Paula Oulego

Kinetics and Pathways of Cyanide Degradation at High Temperatures and Pressures

The degradation of cyanide was performed in a 1-L semibatch reactor at temperatures between 393 and 473 K and at total pressures in the range of 2.0-8.0 MPa. The initial pH of the solution was set at 11, whereas initial concentrations ranged from 3.85 to 25 mM, which resemble the typical concentrations of cyanide-containing wastewater. The change with time of cyanide concentration, intermediates, and final products was analyzed in order to elucidate the reaction pathways. The experimental results suggest two parallel pathways of alkaline hydrolysis for the degradation of the pollutant. Formate and ammonia were identified as the final reaction products for one of the pathways, whereas carbon dioxide, nitrogen, and hydrogen were considered to be the final products for the other one. The degradation reaction results were fitted to first-order kinetic equations with respect to cyanide, giving respectively activation energies of 108.2 ± 3.3 and 77.6 ± 3.0 kJ/mol. Consequently, the formation of formate and ammonia is favored at high temperatures, whereas low temperatures favored the pathway leading to the formation of carbon dioxide and nitrogen.

Valuable compounds from sewage sludge by thermal hydrolysis and wet oxidation. A review

Sewage sludge is considered a costly waste, whose benefit has received a lot of attention for decades. In this sense, a variety of promising technologies, such as thermal hydrolysis and wet oxidation, are currently employed. Thermal hydrolysis is used as a pretreatment step ahead of anaerobic digestion processes and wet oxidation is intended for the solubilization and partial oxidation of the sludge. Such processes could be utilized for solubilizing polysaccharides, lipids, fragments of them and phosphorus (thermal hydrolysis) or for generating carboxylic acids (wet oxidation). This article compiles the available information on the production of valuable chemicals by these techniques and comments on their main features. Temperature, reaction duration times and sludge characteristics influence the experimental results significantly, but only the first two variables have been thoroughly studied. For thermal hydrolysis, a rise of temperature led to an increase in the solubilized biomolecules, but also to a greater decomposition of proteins and undesirable reactions of carbohydrates with themselves or with proteins. At constant temperature, the amounts of substances that can be recovered tend to become time independent after several minutes. Diluted and activated sludges seem to be more readily hydrolyzable than the thickened and primary ones. For wet oxidation, the dependence of the production of carboxylic acids with temperature and time is not simple: their concentration can increase, decrease or go through a maximum. At high temperatures, acetic acid is the main carboxylic acid obtained. Concentrated, fermented and secondary sludge seem to be more suitable for yielding higher amounts of acid than diluted, undigested and primary ones.

Simultaneous oxidation of cyanide and thiocyanate at high pressure and temperature

Thiocyanate and cyanide are important contaminants that frequently appear mixed in industrial effluents. In this work the wet oxidation of mixtures of both compounds, simulating real compositions, was carried out in a semi-batch reactor at temperature between 393 K and 483 K and pressure in the range of 2.0-8.0 MPa. The presence of cyanide (3.85 mM) increased the kinetic constant of thiocyanate degradation by a factor of 1.6, in comparison to the value obtained for the individual degradation of thiocyanate, (5.95 ± 0.05) × 10(-5)s(-1). On the other hand, the addition of thiocyanate (0.98 mM) decreased the degradation rate of cyanide by 16%. This revealed the existence of synergistic and inhibitory phenomena between these two species. Additionally, cyanide was identified as an intermediate in the oxidation of thiocyanate, and formate, ammonia and sulfate were found to be the main reaction products. Taking into account the experimental data, a reaction pathway for the simultaneous wet oxidation of both pollutants was proposed. Two parallel reactions beginning from cyanate as intermediate were considered, one yielding ammonia and formate and the other giving carbon dioxide and nitrogen as final products.

Characterization of sinter flue dust to enhance alternative recycling and environmental impact at disposal

Dust emission is one of the main environmental pollution impacts associated with steelmaking. In this sense, electrostatic precipitators (ESP) are regarded as the best available technique for treating this type of emission, thus generating two differentiated fractions: coarse and fine. Thorough chemical and structural characterization of both materials was carried out to recycle these byproducts in either the sintering process or other steps of pig iron production. Both types of dusts are crystalline heterogeneous materials mainly composed of sepiolite (Mg8Si12(OH)2·12H2O), hematite (Fe2O3) and calcite (CaCO3), the coarse fraction containing low amounts of Na (0.38 ± 0.04%) and K (0.17 ± 0.02%), which adversely affect blast furnace operation. Hence, the coarse fraction is suitable for recycling, whereas the fine one presents higher concentrations of these alkali elements. Besides, textural characterization revealed that dust particulates are essentially macroporous materials, with specific surface area values of 21.6 m2/g for the coarse fraction and 33.7 m2/g for dust fines. In order to ensure inoffensive dumpsites, the environmental behavior associated with dust particles accumulated in disposal areas was also evaluated by performing leaching studies simulating different rainfall scenarios. It was found that the specific leaching rates of Ca, Mg, K and S varied between 0.072 ± 0.001 and 0.75 ± 0.01 µgelement/(gdust·d), whereas slower leaching rates were obtained for heavy metals (Fe, Mn and Cu), the values ranging from (1.20 ± 0.1) × 10-4 to (1.8 ± 0.1) × 10-3 µgelement/(gdust·d). These low rates indicate that the leaching of sinter dusts compounds has minimal environmental impact.

