Assessment of two non-invasive techniques for measuring turbulent benthic fluxes in a shallow lake

Benthic fluxes refer to the exchange rates of nutrients and other compounds between the water column and the sediment bed in aquatic ecosystems. Their quantification contributes to our understanding of aquatic ecosystem functioning. Near-bed hydrodynamics plays an important role at the sediment-water interface, especially in shallow lakes, but it is poorly considered by traditional measuring techniques of flux quantification, such as sediment incubations. Thus, alternative sampling techniques are needed to characterize key benthic fluxes under in-situ hydrodynamic conditions. This study aimed to evaluate the performance of two promising methods: relaxed eddy accumulation (REA) and mass transfer coefficient (MTC). We applied them in a hyper-eutrophic shallow lake to measure the fluxes of ammonium, phosphate, iron, and manganese ions. For the first time, REA revealed hourly nutrient flux variations, indicating a strong lake biogeochemical dynamics at short time-scales. Daily average fluxes are of similar orders of magnitude for REA and MTC for ammonium (24 and 42 mmol m2 d-1), manganese (1.0 and 0.8), and iron (0.8 and 0.7) ions. They are one order of magnitude higher than fluxes estimated from sediment incubations, due to the difficulty in reproducing in-situ oxygen and hydrodynamic conditions in the laboratory. Although the accuracy of both techniques needs to be improved, the results revealed their potential: REA follows the short-term biogeochemical dynamics of sediments, while MTC could be widely used for lake monitoring because of its simpler implementation.

Computational fluid dynamics analysis of a micro-scale chamber for measuring organic chemical emission parameters

Computational fluid dynamics simulations are used to model the velocity field and the transport of a passive scalar within a micro-scale chamber used to measure diffusional transport through various building materials. Comparisons of solutions obtained using a steady, laminar flow assumption with velocity measurements obtained from hot-wire anemometry show that the numerical method generally underpredicts the near surface velocity field. The results improve for higher flow rates and for carpeted test materials, modeled as a porous resistive layer. Calculations involving scalar transport within the upper chamber of the sampling device are performed for different flow rates and Schmidt numbers. The results are used to develop a model for the convective mass transfer coefficient, correlated as a function of the Reynolds and Schmidt numbers as well as the porosity of the carpet. This model is integrated into a steady-state mass transport model for predicting the diffusion of gaseous formaldehyde through various test materials. Predictions of diffusion and partition coefficients for vinyl flooring, gypsum wall board, and carpet are within the ranges of literature data. The results indicate that a perfectly mixed upper part of the sampling device is an adequate assumption.

Assessment of biodegradation kinetics and mass transfer aspects in attached growth bioreactor for effective treatment of Brilliant green dye from wastewater

In this study, Bacillus licheniformis immobilized with low-density polyethylene (LDPE) was employed to degrade Brilliant Green (BG) dye from wastewater in a packed bed bioreactor (PBBR). Bacterial growth and extracellular polymeric substance (EPS) secretion were also assessed under different concentrations of BG dye. The impacts of external mass transfer resistance on BG biodegradation were also evaluated at different flow rates (0.3 - 1.2 L/h). A new mass transfer correlation [Formula: see text] was proposed to study the mass transfer aspects in attached-growth bioreactor. The intermediates, namely 3- dimethylamino phenol, benzoic acid, 1-4 benzenediol, and acetaldehyde were identified during the biodegradation of BG and, subsequently degradation pathway was proposed. Han - Levenspiel kinetics parameters μ_max and K_s were found to be 0.185 per day and 115 mg/L, respectively. The new insight into mass transfer and kinetics support the design of efficiently attached growth bioreactor to treat a wide range of pollutants.

