Model Sensitivity Analysis for Biotrickling Filter Treatment of Graywater Simulant and Waste Gas. II

A detailed sensitivity analysis was conducted to identify key parameters for a biotrickling filter simultaneously treating graywater and waste gas containing ammonia and hydrogen sulfide contaminants. Sampling-based approaches were applied to quantitatively assess the sensitivity of both design and intrinsic model parameters. Specifically, the sensitivity of contaminant removal rates under system conditions was investigated. Results suggested that contaminant removal rates can be substantially improved by increasing the fraction of wetted area in a biotrickling filter. Although recirculation flow rate is insensitive when considering liquid contaminant removal, increasing this parameter improves gas removal efficiency and also increases wetted area within the biotrickling filter. Reactor performance can also be improved by increasing gas and liquid residence times. Contaminant diffusivity through the biofilm is an important parameter and should be accurately assessed. This study differentiated key from insignificant biotrickling filter reactor design parameters for the biotrickling filter and provides guidance for similar research applications.     

Behavior of Field-Scale Biotrickling Filter under Nonsteady State Conditions

The performance of a field-scale biotrickling filter was investigated for the treatment of styrene vapors released from a bathtub manufacturing process. The two-stage biotrickling filter was operated in series with an average gas flow rate of 350 m3?h?1 corresponding to an overall empty bed gas contact time of 84 s. Daily average values of styrene removal efficiency varied from 40 to 90% with inlet concentrations ranging between 0.4 and 1.7 g?m?3. System performance was not significantly affected by changes in temperature and was moderately susceptible to 3-day starvation or complete system shutdown. After 7 months of styrene treatment, toluene contaminated air was fed to the system and experiments were performed in which styrene and toluene were fed alternately at 3-h intervals. While styrene elimination remained unchanged over the cycles, the elimination capacity of toluene increased with the number of cycles, indicating some adaptation of the process culture to the new contaminant. Overall, the results suggest that biotrickling filters for air pollution control can be successful even under greatly varying operating conditions.     

Conversion of Full-Scale Wet Scrubbers to Biotrickling Filters for H2S Control at Publicly Owned Treatment Works

Until recently, biological treatment of odors in biofilters or biotrickling filters was thought to require a longer gas contact time than chemical scrubbing, hence bioreactors for air treatment required a larger footprint. This paper discusses the conversion of chemical scrubbers to biological trickling filters. Initially, research was conducted with a laboratory-scale biotrickling filter. An effective open-pore polyurethane packing material was identified and H2S biotreatment performance was quantified. Key technical issues in determining the general suitability of converting wet scrubbers to biotrickling filters were identified, and a generic ten-step conversion procedure was developed. Following the laboratory research, five full-scale chemical scrubbers treating odorous air at the Sanitation District of Orange County, Calif., were converted to biotrickling filters. The original airflow rate was maintained, resulting in a gas contact time as low as 1.6–3.1?s. The converted biotrickling filters demonstrated an excellent capability for treating high H2S concentrations to concentrations below regulatory limits. This study shows outstanding potential for converting chemical scrubbers to biotrickling filters at publicly owned treatment works.     

Effect of Biotrickling Filter Operating Parameters on Chlorobenzenes Degradation

In this paper the effect of operating parameters on biotrickling filter performance degrading chlorobenzene and o-dichlorobenzene mixture were studied. The large laboratory scale biofilter, total volume 40 L, filled with inert packing material was used. The biomass adaptation and cultivation were performed in a batch fermentor and were used to inoculate the biotrickling filter. After a starting period, the influence of the substrate load increase, liquid recirculation flow rate, and empty bed retention time on elimination capacity and removal efficiency were found. The most important recirculation liquid parameters were analyzed every day, that is: concentration of metabolites, dissolved organic carbon, nitrate, chloride, and biomass. A good correlation was found between intermediate concentration and the removal efficiency of the biotrickling filter. The measurements of the absorbance, very easy and rapid, can be used as a control parameter of the biofiltration efficiency.     

