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Dissolved
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Oxygen
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Measurements
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According
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to
...
...
...
...
...
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,
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bubble
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formation
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potential
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in
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the
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water
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should
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be
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18
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mL/L.
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Our
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measured
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values
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for
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gas
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removal
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were
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5.09
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mL/L
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and
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1.99
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mL/L
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for
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Sand
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40
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and
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Sand
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30,
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respectively.
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Because
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measured
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gas
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removal
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was
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so
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much
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lower
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than
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the
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theoretical
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value,
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we
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twice
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measured
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the
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dissolved
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concentration
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at
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each
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sampling
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port
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to
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determine
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which
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of
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the
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components
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was
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not
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functioning
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effectively.
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Procedure
Sampling Points:
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Water
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Source,
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Aerator
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Effluent,
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Sand
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Filter
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Effluent,
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Bubble
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Collector
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Effluent
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Dissolved
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oxygen
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probes
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were
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used
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to
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measure
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the
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concentration
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of
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dissolved
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oxygen
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in
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samples
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of
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water
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taken
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from
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the
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water
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source
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and
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effluents
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from
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the
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aerator,
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the
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sand
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filter,
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and
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the
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bubble
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collector.
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Two
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different
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probes
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were
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used
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in
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samples
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from
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each
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point
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to
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confirm
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results.
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After
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each
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probe
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was
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assembled,
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it
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was
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placed
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in
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a
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solution
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of
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sodium
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sulfite
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to
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ensure
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a
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zero
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reading.
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Both
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probes
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we
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used
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accurately
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read
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the
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dissolved
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oxygen
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concentration
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in
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the
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sodium
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sulfite
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as
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"0".
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To
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further
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ensure
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the
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probes'
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accuracy,
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they
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separately
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were
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placed
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in
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a
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sample
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of
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tap
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water,
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which
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should
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have
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a
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dissolved
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oxygen
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content
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near
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8
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mg/L.
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Though
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the
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readings
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were
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noisy,
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both
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probes
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read
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that
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the
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dissolved
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oxygen
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concentration
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in
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the
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tap
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water
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was
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within
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0.5
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mg/L
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of
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8
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mg/L.
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In
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a
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large
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beaker,
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water
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was
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collected
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from
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a
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sampling
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port
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at
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the
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first
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point,
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just
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beyond
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the
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water
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source.
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The
...
probe
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was
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inserted
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near
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the
...
center
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of
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the
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water
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sample
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and
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kept
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stable
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with
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a
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ring
...
stand.
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After
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the
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probe
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membrane
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came
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in
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equilibrium
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with
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the
...
water,
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the
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dissolved
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oxygen
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reading
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was
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recorded,
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and
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the
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probe
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was
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returned
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to
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the
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sodium
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sulfite
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solution.
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The
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beaker
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was
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emptied
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and
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refilled
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with
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water
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from
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the
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next
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sampling
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port.
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This
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was
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repeated
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until
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water
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from
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all
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four
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sampling
...
ports
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had
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been
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tested
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with
...
one
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probe. For the measurements taken with the sand filter in place, the process was repeated with Probe 2.
With the sand filter in place, water temperature remained at 20.8 °C while measurements with Probe 1 were taken. We encountered a problem while using Probe 2. The system that controls water temperature was temporarily out of order, and we began measurements with the source water temperature at about 33 °C. As we continued measurements (from the sampling port just beyond the water source down the line), water temperature dropped to 21 °C. Measurements were taken with Probe 1 after the system had been running for several hours; for Probe 2, the system had been running for about 45 minutes when measurement began.
In the absence of sand, water temperature stayed at 21.4 °C during the experiment. The system had been running for several hours prior to taking DO measurements. This ensured that the water was supersaturated throughout the system.
Results and Discussion
The results were very unexpected. Table 1. shows the first set of DO measurements taken after the Sand 40 experiment was performed. Water temperature was 20.8 °C when Probe 1 was used. Water temperature varied from about 33 to 21 °C while Probe 2 was used to measure dissolved oxygen concentrations, which may have affected the measured dissolved oxygen concentrations for the first trial of the second probe.
