Heat and mass transfer during the coffee drying process

For a better comprehension of heat and mass transfer during the coffee drying process and optimization of the industrial application transport coefficients and coffee properties were determined. Heat transfer coefficients were measured for different air velocities and were found to follow the known dimensionless equations for the flow surrounding a sphere. Thermal conductivities and effective diffusion coefficients were measured as a function of moisture content as well as volume and densities of the coffee beans. The mentioned properties depend directly on the humidity of the coffee beans rather than on the drying conditions. Sorption behaviour was investigated and temperature dependent parameters for the Guggenheimer–Anderson–deBoer-isotherm (GAB) were determined according to the Arrhenius relationship.     

Application of compression test in analysis of mechanical and color changes in grapefruit juice powder as related to glass transition and water activity

Physicochemical and structural properties of grapefruit juice powder were studied as affected by water activity. Powdered juice was obtained by freeze-drying and equilibrated at different water vapor pressure atmospheres in order to give samples with water activity in the range of 0-0.84. The mechanical properties of the powder were measured by confined compression tests and the compressed samples, which presented uniform surface and thickness, were subjected to color analysis. The maximum force attained during the compression tests and the color coordinates could be quantified with good reproducibility. The results were related to water activity and to glass transition temperature. The occurrence of mechanical changes in the powder was shown to precede significant color changes with increasing water activity. Considering the susceptibility to stickiness, the stability limit was observed at T−T_g ≈ 2 °C, with a high degree of mechanical changes being detected at T−T_g ≈ 16 °C, whereas for significant color changes this critical temperature difference was around 32 °C.     

Kinetic studies of dyes sorption from aqueous solutions onto the strongly basic anion-exchanger Lewatit MonoPlus M-600

The sorption of Tartrazine, Allura Red, Sunset Yellow and Indigo Carmine from aqueous solutions onto the strongly basic anion-exchanger (Lewatit MonoPlus M-600) of dimethylethanolamine functional groups and styrene–divinylbenzene matrix was investigated. The experimental data obtained at 50, 100, 200, 300 and 500 mg/dm³ initial concentrations at 20 °C were applied to the pseudo-first order, pseudo-second order and Weber–Morris kinetic models. The calculated sorption capacities (q_1,cal) and the rate constant of the first-order adsorption (k₁) were determined. The pseudo-second order kinetic constants (k₂) and capacities (q_2,cal) were calculated from the plots of t/q_t vs. t, 1/q_t vs. 1/t, 1/t vs. 1/q_t, q_t/t vs. q_t and 1/q₂ − q_t vs. t for type 1, type 2, type 3, type 4 and type 5 of the pseudo-second order expression, respectively.     

Modeling, rate-limiting step investigation, and enhancement of the direct bio-regeneration of perchlorate laden anion-exchange resin

Anion-exchange with high perchlorate affinity resins is one of the most promising technologies for removing low levels of perchlorate. However, the traditional brine desorption technique is difficult and costly for regeneration of this type of resin. Previously, a direct bio-regeneration method by contacting the spent high perchlorate affinity resin with the perchlorate-reducing bacteria was proved feasible. This research is a further study of that method. Firstly, a direct bio-regeneration process model, based on the physicochemical and biological fundamentals, was developed and calibrated with experimental data. Thereafter, the rate-limiting step in regeneration of the high perchlorate affinity resin was investigated. Methods to enhance the regeneration efficiency were developed. The results indicated that the calibrated model well described the regeneration process. It thus might provide useful insights into the regeneration system. The results also demonstrated that the perchlorate desorption from the loaded resin could be the rate-limiting step. Addition of proper amount of counter anions such as chloride and sulfate improved the regeneration efficiency because these anions could promote both the extent and rate of perchlorate desorption from the loaded resin. These findings aided us in achieving good and efficient regeneration of high perchlorate affinity resins like the A-530E and SR-7 resins. The findings also suggested that the application of bacteria that could efficiently reduce perchlorate in highly saline solution would make the method more promising for the regeneration of high perchlorate affinity resins.     

Fate and distribution of pharmaceuticals in wastewater and sewage sludge of the conventional activated sludge (CAS) and advanced membrane bioreactor (MBR) treatment

In this paper we report on the performances of full-scale conventional activated sludge (CAS) treatment and two pilot-scale membrane bioreactors (MBRs) in eliminating various pharmaceutically active compounds (PhACs) belonging to different therapeutic groups and with diverse physico-chemical properties. Both aqueous and solid phases were analysed for the presence of 31 pharmaceuticals included in the analytical method. The most ubiquitous contaminants in the sewage water were analgesics and anti-inflammatory drugs ibuprofen (14.6-31.3 μg/L) and acetaminophen (7.1-11.4 μg/L), antibiotic ofloxacin (0.89-31.7 μg/L), lipid regulators gemfibrozil (2.0-5.9 μg/L) and bezafibrate (1.9-29.8 μg/L), β-blocker atenolol (0.84-2.8 μg/L), hypoglycaemic agent glibenclamide (0.12-15.9 μg/L) and a diuretic hydrochlorothiazide (2.3-4.8 μg/L). Also, several pharmaceuticals such as ibuprofen, ketoprofen, diclofenac, ofloxacin and azithromycin were detected in sewage sludge at concentrations up to 741.1, 336.3, 380.7, 454.7 and 299.6 ng/g dry weight. Two pilot-scale MBRs exhibited enhanced elimination of several pharmaceutical residues poorly removed by the CAS treatment (e.g., mefenamic acid, indomethacin, diclofenac, propyphenazone, pravastatin, gemfibrozil), whereas in some cases more stable operation of one of the MBR reactors at prolonged SRT proved to be detrimental for the elimination of some compounds (e.g., β-blockers, ranitidine, famotidine, erythromycin). Moreover, the anti-epileptic drug carbamazepine and diuretic hydrochlorothiazide by-passed all three treatments investigated.Furthermore, sorption to sewage sludge in the MBRs as well as in the entire treatment line of a full-scale WWTP is discussed for the encountered analytes. Among the pharmaceuticals encountered in sewage sludge, sorption to sludge could be a relevant removal pathway only for several compounds (i.e., mefenamic acid, propranolol, and loratidine). Especially in the case of loratidine the experimentally determined sorption coefficients (K_ds) were in the range 2214-3321 L/kg (mean). The results obtained for the solid phase indicated that MBR wastewater treatment yielding higher biodegradation rate could reduce the load of pollutants in the sludge. Also, the overall output load in the aqueous and solid phase of the investigated WWTP was calculated, indicating that none of the residual pharmaceuticals initially detected in the sewage sludge were degraded during the anaerobic digestion. Out of the 26 pharmaceutical residues passing through the WWTP, 20 were ultimately detected in the treated sludge that is further applied on farmland.     

