E. Palazzi

Toluene and styrene removal from air in biofilters

Abstract Two identical sized laboratory-scale biofilters, filled with the same type of packing material, consisting of a mixture of peat and glass beads in a 4:1 volume ratio, are investigated for the purification of toluene and styrene-containing off-gas streams. One of the biofilters was inoculated with a toluene-degrading strain of Acinetobacter sp. NCIMB 9689, and the other with a styrene-degrading strain of Rhodococcus rhodochrous AL NCIMB 13259. For both pollutants, different sets of continuous experiments were conducted in the biofilter columns, varying both the inlet pollutant concentration and the superficial gas velocity. Maximum elimination capacities of 242 and 63 g m packing material −3 h −1 packing material were recorded for toluene and styrene, respectively. Furthermore, the deodorization (defined as the achievement of a pollutant concentration in the effluent gas below the pollutant olfactory threshold value) of toluene and styrene-containing waste-gases was also considered. This was achieved, operating at maximum inlet concentrations of 1.99 and 0.20 g m −3 and at superficial gas velocities of 17.8 and 122 m h −1 , respectively.

A framework for risk assessment and decision-making strategies in dangerous good transportation

The risk from dangerous goods transport by road and strategies for selecting road load/routes are faced in this paper, by developing an original site-oriented framework of general applicability at local level. A realistic evaluation of the frequency must take into account on one side inherent factors (e.g. tunnels, rail bridges, bend radii, slope, characteristics of neighborhood, etc.) on the other side factors correlated to the traffic conditions (e.g. dangerous goods trucks, etc.). Field data were collected on the selected highway, by systematic investigation, providing input data for a database reporting tendencies and intrinsic parameter/site-oriented statistics. The developed technique was applied to a pilot area, considering both the individual risk and societal risk and making reference to flammable and explosive scenarios. In this way, a risk assessment, sensitive to route features and population exposed, is proposed, so that the overall uncertainties in risk analysis can be lowered.

Fermentation of hardwood hemicellulose hydrolysate byPachysolen tannophilus, candida shehatae andPichia stipitis

SummaryHardwood hemicellulose hydrolysate has been utilized as a substrate for ethanol production. Among the three different yeasts tested, the best performances have been obtained, in decreasing order, usingPachysolen tannophilus, Candida shehatae andPichia stipitis. Several pretreatments of this raw material have been studied to improve ethanol yields; in one such pretreatment a strain ofP. tannophilus produced ethanol with a yield of 0.29 gethanol/gsugars (gP/gS); which is only 15% less than the values observed with synthetic media. Neither aeration nor acetone addition improved the fermentation of this substrate; in fact, only a marked stimulation of biomass growth has been observed at the expense of both ethanol and xylitol production.

Process development of continuous hydrogen production by Enterobacter aerogenes in a packed column reactor

Abstract Hydrogen bioproduction from agro-industrial residues by Enterobacter aerogenes in a continuous packed column has been investigated and a complete reactor characterization is presented. Experimental runs carried out at different residence time, liable of interest for industrial application, showed hydrogen yields ranging from 1.36 to 3.02 mmolH2mmol−1glucose or, in other words, from 37.5% to 75% of the theoretical hydrogen yield. A simple kinetic model of cell growth, validated by experimental results and allowing the prediction of biomass concentration profile along the reactor and the optimization of superficial velocity, is suggested. By applying the developed approach to the selected operative conditions, the identification of the optimum superficial velocity v0,opt of about 2.2 cm h−1 corresponding to the maximum hydrogen evolution rate H˙2g,max, was performed.

Evaluation of diffusional resistances in the process of glucose isomerization to fructose by immobilized glucose isomerase

A kinetic model presented in a previous work is employed to carry out a systematic study dealing with the relative importance of intraparticle and interparticle diffusional resistances in the process of glucose isomerization to fructose by immobilized glucose isomerase. An analytical generalized expression of the effectiveness factor is obtained, which promises to be particularly useful for design purposes. Finally, the role of each of the main parameters influencing the catalyst effectiveness factor is put in evidence and discussed within the whole range of possible operative conditions.

Generalized linearization of kinetics of glucose isomerization to fructose by immobilized glucose isomerase.

The kinetic parameters of both glucose isomerization to fructose and immobilized glucose isomerase (GI) inactivation calculated under different conditions are compared and discussed. Utilizing these figures, the possibility of generalizing a linear model, previously proposed for the kinetics of glucose isomerization by immobilized glucose isomerase, is investigated, so as to apply them to whole ranges of temperature and concentrations of actual interest in industrial processes. The proposed model is a satisfactory approximation of the more involved Briggs-Haldane approach and substantially simplifies the problem of optimizing an industrial fixed-bed column for high-fructose corn syrup (HFCS) production.

