Emissions from baled municipal solid waste: II. Effects of different treatments and baling techniques on the emission of volatile organic compounds.

This paper focuses on the volatile organic compound emissions from baled municipal solid waste (MSW). The analytical methodology was based on sampling with adsorbent tubes once a month during seven occasions within a time period of 1 year. Automated analyses were carried out on-line work-up with thermal desorption directly connected to a gas chromatograph-mass spectrometer. The effect of different baling techniques, cylindrical and rectangular baling was compared. It was found that cylindrically baled MSW emitted larger concentration of esters than their rectangular counter parts. Conversely, aromatic compounds emissions dominated in rectangularly baled MSW. This indicates that different degradation mechanisms operate in the waste bales. Cylindrical and rectangular bales are generally wrapped with six layers of 250 microm thick low density polyethylene (LDPE). It was observed that by wrapping an extra six layers of LDPE film onto the bales, the emissions from cylindrical bales increased while emissions from the rectangular counterpart decreased. Over time, the volatile organic compound emissions from cylindrical bales decreased two orders of magnitudes from 96.2 +/- 20.8 microg m(-3) in September 2003 to 0.80 +/- 0.07 microg m(-3) in July 2004. The rectangular bales exhibited an almost identical relative emission reduction from 54.4 +/- 4.3 microg m(-3) in September 2003 to 0.46 +/- 0.02 microg m(-3) in July 2004. Future work will concentrate on full-scale storages, taking into account waste type, storage size, temperature development and the different baling techniques among other variables.     

Modelling C and N mineralization during decomposition of anaerobically digested and composted municipal solid waste.

Application of municipal solid waste (MSW) to arable land can be used to close the nutrient cycle between urban and rural areas. The aim of the current study was to quantify net N mineralization and respiration from composted MSW (CMSW) and anaerobically digested MSW (ADMSW) applied to soil, and to test whether a simple relationship between net N mineralization and respiration that was developed for plant materials, was applicable for these types of MSW. In a laboratory experiment, CMSW and ADMSW were incorporated into soil and incubated at 15 degrees C. During the 149-day experiment, netN mineralization and respiration were determined. Cumulative respiration derived from both MSW types was very steep during the first 30 days, after which it levelled off. However, calculated on the basis of applied C, the ADMSW was 10 times more degradable than the CMSW. Both MSW types caused initial net N immobilization followed by re-mineralization. A simple model based on the relationship between net N mineralization and respiration was only applicable for the MSW after significant modifications. If farmers are to recognize CMSW and ADMSW as valuable fertilizers, it is important that they can be produced with higher maturity, in order to avoid initial N immobilization.     

Sensori-motor learning and its relevance for task specialization in bumble bees

Individual bees often restrict their visits to only a few species out of the multitude of available plants. This flower constancy is likely caused by limitations of memory for motor patterns, sensory stimuli, or reward levels. Here we test the implications of sensori-motor learning and memory for flower constancy. Artificial “flowers” with two distinct “morphologies” were used, so that in each flower type, a different motor pattern was needed to reach the nectar. As in natural flowers, these morphological types were associated with sensory signals (blue and yellow color stimuli). Bees which learned only a single task were more efficient in several ways than those which had learned two: they made fewer errors, had shorter flower handling times, took shorter times to correct errors, and transitions between flowers were initially more rapid. For bees which had learned two tasks, performance depended strongly on the training schedule: if each task was learned with blocked trials, the memory for the second appeared to interfere with that for the first. Interference affected only the association between flower signal and motor pattern, not the motor pattern itself. This was not the case if bees were trained for both tasks with alternating trials. In that case, bees rapidly learned both tasks, albeit with worse saturation levels than bees which had learned only one. Bees transferred the experience gained on one task to a second task: their initial performance on the second task was better than their initial performance on the first. On the other hand, performance on the second task in the saturation level (in which bees no longer improve their efficiency) was worse than on the first task (negative transfer). In the saturation phase, performance did not directly depend on switch frequency, but on whether the bee had one or two options in memory. Thus, while bees would become proficient at two tasks more quickly if their acquisition phase included switches, such switches had no measurable effect in the saturation phase. The implications of these findings for foraging are discussed using modern learning theory. Received: 4 April 1997 / Accepted after revision: 8 August 1997     

