Carlo Solisio

Bioleaching of zinc and aluminium from industrial waste sludges by means of Thiobacillus ferrooxidans.

Biological solubilisation of heavy metals contained in two different kinds of industrial wastes was performed in batches employing a strain of Thiobacillus ferroxidans. The wastes tested were: a dust coming from the iron-manganese alloy production in an electric furnace (sludge 1) and a sludge coming from a process treatment plant of aluminium anodic oxidation (sludge 2). The experimental results pointed out the ability of the used strain to maintain the environment, that initially has a pH about 8, at strongly acid conditions (pH 2.5-3.5), producing sulphuric acid that is the chemical agent responsible for the metals solubilisation. At wastes initial concentration of 1%, the percentage of solubilised metals was 76 and 78% for the wastes 1 and 2, respectively, but the lag phase was considerably longer for sludge 2 than for sludge 1, indicating a different affinity of microorganisms for the solid phase. Increasing the initial slurry concentration, the percentage of removed metal reached 72-73% for the sludge 1, while in case of sludge 2, the total amount of solubilized metal progressively decreased. Two kinetic models are proposed to describe the trends of metals solubilization curves.

Cadmium, Zinc, Copper, Silver and Chromium(III) removal from wastewaters by Sphaerotilus natans

Abstract Living cells of Sphaerotilus natans are used for heavy metals (Cd, Zn, Cu, Ag, and Cr) removal from aqueous solutions simulating the polluting power of acid industrial wastewaters. At low metal concentrations (<25 mg/l) this microorganism is able to remove within 8–15 days Cd, Zn, Cu, and Ag with excellent yields (from 81 to 99%) often increasing with starting metal concentration. The yield observed for Cr(III) removal, never exceeding 60%, is not appreciably influenced by the starting biomass level; in addition, the time necessary to reach the equilibrium concentration is always remarkably longer (>30 days) than for the other metals. At much higher concentrations, the removal of all the metals is strongly affected in terms of both yield reduction and increase in the time necessary to reach the equilibrium concentrations. Under the hypothesis of mass transfer limitation, the kinetic study of batch runs suggests that metal diffusion from the bulk to the surface of S. natans clumps could be responsible not only for the simple biosorption of the tested metallic micronutrients or abiotic metals, but even for the cell penetration by ions of biological significance, like Mg2+ and Fe3+.

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.

Effects of pH on chromate(VI) adsorption by Spirulina platensis biomass: batch tests and FT-IR studies

Raw and methylated biomass of Spirulina platensis was employed in chromate batch adsorption tests at pH range 1-7. The acid conditions seemed to favour the removal of chromium (Cr) with a yield of 87.0 and 97.6% by using raw and methylated biomass, respectively. However, the chromate and total chromium determination, carried out in the same sample, evidenced that a fraction of the initial chromate present in solution was reduced to Cr(III). This was ascribed to the presence of reducing groups on the biomass surface, active in the acid medium. The data showed that the methylated biomass was able to operate an effective Cr(VI) removal only. In fact, the biomass treatment allowed a lowering of the amount of negative functional groups, making the biomass surface available to bind the anions. The real best efficiency of Cr(VI) removal (83.5%) was obtained by methylated biomass of S. platensis at pH about 7.0. The nature of the biomass/chromate interactions was investigated by Fourier transform infrared spectroscopy (FT-IR) analysis. The bands ascribing to the adsorbed Cr(VI) species were well evident in the spectra of the biomass after adsorption, confirming this experimental finding.

The anaerobic digestion of surplus activated sludge in a fixed-film bioreactor

Abstract It is necessary to identify the best operating conditions of the reactor to achieve a satisfactory performance of an anaerobic digester. This paper discusses the performance of a particular fixed-film bioreactor with sponges as support. This evaluation was made at laboratory scale through a comparison between a fixed-film bioreactor and a conventional continuous stirred tank reactor (CSTR). The results show good reactor productivity as well as satisfactory sludge stabilization.

