Filomena Costa

Kinetics of biodegradation of diethylketone by Arthrobacter viscosus

The performance of an Arthrobacter viscosus culture to remove diethylketone from aqueous solutions was evaluated. The effect of initial concentration of diethylketone on the growth of the bacteria was evaluated for the range of concentration between 0 and 4.8xa0g/l, aiming to evaluate a possible toxicological effect. The maximum specific growth rate achieved is 0.221xa0h−1 at 1.6xa0g/l of initial diethylketone concentration, suggesting that for higher concentrations an inhibitory effect on the growth occurs. The removal percentages obtained were approximately 88%, for all the initial concentrations tested. The kinetic parameters were estimated using four growth kinetic models for biodegradation of organic compounds available in the literature. The experimental data found is well fitted by the Haldane model (R2xa0=xa01) as compared to Monod model (R2xa0=xa00.99), Powell (R2xa0=xa00.82) and Loung model (R2xa0=xa00.95). The biodegradation of diethylketone using concentrated biomass was studied for an initial diethylketone concentration ranging from 0.8–3.9xa0g/l in a batch with recirculation mode of operation. The biodegradation rate found followed the pseudo-second order kinetics and the resulting kinetic parameters are reported. The removal percentages obtained were approximately 100%, for all the initial concentrations tested, suggesting that the increment on the biomass concentration allows better results in terms of removal of diethylketone. This study showed that these bacteria are very effective for the removal of diethylketone from aqueous solutions.

Bioremoval of diethylketone by the synergistic combination of microorganisms and clays: uptake, removal and kinetic studies

The performance of two bacteria, Arthrobacter viscosus and Streptococcus equisimilis, and the effect of the interaction of these bacteria with four different clays on the retention of diethylketone were investigated in batch experiments. The uptake, the removal percentages and the kinetics of the processes were determined. S. equisimilis, by itself, had the best performance in terms of removal percentage, for all the initial diethylketone concentrations tested: 200, 350 and 700xa0mg/L. The uptake values are similar for both bacteria. A possible mechanism to explain the removal of diethylketone includes its degradation by bacteria, followed by the adsorption of the intermediates/sub-products by the functional groups present on the cells surfaces. The assays performed with bacteria and clays indicated that the uptake values are similar despite of the clay used, for the same microorganism and mass of clay, but in general, higher values are reached when S. equisimilis is used, compared to A. viscosus. Kinetic data were described by pseudo-first- and pseudo-second-order models.

Vermiculite bio-barriers for Cu and Zn remediation: an eco-friendly approach for freshwater and sediments protection

The increase in heavy metal contamination in freshwater systems causes serious environmental problems in most industrialized countries, and the effort to find eco-friendly techniques for reducing water and sediment contamination is fundamental for environmental protection. Permeable barriers made of natural clays can be used as low-cost and eco-friendly materials for adsorbing heavy metals from water solution and thus reducing the sediment contamination. This study discusses the application of permeable barriers made of vermiculite clay for heavy metals remediation at the interface between water and sediments and investigates the possibility to increase their efficiency by loading the vermiculite surface with a microbial biofilm of Pseudomonas putida, which is well known to be a heavy metal accumulator. Some batch assays were performed to verify the uptake capacity of two systems and their adsorption kinetics, and the results indicated that the vermiculite bio-barrier system had a higher removal capacity than the vermiculite barrier (+34.4 and 22.8xa0% for Cu and Zn, respectively). Moreover, the presence of P. putida biofilm strongly contributed to fasten the kinetics of metals adsorption onto vermiculite sheets. In open-system conditions, the presence of a vermiculite barrier at the interface between water and sediment could reduce the sediment contamination up to 20 and 23xa0% for Cu and Zn, respectively, highlighting the efficiency of these eco-friendly materials for environmental applications. Nevertheless, the contribution of microbial biofilm in open-system setup should be optimized, and some important considerations about biofilm attachment in a continuous-flow system have been discussed.