Interaction of Soil Air Permeability and Soil Vapor Extraction

A new theoretical model to analyze the measurements obtained from a typical soil column venting experiment is proposed. The principles of mass transfer, Darcy's law, and air compressibility in the form of pressure-volume relationships were coupled to calculate the contaminant concentration in the gas phase (air), and the rate of contaminant removal. The proposed model relates soil air permeability with the contaminant removal and is capable of calculating the variation of soil air permeability with time during the venting process. The contaminated sand sample was idealized as a system of straight capillary tubes in the direction of flow, lined by the liquid contaminant. A closed-form solution for radial diffusion of the contaminants in a cylinder, coupled with axial advection of air, was used to model contaminant removal. The results from the mass transfer model were then used to trace the change of soil air permeability with time. The model also uses, as an alternative approach, a modified form of Darcy's law for compressible flow.     

Nonequilibrium Nonaqueous Phase Liquid Mass Transfer Model for Soil Vapor Extraction Systems

Soil vapor extraction is a popular soil remediation technology that is hampered by less than optimal performance in the field due to mass transfer limitations. Therefore, laboratory column venting experiments were completed to quantify mass transfer limitations for the removal of multicomponent nonaqueous phase liquid (NAPL) contaminants from a silt loam soil at three water contents. The observed mass transfer limitations were quantified using a four phase multicomponent, nonequilibrium contaminant transport model based on first-order mass transfer kinetics. The overall mass transfer coefficient Kga was treated as a variable and modeled as a linear function of the NAPL volumetric fraction using two adjustable parameters (m, the slope parameter and Kgamin, the intercept). Both were back calculated from column venting data. The agreement between the calibrated model and experimental results were favorable for the removal of single and binary contaminants under conditions ranging from near equilibrium to severe mass transfer limitations and extended tailing. A strong dependency of Kga on water content was evident by the differences in Kgamin and to a lesser extent, m, at the three water contents investigated. A single expression Kga captured the performance of both components in the binary mixture. For the quaternary venting experiments a single expression for Kga captured the performance of all four components well under air dry conditions. However, the agreement between the hexane model versus the experimental result deteriorated significantly as the water content increased. This difference is attributed to hexane’s lower affinity for the water phase relative to the other three components in the mixture.     

Hydrodynamic Characteristics in Biotrickling Filters as Affected by Packing Material and Hydraulic Loading Rate

Hydrodynamics in biotrickling filters can be strongly influenced by packing material geometry and hydraulic loading rate. While it is generally accepted that increasing wetted area in a biotrickling filter can improve process performance, additional research on synthetic packing materials and parameters that improve hydrodynamics, resulting in increased wetted area, is desirable. For this research, a series of tracer tests was conducted to compare hydrodynamics in bench scale biotrickling filters with three different packing materials under three different flow rates. Results suggest that of the three packing materials, the material with the highest specific surface area resulted in channeling and excessive formation of stagnant zones within the biotrickling filters. Liquid distribution through the biotrickling filters substantially improved at a hydraulic loading rate of 1.9?m/hr for all packing materials, but based on these experiments, improvements were minimal when the hydraulic loading rate was increased further. The presence of a biofilm increased mean residence time in biotrickling filters and the factor by which the increase was observed decreased with increasing hydraulic loading rate.     

Subsurface Radioactive Contaminant Transport Modeling Using Particle and Kalman Filter Schemes

Contamination of groundwater by radioactive contaminants can be harmful to the environment. Various prediction models have been adopted to simulate the state of contaminants in the subsurface. Conventional numerical models are simplified by approximation and the model parameters are assumed to be constant, thereby introducing error to the prediction results. Particle and Kalman filters are used in this research to simulate the radioactive contaminant cobalt-57 transport in a subsurface environment by using a two-dimensional advection-dispersion model. A radioactive contaminant concentration was predicted spatially and temporally within boundary conditions. The errors in the prediction results were assessed by using the root-mean-square-error (RMSE) equation. The results show that the Kalman filter performs better than the particle filter when the prediction model is linear. Furthermore, the results from filters are closer to the true value in comparison with the numerical solution, and the filters are capable of reducing the RMSE of the numerical solution by approximately 80%.     

Mass Transfer of Ozone in Semibatch Stirred Reactor

The mass transfer of ozone from the gaseous phase into the aqueous phase plays an important role in determining the efficiency of ozonation. In this study, a mass-transfer model has been developed to simultaneously predict concentrations of the dissolved and outlet gaseous ozone in a semibatch reactor. A model in which the liquid phase is described as well mixed and the gas phase is described as a plug-flow system was used to estimate the mass transfer of ozone in both laboratory and pilot reactors. The self-decomposition of ozone was also incorporated into the model. The mass-transfer coefficient was found to increase with increasing gas flow rate, temperature, and ionic strength in the solution. Using a sensitivity analysis, the partition coefficient α was found to be the most sensitive factor that affects the concentration profile of dissolved ozone. However, the outlet gaseous concentration of ozone is quite insensitive to all physical parameters investigated in this study.     

