Dissolved Air Flotation of Flocs
Overview
| Wiki Markup |
|---|
h1. Floating Flocs h2. Overview {float:left|border=2px solid black}!floating-floc-edit.jpg|width=400px, height="300"!{float} |
Floating
...
flocs
...
in
...
the
...
sedimentation
...
tanks
...
of
...
AguaClara
...
plants
...
in
...
Tamara,
...
Ojojona,
...
and
...
Marcala
...
result
...
in
...
polluted
...
effluent
...
water.
...
While
...
some
...
treatment
...
plants
...
use
...
floating
...
floc
...
to
...
treat
...
water,
...
AguaClara
...
plants
...
rely
...
on
...
flocs
...
settling
...
out
...
at
...
the
...
bottom.
...
The
...
floating
...
flocs
...
problem
...
is
...
thought
...
to
...
stem
...
from
...
supersaturation
...
of
...
influent
...
water,
...
which
...
occurs
...
when
...
the
...
dissolved
...
gas
...
pressure
...
is
...
greater
...
than
...
the
...
local
...
solution
...
pressure.
...
Because
...
the
...
water
...
is
...
supersaturated,
...
gas
...
bubbles
...
naturally
...
tend
...
to
...
form
...
in
...
order
...
to
...
bring
...
the
...
dissolved
...
gas
...
concentration
...
in
...
the
...
water
...
to
...
equilibrium
...
with
...
the
...
surrounding
...
pressure.
...
The
...
cause
...
floating
...
flocs
...
problem
...
is
...
thought
...
to
...
be
...
bubbles
...
forming
...
on
...
or
...
attaching
...
to
...
flocs,
...
lifting
...
them
...
to
...
the
...
surface.
...
The
...
Dissolved
...
Air
...
Flotation
...
of
...
Flocs
...
Team
...
(DAFF or Floating Flocs)
...
has
...
been
...
focusing
...
on
...
lowering
...
the
...
bubble
...
forming
...
potential
...
of
...
the
...
water
...
entering
...
the
...
sedimentation
...
tank.
...
The
...
team
...
was
...
working
...
with
...
a
...
backwashed
...
sand
...
filter
...
using
...
this
...
...
...
.
...
We
...
believed
...
that
...
providing
...
sand
...
as
...
an
...
alternative
...
surface
...
on
...
which
...
bubbles
...
can
...
form
...
and
...
rise
...
out
...
of
...
the
...
water
...
would
...
stop
...
the
...
floating
...
flocs
...
problem;
...
however,
...
research
...
has
...
shown
...
that
...
the
...
sand
...
used
...
did
...
not
...
aid
...
but
...
rather
...
inhibited
...
gas
...
removal.
...
Literature
...
regarding
...
bubble
...
formation,
...
which
...
can
...
be
...
found
...
in
...
the
...
Floating
...
Floc
...
...
...
,
...
indicate
...
that
...
rough,
...
hydrophobic
...
surfaces
...
are
...
most
...
conducive
...
to
...
bubble
...
formation.
...
The
...
shortcoming
...
of
...
the
...
fluidized
...
sand
...
bed
...
method
...
is
...
believed
...
to
...
be
...
due
...
to
...
the
...
sand
...
particles'
...
lack
...
of
...
hydrophobicity.
...
The
...
team's
...
future
...
plans
...
include
...
studying
...
the
...
effects
...
of
...
hydrophobic
...
surfaces
...
and
...
surfactants
...
on
...
surface
...
tension
...
and
...
bubble
...
formation,
...
while
...
trying
...
to
...
develop
...
a
...
new
...
solution
...
to
...
the
...
floating
...
floc
...
problem.
...
The
...
team
...
has
...
been
...
focusing on gas
...
removal mechanisms;
...
however, in light of the recent failure of the sand filter method, the team will also focus on possibly developing a method to stop flocs themselves from reaching the surface. Any approach developed for stopping flocs would be constrained by preventing floc break up. The team's tentative plan for future research can be found on the Floating Flocs Team's Future Challenges page.
Objective
The main objective of Dissolved Air Floating Flocs Team is to develop a physically feasible and cost-effective solution to the problem of floating flocs at AguaClara plants. The team was previously working with a backwash sand filter. However, research has shown that sand does not facilitate, but rather inhibits, bubble formation. The team plans to focus on developing a method to either remove gas from supersaturated water or stop flocs from floating to the surface even in the presence of bubbles.
Floating Flocs Team Semester Goals and Meeting Minutes
Floating Flocs Team Research Proposal
Floating Flocs Team Future Challenges
Previous Research
Previous Fluidized Bed Method Research: Links are separated by adaptations made to the system
- Final Results from the Fluidized Bed Method
This page contains experimental results from the final stage of the sand filter set up. It was concluded that the sand filter would not provide a suitable mechanism for gas removal, because experimental results suggest that sand seems to inhibit rather than facilitate gas removal. The main modification made to the set up from last semester was the installment of a taller pressurized aerator to increase the residence time of the bubbles in an attempt to achieve more consistent supersaturation of the influent water into the sand filter. A more detailed description of changes made to the system along with a diagram of the current setup can be viewed here.
- Fluidized Bed after Super Saturator
This page contains experimental results for gas removal as a function of grain size and preliminary results for gas removal as a function of sand bed depth. These are the results obtained using a pressurized aerator to super saturate the incoming water. The performance of the fluidized bed was monitored with a bubble collector. Although this technique shows great promise, the extent of supersaturation of the raw water was not necessarily held constant for the various experiments especially since the flow rates through the aerator varied.
- Bubble Volume Measurement Method Development.
These are the results gained from the second stage of our experimental setup, which included no DO probes and instead collected the volume of the bubbles formed in the filter in order to monitor oxygen removal rates.
- Fluidized Bed and Dissolved Oxygen Measurements.
These are the results gained from our initial experimental setup, which consisted of the flow accumulator with a DO probe, the glass filter column, and a collection beaker containing another DO probe.
Previous Aeration Method Research:
- Floating Flocs Aeration Method
This page discusses past research on the aeration approach to dissolved oxygen removal. The aeration approach attempted to use bubbles as a catalyst to increase the rate of dissolved oxygen transfer out of solution by allowing dissolved oxygen to diffuse into the bubbles. This would increase the bubble size and cause the bubble to rise faster.
- Theoretical Modeling of Aeration Method
This page discusses the theory behind the Aeration method and contains mathematical models predicting air flow through orifices of different sizes and variable length pipes.
Additional Information
Floating Flocs Team Annotated Bibliography
Aeration Method Quiz
This quiz checks that you have a basic understanding of the principles behind the aeration method.