Reduced Air Flow Rate Research Articles

Alternating anoxic feast/aerobic famine condition for improving granular sludge formation in sequencing batch airlift reactor at reduced aeration rate

In this study the influence of a pre-anoxic feast period on granular sludge formation in a sequencing batch airlift reactor is evaluated. Whereas a purely aerobic SBR was operated as a reference (reactor R2), another reactor (R1) was run with a reduced aeration rate and an alternating anoxic-aerobic cycle reinforced by nitrate feeding. The presence of pre-anoxic phase clearly improved the densification of aggregates and allowed granular sludge formation at reduced air flow rate (superficial air velocity (SAV) = 0.63 cm s −1). A low sludge volume index (SVI 30 = 45 mL g −1) and a high MLSS concentration (9–10 g L −1) were obtained in the anoxic/aerobic system compared to more conventional results for the aerobic reactor. A granular sludge was observed in the anoxic/aerobic system whilst only flocs were observed in the aerobic reference even when operated at a high aeration rate (SAV = 2.83 cm s −1). Nitrification was maintained efficiently in the anoxic/aerobic system even when organic loading rate (OLR) was increased up to 2.8 kg COD m −3 d −1. In the contrary nitrification was unstable in the aerobic system and dropped at high OLR due to competition between autotrophic and heterotrophic growth. The presence of a pre-anoxic period positively affected granulation process via different mechanisms: enhancing heterotrophic growth/storage deeper in the internal anoxic layer of granule, reducing the competition between autotrophic and heterotrophic growth. These processes help to develop dense granular sludge at a moderate aeration rate. This tends to confirm that oxygen transfer is the most limiting factor for granulation at reduced aeration. Hence the use of an alternative electron acceptor (nitrate or nitrite) should be encouraged during feast period for reducing energy demand of the granular sludge process.

Spray deposits and losses in different sized apple trees from an axial fan orchard sprayer: 3. Effects of air volumetric flow rate

As part of a wider study to optimise the adjustment of axial fan orchard sprayers to suit differing modern crop structures, three field experiments compared the effects of reductions in air volumetric flow rate (from 11.3 to 7.5 to 4.1m3s−1) on spray deposits and losses to young dwarf, dwarf and semi-dwarf apple trees. Reducing the air volumetric flow (achieved by reducing the speed of rotation of the fan without changing the air ducting or orifice size) from the high to the medium rate did not significantly affect mean deposits on the target trees but the lowest air flow rate increased mean deposits on leaves, flowers and fruits significantly in two experiments. In the other experiment, done in the early season in higher wind speed conditions, mean deposits were decreased by the lowest air flow rate treatment which made the spray plume vulnerable to cross-winds. Decreasing the air flow rate generally increased mean deposits in tree zones close to the sprayer and decreased those in zones furthest from the sprayer. The leaf-to-leaf distributions of deposits in the centre of the trees were not affected significantly by the reductions in air flow rate. Decreasing the air flow rate substantially increased the percentage spray cover on downward-facing water sensitive papers fixed horizontally in the centre of the trees but decreased cover on upward facing papers. The medium air flow rate gave at best only small (<50%) reductions in spray drift but the lowest air flow rate treatment significantly reduced drift by 55–93%. Deposits on ground sampling lines increased correspondingly. Drift amounts were greatest and the reductions in drift due to the reduced air flow rates were least in stronger winds conditions early in the season when the canopy was least dense.Taken together, these results indicate that large reductions in air volumetric flow rate can substantially reduce spray drift from axial fan sprayers without adversely affecting the variability of deposits on either leaf surface though the relative mean amounts on the upper versus the lower leaf surface can change substantially. The reductions make the spray plume more vulnerable to cross-winds which can reduce spray penetration. The extent that reductions can be made depends on wind conditions and tree density. However, the provision for air flow adjustment on many commercial sprayers is generally inadequate to maintain an optimal spray distribution pattern across the broad range of orchard structures that exist on many commercial farms in the UK. Other practical difficulties of greatly reducing the air flow rate are discussed.

