Jein-Wen Chen

Size-dependent PM10 indoor/outdoor/personal relationships for a wind-induced naturally ventilated airspace

We applied a simple size-dependent indoor air quality model associated with a compartmental lung model to characterize PM10 indoor–outdoor–personal exposure relationships for wind-induced naturally ventilated residences in Taiwan region. The natural ventilation rate was quantified by the opening effectiveness for sidewall opening (SP) and covered ridge with sidewall opening (CRSP) type homes. The predicted PM10 mass indoor/outdoor (I/O) ratios were 0.15–0.24 and 0.20–0.32, respectively, for SP and CRSP type homes. Results demonstrate that PM10 I/O ratios for a wind-induced naturally ventilated airspace depend strongly on the ambient PM size distributions, building openings design (e.g. height to length ratio of openings and roof slope), wind speed and wind angle of incidence. The predictions from our lung model agreed favorable with the experimental deposition profiles in extrathoracic (ET), bronchial–bronchiolar (BB), and alveolar–interstitial (AI) regions. Our results demonstrate that ET region has higher PM10 mass lung/indoor ratios (for north Taiwan region: 0.67–0.78; for central: 0.66–0.74) than that of BB (for north: 0.36–0.57; for central: 0.33–0.47) and AI regions (for north: 0.05–0.35; for central: 0.02–0.22). The present approach can be used in the future to appraise the significance of inter-subject lung morphology and breathing physiology variability for PM deposition and dose calculations.

Linking biokinetics and consumer-resource dynamics of zinc accumulation in pond abalone Haliotis diversicolor supertexta

A dynamic model that links biokinetics and consumer-resource dynamics for describing zinc (Zn) accumulation in abalone Haliotis diversicolor supertexta has been developed and then applied to Zn data from real abalone farms. The biokinetic parameters used in this study, uptake and depuration rate constants of abalone and their food source, red alga Gracilaria tenuistipitata var. liui, were obtained from a laboratory 14-d exposure experiment. We carried out a sensitivity analysis of the model by using the fractional factorial design technique, taking into account the influence of consumer-resource-related parameters such as growth and death rates and biomass and biokinetic parameters characterized by bioconcentration factor. Results indicate that the response time of biomagnification dynamics of Zn accumulation in abalone was influenced mainly by the growth rate of algae and biomass and the death rate of abalone and by interactions algae biomass and abalone death rate and abalone and algae biomass. New algae production results in substantially higher values of biomagnification factor. The linked model was then applied to field observations from a real-life situation of variable Zn concentrations occurring in abalone farms. Simulation results show that the predicted values are within a factor of 2 of the measured values (% errors range from 5.3 +/- 4% to 44.1+/- 8%). Both model analysis and model application to the abalone farms suggest that the linking influences between biokinetics and consumer-resource dynamics support Zn accumulation in H. diversicolor supertexta and in G. tenuistipitata var. liui as functions of Zn concentration in water and abundance of food occurring in abalone farms.

An optimal trace zinc biomonitor (Haliotis diversicolor supertexta) control system design in aquacultural ecosystems

Abstract The purpose of this paper is to synthesize an optimal trace metal biomonitor control system to efficiently manage aquacultural water quality. A biomonitor organism of gastropod mollusc Haliotis diversicolor supertexta was chosen to estimate zinc (Zn) bioaccumulation. The bioaccumulation dynamics of Zn by H. diversicolor supertexta from an alga Gracilaria tenuistipitata var. liui and ambient water in aquaculture ponds is developed based on a six-compartment pharmacokinetic model. A linear control model based on the dynamic bioaccumulation model is developed to design an optimal feedback biomonitor control system. Linear quadratic regulators (LQRs) with output feedback control of a linear-invariant system are assigned for design algorithm and an optimal proportional plus integral (PI) feedback control strategy is synthesized. Numerical results from the model implementation show that the optimal selection of tuning parameters and the resulting costs vary with desired equilibrium state. The designed optimal feedback biomonitor control system, when suitably tuned, gives a satisfactory monitor of mollusc Zn bioaccumulation. The biomonitor control system developed accounting for bioaccumulation dynamics of Zn in the target tissues of molluscs can be used in the future to evaluate the effects of suspended solid removal devices and biofilters and/or other control scenarios on water quality management in aquacultural ecosystems.

