64
Tecnología y Ciencias del Agua
, vol. VIII, núm. 2, marzo-abril de 2017, pp. 61-70
Chen
et al.
,
Reactivation of hypersaline aerobic granular sludge after low temperature storage
•
ISSN 2007-2422
to flow out with the upflow air stream. Mean-
while, it was even found that some fragmentary
particles appeared, on which a large number of
breeding filamentous bacteria were observed.
With the running of reactor, small particles
and fragmentary sludge were disappearing
constantly, and then, overgrowth of filamentous
bacteria on granules was effectively controlled.
At the end of experiment (the 70th cycle), the
loose surface of granules developed to smooth,
with a little compact structure and the color
recovered to yellow (figure 1b). Average particle
size reached up to 0.99 mm and dispersion was
only 0.376, which also indicated that revived
aerobic granulation had a relative symmetrical
particle distribution. Results show that granules
experienced a process of particle disintegration,
fragmentary particles, filamentous bacteria-like
particles, and dense granules during more than
one month recovery, and finally appearance of
granular sludge recovered to initial character-
istics before stored. During the re-cultivation,
microbes of granules grew up rapidly, resulting
in an increase of particles size.
Settling property
SVI is an index to measure the sedimentation
performance of activated sludge, which can
reflect the loose structure and the coagulation
performance. Changes in parameters such as
SVI and MSV for various operating phase are
shown in figure 2.
As presented in figure 2, within 27 cycles
after the reactor was in operation and begun to
aerate, eventual fragmented sludge appeared
in the reactor and settling property of granules
deteriorated. The profile of SVI showed a rising
trend during the operation phase I and II, which
indicated the SVI reached up to the maximum
of 95.21 ml g
-1
and MSV fell down to the mini-
mum of 0.26 m h
-1
at the 27th cycle. Microscopic
analysis revealed that massive filamentous
bacteria multiplied surrounding the granules.
In order to prevent the situation on a further de-
terioration, some strategies, such as improving
influent organic loading, increasing the water
alkalinity and aeration rate, and shortening
reactor settling time and so on, were adopted
to inhibit overgrowth of filamentous bacteria
on granules and improve settling performance
after operation phase II. Research showed that
settling property was gradually taking a favor-
able turn after filamentous bacteria separated
form granules and subsequently washed out
with effluent form the reactor, and sludge
bulking can be controlled effectively. Influent
organic loading and temperature of reactor im-
proved after operation cycle 41, with the result
that sludge morphology changed with smooth
Figure 1. Appearance characteristic of hypersaline aerobic granular sludge before/after storage (a: before storage;
b: after storage).
