Effects of limestone addition and sintering on heavy metal leaching from hazardous waste incineration slag

Hazardous waste incineration (HWI) in rotary kilns and the disposal of the residual slag on landfills play an important role in German waste treatment. In order to save disposal costs the elution behaviour of HWI-slag should be further optimised. Quality-improved slag may be disposed off on cheaper landfill sites still applying to landfill regulations. In a new process-integrated approach hazardous waste is mixed with limestone, which initiates chemical reactions with heavy metals in the rotary kiln yielding new compounds of different solubility. In this work HWI-slag/limestone mixtures are thermally treated and then examined by elution tests. Experimental data indicate that the heavy metals pertinent to landfill class assignment of a HWI-slag share a solubility minimum at a CaO-content of about 15%. Such improved HWI-slags are allowed to be disposed off on cheaper landfill sites. Furthermore, a new combination of thermodynamic calculation methods is applied to predict heavy metal solubility for different process conditions. Used models hold the opportunity to explain the tendencies of heavy metal leaching and propose plausible chemical reactions. With it, a new tool to examine the impact of temperature treatment and slag composition on heavy metal elution from HWI-slag is presented.     

Assessment of the nitrogen and carbon budget of two managed temperate grassland fields

Greenhouse gas budgets as well as the productivity of grassland systems are closely related to the carbon (C) and nitrogen (N) cycles. Within the framework of the CarboEurope and NitroEurope projects we have measured C and N exchange on the field scale at the grassland site Oensingen previously converted from arable rotation. The site is located on the Swiss Central Plateau and consists of two parallel fields of equal size. One field was subjected to intensive management with average nitrogen input of 230 kg-N ha⁻¹ year⁻¹ and 4–5 cuts per year, and the other to an extensive management with no fertilisation and less frequent cutting. The total C budget of the fields was assessed by measuring the CO₂ exchange by eddy covariance and analysing the carbon import by manure application and export by harvest. The N budget of the managed grassland is more complex. Besides the management related import and export, it includes gaseous exchange in many different forms (NO, NO₂, HNO₃, N₂O, NH₃, N₂) needing different analytical techniques, as well as input by rain and leaching of N-compounds with the soil water. The main (“level-3”) field sites in the NitroEurope project are supposed to measure 95% of the N fluxes at the field scale. For several of the N fluxes specific measurements have been performed for 1 year or longer at the site. Some of the remaining N budget components (dry and wet deposition) could be estimated from results of a national deposition network, while other components (NH₃ and N₂ emission) were estimated based on literature parameterisations. However, we found indications that the (systematic) uncertainties of these estimated N-fluxes are large and that it is important to make site-specific measurement for all relevant budget components. The suitability of corresponding experimental methods is discussed.Analysis of the C budget over a 6-year period (2002–2007) showed a significant mean difference between the two newly established grassland fields with a likely net carbon loss for the extensive management and a net sequestration for the intensive management. Since the C/N ratio of the soil organic matter of the grassland is constrained in a rather narrow range around 9.3, the change in the soil carbon pool is supposed to be accompanied by a corresponding change in the N storage. This approach provided an alternative method to check the N budget of the two grassland fields derived from the individual N fluxes.     

Volatile chemicals from leaf litter are associated with invasiveness of a neotropical weed in Asia

Some invasive plant species appear to strongly suppress neighbors in their nonnative ranges but much less so in their native range. We found that in the field in its native range in Mexico, the presence of Ageratina adenophora, an aggressive Neotropical invader, was correlated with higher plant species richness than found in surrounding plant communities where this species was absent, suggesting facilitation. However, in two nonnative ranges, China and India, A. adenophora canopies were correlated with much lower species richness than the surrounding communities, suggesting inhibition. Volatile organic compound (VOC) signals may contribute to this striking biogeographical difference and the invasive success of A. adenophora. In controlled experiments volatiles from A. adenophora litter caused higher mortality of species native to India and China, but not of species native to Mexico. The effects of A. adenophora VOCs on seedling germination and growth did not differ between species from the native range and species from the nonnative ranges of the invader. Litter from A. adenophora plants from nonnative populations also produced VOCs that differed quantitatively in the concentrations of some chemicals than litter from native populations, but there were no chemicals unique to one region. Biogeographic differences in the concentrations of some volatile compounds between ranges suggest that A. adenophora may be experiencing selection on biochemical composition in its nonnative ranges.     

Decision making in ant foragers (<Emphasis Type="Italic">Lasius niger</Emphasis>) facing conflicting private and social information

Foragers of many ant species use pheromone trails to guide nestmates to food sources. During foraging, individual workers can also learn the route to a food source. Foragers of the mass-recruiting ant Lasius niger use both pheromone trails and memory to locate a food source. As a result, an experienced forager can have a conflict between social information (trail pheromones) and private information (route memory) at trail bifurcations. We tested decision making in L. niger foragers facing such an informational conflict in situations where both the strength of the pheromone trail and the number of previous visits to the food source varied. Foragers quickly learned the branch at a T bifurcation that leads to a food source, with 74.6% choosing correctly after one previous visit and 95.3% after three visits. Pheromone trails had a weaker effect on choice behaviour of naïve ants, with only 61.6% and 70.2% choosing the branch that had been marked by one or 20 foragers versus an unmarked branch. When there was a conflict between private and social information, memory overrides pheromone after just one previous visit to a food source. Most ants, 82–100%, chose the branch where they had collected food during previous foraging trips, with the proportion depending on the number of previous trips (1 v. 3) but not on the strength of the pheromone trail (1 v. 20). In addition, the presence of a pheromone trail at one branch in a bifurcation had no effect on the time it took an experienced ant to choose the correct branch (the branch without pheromone). These results suggest that private information (navigational memory) dominates over social information (chemical tail) in orientation decisions during foraging activities in experienced L. niger foragers.     