Compartmental human respiratory tract modeling of airborne dust exposure from feeding in swine buildings

Abstract A simple size-dependent compartmental model was developed to describe airborne dust exposure dynamics for the human respiratory tract (HRT) in mechanically ventilated swine buildings. Transport mechanisms of airborne dust for HRT include respiration, gravitational settling, turbulent diffusive deposition, inertial impaction, interception deposition loss, and dust clearance. The dominant deposition mechanism in the lung regions was found to be the inertial impaction rate, in which the order of magnitude ranged from 10−3 to 10−1 sec−1. Results demonstrate that the extrathoracic region has a higher airborne dust mass lung/indoor ratios (0.71-0.87) than do the bronchial regions (0.41-0.74), the bronchiolar region (0.12-0.61), and the alveolar-interstitial region (0.01-0.49). The predictions from the HRT model agreed favorably with the experimental deposition profiles in the nasal passage, pharynx, bronchial, bron-chiolar, and alveolar-interstitial regions, whereas the rms errors of the total deposition fraction between predicted values and ICRP66 and Non-ICRP66 were 0.15 and 0.07, respectively. Simulation results show that breathing via the nose has both a higher deposition fraction and a higher exposure dose in the size ranges 0.01-10 μm than does breathing orally.

Microbial Degradation of Livestock-Generated Ammonia Using Biofilters at Typical Ambient Temperatures

Abstract The purpose of this research was to neutralize livestock-generated ammonia by using biofilters packed with inexpensive inorganic and organic packing material combined with multicultural microbial load at typical ambient temperatures. Peat and inorganic supporting materials were used as biofiltration matrix packed in a perfusion column through which gas was transfused. Results show the ammonia removal significantly fell in between 99 and 100% when ammonia concentration of 200 ppmv was used at different gas flow rates ranged from 0.030 to 0.060 m3 h−1 at a fluctuating room temperature of 27.5 ± 4.5°C (Mean ± SD). Under these conditions, the emission concentration of ammonia that is liberated after biofiltration is less than 1 ppmv (0.707 mg m−3) over the period of our study, suggesting the usage of low-cost biofiltration systems for long-term function is effective at wider ranges of temperature fluctuations. The maximum (100%) ammonia removal efficiency was obtained in this biofilter was having an elimination capacity of 2.217 g m−3 h−1. This biofilter had high nitrification efficiencies and hence controlled ammonia levels with the reduced backpressure. The response of this biofilter to shut down and start up operation showed that the biofilm has a superior stability.

Dynamic model for predicting dust-borne odour concentrations in ventilated animal housing

Abstract The behavior of the interaction among odour, airborne dust, and dust-borne odour in a ventilated enclosure was studied from a dynamic point of view. Various parameters are of interest including the odour emission from stored manure, the role of ventilation as a removal mechanism, and the behavior of the ambient airborne dust present in the animal housing. Gas-phase (odour), airborne dust-phase, and adsorbed-phase (dust-borne odour) were included in the model to reflect the dynamic and time-dependent scheme such as odour degradation, adsorption of odour to the existing airborne dust, ventilation, and surface deposition. The derived dynamic equations are sufficiently general to take into account the simultaneous removal effects of turbulent diffusive deposition, gravitational sedimentation, and airflow within a ventilated enclosure. A sensitivity analysis for evaluating the parameters such as ventilation rate, dust particle size, and ambient aerosol profile is also presented. The model can be used in the future to evaluate the dust-borne odour exposure as a function of environmental and other parameters such as aerosol profile, ventilation rate, and enclosure dimension.

Modelling lumped-parameter sorption kinetics and diffusion dynamics of odour-causing VOCs to dust particles

Abstract An analytical algorithm is presented for fast simulation of the adsorption kinetics and diffusion dynamics of odour-causing volatile organic compounds (VOC-odour) which originate in the stored swine manure to airborne dust particles in a ventilated airspace. The model is an extension to the well-known lumped-parameter model (LPM) that incorporates a Langmuir–Hinshelwood (LH) kinetic concept dependent on VOC-odour concentration with diffusion limitation. The basic idea behind the model implementation is to couple the calculations of the two major processes in the VOC-odour/dust particle system: VOC-odour diffusion based on the homogeneous surface diffusion model (HSDM) and surface reaction based on the LH kinetics in an LPM scheme. The LPM employs Laplace transforms and gamma distributions of the rate coefficient to produce a lumped-parameter gamma model (LPGM) for kinetic equation of VOC-odour adsorption to airborne dust particles, whereas the HSDM incorporates the age and size distributions of airborne dust for evaluating the dust-borne VOC-odour dynamics. The integrate assessment of VOC-odour sorption kinetics and diffusion dynamics allows to relate the adsorption rate coefficient, reaction order, and surface effective diffusivity in a complex VOC-odour/dust particle system. The LPGM fitted well with the data obtained numerically from HSDM and successfully determined the adsorption rate coefficient and reaction order for each sorption process.

