Biomedical subjects

A Ayol

Publications and source records attributed to A Ayol.

4 recordsLinked to original sources

PubMed2006

Toward efficient sludge processing using novel rheological parameters: dynamic rheological testing.

Materials known as complex fluids exhibit a transitional behaviour between their solid and liquid states. Sludges produced at different treatment stages of wastewater treatment are examples of these materials, since they exhibit solid behaviour within shorter time frames and liquid behaviour over longer durations. These sludges can also change from solid-like to liquid-like, or vice versa, when subjected to even a slight deformation; this stems from their complex makeup, which includes both particulate materials and polymeric gels, including both biopolymers and the synthetic polymers used in conditioning them. This paper focuses on two means of quantifying dynamic rheological test results: (1) the linear viscoelastic behaviour (LVE) of sludge samples, as measured by the strain sweep analysis storage (G') and loss moduli (G"); and (2) the flow curve, which presents the relationship between the shear viscosity and shear rate and determines the yield stress values of samples using the strain sweep test mode. With these methods, sludges can be more accurately characterised, allowing better prediction of their behaviour in treatment and transport processes.

Elasticity↗

PubMed2006

Evaluation of conditioning responses of thermophilic-mesophilic anaerobically and mesophilic aerobically digested biosolids using rheological properties.

One of the most crucial processes in biosolids management is stabilisation, which is typically accomplished using either anaerobic or aerobic digestion processes. Although there are many advantages to both of these methods--such as reduction of volatile organic matter, pathogen content, and offensive odours--one common disadvantage is that digested biosolids exhibit poor dewaterability characteristics. The deterioration in dewaterability of digested biosolids leads to increases in polymer requirements, connoting higher conditioning costs. Many studies have examined this phenomenon based on conventional filterability tests such as capillary suction time and specific resistance to filtration. However, these test methods are limited in their ability to predict full-scale dewatering behaviour (particularly in centrifugation), and do not regard handling properties as being important for sludge transport. For this purpose, new rheometric methods may assist in predicting sludge behaviour, potentially allowing optimisation of stabilisation and conditioning processes relative to the desired sludge properties. This paper investigates the possible utility of these methods. Classical methods for characterising biosolids, such as filtration tests, are compared with yield stress values and other rheological properties as determined using the steady-shear rate sweep test. The rheological behaviours are compared for different sludge types, including raw and polymer conditioned thermophilic anaerobically, mesophilic anaerobically, and mesophilic aerobically digested biosolids. The paper demonstrates the determination of specific energy values associated with breakdown of the flocculated matrix. Robust modelling approaches are employed to optimise the conditioning of the digested samples, and to shed light on commonly used rheological models such as Bingham, Herschel-Bulkley, and Ostwald equations.

Aerobiosis↗

PubMed2004

Use of drainability and filterability simulations for evaluation of oxidative treatment and polymer conditioning of sludge.

In the traditional view of sludge structure, a two-phase system is visualized. The solid phase is often illustrated as consisting of uniform, spherical, negatively charged particles. This simplistic picture limits the understanding of both conditioning and dewatering. Specifically, it limits us to only two strategies for destabiiization: charge neutralization (using cationic coagulant species with either uniform or patch effects), and bridging (using polymeric flocculants). In fact, the situation is more complex in many respects. In this paper, we compared chemical conditioning of anaerobically digested biosolids using (1) conventional polymeric flocculation, and (2) treatment by chemical oxidants. Since these strategies may alter dewatering behavior by very different mechanisms, we report comparisons using a lab-scale simulator of belt press dewatering, including separate steps for the drainage and filtration processes. This allows greater insight into the effects of these conditioning methods and how they might be properly employed.

Delaware↗

PubMed2004

Physical characteristics of a waste activated sludge: conditioning responses and correlations with a synthetic surrogate.

The efficient and economic management of waste activated sludge (WAS) requires a proper understanding of the sludge's material properties. Though there has been much study of WAS, an adequate linkage between its physical and chemical properties has been elusive. In particular, the conditioning and dewatering of WAS are expensive operations, and the addition of polymer to WAS leads to even more complex material behavior that is difficult to optimize. This paper reports on an extensive characterization of WAS, both with and without polymer conditioning. We combined the classical "jar test" approach with less conventional rheometric and electrokinetic measurements. In addition to the use of sampled WAS, a synthetic surrogate sludge was formulated, attempting to duplicate properties of WAS and allow more extensive characterization of a reproducible surrogate to WAS. Results with both the synthetic surrogate and WAS indicated that the traditional, electrokinetic, and rheological properties were related. However, the dose optima by rheometry were somewhat higher in both cases.

Delaware↗