Saleh Al Arni

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.

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

Linearized kinetic models for the simulation of the mesophilic anaerobic digestion of pre-hydrolyzed woody wastes

The most common kinetic models available in the literature to describe the COD consumption during batch anaerobic digestion are checked and compared in their linearized forms in the case of prehydrolyzed mixtures simulating the composition of woody wastes. The introduction of the COD value at the end of batch digestion in both the First Order and the Monod models allows one to take into account the deviations due to the progressive increase in the fraction of difficultly-digestible substances present in the medium. The so-modified version of the First Order model as well as that proposed by Singh and co-workers not only show the best fits to the experimental data but also demonstrate that they are the simplest and easiest ones for immediate use.

Chlorella vulgaris as a lipid source: Cultivation on air and seawater-simulating medium in a helicoidal photobioreactor

The freshwater microalga Chlorella vulgaris was cultured batchwise on the seawater‐simulating Schlösser medium either in a 1.1‐L‐working volume helicoidal photobioreactor (HeP) or Erlenmeyer flask (EF) as control and continuously supplying air as CO2 source. In these systems, maximum biomass concentration reached 1.65 ± 0.17 g L−1 and 1.25 ± 0.06 g L−1, and maximum cell productivity 197.6 ± 20.4 mg L−1 day−1 and 160.8 ± 12.2 mg L−1 day−1, respectively. Compared to the Bolds Basal medium, commonly employed to cultivate this microorganism on a bench‐scale, the Schlösser medium ensured significant increases in all the growth parameters, namely maximum cell concentration (268% in EF and 126% in HeP), maximum biomass productivity (554% in EF and 72% in HeP), average specific growth rate (67% in EF and 42% in HeP), and maximum specific growth rate (233% in EF and 22% in HeP). The lipid fraction of biomass collected at the end of runs was analyzed in terms of both lipid content and fatty acid profile. It was found that the seawater‐simulating medium, despite of a 56–63% reduction of the overall biomass lipid content compared to the Bolds Basal one, led in HeP to significant increases in both the glycerides‐to‐total lipid ratio and polyunsaturated fatty acid content compared to the other conditions taken as an average. These results as a whole suggest that the HeP configuration could be a successful alternative to the present means to cultivate C. vulgaris as a lipid source.

Doxycycline Degradation by the Oxidative Fenton Process

Doxycycline is a broad-spectrum tetracycline occurring in domestic, industrial, and rural effluents, whose main drawback is the increasing emergence of resistant bacteria. This antibiotic could be degraded by the so-called Fenton process, consisting in the oxidation of organic pollutants by oxygen peroxide (H2O2) in the presence of Fe2

Adsorption of inorganic mercury from aqueous solutions onto dry biomass of Chlorella vulgaris: kinetic and isotherm study

ABSTRACT This study focused on kinetics and equilibrium isotherms of mercury biosorption from water using dry biomass of Chlorella vulgaris as biosorbent at pH 5.0. Biosorption tests were performed at 2.0 g/L biomass dosage varying initial Hg concentration from 11.0 to 90.6 mg/L. The Lagergren equation was found to best describe the process, with R2 of 0.984 and specific rate constant of 0.029 ± 0.004 min−1. Although equilibrium data were well fitted by the Dubinin and Radushkevich isotherm (R2 = 0.870; qDR = 16.6 mg/g), important insights on phenomenological events occurring at equilibrium were concurrently provided by the Lamgmuir one (R2 = 0.826; q0 = 32.6 mg/g; KL = 0.059 L/mg). FT-IR analysis confirmed that Hg biosorption took place via physisorption. Since C. vulgaris is a fresh-water microalga that can be easily cultivated anywhere, these promising results suggest its possible use as an effective, low-cost biosorbent to treat industrial effluents contaminated by this metal. GRAPHICAL ABSTRACT