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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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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
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probe
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was
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inserted
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near
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the
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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
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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
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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
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ports
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had
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been
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tested
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with
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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. Regarding the dissolved oxygen measurements in the absence of sand, the similar procedure and calibration method was used as described above. Water temperature stayed constant around 21.4 C throughout the experiment. The system with no sand inside was left running for several hours prior to taking DO measurements. This ensured that the water was supersaturated throughout the system. 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, which may have affected the measured dissolved oxygen concentrations for the first trial of the second probe. {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} |
Visual
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observation
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of
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the
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samples
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taken
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support
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the
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dissolved
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oxygen
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concentrations
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measured.
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The
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samples
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were
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very
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cloudy
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with
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small
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bubbles,
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indicative
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of
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supersaturation.
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If
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the
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system
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were
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working
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properly,
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the
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dissolved
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oxygen
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concentration
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would
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decrease
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from
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the
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aerator
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to
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the
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bubble
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collector,
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and
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the
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water
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taken
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from
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the
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sand
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filter
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effluent
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and
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the
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bubble
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collector
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effluent
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would
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contain
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large
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bubbles.
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We
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observed
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that
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no
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large
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bubbles
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were
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present
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in
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either
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sample
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but
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very
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small
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bubbles
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were
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abundant
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in
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both.
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These
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results
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indicated
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a
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problem
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with
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the
...
setup
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or
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the
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fluidized
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bed
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method.
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Pressure
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measurements
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were
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taken
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and
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the
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head
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loss
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through
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the
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sand
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filter
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was
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calculated
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to
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ensure
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that
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large
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head
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loss
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through
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the
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system
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in
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combination
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with
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pressure
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build
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up
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in
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the
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setup
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was
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not
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resulting
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in
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tiny
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bubbles
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being
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reincorporated
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into
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solution.
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The
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results
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of
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these
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calculations
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can
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be
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found
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in
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the
...
...
...
...
...
...
...
file.
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The
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measured
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head
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loss
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through
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the
...
system
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seemed
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to
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match
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up
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fairly
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well
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to
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theoretical
...
expectations.
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In
...
order
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to
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assess
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the
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effectiveness
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of
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the
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fluidized
...
bed
...
method,
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a
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control
...
experiment
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was
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performed
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without
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sand
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and
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dissolved
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oxygen
...
measurements
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were
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taken
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at
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the
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end
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of
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the
...
experiment
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before
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stopping
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the
...
setup.
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The
...
results
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can
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be
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found
...
below
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in
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Table
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2.
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Juxtaposition
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of
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the
...
results
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from
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Table
...
1
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and
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Table
...
2
...
indicate
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that
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the
...
fluidized
...
bed
...
method
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was
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not
...
effective
...
at
...
removing
...
gas,
...
because
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the
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presence
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of
...
sand
...
did
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not
...
significantly
...
decrease
...
the
...
dissolved
...
oxygen
...
concentration
...
in
...
the
...
water.
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{float:left|border=12px solid white|width="200"} 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|11.6|16.0|16.0|16.0|21.4| |3|530|11.4|16.0|16.0|15.9|21.4| {float} \\ \\ 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. |
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.