Four identical bench-scale upflow anaerobic sludge blanket (UASB) reactors,
R1, R2, R3 and R4, were used to assess nitrophenols degradation at four di
fferent hydraulic retention times (HRT). Reactor RI was used as control, wh
ereas R2, R3, and R4 were fed with 2-nitrophenol (2-NP), 4-nitrophenol (4-N
P), and 2,4-dinitrophenol (2,4-DNP), respectively. The concentration of eac
h nitrophenol was gradually varied from 2 to 30 mg/l during acclimation. Af
ter acclimation reactors were operated under steady-state conditions at fou
r different HRTs - 30, 24, 18, and 12 h, to study its effect on the removal
of nitrophenols. Overall removal of 2-NP and 4-NP was always more than 99%
but 2,4-DNP removal decreased from 96% to 89.7% as HRT was lowered from 30
to 12 h. 2-Aminophenol (2-AP), 4-aminophenol (4-AP) and 2-amino,4-nitrophe
nol (2-A,4-NP) were found to be the major intermediates during the degradat
ion of 2-NP, 4-NP and 2,4-DNP, respectively. Out of the total input of nitr
ophenolic concentration (30 mg/l), on molar basis, about 41.2-48.4% of 2-NP
, 59.4-68% of 4-NP, 30-26.6% of 2,4-DNP was recovered in the form of their
respective amino derivatives at 30-12 h HRT. COD removal was 98-89%, 97-56%
, 97-52%, and 94-46% at 30-12 h HRT for R1, R2, R3 and R4, respectively. Av
erage cell growth was observed to be 0.15 g volatile suspended solid (VSS)
per g COD consumed. Methanogenic inhibition was observed at lower HRTs (18
and 12 h), however denitrification was always more than 99% with non-detect
able level of nitrite. The granules developed inside the reactors were blac
k in color and their average size varied between 1.9 and 2.1 mm. (C) 2001 E
lsevier Science Ltd. All rights reserved.