An improved Chemcatcher-based method for the integrative passive sampling of 44 hydrophilic micropollutants in surface water - Part B: Field implementation and comparison with automated active sampling

Integrative passive sampling is particularly useful in the monitoring of hydrophilic contaminants in surface water, but the impact of hydrodynamics on contaminant uptake still needs to be better considered. In part A (Glanzmann et al., 2023), Chemcatcher-like hydrophilic samplers (i.e., SDB-RPS extraction disks covered by PES microporous membranes) were calibrated to determine the sampling rates R_S of 44 hydrophilic contaminants (pesticides, pharmaceuticals, industrial products) taking into account the hydrodynamic conditions. In this study, Chemcatcher-like passive sampling devices that allowed co-deploying hydrophilic samplers and performance reference compounds (PRC)-spiked silicone disks were tested in a Swiss river with intermediate water velocities (5-50 cm s^-1, 23 cm s^-1 on average) during 11 consecutive 14-day periods. The PRC dissipation from silicone disks - combined with the calibration data from part A - allowed to determine in-situ R_S that took into account hydrodynamic conditions. The obtained aqueous time-weighted average (TWA) concentrations were found to be robust with good concordance between duplicates (mean quotient of 1.16 between the duplicates). For most measurements (76 %), TWA concentrations showed no major difference (<factor 2) from concentrations obtained with automated sampling (14-day composite samples). This observation was also valid for TWA concentrations calculated with extrapolated R_S at infinite water velocity (R_S,MAX), revealing that the added value of using in-situ R_S compared to R_S,MAX is limited above intermediate water velocities (>20 cm s^-1). R_S from the literature (R_S,LIT) - obtained at water velocities between 8 and 37 cm s^-1 - were also shown to provide comparable TWA concentrations in the studied hydrodynamic conditions (average water velocity of 24 cm s^-1). The estimated errors due to the use of R_S,MAX or R_S,LIT rather than in-situ R_S are given as a function of the water velocity to determine in which conditions the developed method is required (or not) in monitoring programs.

Modeling of NO mass transfer characteristics absorbed in sodium persulfate solution with a bubble reactor

Sodium persulfate solution is considered as an effective wet denitrification medium, however, it is unclear that the influence of the operating conditions on mass transfer characteristics parameters during the absorption of NO with sodium persulfate solution. To determine the key mass transfer characteristics parameters, the specific interfacial area a and the mass transfer coefficients kL,  kG, were determined based on the Danckwerts method during CO₂ absorption in a bubble column. kL, kG  and a were calculated by correlations between the mass transfer coefficients of NO and CO₂. Results showed that the specific interfacial area increased 77.64 m^-1, the liquid phase mass transfer coefficient increased 2.49 × 10^-4 m·s^-1, and the gas phase mass transfer coefficient increased 0.71 × 10^-5mol·Pa^-1·s^-1·m^-2 with superficial gas velocity increasing from 0.6 to 1.4 L·min^-1. With the temperature of sodium persulfate solution increasing from 293 to 333 K, the specific interfacial area decreased 42.66 m^-1, while the liquid phase mass transfer coefficient and the gas phase mass transfer coefficient increased 3.89 × 10^-4 m·s^-1 and 1.18 × 10^-5mol·Pa^-1·s^-1·m^-2, respectively. The experiments results determined the correlations of a, kL, and kG  with the temperature of the absorption phase and the superficial velocity of the gas. It can serve as a guide to the enhancement of the sodium persulfate wet denitrification process.

Changes in solution turbidity and color during paracetamol removal in laboratory and pilot-scale semicontinuous ozonation reactors

Injecting ozone by means of a venturi device causes an increase in the mass transfer coefficient with respect to gas dissolution through a microdiffuser. Moreover, it was observed that significant turbidity levels are not formed (<1 NTU) when using a microdiffuser, probably due to the relatively high stirring which avoids formation of intermolecular hydrogen bonds. On the contrary, employing a venturi injector led to the production of high turbidity levels in water (up to 20 NTU). This indicates that formation of supramolecular structures causing this turbidity requires the presence of certain facilitating species which are formed through ozone decomposition mechanisms. The maximum ozone transfer takes place when operating at pH0 9.0, that is, when this value is close to the pKa and employing a dose of R = 115 mol O3/mol Pa0. Under these conditions, the degradation of paracetamol generates color, which is attributed to the presence of condensation products from pyrogallol, catechol, resorcinol, acetamide, oxalic acid and 4-aminophenol. Once paracetamol is fully degraded and solution turns colorless, turbidity grows (>20 NTU). This is attributed to formation of high molecular weight structures from 4-aminophenol and oxamide. Operating with large ozone excess (R = 500 mol O3/mol Pa0), the maximum ozone transfer rate is achieved at pH0 = 12.0. Under these conditions, the pollutant is fully removed together with water aromaticity and oxalic acid (able to form linear structures through hydrogen bonding) is detected during color development. Then, turbidity is formed due to cyclic dimer formation from acetic acid.