Simplified kinetics and thermodynamics of geraniol acetylation by lyophilized cells of Aspergillus oryzae

Kinetics and thermodynamics of geranyl acetate production by direct geraniol acetylation with lyophilized cells of Aspergillus oryzae were studied in n-heptane and compared with those of ethanol acetylation. Batch tests were performed varying the starting substrates equimolar level from 25 to 150 mM, the cell concentration from 5.0 to 30 g l−1, and the temperature from 30 to 95°C. The progressive increase in the starting product formation rate observed with increasing temperature up to 80°C and the successive fall beyond this value confirmed the occurrence of reversible biocatalyst inactivation. The simplified Arrhenius model was used to estimate the apparent activation enthalpies of both the acetylation of geraniol (ΔH# = 35 kJ mol−1) and the reversible inactivation of the biocatalyst (ΔH#i = 150 kJ mol−1). The thermodynamic parameters of the irreversible enzyme denaturation were also estimated by residual activity tests performed on lyophilized cells previously exposed in the solvent at different temperatures for variable times (ΔH#d = 28 kJ mol−1; ΔS#d = −0.28 kJ mol−1 K−1). These results on the whole suggest that the reversible inactivation and the irreversible denaturation of mycelium-bound carboxylesterases are thwarted by increases either in the hydrophobicity or in the molecular weight of the alcoholic substrate.

Mathematical modelling and optimization of hydrogen continuous production in a fixed bed bioreactor

The purpose of this paper is to investigate, both theoretically and experimentally, hydrogen production from agro-industrial by-products using a continuous bioreactor packed with a mixture of spongy and glass beads and inoculated with Enterobacter aerogenes. Replicated series of experimental runs were performed to study the effects of residence time on hydrogen evolution rate and to characterize the critical conditions for the wash out, as a function of the inlet glucose concentration and of the fluid superficial velocity. A further series of experimental runs was focused on the effects of both residence time and inlet glucose concentration over hydrogen productivity. A kinetic model of the process was developed and showed good agreement with experimental data, thus representing a potential tool to design a large-scale fermenter. In fact, the model was applied to the optimal design of a bioreactor suitable of feeding a phosphoric acid fuel cell of a target power.

Influence of process variables on the modelling and design of a rotating biological surface

Abstract An investigation of the Rotating Biological Surface (RBS) process variables to determine the efficiency of BOD 5 removal from wastewater is presented. Operating parameters including influent substrate concentration, liquid retention time, stage temperature, flow rate, disk surface area, hydraulic loading, disk rotational speed, disk sizes, number of disks, fractional submergence, were evaluated. The process parameters were obtained from a pilot scale RBS plant constructed and applied to the treatment of municipal and industrial wastewater and from the literature. The data were employed to determine a kinetic equation of general application, whch tends to the well-known Michaelis-Menten equation for municipal wastewater and easily degradable substrates. The study shows that influent BOD 5 concentration, the type of substrate, hydraulic loading, stage number and wastewater temperature are the most significant variables predicting the RBS system performance. The model presently developed was verified by field data concerned with the treatment of domestic and low strength industrial wastewater. The obtained model for urban wastewater cannot be applied to high strength industrial wastewaters where poorly biodegradables substrates are present together with easily degradable substrates. The situation has been verified by treating straw paper and tannery wastewaters. For those substrates a more complex equation has been obtained that becomes the Michaelis-Menten type equation at high values of a BOD fraction in the effluent.

Ethanol acetylation by mycelium-bound carboxylesterase of Aspergillus oryzae: estimation of thermodynamic parameters and integral productivity

The results collected at different temperatures for ethanol acetylation by cell-bound carboxylesterase from lyophilized cells of Aspergillus oryzae have been used to investigate the kinetics and thermodynamics of this esterification in n-heptane. The occurrence of reversible unfolding followed by irreversible denaturation of the enzyme has been proposed to explain the increase in the starting rate of ethyl acetate formation with temperature observed up to 55 °C and the consequent fall beyond this threshold. The Arrhenius model has been used to estimate the apparent activation enthalpies of both the acetylation reaction (ΔH≠ = 29–33 kJ mol−1) and reversible enzyme unfolding (ΔH≠u = 56–63 kJ mol−1). The results of residual activity tests performed with cells previously exposed at different temperatures for variable times enabled us also to estimate the first-order rate constant of irreversible denaturation (2.40 × 10−3 h−1 < kd < 8.11 × 10−3 h−1) as well as the related thermodynamic parameters (ΔH≠d = 22 kJ mol−1; ΔS≠d = −0.29 kJ mol−1 K−1). This last phenomenon proved particularly slow for the system under consideration, probably because the biocatalyst link to the mycelium was able to improve its thermostability. In view of future continuous application, the effects of operating time, starting substrate concentration and temperature on the theoretical integral productivity of a fixed-bed column filled with this biocatalyst have been investigated.