Maria Cristina Vila

Advanced numerical tools applied to geo-environmental engineering: soils contaminated by petroleum hydrocarbons, a case study

Contaminated soils can be considered as a heterogeneous, anisotropic and discontinuous geo-system, whose properties vary in time and space. Focusing on the remediation of a real contaminated site (a refinery located in northern Portugal), soil samples contaminated with petroleum hydrocarbons were subject to laboratory studies. The results of contaminant degradation kinetics tests led to the development of a distributed parameter model describing simultaneously the time evolution of biomass and contaminant degradation. Several phenomena were globally taken into account in this model: the volatilization, a fast kinetics component, a slow kinetics component and the refractory hydrocarbons for the time scale used in the experiments. To complement kinetics tests the soil contaminated was submitted to respirometric tests. The a priori unpredictability of the respirometric results justified the continuous measurement of oxygen and carbon dioxide concentrations and of temperature in the soil atmosphere, resulting in a huge volume of data. Several mathematical techniques were used in respirometry data treatment, namely: time series, system identification and wavelets theories.

Preventing acid mine drainage from mine tailings.

Mining activity always has high impact on its surroundings, beingwaste deposition the cause of multiple and complex problems to the environment. One of them is Acid Mine Drainage (AMD), causing acid water percolation through large areas in the mine site. Portugal was a prosper tungsten producer from the beginning of the 20th century, having its apogee during World War II. Nowadays there are millions of tons of mine residues deposited in either stock piles or in tailing dams, most of them abandoned, and only one mine still producing tungsten. Available experimental tests to evaluate the acid production potential are listed and commented. Fresh tailings from the still active Panasqueira mine were used as a case study. Laboratory scale tests allowed us to predict the AMD potential as well as its kinetics, which constitutes a very important tool in tailings management. Pilot scale experiments tested the effect of different cover types, including an organic compound host of oxygen consumer microorganisms, in preventing and reducing AMD.