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Hydrotreating catalysts (HTCs) are a waste byproduct of the petroleum refining industry. The recovery of intrinsic and sorbed metals from spent catalysts is desirable for meeting environmental disposal regulations, as well as for the metal resell value. In this study, innovative process schemes for metal recovery from end-of-life (i.e., spent) HTCs were tested in laboratory experiments and compared by process analysis. Synthetic leach liquors containing Al, Mo, Ni, and V were prepared resembling both chemical leaching and bioleaching methods for metal extraction from spent catalysts. Subsequently, metals in the leach liquor were recovered individually according to two pH-dependent process schemes: (i) Mo and Ni were separated first and Al was removed last, and (ii) Al was removed first. The second metal separation process gave the best results in terms of selectivity, whereby 65% of Al was recovered by precipitation at pH 4.0, 87% of Mo was precipitated by sulfide addition at pH 0.5, 52% of Ni was precipitated by sulfide addition at pH 3.5, and 65% of V was recovered by hydroxide complexation at pH 6.0. Experimental data of metal precipitation were used to perform a process analysis comparing chemical leaching and bioleaching for different input flow rates and product depreciation in a simulated commercial-scale plant. Simulation results indicate that chemical leaching is of superior performance over biological leaching in terms of metal recovery, which decrease the payback time for the capital investment to build the plant. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 703–712, 2015

Background A major obstacle to the application of microalgae for bio-fuel production is light intensity reduction in high density cultures. Mixotrophic operation can solve this problem by exploiting the ability of microalgae to grow on organic carbon in dark conditions. In this article, mixotrophic growth of Nannochloropsis oculata and Chlorella vulgaris is analyzed. The influence of nitrate and glucose concentration on cell growth in 300 mL Erlenmeyer flasks was investigated using an experimental factorial design. The analysis was extended and validated by analyzing mixotrophic growth in a 6 L bubble column. Results The addition of glucose at concentration 0.1 g L-1 inhibited or enhanced the growth of Chlorella depending on nitrate concentration, while it increased the growth rate of Nannochloropsis at all nitrate concentrations tested. Statistically significant interaction between glucose and nitrate concentration was revealed for Chlorella; negligible interaction was found for Nannochloropsis. A kinetic characterization, shedding light on the influence of glucose on microalgal growth, was conducted through identification of a Monod-like model. Experimental tests in 6 L bubble column confirmed for both Chlorella and Nannochloropsis the possibility to significantly enhance growth in the presence of light deficiency through mixotrophic operation. Conclusions Mixotrophic growth is governed by the interaction between organic carbon and nitrogen. This can have a profound impact on kinetic modeling of microalgal growth and on the operation of cultivation systems. Controlling the C/N ratio is in particular fundamental to optimize reactor operation. © 2013 Society of Chemical Industry

BACKGROUND: In this study a comparison between two continuously operating fixed-bed column systems was performed in order to select the best operating conditions in terms of organic sources for sulphate reducing bacteria (SRB). The first column system (solid substrate, SS) was filled with a solid reactive mixture containing the organic matter necessary for SRB growth, while the second one (liquid substrate, LS) was filled with inert material and continuously fed by ethanol. RESULTS: In the SS column 50 ± 10% sulphate abatement was reached at steady state, while metals were totally removed. Blank tests showed that biosorption was mainly responsible for both sulphate and metal removal. In the LS column, sulphate abatement was 70 ± 10% at steady state against 10 ± 5% of an identical column without inoculum (blank liquid substrate, BLS). Comparison with BLS showed that the main mechanism operating in this system was bioprecipitation. Estimated degradation rate constants for both SS and LS columns indicate similar performances (0.008 ± 0.001 and 0.0085 ± 0.0005 d ―1 for SS and LS, respectively). CONCLUSIONS: LS column systems offer a valid alternative to conventional SS systems, avoiding the use of potentially harmful wastes as organic sources for SRB metabolism.

Experimental runs on the inversion of sucrose by means of immobilized beta-fructooxidase are reported. External mass-transfer and axial dispersion phenomena have been analyzed. It has been observed that external mass-transfer plays a significative role in the overall kinetics, while axial dispersion phenomena are negligible.