Double sampling for stratification for the monitoring of sparse tree populations: the example of Populus euphratica Oliv. forests at the lower reaches of Tarim River, Southern Xinjiang, China

Desertification is a pressing issue in the dry Tarim River basin, which is under anthropogenic stresses. In this study, double sampling for stratification (DSS) is employed to inventory Populus euphratica Oliv. forests in the lower reaches of the Tarim River Basin in Xinjiang, China. The two objectives were evaluating DSS as a sampling technique for monitoring desertification and generating baseline information for permanent observation. Here, DSS consists of two phases: in phase 1, crown cover is observed on a large sample of plots on a high resolution satellite image, and these photo-plots are stratified into five crown cover strata. Phase 2 is a stratified random sample from these photo-plots and the sampled plots are field observed. Approximately 32% of the study area is without P. euphratica trees. As expected, estimated mean poplar tree density and basal area increase with crown cover. DSS takes advantages of stratification (fieldwork efficiency and statistical precision) without the need for a priori strata delineation. It proves feasible for inventory the sparse poplar population and holds promise for the assessment of trees outside the forest, where density varies considerably and pre-stratification is intractable. It can be integrated into permanent observation systems for monitoring vegetation changes.     

The use of navigation systems in naturalistic driving

Objective: In this study, we assessed the use of portable navigation systems in everyday driving by applying in-vehicle naturalistic driving.

Method: Experienced users of navigation systems, 7 females and 14 males, were provided with a specially equipped vehicle for approximately 1 month. Their trips were recorded using 4 cameras, Global Positioning System (GPS) data, and other sensor data. The drivers’ navigation system use data were coded from the video recordings, which showed how often and for how long the system was activated and how often and for how long a driver operated the system.

Results: The system was activated for 23% of trips, predominantly on longer and unique trips. Analyses of the percentage of time for which the speed limit was exceeded showed no evidence of differences between trips for which the navigation system was used or not used. On trips for which the navigation system was activated, participants spent about 5% of trip time interacting with the device. About 40% of interacting behavior took place in the first 10% of the trip time, and about 35% took place while the car was standing still or moving at a very low speed; that is, 0–10 km/h.

Conclusion: These results shed light on how and when drivers use navigation systems. They suggest that although drivers regulate their use of such systems to some extent, they often perform risky tasks while driving.     

Levels of PCDD/Fs and trace elements in superficial soils of Pavia Province (Italy)

Trace elements and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were analyzed in soils from rural and light-industrialized sites (n=168) of Province of Pavia (Northern Italy). Most of the trace element values fit in typical ranges of concentrations in soils and are similar to the ones reported for rural sites in Italy or sites with no direct anthropogenic impact. Total concentrations of 2,3,7,8 chlorine substituted PCDD/Fs in superficial soils ranged between 24.4 and 1287 pg g(-1) dw (0.5-28.9 pg WHO(98)-TEQ g(-1) dw). The North Eastern part of the Province presented significantly higher levels (p<0.001) than the rest of the Province for As, Cd, Hg, Pb, Zn and PCDD/Fs. While the existence of a defined heavy metal polluting source for this specific site has been suggested, in the case of PCDD/Fs, profiles were not linked to any specific emission source fingerprint. In the whole extension of Pavia Province, OCDD/F dominated the 2,3,7,8 chlorine substituted congener soil pattern, followed by the 1,2,3,4,6,7,8 hepta-CDD/F congener. Principal Component Analysis (PCA) showed that this profile could not be associated to any described PCDD/F emission source fingerprint and was relatively similar to the baseline deposition of sites with no direct impact of PCDD/F emission sources independently of land use.     

Biochar and hydrochar effects on greenhouse gas (carbon dioxide, nitrous oxide, and methane) fluxes from soils

With a growing world population and global warming, we are challenged to increase food production while reducing greenhouse gas (GHG) emissions. We studied the effects of biochar (BC) and hydrochar (HC) produced via pyrolysis or hydrothermal carbonization, respectively, on GHG fluxes in three laboratory incubation studies. In the first experiment, ryegrass was grown in sandy loam mixed with equal amounts of a nitrogen-rich peanut hull BC, compost, BC+compost, double compost, or no addition (control); wetting-drying cycles and N fertilization were applied. Biochar with or without compost significantly reduced NO emissions and did not change the CH uptake, whereas ryegrass yield was significantly increased. In the second experiment, 0% (control) or 8% (w/w) of BC (peanut hull, maize, wood chip, or charcoal) or 8% HC (beet chips or bark) was mixed into a soil and incubated at 65% water-holding capacity (WHC) for 140 d. Treatments included simulated plowing and N fertilization. All BCs reduced NO emissions by ～60%. Hydrochars reduced NO emissions only initially but significantly increased them after N fertilization to 302% (HC-beet) and 155% (HC-bark) of the control emissions, respectively. Large HC-associated CO emissions suggested that microbial activity was stimulated and that HC was less stable than BC. In the third experiment, nutrient-rich peanut hull BC addition and incubation over 1.5 yr at high WHCs did not promote NO emissions. However, NO emissions were significantly increased with BC after NHNO addition. In conclusion, BC reduced NO emissions and improved the GHG-to-yield ratio under field-relevant conditions. However, the risk of increased NO emissions with HC addition must be carefully evaluated.     

Groundwater Flow Model Calibration of a Coastal Multilayer Aquifer System Based on Statistical Sensitivity Analysis

Environmental Modeling & Assessment - The identification of the hydrological processes taking place at coastal systems and the interaction between aquifers and the sea have been key features...