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Plant brochure designed by Charles L.
Woodruff 1999 and revised in June 2004.
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Oxidation Ditch - BioDenipho Process
Description |
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| A characteristic feature
of the BioDenipho process is the alternating mode of operation within the
oxidation ditches. The ambient conditions within the oxidation ditches are
alternated between oxic and anoxic. This enables nitrification and
denitrification to be carried out in the same basin and eliminates the need
for an internal recycle line. In addition, the influent wastewater can be
directed to either of the two interconnected oxidation ditches, depending on
the status of the process. Similarly, effluent can be discharged from either
ditch. However, effluent discharge is continuous, and will always exit from
an oxic ditch to ensure that the concentration of ammonia in the effluent is
minimized. As stated
previously, the influent can be directed into either oxidation ditch 1 or 2,
depending upon the status of the process (Figure 2.5). The mixed liquor can
flow from Ditch 1 to ditch 2, and vice versa, depending on the hydraulic
gradient produced. If a common wall design is incorporated, the mixed liquor
will flow from ditch to ditch through a port in the common wall. If the
ditches are independent of one another, the mixed liquor will flow through
interconnecting piping. The mixed liquor exits the oxidation ditches by
flowing over a motorized adjustable effluent weir and is directed to final
clarification (or other treatment units). |
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Figure 2.5: Alternating
flow schematic |
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Both Ditches 1 and 2
contain a number of surface aerators (rotors) to provide the required oxygen
supply. In addition, submerged mixers are installed to keep the activated
sludge in suspension when the rotors are not in operation. This will be
discussed further in the next section.
he BioDenipho mode of Phased Isolation Ditch (PID) technology has several
operating cycles which are controlled using a SCADA system and allow the
oxidation ditch system the flexibility of accommodating various influent
loadings and flow conditions. As previously discussed, the process removes
nitrogen by alternating the environment within the oxidation ditches between
oxic and anoxic conditions. Varying the time allocated to oxic and anoxic
conditions within each ditch varies the actual process volume accordingly.
Besides the ability to vary the
oxic/anoxic process volume within a particular phase, the BioDenipho process
allows for combining the various phases listed below. This allows the plant
the flexibility to accommodate a wide range of influent conditions. As
depicted in Table 2.1, Phases F-J are mirror images of Phases A-E.
Therefore, when selecting a particular phase, there is a corresponding phase
which is a mirror image of the phase selected. For example, if Phase A is
selected, the corresponding Phase F is automatically selected. Phase A
cannot be selected without automatically selecting Phase F. When selecting
phases and associated phase lengths, we strongly recommend that the time
allocated for an oxidation ditch discharging under anoxic conditions not
exceed 45 minutes to prevent short circuiting and carry-over of BOD and/or
ammonia. Table 2.1 illustrates the corresponding pairs of phases. Table 2.2
describes each individual phase and the process conditions occurring within
each oxidation ditch during a given phase. Please note that the time range
common to each phase listed in Table 2.2 is between 0-2 hours. |
N = Nitrification DN =
Denitrification
Note: Shaded phases are used during normal operation. |
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Selected
Phase |
Flow Pattern/
Process Conditions |
Corresponding Phase
(Mirror Image) |
Flow Pattern/
Process Conditions |
| (Note: Shaded phases are
used during normal operation.) |
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Phase |
Flow Pattern/
Process Conditions |
Stand. Operating
Time (hrs) |
Ditch 1 |
Ditch 2 |
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A |
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0.5 |
Denitrification
Mixers on only
Weir down |
Nitrification
Mixers/rotors on
Weir up |
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B |
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1.5 |
Denitrification
Mixers on only
Weir up |
Nitrification
Mixers/rotors on
Weir down |
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C |
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0.5 |
Nitrification
Mixers/rotors on
Weir up |
Nitrification
Mixers/rotors on
Weir down |
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D |
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0.25 |
Denitrification
Mixers on only
Weir up |
Denitrification
Mixers on only
Weir down |
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E |
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0.5 |
Nitrification
Mixers/rotors on
Weir up |
Nitrification
Mixers/rotors on
Weir down |
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F |
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0.5 |
Nitrification
Mixers/rotors on
Weir up |
Denitrification
Mixers on only
Weir down |
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G |
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1.5 |
Nitrification
Mixers/rotors on
Weir down |
Denitrification
Mixers on only
Weir up |
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H |
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0.5 |
Nitrification
Mixers/rotors on
Weir down |
Nitrification
Mixers/rotors on
Weir up |
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I |
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0.25 |
Denitrification
Mixers on only
Weir down |
Denitrification
Mixers on only
Weir up |
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J |
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0.5 |
Nitrification
Mixers/rotors on
Weir down |
Nitrification
Mixers/rotors on
Weir up |
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