Mario Zilli

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.

Biogas production and valorization by means of a two-step biological process

The scope of this research work was to investigate biogas production and purification by a two-step bench-scale biological system, consisting of fed-batch pulse-feeding anaerobic digestion of mixed sludge, followed by methane enrichment of biogas by the use of the cyanobacterium Arthrospiraplatensis. The composition of biogas was nearly constant, and methane and carbon dioxide percentages ranged between 70.5-76.0% and 13.2-19.5%, respectively. Biogas yield reached a maximum value (about 0.4 m(3)(biogas)/kg COD(i)) at 50 days-retention time and then gradually decreased with a decrease in the retention time. Biogas CO(2) was then used as a carbon source for A. platensis cultivation either under batch or fed-batch conditions. The mean cell productivity of fed-batch cultivation was about 15% higher than that observed during the last batch phase (0.035+/-0.006 g(DM)/L/d), likely due to the occurrence of some shading effect under batch growth conditions. The data of carbon dioxide removal from biogas revealed the existence of a linear relationship between the rates of A. platensis growth and carbon dioxide removal from biogas and allowed calculating carbon utilization efficiency for biomass production of almost 95%.

Sugarcane bagasse as alternative packing material for biofiltration of benzene polluted gaseous streams: a preliminary study

Removal of benzene vapor from gaseous streams was studied in two identically sized lab-scale biofiltration columns: one filled with a mixture of raw sugarcane bagasse and glass beads, and the other one packed with a mixture of ground sugarcane bagasse and glass beads, in the same volume ratio, as filter materials. Separate series of continuous tests were performed, in parallel, under the same operating conditions (inlet benzene concentration of 10.0, 20.0 or 50.0 mg m(-3), and superficial gas velocity of 30.6, 61.2 or 122.4 m h(-1)) in order to evaluate and compare the influence of the packing material characteristics upon the biofilter effectiveness. The maximum elimination capacities obtained, at an inlet load of 6.12 g m(-3) h(-1), were 3.50 and 3.80 g m(-3)packibng material h(-1) with raw and ground sugarcane bagasse, respectively. This was a preliminary study and the results obtained suggest only a limited application with more work needed.

Toluene vapour removal in a laboratory-scale biofilter

Abstract A bench-scale biofilter with a 0.5-m high filter bed, inoculated with a toluene-degrading strain of Acinetobacter sp. NCIMB 9689, was used to study toluene removal from a synthetic waste air stream. Different sets of continuous tests were conducted at influent toluene concentrations ranging over 0.1–4.0 g m−3 and at superficial gas velocities ranging over 17.8–255 m h−1. The maximum volumetric toluene removal rate for the biofilter (242 g m−3 h−1) was obtained at a superficial gas velocity of 127.5 m h−1 (corresponding to a residence time of 28 s) and a toluene inlet concentration of 4.0 g m−3. Under these operating conditions, toluene removal efficiency was only 0.238, which suggested that effective operation required higher residence times. Removal efficiencies higher than 0.9 were achieved at organic loads less than 113.7 g m−3 h−1. A macro-kinetic study, performed using concentration profiles along the bioreactor, revealed this process was limited by diffusion at organic loads less than 100 g m−3 h−1 and by biological reaction beyond this threshold.

Macro-kinetic investigation on phenol uptake from air by biofiltration: Influence of superficial gas flow rate and inlet pollutant concentration.

The macro‐kinetic behavior of phenol removal from a synthetic exhaust gas was investigated theoretically as well as experimentally by means of two identical continuously operating laboratory‐scale biological filter bed columns. A mixture of peat and glass beads was used as filter material. After sterilization it was inoculated with a pure strain of Pseudomonas putida, as employed in previous experimental studies. To determine the influence of the superficial gas flow rate on biofilter performance and to evaluate the phenol concentration profiles along the column, two series of continuous tests were carried out varying either the inlet phenol concentration, up to 1650 mg · m−3, or the superficial gas flow rate, from 30 to 460 m3 · m−2 · h−1. The elimination capacity of the biofilter is proved by a maximum volumetric phenol removal rate of 0.73 kg · m−3 · h−1. The experimental results are consistent with a biofilm model incorporating first‐order substrate elimination kinetics. The model may be considered a useful tool in scaling‐up a biofiltration system. Furthermore, the deodorization capacity of the biofilter was investigated, at inlet phenol concentrations up to 280 mg · m−3 and superficial gas flow rates ranging from 30 to 92 m3 · m−2 · h−1. The deodorization of the gas was achieved at a maximum inlet phenol concentration of about 255 mg · m−3, operating at a superficial gas flow rate of 30 m3 · m−2 · h−1.

