Volume 66, Issue 6

A short-term aerobic stabilization of digested waste in the final methane phase was studied. The effect of aeration rate on the reduction of leachate parameters and on the rate of CO2 production and O2 assimilation was investigated. Experimental simulation of aerobic landfill stabilization was carried out using lysimeters. When testing the effect of aeration rate on the reduction of leachate indices (BOD5, COD, N-NH4+), it was reported that the most significant reduction was obtained at the highest rate of aeration and the smallest reduction of leachate indices was attained not at the lowest but at medium aeration rates. Both the rate of CO2 production and the O2 assimilation reached their highest values in the lysimeters aerated at a high rate of aeration. The proposed mathematical model which consists of a system of five differential equations describing CO2 production, O2 assimilation and the changes of organic carbon content in the leachate correspond well with the experimental data.

The most promising technology to generate energy is the production of biogas from agricultural feedstock. This technology allows obtaining high biogas yields per hectare. Biogas of high methane content can be produced from various kinds of energy crops, animal manure, and other organic waste. This paper presents results of both biochemical methane potential (BMP) assay of Canary grass (Phalaris canariensis) and its anaerobic co-digestion with cheese whey and glycerin fraction in a large laboratory scale as well as the kinetics of both co-digestion and digestion of Canary grass alone. The suggested mathematical description of the anaerobic co-digestion process gave satisfying conformity with the experimental data.

Influence of model complexity on the separation equipment performance was investigated. As an example, separation of azeotrope formed by 2-methoxy-2-methylpropane and methanol was considered using butan-1-ol as an extractive solvent. Non-equilibrium model of a column for extractive distillation accounting for the mass and heat transfer rates was composed according to the rigorous Maxwell-Stefan theory. An empirical AICHE correlation was adopted for the calculation of binary mass transfer coefficients at column trays. Results of the column steady-state operation were compared with those obtained assuming different equilibrium models. Effect of the quality of the vapor-liquid equilibrium (VLE) description on the results of the separation simulation considering real behavior of either liquid or both equilibrium phases was tested. Real behavior of the liquid phase was computed according to the NRTL equation taking into account binary and, in some cases, also ternary equilibrium data. In case of real behavior of the vapor phase, the equation of state in the form of virial expansion was employed. Qualitative agreement was found comparing the simulation results calculated by equilibrium and non-equilibrium models of the extractive distillation column while using the same description of ternary VLE.

Experimental results of gas hold-up, power consumption and residence time of gas bubbles in a gas-solid-liquid system produced in an agitated vessel equipped with a high-speed impeller and a vertical tubular coil are presented in this paper. Critical agitator speed, needed for the dispersion of gas bubbles and solid particles in liquid were also identified. The studies were carried out in an agitated vessel of the inner diameter D = 0.634 m and the working liquid volume of about 0.2 m3. A tubular coil of the diameter of 0.7D, consisting of 24 vertical tubes of the diameter of 0.016D, was located inside the flat-bottomed vessel. The agitated vessel was equipped with a Rushton turbine with six blades or an A 315 impeller with four blades. Both impellers had diameter, d, equal to 0.33D. The vessel was filled with liquid up to the height H = D. In this study, air and particles of sea sand with the mean diameter of 335 μm and the concentration of up to 3.0 mass % were dispersed in distilled water as the liquid phase. The measurements were carried out within the turbulent regime of the fluid flow in the agitated vessel. Results of the measurements were processed graphically and mathematically. Lower values of the critical agitator speed, n JSG, needed for simultaneous dispersion of gas bubbles and particles with the solids concentration from 0.5 mass % to 2 mass %, were obtained for the vessel equipped with the A 315 impeller. Higher values of the specific power consumption were reached for the vessel with the Rushton turbine. Higher values of the gas hold-up and residence time of the gas bubbles in the fluid were obtained for the system equipped with the Rushton turbine. Results of the gas hold-up as a function of the specific power consumption, superficial gas velocity and solids concentration were approximated with good accuracy using Eq. (5).

Results of experimental analysis concerning gas hold-up and average residence time of gas bubbles in a three-phase gas-solid-liquid system produced in a baffled, double-impeller vessel are presented. Measurements were carried out in a vessel with the internal diameter of 0.288 m. Two different double-impeller configurations were used for agitation: Rushton turbine (lower) — A 315 (upper) and Rushton turbine (lower) — HE 3 (upper). Upper impellers differed in the fluid pumping mode. Coalescing and non-coalescing systems were tested. Liquid phases were distilled water (coalescing system) and aqueous solutions of NaCl (non-coalescing systems). The ability of gas bubbles to coalesce in the liquid was described using parameter Y. Dispersed phases were air and particles of sea sand. The experiments were conducted at seven different gas flow rates and two particle loadings. Effects of the ability of gas bubbles to coalesce (liquid phase properties), operating parameters (superficial gas velocity, impeller speed, solids loadings), and of the type of the impeller configuration on the investigated parameters were determined. The results were approximated mathematically. For both impeller configurations tested, significantly higher gas hold-up values were obtained in the non-coalescing gas-solid-liquid systems compared to the coalescing one. Out of the tested impeller systems, the RT-A 315 configuration proved to have better performance ensuring good gas dispersion in the liquid in the three-phase systems.

