Marco Del Borghi

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.

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.

Co-digestion of municipal sewage sludges and pre-hydrolysed woody agricultural wastes.

Material balance has been used to evaluate the COD behaviour and the time required for fed-batch digestion of mixtures of domestic sludges and pre-hydrolysed agricultural wastes. Pre-hydrolysis of the feed materials has been used to penetrate the strong lignocellulosic structure of these wastes as well as to increase the fraction of soluble organic substances in the mixture. The influence of the organic loading rate on the main process parameters (methane, carbon dioxide, total biogas productions and their respective conversion yields) has also been investigated. The organic load has been varied from 0.8 up to 6.1 g COD dm -3 day -1 , corresponding to a range of volatile solids load of 0.6-4.5 g vs dm -3 day -1 for the material under consideration. These values are slightly higher than those usually employed in conventional digester for domestic sewage sludges. However, methane production reached a maximum rate of only 5.6 mmol dm -3 day -1 at an organic loading rate of 4.6 g COD dm -3 day -1 , while both CH 4 content and production of biogas rapidly fell over 2.2 g COD dm -3 day -1 . On the whole, these results suggest that removal of lignin is necessary in order to carry out the continuous anaerobic digestion of pre-hydrolysed agricultural wastes rich in woody materials.

Simultaneous effects of immobilization and substrate protection on the thermodynamics of glucose isomerase activity and inactivation

The influence of enzyme immobilization on the main thermodynamic quantities of glucose isomerization to fructose and vice versa was studied in batch tests by using a commercial immobilized glucose isomerase. The values calculated for the immobilized system showed, when compared with those reported for the native enzyme, higher equilibrium constants at T > 70°C and simultaneous increases in both standard enthalpy and entropy changes of reaction. Activation enthalpy and entropy changes of both forward and reverse enzyme-catalyzed reactions were calculated from the initial glucose isomerase activity evaluated at different temperatures by the Briggs-Haldane model. The activation enthalpy of the forward reaction was about 24% less than that of the native enzyme. Enzyme inactivation tests performed at different temperatures and sugar equilibrium concentrations confirmed the existence of the so-called substrate protection phenomenon which resulted in a 29–36% reduction in the decay constant. A slight increase in the activation free enthalpy of the inactivation reaction was also shown.

Biological removal of phosphorus from wastewaters by alternating aerobic and anaerobic conditions

Abstract A new process alternating aerobic and anaerobic conditions has been tested for continuous removal of phosphorus from wastewaters. Preliminary batch runs have been carried out at different temperatures (5 ÷ 35°C) to study the effect of stress related to changes of temperature, inoculating a synthetic medium with the biomass from the same plant operating in continuous mode. The continuous system, which appeared capable of ensuring phosphorus removals higher than 90% at relatively high phosphate levels, is now studied mainly during the transitions between aerobic and anaerobic stages. The present results show, for the first time, a direct influence of dissolved oxygen level on pH and allow reasonable hypotheses on the mechanisms for both carbon and phosphorus routes.

Improvement of Alcohol Fermentation of a Corn Starch Hydrolysate by Viscosity-Raising Additives

Aim of this work is to investigate the simultaneous effects of viscosity and temperature on the productivity of the alcohol fermentation of starch hydrolysate by Saccharomyces cerevisiae. Batch fermentations have been carried out at given pH, broth composition, inoculum, and agitation intensity, but at varying temperature (24<T<46 °C) or concentration of carboxymethyl cellulose (0.4< C CMC < 2.0 g/L), chosen as viscosity-raising additive. The results of tests carried out at given viscosity demonstrate that the volumetric productivity increases with temperature up to an optimal value (32-36°C). At higher temperatures a productivity drop occurs. In addition, a viscosity increase up to about 12 g m -1 s -1 (value determined at 30 °C) improves the fermentation kinetics, while the process is strongly negatively affected at viscosity values higher than this threshold. Both the Arrhenius and the so-called thermodynamic models have then been used to estimate the related thermodynamic quantities referred to both fermentation and thermal deactivation. A comparison of the values of these quantities suggests that both cell growth repression provoked by mass transfer limitations due to viscosity rise and the reduction of product inhibition are possible simultaneous causes of the observed productivity enhancement at low CMC levels.

Influence of nutrient concentration in new operating criteria for biological removal of phosphorus from wastewaters

Abstract The actual practicability of biological treatment of effluents heavily polluted by phosphoric compounds is evaluated in this paper. Preliminary batch tests have shown that high COD levels inhibit phosphorus release during anaerobic conditions but allow, at the same time, a more efficacious removal during the subsequent aerobic stage. Removal yields exceeding 60% have been calculated for an influent COD level of about 840 mg/l. The A/O process, suitably modified so as to alternate aerobic and anaerobic phases in the same reactor, has been tested for the biological removal of phosphorus in synthetic wastewaters with high phosphate concentrations. The start-up phase, carried out with a synthetic solution having a starting phosphorus concentration of 10 mg/l, showed average phosphate and COD removals of 78 and 90%, respectively. The results obtained after reaching steady-state conditions, by feeding P concentrations up to 100 mg/l, seem to indicate this process as an excellent means of reducing phosphorus emissions into the environment and therefore may contribute to the solution of eutrophication-related problems. Removals higher than 90% have been assured for wastewaters containing phosphate levels up to 70 mg/l; at higher concentrations, the system proved capable of tolerating phosphate overloading for no more than 10 days; yield then rapidly fell to zero.

Estimation of viscosity of highly viscous fermentation media containing one or more solutes

Abstract Viscosity and density data are collected at different temperatures for aqueous solutions of glucose, carboxymethyl cellulose (CMC), or both the solutes and used to check the form of a predictive model proposed in this study for viscosity estimation of mixtures of non-electrolyte solutes in Newtonian fermentation broths. The model, which derives from the well-known Guzman–Andrade equation and is based on the Eyring theory, supposes a separate contribution of each solute to total viscosity, which linearly increases with solute concentration and exponentially decreases with temperature. Percentage deviations between theoretical and experimental viscosity values of both, the binary and ternary mixtures, are usually

Inhibition of the fermentation of oak hemicellulose acid-hydrolysate by minor sugars

Synthetic xylose media and detoxified oak hemicellulose acid-hydrolysates with different starting xylose contents were fermented batchwise by two strains of Pachysolen tannophilus. Maximum productivities were calculated from the experimental data of ethanol concentration using a graphical procedure. The kinetic parameters calculated for the fermentations of both carbon sources indicate that a competitive inhibition is exerted by the minor sugars (arabinose, rhamnose, and galactose) that are metabolised only slowly or not at all.

Treatment of effluent containing micropollutants by means of activated carbon

Different amounts of granular activated carbon (GAC) have been tested for the removal of aliphatic and aromatic micropollutants contained in a liquid stream coming from an industrial plant. Tests have been carried out in a JAR-Test apparatus, using plugged flasks, in order to eliminate the oxygen influence on the adsorption process and to obtain information for studying the process in a pilot plant. The removal of aliphatic compounds resulted better than aromatic ones, probably because these substances are enveloped by water molecules which make adsorption on the GAC surface easier; in contrast, aromatic compounds show a lower affinity for the GAC, owing to their steric conformation. The good results obtained confirm that the proposed system is applicable to the examined effluent, even when the concentration of the pollutant load varies. In the latest part of this work, a plan for the construction of a full-scale plant to treat the examined wastewater has been developed.