Treatment of benzene-contaminated airstreams in laboratory-scale biofilters packed with raw and sieved sugarcane bagasse and with peat

Three identical upflow laboratory-scale biofilters, inoculated with thebenzene-degrading strain Pseudomonas sp. NCIMB 9688 but filled up with different packing media (PM), specifically raw sugarcane bagasse, sieved sugarcane bagasse and peat, were employed to eliminate benzene from waste air. Biofilters performances were evaluated by continuous runs in parallel at different influent benzene concentrations, sequentially stepped up through three different superficial gas velocities (31, 61, and 122 m h-1). The peat-packed biofilter exhibited the best performances over the whole experimentation, ensuring removal efficiency of 100% for influent benzeneconcentrations ≤0.05 g m-3, regardless of the superficial gas velocity, and up to 0.4 g m-3 at 31 m h-1. Maximum elimination capacities ofbiofilters packed with raw and sieved sugarcane bagasse and with peat were 3.2, 6.4 and 26 g mPM-3 h-1 at 6.1, 12 and 31 g mPM-3 h-1 loading rates, resulting in 52, 53 and 84% removals, respectively. The bacterial concentrationdistribution along the medium was shown to depend on the benzene loading rate and a correlation between specific benzene elimination rate and biomass concentration was established for biofilters packed with sieved sugarcane bagasse and peat. The macrokinetics of the process were also studied using the profiles of benzene and biomassconcentrations, collected under different conditions over the height of both biofilters, and a zeroth-order kinetic model was shown to describe successfully the degradation process.

Mycelium-bound carboxylesterase from Aspergillus oryzae: an efficient catalyst for acetylation in organic solvent

Dry mycelium of a strain of Aspergillus oryzae efficiently catalyzed the esterification between free acetic acid and primary alcohols (geraniol and ethanol) in organic solvent. The growth conditions to obtain high activity of mycelium-bound enzymes were firstly evaluated. A medium containing Tween 80 as carbon source furnished mycelium with the highest activity in the hydrolysis of alpha-naphthyl esters (alpha-N-acetate, butyrate, caprylate). Dry mycelium was employed to select suited conditions for an efficient acetylation of ethanol and geraniol in heptane. Maximum productions were obtained using 30 g l(-)(1) of lyophilized cells: 12.4 g l(-)(1) of geranyl acetate were produced at 80 degrees C starting from 75 mM geraniol and acetic acid (84% molar conversion) and 4.1 g l(-)(1) of ethyl acetate at 50 degrees C from 50 mM ethanol and acetic acid (94% molar conversion) after 24 h. The stability of the mycelium-bound carboxylesterases are notable since only 10-30% loss of activity was observed after 14 days at temperatures between 30 and 50 degrees C.

Hydrogenolysis of organochlorinated pollutants: Kinetics and thermodynamics

Abstract Hydrogenolysis is one of the most promising innovating technologies because it allows the toxic organic chlorides to change quickly into their correspo

Metabolic study of the adaptation of the yeast Candida guilliermondii to sugarcane bagasse hydrolysate

Abstract. Batch xylitol production from concentrated sugarcane bagasse hydrolysate by Candida guilliermondii was performed by progressively adapting the cells to the medium. Samples were analyzed to monitor sugar and acetic acid consumption, xylitol, arabitol, ethanol, and carbon dioxide production, as well as cell growth. Both xylitol yield and volumetric productivity remarkably increased with the number of adaptations, demonstrating that the more adapted the cells, the better the capacity of the yeast to reduce xylose to xylitol in hemicellulose hydrolysates. Substrate and product concentrations were used in carbon material balances to study in which way the different carbon sources were utilized by this yeast under microaerobic conditions, as well as to shed light on the effect of the progressive adaptation to the medium on its fermentative activity. Such a theoretical means allowed estimation for the first time of the relative contribution of each medium component to the formation of the main products of this fermentation system.

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.