Effect of mixing intensity on biodegradation of phenol in a moving bed biofilm reactor: Process optimization and external mass transfer study

In this work, an effort has been made to design the process variables and to analyse the impact of mixing intensity on mass transfer diffusion in a moving bed biofilm reactor (MBBR). A lab-scale MBBR, filled with Bacillus cereus GS2 IIT (BHU) immobilized-polyethylene biocarriers, was employed to optimize the process variables, including mixing intensity (60-140 rpm), phenol concentration (50-200 mg/L), and hydraulic retention time (HRT) (4-24 h) using response surface methodology. The optimum phenol removal of 87.64 % was found at 100 rpm of mixing intensity, 200 mg/L of phenol concentration, and 24 h of HRT. The higher mixing intensity improved the substrate diffusion between the liquid phase and the surface of the biofilm. The external mass transfer coefficients were found in the range of 1.431 × 10^-5-1.845 × 10^-5 m/s. Moreover, the detection of catechol and 2-hydroxymuconic semialdehyde revealed that the Bacillus sp. followed the meta-cleavage pathway during the biodegradation of phenol.

Effect of air velocity, temperature, and relative humidity on drying kinetics of rubberwood

Kiln drying of rubberwood lumbers is a complex transport phenomenon for realistic modeling and simulation. To decouple this complexity, researchers usually divide their research into two parts. The first one is single-lumber drying kinetics to describe how wood lumber responds to its surface conditions. Then they combine this drying kinetics with a lumped transport model or dispersion model or computational fluid dynamics. The mathematical models are then solved numerically to predict the industrial kiln drying behaviors. This work focuses on the drying kinetics of stacked rubberwood lumbers using hot air at different air velocity (0.5, 1.5, 2.5, 3.5, 4.0 m/s), relative humidity (6-67% relative humidity (RH)) and temperature (60-100 °C). The drying kinetics followed the conventional drying theory. However, the two drying periods, namely constant and falling rate (CRP and FRP), were not distinct. As the air velocity increased, the transition from CRP to FRP is faster. The middle of the transition period (at critical moisture content, CMC) moves closer to the fiber saturation point (FSP). The overall mass transfer coefficients in the falling rate period for stacked rubberwood drying were lower than those predicted by the Ananias correlation. Hence, a modified formula was proposed, representing the overall moisture transfer coefficients as a function of air velocity, temperature, relative humidity, and lumbers thickness for the range of variables under investigation satisfactorily. In general, the drying rate and the overall moisture transfer coefficient increased with increasing air velocity, drying temperature, and decreasing RH. Relative humidity directly affects the driving force of moisture transfer rate because higher RH is associated with higher equilibrium moisture content. A lumped parameter model for kiln drying was also developed. After being integrated with the estimated mass transfer coefficient, the model can predict the moisture profiles in lab-scale kiln drying satisfactory, although the model needs more validation data. These kinetic parameters and correlation for stacked rubberwood drying can be used in more complex models and process optimization in future research.

