Secondary sludge from municipal wastewater treatment plant is proposed as a promising alternative lipid feedstock for biodiesel production. A deep study combining different type of raw materials (sludge coming from the oxic, anoxic and anaerobic steps of the biological treatment) with different technologies (liquid-liquid and solid-liquid extractions followed by acid catalysed transesterification and in situ extraction-transesterification procedure) allows a complete comparison of available technologies. Different parameters - contact time, catalyst concentration, pretreatments - were considered, obtaining more than 17% FAMEs yield after 50min of sonication with the in situ procedure and 5% of H2SO4. This result corresponds to an increment of more than 65% respect to the best results reported at typical conditions. Experimental data were used to propose a mathematical model for this process, demonstrating that the mass transfer of lipids from the sludge to the liquid is the limiting step.

Naproxen (NPX) degradation was investigated by anodic oxidation both at constant potential and by cyclic voltammetry, using this last technique for optimizing reaction conditions and catalyst properties. Three MWCNTs-promoted electrodes were used (MWCNT, MWCNT-COOH and MWCNT-NH₂) and a two steps oxidation process being observed in all the cases. At the optimized conditions (volume of MWCNT = 15 μL), the influence of the scan rate indicates the diffusion – adsorption control of the process. Likewise, the kinetic study of NPX degradation at fix potential, considering two different stirring speeds (250 and 500 rpm), indicates that degradation rate increases with the stirring speed. After 20 h, NPX is degraded even an 82.5%, whereas the mineralization reaches almost 70% as it was obtained from total organic carbon analysis. PH effect was also analysed, in the range 5–11, observing a positive effect at low pH. Concerning the surface chemistry of the electrode, MWCNT-NH₂, with the highest isoelectric point (4.70), is the most promising material due to the improved interactions with the reactant. From these observations, a pathway is proposed, which includes two steps of electrochemical oxidation followed by subsequent oxidation steps, until mineralization of the NPX, attributed mainly to active chlorine species and ·OH.