Modelling of wastewater treatment plants--how far shall we go with sophisticated modelling tools?

Several levels of complexity are available for modelling of wastewater treatment plants. Modelling local effects rely on computational fluid dynamics (CFD) approaches whereas activated sludge models (ASM) represent the global methodology. By applying both modelling approaches to pilot plant and full scale systems, this paper evaluates the value of each method and especially their potential combination. Model structure identification for ASM is discussed based on a full-scale closed loop oxidation ditch modelling. It is illustrated how and for what circumstances information obtained via CFD (computational fluid dynamics) analysis, residence time distribution (RTD) and other experimental means can be used. Furthermore, CFD analysis of the multiphase flow mechanisms is employed to obtain a correct description of the oxygenation capacity of the system studied, including an easy implementation of this information in the classical ASM modelling (e.g. oxygen transfer). The combination of CFD and activated sludge modelling of wastewater treatment processes is applied to three reactor configurations, a perfectly mixed reactor, a pilot scale activated sludge basin (ASB) and a real scale ASB. The application of the biological models to the CFD model is validated against experimentation for the pilot scale ASB and against a classical global ASM model response. A first step in the evaluation of the potential of the combined CFD-ASM model is performed using a full scale oxidation ditch system as testing scenario.

Assessment of nasal patency by rhinoscopic measurement of cross sectional nasal airway area: correlation with subjective nasal symptoms.

Assessment of nasal patency by the recording of nasal symptom scores was compared with an objective method of determining nasal airway area using a fiberoptic rhinoscope. Sixty patients with active allergic rhinitis and nasal congestion requiring treatment were studied. Nasal symptoms were recorded and nasal airway area was measured before and at fixed time intervals after administration of either pseudoephedrine or oxymetazoline. Both methods detected a decongestant response to both drugs, and the symptom of congestion correlated with the measured nasal airway area. Rhinoscopic measurement of cross sectional nasal airway area is an objective method that may be used to complement other methods for evaluation of nasal patency.

Evaluation of nasal patency by fiberoptic rhinoscopy.

A novel method of assessing anterior nasal patency by flexible fiberoptic rhinoscopy was evaluated in two centers by comparison with active anterior rhinomanometry. Rhinoscopy and rhinomanometry were performed 20 times on each of 14 subjects during 14 to 26 minutes. The procedure was videotaped, and nasal airway area was measured from a video monitor. The mean coefficients of variation for rhinoscopy and rhinomanometry were 14% and 19%, respectively. Another investigator examined five subjects by rhinoscopy 30 times in 15 minutes; the mean coefficient of variation was 9%. These means were not significantly different. Rhinoscopy and rhinomanometry were performed at 30-minute intervals for a 6-hour period in 13 subjects. Three investigators independently evaluated results for changes in nasal function characteristic of the nasal cycle. Rhinoscopy detected the nasal cycle in an average of 72% of subjects and rhinomanometry in 49%. Both methods detected the response to topically applied oxymetazoline and methacholine. Results indicate that, whereas the two procedures evaluate different aspects of nasal function, their precision is similar. Rhinoscopy additionally permits evaluation of nasal mucosal changes occurring from disease or treatment.

The effects of H1 and H2 antihistamines on histamine inhalation challenges in asthmatic patients.

This study was designed to examine the effect of an H1 antihistamine, chlorpheniramine, an H2 antihistamine, cimetidine, and the combination of chlorpheniramine and cimetidine on histamine-induced bronchoconstriction in a double-blind, randomized protocol on 11 patients with asthma. Each patient underwent a histamine inhalation challenge on 5 separate days. After a control day, histamine inhalation challenges were performed 2 h after the administration of a single oral dose of 8 mg of chlorpheniramine, 300 mg of cimetidine, the combination of chlorpheniramine and cimetidine, or placebo. Baseline pulmonary function measurements were not significantly altered by the 4 treatments. Body plethysmography data and measurements from the forced vital capacity maneuver were obtained before and after the histamine inhalation challenges. The provocation dose of histamine that produced a 20% decrease in forced expiratory volume in one second, a 35% decrease in mean forced expiratory flow during the middle half of the forced vital capacity, and a 50% decrease in specific airway conductance was significantly increased after administration of chlorpheniramine (p less than 0.002) and decreased after administration of cimetidine (p less than 0.02), where as no significant effect was noted after the combination of chlorpheniramine and cimetidine. The results suggest the presence of both H1 and H2 receptors in the airways of asthmatic patients.