DICDEA

ABSTRACT In this work, the steam gasification of scrap tires was investigated as a sustainable and cost-effective alternative to tire landfill disposal. Steam activation of the char derived from the tire residues of the gasification process was carried out at constant temperature and feeding ratio between gasifying agent and char, using different activation times (180 and 300 min). The complete characterization of all intermediate products of the processes, namely, raw material (tire), gasification products (char and syngas) and activation products (adsorbents, named Tirecarb), was performed. The adsorbents obtained from tire gasification were used to remove cadmium ions from aqueous solutions at 25 °C and pH 7. The experimental results showed that the higher the activation time, the higher the cadmium adsorption capacity. Experiments were carried out under the same conditions using a conventional activated carbon, and additional comparisons with other experimental results on Cd(II) adsorption on low-cost sorbents available in the relevant literature are also reported. In both cases, Tirecarb was found to show the highest cadmium adsorption capacity.

In this work, an array of deep passive wells filled with activated carbon, namely a Discontinuous Permeable Adsorptive Barrier (PAB-D), has been proposed for the remediation of an aquifer contaminated by tetrachloroethylene (PCE). The dynamics of the aquifer in the particular PAB-D configuration chosen, including the contaminant transport in the aquifer and the adsorption onto the barrier material, has been accurately performed by means of a computer code which allows describing all the phenomena occurring in the aquifer, simultaneously. A PAB-D design procedure is presented and the main dimensions of the barrier (number and position of passive wells) have been evaluated. Numerical simulations have been carried out over a long time span to follow the contaminant plume and to assess the effectiveness of the remediation method proposed. The model results show that this PAB-D design allows for a complete remediation of the aquifer under a natural hydraulic gradient, the PCE concentrations flowing out of the barrier being always lower than the corresponding Italian regulation limit. Finally, the results have been compared with those obtained for the design of a more traditional continuous barrier (PAB-C) for the same remediation process.

ABSTRACT This paper presents a theoretical and experimental study of cavitation as an advanced oxidation process. The degradation rate of p-nitrophenol (PNP) was experimentally investigated and used as an estimator of the sonochemical effect in hydrodynamic cavitation. The PNP initial concentration was varied in the range 0.1–1 g L−1 and the pressure in the range 0.2–0.7 MPa, with a corresponding flow rate of 3.5–6.9 L min−1. In terms of removal rate and energy efficiency, an optimal inlet pressure value was found close to 0.4 MPa and cavitation number of 0.25. The calculated first-order kinetic constant values show the existence of an optimal configuration: k = 1.13 × 10−2 min−1 at 0.45 MPa with a value for the electrical energy per order EEO = 66.7 kWh m−3. Moreover, the kinetic data was purged from the influence of the experimental apparatus configuration, allowing for the evaluation of an intrinsic kinetic constant. The physical–chemical behavior of hydrodynamic cavitation is discussed on the basis of single bubble dynamics. The numerical simulations, at different inlet pressures, provided a good explanation of the values observed. Furthermore, a simple energy balance on cavitating bubbles, taking into account for the actual production of cavitating events, gave a further confirmation of the experimental trends.