A part from the calculation model proposed by Zeeman and Lettinga (1999) (see Table 6), the volume of the UASB reactor can be determined based on organic loading and upflow velocity. The reactor volume based on acceptable organic loading rate (OLR) is given by:

with:

V: volume of the reactor, m³

Q: influent flow rate, m³/d

C: influent COD, kg COD/m³

OLR: acceptable organic loading rate, kg COD/m³.d

The acceptable organic loading rate depends largely on the biodegradability of sewage, on the operational temperature and the average sludge retention time (See table 6). For design purposes OLR given in Tables 3 and 4 can be used for preliminary dimensioning of the UASB reactor under different sewage and environmental conditions. In addition to reactor sizing based on OLR, the upflow velocity (equation 2) should be less than the admissible upflow velocity (Table 6).

with:

Vup: upflow velocity, m/hr

H: reactor height, m

HRT: Hydraulic retention time, hr