The MBR Book: Principles and Applications of Membrane

154 The MBR Book
Table 3.24 Biokinetic constants
Constant Range Unit Constant Range Unit
K s 6–192 g/m 3 K n 0.01–0.1 g NH 4-N/m 3
k e 0.023–0.2 per day k e,n 0.025–0.15 per day
µ m 3–13.2 per day � m,n 0.2–2.21 per day
Y 0.28–0.67 kg VSS/kg COD Y n 0.1–0.15 kg VSS/kg NH 4-N
3.3.2 Biokinetic constants
The design of an MBR from biokinetic considerations relies on assumptions regarding
values of the biokinetic constants, as is the case with other aerobic treatment processes.
Ranges of values are summarised in Table 3.24 below. A more comprehensive listing
of biokinetic constants, along with references identifying their origins is provided in
Appendix B. Typical values of K s � 60, k e � 0.08, � m � 8, Y � 0.4, K n � 0.07,
k e,n � 0.1, � m,n � 0.7, Y n � 0.13 have been used in the example design that follows
in Section 3.3.3. Note that the values selected are not necessarily the most appropriate
for an MBR.
3.3.3 Design calculation
A complete design for an immersed membrane bioreactor (iMBR) can be carried out
on the basis of the information presented, provided the nature of the interrelationship
can be determined between aeration and:
(a) permeability and cleaning protocol for the membrane permeation component,
(b) feed water quality, flows and biokinetics for the biological component.
Whilst it is possible to base the latter on biokinetics, the former cannot reasonably
be calculated from first principles. The calculation for an HF technology based on a
flow of 5 MLD is detailed below. Equation (3.19) has been used to correlate aeration
with flux. Assumptions concerning the organic content of the feed (Table 3.25), values
for biokinetic constants (Table 3.26), biotreatment operation (Table 3.27) membrane
operation (Table 3.28) and aeration operation (Table 3.29) lead to the system
design an operating parameters detailed in subsequent tables (Tables 3.30–3.36).
Shaded cells refer to calculated values. Sludge disposal costs are excluded since costs
associated with this are process dependent post-treatment of the sludge, such as thickening,
has a large impact on disposal costs. However, in large full-scale plants sludge
treatment and disposal can be assumed to be small compared with power costs.
The design of a pumped sidestream membrane bioreactor (sMBR) is, in principle,
somewhat more straightforward than an iMBR since membrane permeation is carried
out by crossflow filtration without air. In this case a correlation of permeability
and flux with crossflow velocity can provide the information needed to calculate
energy demand for pumping, based on Equation (3.1) along with the classical biokinetic
expressions for oxygen demand by the biomass.
A much discussed issue in iMBR technology is the relative costs of processes based
on FS and HF module configurations. Considerable effort has been devoted to increasing