Bayesian Storm-Water Quality Model and Its Application to Water Quality Monitoring

A Bayesian statistical approach for determining the parameter uncertainty of a storm-water treatment model is reported. The storm-water treatment technologies included a sand filter and a subsurface gravel wetland. The two field systems were loaded and monitored in a side-by-side fashion over a two-year period. The loading to each system was storm-water runoff generated by ambient rainfall on a commuter parking lot. Contaminant transport is simulated by using a one-dimensional advection-dispersion model. The unknown parameters of the model are the contaminant deposition rate and the hydrodynamic dispersion. The following contaminants are considered in the study: total suspended solids, total petroleum hydrocarbons–diesel range hydrocarbons, and zinc. Parameter uncertainties are addressed by estimating the posterior probability distributions through a conventional Metropolis-Hastings algorithm. Results indicate that the posterior distributions are unimodal and, in some instances, exhibit some level of skewness. The Bayesian approach allowed the estimation of the 10th, 25th, 50th, 75th, and 95th percentiles of the posterior probability distributions. The prediction capabilities of the model were explored by performing a Monte Carlo simulation using the calculated posterior distributions and two rainfall-runoff events not considered during the calibration phase. The objective is to estimate effluent concentrations from the treatment systems under different scenarios of flow and contaminant loads. In general, estimated effluent concentrations and the total estimated mass fell within the defined uncertainty limits.     

Inactivation of Cryptosporidium Oocysts in a Pilot-Scale Ozone Bubble-Diffuser Contactor. I: Model Development

A mathematical model was developed to simulate the performance of a pilot-scale ozone bubble-diffuser column. The reactor hydrodynamics was represented with the axial dispersion reactor model. An analytical solution was developed for the liquid and gas phase ozone mass balances in which dissolved ozone decomposes by first-order kinetics. Numerical approximations were provided for the mass balances for viable microorganisms and the more general case of dissolved ozone decomposition through a second-order reaction with fast ozone demand in natural organic matter. Model components required to predict the liquid and gas phase ozone concentration and viable microorganism number density profiles throughout the bubble-diffuser column included input parameters (liquid and gas flow rates, influent gas and dissolved ozone concentrations, temperature, and countercurrent or cocurrent operation mode), empirical correlations (dispersion number, volumetric mass transfer coefficient, Henry’s law constant), and batch or semibatch kinetic information (ozone decomposition rate constants and fast-ozone demand, and microorganism inactivation lag phase and rate constant). A sample model run for the case of first-order ozone decomposition revealed that the analytical and numerical solutions were practically identical.     

首钢大型高炉布袋除尘系统煤气温度的控制

介绍了在炼铁高炉煤气布袋除尘系统中,调节荒煤气温度来适应布袋除尘器布袋材质的许用温度的一项新技术。该技术采用热管做传热元件,并用水做降温介质,用管网蒸汽做升温介质,利用水的相变调节煤气温度。     

Biotrickling Filtration for Control of Volatile Organic Compounds from Microelectronics Industry

This study investigated the transient and steady-state performance of a bench-scale biotrickling filter for the removal of an organic mixture (acetone, toluene, and trichloroethylene) typically emitted by the microelectronics industry. The microbial consortium consisting of seven bacterial strains that were fully acclimated prior to inoculation onto activated carbon media. Among the seven strains, the Pseudomonas and Sphingomonas strains appeared to be the major groups degrading toluene (>25?ppmv/h?108 cell) and trichloroethylene (>2.3?ppmv/h?108 cell), while Mycobacteria and Acetobacteriaceae strains were the primary decomposers of acetone (>90?ppmv/h?108 cell). The column performance was evaluated by examining its responses to the fluctuating influent total hydrocarbon concentrations, which varied from 850 to 2,400 ppmv. Excellent steady-state removal efficiencies greater than 95% were consistently observed, and system recovery was typically within two days after a significant increase in the inlet loading was experienced. The overall mass-transfer rate and the biokinetic constants were determined for each organic component. Mathematical simulations based on these parameters demonstrated that the removal of acetone was kinetically limiting, whereas the removals of toluene and trichloroethylene were at least partially mass-transfer limiting.     