Separation performance of sodium, lithium, potassium and hydrogen ionic forms of a commercial cation exchanger, Diaion UBK 530, based on a styrene-divinylbenzene copolymer resin support was studied. The adsorbents were applied to the separation of galactooligosaccharides from their mixture with lactose, glucose and galactose. Separation performance of the hydrogen ionic form of the adsorbent was superior to that of other adsorbent forms. A much higher yield of galactooligosaccharides of the requested purity was achieved for this adsorbent form owing to its better kinetic properties. Adsorption properties of individual adsorbents were discussed in relation to possible adsorption mechanisms.

Oxides of transition metals could be suitable alternatives to catalysts based on noble metals in the oxidation processes used for the abatement of volatile organic compounds. Mixed oxides of transition metals can exhibit good efficiency and thermal stability, as well as being inexpensive. In this work, oxide catalysts containing various combinations of Cu, Co, Ni, Mn, and Al, grained or supported on oxidised aluminium foil Al2O3/Al, were studied in terms of their chemical and physical properties, including their chemical composition, porous structure, phase composition, reducibility, and activity in total ethanol oxidation. Ternary co-precipitated catalysts in the form of grains obtained from layered double hydroxide-like precursors were highly active, especially those containing manganese. Deposition of the selected precursors on an anodised aluminium foil-support afforded less active catalysts, mainly because the required metal molar ratios were not achieved, and insufficient amounts of metals were deposited. However, by controlling the preparation conditions (pH), higher loading of active components and higher catalytic activity were obtained.

Two types of sewage sludge anaerobic digestion were carried out: mesophilic and thermophilic. Metal speciation analysis was performed revealing some changes in the chemical form of the metals during the stabilization process of sludge. After both methane fermentation processes, a comparable level of organic matter distribution was obtained (≈ 40 %). The amount of produced methane during thermophilic and mesophilic digestion was 560 mL of CH4 and 580 mL of CH4 from 1 g of removed organic matter, respectively. Low concentration of heavy metal ions in the liquid phase of sludge was observed. Metal ions precipitated and remained bound throughout the stabilization process. No accumulation of heavy metals in the mobile fractions of sludge (exchangeable and carbonate) was observed for either digestion process. The highest increase of zinc, copper, nickel, cadmium, and chromium concentration was observed in the organic-sulfide fraction, whereas the highest increase of lead was found in the residual fraction.

The impact of UV and VIS irradiation and specific nitrogen modification on a 5%Cu/5%TiO2/SiO2 catalyst in the course of oxidation of ammonia was investigated. It was demonstrated that both UV and VIS irradiation increased the conversion of the reactant in the reaction studied. Due to a good distribution of titanium dioxide and copper on the surface of the support, higher ammonia conversion was achieved. Physico-chemical characterisation of the catalysts studied using methods such as BET, SEM-EDS, TPD (NH3), and TPD (CO2) was carried out.

Antioxidant status of foods, plant, or fruit products is generally characterized by means of spectroscopic methods. Methods like HPLC, UV-VIS, or MS spectroscopy are used to understand the chemical and physical properties of different samples, and also EPR spectroscopy seems to be a valuable tool to characterize antioxidant activity of juice beverages. In this technique, certain antioxidants present in fruit juices interact with free radicals interrupting the chain reaction that can possibly damage essential molecules. Recording the EPR signal decay caused by the reaction with a natural or artificial reducing agent, it is possible to draw conclusions about the antioxidant capability of materials. IRMS is a powerful tool to distinguish between an authentic fruit juice and a juice obtained by concentrate dilution. This technique allows also the detection of commercial C4 cane or corn derived sugar syrups in C3 fruit juices. In the present study, four commercial fruit juices were investigated using stable isotope measurements (oxygen, hydrogen, and carbon) and EPR measurements in order to check the correct labeling in the Romanian markets and to compare antioxidant activity of the studied juices and the reference. It was proven that the number of paramagnetic species decreases in time with different reaction rates and this was correlated with the antioxidant activity of the studied juices. Stable isotope ratio measurements have demonstrated that the fruit juices studied were reconstructed from concentrates with tap water, according to their label.

This paper deals with two (main) problems of specific gold etching from parts of industrial equipment (e.g., supporting inserts into chambers for physical or chemical vapor deposition). First part of the paper is focused on selective etching of gold from aluminum substrates. Selectivity of the reaction, i.e. leaving substrates intact, is crucial. For this reason, the environmentally friendly and safe method of etching gold in a thiourea solution was tested. This method, while well described in literature, does not preserve various substrates (e.g., aluminum, stainless steel). The main goal of this part of the paper was to understand the mechanism of the reaction and to improve the reaction selectivity towards the aluminum alloy substrate. Thus, different acidifying agents were tested. Second part of the paper is focused on recovery (reduction) of gold from thiourea solutions. Chemical, electrochemical, and biological reduction were tested for gold recovery.