Modelling of moisture migration during convective drying of pineapple slice considering non-isotropic shrinkage and variable transport properties

The present work aims to develop a 3-dimensional finite element (FE) model to analyze moisture migration during drying of pineapple ring considering moisture dependent diffusion coefficient (D) and mass transfer coefficient (h_m) along with radial and longitudinal shrinkage. Pineapple rings were dried at 70 °C temperature and 0.6 m/s air velocity to study the moisture loss and shrinkage kinetics during drying. Thickness, outer radius and inner radius of hollow cylindrical pineapple slices were reduced by 79.3%, 32.2%, and 51.2%, respectively due to the occurrence of shrinkage during drying. Non-linear regression analysis showed the quadratic model to best fitted to the experimental moisture ratio data for explaining the shrinkage phenomenon in pineapple slice during drying. Shrinkage was accommodated into FE modelling using the arbitrary lagrange-eulerian method. Consideration of variable D showed better agreement with the experimental data than consideration of constant D, however constant and variable h_m predicted similar results. Incorporation of shrinkage phenomena during modelling led to prediction of more accurate result showing 0.06% deviation from experimental curve, but neglecting the shrinkage resulted in a 17% deviation. Hence, model developed with consideration of shrinkage along with variable D and h_m presented best fit with experimental drying curve. Developed model allowed the visualization of spatial moisture profile within the sample during drying, which would be useful for estimating the correct drying time, optimizing and designing of drying process.

Analysis of volumetric mass transfer coefficient (k L a) in small- (250 mL) to large-scale (2500 L) orbitally shaken bioreactors

In this study, the combination of dimensional analysis (DA) and analysis of variance (ANOVA) was used to predict the volumetric mass transfer coefficient (k _L a) values under different operating conditions for orbitally shaken bioreactors (OSRs) with different filling volumes. It was found that Reynolds number and the interaction between Froude number and geometric number have the largest impact on k _L a with impact indexes of 7.41 and 7.50, respectively. Moreover, the volume number has the largest negative impact on k _L a, with an impact index of - 5.34. Thus, an effective way to increase the oxygen supply is by increasing the shaking speed and shaking diameter or decreasing the vessel diameter. However, cell cultivation with a higher filling volume will have an increased risk of oxygen scarcity. Therefore, with the help of the k _L a prediction model, a suitable operating condition can be determined effectively and easily.

Alum sludge as an efficient sorbent for hydrogen sulfide removal: Experimental, mechanisms and modeling studies

This paper firstly reported a systematic study of using alum sludge (waterworks residue) for H₂S adsorption. Various trials were performed at ambient temperature in a fixed bed column to study the effects of H₂S flow rate, sorbent bed depth on the alum sludge adsorption efficiency of H₂S. The Breakthrough Curves were simulated by the Thomas model, Bed Depth Service Time model and Yoon-Nelson models. The mechanisms of H₂S adsorption onto alum sludge was examined by different physiochemical characterizations of exhausted and raw alum sludge. Moreover, the mass transfer coefficients were determined from mathematical descriptions of breakthrough curves. The alum sludge adsorption capacity was determined to be 374.2 mg of H₂S/g, slightly decreasing with the increasing flow rate and increasing with the increasing bed depth. All the three models successfully predict breakthrough curves which could be used for scaling-up purposes. The microporous structure, alkaline pH and the inherent metal species of the alum sludge promoted the formation of metal sulphate species. This study demonstrated that alum sludge could be used as cost-effective, largely available, and efficient sorbent for H₂S removal.

Effect of size variation on microbubble mass transfer coefficient in flotation and aeration processes

Microbubble technology dramatically raises the efficiency of the flotation and aeration processes of water treatment plants (WTPs), which see extensive use in developed countries. A local institution, Indonesia Water Institute, has tried to investigate microbubble technology intended for lab-scale WTP. However, the current reactor system does not yet meet the microbubble criteria, especially as it has had few investigations of its abilities in flotation and aeration. This study aims to analyze the effect of size variations that affect the rising velocity and mass transfer coefficient (kLa) of aeration contact time. Three local spargers were used to produce microbubbles. Bubble diameters were measured optically and analyzed using ImageJ software. The dissolved oxygen (DO) concentration was measured every minute using an automated sensor so that the kLa could be determined. Of the three spargers, the smallest bubble size was produced by the vortex type with an average bubble diameter of 89 μm and the slowest rising velocity of 17.67 m/h. It also yielded the highest kLa of 0.297/min, which gave an aeration contact time of 3.64 minutes. The experimental uses of three local spargers revealed that the smaller the microbubble diameter, the higher the mass transfer coefficient in flotation and aeration processes. This research can be the basis for developing microbubble technology for WTP in Indonesia.

