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  • Mineralization of olive mill wastewater over DSA
    Publication . Gonçalves, M. R.; Correia, J. P.; Marques, Isabel Paula
    Bioenergy recovery from olive mill wastewater (OMW) has been effectively accomplished by anaerobic digestion [1]. Nevertheless, a post treatment is required to attain the discharge limit values. After the anaerobic treatment of OMW, the main issues are related to the remaining organic matter (COD), recalcitrant phenolic compounds (40-50%) and effluent dark-brown colour. The electrochemical treatment is proposed in this work as a final step to mineralise the OMW non-biodegradable fraction. The electrochemical oxidation of OMW anaerobically digested was investigated over DSAs. The performance of RuO2 and IrO2 based DSAs was studied by cyclic voltammetry and bulk electrolysis. The experiments were carried out with alkaline samples from the anaerobic reactor comprising 1 to 10 g COD/L, depending to the digester operational conditions. KNO3 was used as electrolyte, alternatively to the preferred NaCl [2], to avoid obtaining an effluent with higher toxicity than the initial one. It was found that RuO2 based anode was significantly more efficient than IrO2, mainly for the COD removal (Figure 1). With an electrolysis charge of Q=1517 C it was obtained COD removals of 9 and 52%, phenols removals of 72 and 98% and colour removal of 61 and 98%, for IrO2 and RuO2 type DSAs, respectively. The exclusion of the centrifugation/filtration step before the electrochemical treatment was considered, since the anaerobic treatment step reduces considerably the solids fraction. It is concluded that the electrochemical oxidation over DSAs is a suitable second step treatment for OMW disposal after the recovery of its energetic potential. The outcome energy from biogas production can balance or reduce the costs of the electrochemical treatment.
    2011-06-19Conference object Open access Show more
  • Modelling of the IPS buoy wave energy converter including the effect of non-uniform tube cross-section
    Publication . Falcão, António F. de O.; Cândido, José J.; Justino, Paulo Alexandre; Henriques, João C. C.
    An important class of floating wave energy converters (that includes the IPS buoy, the Wavebob and the PowerBuoy) comprehends devices in which the energy is converted from the relative (essentially heaving) motion between two bodies oscillating differently. The paper considers the case of the IPS buoy, consisting of a floater rigidly connected to a fully submerged vertical (acceleration) tube open at both ends. The tube contains a piston whose motion relative to the floater-tube system (motion originated by wave action on the floater and by the inertia of the water enclosed in the tube) drives a power take-off mechanism (PTO) (assumed to be a linear damper). To solve the problem of the end-stops, the central part of the tube, along which the piston slides, bells out at either end to limit the stroke of the piston. The use of a hydraulic turbine inside the tube is examined as an alternative to the piston. A frequency domain analysis of the device in regular waves is developed, combined with a one-dimensional unsteady flow model inside the tube (whose cross-section is in general nonuniform). Numerical results are presented for a cylindrical buoy in regular waves, including the optimization of the acceleration tube geometry and PTO damping coefficient for several wave periods.
    2011-06-19Conference object Open access Show more