| dc.description.abstract | Wastewater treatment systems are implemented to remove wastewater pollutants before
discharge into receiving water bodies. Wastewater can negatively affect the ecosystem of the
receiving water body if proper treatment is not conducted. Despite its importance, small coverage
of wastewater treatment systems has been achieved worldwide mainly due to the related high
construction and operating costs. According to the Food and Agriculture Organization, about 80%
of the world’s wastewater generation is discharged into the environment without any treatment,
especially in low-income countries. Anaerobic biological wastewater treatments could be an answer
to reduce treatment costs. Anaerobic technologies offer advantages over competing technologies
such as reduced land footprint, small reactor volume, reduced excess sludge production, and the
ability to recover energy through methane capture. The most widespread anaerobic technology
worldwide is the Upflow Anaerobic Sludge Blanket (UASB) reactor. The UASB reactor uses an
upward flow to produce granular sludge capable of treating high organic loads. Although there is
extensive information on the microbiology of these granules and their efficiency in treating
different wastewater qualities, further research is required to better understand the relationship
between granule formation and reactor hydrodynamics. Flow hydrodynamics, almost entirely
controlled by the reactor's Influent Distribution System (IDS), is key to consider during the UASB
reactor’s design since it modules the substrate distribution inside the reactor and the formation of
stagnant and short-circuited zones. The IDS role is critical, especially during the reactor's start-up
stage when the granular sludge starts to form. This thesis aimed to advance our understanding of
the flow hydrodynamics impact on the operation and efficiency of the UASB reactor during its startup stage. The research was divided into two main stages. The first stage was dedicated to physically
modeling the reactor using a Froude dynamic similitude scaled reactor and developing an
automated tracer testing system. This system allowed us to determine the importance of
controlling the test water's conductivity, temperature variation, and surface tension during the
tracer tests. The second stage was devoted to numerically modeling the hydrodynamics of the UASB
reactor using computational fluid dynamics (CFD) simulations. Initially, the research focused on
finding the turbulence closure model that best reproduced the reactor’s hydrodynamics. Thus, CFD
simulations were conducted using the realizable k-epsilon model to assess the potential volume of
granule generation for IDS configurations commonly used in the literature. The simulations
confirmed that the IDS configuration recommended by the design guidelines has a high
performance in reducing stagnant and short-circuited zones. This research proposed a novel IDS
configuration that generated a granulation volume 22% larger than the recommended IDS
configuration, potentially reducing UASB reactor start-up time. The research demonstrates the
potential of using physical and numerical techniques as a basis for the model-based design
approach to solve problems specific to UASB reactors, an approach that could be extrapolated to
other types of reactors. | |
