Environmental Engineering Reference
In-Depth Information
we propose to call SonoPhotoCatalytic Cavitation (SPCC). SPCC describes the combined
effects of ultrasound with heterogeneous photocatalysis taking place within a cavitation,
producing a resonant vortex chamber tuned to produce sonoluminescence. We draw on the
parallels on how these existing technologies may be combined and applied to water reme-
diation or potable water treatment by the advent of new materials brought about in the rapidly
growing ield of applied nanotechnology to produce highly eficient photocatalyst coatings
combined with drag-reducing nanocoatings into both the realms of sound and light.
Cavitation and heterogeneous photocatalysis effects and processes are already being
effectively used to treat water from undesired contaminants as alternative treatments.
They do so without the use of additional chemical compounds and are already very effec-
tively implemented in industrial water systems, as well as municipal potable water and
wastewater treatment plants. Each of these methods in and by itself has some great and
fascinating potential, but they also have some limitations on how and in what settings
they may be applied effectively.
In the case of heterogeneous photocatalysis or also known as advanced oxidation pro-
cess (AOP), it is the very optical properties of the water to be treated that limit its eficiency.
To properly treat inluent water, maximum contact surface must be achieved between the
target water molecules and the photon-activated TiO
2
surface, where different highly reac-
tive transitory species must act for mineralization of organic compounds and disinfection
of water pathogens.
This can be achieved by maximizing the surface area of contact between the photo-
catalytic region of a reactor and the water molecules to be treated, and/or extending the
residence time in the chamber. The work of maximizing the surface area can be read-
ily achieved by using larger reactors, or by using photocatalytic mesoporous materials,
greatly increasing the contact with water being treated; however, they suffer in that light
cannot readily excite and reach the internal structures owing to tortuosity, and thus excite
the electrons into the outer orbital to produce the hydroxyl radicals upon orbital decay.
In the case of vortex cavitation, where the contaminants may be dynamically separated
from the target water by coarse centrifugal effects, sonoluminescence is rarely achieved
nor detected unless specialized and sensitive equipment is used, and rarely is the case that
cavitation alone has the capacity to achieve the ideal conditions of producing sonolumi-
nescence within the target water samples.
Photocatalysis and cavitation share the potential capacity to produce highly reactive
hydroxyl radicals, which are especially important with respect to not only degradation of
organic compounds, but also of other impurities commonly found in water such as dis-
solved metal salts or dyes. In the special case of sonophotocatalytic cavitation, which is a
photocatalytic reaction coupled with ultrasonic irradiation or the simultaneous irradiation
of ultrasound and light with a photocatalyst, it is believed that those limitations of photo-
catalysis or cavitation, each in isolation, can be mitigated. It is believed that SPCC can be
optimized using the current advances in sonophotocatalytic and cavitation to perform as
well as either alone, and in addition, to be capable of treating water not only from these
undesired contaminants, but to also provide it with an enhanced set of ancillary prop-
erties that can have profound implications in various water treatment applications and
processes. Water remediation from persistent and emergent contaminants, cooling tower
water systems decalciication, digester systems, emulsiication and mixing, concrete hard-
ening and curing optimization, calcium removal, ballast water discharge from biologi-
cal or oil contaminants, enhancing organic reactions, mining wastewater remediation for
slurry and sludge, selective contaminant isolation, and ice fabrication industries are just a
few of them, which are discussed below.