Biodegradation of dissolved humic substances by fungi

Humic and fulvic acids constitute humic substances, a complex mixture of many different acids containing carboxyl and phenolate groups, which are not only the principal soil fertility factors but also the main pollutants present in landfill leachates or natural organic matter in water. Due to their low bacterial biodegradability, fungal biodegradation processes are key for their removal. The present study compiles and comments all the available literature on decomposition of aqueous humic substances by fungi or by their extracellular enzymes alone, focusing on the influence of the reaction conditions. The biodegradation extent mainly depends on the characteristics and concentration of the humic compounds, the type of microorganisms selected, the inoculation mode, the C and N sources, the presence of certain chemicals in the medium, the availability of oxygen, the temperature, and the pH.

Easy and Cost Effective Preparation of Cellulose Beads from Almond Shell: Characterization and Application in Copper (II) Adsorption from Aqueous Solutions

Cellulose is the most abundant biopolymer on earth and it is frequently extracted from plant sources. Generally, its use implies the dissolution of cellulose and for this “green” solvents are required. In this sense, ionic liquids (ILs) have been gradually used to dissolve cellulose due to their environmental friendliness. In particular, 1-Butyl-3-methylimidazolium chloride (BmimCl) has been employed as an effective solvent in the dissolution of cellulose. The regenerated cellulose can be potentially used in various fields, such as biomedical science, pharmaceutical health care, cosmetics, energy science, and water treatment. So far, water treatment technologies have focused on the removal of various kinds of toxic pollutants, heavy metals being one of the main ones.

Protein recovery from solubilized sludge by hydrothermal treatments

New alternatives for sludge management have been developed in recent years, with hydrothermal treatments being one of the most attractive ones. Even though many studies have been made on the application of hydrothermal treatments as pre-treatment or end-line technologies for sludge stabilisation and/or minimization, there is a lack of knowledge about the products generated during the process and its characteristics. This information is a crucial step for the assessment of the recovery of valuable products of the sludge, mainly proteins, humic acids and carbohydrates, which can considerably improve the economic balance of the hydrothermal treatment. This work assesses, for the first time, the potential of hydrothermally hydrolysed sludge as renewable source for proteins recovery. For this purpose, firstly, the concentrations and properties of the main soluble biopolymers generated during the hydrothermal treatment, either in presence (wet oxidation, WO) or absence (thermal hydrolysis, TH) of oxygen, were measured, determining the reaction time necessary for a maximum solubilisation. Peak concentrations of 7.7g/l (0.291g/gVSSo) of proteins for WO and 7.2g/l (0.272g/gVSSo) for TH, were achieved at 87min of experiment. Afterwards, different separation methods, usually applied at industrial scale, were assessed for the separation of protein from the hydrolysed sludge, in terms of protein recovery and selectivity. Ammonium sulphate addition was found to be the best separation method, achieving 87% and 86% of protein recovery for TH and WO samples respectively, and the highest selectivity. Although further studies are required in order to achieve complete protein purification, a new perspective in sludge management is now open, by recovering valuable compounds.

Flow cytometric characterization of bacterial abundance and physiological status in a nitrifying-denitrifying activated sludge system treating landfill leachate

Flow cytometry has recently been presented as a research tool in the assessment of the viability/activity of activated sludge from municipal wastewater treatment plants, but it has not put in practice for industrial biotreatments yet. In this study, for the first time ever, the reliability and significance of the multiparameter flow cytometry applied to the biological nitrification-denitrification treatment of leachate have been evaluated. Using a double staining procedure (cFDA/PI), the viable, damaged, and dead subpopulations were determined, and the results were compared to those obtained with conventional methods, such as nitrogen and oxygen uptake rates or plate counting. Flow cytometry showed that viable cells represented approximately 47% of the total population, whereas active cells accounted for 90%. For both sludge from nitrification and denitrification processes, with less than 1% of them being also culturable in plate. Either flow cytometry or uptake rates revealed that health status of sludge remained constant throughout the biotreatment, which is consistent with the high recirculation rates. Under anaerobic starvation conditions, physiological status of sludge remained constant as well as specific oxygen and denitrification rates. Nevertheless, both the culturability in plate and the nitrification rate significantly decreased. These findings proved that multiparameter flow cytometry is a useful tool for the assessment of the viability and activity of sludge from a nitrification-denitrification biotreatment process. These results gathered all the bacterial communities in the sludge, so the decay in minority populations, such as nitrifying bacteria, requires the use of a complementary technique to evaluate specific activities.