The MBR Book: Principles and Applications of Membrane

46 The MBR Book
2.2.4.4 Nitrification kinetics
Equations (2.2–2.12) are primarily concerned with the degradation of organic carbon
in the feed. It is common practice to extend the SRT and HRT in the aeration
basin to achieve the degradation of ammonia (NH 4-N). The effluent nitrogen concentration
(N e g/m 3 ) can be estimated by:
N
(2.13)
where � n,m is the maximum specific growth rate of nitrifying bacteria, K n is the half
saturation coefficient for nitrification, k e,n is the death rate coefficient for nitrifying
bacteria and � n is the specific growth of nitrifying bacteria which can be found from:
m
e
n
1
�
u
x
(2.14)
Literature values for the nitrification constants along with the heterotrophic constants
can be found in Appendix B. Sludge production from nitrification is given by:
QYnNOx Pxaut
,
1 k
� � �
(2.15)
where Y n is the nitrification sludge yield (g VSS/g NH 4-N) and NO x is the concentration
of NH 4-N that is oxidised (mg/L) to form nitrate. To calculate the NO x, a nitrogen balance
can be performed on the system:
NO = N �N�0.12P (2.16)
where N is the influent total Kjeldahl (biochemically-oxidisable) nitrogen concentration
(TKN, mg/L). NO x is used to determine P x, NO x can be estimated at the first attempt and
iterated to find values for NO x and P x,aut.
Nitrifying bacteria operate more slowly than carbon degraders such that, to achieve
nitrification, a longer HRT is required; nitrifiers are slower growing and require a
longer SRT. An SRT of around 10 days is required to allow full growth of the nitrifying
community (Huang, 2001). Fan et al. (1996) reported that perfect nitrification,
that is, all of influent TKN converted to NO 3 � , can be achieved in an MBR.
2.2.5 Aeration
Kn( mn
� ke,n)
�
m �k�m n,m e,n n
e,n x
x e x
2.2.5.1 Fundamentals
In conventional aerobic biological wastewater treatment processes, oxygen is usually
supplied as atmospheric air, either via immersed air-bubble diffusers or surface aeration.
Diffused air bubbles (via fine-bubble aeration) are added to the bulk liquid (as in an
ASP, biological aerated filters (BAFs), fluidised bioreactors, etc.), or oxygen transfer