This study involves the development of a biofilm
reactor that supports growth of a deep biofilm on a gas
permeable membrane. The reactor solution is not aerated,
and oxygen is supplied through the membrane. The reactor
is termed a substratum-aerated-biofilm reactor or SAB.
With adequate concentrations of electron-donors and
electron-acceptors, a deep biofilm grows on the membrane
and is comprised of different layers of bacterial activity.
The aerobic layers are near the membrane support, while the
anaerobic layers are near the biofilm-liquid boundary.
In the SAB, the substrate diffuses from the bulk
liquid into the biofilm to react. Oxygen diffuses through
the membrane into the biofilm. All products likewise are
transported by molecular diffusion through the biofilm and
into the bulk liquid.
The reactors consisted of a reactor wall made of a
plexiglass cylinder with the gas permeable membrane supported
on a shallow rotating cup. The cup was designed so
that the cup and the membrane function as a flat plate.
The flat plate was utilized for support of the biological
growth, transfer of oxygen, and mixing of the bulk liquid
and the gas phase.
The experiments were conducted in completely mixed,
continuous-flow reactors maintained at 25°C with a
hydraulic detention of 8 hours. Pure oxygen was delivered
to a gas compartment under the membrane. All reactors were
fed a synthetic waste buffered to pH 7.0. The background
solution for the feed solution was made from distilled
water combined with adequate inorganic nutrients and
vitamins. The background solution was supplemented with
acetate and ammonia to obtain the desired substrate compositions.
Combined nitrification and heterotrophic oxidation
activity resulted when the SABs where fed 5 or 10 mg/1
acetate, and 10 mg-N/1 ammonia. Combined nitrification,
heterotrophic oxidation, and denitrification resulted with
acetate concentration of 20, 40, and 100 mg/1, and 10 mg-
N/1 ammonia. Combined heterotrophic oxidation and fermentation
resulted with acetate concentration of 800 mg/1, and
10 mg-N/1 ammonia. A series of mass balances were
developed to determine the fate of the nitrogen compounds
and acetate. These results showed that the flux values for
carbon oxidation, nitrification, denitrification, and
fermentation are higher than those reported for competing
technologies such as rotating biological contactors
