Optimization of Bioscrubber Performances: Experimental and Modeling Approaches

The deodorization efficiency of a suspended-growth bioscrubber was characterized from an experimental and theoretical approach, in order to optimize such systems for the treatment of polluted air from wastewater low lift station. A model of prediction of volatile compound removal efficiencies was developed according to operating conditions and contact mode (packed and spray column). The predictive ability of the model was validated from transfer data obtained with two representative molecules (ethanol and hydrogen sulfide) on a laboratory scale device. The theory takes into account the hydrodynamic characteristics of the fluids flowing in the contactor, which were defined from a previous experimental residence time distribution study. A study of parametric sensitivity of the model was then conducted to evaluate the influence of operating conditions (gas and liquid flow rates, contact mode, washing solution characteristics), hydrodynamic parameters of each flow (liquid holdup in the column, hydrodynamic behavior of the liquid flow, axial dispersion of the gas flow), and biodegradation step on the deodorization efficiency of a bioscrubber applied to the treatment of a polluted gas containing ethanol. The assumptions of sizing and optimization were confirmed on a suspended-growth bioscrubber used for the deodorization of an exhaust gas emitted by a wastewater low lift station.     

BTEX Removal from Produced Water Using Surfactant-Modified Zeolite

Produced water (water generated during recovery of petroleum) contains large amounts of various hazardous organic compounds such as benzene, toluene, ethylbenzene, and xylenes (BTEX). With increasing regulations governing disposal of this water, low-cost treatment options are necessary. This study evaluated the effectiveness of surfactant-modified zeolite (SMZ) for removal of BTEX from produced water. The long-term effectiveness of SMZ for BTEX removal was investigated along with changes in sorption properties with long-term use. The results of these investigations show that SMZ completely removes BTEX from produced water up to a compound-specific capacity, and that SMZ can be regenerated via air sparging without loss of sorption capacity. The BTEX mobility in laboratory columns of SMZ was in the order of decreasing water solubility and increasing Kow. The most soluble compound, benzene, began to elute at 8 pore volumes (PV), while the least soluble compounds, ethylbenzene and xylenes, began to elute at 50 PV. After treating 4,500 PVs of water in the column system over 10 sorption/regeneration cycles, no significant reduction in sorption capacity of the SMZ for BTEX was observed. The mean Kds determined in these column experiments ranged from 18.3?L/kg for benzene to 95.0?L/kg for p- and m-xylene. Laboratory columns were upscaled to create a field-scale SMZ treatment system. The field-scale system was tested at a natural gas produced-water treatment facility near Wamsutter, Wyo. We observed even greater sorption of BTEX in the field column than predicted from the laboratory results. In the field column, initial benzene breakthrough occurred at 10 PV and toluene breakthrough began at 15 PV, and no breakthrough of ethylbenzene or xylenes occurred throughout the 80 PV experiment. The field and laboratory results, along with the low price of SMZ (about $460?per?metric?t), suggest that SMZ has a potential role in a cost-effective produced water treatment system.     

Modeling of Aqueous BTEX Adsorption in Column and Multistage Adsorbers

Theoretical and experimental investigations have been conducted on the adsorption characteristics of benzene, toluene, ethylbenzene, and xylene (BTEX) by macroreticular resins. A theoretical model is proposed for describing the BTEX breakthrough curves of the adsorption column. The column adsorption model contains two model parameters, τ and K, that are conveniently estimated using the observed breakthrough data. The model was tested for benzene adsorption with a flow rate between 12 and 30 mL∕min, inlet concentration between 200 and 500 mg∕L, and temperature between 30 and 60°C. Excellent fit of the model to the measured data was obtained. The proposed model hence offers a convenient means for accurate predictions of the adsorption capacity and breakthrough point of a column BTEX adsorption process. Also developed are the mass balance equations representing countercurrent multistage adsorption process. The countercurrent multistage adsorption process has been shown to save a significant amount of adsorption resin in achieving the same BTEX removal as the single-stage process. Experimental tests for a two-stage example verify that up to 60% of the Ambersorb resin can be saved over a single-stage process.     

