Nuno Lapa

This work aimed to study the effect of different pre-treatments applied to a potato peel residue, in a thermophilic Anaerobic Digestion (AD) process. All samples were subjected to a mechanical pre-treatment through milling to a particle size below 2 mm. The thermal pre-treatments applied consisted of autoclaving the residue at a gauge pressure of 1.2 bar, under a temperature of 122°C, and for 20, 35 and 55 minutes: assays E122.20, E122.35 and E122.55, respectively. The control assay was performed on a ground residue, which was not submitted to any thermal pre-treatment. All pre-treated residues were subjected to an AD process in a CSTR reactor at 49±1°C. The experimental data showed that the highest methane percentages were very similar (about 92% v/v) for all samples submitted to the thermal pre-treatments. For the control assay, the highest percentage of methane was 87.9% (v/v). The highest biogas yields were recorded in the trial E122.35 (646±50 cm3.g-1 CODremoved), against only 250±20 cm3.g-1 CODremoved for the control assay. The highest biogas yields for VSremoved were attained in the assays E122.55 and E122.35, with values of 646±48 cm3.g-1 VSremoved and 634±59 cm3.g-1 VSremoved, respectively. Globally, the yields registered for the assay E122.35 were similar to those determined in the assay E122.55. Due to the lower energy consumption during the pre-treatment performed in the assay E122.35, this was considered to be the most suitable pre-treatment for this type of residue.

The present work aims to perform a characterization of chars obtained in the co-pyrolysis of waste mixtures composed by plastics, tires and pine biomass, to provide knowledge about the composition, leaching behavior and risk assessment of these materials in order to define strategies for their possible valorization or safe disposal. The chars were submitted to sequential solvent extractions with organic solvents of increasing polarity that allow the recovery of significant amounts of the pyrolysis oils trapped in the crude chars improving the yield of the pyrolysis liquids. An acidic demineralization procedure was successfully applied to the chars and high efficiency removals of the majority of the heavy metals were achieved. The demineralization study also demonstrated that hazardous heavy metals such as chromium, nickel and cadmium are significantly immobilized in the char matrix, and other heavy metals of concern such as zinc and lead will not represent a leaching problem if acidic conditions were not used. The obtained chars present sufficient quality and characteristics to be used as fuel or alternatively, to be used as adsorbents or precursors of activated carbon.

Two combustion tests were performed in a fluidized bed combustor of a thermo-electric power plant: (1) combustion of coal; (2) co-combustion of coal (68.7% w/w), sewage sludge (9.2% w/w) and meat and bone meal (MBM) (22.1% w/w).

Three samples of ashes (bottom, circulating and fly ashes) were collected in each combustion test. The ashes were submitted to the following assays: (a) evaluation of the leaching behaviour; (b) stabilization/solidification of fly ashes and evaluation of the leaching behaviour of the stabilized/solidified (s/s) materials; (c) production of concrete from bottom and circulating ashes. The eluates of all materials were submitted to chemical and ecotoxicological characterizations. The crude ashes have shown similar chemical and ecotoxicological properties. The s/s materials have presented compressive strengths between 25 and 40 MPa, low emission levels of metals through leaching and were classified as non-hazardous materials. The formulations of concrete have presented compressive strengths between 12 and 24 MPa. According to the Dutch Building Materials Decree, some concrete formulations can be used in both scenarios of limited moistening and without insulation, and with permanent moistening and with insulation.

This work aimed to study the recovery of two types of waste by the process of pyrolysis. The obtained results show that the adding of a plastic mix improves the overall efficiency of the slow pyrolysis of pine. Therefore, it was possible to achieve higher liquid yields and less solid product than in the classic slow pyrolysis carbonization of biomass. The obtained liquids showed heating values similar to that of heating fuel oil. The gas products had energetic contents superior to that of producer gas, and the obtained solid fractions showed heating values higher than some coals. There were also identified some typical products of fast biomass pyrolysis used as raw material in several industries. The effects of experimental conditions in product yield and composition were also studied. The parameters that showed higher influence were (with its increase): reaction time on gas product composition (increase of the alkane content) and on liquid composition (increase in aromatics content); reaction temperature on product yield (decrease of liquid yield with increase of solids and gases) and on gas product composition (increase in alkane content); initial pressure on liquid composition (increase in the aromatics content) and mainly the pine content of the initial mixture on products yield (increase of gas and solid yield with a decrease in liquids) and on the gas product composition (favouring CO and CO2 formation).