Study on the effects of alcohol-enhanced air sparging remediation in a benzene-contaminated aquifer: a new insight

In this study, the effects of medium carbon chain alcohol (1-heptanol)-enhanced air sparging (AS) on the remediation of benzene-contaminated aquifers in different media (medium sand, channelized flow; gravel, bubbly flow) were investigated by comparison with a commonly used surfactant (sodium dodecylbenzene sulfonate (SDBS)). The results showed that the addition of 1-heptanol and SDBS significantly increased the air saturation in AS process under different airflow modes. Combined with water retention curves, 1-heptanol had the same effect on reducing the surface tension of groundwater and stabilizing bubbles as SDBS. In the study of benzene pollution removal, when the removal efficiency of the benzene pollutant exceeded 95%, the time required for surfactant-enhanced AS (SEAS) and alcohol-enhanced AS (AEAS) in medium sand was shortened by 28.6% and 52.4%, respectively, and the time required for SEAS and AEAS in gravel media was shortened by 16.7% and 58.3%, respectively, compared with the time required for AS. This finding indicated that the addition of SDBS or 1-heptanol could significantly increase the removal rate of benzene pollutants. Under the same surface tension conditions, the removal effect of 1-heptanol on the benzene pollutant was better than that of SDBS. This difference was due to the disturbance of the flow field during AEAS process causing the 1-heptanol on the gas-liquid interface to volatilize in the carrying gas, thereby inducing Marangoni convection on the interface, enhancing the gas-liquid mass transfer rate, and increasing the removal rate of benzene on the interface. Therefore, 1-heptanol is promising as a new reagent to enhance AS to remediate groundwater pollution.

Cationic reverse micellar based purification of recombinant glutaminase free L-asparaginase II of Bacillus subtilis WB800N from fermentation media

Reverse micellar extraction (RME), a liquid-liquid based separation is a versatile tool for protein purification. A statistical approach was employed for the purification of recombinant glutaminase free anti-cancerous enzyme viz., l-asparaginase II to evaluate the effects of RME in current study. The cationic system (CTAB/iso-octane/hexanol/butanol) was used in RME to optimize both forward and backward protein extraction efficiency. By adapting Taguchi's orthogonal array (OA), maximum forward extraction efficiency (FEE) of 86.98% with 84.82% enzyme activity recovery and 1.04 times purification fold achieved with the optimized parameters. Under the optimal levels, the back extraction efficiency (BEE) was observed to be 96.97% with 93.07% enzyme activity recovery and 1.38 times purification fold. Further, mass transfer kinetic studies of RME indicated the mass transfer coefficients of forward and backward extraction to be 0.049 min^-1 and 0.036 min^-1 respectively.

Evaluation of ammonia recovery from swine wastewater via a innovative spraying technology

An innovative spraying system for NH₄⁺-N removal and recovery was investigated under different pH, temperature, spraying frequency and rate by using spraying system. Results showed that NH₄⁺-N removal efficiency and mass transfer coefficient (K_La) value in swine wastewater (SW) remarkably increased with increasing of temperature, spraying frequency and rate due to promoting the diffusion of NH₃ molecules caused by increasing specific surface of SW molecule, and high shear force and temperature difference between SW and circulating heating tube. Considering the cost and discharge standard, the optimum parameters for NH₄⁺-N removal from SW using spraying system were alkaline, 0.24 m³ h^-1 of continuous spraying, and 45 °C circulating water, and the NH₄⁺-N decreased from 591.2 to 68.9 mg L^-1 (<80 mg L^-1) after 8 h treatment, and this value corresponded to 88.35% removal rate. Furthermore, over 85% recovery rate for NH₄⁺-N could be obtained through absorption of phosphoric acid.