Fate of beta blockers and psycho-active drugs in conventional wastewater treatment

The removal of beta blockers and psycho-active drugs was investigated in a representative conventional German WWTP by long-term measurement campaigns along different biological treatment processes. The activated sludge treatment with an elevated SRT of 18 d was the only process which led to a significant removal of certain beta blockers and psycho-active drugs. The removal efficiency was below 60% for all compounds except for the natural opium alkaloids codeine and morphine being removed by more than 80%. Primary biological transformation and sorption onto sludge as the main removal mechanisms were examined in lab-scale batch experiments. Sorption onto activated sludge was found to be negligible (<3%). The biological transformation could be described by pseudo-first order kinetics and the transformation constants k_biol were used to predict the removal of beta blockers and psycho-active drugs in an activated sludge unit with a model. For most compounds the removal efficiencies measured on the full-scale WWTP were within the 95% confidence intervals predicted by the model. The results from full-scale measurements and modeling indicate that biological transformation in the nitrification tank together with parameters such as the sludge retention time and the temperature is crucial regarding the biological transformation of beta blockers and psycho-active drugs in conventional WWTPs.     

Pentachlorophenol removal from aqueous matrices by sorption with almond shell residues

Sorption with activated carbon has been the technique preferred for pentachlorophenol (PCP) removal from contaminated waters, but regeneration needs and high operation costs are supporting a renewed interest in the search for alternative sorbents. Among them, almond shell, an agricultural by-product, provides interesting economical advantages, once shells account for 50% (in mass) of the whole almond. In this work, the capacity of almond shells to remove PCP from waters without previous activation was studied in batch conditions. While PCP analysis was performed solid-phase microextraction (SPME) followed by gas chromatography with electron capture detection (GC-ECD), mercury porosimetry and Fourier transform infrared spectroscopy (FTIR) provided a preliminary physical and chemical characterization of the sorbent. Almond shells were essentially a macroporous material, with an average surface area of 12.9+/-2.8 m2/g. The efficiency of PCP removal was 93+/-14%, in 24 h, with an initial concentration of 100 microg/l PCP and 5 microg PCP/g shell. Isotherm data adjusted better to Freundlich equation, where K(F) and 1/n were 0.075+/-0.081 mg(1-1/n) l(1/n) and 1.882+/-0.289, respectively. Average desorption efficiency was 7%, indicating strong adsorption capacity. Results proved that almond shells may be an excellent low-cost alternative for PCP removal from contaminated waters.     

Review of second-order models for adsorption systems

Applications of second-order kinetic models to adsorption systems were reviewed. An overview of second-order kinetic expressions is described in this paper based on the solid adsorption capacity. An early empirical second-order equation was applied in the adsorption of gases onto a solid. A similar second-order equation was applied to describe ion exchange reactions. In recent years, a pseudo-second-order rate expression has been widely applied to the adsorption of pollutants from aqueous solutions onto adsorbents. In addition, the earliest rate equation based on the solid adsorption capacity is also presented in detail.     

Pb(II) biosorption using anaerobically digested sludge

Removal of Pb(II) by using resting cells of anaerobically digested sludge (ADS) obtained from a nearby wastewater treatment plant was examined. Firstly, sorption kinetic and equilibrium experiments were conducted using agitated, thermostated (25 degrees C) batch reactors. The maximum Pb(II) sorption capacity was found to be very high (1,750 mg/g dry ADS or 8.45 mmol/g dry ADS). At all initial Pb(II) concentrations tested, sorption resulted in neutralization with an increase in the solution pH from an initial value of 4.0-5.5 to an equilibrium value of 7.0-8.0, at which Pb(II) can precipitate as hydroxide. The removal of Pb(II) by ADS was found to involve bioprecipitation as well as biosorption. FTIR spectrometry highlighted carboxyl groups present on the surface of ADS as the major functional groups responsible for biosorption. Secondly, a three-stage semi-continuous pseudo-counter current reactor system was tested to reduce ADS requirement in comparison to a conventional single-stage batch reactor. At an initial Pb(II) concentration of about 200 mg/L, an effluent Pb(II) concentration of 1.3 mg/L was achieved in the three stage reactor, corresponding to a metal removal capacity of 682.7 mg/g dry ADS (3.30 mmol/g), in comparison to 1.9 mg/L and 644.0 mg/g dry ADS (3.10 mmol/g) for the single-stage batch reactor.