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.     

Load Dampening System for Vapor Phase Bioreactors

Vapor phase bioreactors are receiving increasing attention as a cost-effective treatment method for air contaminated with volatile organic compounds (VOCs). In this study, a novel absorption and humidification system was evaluated for its ability to dampen transient VOC loads, and to reduce their detrimental effects on a downstream bioreactor. A model based on the mass transfer characteristics of two target compounds (acetone and toluene) was developed and takes into account a closed water recirculation loop that minimizes fugitive emissions and simultaneously humidifies the inlet gas stream. When water is used as the scrubbing liquid, model and experimental results indicate that the system effectively dampens hydrophilic compounds and segregates them from the hydrophobic compounds in the waste gas stream. The response of a vapor phase bioreactor to the pretreated stream has also been assessed, and results indicate that the load dampening system works effectively for hydrophilic, but not hydrophobic, VOCs. However, when an organic cosolvent is used in conjunction with water, hydrophobic VOCs can also be dampened efficiently.     

基于(火用)效率目标的环冷机余热回收系统操作参数优化

摘要：针对烧结环冷机余热回收利用率不高的难题,采用分析法建立了评价某钢铁厂烧结环冷机余热回收系统运行效率的效率模型。基于多孔介质模型、局部非热平衡方程、真实气体SRK方程建立环冷机内气固两相换热模型。通过CFD仿真模拟,探究料层高度、循环风机输入烟气温度、烧结矿底部入口风速三项可控环冷机运行工艺参数对系统效率的影响规律。结果表明,料层厚度在1～1.5 m区间每增加0.1 m,效率增加0.8%～1.1%;循环风温在100～140℃之间每增加10℃,效率增加1.4%～1.5%;烧结矿底部入口风速在0.9～1.9 m/s之间每增加0.1 m/s,效率降低0.18%～0.24%。在此基础上,基于工业运行数据建立效率正交试验优化模型,提高了该余热回收系统3.42%的效率。     

Modeling Urban Storm-Water Quality Treatment: Model Development and Application to a Surface Sand Filter

A mathematical and statistical model for simulating contaminant removal from a surface sand filter is reported. The model was based on a mass balance equation and an advection-dispersion transport model. The unknown parameters of the model were the deposition rate and the hydrodynamic dispersion. Changes in space were allowed within the filter media depth and time variability of flow and influent contaminant concentration were taken into account. System field monitoring was performed between 2004 and 2006. A total of 17 storms were selected for the study. Runoff constituent analyses included: total suspended solids, total petroleum hydrocarbons-diesel range hydrocarbons, and zinc. The objective was to explore the capabilities of a two parameter model for predicting effluent contaminant concentrations. Optimized model parameter values were calculated on a storm by storm basis. Thereafter, a gamma distribution was fitted to the optimized values. A Monte Carlo simulation was performed to explore the predicting capabilities of the model by using two storms left for validation. Results of the validation phase show an acceptable performance of the model since, in general, estimated effluent concentrations fell within the uncertainty limits.     

A simplified model for the oxidation of disintegrated steel streams

A model is suggested for calculation of oxidation of disintegrated steel streans by mass transfer of oxygen to the droplets. The mass transfer of oxygen into the cylindrical space occupied by droplets and gas occurs by bulk flow and diffusion. Driving force for the bulk flow of air is the suction developed by the consumption of oxygen molecules and by acceleration. The differential equations describing the vertical gas velocity and the oxygen concentration of the gas phase are solved simultaneously. The increase of oxygen content of the metal phase is computed for a steel stream disintegrated into droplets of various sizes.     

Model experiments on mass transfer in ladle metallurgy

Model experiments on mass transfer in gas-stirred ladles were carried out in reactors of different geometric dimensions. The model system consists of: water, cyclohexan as model slag, iodium as element to be extracted from water into slag phase, and compressed air as stirring gas. The experimental results show that when using an eccentric bottom nozzle, rate constants of mass transfer are always smaller than with centric gas injection. Centric stirring leads to comparatively larger increases of rate constants if a certain gas flow rate is exceeded. Both results can be explained by different emulsification conditions of slag phase. Theoretical calculations of residence times show that mainly the emulsification of small droplets taken along by the recirculation flow is responsible for accelerations of mass transfer in gas-stirred ladles.