Compensating effect of ultrasonic waves on retarding action of nanoparticles in drops liquid-liquid extraction

The influence of ultrasonic waves on liquid-liquid extraction of circulating drops and in the presence of magnetite nanoparticles was investigated. Experiments were conducted in a column equipped with an ultrasound transducer. The frequency and intensity of received waves, measured by the hydrophone standard method, were 35.40 kHz and 0.37 mW/cm², respectively. The recommended chemical system of cumene-isobutyric acid-water was used in which mass transfer resistance lies in the aqueous phase. Nanoparticles, within concentration range of (0.0003-0.0030) wt%, were added to the aqueous continuous phase. The presence of nanoparticles and ultrasonic waves provided no sensible change in drop size (within 2.49-4.17 mm) and measured terminal velocities were close to Grace model. However, presence of nanoparticles, caused mass transfer to decrease. This undesired effect was significantly diminished by using ultrasonic waves so that mass transfer coefficient increased from (73.0-178.2) to (130.2-240.2) µm/s, providing a 55.6% average enhancement. It is presumably due to disturbing the accumulated nanoparticles around the drops. The current innovative study highlights the fact that using ultrasonic waves is an interesting way to improve liquid-liquid extraction in the presence and absence of nanoparticles.

Effects of roughness and permeability on solute transfer at the sediment water interface

Understanding the mechanisms of solute transfer across the sediment-water interface plays a crucial role in water quality prediction and management. In this study, different arranged particles are used to form typical rough and permeable beds. Large Eddy Simulation (LES) is used to model the solute transfer from the overlying water to sediment beds. Three rough wall turbulence regimes, i.e., smooth, transitional and rough regime, are separately considered and the effects of bed roughness on solute transfer are quantitatively analyzed. Results show that the classic laws related to Schmidt numbers can well reflect the solute transfer under the smooth regime with small roughness Reynolds numbers. Under the transitional regime, the solute transfer coefficient (K_L⁺) is enhanced and the effect of Schmidt number is weakened by increasing roughness Reynolds number. Under the rough regime, the solute transfer is suppressed by the transition layer (Brinkman layer) and controlled by the bed permeability. Moreover, it is found that water depth, friction velocity and bed permeability can be used to estimate the solute transfer velocity (K_L) under the completely rough regime.

Development of an X-Shape airlift photobioreactor for increasing algal biomass and biodiesel production

The aim of this work was to develop a high efficient photobioreactor for increasing biomass and lipid production in microalgae by assessment of the hydrodynamic properties and k_La which are important parameters for improving the algal cultivation efficiency. We designed three different photobioreactors (H-Shape, X-Shape and serial-column). Among them, X-Shape showed the highest hydrodynamic properties and k_La for algal cultivation. Thus, we evaluated the biomass and the lipid production in a 20L scale-up X-Shape photobioreactor. The biomass and lipid production from X-Shape photobioreactor are 1.359±0.007gL^-1 and 117.624±3.522mgL^-1, respectively; which are 30.05% and 23.49% higher than those from the control photobioreactor. Finally, we observed the lipid from X-Shape had high MUFAs, CN and low IV, which is suitable for high quality of biodiesel, suggesting that it can be practicably utilized for mass production of algal biofuel.

Validation of kinetic modeling of progesterone release from polymeric membranes

Mathematical modeling in drug release systems is fundamental in development and optimization of these systems, since it allows to predict drug release rates and to elucidate the physical transport mechanisms involved. In this paper we validate a novel mathematical model that describes progesterone (Prg) controlled release from poly-3-hydroxybutyric acid (PHB) membranes. A statistical analysis was conducted to compare the fitting of our model with six different models and the Akaike information criterion (AIC) was used to find the equation with best-fit. A simple relation between mass and drug released rate was found, which allows predicting the effect of Prg loads on the release behavior. Our proposed model was the one with minimum AIC value, and therefore it was the one that statistically fitted better the experimental data obtained for all the Prg loads tested. Furthermore, the initial release rate was calculated and therefore, the interface mass transfer coefficient estimated and the equilibrium distribution constant of Prg between the PHB and the release medium was also determined. The results lead us to conclude that our proposed model is the one which best fits the experimental data and can be successfully used to describe Prg drug release in PHB membranes.

