has been studied in relation to the degree of periodate oxidation to dialdehyde derivatives, by measuring oxygen consumption and mineralization to carbon dioxide. A higher degree of oxidation of dialdehyde starch and dialdchyde inulin results in a lower rate at which the polymers are biodegraded. It is demonstrated that the biodegradation rate of dialdehyde inulin derivatives decreases more than that of equivalent starch derivatives. The differences in biodegradation behavior between dialdehyde starch and dialdehyde inulin, resulting from comparable modifications, are discussed in terms of conformational structure.     

Monitoring nitrate leaching from submerged drains

Monitoring nitrate N (NO3-N) leaching is important in order to judge the effect that agricultural practices have on the quality of ground water and surface water. Measuring drain discharge rates and NO3-N concentrations circumvents the problem of spatial variability encountered by other methods used to quantify NO3-N leaching in the field. A new flow-proportional drainage water sampling method for submerged drains has been developed to monitor NO3-N leaching. Both low and high discharge rates can be measured accurately, and are automatically compensated for fluctuations in ditch-water levels. The total amount of NO3-N leached was 10.6 kg N ha(-1) for a tile-drained silt-loam soil during the 114-d monitoring period. The NO3-N concentrations fluctuated between 5 mg L(-1) at deep ground water levels and 15 mg L(-1) at shallow levels, due to variations in water flow. A flow-proportional drainage water sampling method is required to measure NO3-N leaching accurately under these conditions. Errors of up to 43% may occur when NO3-N concentrations in the drainage water are only measured at intervals of 30 d and when the precipitation excess is used to estimate cumulative NO3-N leaching. Measurements of NO3-N concentrations in ground water cannot be used to accurately estimate NO3-N leaching in drained soils.     

Alfalfa rapidly remediates excess inorganic nitrogen at a fertilizer spill site

By 19%, standard remediation techniques had significantly reduced the concentration of nitrate nitrogen (NO3- -N) in local ground water at the site of a 1989 anhydrous ammonia spill, but NO3- -N concentrations in portions of the site still exceeded the public drinking water standard. Our objective was to determine whether local soil and ground water quality could be improved with alfalfa (Medicago sativa L.). A 3-yr study was conducted in replicated plots (24 by 30 m) located hydrologically upgradient of the ground water under the spill site. Three alfalfa entries ['Agate', Ineffective Agate (a non-N2-fixing elite germplasm similar to Agate), and MWNC-4 (an experimental germplasm)] were seeded in the spring of 1996. Corn (Zea mays L.) or wheat (Triticum aestivum L.) was seeded adjacent to the alfalfa each year. Crops were irrigated with N-containing ground water to meet water demand. During the 3-yr period, about 540 kg of inorganic N was removed from the aquifer through irrigation of 4.9 million L water. Cumulative N removal from the site over 3 yr was 972 kg N ha(-1) in Ineffective Agate alfalfa hay, compared with 287 kg N ha(-1) for the annual cereal grain. Soil solution NO3- concentrations were reduced to low and stable levels by alfalfa, but were more variable under the annual crops. Ground water quality improved, as evidenced by irrigation water N concentration. We do not know how much N was removed by the N2-fixing alfalfas, but it appears that either fixing or non-N2-fixing alfalfa will effectively remove inorganic N from N-affected sites.     

Transforming open mining pits into fish farms: Moving towards sustainability

The legacy of mining activities has typically been land ‘returned to wildlife’, or, at some sites, degraded to such an extent that it is unsuitable for any alternate use. Progress towards sustainability is made when value is added in terms of the ecological, social and economic well‐being of the community. In keeping with the principles of sustainable development, the innovative use of flooded open pits and tailings impoundments as commercial, recreational or ornamental fish farms should be considered in some locations, as it could make a significant contribution to the social equity, economic vitality and environmental integrity of mining communities. This article highlights the growing significance of aquaculture and explores the benefits and barriers to transforming flooded pits and impoundments into aquaculture operations. Among other benefits, aquaculture may provide a much‐needed source of revenue, employment and, in some cases, food to communities impacted by mine closure. Further, aquaculture in a controlled closed environment may be more acceptable to critics of fish farming who are concerned about fish escapes and viral transmissions to wild populations. Despite the potential benefits, aquaculture in flooded pits and impoundments is not without its complications — it requires a site‐specific design approach that must consider issues ranging from metals uptake by fish, to the long‐term viability of the aquatic system as fish habitat, to the overall contribution of aquaculture to sustainability.     

RELATION OF NITRATE CONCENTRATIONS TO BASEFLOW IN THE RACCOON RIVER,IOWA1

ABSTRACT: Excessive nitrate‐nitrogen (nitrate) export from the Raccoon River in west central Iowa is an environmental concern to downstream receptors. The 1972 to 2000 record of daily streamflow and the results from 981 nitrate measurements were examined to describe the relation of nitrate to streamflow in the Raccoon River. No long term trends in streamflow and nitrate concentrations were noted in the 28‐year record. Strong seasonal patterns were evident in nitrate concentrations, with higher concentrations occurring in spring and fall. Nitrate concentrations were linearly related to streamflow at daily, monthly, seasonal, and annual time scales. At all time scales evaluated, the relation was improved when baseflow was used as the discharge variable instead of total streamflow. Nitrate concentrations were found to be highly stratified according to flow, but there was little relation of nitrate to streamflow within each flow range. Simple linear regression models developed to predict monthly mean nitrate concentrations explained as much as 76 percent of the variability in the monthly nitrate concentration data for 2001. Extrapolation of current nitrate baseflow relations to historical conditions in the Raccoon River revealed that increasing baseflow over the 20th century could account for a measurable increase in nitrate concentrations.     