A transfer function model to describe odor causing VOCs transport in a ventilated airspace with mixing/adsorption heterogeneity

Abstract The ability of a transfer function modeling technique is evaluated to explain the odor causing VOCs (VOC-odor) transport processes influenced by heterogeneity of adsorption surface of ambient aerosol and air mixing pattern in a ventilated airspace. An advection–reaction impulse/step response function is used to generalize the dynamic transport of VOC-odor in heterogeneous mixing/adsorption ventilated airspace. The system process presented by an ensemble transfer function is solved analytically in the Laplace domain. The model requires the specification of probability density function (pdf) for residence time of airflow and for both equilibrium linear partitioning and first-order mass transfer rate parameters of gas/solid phase to quantify the specific air mixing pattern and transport processes. The model predicts the ensemble mean VOC-odor concentrations for a variety of adsorption kinetics and mixing pattern combinations as a function of the boundary impulse/step response inputs as well as residence time and adsorption rate statistics. The general behavior of output VOC-odor profiles is analyzed through the effects of mean adsorption rate coefficient, mean linear partitioning constant, mixing efficiency, mean residence time and coefficient of variations of both linear partitioning and rate coefficients. This study indicates that when mixing/adsorption heterogeneity exists, simple complete mixing assumption and simple distribution of rate constant are inherently not sufficient to represent a more generally distributed mixing/adsorption process of VOC-odor transport in a ventilated airspace.

A transfer function technique to describe odor causing VOCs transport in a ventilated airspace with mixing/adsorption heterogeneity

A model describing odor causing volatile organic compounds (VOC-odor) transport in a ventilated airspace influenced by heterogeneity of adsorption surface of ambient aerosol and air mixing pattern is proposed and analyzed based on a transfer function modeling technique. In this study an advection-reaction impulse/step response function for VOC-odor is assumed. The system process presented by an ensemble transfer function is solved analytically in the Laplace domain. The analytical results are then numerically inverted using a modified fast Fourier transform algorithm. The model requires the specification of probability density function for residence time of airflow and for both equilibrium linear partitioning and first-order mass transfer rate parameters to quantify the specific air mixing pattern and transport processes. The model predicts the ensemble mean VOC-odor concentrations for a variety of adsorption kinetics and mixing pattern combinations as a function of the boundary impulse/step response inputs as well as residence time and adsorption rate statistics. The general behavior of output VOC-odor profiles is analyzed through the effects of mean adsorption rate coefficient, mean linear partitioning constant, mixing efficiency, mean residence time and coefficient of variations of both linear partitioning and rate coefficients. It indicates that when mixing/adsorption heterogeneity exists, simple complete mixing assumption and simple distribution of rate constant is inherently not sufficient to represent a more generally distributed mixing/adsorption process of VOC-odor transport in a ventilated airspace.

Dynamic mathematical model for biotransformation and mass transfer of livestock generated voc‐odor in a bioactive dust particle system

A multi-step mass transfer-biodegradation model is developed to describe the bioactive adsorber dynamics for the biotreatment of livestock generated odor causing VOCs (VOC-odor) based on a biologically active dust particle (BADP) process. The BADP process employs dust particles with adsorbat-acclimated microbial culture to form the bioactivated dust particles (BDP) for the simultaneously adsorption, mass transfer, and biodegradation of VOC-odor. The model incorporating age and size distributions of BDP considers the equilibrium partitioning of VOC-odor at BDP and bulk gas interface that followed by two kinetic processes occurring in the bulk and solid phases: bulk gas mass transfer-biodegradation and BDP biofilm diffusion-biodegradation. Analytical equations indicate that the overall biotransformation rate of VOC-odor in a BADP process is controlled by BDP-bulk gas equilibrium processes represented by the slowest of two kinetic processes determined by a dimensionless group: the Thiele modulus (phi 2), the Damkohler number (Da) and the Biot number (Bi). Computer simulations demonstrate that the most favorable performance of a BADP system in reducing VOC-odor concentrations is operated under Bi < 1, Da < 1, or Bi > 1 phi 2 < 1; indicating diffusion-biodegradation controlled. The dimensionless group can be used to identify the dominant rate-limiting processes and to evaluate the overall biomineralization rate in a BADP process. Simulation results allow the determination of preliminary design for prototype development.