Performance analysis of a continuous serpentine flow reactor for electrochemical oxidation of synthetic and real textile wastewater: Energy consumption, mass transfer coefficient and economic analysis

A continuous flow electrochemical reactor was developed, and its application was tested for the treatment of textile wastewater. A parallel plate configuration with serpentine flow was chosen for the continuous flow reactor. Uniparameter optimization was carried out for electrochemical oxidation of synthetic and real textile wastewater (collected from the inlet of the effluent treatment plant). Chemical Oxygen Demand (COD) removal efficiency of 90% was achieved for synthetic textile wastewater (initial COD - 780 mg L^-1) at a flow rate of 500 mL h^-1 (retention time of 6 h) and a current density of 1.15 mA cm^-2 and the energy consumption for the degradation was 9.2 kWh (kg COD)^-1. The complete degradation of real textile wastewater (initial COD of 368 mg L^-1) was obtained at a current density of 1.15 mA cm^-2, NaCl concentration of 1 g L^-1 and retention time of 6 h. Energy consumption and mass transfer coefficient of the reactions were calculated. The continuous flow reactor performed better than batch reactor with reference to energy consumption and economy. The overall treatment cost for complete COD removal of real textile wastewater was 5.83 USD m^-3.

Developing a vacuum thermal stripping - acid absorption process for ammonia recovery from anaerobic digester effluent

To prevent acetoclastic methanogens from ammonia inhibition in anaerobic digestion of protein-rich substrates, ammonia needs to be removed or recovered from digestate. This paper presents an innovative ammonia recovery process that couples vacuum thermal stripping with acid absorption. Ammonia is stripped out of digestate boiling at a temperature below the normal boiling point due to vacuum. Stripped ammonia is absorbed to a sulfuric acid solution, forming ammonium sulfate crystals as a marketable product. Three common types of digestate were found to have boiling point temperature-vacuum curves similar to water. Seven combinations of boiling temperature and vacuum (50 °C 16.6 kPa, 58 °C 20.0 kPa, 65 °C 25.1 kPa, 70 °C 33.6 kPa, 80 °C 54.0 kPa, 90 °C 74.2 kPa, and 100 °C 101.3 kPa) were tested for batch stripping of ammonia in dairy manure digestate. 93.3-99.9% of ammonia was stripped in 3 h. The Lewis-Whitman model fitted ammonia stripping process well. Ammonia mass transfer coefficient was significantly higher at boiling temperature 65-100 °C and vacuum pressure 25.1-101.3 kPa than 50-58 °C and 16.6-20.0 kPa. The low ammonia saturation concentrations (0-24 mg N/L) suggested a large driving force to strip ammonia. The optimum boiling point temperature - vacuum pressure for ammonia recovery in a recirculation line of a mesophilic digester was 65 °C and 25.1 kPa, at which the ammonia mass transfer coefficient was as high as 37.3 mm/h. Installation of a demister and liquid trap could avoid negative effects of higher stripping temperature and stronger vacuum on formation of ammonium sulfate crystals. Pilot tests demonstrated that high-purity ammonium sulfate crystals could be produced by controlling sulfuric acid content and maintaining acid solution saturated with ammonium sulfate. Although volatile organic compounds such as cyclohexene were found in the final acid solutions, no volatile organic compounds were found in the recovered crystals.

