The removal of SOM is achieved by the oxidation of carbonaceous matter, which is accomplished by the aerobic growth of heterotrophic bacteria. The biochemical transformation is described by the following normalized mass based stoichiometric equation in which the carbonaceous matter is a carbohydrate (CH2O) and the nitrogen source for the bacteria is ammonium (NH+4).
CH2O+ 0.309 O2 + 0.085 NH+4 + 0.289 HCO3– → 0.535 C5H7O2N + 0.633 CO2 + 0.515 H2O
The oxidation of ammonia to nitrate is accomplished by the aerobic growth of chemolithotrophic, autotrophic bacteria and is described by the following normalized mass based stoichiometric equation. The overall equation describes the two-step process in which ammonia is converted to nitrite by Nitrosifyers, and nitrite is converted to nitrate by Nitrifyers.
NH+4 + 3.30 O2 + 6.708 HCO3– → 0.129 C5H7O2N + 3.373 NO–3 + 1.041 H2O + 6.463 H2CO3
The final step in the removal of nitrogen from the waste stream occurs when carbonaceous matter is oxidized by the growth of heterotrophic bacteria utilizing nitrate as the terminal electron accepter. The equation describing the biochemical transformation depends on the organic carbon source utilized. The following is the normalized mass based stoichiometric equation with the influent waste stream as the organic carbon source.
NO–3 + 0.324 C10H19O3N → 0.226 N2 + 0.710 CO2 + 0.087 H2O + 0.027 NH3 + 0.274 OH–
Biological removal of nitrogen has been the focus of much attention and many of today’s wastewater treatment plants incorporate it. However, the difficultly in promoting these biochemical transformations in one reactor is the different environmental conditions required for each transformation.
This Amphidrome® process is designed to achieve the above reactions simultaneously within one reactor. The aerobic environment within the filter promotes the first two reactions. The return flow, to the anoxic/equalization tank, mixes the nitrates with organic carbon in the raw influent, and with organic carbon that has been released from the stored sludge. The anoxic environment within the filter promotes denitrification, the third reaction.