Biomedical subjects

Tom Stephenson

Publications and source records attributed to Tom Stephenson.

3 recordsLinked to original sources

PubMed2005

Biomass characteristics and membrane aeration: toward a better understanding of membrane fouling in submerged membrane bioreactors (MBRs).

Fouling in submerged membrane bioreactors (MBRs) was studied under different operating conditions and with varying biomass characteristics. Fouling rates were determined using a flux-step method for seven biomass conditions with mixed liquor solids concentrations ranging from 4.3 to 13.5 g x l(-1), six permeate fluxes (5.5, 11.0, 16.5, 22.0, 27.5, and 33.0 l x m(-2) x h(-1)), and three membrane airflow velocities (0.07, 0.10, and 0.13 m x s(-1)). Statistical analysis was used to specify the degree of influence of each of the biomass characteristics (solids concentration, dewaterability, viscosity, particle size distribution, concentrations of protein and carbohydrate in the soluble microbial products, SMP, and extracellular polymer substances, EPS), the permeate flux and the membrane aeration velocity on the membrane fouling rate. Among all these variables, only the permeate flux, the solids concentration (correlated to the viscosity and the dewaterability), the carbohydrate concentration in the EPS, and the membrane aeration velocity were found to affect the fouling rate. The permeate flux had the greatest effect. A transitional permeate flux was observed between 16.5 and 33 l x m(-2) x h(-1), below which no significant fouling was observed regardless of the biomass characteristics, the permeate flux, and the membrane aeration velocity.

Bacteria, Aerobic↗

PubMed2002

Effect of influent organic content on digested sludge extracellular polymer content and dewaterability.

The organic composition of the feed sludge to six laboratory-scale anaerobic digesters was adjusted by substituting a proportion of the primary sludge for glucose or propionic acid solution. Substitution with glucose caused an increase in the microbial extracellular polymer (ECP) content of the digested sludge, which altered the particle size distribution of the sludge and made the sludge more difficult to dewater. Substitution with propionic acid gave similar results to the control. The relationship between the digested sludge extracted ECP yield and sludge filtrability determined using the capillary suction time test was significant at the P = 0.01 level. The level of ECP for optimum sludge dewaterability was calculated as 17.2 mg g(-1) SS. The protein and carbohydrate composition of the extracted polymer did not appear to affect the sludge dewaterability. Results present will allow predictions to be made into the effect that changes in the influent sewage composition has on essential downstream processes.

Bacteria, Anaerobic↗

PubMed2002

Off-line particle size analysis of digested sludge.

Particle size analysis was carried out on six samples of digested sludge using laser diffraction. The digested sludge was produced in laboratory-scale reactors under different feed regimes based on a mixture of primary and waste activated sludge (WAS). Laser diffraction proved capable of providing rapid, reproducible results of the particle size distribution of each sample, and highlighted differences between the different treatments. An increase in the level of WAS in the digester feed sludge led to a shift in the size distribution, with a decrease in the number of smaller sized particles.

Automation↗