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Then the process was repeated, with measurements taken with the other probe. Water temperature remained at 20.8 °C while measurements with Probe 1 were taken. We encountered a problem while using Probe 2. The system that controls water temperature was temporarily out of order, and we began measurements with the source water temperature at about 33 °C. As we continued measurements (from the sampling port just beyond the water source down the line), water temperature dropped to 21 °C. h2. Results and Discussion The results were very unexpected. Table 1. shows the first set of DO measurements taken after the Sand 40 experiment was performed. Water temperature was 20.8 °C when Probe 1 was used. Water temperature varied from about 33 to 21 °C while Probe 2 was used to measure dissolved oxygen concentrations. {float:left|border=12px solid white|width="200"} h5. Table 1.: Dissolved Oxygen Concentrations (DO) Measurements with Sand. || Sampling Port || DO (mL/L), Probe 1, Trial 1 || DO (mL/L), Probe 1, Trial 2 || DO (mL/L), Probe 2, Trial 1 || DO (mL/L), Probe 2, Trial 2 || | Water Source | 9.8 | 10.2 | 8.7 | 12.1 | | Beyond Aerator | 15.5 | 14.2 | 11.8 | 15.2 | | Beyond Sand Filter | 17 | 16.3 | 11.9 | 15.3 | | Beyond Bubble Collector | 17.8 | 16.2 | 12.3 | 15.7 | {float} \\ In addition, water taken from sampling ports beyond the sand filter and the bubble collector were very cloudy with small bubbles. If the system were working properly, the dissolved oxygen concentration would decrease from the aerator to the bubble collector, and the water taken from the sand filter effluent and the bubble collector effluent would contain large bubbles. We observed that no large bubbles were present in either sample--but very small bubbles were abundant in both. This indicated that the sand was not effective in removing gas. ------- Table 2. shows the second set of DO measurements taken after the Sand 30 experiment was performed. |
Visual observation of the samples taken support the dissolved oxygen concentrations measured. The samples were very cloudy with small bubbles, indicative of supersaturation. If the system were working properly, the dissolved oxygen concentration would decrease from the aerator to the bubble collector, and the water taken from the sand filter effluent and the bubble collector effluent would contain large bubbles. We observed that no large bubbles were present in either sample but very small bubbles were abundant in both. These results indicated a problem with the setup or the fluidized bed method. Pressure measurements were taken and the head loss through the sand filter was calculated to ensure that large head loss through the system in combination with pressure build up in the setup was not resulting in tiny bubbles being reincorporated into solution. The results of these calculations can be found in the Floating Floc Head Loss Calculations MathCAD file. The measured head loss through the system seemed to match up fairly well to theoretical expectations.
In order to assess the effectiveness of the fluidized bed method, a control experiment was performed without sand and dissolved oxygen measurements were taken at the end of the experiment before stopping the setup. The results can be found below in Table 2. Juxtaposition of the results from Table 1 and Table 2 indicate that the fluidized bed method was not effective at removing gas, because the presence of sand did not significantly decrease the dissolved oxygen concentration in the water.
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h5. Table 2.: Dissolved Oxygen Concentrations (DO) Measurements in the Absence of Sand
||Trial||Flowrate (ml/min)|| Source water DO (mg/L)||After Aerator DO (mg/L)||After Sand Filter DO (mg/L)||After Bubble Collector DO (mg/L)||Temperature (C)||
|1|530|12.0|15.3|15.6|16.1|21.4|
|2|530|11.0|14.3|16.2|15.0|21.4|
|3|530|11.6|16.0|16.0|16.0|21.4|
|43|530|11.4|16.0|16.0|15.9|21.4|
{float}
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The DO concentrations are quite consistent, with the exception of the Trial 2. It is possible that this might be a faulty reading that occurred only during this particular trial.
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h2. Conclusions
The DO measurements confirm the results from the Control Experiment where it was shown that the sand is inhibiting the process of gas removal. DO measurements taken from various sampling points indicate that there is only a slight increase in the DO concentration as the water flows from the sand filter through aerator to the bubble collector. This might suggest that the bubble collector is collecting excess gas coming from the aerator.
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Conclusions
The DO measurements confirm the results from the Control Experiment where it was shown that the sand is inhibiting the process of gas removal. DO measurements taken from various sampling points indicate that there is only a slight increase in the DO concentration as the water flows from the sand filter through aerator to the bubble collector. This might suggest that the bubble collector is collecting excess gas coming from the aerator.