Info

NH4+

Organics

Liquid Aerobic film biofilm d

Anoxic biofilm cn c "O

Figure 5.24 Cross-section of a clinoptilolite stone with aerobic and anoxic biofilm.

Figure 5.25 Clinoptilolite stone covered by SND bio-film, as seen under a micro scope.

Conclusions

The following conclusions can be made concerning the simultaneous nitrification and denitrification (SND) on basis of the experiments described:

1) Nitrification and denitrification occur simultaneously with different loadings.

2) The results show that a higher flow through the reactor permits greater daily loading with the same removal efficiency.

3) If no carbon source was added to the influent, nitrate and nitrite was recovered, showing that only nitrification occurs.

4) The SND is not able to treat organically bounded nitrogen.

5) The SND is relatively easy to start and fairly trouble free to maintain. In general the response of the reactor to changes is immediate and steady state conditions were apparently achieved quickly.

6) The faster nitrogen removal for this process, compared with suspended cultures, is partly due to a higher concentration of microorganisms, but it must be anticipated that some "additional effect" (i.e. ion-exchange) is needed to explain the high removal rate.

7) The pilot-plant experiments show an SND removal of 0.45 to 1.0 kg N /m3 bed volume * day, while laboratory columns have shown up to 4 to 5 times higher efficiency.

8) This study has shown that a simultaneous nitrification and denitrification is a technologically feasible process for nitrogen control.

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