Browsing by Author "Lourenco, N."
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- Is filter packing important in a small-scale vermifiltration process of urban wastewater?Publication . Lourenco, N.; Nunes, L.Nowadays, natural resources are under increasing stress which fosters wastewater reuse planning and emphasizes on the decentralized wastewater treatment. Vermifiltration has been described as a viable alternative to treat domestic and urban wastewater, but few studies have focused on the impact of different filter packings on vermifiltration performance. This study evaluates the effect of vermicompost and sawdust in a single-stage vermifilter (VF) for urban wastewater treatment. After an acclimation period of 45 days, urban wastewater from a combined sewage collection system was applied continuously for 24 h. Earthworm stock density was of 20 g L-1, HRT of 6 h, HLR of 0.89 m(3) m(-2) day(-1) and OLR of 7.38 g BOD5 day(-1). System performance was assessed by the removal efficiencies of BOD5, COD, TSS, NH4 (+), TN and TP, and fecal coliforms and helminth eggs elimination. Vermicompost (VE) and sawdust (SE) were tested, using an earthworm abundance of 20 g L-1. Treatment efficiencies were 91.3% for BOD5, 87.6% for COD, 98.4% for TSS and 76.5% for NH4 (+) in VE, and 90.5% for BOD5, 79.7% for COD, 98.4% for TSS and 63.4% for NH4 (+) in SE. Earthworms contributed to reduce NH4 (+) and TN removal and to increase NO3 (-) concentration. No treatment was able to eliminate fecal coliforms down to guidelines values for wastewater irrigation as helminth eggs were completely eliminated. Single-stage vermifiltration system using both filter packings is inconsistent and cannot meet EU guideline values for discharge in sensitive water bodies and WHO guidelines for irrigation with treated wastewater.
- Spatiotemporal distribution of the seismicity along the Mid-Atlantic Ridge north of the Azores from hydroacoustic data: Insights into seismogenic processes in a ridge-hot spot contextPublication . Goslin, J.; Perrot, J.; Royer, J. -Y.; Martin, C.; Lourenco, N.; Luis, J.; Dziak, R. P.; Matsumoto, H.; Haxel, J.; Fowler, M. J.; Fox, C. G.; Lau, A. T. -K.; Bazin, S.The seismicity of the North Atlantic was monitored from May 2002 to September 2003 by the 'SIRENA array' of autonomous hydrophones. The hydroacoustic signals provide a unique data set documenting numerous low-magnitude earthquakes along the section of the Mid-Atlantic Ridge (MAR) located in a ridge-hot spot interaction context. During the experiment, 1696 events were detected along the MAR axis between 40 degrees N and 51 degrees N, with a magnitude of completeness level of m(b) approximate to 2.4. Inside the array, location errors are in the order of 2 km, and errors in the origin time are less than 1 s. From this catalog, 15 clusters were detected. The distribution of source level (SL) versus time within each cluster is used to discriminate clusters occurring in a tectonic context from those attributed to non-tectonic (i.e. volcanic or hydrothermal) processes. The location of tectonic and non-tectonic sequences correlates well with regions with positive and negative Mantle Bouguer Anomalies (MBAs), indicating the presence of thinner/colder and thicker/warmer crust respectively. At the scale of the entire array, both the complete and declustered catalogs derived from the hydroacoustic signals show an increase of the seismicity rate from the Azores up to 43 degrees 30'N suggesting a diminishing influence of the Azores hot spot on the ridge-axis temperature, and well correlated with a similar increase in the along-axis MBAs. The comparison of the MAR seismicity with the Residual MBA (RMBA) at different scales leads us to think that the low-magnitude seismicity rates are directly related to along-axis variations in lithosphere rheology and temperatures.
- Variation of magnetic properties in sedimentary rocks hosting the Foum Zguid dyke (southern Morocco): combined effects of re-crystallization and Fe-metasomatismPublication . Silva, P. F.; Henry, B.; Marques, F. O.; Mateus, A.; Madureira, P.; Lourenco, N.; Miranda, J. M.The effects of dyke intrusion on the magnetic properties of host sedimentary rocks are still poorly understood. Therefore, we have evaluated bulk magnetic parameters of standard palaeomagnetic samples collected along several sections across the sediments hosting the Foum Zguid dyke in southern Morocco. The study has been completed with the evaluation of the magnetic fabric after laboratory application of sequential heating experiments. The present study shows that: (1) close to Fourn Zguid dykes, the variations of the bulk magnetic parameters and of the magnetic fabric is strongly related with re-crystallization and Fe-metasomatism intensity. (2) The thermal experiments on AMS of samples collected farther from the dyke and, thus, less affected by heating during dyke emplacement, indicate that 300-400 degrees C is the minimum experimental temperature necessary to trigger appreciable transformations of the pre-existing magnetic fabrics. For temperatures higher than ca. 580 degrees C, the magnetic fabric transformations are fully realized, with complete transposition of the initial fabric to a fabric similar to that of samples collected close to the dyke. Therefore, measured variations of the magnetic fabric can be used to evaluate re-crystallization temperatures experienced by the host sedimentary rock during dyke emplacement. The distinct magnetic behaviour observed along the cross-sections strongly suggests that samples collected farther from the dyke margins did not experience thermal episodes with temperatures higher than 300 degrees C after dyke emplacement. (3) AMS data shows a gradual variation of the magnetic fabric with distance from the dyke margin, from sub-horizontal K-3 away from the dyke to vertical K3 close to the dyke. Experimental heating shows that heat alone can be responsible for this strong variation. Therefore, such orientation changes should not be unequivocally interpreted as the result of a stress field (resulting from the emplacement of the dyke, for instance). (4) Magnetic studies prove to be a very sensitive tool to assess rock magnetic transformations, thermally and chemically induced by dyke intrusion in hosting sediments. (c) 2005 Elsevier B.V. All rights reserved.