Modeling Mass Removal during In Situ Air Sparging

A model was developed to simulate mass removal during in situ air sparging. The model captures the physical characteristics of the air plume and employs conventional methods to simulate mass transfer. A parametric study was conducted using the model to assess how chemical properties, the operational method, and media affect mass removal during in situ air sparging. Mass removal is particularly sensitive to Henry's law constant, and the aqueous diffusion coefficient when Henry's law constant is high. Simulations of pulsed and continuous air injection show that pulsed injection can yield greater mass removal than continuous air injection for certain pulse cycles. Mass removal is generally greater at higher injection rates, but the increase in mass removal diminishes as the injection rate increases. Parametric analysis also showed that mass is removed faster when air channels are narrower or more tortuous (i.e., in coarser or more well-graded formations).     

Temperature Effects of Trickle-Bed Biofilter for Treating BTEX Vapors

Effects of temperature change in the range of 15–50°C on the performance of a trickle-bed biofilter for treating benzene, toluene, ethylbenzene and o-xylene (BTEX) vapors in air streams were investigated. In the steady-state condition, the BTEX removal efficiency increased as the operating temperature increased in the range of 15–30°C. However, an opposite trend was observed between 30 and 50°C. The trickle-bed biofilter appears to be an effective treatment process in the temperature range of 25–35°C. The microscopic observations showed that the morphologies of the leading microorganisms within the first-stage biofilm were rod-shaped bacteria in association with filaments, bacilli, and cocci at 15, 30, and 50°C, respectively. A theoretical evaluation on the temperature coefficient (θ) indicated that the temperature effects on the performance of a trickle-bed biofilter are more significant under lower BTEX loading rates. Furthermore, the mean θ value for a trickle-bed biofilter was equal to 1.021, which is in the typical range of some commonly used aerobic processes (1.0–1.10).     

Numerical Modeling of Inclusion Removal in Electromagnetic Stirred Steel Billets

To investigate the inclusion removal in billets cast under electromagnetic stirring (EMS) influence, a numerical model has been developed to compute the magnetic field, the Lorentz force, the steel flow velocities, and the particle transport within the liquid pool. The electromagnetic field was described by the Maxwell equations and the finite element method was applied using a commercial package. The turbulent fluid flow was described by the Navier‐Stokes equation and by the Reynolds Stress model and the finite volume method was applied using another numerical package. The time average of the Lorentz force was calculated in each element center and this value was applied as a body force in the Navier‐Stokes equation. The magnetic flux density profile was compared with the data obtained in the stirrer of the steel plant. The particle transport model includes the drag force, the buoyancy force and the random walk model, to include the turbulence effects on the particle trajectory. The inclusion removal was calculated and analysed in function of casting speed and stirring current for one size section of mold. The inclusions considered in the calculations have a fixed density and four values of diameter. The numerical results of the electromagnetic model are in agreement with the experimental measurements. A good relationship between the electromagnetic model and the fluid flow model could be shown. An interesting effect is the break of the rotation motion due to the EMS by the jet from the nozzle. The fraction of inclusions removed by the top surface of the mold was improved due to the EMS.     

Performance of a Biofilm Airlift Suspension Reactor for Synthetic Wastewater Treatment

Performance stability of a biofilm airlift suspension reactor (BASR) was studied using ethanol as a substrate. The main objective of this research was to investigate the applicability of the reactor as a wastewater treatment process by examining the effects of soluble chemical oxygen demand (SCOD) loading rate and hydraulic retention time (HRT) on the performance of the reactor. SCOD removal of 90% or higher was achieved at an HRT of 45 min with loading rates from 10 to 18 kg SCOD/m3?day. Similar results were obtained at HRTs of 60 and 90 min and a SCOD loading rate of 10 kg SCOD/m3?day. Nitrification occurred in the system when the ratio of SCOD to ammonia nitrogen was changed from 10:1 to 6:1. The morphology of the biofilm in the BASR was denser and thicker when nitrifiers grew in the biofilm. Filamentous overgrowth was observed from time to time and proper chlorine dose successfully suppressed its growth. The oxygen uptake rate was an effective tool for monitoring the effect of chlorination.     