Latex paint as a delivery vehicle for diethylphthalate and di-n-butylphthalate: predictable boundary layer concentrations and emission rates

The description of emission processes of volatile and semi-volatile organic compounds (VOCs and SVOCs) from building products requires a detailed understanding of the material and the air flow conditions at the surface boundary. The mass flux between the surface of the material and air depends on the mass transfer coefficient (hm) through the boundary layer, the gas phase concentration of the target compound immediately adjacent to the material (y0), and the gas-phase concentration in bulk air (y(t)). In the present study emission experiments were performed in two chambers of quite different sizes (0.25 m(3) and 55 m(3)), and, in the larger chamber, at two different temperatures (23°C and 30°C). The emitting material was latex wall paint that had been doped with two plasticizers, diethylphthalate (DEP) and di-n-butylphthalate (DnBP). The phthalate content in the paint was varied in the small chamber experiment to evaluate the impact of the initial concentration in the bulk material (C0) on the emission rate. Boundary layer theory was applied to calculate hm for the specific phthalates from the Sherwood number (Sh) and the diffusion coefficient (Dair). Then y0 was determined based on the bulk gas-phase concentration at steady state (y¯). For both, DEP and DnBP, the y0 obtained was lower than the respective saturation vapor pressure (Ps). Furthermore, for both phthalates in latex paint, the material/air partition coefficient (C0/y0) was close in value to the octanol/air partition coefficient (KOA). This study provides a basis for designing phthalate emitting reference materials that mimic the emission behavior of common building materials.

Numerical simulation of ultrasonic enhancement on mass transfer in liquid-solid reaction by a new computational model

Mass transfer coefficient is an important parameter in the process of mass transfer. It can reflect the degree of enhancement of mass transfer process in liquid-solid reaction and in non-reactive systems like dissolution and leaching, and further verify the issues by experiments in the reaction process. In the present paper, a new computational model quantitatively solving ultrasonic enhancement on mass transfer coefficient in liquid-solid reaction is established, and the mass transfer coefficient on silicon surface with a transducer at frequencies of 40 kHz, 60 kHz, 80 kHz and 100 kHz has been numerically simulated. The simulation results indicate that mass transfer coefficient increases with the increasing of ultrasound power, and the maximum value of mass transfer coefficient is 1.467 × 10(-4) m/s at 60 kHz and the minimum is 1.310 × 10(-4) m/s at 80 kHz in the condition when ultrasound power is 50 W (the mass transfer coefficient is 2.384 × 10(-5) m/s without ultrasound). The extrinsic factors such as temperature and transducer diameter and distance between reactor and ultrasound source also influence the mass transfer coefficient on silicon surface. Mass transfer coefficient increases with the increasing temperature, with the decreasing distance between silicon and central position, with the decreasing of transducer diameter, and with the decreasing of distance between reactor and ultrasound source at the same ultrasonic power and frequency. The simulation results indicate that the computational model can quantitatively solve the ultrasonic enhancement on mass transfer coefficient.

Kinetic modeling on CO₂ capture using basic oxygen furnace slag coupled with cold-rolling wastewater in a rotating packed bed

In this study, direct and indirect carbonation of basic oxygen furnace slag (BOFS) coupled with cold-rolling wastewater (CRW) was carried out via a rotating packed bed (RPB). The solid products were qualitatively characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) and quantitatively analyzed with thermogravimetric analysis (TGA). The leachate was analyzed with inductively coupled plasma-optical emission spectroscopy (ICP-OES). The results indicate that the maximum achievable carbonation conversion (MACC) of BOFS was 90.7%, corresponding to a capture capacity of 0.277 g CO₂/g of BOFS, by direct carbonation with CRW under a rotation speed of 750 rpm at 30 °C for 20 min. In addition, CO₂ mass balance among the gas, liquid, and solid phases within an RPB was well-developed, with an error less than 10%, to confirm the actual CO₂ capture capacity of BOFS with precision and accuracy. Furthermore, a reaction kinetic model based on mass balance was established to determine the reaction rate constant for various liquid agents (CRW and pure water). It was concluded that co-utilization of alkaline wastes including BOFS and CRW via the RPB is a novel approach for both enhancing CO₂ capture capacity and reducing the environmental impacts of alkaline wastes.