Rasmussen R.S.,Technical University of Denmark |
Aquaculture International | Year: 2010
This study describes growth variation within groups of salmonids and the relation to initial fish weights and feeding levels. PIT-tagged rainbow trout (RT) and brook trout (BT) of start weight 120-170 g were reared in separate tanks for 9 weeks. Both species were fed each day either a high ration close to satiation (H) or half of this ration (L). Four experimental groups (RT-H, RT-L, BT-H, BT-L) were studied with regard to their propensity to increase weight in accord with their initial weight. The slope of the regression line between initial weights (g) and weight increases for individuals in each tank in each period was applied as indicator for this propensity (termed "slope"). All calculated slopes in the experiment were positive which indicates the general ability of weighty fish to gain more weight than smaller individuals. The average slope during all 9 weeks was 2-4 times higher for RT-L (5.91) than for all other groups (RT-H: 1.50, P < 0.01; BT-H: 1.76, P < 0.01 and BT-L: 2.88, P < 0.05), indicating the particular propensity of large RT to gain weight when feed was restricted. Overall, ration level had large impact on slopes (H: 1.63, L: 4.39, P < 0.01), while this was not the case for species (RT: 3.71, BT: 2.32, P > 0.05). The magnitude of slopes decreased over time (weeks 0-3:4.27, weeks 3-6:3.02 and weeks 6-9:1.74, P < 0.05). The observed differences in weight gains between experimental groups were reflected in differences in coefficients of variations (CVs) for body growth. RT had larger body weight (BW) CVs compared to BT (0.257 vs. 0.206, P < 0.01) indicating more uneven feed share among RT than among BT in general. RT-L had significantly higher BW CVs than all other groups (0.300 vs. 0.184-0.229, P < 0.01). The observed differences in weight gains enhance size variations in terms of higher CVs, and this may have implications for feeding tactics in aquaculture where large size variations in groups may be disadvantageous to fish farmers. © 2010 Springer Science+Business Media B.V.
Damgaard I.,Technical University of Denmark |
Bjerg P.L.,Technical University of Denmark |
Jacobsen C.S.,Geological Survey of Denmark |
Tsitonaki A.,ORBICON |
And 2 more authors.
Groundwater Monitoring and Remediation | Year: 2013
At a low permeability clay till site contaminated with chlorinated ethenes (Gl. Kongevej, Denmark), enhanced reductive dechlorination (ERD) was applied by direct push injection of molasses and dechlorinating bacteria. The performance was investigated by long-term groundwater monitoring, and after 4 years of remediation, the development of degradation in the clay till matrix was investigated by high-resolution subsampling of intact cores. The formation of degradation products, the presence of specific degraders Dehalococcoides spp. with the vinyl chloride (VC) reductase gene vcrA, and the isotope fractionation of trichloroethene, cis-dichloroethene (cis-DCE), and VC showed that degradation of chlorinated ethenes occurred in the clay till matrix as well as in sand lenses, sand stringers, and fractures. Bioactive sections of up to 1.8 m had developed in the clay till matrix, but sections, where degradation was restricted to narrow zones around sand lenses and stringers, were also observed. After 4 years of remediation, an average mass reduction of 24% was estimated. Comparison of the results with model simulation scenarios indicate that a mass reduction of 85% can be obtained within approximately 50 years without further increase in the narrow reaction zones if no donor limitations occur at the site. Long-term monitoring of the concentration of chlorinated ethenes in the underlying chalk aquifer revealed that the aquifer was affected by the more mobile degradation products cis-DCE and VC generated during the remediation by ERD. © 2012, National Ground Water Association.
Peruzzi E.,CNR Institute of Ecosystem Study |
Nielsen S.,ORBICON |
Macci C.,CNR Institute of Ecosystem Study |
Doni S.,CNR Institute of Ecosystem Study |
And 3 more authors.
