**Bio-air**

It is calculated based on total oxygen demand and oxygen transfer efficiency (*OTE*). Total oxygen demand can be calculated as follow using the equation (4) here for the condition described in the case example.

=1,112.8 kg O_{2}/day

Specific oxygen demand per wastewater volume is calculated at 0.309g/L by dividing the oxygen demand (*O _{2}*) by feed flow rate,

*Q*(3,600m

^{3}/day).

As shown in equation (2) here, α-, β-, and θ-factors, average saturation DO in aeration tank (*DO*_{S}), fouling factor, *f*, and specific *SOTE* are required to estimate *OTE*. First of all, α-factor is calculated using the equation in Fig. 1 here (Krampe, 2002).

=0.415

*DO*_{S} is also required and can be calculated using equation (4) here. Alternatively, the calculator in the same page with the equation (4) can be used.

= 11.0 mg/L

Next, *OTE* is calculated using equation (2) here. The median values summarized in Table 2 here are used for all unknown variables.

=0.078 (or 7.8%)

Total biological air flow rate can be calculated using the already calculated oxygen demand, *OTE*, and the oxygen content of air, *i.e*. 0.275 kg O^{2}/m3 at the condition blower performances are rated for (20 ^{o}C, 36% relative humidity, sea level).

=52,000 m^{3} air/day or 0.60 m^{3}/s

The moisture content of air is typically not a significant source of error in the calculation considering the other errors in oxygen demand, *OTE*, *etc*. But, it might be worth while to take humidity effect into account at high ambient temperature (>30^{o}C) with high relative humidity. The spread sheet here provides a method to calculate accurate oxygen content in the air.

The head pressure required is calculated as

= 49.0 kPa

**Scouring air**

** **Scouring air flow is given as 0.9 Nm^{3}/s the case study. The specific aeration demand based on membrane surface area (*SAD _{m}*) is calculated at 0.36 m

^{3}/m

^{2}/hr. The total head pressure required can be calculated by adding nozzle submergence and head loss in the pipe and the nozzle (H

_{S}+H

_{L,S}),

*i.e*. 3.5 m H

_{2}O or 34.3 kPa.

After blower power (*P _{w}*) is calculated using equation (1) here, SED is calculated for biological air and membrane scouring using the following equation.

© Seong Hoon Yoon