Biodegradation of Diethylketone by Penicillium sp. and Alternaria sp. - A Comparative Study Biodegradation of Diethylketone by Fungi

Two contaminating fungi were isolated from a bioreactor containing diethylketone and Streptococcus equisimilis, subsequently characterized at molecular level and identified as belonging to the Alternaria and Penicillium genera. The ability of these fungi to biodegrade DEK is evaluated. The kinetic parameters are estimated using four growth kinetic models for biodegradation of organic com- pounds available in literature. The experimental data for Alternaria sp. and Penicillium sp. was found to be better fitted by the Haldane and the Luong respectively. Biodegradation rate kinetics was evalu- ated using zero-order, pseudo-first order, pseudo-second order and three-half order models. The pseudo-second-order model was found suitable for all the concentrations of DEK tested for the biodeg- radation assays using Penicillium sp. whereas for the Alternaria sp. this model just describes properly the assays with ini- tial concentrations of DEK higher than 0.5 g/L. The percentage of biodegraded DEK were approximately 100%, for all the initial concentrations tested.

Sorption studies of diethylketone in the presence of Al3+, Cd2+, Ni2+ and Mn2+, from lab-scale to pilot scale

ABSTRACT The toxic effects of diethylketone (DEK) in aqueous solution with different concentrations of Al3+, Cd2+, Ni2+ and Mn2+ were evaluated at lab-scale. It was established that Streptococcus equisimilis is able to efficiently remove DEK with different concentrations with heavy metals. It was proved that this joint-system has excellent capacity to biodegrade high concentrations of DEK in the presence of Al3+, Cd2+, Ni2+ and Mn2+. With the exception of Al3+, the uptake for all metals increased as the initial concentration of each metal in the mixed solution increased. The breakthrough curves are best described by the Adams and Bohart model for Cd2+, by the Yoon and Nelson model for Ni2+ and by the Wolborska model for Mn2+.

Permeable Biosorbent Barrier for Wastewater Remediation

Chromium is one of the heavy metals that significantly affect water quality in Mongolia. The present study is focused on the remediation of surface water contaminated with chromium (III) by a permeable barrier in order to prevent sediment pollution. The adsorption capacity of the selected materials (13X zeolite and vermiculite) was investigated at different sorbent dosages, pH and initial Cr(III) concentration. The equilibrium adsorption studies showed that vermiculite has a higher Cr(III) removal efficiency in comparison with 13X zeolite. A fungal isolate obtained from the sediment samples collected near Tuul River (Mongolia) was selected from enriched Luria-Bertani medium, showing a good performance for Cr(III) removal (78.2% for an initial concentration of 50xa0mg/L). The fungal isolate was genetically typed by DNA sequencing and was identified as belonging to the Alternaria alternata species. 13X zeolite showed the best performance for Cr removal in the permeable barrier assays compared to vermiculite, achieving a total removal of 96% and a global uptake of 2.49xa0mg/g. After 13xa0days of operation none of the barriers reached saturation with chromium.

Pilot-scale sorption studies of diethylketone in the presence of Cd2+ and Ni2+

ABSTRACT The effect of pH on the sorption capacity of vermiculite towards cadmium and nickel was tested in batch systems and it was shown that the sorption percentages increase with an increase in the mass of vermiculite and with an increase in the initial pH. Maximum sorption percentages were obtained for a pH of 8 and 4u2005g of vermiculite (86.5% for Cd2+ and 86.1% for Ni2+, for solutions with 100u2005mg/L of metal). As a consequence, it was possible to establish a range of optimal pH for biosorption processes, by combining the so determined optimal sorption pH of vermiculite with the optimal growth pH of Streptococcus equisimilis, a bacterium used to treat contaminated water. Pilot-scale experiments with a S. equisimilis biofilm supported on vermiculite were conducted in closed-loop conditions, aiming to treat large volumes of diethylketone aqueous solutions, eventually containing Cd2+ or Ni2+. The excellent capacity of this joint system to simultaneously biodegrade diethylketone and biosorb Cd2+ or Ni2+was proved. The removal percentage and the uptake increase through time, even with the replacement of the initial solution by new ones. The breakthrough curves that best describe the results achieved for Cd2+ and Ni2+ are respectively the Adams–Bohart and the Yoon and Nelson model.