Water Science and Technology | Year: 2013
In this study, results about sludge stabilization in reed bed systems (RBSs) after the entire period of operation in two different systems situated in Denmark (Helsinge 42,000 population equivalent (p.e.) - 10 years) and in Italy (La Fontina, 30,000 p.e. - 6 years) were presented. In order to evaluate the process of sludge stabilization, parameters that highlighted the biochemical and chemico-structural properties of organic sludge matter have been determined. The level of total and soluble nutrients, and enzyme activities, parameters related to overall microbial activity, showed that stabilization of the sludge similarly occurred in both RBSs, even though in different landscape ecosystems. The chemical-structural characterization of sludge organic matter highlighted how the processes of stabilization have occurred satisfactorily in both RBSs; in fact, significant levels of pyrolytic indices for mineralization and humification were reached. The successful stabilization of organic matter occurred in both RBSs and was confirmed by the absence of Escherichia coli, and also by the results of organic compounds (polycyclic aromatic hydrocarbons, linear alkyl benzene sulfonates, nonylphenol ethoxylates, di-2-ethylhexyl- phthalate) and heavy metals. © IWA Publishing 2013.
Broholm M.M.,Technical University of Denmark |
Hunkeler D.,University of Neuchatel |
Tuxen N.,ORBICON |
Jeannottat S.,University of Neuchatel |
Scheutz C.,Technical University of Denmark
Chemosphere | Year: 2014
The fate and treatability of 1,1,1-TCA by natural and enhanced reductive dechlorination was studied in laboratory microcosms. The study shows that compound-specific isotope analysis (CSIA) identified an alternative 1,1,1-TCA degradation pathway that cannot be explained by assuming biotic reductive dechlorination. In all biotic microcosms 1,1,1-TCA was degraded with no apparent increase in the biotic degradation product 1,1-DCA. 1,1,1-TCA degradation was documented by a clear enrichment in 13C in all biotic microcosms, but not in the abiotic control, which suggests biotic or biotically mediated degradation. Biotic degradation by reductive dechlorination of 1,1-DCA to CA only occurred in bioaugmented microcosms and in donor stimulated microcosms with low initial 1,1,1-TCA or after significant decrease in 1,1,1-TCA concentration (after~day 200). Hence, the primary degradation pathway for 1,1,1-TCA does not appear to be reductive dechlorination via 1,1-DCA. In the biotic microcosms, the degradation of 1,1,1-TCA occurred under iron and sulfate reducing conditions. Biotic reduction of iron and sulfate likely resulted in formation of FeS, which can abiotically degrade 1,1,1-TCA. Hence, abiotic degradation of 1,1,1-TCA mediated by biotic FeS formation constitute an explanation for the observed 1,1,1-TCA degradation. This is supported by a high 1,1,1-TCA 13C enrichment factor consistent with abiotic degradation in biotic microcosms. 1,1-DCA carbon isotope field data suggest that this abiotic degradation of 1,1,1-TCA is a relevant process also at the field site. © 2014 Elsevier Ltd.
Water Science and Technology | Year: 2011
The dewatering of the sludge with loss on ignition between 50 and 65% will have a maximal drainage on the order of 0.008-0.020 L/s/m2. Dewatering of the sludge with loss of ignition higher than 65% of dry solids will have a maximal drainage on the order of only 0.001-0.004 L/s/m2, approximately five to 10 times lower. It can be seen that there is a tendency for the achievable dewatering result to increase with the decrease of loss on ignition or fat in the feed sludge. The correlation shows that if the loss of ignition is higher than 65% of dry solids in the feed sludge the dewatering results in approximately 10% dry solid or lower in the sludge residue, and in approximately 5% dry solid or lower in the sludge residue if the fat concentration is above 10,000 mg/kg ds in the feed sludge. In systems treating sludge with high contents of fat (15,000-30,000 mg/kg ds) and oil (2,300-7,000 mg/kg ds) and if the loss of ignition is higher than 65% (between 65-76%) the dewatering efficiencies only achieve 5-15% dry solid in the sludge residue. In systems treating sludge with low contents of fat (4,000-8,000 mg/kg ds) and oil (50-2,000 mg/kg ds) and with loss on ignition between 50-65% contents of organic solids the dewatering efficiencies achieve 20-37% dry solid in the sludge residue. © IWA Publishing 2011.