Neural Network Modeling of Organics Removal by Activated Carbon Cloths

The adsorption of organic compounds onto an activated carbon cloth is studied in a dynamic reactor. An experimental design is carried out to investigate the influence of operating conditions (initial concentration C0, flow velocity U0, and bed thickness Z) and adsorbate's characteristics. A slow intraparticular diffusion is shown by flattened breakthrough curves, and adsorption capacities are high and range between 50 and 250 mg g?1. The transfer zone Z0, assessed by the Adams and Bohart equation, is low (3 mm). All experimental results are modeled by a neural network to take into account the specific diffusion of cloths. Parameters related to the adsorbate-adsorbent affinity in a batch reactor are consequently introduced in the input layer of the neural network (intraparticular coefficient Kw and Freundlich parameters Kf and l∕n), added to operating conditions whose influence was shown (C0, U0, and Z) and time t. The statistical quality of the neural network modeling is high (r2 = 0.956). Furthermore, the Garson connection weight method allows the relative influence of input neurons to be determined. This analysis confirms the influence of parameters relative to adsorbant-adsorbate affinity.     

Modeling the Removal of Arsenic by Iron Oxide Coated Sand

An arsenic filtration experiment using iron oxide coated sand was modeled using the USGS geochemical program PHREEQC. Despite some uncertainty regarding the initial conditions of the groundwater and the simplicity of the model, it replicated the experimental results within 10%. The original experiment filtered 165 bed volumes to concentrations less than 0.01 mg/L As and approximately 210 bed volumes to 0.05 mg/L As. The model filtered 168 bed volumes to 0.01 mg/L As and 228 bed volumes to 0.05 mg/L.     

Case Study of Fluvial Modeling of River Responses to Dam Removal

A plan was made to remove Matilija Dam on the Ventura River. With dam removal, the delta in the reservoir and the downstream channel were expected to undergo major changes in morphology. The FLUVIAL-12 model was employed to simulate reservoir and river channel responses after dam removal. As a first step, the model was calibrated using the Ventura River data to establish its validity. In calibration, the model was used to simulate the fluvial processes starting from the time of dam completion. The simulated sediment deposition above the Matilija Dam matches closely with the deposits measured by the U.S. Bureau of Reclamation. A large amount of sediment was stored in the reservoir; some of the stored sediment would be transported downstream after dam removal. An important consequence of dam removal is the major increase of sediment release to the river channel downstream. The sediment supply to the downstream reach is not only from the stored sediment in the reservoir but also from natural sediment inflow from the upstream watershed. Therefore, sediment supply to the downstream reach will exceed the natural sediment flow before the dam presence. This situation tends to overload the downstream reach with sediment, resulting in excessive deposition. The amount of sediment release from the area above the removed dam is closely related to the changes in reservoir morphology. It is necessary to model changes in the channel bed profile and channel width during erosion in order to determine the amount of sediment removal. The amount of sediment release may not be simulated using an erodible-bed model but it may be determined using an erodible boundary model.     

Modeling Flow and Pollutant Removal of Wet Detention Pond Treating Stormwater Runoff

A mathematical model of pollutant removal by wet ponds was developed based on the mass balance principle and the release–storage equation. The release–storage equation can be linear or nonlinear depending on the wet pond shape and the spillway crest features. If the exponent index of the storage relationship (d) is equal to the index of the outflow equation (b), the wet pond hydrological routing model is linear. Otherwise, the model is nonlinear. Substituting the release–storage equation into the continuity equation produces a nonlinear ordinary differential equation (ODE). A Runge–Kutta method was used to solve the resulting nonlinear ODE. When the ratio of indexes d/b = 2/3, the hydrologic wet pond model reduces to a special case that leads to an implicit analytical solution. The pollutant removal and flow routing models were tested with data obtained from an actual wet pond for treating highway runoff. The predicted flow discharges and pollutant concentrations compared well with the observed data.     