Reverse quantitative structure-activity relationship for modelling the sorption of esfenvalerate to dissolved organic matter. A multivariate approach

The sorption of the pyrethroid, esfenvalerate, to the dissolved and/or dispersed fraction of eight different natural humic compounds has been investigated. The dissolved organic matters (DOMs) included in this study originate from ground water, soil pore water, and surface waters. Sorption was modelled at DOM concentration levels where equilibrium partitioning of esfenvalerate between DOM and the aqueous bulk phase prevails. The inherent characteristics of the eight different humic materials, quantified in the preceding paper by Thomsen et al. (2002, this issue (PII: S0045-6535(02)00335-1)), have been used as explanatory variables for modelling this equilibrium partitioning. Using a reverse QSAR approach based on by projection-into-latent-structure regression (PLS-R) inherent sorbent properties determining for the sorption affinity of esfenvalerate to DOM were analysed. For all humic substances a decrease in the DOM-normalised equilibrium-partitioning coefficient, K_DOM, with increasing concentration of DOM was observed. Significant variations in K_DOM values, as function of the inherent characteristics of the individual humic substances, were found at DOM concentrations of 75 and 100 ppm, respectively. The latter is a strong indication of variations in sorption mechanisms of esfenvalerate to DOM of varying inherent properties. Groupings in the principal property space quantifying DOMs may indicate that separate models are needed for quantifying the equilibrium partitioning to different classes of DOM.     

Mobility of chloroaromatic compounds in soil: case studies of Swedish chlorophenol-contaminated sawmill sites

This paper summarizes recent studies on the environmental fate of chloroaromatic compounds in chlorophenol (CP)-contaminated soil and groundwater at Swedish sawmill sites. Relative proportions of CPs, polychlorinated phenoxy phenols (PCPPs), polychlorinated diphenyl ethers (PCDEs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) were determined in preservatives, particulate organic matter (POM), dissolved organic matter (DOM), groundwater, and particles filtered from groundwater. All compound classes were found in the different compartments. The fraction of PCPPs, PCDEs, PCDDs, and PCDFs had increased in the soil samples relative to the proportions in the preservatives. This increase showed correlation with the hydrophobicity, that is, PCDDs had the largest increase. Similar correlation was found between hydrophobicity and the importance of partitioning to POM over DOM. The more water soluble compound group, CP, was found equally distributed between POM and DOM. For PCPPs, PCDEs, PCDDs, and PCDFs, the relative partitioning to POM increased with increased hydrophobicity. Despite the relative partitioning towards POM, compared with DOM, cotransport with DOM and suspended colloidal fractions was found to substantially increase the transport of these compounds in the groundwater samples.     

Phosphorus leaching in relation to soil type and soil phosphorus content

Phosphorus losses from arable soils contribute to eutrophication of freshwater systems. In addition to losses through surface runoff, leaching has lately gained increased attention as an important P transport pathway. Increased P levels in arable soils have highlighted the necessity of establishing a relationship between actual P leaching and soil P levels. In this study, we measured leaching of total phosphorus (TP) and dissolved reactive phosphorus (DRP) during three years in undisturbed soil columns of five soils. The soils were collected at sites, established between 1957 and 1966, included in a long-term Swedish fertility experiment with four P fertilization levels at each site. Total P losses varied between 0.03 and 1.09 kg ha(-1) yr(-1), but no general correlation could be found between P concentrations and soil test P (Olsen P and phosphorus content in ammonium lactate extract [P-AL]) or P sorption indices (single-point phosphorus sorption index [PSI] and P sorption saturation) of the topsoil. Instead, water transport mechanism through the soil and subsoil properties seemed to be more important for P leaching than soil test P value in the topsoil. In one soil, where preferential flow was the dominant water transport pathway, water and P bypassed the high sorption capacity of the subsoil, resulting in high losses. On the other hand, P leaching from some soils was low in spite of high P applications due to high P sorption capacity in the subsoil. Therefore, site-specific factors may serve as indicators for P leaching losses, but a single, general indicator for all soil types was not found in this study.