Reducing the Effects of Dredged Material Levees on Coastal Marsh Function: Sediment Deposition and Nekton Utilization

Dredged material levees in coastal Louisiana are normally associated with pipeline canals or, more frequently, canals dredged through the wetlands to allow access to drilling locations for mineral extraction. The hydrologic impact on marshes behind the levee is of concern to coastal resource managers because of the potential impact on sediment transport and deposition, and the effect on estuarine organism access to valuable nursery habitat. This study examined the effects of gaps in dredged material levees, compared to continuous levees and natural channel banks, on these two aspects of marsh function. Field studies for sediment deposition were conducted biweekly for a year, and nekton samples were collected in spring and fall. Variation in nekton density among study arears and landscape types was great in part because of the inherent sampling gear issues and in part because of differences in characteristics among areas. Nekton densities were generally greater in natural compared to leveed and gapped landscapes. Differences in landscape type did not explain patterns in sediment deposition. The gaps examined appear to be too restrictive of marsh flooding to provide efficient movements of floodwaters onto the marsh during moderate flooding events. The “trapping” effect of the levees increases sediment deposition during extreme events. Gapping material levees may be an effective method of partially restoring upper marsh connection to nekton, but this method may work best in lower elevation marshes where nekton use is greater.     

Using surfactant-modified clays to determine sorption mechanisms for a representative organic base, quinoline

Sorption of a representative ionizable nitrogen heterocycle, quinoline (pKa = 4.92), was investigated to determine the relative contributions of the neutral and protonated species to the overall process. Batch sorption experiments were conducted on surfactant-modified clays that were synthesized from the exchange of hexadecyltrimethylammonium cations for resident sodium cations on a specimen smectite (Swy-2) at 0, 60, 80, and 100% of the clay's cation exchange capacity (CEC). Hexadecyltrimethylammonium exchange creates highly effective organic partitioning domains within the clay interlayers in proportion to their coverage on the exchange complex. The fractionally exchanged clays, therefore, provided discrete exchange and organic partitioning domains for the protonated and neutral species of quinoline. Data were described by a combined Langmuir-linear isotherm that permitted independent characterization of both sorption components. Results indicated that cationic sorption dominated but that the neutral species can contribute substantially given sufficient organic carbon content relative to the CEC and at pH above the pKa of quinoline. The data obtained in this study for quinoline demonstrated that the combined isotherm (including cation exchange and hydrophobic partitioning terms) describes sorption data and compares favorably with the purely empirical Freundlish isotherm.     

Modeling Parent and Metabolite Fate and Transport in Subsurface Drained Fields With Directly Connected Macropores1

Abstract: Few studies exist that evaluate or apply pesticide transport models based on measured parent and metabolite concentrations in fields with subsurface drainage. Furthermore, recent research suggests pesticide transport through exceedingly efficient direct connections, which occur when macropores are hydrologically connected to subsurface drains, but this connectivity has been simulated at only one field site in Allen County, Indiana. This research evaluates the Root Zone Water Quality Model (RZWQM) in simulating the transport of a parent compound and its metabolite at two subsurface drained field sites. Previous research used one of the field sites to test the original modification of the RZWQM to simulate directly connected macropores for bromide and the parent compound, but not for the metabolite. This research will evaluate RZWQM for parent/metabolite transformation and transport at this first field site, along with evaluating the model at an additional field site to evaluate whether the parameters for direct connectivity are transferable and whether model performance is consistent for the two field sites with unique soil, hydrologic, and environmental conditions. Isoxaflutole, the active ingredient in BALANCE^® herbicide, was applied to both fields. Isoxaflutole rapidly degrades into a metabolite (RPA 202248). This research used calibrated RZWQM models for each field based on observed subsurface drain flow and/or edge of field conservative tracer concentrations in subsurface flow. The calibrated models for both field sites required a portion (approximately 2% but this fraction may require calibration) of the available water and chemical in macropore flow to be routed directly into the subsurface drains to simulate peak concentrations in edge of field subsurface drain flow shortly after chemical applications. Confirming the results from the first field site, the existing modification for directly connected macropores continually failed to predict pesticide concentrations on the recession limbs of drainage hydrographs, suggesting that the current strategy only partially accounts for direct connectivity. Thirty‐year distributions of annual mass (drainage) loss of parent and metabolite in terms of percent of isoxaflutole applied suggested annual simulated percent losses of parent and metabolite (3.04 and 1.31%) no greater in drainage than losses in runoff on nondrained fields as reported in the literature.