Plant types, biological phosphorus removal
8.2.
If the stoichiometric coefficient VHAc,Po4 = 0.1 kg P/kg COD, the biological phosphorus
process has removed
(SHAc,1- SHAc,2) · VHAc,P04 = (0.060- 0.006) · 0.1 = 0.0054 kg P/m 3
from the wastewater.
(Provided that such an amount of dissolved phosphate has been available in the raw
wastewater. This will normally be the case in Denmark. In Norway, Sweden and many
other countries, the content of phosphate in wastewater is only half of the amount
found in Denmark. This is due to a combination of a smaller consumption of detergent
and larger volumes of wastewater per person).
Plant types, biological phosphorus
removal
All plant designs for biological phosphorus removal consist of a combination of
biological phosphorus removal and an aerobic process (oxidation of organic
matter). The reason is that in order to function the process requires that the microorganisms are alternately exposed to aerobic and anaerobic conditions.
Biological phosphorus removal can also be combined with nitrification and denitrification in a combined activated sludge process, but not with nitrification alone in a
combined activated sludge process. In the literature, very little information is
available about plant types and the design of biological phosphorus removal plants
/1/.
8.2.1 Biological phosphorus removal with
nitrification-denitrification and an internal
carbon source
Fig 8.2 shows two typical plant designs. In the anaerobic tank it has been attempted
to establish something which resembles plug flow. In one of the examples in the
form of a number of ideally mixed tanks in series, in the other example in the form
of a long, plug flow tank. Plug flow ensures to a certain degree that there are parts
of the anaerobic front tank where no nitrate is present even if nitrate should be
present in the return flow from sludge treatment. Any nitrate present will be
removed in the first part of the anaerobic tank (hence it is not anaerobic after all)
which will then function as a denitrification tank. This is inconvenient as far as the
process is concerned, as easily degradable organic matter, which could otherwise
have been used for the biological phosphorus removal, will disappear.
276
8.2.
If the stoichiometric coefficient VHAc,Po4 = 0.1 kg P/kg COD, the biological phosphorus
process has removed
(SHAc,1- SHAc,2) · VHAc,P04 = (0.060- 0.006) · 0.1 = 0.0054 kg P/m 3
from the wastewater.
(Provided that such an amount of dissolved phosphate has been available in the raw
wastewater. This will normally be the case in Denmark. In Norway, Sweden and many
other countries, the content of phosphate in wastewater is only half of the amount
found in Denmark. This is due to a combination of a smaller consumption of detergent
and larger volumes of wastewater per person).
Plant types, biological phosphorus
removal
All plant designs for biological phosphorus removal consist of a combination of
biological phosphorus removal and an aerobic process (oxidation of organic
matter). The reason is that in order to function the process requires that the microorganisms are alternately exposed to aerobic and anaerobic conditions.
Biological phosphorus removal can also be combined with nitrification and denitrification in a combined activated sludge process, but not with nitrification alone in a
combined activated sludge process. In the literature, very little information is
available about plant types and the design of biological phosphorus removal plants
/1/.
8.2.1 Biological phosphorus removal with
nitrification-denitrification and an internal
carbon source
Fig 8.2 shows two typical plant designs. In the anaerobic tank it has been attempted
to establish something which resembles plug flow. In one of the examples in the
form of a number of ideally mixed tanks in series, in the other example in the form
of a long, plug flow tank. Plug flow ensures to a certain degree that there are parts
of the anaerobic front tank where no nitrate is present even if nitrate should be
present in the return flow from sludge treatment. Any nitrate present will be
removed in the first part of the anaerobic tank (hence it is not anaerobic after all)
which will then function as a denitrification tank. This is inconvenient as far as the
process is concerned, as easily degradable organic matter, which could otherwise
have been used for the biological phosphorus removal, will disappear.
276