Influence of Temperature on Cadmium Removal by Sphaerotilus natans from Acidic Solutions

A culture of Sphaerotilus natans (NCIMB 11196) was used for cadmium removal from acidic solutions, simulating the composition of industrial wastewaters. Tests were carried out at temperatures increasing from 15 up to 40°C, to check the actual possibility of utilizing a biological system to remove this heavy metal from water as well as to shed light on the phenomenon responsible for its uptake. The highest values of the specific growth rate of this microorganism (µ max = 0.11 to 0.13 h− 1) and cadmium removal rate (k r = 0.15 h− 1) were obtained within 25 to 30°C. Under these conditions, biomass was able to increase the pH of the medium from 4.0 up to 7.0 to 7.8. The data of µ max and k r collected at different temperatures were finally used to estimate, according to Arrhenius, the thermodynamic parameters of cell growth and cadmium removal as well as of the related thermal inactivations. On the basis of these results, cadmium seemed to be removed by S. natans following a mechanism controlled by cell growth, implying the quick electrostatic attraction of ions to the negative charges present on the cell surface.

Removal of bivalent and trivalent ions by Spirulina platensis biomass: batch experiments and biosorbent characterisation

The removal of cadmium and chromium, at comparable initial molar concentration (1, 2, 4 mM) has been studied employing progressively increasing concentrations of S. platensis dry biomass. The highest yield of Cd removal (≥98%) was obtained with 2 g l−1 of this biosorbent, whereas no more than 77.5% of Cr was removed with 4 g l−1 biomass. The FT-IR analysis evidenced that the ions removal occurs by interaction mainly between metal and carboxylate groups present on the cell wall. Moreover, whereas Cd was also bound with the OH and amide groups, Cr interacted preferentially with OH groups.

Spirulina platensis BIOMASS AS ADSORBENT FOR COPPER REMOVAL BIOMASA DE Spirulina platensis COMO ADSORBENTE PARA LA ELIMINACIÓN DE COBRE

Abstract Dry biomass of Spirulina platensis was used as biosorbent for copper removal from water. Because of the limited uptake capability shown when used in this condition, this material was subject to pre-hydration for 24 h before use. The results of these tests demonstrate that biomass pre-hydration allowed for an increase in metal removal yield from 0.81 to 0.91. Additional tests were also performed at variable starting concentrations either of biomass or copper with the aim of optimizing the adsorption process of this metal. Copper was almost entirely removed at the lowest metal concentration (Cuo = 0.1 g/L) when using relatively high starting biomass levels (X o ≥ 2.0 g/L), whereas the removal yield appreciably decreased with increasing Cuo and decreasing X o , respectively. These results could be useful to design a process for real-scale copper removal from spent lees from distilleries, before sending it to conventional wastewater treatment. Resumen La biomasa desecada de Spirulina platensis fue usada como biosorbente para la eliminación del cobre en el agua. Debido a la pequeña capacidad de eliminación cuando se usa en ese estado, el material fue sometido a prehidratación por 24 horas antes de ser usado. Los resultados de las pruebas demuestran que la biomasa prehidratada permitió incrementar el rendimiento de eliminación desde 0,81 hasta 0,91. Pruebas adicionales fueron efectuadas a concentraciones variables de biomasa y de cobre con el objetivo de optimizar el proceso de adsorción de este metal. El cobre fue casi totalmente eliminado a la concentración de metal más baja (Cuo = 0,1 g/L) cuando se usaron concentraciones de biomasa relativamente elevadas (X o ≥ 2,0 g/L), mientras el rendimiento de remoción bajó significativamente incrementando Cuo y disminuyendo X o , respectivamente. Estos resultados podrian ser útiles para diseñar un proceso de eliminación en escala real del cobre contenido en las lias residuales de destilerías, antes de enviarlas para el tratamiento tradicional de los efluentes. Palabras clave: Cobre, eliminación metales pesados, biosorción, Spirulina platensis, biomasa desecada

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

A Maximum Likelihood-based Method for the Nonlinear Estimation of Equilibrium Adsorption Parameters

Adsorption technologies are widely employed in many important separation processes, especially in fine chemistry and environmental control. Thus, the increasing pressure for cost reduction in the operation of industrial plants, which calls for the use of efficient design techniques based on scientifically advanced methods, has led to the development of sophisticated physical chemical models for the description of adsorption equilibrium parameters. To account for the complex phenomena that take place at the microscopic level in the adsorption process, the most recently developed models require the estimation of a number of parameters higher than the ones present in the traditional Langmuir and Freundlich models. On the other hand, the presence of an increased number of strongly correlated parameters requires the use of suitable statistical methods for the information contained in the experimental results to be utilized efficiently. In this article we present a method that generalizes previous identification procedures to complex models containing an arbitrary number of parameters. The sensitivity of the resulting estimates on error distributions assumed and theoretical models chosen is examined using both simulated and experimental data.