气幕挡墙中间包夹杂物去除的水模型研究

以连铸1500mm×250mm板坯的中间包为原型,几何相似比1/3,采用自制多孔透气砖进行中间包底吹气的水模型试验。结果表明,气幕挡墙中间包中,夹杂物通过斯托克斯机理上浮,气泡吸附和钢液上扬流动而上浮去除;当吹气量≥0.08m~3/h,距入口中心533～800mm处形成有效的气幕挡墙,显著改善钢液流动性,夹杂物去除率由不吹气的44.86%增加至72.86%,并改善小颗粒夹杂物的去除。工业试验表明,采用气幕挡墙,使T[O]降低12%以上。     

Removal of tetrachloroethylene in an anaerobic column bioreactor

Removal of tetrachloroethylene (perchloroethylene; C2Cl4) by microbial consortia from two sites with different C2Cl4 exposure histories was examined in a bench-scale anaerobic column bioreactor. It was hypothesized that optimal removal would be observed in the reactor packed with sediments having an extensive exposure history. Microbial consortia were enriched from hyporheic-zone (HZ) sediments from the Portneuf aquifer near Pocatello, Idaho, and from industrial-zone (IZ) sediments from a highly contaminated aquifer in Portland, Oregon. Lactate and acetate were the electron donors during experiments conducted over 9 and 7 months for HZ and IZ sediments, respectively. In the HZ bioreactor, the retention time ranged from 31 h to 81 h, and inlet C2Cl4 concentrations ranged from 0.1 ppm to 1.0 ppm. Dechlorination of C2Cl4 averaged 60% and reached a maximum of 78%. An increase in C:N from 27:1 to 500:1 corresponded to an 18% increase in removal efficiency. Trichloroethylene production corresponded to decreased effluent C2Cl4; further intermediates were not detected. In the IZ bioreactor, the retention time varied from 34 h to 115 h; the inlet C2Cl4 concentration was 1.0 ppm. C2Cl4 removal averaged 70% with a maximum of 98%. Trichloroethylene and cis-dichloroethylene were detected in the effluent. Increases in C:N from 50:1 to 250:1 enhanced dechlorination activity.     

Removal of Redundant Relationships in an AON Project Network for Evaluating Schedule Complexity

Since redundant relationships in an activity-on-node (AON) project network indicate that the schedule is more complex than it actually is, they should not be considered when evaluating the schedule complexity. However, identifying the relationships that can be removed while maintaining the project logic is not an easy task. For this purpose, this paper proposes a methodology, adapted from interpretive structural modeling, that basically transforms an AON project network into a network called minimum-edge diagraph which contains no redundant relationships. The methodology steps are explained through a demonstrative example of a simple hypothetical project. The application of the methodology to the AON network of a real construction project shows that it is easy to use yet effective in removing redundant relationships.     

Modeling of Cadmium Removal from Domestic Wastewater in Constructed Wetlands Using STELLA Simulation Program

A mathematical model was developed to simulate cadmium removal from wastewater in free water surface (FWS) and subsurface flow (SF) constructed wetlands using STELLA simulation program. The model simulated the accumulation of cadmium in soil (Cds), uptake by plants (Cdp), and residual concentration in effluent (Cdww_eff). The model was calibrated using one-half of the experimental data for the adjustment of the coefficients and the remaining data for model verification. The comparison of simulated and experimental values of Cds, Cdp, and Cdww_eff showed good agreement. The results indicated that the developed mathematical model could be useful for predicting the fate of cadmium when treating domestic effluents in constructed wetlands.     

Modeling As(V) Removal in Iron Oxide Impregnated Activated Carbon Columns

Iron oxide impregnated onto an activated carbon (FeAC) has a high arsenic (As) removal capacity with the potential to be used in existing activated carbon column systems. Objectives of this research were to investigate As(V) removal from aqueous-phase systems using fixed-beds packed with FeAC and to determine if the triple layer model (TLM) with the homogeneous surface diffusion model (HSDM) could describe As(V) removal in the columns. Rapid small-scale column tests (RSSCT) were conducted at various empty bed contact times (EBCT). Effluent As(V) breakthrough (10?μg/L) was incipient for the 0.20-min EBCT experiment, whereas ～ 2300 bed volumes of water at 1-mg/L inlet concentration of As(V) was treated at an EBCT of 2.1?min before breakthrough occurred. The TLM with three As(V)-FeAC surface reactions coupled with the HSDM provided accurate prediction of As(V) removal in the RSSCT.