CONSEQUENCES OF LONG-TERM INFLAMMATION: The Natural History of Asthma

Although asthma is classically defined as reversible airflow obstruction, and often remits in younger subjects with milder disease, the natural history of asthma is that various degrees of airflow obstruction may persist and, in the long-term, asthma may become moderately to fully irreversible. Severe, irreversible airflow obstruction may develop despite apparently appropriate therapy and in the absence of other risk factors, such as smoking and environmental insults. All studies of subjects with persisting asthma show increased decline in lung function compared with normal subjects. Persistent abnormal physiology is reflected both in reduced airflow rates and in increased airway responsiveness. The cellular and molecular mechanisms of airway remodeling are described elsewhere in this issue. Questions not yet clearly answered are the reasons for these persistent abnormalities in some asthmatics, and which subjects are most at risk. Factors that adversely impact the outcome as adults identified relatively consistently among many longitudinal studies of the natural history of asthma include: Female gender. Environmental tobacco smoke exposure in childhood. Personal tobacco smoking in adolescence and adulthood. Age of onset of symptoms. Severity of childhood asthma. Duration of asthma. Severity of lung function abnormality in childhood. Bronchodilator reversibility. Degree of airway hyperresponsiveness. Delay in initiating anti-inflammatory therapy. Remission among adult asthmatics is uncommon, but is associated with better initial lung function, young age, male gender, and lesser degrees of airway responsiveness. The role of atopy remains controversial. Conversely, risk factors for death from asthma include older age, smoking, atopy, impaired lung function, and moderate to high reversibility. Treatment can improve lung function, reduce airway responsiveness, and improve quality of life. The overall effect of treatment on the natural history of the disease is not yet clear, despite significant short-term improvements from effective anti-inflammatory therapy.

Study of Constant Airflow Rate and Constant Room Pressure Control Systems for Physical Containment Laboratories

This study discusses various control systems that can keep the room pressure and supply/exhaust airflow rate at constant levels in "other rooms" of a highly airtight containment facility when the supply/exhaust airflow is shut off in one of the rooms for decontamination purposes. This study has shown that the constant air volume control system (CAV) allows hysteresis to occur at small differentials on the performance curve of the static pressure differentials and that this hysteresis can cause wide fluctuations in room pressure. In contrast, the variable air volume, central processing unit (VAV-CPU) control system can maintain both airflow rates and room pressures. Each room pressure was controllable to the set level, with an error of less than ±0.5 mmH2O even during transient distur bances. This control system limited fluctuations in the airflow to and from each room to 5 percent during the transient responses. This control system also allows power savings in the operation of supply/exhaust fans, because of the reduced airflow rate and the static pressure of the fans, and is considered to be an excellent control system.

The influence of lung volume on expiratory flow rates in diffuse interstitial lung disease.

This study evaluated maximum expiratory flow rates with respect to lung volume and maximum recoil pressure in selected patients with diffuse interstitial lung disease who had normal large airway function by standard technique. Coefficient of retraction was normal or greater than normal in all. Peak flow varied directly with lung volume as in normals. At 50% vital capacity (VC) and 25% VC, the absolute flow rates varied from higher to lower than normal. However, when flow was adjusted to volume, the flow/volume ratio was normal or high in all. Flow/volume ratio at mid-lung volume appeared to increase with increase in coefficient of retraction. Patients with frequency dependence of compliance had lower flow/volume ratios at 25% VC than those without, although still within normal range. Thus, despite recognized wide variations in normals, the flow/volume ratio is pertinent to the evaluation of reduced air flow rates in in interstitial lung disease to distinguish abnormal upstream airway resistance from volume-dependent reduction of flow rate. An effort-independent flow rate that yields a supernormal flow/volume ratio suggests increased recoil properties of the respiratory system.