9.1.3. Oxygen Transfer Efficiency and Flotation
The VSB system achieves very high oxygen transfer efficiency (OTE)—greater than
75% OTE was measured routinely. These high oxygen transfer rates are associated with
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92 N. K. Shammas et al.
the pressure and depth at which compressed air is introduced to the bioreactor. Despite an
average oxygen transfer efficiency in excess of 70%, dissolved oxygen was limited in the
system due to the overloaded conditions (the four installed 450-scfm compressors can provide
approximately 32,000 lb O2/d). The overloaded conditions in the plant necessitated additional
aeration capacity. A diesel compressor with 1,000 scfm aeration capacity was installed as a
temporary measure. This unit was eventually replaced with an electric compressor capable of
delivering 1350 scfm. With the additional compressor, an average oxygen transfer efficiency
of 73.4% was attained at 100◦F, providing a total of approximately 48,000 lb O2/d. While
oxygen was still limited in the system improvements were noted with respect to flotation and
dewatering (11, 13)