Biomedical subjects

John S Gulliver

Publications and source records attributed to John S Gulliver.

4 recordsLinked to original sources

PubMed2006

Gas transfer from air diffusers.

The bubble and surface volumetric mass transfer coefficients for oxygen, k(L)a(b) and k(L)a(s), are separately determined for 179 aeration tests, with diffuser depths ranging from 2.25 to 32 m, using the DeMoyer et al. 12003. Impact of bubble and free surface oxygen transfer on diffused aeration systems. Water Res 37, 1890-1904] mass transfer model. Two empirical characterization equations are developed for k(L)a(b) and k(L)a(s), correlating the coefficients to air flow, Qa, diffuser depth, hd, cross-sectional area, Acs, and volume, V. The characterization equations indicate that the bubble transfer coefficient, k(L)a(b), increases with increasing gas flow rate and depth, and decreases with increasing water volume. For fine bubble diffusers, k(L)a(b) is approximately six times greater than k(L)a(b) for coarse bubble diffusers. The surface transfer coefficient, k(L)A(s), increases with increasing gas flow rate and diffuser depth. The characterization equations make it possible to predict the gas transfer that will occur across bubble interfaces and across the free surface with a bubble plume at depths up to 32 m and with variable air discharge in deep tanks and reservoirs.

Bioreactors↗

PubMed2003

Impact of bubble and free surface oxygen transfer on diffused aeration systems.

The primary location of oxygen transfer in a diffused aeration system is examined by separately determining the surface air-water and bubble-water mass transfer coefficients. The mass transfer model developed to determine the mass transfer coefficients advances the McWhirter and Hutter (A.I.Ch.E. J. 35(9) (1989) 1527) model by tracking oxygen and nitrogen transfer into and out of the bubbles as they rise to the water surface. The resulting vertical profiles of the liquid-phase equilibrium concentration inside the bubble and the gas-phase oxygen composition give insight into how the bubble-water concentration gradient changes over depth. The surface mass transfer coefficient, k(Ls)a(s), is 59-85% of the bubble mass transfer coefficient, k(L)a(b), and the driving concentration difference is smaller for surface transfer. Surface transfer and bubble transfer both contribute significantly to oxygen transfer; however, bubble transfer is the primary mode of oxygen transfer for this system at the air flow rates used. Further experiments demonstrate that most of the surface transfer occurs above the bubble plume.

Air Movements↗

PubMed2003

Modeling of phosphorus dynamics in aquatic sediments: I--model development.

A model is developed to study the phosphorus dynamics in aquatic sediments and to conduct dynamic predictions of phosphorus release across a sediment-water interface. The model focuses on the sediment active layer below the sediment-water interface and is based on primary mechanisms regulating phosphorus behavior in sediments, including effective diffusion, bioturbation mixing and burial processes (transport), organic decomposition, sorption kinetic processes and non-linear partitioning (mobilization). The effects of environmental factors such as dissolved oxygen and temperature are taken into account. The model is solved by numerical integration. The primary difference from models in the literature is that the model directly describes the dynamic behavior of dissolved, particulate exchangeable ortho-phosphorus and organic phosphorus in sediments, and incorporates dynamic sorption and non-linear partitioning processes. These improve model mechanisms and allow regulation of phosphorus flux through the sediment reservoir that acts as both a source and sink of phosphorus.

Biological Availability↗

PubMed2003

Modeling of phosphorus dynamics in aquatic sediments: II--examination of model performance.

A sediment phosphorus model, describing dynamics of organic phosphorus, dissolved reactive phosphorus and exchangeable particulate phosphorus, is applied to five monitoring stations in Chesapeake Bay, USA, to examine model performance in predicting sediment-water phosphorus exchange. The model was fit to 1 year of field measurements, and verified over 3 years at five sampling stations. The results show that the simulated concentrations of phosphorus reasonably correspond to model mechanisms and field observations in both spatial and temporal variations. Predicted release fluxes of phosphorus are consistent with field measurements and improved over those obtained by existing sediment phosphorus models. The model incorporates the effects of dissolved oxygen and non-linear, non-equilibrium sediment sorption in phosphorus dynamics. A sensitivity analysis indicates the importance of the non-linear, non-equilibrium sorption processes to accurate prediction of sediment-water phosphorus flux.

Environmental Monitoring↗